A method and device for predicting sediment in a river basin

Abstract

The application provides a catchment sediment prediction method, which comprises the following steps: collecting various types of basic data of a target catchment, arranging the basic data into a grid form and performing unified spatial registration, and dividing the basic data based on small catchment boundaries as spatial units for sediment prediction; for each small catchment, gravity erosion, debris flow erosion, gully erosion and slope erosion are predicted respectively to obtain the future spatio-temporal distribution of various types of erosion and total erosion in the target catchment; the future sediment yield and deposition of each small catchment are calculated respectively for the four types of erosion; based on the future sediment yield, the upstream and downstream relationships of each small catchment in the target catchment are considered to calculate the suspended sediment transport capacity of the small catchment in the main river system in sections, and the distribution of the suspended sediment transport capacity along the flow direction of the main river system is predicted by combining the dredging, reservoir sedimentation and the input and output of the suspended sediment in the river section. The application can predict the spatio-temporal distribution of sediment in the multi-physical process of catchment erosion, catchment sediment yield and river sediment transport.

Description

TECHNICAL FIELD

[0001] The present application belongs to the fields of watershed environment governance, soil and water conservation, mountain disaster and environment, remote sensing information technology, and particularly relates to a watershed sediment prediction method and device. BACKGROUND

[0002] Watershed erosion is a geomorphic process of displacement of surface materials under the action of external forces. The materials produced by watershed erosion enter the river system and become sediment, which is transported to the downstream or deposited in the river channel. Watershed erosion and sediment transport are key physical processes of watershed surface evolution and landform shaping, and also have a profound impact on human economic and social activities in the watershed. Although erosion, sediment transport, sediment deposition and output from the watershed are continuous physical processes, the current research on watershed erosion and sediment production and sediment transport is generally fragmented. Watershed erosion is generally the research topic in the field of soil and water conservation, mainly focusing on slope erosion process, while sediment transport is generally the focus in the field of water conservancy engineering, and the correlation between slope erosion and sediment supply to river channel is still weak. However, with the intensification of climate change and human activities, the adverse effects of watershed water-sediment coupling on infrastructure are gradually increasing, and even may cause disasters. For example, the increase of erosion and sediment transport in the upstream of the watershed can accelerate the sedimentation of reservoirs in the watershed and downstream, reduce the reservoir regulation capacity, and fail to effectively reduce the peak of flood in the flood season, thereby reducing the protection of downstream towns and other places. The demand for understanding the spatio-temporal distribution of erosion and sediment from the watershed scale and predicting the future climate pattern is increasingly strong. Reasonable prediction of the future spatio-temporal distribution of watershed sediment will help to take preventive measures in advance and reduce the adverse effects of climate change on the social, economic and ecological development of the watershed.

[0003] The existing prediction of future spatio-temporal distribution of watershed sediment generally focuses on the river system, i.e. based on the historical observation data of hydrological stations, mainly considering the transport process of sediment in the river, and the combination of slope erosion, branch channel confluence and main river sediment transport is not enough, resulting in high dependence on historical observation data. In addition, the existing calculation method of erosion mainly focuses on slope erosion, while the gravity erosion (gravity unloading dominated disasters such as collapse and landslide) and debris flow erosion and channel erosion processes which are common in the edge area of Qinghai-Tibet Plateau and are concentrated in sediment production are less concerned, and lack of quantitative description, or the quantitative description greatly depends on field observation, which is difficult and costly. Although the erosion and sediment transport numerical model based on the material transport dynamics model can theoretically express the erosion-sediment production-transport process, such model generally requires high input data, has many parameters to be calibrated, and has large calculation amount and is not easy to converge. In view of the practical needs of the foregoing watershed sediment budget and the problems existing in the existing methods, it is necessary to develop a watershed sediment prediction method based on the physical mechanism of watershed erosion-sediment production-transport and simple calculation. SUMMARY

[0004] The present application aims at the shortcomings and deficiencies of the existing watershed sediment prediction method, and provides a watershed sediment prediction method which can comprehensively quantify the spatial and temporal distribution of sediment in the process of watershed erosion, watershed sediment production and river sediment transport. The method comprehensively considers and quantifies different types of erosion, provides sediment transport ratio calculation method for each type of erosion, and finally quantifies the sediment transport process in the river, which can provide technical support for watershed comprehensive management, and has important popularization and application prospect.

[0005] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0006] The present application provides a watershed sediment prediction method, which comprises the following steps:

[0007] Step S1, collecting the basic data of the target watershed, including rainfall, soil, vegetation, terrain, orthophoto and hydrological data, wherein the rainfall, vegetation and hydrological data are obtained by using current data and / or future data based on future climate mode data of the target watershed, the soil, terrain and orthophoto data are all obtained by using historical data of the target watershed; arranging all kinds of basic data into grid form and performing unified spatial registration, setting the small watershed boundary as the spatial unit of sediment prediction, dividing all kinds of basic data based on the small watershed boundary, and dividing the small watershed scale basic data into time periods based on the time scale requirement of sediment prediction;

[0008] Step S2, for each small watershed, the erosion amount is predicted according to different erosion types, i.e. gravity erosion, debris flow erosion, channel erosion and slope erosion, to obtain the future spatial and temporal distribution of all kinds of erosion amount and total erosion amount in the target watershed; wherein,

[0009] For gravity erosion, the historical spatial and temporal distribution of gravity erosion amount is obtained by using multi-period historical orthophoto of the target watershed and the area-volume relationship of collapse and landslide, the statistical characteristic value of gravity erosion amount in the historical period of small watershed scale is obtained based on the historical spatial and temporal distribution, and the corresponding statistical characteristic value is selected as the future gravity erosion amount of small watershed scale according to the risk management requirement;

[0010] For debris flow erosion, all effective rainfall field information of the small watershed in the future period is obtained according to the future rainfall data, and the future debris flow erosion amount of small watershed scale is obtained based on the effective rainfall field information;

[0011] For channel erosion, the channel in the small watershed scale is divided into several channel segments, the historical channel erosion rate of each channel segment is calculated according to the historical topographic data, and the historical channel erosion amount in the small watershed scale is calculated based on the historical channel erosion rate; a multiple regression relationship between the historical channel erosion amount, rainfall and topographic parameters is established, and the channel erosion rate under the rainfall condition of the future climate mode is calculated based on the multiple regression relationship, so as to obtain the future channel erosion amount in the small watershed scale;

[0012] For slope erosion, the soil erosion amount in the grid scale in the future period is calculated by correcting the universal soil loss equation RUSLE according to the rainfall and vegetation data in the future climate mode, so as to obtain the future slope erosion amount in the small watershed scale;

[0013] Step S3, the future sediment yield and deposition amount of each type of erosion are respectively predicted, and the future temporal and spatial distribution of the sediment yield and deposition amount of the target watershed is obtained according to the future sediment yield and deposition amount of each type of erosion in the small watershed scale; wherein,

[0014] For gravity erosion, the historical sediment yield and deposition amount of gravity erosion in the small watershed scale are calculated, specifically, the historical sediment yield of gravity erosion is calculated based on the multi-period historical orthographic image and the area-volume relationship of collapse and landslide and according to the amount of river material input by the collapse and landslide connected with the river system; the ratio of the gravity erosion sediment yield to the gravity erosion amount is defined as the gravity erosion sediment transport ratio, the historical gravity erosion sediment transport ratio of each small watershed is calculated according to the historical temporal and spatial distribution of the gravity erosion amount, a multiple regression relationship between the historical gravity erosion sediment transport ratio, the main river flow, the main river water depth and the volume of the collapse and landslide is established, the future gravity erosion sediment transport ratio is calculated based on the multiple regression relationship and the runoff data under the future climate mode, the future gravity erosion sediment yield in the small watershed scale is calculated by the future gravity erosion amount in the small watershed scale and the future gravity erosion sediment transport ratio; the future gravity erosion deposition amount in the small watershed scale is obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion amount in the small watershed scale;

[0015] For debris flow erosion, it is assumed that the river system geometry does not change over time in the hundred-year scale, the main river flow is extracted based on the runoff data under the future climate mode, the future debris flow erosion sediment transport ratio in the small watershed scale is calculated according to the specific gravity and flow of the debris flow and the main river in the future period, and the entry angle, the future debris flow erosion sediment yield and deposition amount in the small watershed scale are calculated according to the sediment transport ratio;

[0016] For gully erosion and slope erosion, first, the sediment connectivity index of the grid scale in the small watershed is calculated based on the historical terrain data and future vegetation data, and the future sediment transport ratio of the small watershed scale is calculated based on the sediment connectivity index. Then, the future gully erosion sediment yield and deposition of the small watershed scale, and the future slope erosion sediment yield and deposition of the small watershed scale are calculated according to the future sediment transport ratio of the small watershed scale, respectively.

[0017] Step S4, based on the future sediment yield of each time period of all small watersheds in the target watershed predicted in step S3, the suspended sediment transport capacity of the small watershed in the main river system is calculated in sections according to the upstream and downstream relationship of the small watershed in the target watershed. The position of the river, and the distribution of the suspended sediment transport capacity along the flow direction of the main river system is predicted by combining the dredging, reservoir sedimentation and the input and output of the suspended sediment in the river section. The output of the suspended sediment caused by dredging is obtained based on the average of the historical dredging data; the output of the suspended sediment in the river section caused by reservoir sedimentation is calculated based on the effective reservoir capacity and the future runoff data.

[0018] In some embodiments, the time resolution of the rainfall data in the basic data collected in step S1 is not less than 3h, the soil data includes the organic matter content in sand, silt and clay of the surface soil, the vegetation data includes the normalized vegetation index and the vegetation type, the terrain data adopts a digital elevation model with a spatial resolution of not less than 30m, and the hydrological data includes the river system data, flow and runoff in the target watershed. The basic data also includes historical land use types for calculating the dimensionless soil and water conservation measure factor; the spatial resolution used for uniform spatial registration of various types of grid form basic data is consistent with the spatial resolution of the digital elevation model;

[0019] The small watershed is the watershed corresponding to the minimum first-order river in the Horton law, and the target watershed is divided into I small watersheds B1, B2, … B i ,…B I based on the digital elevation model, and the area, terrain elevation difference, average slope, gully length, gully width and gully slope of each small watershed are counted. The time length used for time period division of various types of basic data is equal.

[0020] In some embodiments, in step S2,

[0021] For gravity erosion prediction, specifically including: identifying the newly added collapse landslide area in the historical period T j by the multi-period historical orthographic image of the target watershed, calculating the total volume of the material released by the collapse landslide in the small watershed B j in the historical period T i according to the collapse landslide area and the collapse landslide area-volume correlation system, and taking the total volume of the material released by the collapse landslide in the small watershed B j in the historical period T iGravitational erosion (E) G ) ij Based on this gravitational erosion amount (E) G ) ij The historical spatiotemporal distribution of gravity erosion is obtained; based on the historical spatiotemporal distribution of gravity erosion, a cumulative probability distribution curve of historical gravity erosion in each sub-basin is constructed; according to risk management requirements, the corresponding statistical characteristic value is selected from the cumulative probability distribution curve as the future time period T. f Small watershed B i Gravitational erosion (E) G ) if ;

[0022] For debris flow erosion prediction, the specific methods include: obtaining small watershed B based on rainfall data from future climate models. i In the future time period T f Information on all valid rainfall events within the timeframe is collected, including the duration and average intensity of each event. Based on historical rainfall data and established threshold triggering conditions, it is determined whether each valid rainfall event will trigger a debris flow in the future. If a valid rainfall event is determined not to trigger a debris flow, the ejecta volume for that event is set to 0. If a valid rainfall event is determined to trigger a debris flow, the ejecta volume for that event is calculated. The future timeframe T is then statistically analyzed. f Small watershed B i The total volume of debris ejected by the mudslide is used as the future time period T. f Small watershed B i Debris flow erosion (E D ) if ;

[0023] For gully erosion prediction, the specific methods include: based on historical topographic data, analyzing historical time periods T... j Small watershed B i The gully is divided into several gully segments. The historical erosion rate of each gully segment is calculated, and the historical time period T is calculated based on the historical erosion rate. j Small watershed B i The amount of gully erosion (E) g ) ij Historical gully erosion was obtained; a multiple regression relationship was established between historical gully erosion and average annual rainfall, slope, and gully width. Based on this multiple regression relationship, the gully erosion rate under future climate model rainfall conditions was calculated, thus obtaining the future gully erosion (Ei) at the small watershed scale. g ) if ;

[0024] For slope erosion prediction, the specific steps include: calculating the soil erosion modulus for each grid in the future time period using rainfall and vegetation data from future climate models by modifying the general soil loss equation RUSLE, and then multiplying it by the grid area to obtain the grid-scale future time period T. f Soil erosion; small watershed B i The future time period T is obtained by summing the soil erosion of each grid cell within the range for future time periods. f Small watershed B i Slope erosion (E) S ) if ;

[0025] The summation of the predicted four types of erosion amounts yields the future time period T. f Inland small watershed B i Total erosion (E) if .

[0026] In some embodiments, in step S2, the historical time period T is calculated according to the following formula. j Small watershed B i Gravitational erosion (E) G ) ij :

[0027]

[0028] In the formula, ρ G The density of the collapsed and landslide material; (V) G ) k For historical period T j Small watershed B i The amount of material released by the k-th landslide, where K is the historical time period T. j Small watershed B i Total number of internal collapses and landslides; volume V of material released for a single collapse or landslide. G Calculate according to the following formula:

[0029]

[0030] In the formula, A G The area of ​​a single landslide is denoted by α and γ, where α is 0.05 ± 0.02, γ is 1.1 to 1.3 for soil landslides, and γ is 1.3 to 1.6 for rock landslides.

[0031] The small watershed B i In the future time period T f All valid rainfall events within the area can be obtained using the following steps:

[0032] First, based on the rainfall data from the future climate model after spatial division, the rainfall data for each time period t in the small watershed is calculated using the following formula. τ Average rainfall within:

[0033]

[0034] In the formula, For small watershed B i In the future time period t τ Average rainfall within, t τ M represents the temporal resolution of future rainfall data, and B represents the small watershed. i The total number of grid cells within, For small watershed B i The m-th grid cell will be in the future time period t. τ The amount of rainfall;

[0035] Small watershed B i During time period t τ average rainfall Divide by the time period t τ As a small watershed B i During time period t τ The average rainfall intensity;

[0036] Iterate through each future time period T f We obtained the time series matrix of rainfall intensity for each small watershed, and then determined the rainfall intensity of each small watershed in each future time period T in chronological order. f The rainfall intensity is used to determine the start of a valid rainfall event. A valid rainfall event begins when the rainfall intensity exceeds a first preset value, and ends when the rainfall intensity falls below the first preset value but continues for at least a second preset value. A valid rainfall event is defined as the period during which the rainfall intensity continuously exceeds the first preset value. The duration D and average rainfall intensity of each valid rainfall event are recorded. Thus, obtain small watershed B i In the future time period T f Information on all valid rainfall events within the region;

[0037] The method of determining whether effective rainfall events in the future will trigger debris flows based on rainfall thresholds set using historical rainfall data is as follows:

[0038] Let the rainfall threshold be I. c The following formula is used to calculate the results on a small watershed basis:

[0039] I c =α D D -β

[0040] In the formula, α D Both β and β are constants set based on historical rainfall data;

[0041] When the average rainfall intensity of an effective rainfall event deems that the mudslide is not triggered;

[0042] deems that the mudslide is triggered, and the statistical small watershed B i in the future period T f will trigger the mudslide wherein l is the number of the rainfall event that will trigger the mudslide, the total number is L events, D l and are the duration and the average rainfall intensity of the lth rainfall event that will trigger the mudslide in the future period T i of the small watershed B f , and the volume of the mudslide outflow V D is calculated by using the following formula:

[0043]

[0044] wherein Q D is the peak flow of the mudslide; γ D is the bulk density of the mudslide; γ W is the bulk density of the clean water; γ S is the bulk density of the solid matter in the mudslide; Q P is the storm flood flow; K P is the confluence coefficient; F i is the area of the small watershed B i ; D C is the congestion coefficient; T is the duration of a mudslide; L D is the length of the main channel of the mudslide; U D is the velocity of the mudslide; and S is the slope of the channel bed.

[0045] The erosion amount (E f ) of the small watershed B i in the future period T D if is calculated by using the following formula:

[0046]

[0047] wherein ρ D is the density of the mudslide outflow; (V D ) l is the volume of the outflow of the lth mudslide in the future period T f of the small watershed B i .

[0048] The erosion amount (E j ) of the channel of the small watershed B i in the historical period T g ij is calculated by using the following formula:​​​

[0049] (E g ) ij =(G g ) ij ·ΔT

[0050]

[0051] In the formula, L s r is the length of the s-th segment of the channel; s The average annual erosion rate of the slope of the gully section is taken as the average annual rate of change of the cross section of the gully section; ρ is the density of eroded sediment; ΔT is the historical time period T. j Duration;

[0052] The future time period T f Small watershed B i Slope erosion (E) S ) if Calculate according to the following formula:

[0053]

[0054] In the formula, A g A represents the area of ​​a single grid cell. m For small watershed B i The future soil erosion modulus of the m-th grid within the range, in RUSLE, is calculated based on rainfall erosivity factor R and dimensionless vegetation cover factor C, respectively, using rainfall and vegetation data from future climate models. The dimensionless soil and water conservation measure factor P is assigned based on historical slope and current land use type; M represents the small watershed B. i The total number of grid cells within.

[0055] In some embodiments, in step S3

[0056] The historical sediment yield of gravity erosion at the small watershed scale is calculated according to the following steps:

[0057] If the landslide does not occur in a river system, the sediment yield and deposition from gravity erosion caused by the landslide will both be zero. If the landslide does occur in a river system, then the sediment yield and deposition from historical time period T will be zero. j Small watershed B i The amount of sediment yield T′ corresponding to the internal gravity erosion G Calculate according to the following formula:

[0058]

[0059] T G =k G ·ρ·w G ·L G ·h

[0060] h = cQ f

[0061] In the formula, p and P represent the historical time period T, respectively. j Small watershed B i Numbering and total number of landslides and collapses connected to the river system within the area; T G The mass of material input into a river from a single landslide; w G L represents the average distance a single landslide extends from the riverbank into the water, obtained based on historical orthophotos or on-site investigations. G k represents the length of the river segment affected by a single landslide. G ρ is the correction factor; h is the density of eroded sediment; ρ is the density of L. G The average water depth of the corresponding river section; Q is the flow rate of the main river at a single landslide location; c and f are both coefficients;

[0062] To determine the future sediment yield and deposition volume of debris flow erosion, the future time period T is first calculated using the following formula. f Small watershed B i Debris transport ratio (SDR) of internal debris flow erosion D ) if :

[0063]

[0064] In the formula, θ represents the small watershed B. i The angle at which the inner main ditch flows into the main river is obtained based on current or historical water system data; γ m and γ D They are the future time period T. f Small watershed B i The bulk density of the main river and debris flows; q m and q D They are the future time period T. f Small watershed B i The unit width discharge of the main river and the debris flow are given. The unit width discharge of the main river is obtained from hydrological data, and the unit width discharge of the debris flow is calculated as q. D =Q D / w D w D For the future time period T f Small watershed B i The width of the debris flow channel, Q D For the future time period T f Small watershed B i Peak flow rate of debris flow;

[0065] Then based on the sediment transport ratio (SDR) D ) if Calculate the future time period T f Small watershed Bi Debris flow erosion results in sediment yield and deposition:

[0066] (T D ) if =(E D ) if ·(SDR D ) if

[0067] (D D ) if =(E D ) if -(T D ) if

[0068] In the formula, (T) D ) if For the future time period T f Small watershed B i The amount of sediment produced by debris flow erosion, (D D ) if For the future time period T f Small watershed B i The amount of sediment eroded by debris flows;

[0069] To determine the future sediment yield and deposition for gully and slope erosion, the future time period T is first calculated based on the sediment connectivity index at the grid scale within each small watershed. f Small watershed B i Sediment transport ratio (SDR) of gully erosion or slope erosion IC ) if :

[0070]

[0071] In the formula, (SDR) max ) if It is the future time period T f Small watershed B i The theoretically achievable maximum sediment transport ratio is related to the topsoil texture; IC if The future time period T is calculated based on historical topographic data and future vegetation data. f Small watershed B i The average sediment connectivity index is taken as the future time period T. f Small watershed B i The mean of the sediment connectivity index at each grid scale; IC0 and k are correction coefficients for calculating the sediment transport ratio;

[0072] Then based on the sediment transport ratio (SDR) IC ) if Calculate the future time period T f Small watershed Bi the channel erosion amount of the future time period T

[0073] (T g ) if =(E g ) if ·(SDR IC ) if

[0074] (D g ) if =(E g ) if -(T D ) if

[0075] (T S ) if =(E S ) if ·(SDR IC ) if

[0076] (D S ) if =(E S ) if -(T S ) if

[0077] wherein (E g ) if is the channel erosion amount of the future time period T f of the small watershed B i , (T g ) if and (D g ) if are the sediment yield amount and the deposition amount corresponding to the channel erosion amount of the future time period T f of the small watershed B i , (E S ) if is the slope erosion amount of the future time period T f of the small watershed B i , (T S ) if and (D S ) if are the sediment yield amount and the deposition amount corresponding to the slope erosion amount of the future time period T f of the small watershed B i .

[0078] In some embodiments, the sediment connectivity index of a grid scale in a future time period of a small watershed is IC, which is calculated according to the following formula:

[0079]

[0080] IS m =RI m +C·P

[0081]

[0082] In the formula, D up The upslope component of a small watershed reflects the upstream sediment yield potential; The average impedance factor of the upslope catchment area of ​​a small watershed represents the resistance of surface roughness to water and sediment flow. A represents the average slope of the uphill catchment area of ​​a small watershed. up D represents the area of ​​the upslope catchment area of ​​a small watershed; dn d represents the downslope component of a small watershed, reflecting the path resistance of sediment reaching its destination; m W represents the length of the flow path along the steepest downhill direction for the m-th grid cell within a small watershed; m Let SS be the impedance factor of the m-th grid within a certain small watershed; m IS represents the slope gradient of the m-th grid cell within a small watershed; max IS represents the maximum surface index of the small watershed where the raster is located. m RI is the surface index of the m-th grid cell within a small watershed. m Let f be the roughness index of the m-th grid cell within a certain small watershed; To calculate RI m Used A raster moving scan pane, x m x represents the elevation of a certain grid cell. s For the area around a certain grille The average elevation of each grid cell; C is the dimensionless vegetation cover factor obtained from vegetation data based on future climate patterns; P is the dimensionless soil and water conservation measure factor obtained from historical slope and current land use type.

[0083] In some embodiments, step S4 specifically includes:

[0084] Based on the distribution of slope, river width, and river type along the course, the rivers in the target basin are divided into X river segments R1, R2, ... R... x ,…R X The regulations stipulate that at most one reservoir or lake shall be provided in each section of the river, and that the reservoir or lake shall be located at the inlet of the river section.

[0085] Calculate the suspended sediment transport in the target basin for each river segment, for the time period T. f Any section of the river R x Its output suspended sediment load (SS)out )x f for:

[0086]

[0087] In the formula, (SS) in )x f For the future time period T f River section R x The amount of suspended sediment input into the main river from upstream; (I T ) n River section R x The amount of suspended sediment input into the main river from the nth tributary, where n and N are the river section R, respectively. x The internal tributary numbers and total number are then... Indicates the future time period T f River section R x The amount of suspended sediment input into the main river from all tributaries within the river section R x The amount of suspended sediment I input from a tributary into the main river T The future sediment yield of the small watershed is calculated based on the result obtained in step S3; (E) B ) xf For the future time period T f River section R x The particle size of the riverbank erosion is consistent with the mass of suspended sediment, calculated based on the work done by the water flow, and the future time period T f River section R x The riverbank erosion figures are calculated based on runoff data from future climate models; (O F ) xf For the future time period T f River section R x The amount of suspended sediment deposited on the floodplain, based on runoff data from future climate models for the future time period T. f River section R x The average discharge, average settling velocity of suspended sediment, and average area of ​​the floodplain were calculated. (O) D ) xf For the future time period T f River section R x The amount of suspended sediment transported away during irrigation or water diversion projects is taken as R of the river section. x The annual average amount of suspended sediment transported and manually excavated during irrigation or water diversion projects over the years; (O R ) xf For the future time period T f River section R x The amount of suspended sediment in reservoirs or lakes is estimated year by year based on runoff data under future climate models.

[0088] In some embodiments, the amount of suspended sediment I of a tributary inputting into the main river in a single river section is calculated according to the following formula T :

[0089] I T =T Gf ′·(Δ s ) G +T D ·(Δ s ) D +T g ·(Δ s ) g +T S

[0090] wherein T Gf ′ is the amount of sediment produced by the gravitational erosion of the small watershed B f in the future time period T i ; T is the amount of sediment produced by the debris flow erosion of a certain small watershed corresponding to a tributary in a single river section in the future time period T D ; T is the amount of sediment produced by the gully erosion of a certain small watershed corresponding to a tributary in a single river section in the future time period T f ; T is the amount of sediment produced by the slope erosion of a certain small watershed corresponding to a tributary in a single river section in the future time period T g ; (Δ f ) S , (Δ f ) s , (Δ G ) s and (Δ D ) s are the proportions of suspended sediment in T g ′, T Gf and T D , respectively, which are obtained by extracting the proportion of the target watershed suspended sediment characteristic particle size in the current time period grading curve of the collapse landslide accumulation, debris flow accumulation fan and gully slope material, respectively;

[0091] The amount of mass (E g ) f of the particle size conforming to the suspended sediment in the riverbank erosion of the river section R x in the future time period T B is calculated according to the following formula xf :

[0092] (E B ) xf =b(ρ w g(Q B ) xf S xf )(h B ) xf (L B )xf (ρ B ) xf ((Δ s ) B ) xf

[0093] where b is an adjustment parameter; p w is the density of clear water; g is the acceleration of gravity; Q B is the bankfull discharge of the river reach; S is the slope of the river reach; h B is the height of the river bank; L B is the length of the river reach; p B is the density of the bank material; (Δ s ) B is the proportion of suspended sediment in the bank material; and Q B is the bankfull discharge of the river reach, except that the remaining parameters are obtained using historical data, except that the runoff data is obtained based on future climate patterns;

[0094] The amount of suspended sediment (O F ) xf accumulated on the floodplain in the river reach R x during the future time period T f is calculated according to the following formula:

[0095]

[0096] where (Q f ) xf is the average flow through the floodplain in the river reach R f during the future time period T x , which is calculated based on future climate patterns; v xf is the average settling velocity of suspended sediment in the river reach R f during the future time period T x ; and (A f ) xf is the average area of the floodplain in the river reach R f during the future time period T x ;

[0097] When calculating the average annual amount of suspended sediment transported away by irrigation or water diversion projects and the amount of artificial dredging in the river reach R x over the years, the amount of suspended sediment (O D ) xj transported away by irrigation or water diversion projects in the river reach R x during the historical time period T j is calculated according to the following formula:

[0098] (O D ) xj = (Q D ) xj· ΔT · (C D ) xj

[0099] In the formula, (Q D ) xj is the historical period T j River R x The average output flow in the irrigation or water diversion project, (C D ) xj is the historical period T j River R x The average sediment concentration of the output water flow in the irrigation or water diversion project;

[0100] Based on the runoff data under the future climate mode, the suspended sediment deposition amount (O R ) xf in the reservoir or lake of the river section R x in the future period T x is calculated year by year, specifically: taking the current period as the starting point, the product of the suspended sediment amount of the main river input upstream of the river section R x in the current period and the average sediment retention rate of the reservoir or lake of the river section R f in the current period is taken as the suspended sediment deposition amount in the reservoir or lake of the river section R x , and the average sediment retention rate of the reservoir or lake is calculated according to the effective storage capacity of the reservoir or lake and the multi-year average runoff; the effective storage capacity of the reservoir or lake is reduced by the suspended sediment deposition amount in the future one year, and the multi-year average runoff is updated after the annual average runoff of the future one year is increased, and the average sediment retention rate of the reservoir or lake in the future one year is continued to be calculated; then the calculation of the average sediment retention rate of the reservoir or lake in the target river basin in all future years is sequentially continued, and on this basis, the average sediment retention rate and the suspended sediment deposition amount of the reservoir or lake of the river section R x in the future period T R are calculated.

[0101] In some embodiments, the average sediment retention rate of the reservoir or lake of the river section R R in a certain year is calculated according to the following formula:

[0102]

[0103] In the formula, C i is the effective storage capacity of the reservoir or lake; I I is the multi-year average runoff of the reservoir or lake.

[0104] The second aspect of the present application provides a device for predicting the sediment in a river basin, comprising:

[0105] The basic data acquisition module is configured to collect basic data of the target watershed, including rainfall, soil, vegetation, terrain, orthophoto and hydrological data, wherein the rainfall, vegetation and hydrological data are future period data obtained by arranging future climate mode data based on the target watershed, and the soil, terrain and orthophoto data are all historical data of the target watershed; each type of basic data is arranged in a grid form and uniformly spatially registered, a small watershed boundary serving as a spatial unit for sediment prediction is set, each type of basic data is spatially divided based on the small watershed boundary, and each type of basic data at the small watershed scale is time-divisionally divided based on the time scale requirement for sediment prediction.

[0106] The erosion prediction module is configured to predict the erosion amount for each small watershed according to different erosion types, i.e., gravity erosion, debris flow erosion, channel erosion and slope erosion, to obtain the future spatio-temporal distribution of each type of erosion amount and total erosion amount in the target watershed; wherein,

[0107] For gravity erosion, the historical spatio-temporal distribution of gravity erosion amount is obtained by using multi-period historical orthophoto of the target watershed and the area-volume relationship of collapse and landslide, the statistical characteristic value of gravity erosion amount in the historical period at the small watershed scale is obtained based on the historical spatio-temporal distribution, and the corresponding statistical characteristic value is selected as the future gravity erosion amount at the small watershed scale according to the risk management requirement.

[0108] For debris flow erosion, all effective rainfall event information of the small watershed in the future period is obtained according to the future rainfall data, and the future debris flow erosion amount at the small watershed scale is obtained based on the effective rainfall event information.

[0109] For channel erosion, the channels in the small watershed scale are equally divided into several channel segments, the historical channel erosion rate is calculated for each channel segment according to the historical terrain data, the historical channel erosion amount at the small watershed scale is calculated based on the historical channel erosion rate, a multiple regression relationship between the historical channel erosion amount and rainfall and terrain parameters is established, the channel erosion rate under the condition of future climate mode rainfall is calculated based on the multiple regression relationship, and thus the future channel erosion amount at the small watershed scale is obtained.

[0110] For slope erosion, the soil erosion amount at the grid scale in the future period is calculated by modifying the universal soil loss equation RUSLE based on the rainfall and vegetation data under the future climate mode, and thus the future slope erosion amount at the small watershed scale is obtained.

[0111] The sediment production and deposition prediction module is configured to respectively predict the future sediment production amount and the future deposition amount corresponding to each type of erosion, and to obtain the future spatio-temporal distribution of sediment production amount and deposition amount of the target watershed according to the future sediment production amount and the future deposition amount of each type of erosion at the small watershed scale; wherein,

[0112] For gravity erosion, firstly, the historical sediment yield and deposition of small watershed scale gravity erosion are calculated, specifically, the historical sediment yield of gravity erosion is calculated based on multi-period historical orthographic images and the area-volume relationship of collapse and landslide and according to the volume of collapse and landslide inputting river material in the water system; the ratio of gravity erosion sediment yield to gravity erosion amount is defined as the gravity erosion sediment transport ratio, the historical gravity erosion sediment transport ratio of each small watershed is calculated according to the historical spatial and temporal distribution of gravity erosion amount, a multiple regression relationship between the historical gravity erosion sediment transport ratio and the main river flow, the main river water depth and the volume of collapse and landslide is established, the future gravity erosion sediment transport ratio is calculated based on the multiple regression relationship and the runoff data under the future climate mode, and the future gravity erosion sediment yield of small watershed scale is calculated through the future gravity erosion amount of small watershed scale and the future gravity erosion sediment transport ratio; the future gravity erosion deposition of small watershed scale is obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion amount of small watershed scale.

[0113] For debris flow erosion, it is assumed that the water system geometry does not change over time within a hundred-year scale, the main river flow is extracted based on the runoff data under the future climate mode, the future debris flow erosion sediment transport ratio of small watershed scale is calculated according to the specific gravity and flow of debris flow and main river in the future period and the convergence angle, and the future debris flow erosion sediment yield and deposition of small watershed scale are calculated according to the sediment transport ratio.

[0114] For channel erosion and slope erosion, firstly, the sediment connectivity index of grid scale in the small watershed range is calculated based on the historical topographic data and future vegetation data, the future sediment transport ratio of small watershed scale is calculated based on the sediment connectivity index, and then the future channel erosion sediment yield and deposition of small watershed scale and the future slope erosion sediment yield and deposition of small watershed scale are calculated according to the future sediment transport ratio respectively.

[0115] The suspended sediment transport amount prediction module is configured to calculate the suspended sediment transport amount of small watershed in the main river system in sections according to the upstream and downstream relationship of the small watershed convergence river position in the target watershed based on the predicted future sediment yield of all small watersheds in the target watershed in each period, and obtain the distribution of suspended sediment transport amount along the flow direction of the main river system by combining the excavation, reservoir sedimentation and input and output amount of suspended sediment in the river section; wherein the suspended sediment output amount caused by excavation is obtained based on the average of historical excavation data; the suspended sediment output amount caused by reservoir sedimentation is calculated based on the effective reservoir capacity and future runoff data.

[0116] The present application has the following advantages:

[0117] 1. The method comprehensively considers and quantifies the contribution of various erosion types to watershed erosion, especially quantifies two types of erosion with high intensity, i.e. gravity erosion and debris flow erosion, which are often ignored, and has less limitations when applied in areas where collapse and landslide debris flow frequently occur;

[0118] 2. Correlate the erosion-sedimentation-deposition physical processes in small watershed scale, correlate the small watershed sedimentation-main river sedimentation physical processes in river system, realize the quantitative description of the process quantity of the erosion-sedimentation and sedimentation in the target watershed, and give the time and space distribution in the target watershed, so that the main erosion area and the sediment source area in the watershed can be quickly and accurately located, and a powerful tool for precise prevention and repair is provided;

[0119] 3. The method system mainly relies on satellite images and hydrological data, has low requirement for field measurement and sampling, realizes easy control of cost, is suitable for large watersheds, and provides technical support for rapid evaluation and decision of large watershed erosion and sediment management. BRIEF DESCRIPTION OF DRAWINGS

[0120] Figure 1 is the overall flowchart of the watershed sediment prediction method provided by the first aspect of the present application;

[0121] Figure 2 is a small watershed erosion and sediment transport schematic diagram involved in the first aspect of the present application;

[0122] Figure 3 is a schematic diagram of the river section suspended load transport calculation process in the watershed sediment prediction method provided by the first aspect of the present application. DETAILED DESCRIPTION

[0123] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0124] On the contrary, the present application covers any alternative, modification, equivalent method and scheme defined by the claims on the essence and scope of the present application. Further, in order to make the public better understand the present application, some specific details are described in detail in the following detailed description of the present application. The present application can also be completely understood without the description of these details by those skilled in the art.

[0125] Referring to Figure 1 , Figure 2 The first aspect of the present application provides a watershed sediment prediction method, which comprises the following steps:

[0126] Step S1, collect the basic data of the target watershed, including rainfall, soil, vegetation, terrain, orthophoto and hydrological data, wherein the rainfall, vegetation and hydrological data use current data and / or future data based on the future climate model data of the target watershed (the current stage future climate model is generally to 2100, i.e. 75 years in the future), the soil, terrain and orthophoto data all use historical data of the target watershed; arrange various types of basic data into grid form and perform unified spatial registration, set the small watershed boundary as the spatial unit of sediment prediction, divide the various types of basic data based on the small watershed boundary, and divide the various types of basic data of the small watershed scale based on the time scale requirement of sediment prediction;

[0127] Step S2, for each small watershed, the erosion amount is predicted according to different erosion types, i.e. gravity erosion, debris flow erosion, channel erosion and slope erosion, to obtain the future spatio-temporal distribution of various types of erosion amount and total erosion amount in the target watershed; wherein,

[0128] For gravity erosion, the historical spatio-temporal distribution of gravity erosion amount is obtained by using multi-period historical orthophoto of the target watershed and the area-volume relationship of collapse and landslide, the statistical characteristic value of gravity erosion amount in the historical period of small watershed scale is obtained based on the historical spatio-temporal distribution, and the corresponding statistical characteristic value is selected as the future gravity erosion amount of small watershed scale according to the risk management requirement;

[0129] For debris flow erosion, all effective rainfall field information of the small watershed in the future period is obtained according to the future rainfall data, and the future debris flow erosion amount of the small watershed scale is obtained based on the effective rainfall field information;

[0130] For channel erosion, the channels in the small watershed scale are divided into several channel segments, the historical channel erosion rate is calculated for each channel segment according to the historical terrain data, the historical channel erosion amount of the small watershed scale is calculated based on the historical channel erosion rate; a multiple regression relationship between the historical channel erosion amount and rainfall, terrain parameters is established, and the channel erosion rate under the future climate model rainfall condition is calculated based on the multiple regression relationship, so as to obtain the future channel erosion amount of the small watershed scale;

[0131] For slope erosion, the soil erosion amount of the grid scale future period is calculated by modifying the universal soil loss equation RUSLE based on the rainfall and vegetation data under the future climate model, so as to obtain the future slope erosion amount of the small watershed scale;

[0132] Step S3, respectively predict the future sediment yield and future deposition amount corresponding to each type of erosion, and obtain the future spatio-temporal distribution of sediment yield and deposition amount of the target watershed according to the future sediment yield and future deposition amount of each type of erosion of the small watershed scale; wherein,

[0133] For gravity erosion, firstly, the historical sediment yield and deposition of gravity erosion at the small watershed scale are calculated. Specifically, the historical sediment yield of gravity erosion is calculated based on multi-period historical orthographic images and the area-volume relationship of landslides and according to the volume of landslides connected with the river system to input river material. The ratio of gravity erosion sediment yield to gravity erosion amount is defined as the gravity erosion sediment transport ratio. The historical gravity erosion sediment transport ratio of each small watershed is calculated according to the historical spatiotemporal distribution of gravity erosion amount. A multiple regression relationship is established between the historical gravity erosion sediment transport ratio, the main river flow, the main river water depth, and the volume of landslides. Based on this multiple regression relationship and the runoff data under the future climate mode, the future gravity erosion sediment transport ratio is calculated. The future gravity erosion sediment yield at the small watershed scale is calculated by the future gravity erosion amount and the future gravity erosion sediment transport ratio at the small watershed scale. The future gravity erosion deposition at the small watershed scale is obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion amount at the small watershed scale.

[0134] For debris flow erosion, it is assumed that the river system geometry does not change over time within a hundred-year scale. The main river flow is extracted based on the runoff data under the future climate mode. The future debris flow erosion sediment transport ratio at the small watershed scale is calculated according to the specific gravity and flow of the debris flow and the main river in the future period, as well as the input angle. The future debris flow erosion sediment yield and deposition at the small watershed scale are calculated according to the sediment transport ratio.

[0135] For channel erosion and slope erosion, firstly, the sediment connectivity index at the grid scale within the small watershed is calculated based on the historical topographic data and future vegetation data. The future sediment transport ratio at the small watershed scale is calculated based on the sediment connectivity index. The future channel erosion sediment yield and deposition at the small watershed scale, and the future slope erosion sediment yield and deposition at the small watershed scale are calculated according to the future sediment transport ratio, respectively.

[0136] Step S4, based on the future sediment yield of each period in all small watersheds in the target watershed predicted in step S3, the small watershed suspended load transport capacity in the main river system is calculated in sections according to the upstream and downstream relationship of the small watershed input river position in the target watershed, and the distribution of suspended load transport capacity along the flow direction of the main river system is predicted by combining the dredging, reservoir sedimentation, and input and output of suspended load in the river section. The suspended load output caused by dredging is obtained based on the average of historical dredging data. The suspended load output caused by reservoir sedimentation is calculated based on the effective reservoir capacity and future runoff data.

[0137] In some embodiments, step S1 is to collect and preprocess the basic data of the target watershed, specifically including:

[0138] Step S11, basic data collection.

[0139] Collect the basic data of the target basin, including rainfall, soil, vegetation, terrain, orthographic image, etc. Among them, the rainfall data is grid data with a time resolution of 3h or more, which is the current rainfall data and / or the rainfall data under the future climate mode (hereinafter referred to as future rainfall data, and the same below); the soil data is mainly the organic matter content in the sand, silt and clay of the surface soil, which is grid data and historical data of the target basin; the vegetation data is the normalized vegetation index (NDVI) and vegetation type (tree, shrub, etc.), which is grid data and uses current data and / or future data; the terrain data uses historical digital elevation model (DEM) with a spatial resolution of not less than 30m; in addition, the basic data also includes historical land use type, which is used for the calculation of dimensionless water and soil conservation measure factor. These basic data are uniformly spatially registered and uniformly spatially resolved to be consistent with the spatial resolution of DEM. The historical orthographic image of the target area needs multiple periods, and the spatial resolution is consistent and uniformly spatially registered.

[0140] Collect the hydrological data of the target basin, including the river system data in the target basin (which can be extracted from DEM and is historical data) and the flow, runoff and sediment information of the hydrological station (the latter three are current data and / or future data), with a time resolution of at least daily scale. If there is no hydrological station in the target basin, find the nearest hydrological station downstream for water and sediment data; if there is flow, depth, etc. or hydrological data obtained by distributed hydrological model simulation in the target area, collect them.

[0141] Step S12, basic data preprocessing.

[0142] Spatial scale division: set the basin corresponding to the minimum first-order river in Horton's law as a small basin, and divide the target basin into I small basins B1, B2, … B i ,…B I , and calculate the area, terrain elevation difference, average slope, channel length, channel width and channel slope of each small basin.

[0143] Time scale division: determine the time scale of the final output data (such as one year, two years) according to the demand of sediment prediction, and uniformly divide each historical basic data with time sequence characteristics of the target basin collected in step S11 into J historical periods T1, T2, … T j ,…,T J , and similarly, divide each future basic data into F future periods T1, T2, … T f ,…,T F , and each period has a length of ΔT, and the current period data only contains one time unit ΔT of data.

[0144] Future rainfall data preprocessing: first use GIS class analysis tool to obtain the vector data file of each small watershed B i Scope, establish the mapping relationship between the small watershed and the future rainfall data in the form of grid, and calculate the average rainfall in each time period t i τ The calculation method is as follows:

[0145]

[0146] In the formula, The average rainfall of the small watershed B i in the future time period t τ , t τ is the time resolution of the future rainfall data, generally 1h, 3h, M is the total number of grids in the small watershed B i , A g is the area of a single grid, The rainfall of the mth grid in the small watershed B i in the future time period t τ .

[0147] The average rainfall of the small watershed B i in the future time period t τ is divided by t τ , that is, the average rainfall intensity of the small watershed in the period. Traverse each future time period T f to obtain the rainfall intensity time series matrix of each small watershed, and judge the rainfall intensity of each small watershed in each future time period T f in order of time. When the rainfall intensity is greater than 1mm / h, it is considered that a valid rainfall begins, and when the rainfall intensity is less than 1mm / h and continues for not less than 6h, it is considered that the valid rainfall stops. The time period with continuous rainfall intensity greater than 1mm / h is regarded as a valid rainfall, and the rainfall duration D (unit: h) and average rainfall intensity (unit: mm / h) and other indexes are recorded to obtain the total valid rainfall information of the small watershed B i in the future time period T f .

[0148] In some embodiments, step S2 is to predict the erosion amount of the small watershed scale according to different erosion types respectively, and divide the watershed erosion in the future time period T f into four types of gravity erosion, debris flow erosion, channel erosion and slope erosion, see Figure 2 , and the prediction process of each type of erosion amount is described as follows:

[0149] Step S21, gravity erosion amount

[0150] ​Firstly, the historical spatio-temporal distribution of gravity erosion is determined based on multi-period historical orthoimages, specifically:

[0151] Gravity erosion is mainly the erosion caused by landslides and collapses in the basin. Through multi-period historical orthoimages, the area of newly added landslides and collapses in the basin is identified by visual recognition or deep neural network method in the historical period T j , and then the volume of the material released by the landslides and collapses in the historical period T G is estimated according to the relationship between the area and the volume of the landslides and collapses. For a single landslide or collapse, the volume of the material released is calculated as:

[0152]

[0153] where V G is the volume of the material released by a single landslide or collapse, A j is the area of a single landslide or collapse, and α and γ are coefficients, with α generally being 0.05±0.02, γ being 1.1-1.3 for soil landslides and γ being 1.3-1.6 for rock landslides.

[0154] The total volume of the material released by the landslides and collapses in the historical period T i is calculated as: j i G ij

[0155]

[0156] where ρ G is the density of the material of the landslides and collapses, generally being 2.0-2.5 t / m 3 for rock landslides and 1.6-2.3 t / m 3 for soil landslides, K is the total number of landslides and collapses in the historical period T j in the small watershed B i , k is the number of the landslides and collapses in the small watershed B j in the historical period T i , and (V G ) k is the volume of the material released by the kth landslide or collapse in the small watershed B j in the historical period T i .

[0157] Subsequently, the cumulative probability distribution curve of the historical gravity erosion in each small watershed is constructed based on the historical spatio-temporal distribution of the gravity erosion, and the corresponding statistical characteristic value (corresponding to the cumulative probability distribution curve of 1%, 10%, 50%, 90%, 99%, etc., with 50% being the median) is selected from the cumulative probability distribution curve as the future period T​​​​f Gravity erosion amount (E i ) of small watershed B G ) if If the risk management requirement is high, a large statistical characteristic value (such as 90% (meaning that the amount of landslide material exceeds 90% of the historical amount value), 99%, etc.) is selected, and vice versa.

[0158] Step S22, debris flow erosion amount

[0159] Debris flow processes strongly transport the material sources in the small watershed, resulting in channel incision and transporting a large amount of material to the fan at the outlet. The volume of the debris flow outflow is approximately calculated as the debris flow erosion amount of the small watershed. Since the debris flow gully is narrow and deep, it is difficult to directly determine whether it occurs through orthographic images, and the on-site investigation has a high time and cost, and most of the debris flow is triggered by rainfall. Therefore, the future period whether the debris flow occurs is determined by the rainfall threshold trigger condition set through the historical rainfall data, and the rainfall threshold is set as I c , based on formula (4) to calculate in units of small watershed:

[0160] I c = α D D -β (4)

[0161] In the formula, D is the duration (h) of an effective rainfall event in the small watershed for future rainfall data, and α D and β are constants set according to historical rainfall data. For the Wenchuan earthquake area, α D = 66.36, and β = -0.79.

[0162] Based on the set rainfall threshold I c , whether the future period T f small watershed B i each time effective rainfall event triggers a debris flow is determined:

[0163] If , it is considered that the debris flow is not triggered, and the outflow volume is 0.

[0164] If , it is considered that the debris flow is triggered, and the small watershed B i in the future period T f can trigger the debris flow of each time rainfall data , wherein l is the number of rainfall events that can trigger the debris flow, the total number is L times, D l and are the duration of the small watershed B i in the future period T fThe duration and average rainfall intensity of the first rainfall event that could trigger a debris flow were determined, and the volume of debris ejected from the debris flow, V, was calculated using equations (5) to (9). D :

[0165]

[0166] In the formula, Q D Peak flow rate of debris flow (unit: m³) 3 / s); The coefficient 19 / 72 in equation (5) is an empirical coefficient given by the "Design Code for Debris Flow Investigation and Prevention in Hydropower Projects" (NB / T 10139-2019); γ D The density of debris flow is determined through field surveys or regional debris flow characteristics; γ W For the density of clear water, except under extreme conditions of extremely high sediment transport, the density of the main river is unlikely to change significantly compared to clear water. Therefore, the density of the main river can be approximated by the density of clear water, while the density of debris flows should be taken as the density of regional debris flows. S Q is the bulk density of solid materials in a debris flow. P For torrential rain and flood flow; K P For steep slopes in mountainous areas, K is generally used as the confluence coefficient. P =0.7~0.9 (weak surface infiltration, fast runoff velocity), K is generally used in hilly areas. P =0.5~0.7 (medium infiltration and runoff conditions), K in plains or vegetated areas P =0.3~0.5 (strong penetration, slow flow velocity); F i For small watershed B i D. C The congestion coefficient can be obtained by referring to the "Design Flood Calculation Standard for Water Conservancy and Hydropower Projects" (Ministry of Water Resources of the People's Republic of China, 2006) (SL44-2006) in conjunction with on-site investigation; T is the duration of the debris flow at this site (unit: s); L D U represents the length of the main debris flow channel; D S represents the velocity of the debris flow; S represents the slope of the gully bed.

[0167] Finally, calculate the future time period T. f Small watershed B i The total volume of debris ejected by the mudslide is used as the future time period T. f Small watershed B i Debris flow erosion (E D ) if :

[0168]

[0169] In the formula, ρ DThe density of the debris flow ejecta is taken as 1.3–1.8 t / m³ for areas dominated by dilute debris flows. 3 The concentration of viscous debris flow in the dominant area is 2.0–2.4 t / m³. 3 The dominant concentration of transitional debris flows is 1.8–2.0 t / m³. 3 ;(V D ) l For the future time period T f Small watershed B i The volume of ejecta from the lth debris flow.

[0170] Step S23, gully erosion

[0171] Gully erosion refers to the downcutting, lateral erosion, and headward erosion that occur in gullies under the action of rainwater runoff.

[0172] First, based on historical topographic data, the historical time period T is... j Small watershed B i The channel within the channel is divided into several channel segments, and the historical time period T is calculated for each channel segment. j Small watershed B i gully erosion rate (G g ) ij (t / y) is:

[0173]

[0174] In the formula, L s Let r be the length of the s-th segment of the channel. s The historical average annual erosion rate of the slope in the gully section (m 2 / y), which is the historical annual average rate of change of the cross-section of the gully section; ρ is the density of eroded sediment, generally taken as 1.6 t / m³. 3 .

[0175] In Equation (11), the historical annual average rate of change r of the cross-section of the channel section s Generally, cross-sections of ditches at different locations are extracted and calculated after unified georegistration of multiple historical DEMs. If conditions permit, they can also be obtained through long-term field monitoring. The historical annual average rate of change is obtained by dividing the change in cross-sectional area between adjacent periods by the data time interval.

[0176] For gully sections in a stable period (such as flash flood gullies, debris flow gullies, etc., and where no major landslides, mudslides, or debris flows have occurred within the time frame of concern), the historical annual average erosion rate r of the gully section slope is... s The value can be approximated as a constant, meaning that whether the historical annual average erosion rate of the gully slope is obtained through DEM or on-site monitoring, only data with a short time span is needed.

[0177] The historical period T is calculated using the following formula. jSmall watershed B i The amount of gully erosion (E) g ) ij :

[0178] (E g ) ij =(G g ) ij ·ΔT (12)

[0179] This allows us to obtain historical gully erosion data at a small watershed scale.

[0180] Subsequently, a multiple regression relationship was established between historical gully erosion and average annual rainfall, as well as topographic parameters (including slope and gully width) (using conventional multiple linear or nonlinear equations). Based on this multiple regression relationship, the future time period T was calculated. f Small watershed B i gully erosion rate (G g ) if Thus, the future time period T is obtained. f Small watershed B i The amount of gully erosion, i.e., the future gully erosion at a small watershed scale (E g ) if .

[0181] Step S24, Slope erosion

[0182] Slope erosion prediction for the target watershed is achieved by using the Modified Universal Soil Loss Equation (RUSLE) to calculate the future time period T for each grid cell based on rainfall and vegetation data from future climate patterns. f The soil erosion modulus within the grid is then multiplied by the grid area to obtain the grid-scale future time period T. f Soil erosion. The amount of soil erosion in small watershed B. i The future soil erosion amount of each grid within the range is accumulated to obtain the future time period T. f Small watershed B i Slope erosion (E) S ) if . Specifically:

[0183] The future soil erosion modulus at the grid scale is calculated as follows:

[0184] A = R·S·L·K·C·P (13)

[0185] In the formula, A is the future soil erosion modulus (t / (km²)). 2 ·y); R is the rainfall erosivity factor (MJ / (km) 2• y), calculated based on future rainfall data; L and S are dimensionless terrain factors, L is slope length factor, S is slope factor, L and S factors are extracted based on historical digital elevation model of the target area; K is soil erodibility factor (t / MJ), calculated based on historical soil property data of the target area; C is dimensionless vegetation cover factor, obtained based on future NDVI data, P is dimensionless soil and water conservation measure factor, assigned according to historical slope and current land use type.

[0186] The future period T is calculated according to the following formula: f The slope erosion amount (E i ) of the small watershed B S ) if :

[0187]

[0188] In the formula, A g is the area of a single grid, A m is the future soil erosion modulus of the mth grid in the small watershed B i range calculated by modifying the universal soil loss equation RUSLE, and M is the total number of grids in the small watershed B i .

[0189] Step S25, total erosion amount and watershed erosion distribution

[0190] The total erosion amount (E f ) of the small watershed B i in the future period T if is the sum of the aforementioned four erosion amounts, that is:

[0191] (E if ) G + (E if ) D + (E if ) g + (E if ) S (15) if (15)

[0192] Thus, the spatial distribution of the total erosion amount, gravity erosion amount, channel erosion amount and slope erosion amount in the watershed in units of small watershed in the future period T f is also obtained. The above calculation is performed for different future periods, and the future spatiotemporal distribution of each type of erosion amount and total erosion amount in the target watershed can be obtained.

[0193] The total erosion amount of the target watershed in the future period T f is:

[0194]

[0195] This allows us to obtain the change in the total erosion of the target area over future time.

[0196] Understandably, step S2 comprehensively considers and quantifies the contribution of various erosion types to the erosion of the target watershed, especially quantifying gravity erosion and debris flow erosion, which are usually ignored. Moreover, based on future erosion data at the small watershed scale, the future spatiotemporal distribution characteristics of various erosions and total erosion in the target watershed can be obtained, improving the level of detail in watershed erosion prediction.

[0197] In some embodiments, step S3 is to predict the future sediment yield within the target watershed. Similar to step S2, step S3 will also predict the future sediment yield and future sediment volume at the small watershed scale for each of the four erosion types, which are described below:

[0198] Step S31: Future Sand Production and Deposition Due to Gravity Erosion

[0199] First, the historical sediment yield from gravity erosion at the small watershed scale is calculated. Specifically, the mass of landslides input to the river is calculated based on multiple historical orthophotos. Two scenarios are considered: First, if the landslide location is not connected to the river system, the gravity erosion generated by the landslide will not be converted into sediment that can be transported by the water flow. Subsequent gully erosion and slope erosion will continue, which will be calculated in the subsequent gully and slope erosion sections and do not need to be repeated here. Second, if the landslide location is connected to the river system, the portion of the material input to the river from a single landslide is calculated using the following formula:

[0200] T G =k G ·ρ·w G ·L G ·h (17)

[0201] h = cQ f (18)

[0202] In the formula, T G The mass of material input into a river from a single landslide; w G L represents the average distance L extends from the riverbank into the water during a landslide. G The length of the river segment affected by the landslide; both parameters can be obtained by extracting multi-period historical orthophotos of the landslide area; k G The correction factor is typically taken as 0.7-0.8; ρ is the density of eroded sediment; h represents the main river and L... G The average water depth of the corresponding river section; Q is the flow rate of the main river at the location of the landslide, obtained from historical hydrological data; c and f are coefficients, generally taken as c = 0.25 to 0.55 and f = 0.3 to 0.4.

[0203] the historical period T j small watershed B i the sediment yield corresponding to the gravity erosion amount of the historical period T G is:

[0204]

[0205] wherein T G ′ is the historical period T j small watershed B i corresponding to the gravity erosion amount of the historical period T j small watershed B i corresponding to the gravity erosion amount of the historical period T

[0206] According to the sediment yield corresponding to the gravity erosion amount of each historical period in the small watershed scale, the historical spatio-temporal distribution of the gravity erosion amount is obtained.

[0207] Then, the ratio of the gravity erosion sediment yield to the gravity erosion amount is defined as the gravity erosion sediment transport ratio, the historical gravity erosion sediment transport ratio of each small watershed is calculated according to the historical spatio-temporal distribution of the gravity erosion amount, a multiple regression relationship between the historical gravity erosion sediment transport ratio, the main river flow, the main river water depth and the collapse landslide volume is established, and based on the multiple regression relationship and the runoff data under the future climate mode, the future gravity erosion sediment transport ratio is calculated, and the future period T f small watershed B i is set as (SDR D ) if The gravity erosion amount (E f ) i of the small watershed B G in the future period T if obtained in step S21 is multiplied by the gravity erosion sediment transport ratio (SDR f ) i of the small watershed B D in the future period T if to obtain the sediment yield T f ′ corresponding to the gravity erosion amount of the small watershed B i in the future period T Gf , thereby obtaining the future gravity erosion sediment yield of the small watershed scale; the future gravity erosion sediment yield of the small watershed scale is subtracted from the future gravity erosion sediment yield to obtain the future gravity erosion deposition amount of the small watershed scale, i.e. G if (E G ) if -T′ Gf (D G ) if in the future period T f small watershed B i ​deposition amount corresponding to the debris flow erosion amount.

[0208] Step S32, future sediment yield and future deposition of debris flow erosion

[0209] First, calculate the future period T f Small watershed B i The sediment transport ratio of the internal debris flow erosion refers to the proportion of sediment transported by the river to the volume of debris flow outflow, which is calculated by the following formula:

[0210]

[0211] In the formula, (SDR D ) if is the future period T f Small watershed B i The sediment transport ratio of the internal debris flow erosion; θ is the angle of the main gully into the main river in the future period T f Small watershed B i , which is obtained by the current river system distribution in the target watershed. The river system distribution in the scale of 100 years is generally considered unchanged; γ m and γ D are the bulk density of the main river and the debris flow in the future period T f Small watershed B i , the bulk density of the main river changes little in different periods and small watersheds, and is obtained according to historical or current river system data, which is generally taken as a constant value; q m and q D are the unit width flow of the main river and the debris flow in the future period T f Small watershed B i , the unit width flow of the main river is obtained according to the hydrological data under the future climate mode, and the unit width flow of the debris flow is calculated as q D = Q D / w D , w D is the width of the debris flow channel in the future period T f Small watershed B i , and Q D is the peak flow of the debris flow in the future period T f Small watershed B i .

[0212] Then, based on the above sediment transport ratio, the sediment yield (T D ) if and the deposition amount (D D ) if of the debris flow erosion amount corresponding to the debris flow erosion amount in the future period T D Small watershed B if are calculated:

[0213] (T D )if = (E D ) if • (SDR D ) if (21)

[0214] (D D ) if = (E D ) if - (T D ) if (22)

[0215] Step S33, future sediment yield of channel erosion and slope erosion

[0216] Step S331, calculate the sediment connectivity index of each sub-basin at the grid scale in the future period:

[0217]

[0218] In the formula, IC is the sediment connectivity index of a sub-basin at the grid scale, and the larger the value, the higher the sediment connectivity; D up is the uphill component of a sub-basin, reflecting the potential of upstream sediment yield, which is obtained using current period data; is the average impedance factor of the upstream catchment area of a sub-basin in the current period, which characterizes the roughness of the ground surface to hinder the flow of water and sediment; is the average slope (m / m) of the upstream catchment area of a sub-basin in the current period; A up is the area (m 2 ) of the upstream catchment area of a sub-basin in the current period; D dn is the downhill component of a sub-basin in the current period, reflecting the path resistance of sediment to the target; d m is the flow path length (m) of the mth grid in a sub-basin along the steepest downhill direction; W m is the impedance factor (local surface roughness) of the mth grid in a sub-basin; SS m is the slope gradient (m / m) of the mth grid in a sub-basin in the current period; the above D up , A up , D dn , SS m are calculated using current period data.

[0219] Impedance factor W in uphill and downhill component calculation m is calculated through the surface index IS m based on roughness index RI m , vegetation cover factor C and soil and water conservation measure P factor:

[0220]

[0221] In the formula, IS max is the maximum land surface index of the small watershed where the grid is located; the land surface index IS m of each grid is calculated as:

[0222] IS m = RI m + C·P (27)

[0223] The roughness index RI m of the mth grid is calculated as:

[0224]

[0225] In the formula, is the average land surface index of the grids used in the calculation The scanning window of the x m th grid moves by one grid, and x s is the elevation of the certain grid. The average elevation of the grids around the certain grid is calculated. The vegetation factors C and P are the C and P factors (formula 13) that have been calculated in the RUSLE method when calculating slope erosion.

[0226] Step S332, calculate the sediment transport ratio

[0227] For channel erosion and slope erosion, the sediment transport ratio refers to the proportion of the sediment transported away by the river to the erosion amount.

[0228] For the future period T f , the channel erosion or slope erosion sediment transport ratio of each small watershed B i is calculated based on the future sediment connectivity index IC:

[0229]

[0230] In the formula, (SDR IC ) ij is the sediment transport ratio of the channel erosion or slope erosion of the small watershed B f in the future period T i ; (SDR max ) ij is the maximum sediment transport ratio that can theoretically occur in the small watershed B f in the future period T i , which is related to the surface soil texture and generally can be taken as 1; IC if is the average sediment connectivity index of the small watershed B f in the future period T i , which is calculated based on the historical topographic data and future vegetation data, and is taken as the future period Tf Small watershed B i The mean of the sediment connectivity index at each grid scale; IC0 and k are correction coefficients for calculating the sediment transport ratio and need to be calibrated. When IC if When =IC0, we have (SDR) IC ) if =0.5(SDR) max ) if Therefore, IC0 is (SDR) max ) if Half of the value corresponds to the sediment connectivity index, which is generally taken as (SDR). max ) if =1, then IC0 is (SDR) max ) if =0.5 corresponds to the sediment connectivity index value, which needs to be determined by trial calculation; k is generally greater than 0, so you can first take a value between k=1 and 2, substitute it and then try to determine the specific value.

[0231] Step S333: Calculate future sediment yield and future deposition.

[0232] Based on the above sediment transport ratio, the future time period T is calculated. f Small watershed B i The amount of gully erosion (E) g ) if Corresponding sediment yield (T) g ) if and sedimentation amount (D) g ) if :

[0233] (T g ) if =(E g ) if ·(SDR IC ) if (30)

[0234] (D g ) if =(E g ) if -(T D ) if (31)

[0235] Similarly, the future time period T is calculated based on the above sediment transport ratio. f Small watershed B i Slope erosion (E) S ) if Corresponding sediment yield (T) S ) if and sedimentation amount (D) S ) if :

[0236] (T S ) if =(E S ) if ·(SDR IC ) if (32)

[0237] (D S ) if =(E S ) if -(T S ) if (33)

[0238] Thus, the spatial distribution of the sediment yield and deposition amount corresponding to the gravitational erosion, debris flow erosion, channel erosion and slope erosion in the small watershed unit in the future period T f is obtained. The future spatio-temporal distribution of the sediment yield and deposition amount in the target watershed is obtained by calculating the above for different future periods.

[0239] It can be understood that step S3 quantifies the future sediment yield and future deposition amount corresponding to various types of erosion in small watershed units, and obtains the future spatio-temporal distribution characteristics of the sediment yield and deposition amount in the target watershed, thereby providing a prediction of the future evolution law of the sediment source in the watershed.

[0240] In some embodiments, step S4 is a prediction of the river sediment transport amount. After calculating the erosion amount, sediment transport amount and deposition amount in all small watersheds in the target watershed for each future period, the sediment transport amount in the main river system is calculated in sections according to the upstream and downstream relationship of the small watershed into the river position. Considering that the transport distance of the coarser particles in the river system is limited, step S4 mainly predicts the sediment transport of the finer particles, see Figure 3 , which specifically includes the following steps:

[0241] The rivers in the target watershed are divided into X river sections R1, R2, … R x ,…R X according to the slope, river width and river type along the distribution. The slope, river width and river type in each river section do not change significantly. At most one reservoir or lake is provided in each river section, and the reservoir or lake is located at the entrance of the river section.

[0242] The suspended sediment transport amount of the rivers in the target watershed is calculated section by section. For any river section R f in the future period T x , the output suspended sediment amount (SS out ) xf is:

[0243]

[0244] In the formula, (SS) in ) xf For the future time period T f River section R x The amount of suspended sediment input into the main river from upstream; (I T ) n River section R x The amount of suspended sediment input into the main river from the nth tributary, where n and N are the river section R, respectively. x The internal tributary numbers and total number are then... Indicates the future time period T f River section R x The amount of suspended sediment input into the main river from all tributaries within the river; (E B ) xf For the future time period T f River section R x The particle size in the riverbank erosion is consistent with the mass of suspended sediment; (O F ) xf For the future time period T f River section R x The amount of suspended sediment deposited on the floodplain; (O M ) xf For the future time period T f River section R x The amount of artificial sand dredging is determined based on the actual scale of sand dredging in the river channel; (O D ) xf For the future time period T f River section R x The amount of suspended sediment transported away in irrigation or water diversion projects; (O R ) xf For the future time period T f River section R x The amount of suspended sediment in reservoirs or lakes.

[0245] It should be noted that suspended sediment deposition in river systems takes a very long time, generally measured in months or even years. Therefore, suspended sediment deposition in river sections is only considered in two forms: floodplain deposition and reservoir / lake deposition.

[0246] Among them, the amount of suspended sediment I input into the main river from a tributary within a single river section, based on the future sediment yield calculation of the small watershed in step S3, is calculated. T The calculation is as follows:

[0247] I T =T Gf ′·(Δ s ) G +T D ·(Δ s ) D +T g ·(Δs ) g +T S (35)

[0248] T Gf ′ is the future period T f a certain small watershed B corresponding to a tributary in a single river section i the sediment yield corresponding to the gravity erosion amount, taken as the future period T f a certain small watershed B i the total mass of material input into the river by all landslides and landslides connected to the river system within the small watershed B; T D is the future period T f the sediment yield corresponding to the debris flow erosion amount of a certain small watershed B corresponding to a tributary in a single river section; T g is the future period T f the sediment yield corresponding to the gully erosion amount of a certain small watershed B corresponding to a tributary in a single river section; T S is the future period T f the sediment yield corresponding to the slope erosion amount of a certain small watershed B corresponding to a tributary in a single river section; (Δ s ) G , (Δ s ) D , (Δ s ) g are the proportions of suspended sediment in T G ′, T D , and T g , respectively, obtained by extracting the proportion of the target watershed suspended sediment characteristic particle size (such as 0.05mm) in the gradation curve of the landslide accumulation, debris flow accumulation fan and gully slope material, which can be obtained through field investigation and sampling or literature research.

[0249] the future period T f the riverbank erosion amount of the river section R x with a particle size that meets the suspended sediment (E B ) xf Based on the calculation of water flow power:

[0250] (E B ) xf = b(ρ w g(Q B ) xf S xf )(h B ) xf (L B ) xf (ρ B ) xf ((Δ s ) B ) xf(36)

[0251] where b is an adjustment parameter used to adjust the calculation result to match the actual situation; p w is the density of clean water; g is the acceleration of gravity; Q B is the bankfull discharge of the river section, which can be approximately taken as the flood discharge of 1-2 year return period in the absence of measured data; S is the slope of the river section, p wg (Q B ) xf S xf is the flow work of the river section R f in the future period T x ; h B is the height of the river bank; L B is the length of the river section; p B is the density of the bank material; (Delta s ) B is the proportion of suspended sediment in the bank material; among the above parameters, except for the bankfull discharge Q B , which is obtained based on the runoff data under the future climate mode, the rest are obtained using historical data.

[0252] The amount of suspended sediment (O f ) x accumulated on the floodplain in the river section R F in the future period T xf is calculated as:

[0253]

[0254] where (Q f ) xf is the average flow through the floodplain in the river section R f in the future period T x , which is calculated based on the runoff data under the future climate mode; v xf is the average settling velocity of suspended sediment in the river section R f in the future period T x ; (A f ) xf is the average area of the floodplain in the river section R f in the future period T x ; v xf and (A f ) xf are respectively predicted using the respective historical data variation trends for the corresponding values in the future period, and if the historical data shows no trend of increase or decrease, the predicted value is taken as the value in the current period.

[0255] In the calculation of the river section R xThe annual average of the amount of suspended sediment carried away in irrigation or water diversion projects and the amount of artificial dredging in history period T is calculated according to the following formula j River section R x The amount of suspended sediment carried away in irrigation or water diversion projects (O D ) xj ) is calculated as follows:

[0256] (O D ) xj = (Q D ) xj · ΔT · (C D ) xj (38)

[0257] In the formula, (Q D ) xj is the average output flow of the river section R j in the irrigation or water diversion project in history period T x , and (C D ) xj is the average sediment concentration of the output flow of the river section R j in the irrigation or water diversion project in history period T x . Both values are obtained through actual operation mode of the irrigation or water diversion project.

[0258] The amount of suspended sediment deposition (O R ) xf in the reservoir or lake of the river section R f in future period T x is calculated year by year based on runoff data under future climate mode, and is specifically calculated as follows:

[0259] The product of the amount of suspended sediment carried away by the main river upstream of the river section R x in the current period and the average sediment retention rate of the reservoir or lake of the river section R x in the current period is taken as the amount of suspended sediment deposition in the reservoir or lake of the river section R x in the current period, and the average sediment retention rate of the reservoir or lake is calculated according to the effective storage capacity of the reservoir or lake and the multi-year average runoff; the amount of suspended sediment deposition is subtracted from the effective storage capacity of the reservoir or lake in the next year, and the multi-year average runoff is updated after adding the annual average runoff of the next year, and the average sediment retention rate of the reservoir or lake in the next year is continued to be calculated; then the calculation is sequentially continued for the average sediment retention rate of the reservoir or lake in the target basin in all future years, and on this basis, the average sediment retention rate and the amount of suspended sediment deposition of the reservoir or lake of the river section R f in future period T x are calculated.

[0260] Further, the amount of suspended sediment deposition (O R ) xf in the reservoir or lake of the river section R f in a certain year is calculated according to the following formula:x The average sand blocking rate of the reservoir or the lake is calculated according to the following formula:

[0261]

[0262] In the formula, C R is the effective storage capacity (10 3 *m 3 ) of the reservoir or the lake, I R is the multi-year average runoff (10 3 *m 3 ) of the reservoir or the lake.

[0263] It can be understood that the embodiment of the present application can obtain the future prediction of the along-stream distribution of the suspended sediment transport capacity of the river system in the target river basin, and specifically depict the natural process of erosion and sediment production and the future influence of dredging, irrigation, reservoirs and other artificial facilities on the suspended sediment transport.

[0264] The second aspect of the embodiment of the present application provides a river basin sediment prediction device, which comprises:

[0265] The basic data acquisition module is configured to collect the basic data of the target river basin, including rainfall, soil, vegetation, terrain, orthographic image and hydrological data, wherein the rainfall, vegetation and hydrological data are obtained by using current data and / or future period data based on future climate mode data of the target river basin, and the soil, terrain and orthographic image data are obtained by using historical data of the target river basin; the various types of basic data are arranged in a grid form and uniformly spatially registered, the small watershed boundary serving as the spatial unit for sediment prediction is set, the various types of basic data are spatially divided based on the small watershed boundary, and the various types of basic data of the small watershed scale are time-divisionally divided based on the time scale requirement of the sediment prediction;

[0266] The erosion prediction module is configured to predict the erosion amount for each small watershed according to different erosion types, i.e. gravity erosion, debris flow erosion, channel erosion and slope erosion, to obtain the future space-time distribution of the various types of erosion amount and the total erosion amount in the target river basin; wherein,

[0267] For gravity erosion, the historical space-time distribution of the gravity erosion amount is obtained by using the multi-period historical orthographic image of the target river basin and the area-volume relationship of collapse and landslide, the statistical characteristic value of the gravity erosion amount in the historical period of the small watershed scale is obtained based on the historical space-time distribution, and the corresponding statistical characteristic value is selected as the future gravity erosion amount of the small watershed scale according to the risk management requirement;

[0268] For debris flow erosion, the total effective rainfall field information of the small watershed in the future period is obtained according to the future rainfall data, and the future debris flow erosion amount of the small watershed scale is obtained based on the effective rainfall field information;

[0269] For channel erosion, the channels in the small watershed scale are divided into several channel segments, the historical channel erosion rate of each channel segment is calculated according to the historical topographic data, and the historical channel erosion amount of the small watershed scale is calculated based on the historical channel erosion rate; a multiple regression relationship between the historical channel erosion amount, rainfall and topographic parameters is established, and the channel erosion rate under the rainfall condition of the future climate mode is calculated based on the multiple regression relationship, so as to obtain the future channel erosion amount of the small watershed scale;

[0270] For slope erosion, the rainfall and vegetation data under the future climate mode are corrected through the universal soil loss equation RUSLE to calculate the soil erosion amount of the grid scale in the future period, so as to obtain the future slope erosion amount of the small watershed scale;

[0271] The sediment production and deposition prediction module is configured to predict the future sediment production amount and the future deposition amount corresponding to each type of erosion respectively, and to obtain the future spatio-temporal distribution of the sediment production amount and the deposition amount of the target watershed according to the future sediment production amount and the future deposition amount of each type of erosion in the small watershed scale; wherein,

[0272] For gravity erosion, the historical sediment production amount and the deposition amount of the gravity erosion in the small watershed scale are calculated, specifically, the historical sediment production amount of the gravity erosion is calculated based on the multi-period historical orthographic image and the area-volume relationship of the collapse landslide and according to the amount of the river material input by the collapse landslide connected with the water system; the ratio of the gravity erosion sediment production amount to the gravity erosion amount is defined as the gravity erosion sediment transport ratio, the historical gravity erosion sediment transport ratio of each small watershed is calculated according to the historical spatio-temporal distribution of the gravity erosion amount, a multiple regression relationship between the historical gravity erosion sediment transport ratio, the main river flow, the main river water depth and the collapse landslide volume is established, the future gravity erosion sediment transport ratio is calculated based on the multiple regression relationship and the runoff data under the future climate mode, the future gravity erosion sediment production amount of the small watershed scale is calculated through the future gravity erosion amount of the small watershed scale and the future gravity erosion sediment transport ratio; the future gravity erosion deposition amount of the small watershed scale is obtained by subtracting the future gravity erosion sediment production amount from the future gravity erosion amount of the small watershed scale;

[0273] For debris flow erosion, it is assumed that the water system geometry does not change over time in the hundred-year scale, the main river flow is extracted based on the runoff data under the future climate mode, the future debris flow erosion sediment transport ratio of the small watershed scale is calculated according to the specific gravity and flow of the debris flow and the main river in the future period, and the entry angle, and the future debris flow erosion sediment production amount and the deposition amount of the small watershed scale are calculated according to the sediment transport ratio;

[0274] For gully erosion and slope erosion, firstly, the sediment connectivity index of the grid scale in the small watershed is calculated based on the historical terrain data and the future vegetation data, the future sediment transport ratio of the small watershed scale is calculated based on the sediment connectivity index, and then the future gully erosion sediment yield and deposition of the small watershed scale and the future slope erosion sediment yield and deposition of the small watershed scale are calculated according to the future sediment transport ratio, respectively;

[0275] The suspended sediment transport amount prediction module is configured to calculate the suspended sediment transport amount of each small watershed in the main river system according to the upstream and downstream relationship of the position of each small watershed in the target watershed in the target watershed in each period based on the predicted future sediment yield of all small watersheds in the target watershed, and obtain the distribution of the suspended sediment transport amount along the flow direction of the main river system by combining the dredging, reservoir sedimentation and input and output of the suspended sediment in the river section; wherein the suspended sediment output caused by dredging is obtained based on the average of historical dredging data; the suspended sediment output in the river section caused by reservoir sedimentation is calculated based on the effective reservoir capacity and future runoff data.

[0276] It should be noted that the foregoing embodiment of the watershed sediment prediction method is also applicable to the watershed sediment prediction device of the present embodiment, and will not be described here.

[0277] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms must be directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, the different embodiments or examples described in the present specification and the features of the different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0278] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A method of predicting sediment in a drainage basin, characterized by, Comprise: Step S1, collect the basic data of the target watershed, including rainfall, soil, vegetation, terrain, orthophoto and hydrological data, wherein the rainfall, vegetation and hydrological data adopt current data and / or future data based on future climate model data of the target watershed, the soil, terrain and orthophoto data all adopt historical data of the target watershed; arrange various types of basic data into grid form and perform unified spatial registration, set the small watershed boundary as the spatial unit of sediment prediction, divide the various types of basic data based on the small watershed boundary, and divide the small watershed scale various types of basic data based on the time scale requirement of sediment prediction; Step S2, for each small watershed, the erosion amount is predicted according to different erosion types, i.e. gravity erosion, debris flow erosion, channel erosion and slope erosion, to obtain the future spatio-temporal distribution of various types of erosion amount and total erosion amount in the target watershed; wherein, For gravity erosion, the historical spatio-temporal distribution of gravity erosion amount is obtained by using multi-period historical orthophoto of the target watershed and the area-volume relationship of collapse and landslide, the statistical characteristic value of gravity erosion amount in the historical period of small watershed scale is obtained based on the historical spatio-temporal distribution, and the corresponding statistical characteristic value is selected as the future gravity erosion amount of small watershed scale according to the risk management requirement; For debris flow erosion, all effective rainfall field information of small watershed in the future period is obtained according to future rainfall data, and the future debris flow erosion amount of small watershed scale is obtained based on the effective rainfall field information; For channel erosion, the channels in small watershed scale are divided into several channel segments, the historical channel erosion rate of each channel is calculated according to the historical terrain data, the historical channel erosion amount of small watershed scale is calculated based on the historical channel erosion rate; a multiple regression relationship between the historical channel erosion amount and rainfall, terrain parameters is established, and the channel erosion rate under the condition of future climate model rainfall is calculated based on the multiple regression relationship, so as to obtain the future channel erosion amount of small watershed scale; For slope erosion, the soil erosion amount of grid scale future period is calculated by modifying the universal soil loss equation RUSLE based on the rainfall and vegetation data under the future climate model, so as to obtain the future slope erosion amount of small watershed scale; Step S3, respectively predict the future sediment yield and future deposition amount corresponding to each type of erosion, and obtain the future spatio-temporal distribution of sediment yield and deposition amount of the target watershed according to the future sediment yield and future deposition amount of each type of erosion of small watershed scale; wherein, For gravity erosion, firstly, the historical sediment yield and deposition of small watershed scale gravity erosion are calculated. Specifically, the historical sediment yield of gravity erosion is calculated based on multi-period historical orthographic images and the area-volume relationship of landslides and according to the volume of landslide input into the river connected with the river system. The ratio of gravity erosion sediment yield to gravity erosion amount is defined as the gravity erosion sediment transport ratio. According to the historical spatio-temporal distribution of gravity erosion amount, the historical gravity erosion sediment transport ratio of each small watershed is calculated. A multiple regression relationship between the historical gravity erosion sediment transport ratio and the main river flow, the main river water depth and the volume of landslide is established. Based on the multiple regression relationship and the runoff data under the future climate mode, the future gravity erosion sediment transport ratio is calculated. The future gravity erosion sediment yield of small watershed scale is calculated by the future gravity erosion amount and the future gravity erosion sediment transport ratio of small watershed scale. The future gravity erosion deposition of small watershed scale is obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion amount of small watershed scale. For debris flow erosion, it is assumed that the river system geometry does not change over time within a hundred-year scale. The main river flow is extracted based on the runoff data under the future climate mode. The future debris flow erosion sediment transport ratio of small watershed scale is calculated according to the specific gravity and flow of debris flow and main river in the future period, as well as the input angle. The future debris flow erosion sediment yield and deposition of small watershed scale are calculated according to the sediment transport ratio. For channel erosion and slope erosion, firstly, the sediment connectivity index of grid scale within the small watershed is calculated based on the historical terrain data and future vegetation data. The future sediment transport ratio of small watershed scale is calculated based on the sediment connectivity index. The future channel erosion sediment yield and deposition of small watershed scale, and the future slope erosion sediment yield and deposition of small watershed scale are calculated according to the future sediment transport ratio, respectively. In step S4, based on the future sediment yield of all small watersheds in the target watershed in each period predicted in step S3, the small watershed sediment transport capacity of the main river system is calculated in sections according to the upstream and downstream relationship of the small watershed input river position in the target watershed. The distribution of sediment transport capacity along the flow direction of the main river system is predicted by combining the sediment excavation, reservoir sedimentation and the input and output of suspended sediment in the river section. The suspended sediment output caused by sediment excavation is obtained based on the average of historical sediment excavation data. The suspended sediment output caused by reservoir sedimentation is calculated based on the effective reservoir capacity and future runoff data.

2. The method of claim 1, wherein, In the basic data collected in step S1, the time resolution of rainfall data is not less than 3h. Soil data includes the organic matter content in sand, silt and clay of the surface soil. Vegetation data includes normalized vegetation index and vegetation type. Topographic data adopts digital elevation model with spatial resolution not less than 30m. Hydrological data includes river system data, flow and runoff in the target watershed. The basic data also includes current land use type, which is used for calculating the dimensionless water and soil conservation measure factor. The spatial resolution used for unified spatial registration of various grid forms of basic data is consistent with the spatial resolution of the digital elevation model. The small watershed is a watershed corresponding to the minimum first-order river in the Horton law, and the target watershed is divided into I small watersheds B1, B2, … B i ,…B I , based on the digital elevation model, the area, terrain elevation difference, average slope, channel length, channel width and channel slope of each small watershed are counted; the time length adopted for time period division of each type of basic data is equal.

3. The method of claim 1, wherein, In step S2, For gravity erosion prediction, the specific methods include: identifying historical time periods T using multi-period historical orthophotos of the target watershed. j The newly added landslide area within the area is statistically analyzed based on the landslide area and the landslide area-volume relationship for the historical time period T. j Small watershed B i The total volume of material released by the collapse and landslide within the area, as the historical time period T. j Small watershed B i Gravitational erosion (E) G ) ij Based on this gravitational erosion amount (E) G ) ij The historical spatiotemporal distribution of gravity erosion is obtained; based on the historical spatiotemporal distribution of gravity erosion, a cumulative probability distribution curve of historical gravity erosion in each sub-basin is constructed; according to risk management requirements, the corresponding statistical characteristic value is selected from the cumulative probability distribution curve as the future time period T. f Small watershed B i Gravitational erosion (E) G ) if ; For debris flow erosion prediction, the specific methods include: obtaining small watershed B based on rainfall data from future climate models. i In the future time period T f Information on all valid rainfall events within the timeframe is collected, including the duration and average intensity of each event. Based on historical rainfall data and established threshold triggering conditions, it is determined whether each valid rainfall event will trigger a debris flow in the future. If a valid rainfall event is determined not to trigger a debris flow, the ejecta volume for that event is set to 0. If a valid rainfall event is determined to trigger a debris flow, the ejecta volume for that event is calculated. The future timeframe T is then statistically analyzed. f Small watershed B i The total volume of debris ejected by the mudslide is used as the future time period T. f Small watershed B i Debris flow erosion (E D ) if ; For the prediction of gully erosion amount, specifically including: according to the historical terrain data, the historical period T j The small watershed B i The gully in the gully is divided into several gully sections, and the historical gully erosion rate of each gully section is calculated respectively, and the historical gully erosion amount (E g ) ij ) of the historical period T j The small watershed B i Is obtained by calculating the historical gully erosion rate; a multiple regression relationship between the historical gully erosion amount and the annual average rainfall, slope and gully width is established, and the gully erosion rate under the rainfall condition of the future climate mode is calculated based on the multiple regression relationship, so as to obtain the future gully erosion amount (E g ) if ; For the prediction of the slope erosion amount, specifically including: calculating the soil erosion modulus of each grid in the future period by correcting the general soil loss equation RUSLE for the rainfall and vegetation data under the future climate mode, and then multiplying the grid area to obtain the soil erosion amount of the grid in the future period T f ; accumulating the soil erosion amount of each grid in the future period in the small watershed B i to obtain the slope erosion amount (E S ) of the small watershed B i in the future period T f . if ; Summing the predicted four types of erosion amounts to obtain the total erosion amount (E) of the future period T f Inner small watershed B i of the total erosion amount (E) if .

4. The method of claim 3, wherein, In step S2, the history period T is calculated according to the following formula j Small watershed B i : gravitational erosion amount (E G ) ij : wherein p G is the density of the collapsed landslide material; (V G ) k is the volume of material released by the kth collapsed landslide in the historical period T j in the small watershed B i K is the total number of collapsed landslides in the historical period T j in the small watershed B i The volume of material released by a single collapsed landslide V G is calculated according to the following formula: In the formula, A G is the area of a single collapse landslide; α and γ are coefficients, α is 0.05±0.02, γ is 1.1-1.3 for a soil landslide and 1.3-1.6 for a rock landslide; The small watershed B i In the future period T f All effective rainfall field information in the future period T is obtained according to the following steps: Firstly, the average rainfall in each time period t of the small watershed under the future climate pattern after the spatial division is calculated according to the following formula: τ Yt=∑i=1nXi / t wherein is the average rainfall in the future time period t i in the small watershed B τ is the average rainfall in the future time period t τ is the time resolution of the future rainfall data, M is the total number of grids in the small watershed B i is the rainfall in the future time period t i in the mth grid in the small watershed B τ in the future time period t​ The small watershed B i The average rainfall in the time period t τ Divided by the time period t τ The average rainfall intensity in the time period t i The average rainfall intensity in the time period t τ The average rainfall intensity in the time period t​ Iterate through each future time period T f We obtained the time series matrix of rainfall intensity for each small watershed, and then determined the rainfall intensity of each small watershed in each future time period T in chronological order. f The rainfall intensity is used to determine the start of a valid rainfall event. A valid rainfall event begins when the rainfall intensity exceeds a first preset value, and ends when the rainfall intensity falls below the first preset value but continues for at least a second preset value. A valid rainfall event is defined as the period during which the rainfall intensity continuously exceeds the first preset value. The duration D and average rainfall intensity of each valid rainfall event are recorded. Thus, obtain small watershed B i In the future time period T f Information on all valid rainfall events within the region; The rainfall threshold trigger condition set by the historical rainfall data judges whether each field effective rainfall event of a future period triggers a debris flow, and specifically comprises: Let the rainfall threshold be I c in small watershed units as follows: I c = a D D -β In the formula, α D Both β and β are constants set based on historical rainfall data; When the average rainfall intensity of a single effective rainfall event is less than 0.5 mm / h, it is considered that no mudflow is triggered; when the average rainfall intensity of a valid rainfall event is considered to trigger a debris flow, the statistical small watershed B i in the future period T f will trigger a debris flow, the rainfall data P l (D l , ) of each rainfall event, where l is the number of rainfall event that will trigger a debris flow, the total number is L events, D l and are the duration and average rainfall intensity of the lth rainfall event that will trigger a debris flow in the future period T i , and the volume of debris flow V f is calculated by the following formula: D : where Q D is the peak flow of debris flow; γ D is the bulk density of debris flow; γ W is the bulk density of clear water; γ S is the bulk density of solid matter in debris flow; Q P is the flow of storm flood; K P is the confluence coefficient; F i is the area of small watershed B i ; D C is the congestion coefficient; T is the duration of a debris flow; L D is the length of the main channel of debris flow; U D is the velocity of debris flow; S is the slope of the channel bed; said future time period T f small watershed B i debris flow erosion (E D ) if is calculated according to the following formula: wherein p D is the debris density; (V D ) l is the debris volume of the i-th field of debris in the future time period T f is the small watershed B i ​ said historical period T j small watershed B i channel erosion (E g ) ij is calculated according to the following formula: In the formula, L s is the length of the s-th channel segment; r s is the average annual erosion rate of the side slope of the channel segment, which is taken as the average annual change rate of the cross section of the channel segment; p is the density of the eroded sediment; and AT is the length of the historical period T j . the future period T f small watershed B i of the slope erosion amount (E S ) if is calculated according to the following formula: where A g is the single grid area; A m is the small watershed B i is the future soil erosion modulus of the mth grid in the range, in the RUSLE, the rainfall erosivity factor R and the dimensionless vegetation cover factor C are calculated based on the rainfall data and vegetation data under the future climate model, respectively, and the dimensionless water and soil conservation measure factor P is assigned based on the historical slope and the current land use type; M is the total number of grids in the small watershed B i .

5. The method of claim 1, wherein, In step S3, The historical sediment yield of the small watershed scale gravity erosion is calculated according to the following steps: If the collapse and landslide occurs at a position not connected with the river system, the sediment yield and deposition amount of gravity erosion caused by the collapse and landslide are both 0, and if the collapse and landslide occurs at a position connected with the river system, the historical period T j Small watershed B i The sediment yield T' corresponding to the internal gravity erosion amount G is calculated according to the following formula: T G = k G · p · w G · L G · h h = cQ f In the formula, p and P are the historical time periods T j Small watershed B i The number and total number of landslides and collapses connected to the river system T G mass of material input to the river by a single collapse landslide; w G average distance of a single collapse landslide extending from the river bank into the water, based on historical ortho imagery or field investigation; L G length of river section affected by a single collapse landslide; k G correction factor; p is the density of eroded sediment; h G average water depth of the corresponding river section; Q is the flow of the main river at the location of a single collapse landslide; c and f are both coefficients; For the future sediment yield and future deposition amount of debris flow erosion, first, the future period T is calculated in accordance with the following formula f Small watershed B i The sediment transport ratio (SDR D ) if : where θ is the angle of the sub-basin B i with the main river, obtained based on current or historical drainage data; γ m and γ D are the future discharge of the main river and the debris flow, respectively, at time T f ; ρ i and ρ m are the bulk density of the main river and the debris flow, respectively, of the sub-basin B D ; q f and q i are the unit width discharge of the main river and the debris flow, respectively, of the sub-basin B D ; Q D is the peak discharge of the debris flow of the sub-basin B D ; and w D is the width of the debris flow channel of the sub-basin B f . i D f i where θ is the angle of the sub-basin B i with the main river, obtained based on current or historical drainage data; γ m and γ D are the future discharge of the main river and the debris flow, respectively, at time T f ; ρ i and ρ m are the bulk density of the main river and the debris flow, respectively, of the sub-basin B D ; q f and q i are the unit width discharge of the main river and the debris flow, respectively, of the sub-basin B D ; Q D is the peak discharge of the debris flow of the sub-basin B D ; and w D is the width of the debris flow channel of the sub-basin B f . i D f i where θ is the angle of the sub-basin B i with the main river, obtained based on current or historical Then the sediment transport ratio (SDR D ) if Calculate the future period T f Small watershed B i Debris flow erosion of sediment yield and sedimentation: (T D ) if = (E D ) if · (SDR D ) if (DD) if = (ED) if - (T D ) if wherein (T D ) if is the future time period T f is the small watershed B i is the sediment yield of the debris flow erosion, (D D ) if is the future time period T f is the small watershed B i is the deposition of the debris flow erosion; For the future sediment yield and future sediment deposition of channel erosion and slope erosion, firstly, the future time period T f Small watershed B i Sediment transport ratio (SDR IC ) if : where (SDR max ) if is the future time period T f the average sediment connectivity index for the sub-basin B i Theoretically, the maximum sediment transport ratio that can occur is related to the surface soil texture; IC if is the average sediment connectivity index for the sub-basin B f for the future time period T i is the average sediment connectivity index for the sub-basin B f for the future time period T i is the average sediment connectivity index for the sub-basin B IC0 and k are correction coefficients for calculating the sediment transport ratio; Then, based on the sediment transport ratio (SDR IC ) if The future period T f The channel erosion of the small watershed B i corresponding to the sediment yield and deposition, and the slope erosion corresponding to the sediment yield and deposition: (T g ) if = (E g ) if · (SDR IC ) if (Dg) if = (E g ) if - (T D ) if (T S ) if = (E S ) if · (SDR IC ) if (DS) if = (E S ) if - (T S ) if In the formula, (E g ) if is the channel erosion amount of the small watershed B f in the future period T i , (T g ) if and (D g ) if are the sediment yield and deposition amount corresponding to the channel erosion amount of the small watershed B f in the future period T i , respectively. S ) if is the slope erosion amount of the small watershed B f in the future period T i , (T S ) if and (D S ) if are the sediment yield and deposition amount corresponding to the slope erosion amount of the small watershed B f in the future period T i , respectively.

6. The method of predicting sediment of a river basin according to claim 5, wherein, Supposing that the sediment connectivity index of a grid scale in a small watershed in a future period is IC, the following formula is used for calculation: IS m = RI m + C P where D up is the upslope component of a certain small watershed, reflecting the potential of sediment production in the upstream; is the average resistance factor of the upslope catchment area of a certain small watershed, representing the roughness of the surface to the flow of water and sediment; is the average slope of the upslope catchment area of a certain small watershed; A up is the area of the upslope catchment area of a certain small watershed; D dn is the downslope component of a certain small watershed, reflecting the path resistance of sediment to reach the target; d m is the flow path length of the mth grid along the steepest downslope direction within a certain small watershed; W m is the resistance factor of the mth grid within a certain small watershed; SS m is the slope gradient of the mth grid within a certain small watershed; IS max is the maximum surface index of the small watershed where the grid is located; IS m is the surface index of the mth grid within a certain small watershed; RI m is the roughness index of the mth grid within a certain small watershed; is the moving scanning window of x m grids used in the calculation of RI ; x m is the elevation of a certain grid; x s is the average elevation of the x grids around a certain grid; C is the dimensionless vegetation cover factor based on the vegetation data under the future climate scenario; P is the dimensionless soil and water conservation measure factor based on the historical slope and the assigned value of the current land use type.

7. The method of claim 1, wherein, Step S4 specifically comprises: According to the slope, river width, river type along the distribution of the target basin will be divided into X river R1, R2, … R x ,…R X , each river section is provided with at most one reservoir or lake, and the reservoir or lake is located at the entrance of the river section; The suspended sediment transport capacity of the river in the target basin is calculated section by section, and the total suspended sediment transport capacity of the target basin in a time period T is calculated f for any river section R x The output of the suspended sediment transport capacity (SS out ) xf is: where (SS in ) xf is the future sediment yield of the main river in the future time period T f for the river reach R x , and (I T ) n is the amount of suspended sediment input to the main river from the nth tributary in the river reach R x , where n and N are the number and total number of tributaries in the river reach R x , respectively, and is the total amount of suspended sediment input to the main river from all tributaries in the river reach R f in the future time period T x , and for the amount of suspended sediment input to the main river from a certain tributary in the river reach R x , I T is calculated according to the future sediment yield of the small watershed obtained in step S3.(E B ) xf is the amount of suspended sediment in the river bank erosion in the river reach R f in the future time period T x , which is calculated based on the water flow power, and the amount of river bank erosion in the river reach R f in the future time period T x is calculated based on the runoff data under the future climate model.(O F ) xf is the amount of suspended sediment deposited on the floodplain in the river reach R f in the future time period T x , which is calculated based on the average flow through the floodplain, the average settling velocity of suspended sediment, and the average area of the floodplain in the river reach R f in the future time period T x under the future climate model.(O D ) xf is the amount of suspended sediment transported away in irrigation or water diversion projects in the river reach R f in the future time period T x , which is taken as the average annual amount of suspended sediment transported away in irrigation or water diversion projects and the amount of artificial dredging in the river reach R x in previous years.(O R ) xf is the amount of suspended sediment deposited in the reservoir or lake in the river reach R f in the future time period T x , which is calculated year by year based on the runoff data under the future climate model.

8. The method of claim 7, wherein, The amount of suspended sediment I inputted from a branch stream into a main river in a single river section is calculated according to the following formula T : I T = T Gf · (Δ s ) G + T D · (Δ s ) D + T g · (Δ s ) g + T S In the formula, T Gf is the future period T f The gravity erosion amount of the small watershed B i corresponds to the sediment yield; T D is the future period T f The sediment yield corresponding to the debris flow erosion amount of a certain small watershed corresponding to a tributary in a single river section; T g is the future period T f The sediment yield corresponding to the gully erosion amount of a certain small watershed corresponding to a tributary in a single river section; T S is the future period T f The sediment yield corresponding to the slope erosion amount of a certain small watershed corresponding to a tributary in a single river section; (Δ s ) G , (Δ s ) D , (Δ s ) g are the proportions of suspended sediment in T Gf ', T D and T g , respectively, which are obtained by extracting the proportion of the target watershed suspended sediment characteristic particle size in the current period grading curve of the collapse landslide accumulation, debris flow accumulation fan and gully slope material, respectively. The future period T is calculated according to the following formula f River section R x The amount of riverbank erosion of the river section R in which the mass of the particle size conforming to the suspended load (E B ) xf : (E B ) xf = b(p w g(Q B ) xf S xf )(h B ) xf (L B ) xf (ρ B ) xf ((Δ s ) B ) xf where b is an adjustment parameter; p w is the density of clear water; g is the acceleration of gravity; Q B is the bankfull discharge of the river reach; S is the slope of the river reach; h B is the height of the river bank; L B is the length of the river reach; p B is the density of the bank material; (D s ) B is the proportion of suspended sediment in the bank material; and Q B The remaining parameters are obtained using historical data, except for the runoff data, which is obtained based on future climate models. The future period T is calculated according to the following formula f River section R x The amount of suspended load sediment (O F ) xf : wherein (Q f ) xf is the future time period T f is the river reach R x is the average flow of the river over the floodplain, calculated based on runoff data under the future climate scenario;v xf is the future time period T f is the river reach R x is the average settling velocity of suspended sediment in the river reach R; (A f ) xf is the future time period T f is the river reach R x is the average area of the floodplain in the river reach R; The amount of suspended sediment transported away in the irrigation or water transfer project in the year is calculated according to the following formula x The average annual amount of suspended sediment transported away in the irrigation or water transfer project in the history period T is calculated according to the following formula j The river section R x The amount of suspended sediment transported away in the irrigation or water transfer project (O D ) xj : (O D ) xj =(Q D ) xj • ΔT • (C D ) xj where (Q D ) xj is the historical period T j is the reach R x is the average output flow in an irrigation or water diversion project, (C D ) xj is the historical period T j is the reach R x is the average sediment concentration of the output flow in an irrigation or water diversion project; based on the runoff data under the future climate pattern to calculate the future period T year by year f river section R x suspended sediment deposition in the reservoir or lake of the river section R R ) xf Specifically, the product of the suspended sediment amount of the main river input upstream of the river section R x in the current period and the average sand blocking rate of the reservoir or lake of the river section R x in the current period is taken as the suspended sediment deposition in the reservoir or lake of the river section R x in the current period, and the average sand blocking rate of the reservoir or lake is calculated according to the effective storage capacity of the reservoir or lake and the multi-year average runoff; for the next year, the suspended sediment deposition is subtracted from the effective storage capacity of the reservoir or lake, and the multi-year average runoff is updated after the annual average runoff of the next year is increased, and the average sand blocking rate of the reservoir or lake of the next year is continued to be calculated; then by analogy, the average sand blocking rate calculation of the reservoir or lake in the target river basin of all future years is completed, and on this basis, the average sand blocking rate and the suspended sediment deposition of the reservoir or lake of the river section R f in the future period T x are calculated.

9. The method of claim 8, wherein, River Reach R of a certain year x The average sediment retention rate of the reservoir or lake is calculated according to the following formula: In the formula, C R is the effective storage of the reservoir or lake; I R is the mean annual runoff of the reservoir or lake.

10. A device for predicting sediment in a river basin, characterized by comprising: It comprises: A basic data acquisition module configured to collect basic data of a target watershed, including rainfall, soil, vegetation, terrain, orthophoto and hydrological data, wherein the rainfall, vegetation and hydrological data are future period data obtained by arranging future climate mode data based on the target watershed, the soil, terrain and orthophoto data are all historical data of the target watershed; each type of basic data is arranged in a grid form and uniformly spatially registered, a small watershed boundary serving as a spatial unit for sediment prediction is set, each type of basic data is spatially divided based on the small watershed boundary, and each type of basic data of the small watershed scale is time-divisionally divided based on the time scale requirement for sediment prediction; An erosion prediction module configured to predict erosion amounts of different erosion types, i.e., gravity erosion, debris flow erosion, channel erosion and slope erosion, for each small watershed, to obtain future spatiotemporal distribution of each type of erosion amount and total erosion amount in the target watershed; wherein, For gravity erosion, a historical spatiotemporal distribution of gravity erosion amount is obtained by using multi-period historical orthophoto of the target watershed and a collapse landslide area-volume relationship, statistical characteristic values of gravity erosion amount in a historical period of the small watershed scale are obtained based on the historical spatiotemporal distribution, and a corresponding statistical characteristic value is selected as a future gravity erosion amount of the small watershed scale according to risk management requirements; For debris flow erosion, all effective rainfall field information of the small watershed in a future period is obtained according to future rainfall data, and future debris flow erosion amount of the small watershed scale is obtained based on the effective rainfall field information; For channel erosion, channels in the small watershed scale are equally divided into a plurality of channel segments, a historical channel erosion rate is calculated for each channel segment according to historical terrain data, a historical channel erosion amount of the small watershed scale is calculated based on the historical channel erosion rate, a multiple regression relationship between the historical channel erosion amount and rainfall and terrain parameters is established, a channel erosion rate under future climate mode rainfall conditions is calculated based on the multiple regression relationship, and thus a future channel erosion amount of the small watershed scale is obtained; For slope erosion, a future period soil erosion amount of a grid scale is calculated by modifying a universal soil loss equation RUSLE according to rainfall and vegetation data under a future climate mode, and thus a future slope erosion amount of the small watershed scale is obtained; A sediment yield and deposition prediction module configured to predict future sediment yield and future deposition amount corresponding to each type of erosion, respectively, to obtain future spatiotemporal distribution of sediment yield and deposition amount of the target watershed according to future sediment yield and future deposition amount of each type of erosion of the small watershed scale; wherein, For gravity erosion, firstly, the historical sediment yield and deposition of gravity erosion at the small watershed scale are calculated. Specifically, the historical sediment yield of gravity erosion is calculated based on multi-period historical orthographic images and the volume-area relationship of landslides and collapses, and the amount of input river material from landslides and collapses connected with the river system. The ratio of gravity erosion sediment yield to gravity erosion amount is defined as the gravity erosion sediment transport ratio. The historical gravity erosion sediment transport ratio of each small watershed is calculated according to the historical spatio-temporal distribution of gravity erosion amount. A multiple regression relationship is established between the historical gravity erosion sediment transport ratio, the main river flow, the main river water depth, and the volume of landslides and collapses. Based on this multiple regression relationship and the runoff data under the future climate mode, the future gravity erosion sediment transport ratio is calculated. The future gravity erosion sediment yield at the small watershed scale is calculated by the future gravity erosion amount and the future gravity erosion sediment transport ratio at the small watershed scale. The future gravity erosion deposition at the small watershed scale is obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion amount at the small watershed scale. For debris flow erosion, it is assumed that the river system geometry does not change over time within a hundred-year scale. The main river flow is extracted based on the runoff data under the future climate mode. The future debris flow erosion sediment transport ratio at the small watershed scale is calculated according to the specific gravity and flow of the main river and debris flow in the future period, as well as the input angle. The future debris flow erosion sediment yield and deposition at the small watershed scale are calculated according to the future debris flow erosion sediment transport ratio. For channel erosion and slope erosion, the sediment connectivity index at the grid scale within the small watershed is calculated based on the historical topographic data and future vegetation data. The future sediment transport ratio at the small watershed scale is calculated based on the sediment connectivity index. The future channel erosion sediment yield and deposition at the small watershed scale, and the future slope erosion sediment yield and deposition at the small watershed scale, are calculated according to the future sediment transport ratio, respectively. The suspended sediment transport amount prediction module is configured to calculate the suspended sediment transport amount of small watersheds in the main river system in segments according to the upstream and downstream relationship of the small watershed input river position in the target watershed based on the predicted future sediment yield of all small watersheds in the target watershed at each period, and obtain the distribution of suspended sediment transport amount along the flow direction of the main river system by combining the excavation, reservoir sedimentation, and input and output of suspended sediment in the river section. The suspended sediment output caused by excavation is obtained based on the average of historical excavation data. The suspended sediment output caused by reservoir sedimentation is calculated based on the effective reservoir capacity and future runoff data.

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