Drainage basin sediment prediction method and device

Abstract

The invention provides a drainage basin sediment prediction method, which comprises the following steps of: sorting various kinds of collected basic data of a target drainage basin into a grid form, carrying out unified space registration, and dividing the basic data based on a small drainage basin boundary serving as a sediment prediction space unit; for each small watershed, respectively predicting gravitational erosion, debris flow erosion, channel erosion and slope erosion to obtain future spatial and temporal distribution of various erosion amounts and the total erosion amount in the target watershed; for the four types of erosion, the future sediment yield and deposition rate of the small watershed scale are calculated respectively; and on the basis of the future sediment production, the small watershed suspended load sediment transport amount in the main river water system is calculated section by section according to the upstream and downstream relation of the convergence river position of each small watershed in the target watershed, and distribution of the suspended load sediment transport amount in the flowing direction of the main river water system is predicted in combination with sand digging, reservoir sedimentation and the input amount and the output amount of the suspended load in the river reach. The method can predict the sediment space-time distribution in the basin erosion and basin sand-producing river sediment transportation multi-physical process.

Description

Technical Field

[0001] The present invention belongs to the fields of watershed environmental management, soil and water conservation, mountain disasters and environment, remote sensing information technology, and in particular relates to a watershed sediment prediction method and device. Background Art

[0002] Watershed erosion is a geomorphic process in which surface material in a watershed is displaced by external forces. The material produced by watershed erosion enters the river system and becomes sediment, which is transported downstream or deposited in the river channel. Watershed erosion and sediment transport are key physical processes in watershed geomorphic transformation and landform shaping, and also have a profound impact on human economic and social activities within the watershed. Although erosion and sediment production, sediment transport, sediment deposition, and output from the watershed are continuous physical processes, there is currently a widespread disconnect between research on watershed erosion, sediment production, and sediment transport. Watershed erosion is generally a research topic in the field of soil and water conservation, focusing primarily on slope erosion processes, while sediment transport is generally a focus of water conservancy engineering, and its correlation with the sediment replenishment of river channels by slope erosion remains relatively weak. However, with climate change and increased human activity, the adverse impacts of water-sediment coupling on infrastructure within a river basin are gradually increasing, potentially even causing disasters. For example, increased erosion and sediment production and transport upstream of a river basin can accelerate siltation in reservoirs within and downstream of the basin, reducing reservoir regulation capacity. This inability to effectively mitigate flood peaks during the flood season, thereby reducing the protection of downstream towns and cities, is leading to an increasing need to understand the spatiotemporal distribution of erosion and sediment at the river basin scale and to use this information to predict future climate patterns. Reasonable predictions of the future spatiotemporal distribution of sediment in a river basin will facilitate the implementation of preventive measures and mitigate the adverse impacts of climate change on the socio-economic and ecological development of the river basin.

[0003] Existing predictions of the future spatiotemporal distribution of sediment in a watershed generally focus on river systems, extrapolating historical observations from hydrological stations. These predictions primarily consider the transport of sediment within rivers, but fail to adequately integrate the physical processes of slope erosion, tributary gully confluence, and main river sediment transport, resulting in a heavy reliance on historical observations. Furthermore, existing erosion calculation methods primarily focus on slope erosion, with less attention paid to gravity erosion (gravity-unloading disasters such as collapses and landslides), debris flow erosion, and gully erosion, processes common and concentrated in sediment production on the margins of the Qinghai-Tibet Plateau. These predictions lack quantitative descriptions, or rely heavily on field observations, which are both difficult and expensive. While sophisticated numerical models of erosion and sediment transport based on dynamic models of material transport can theoretically represent the erosion-sediment production-transport process, these models often have high input data requirements, require numerous calibrated parameters, and are computationally intensive, making convergence difficult. In view of the actual needs of the aforementioned watershed sediment budget and the problems existing in the existing methods, it is necessary to develop a watershed sediment prediction method that is based on the physical mechanism of watershed erosion-sediment production-sediment transport and is easy to calculate. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings and deficiencies of existing basin sediment prediction methods by proposing a method that comprehensively quantifies the spatiotemporal distribution of sediment across multiple physical processes, including watershed erosion and sediment transport in sediment-producing rivers. This method comprehensively considers and quantifies different types of erosion, provides a method for calculating sediment transport ratios for each type of erosion, and ultimately quantifies the sediment transport process in rivers. This method can provide technical support for comprehensive watershed management and has significant potential for widespread application.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A first aspect of the present invention provides a method for predicting river basin sediment, comprising:

[0007] Step S1: Collect basic data of the target watershed, including rainfall, soil, vegetation, topography, orthophotos, and hydrological data. The rainfall, vegetation, and hydrological data are current data and / or future data compiled based on future climate model data of the target watershed, and the soil, topography, and orthophotos are historical data of the target watershed. Organize the various basic data into a grid format and perform unified spatial registration. Set the boundaries of small watersheds as the spatial units for sediment prediction. Based on the boundaries of the small watersheds, spatially divide the various basic data. Based on the time scale requirements for sediment prediction, divide the various basic data at the small watershed scale into time periods.

[0008] Step S2: For each small watershed, the erosion amount is predicted according to different erosion types, namely gravity erosion, debris flow erosion, gully erosion, and slope erosion, and the future spatiotemporal distribution of each type of erosion amount and the total erosion amount in the target watershed is obtained; wherein,

[0009] For gravity erosion, the historical spatiotemporal distribution of gravity erosion is obtained using multi-period historical orthophotos of the target watershed and the area-volume relationship of collapse and landslides. Based on this historical spatiotemporal distribution, the statistical characteristic values ​​of gravity erosion at the small watershed scale within the historical period are obtained. The corresponding statistical characteristic values ​​are selected as the future gravity erosion at the small watershed scale according to risk management requirements.

[0010] For debris flow erosion, all effective rainfall events in the small watershed in the future period are obtained based on future rainfall data, and the future debris flow erosion amount at the small watershed scale is obtained based on this effective rainfall event information;

[0011] To address gully erosion, the gullies within the small watershed were divided into several equal segments. The historical gully erosion rate was calculated for each segment based on historical topographic data. The historical gully erosion amount at the small watershed scale was calculated based on the historical gully erosion rate. A multiple regression relationship was established between the historical gully erosion amount and rainfall and topographic parameters. Based on this multiple regression relationship, the gully erosion rate under rainfall conditions of the future climate model was calculated, thereby obtaining the future gully erosion amount at the small watershed scale.

[0012] For slope erosion, the modified universal soil loss equation (RUSLE) is used to calculate the soil erosion amount at the grid scale in the future period based on the rainfall and vegetation data under the future climate model, thereby obtaining the future slope erosion amount at the small watershed scale.

[0013] Step S3: predict the future sediment yield and future sedimentation corresponding to each type of erosion respectively, and obtain the future spatiotemporal distribution of sediment yield and sedimentation in the target watershed based on the future sediment yield and future sedimentation of each type of erosion at the small watershed scale; wherein,

[0014] For gravity erosion, the historical sediment yield and deposition of gravity erosion at the small watershed scale were first calculated. Specifically, the historical sediment yield of gravity erosion was calculated based on multiple historical orthophotos and the area-volume relationship of collapses and landslides, and according to the volume of river material input from collapses and landslides connected to the water system. The ratio of gravity erosion sediment yield to gravity erosion volume was defined as the gravity erosion sediment transport ratio. The historical gravity erosion sediment transport ratio of each small watershed was statistically calculated based on the historical spatiotemporal distribution of gravity erosion volume. A multivariate regression relationship was established between the historical gravity erosion sediment transport ratio and the main river flow, main river water depth, and collapse and landslide volume. The future gravity erosion sediment transport ratio was calculated based on this multivariate regression relationship and runoff data under future climate models. The future gravity erosion sediment yield at the small watershed scale was calculated using the future gravity erosion volume at the small watershed scale and the future gravity erosion sediment transport ratio. The future gravity erosion sedimentation at the small watershed scale was obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion volume at the small watershed scale.

[0015] For debris flow erosion, assuming that the geometric structure of the river system does not change over time within a century, the main river flow is extracted based on runoff data under future climate models. The sediment transport ratio of future debris flow erosion at the small watershed scale is calculated based on the bulk density and flow of debris flows and main rivers in the future period, as well as the inflow angle. Based on this sediment transport ratio, the sediment yield and deposition of future debris flow erosion at the small watershed scale are calculated.

[0016] For gully erosion and slope erosion, the grid-scale sediment connectivity index is first calculated within the small watershed based on historical topographic data and future vegetation data. The future sediment transport ratio at the small watershed scale is then calculated based on this sediment connectivity index. The future sediment yield and deposition of gully erosion, as well as the future sediment yield and deposition of slope erosion at the small watershed scale, are then calculated based on this future sediment transport ratio.

[0017] Step S4: Based on the future sediment yields of all small watersheds in the target watershed in each time period predicted in step S3, the suspended sediment transport of the small watersheds in the main river system is calculated section by section according to the upstream and downstream relationship of the locations where each small watershed in the target watershed flows into the river. The distribution of the suspended sediment transport along the flow direction of the main river system is predicted in combination with dredging, reservoir siltation, and the input and output of suspended sediment in the river section. The output of suspended sediment caused by dredging is obtained based on the average value of historical dredging data; the output of suspended sediment in the river section caused by reservoir siltation is calculated based on the effective storage capacity of the reservoir and future runoff data.

[0018] In some embodiments, the basic data collected in step S1 include rainfall data with a temporal resolution of no less than 3 hours, soil data including organic matter content in sand, silt, and clay in the surface soil, vegetation data including normalized vegetation index and vegetation type, terrain data using a digital elevation model with a spatial resolution of no less than 30 meters, and hydrological data including river system data, flow, and runoff within the target watershed. The basic data also includes historical land use types for calculation of dimensionless soil and water conservation measures factors. The spatial resolution used in performing unified spatial registration on basic data in various grid forms is consistent with the spatial resolution of the digital elevation model.

[0019] The small watershed is the watershed corresponding to the smallest level river in Horton's law. Based on the digital elevation model, the target watershed is divided into I small watersheds B1, B2, ... B i ,…B I , count the area, terrain height difference, average slope, channel length, channel width and channel slope of each small watershed; the time length used to divide various basic data into time periods is equal.

[0020] In some embodiments, in step S2,

[0021] For the prediction of gravity erosion, it specifically includes: identifying the historical period T through the multi-period historical orthophotos of the target basin j The newly added collapse and landslide area in the historical period T is calculated based on the collapse and landslide area and the collapse and landslide area-volume relationship. j Small watershed B i The total volume of materials released by collapse and landslide in the historical period T j Small watershed B iGravity erosion (E G ) ij , based on the gravity erosion amount (E G ) ij Obtain the historical spatiotemporal distribution of gravity erosion; construct the cumulative probability distribution curve of the historical gravity erosion of each small watershed based on the historical spatiotemporal distribution of gravity erosion; select the corresponding statistical characteristic value from the cumulative probability distribution curve as the future time period T according to the risk management requirements f Small watershed B i Gravity erosion (E G ) if ;

[0022] For debris flow erosion prediction, it specifically includes: obtaining small watershed B according to rainfall data under future climate model i In the future period T f All effective rainfall event information in the period, including the rainfall duration and average rainfall intensity of each effective rainfall event, is used to determine whether each effective rainfall event in the future period will trigger a debris flow through the rainfall threshold trigger condition set by the historical rainfall data; when it is determined that an effective rainfall event does not trigger a debris flow, the volume of the flushing material of the effective rainfall event is 0; when it is determined that an effective rainfall event triggers a debris flow, the volume of the flushing material of the effective rainfall event is calculated; statistics of the future period T f Small watershed B i The total volume of debris flow outflow is used as the future period T f Small watershed B i The amount of debris flow erosion (E D ) if ;

[0023] The prediction of gully erosion includes: according to the historical topographic data, the historical period T j Small watershed B i The channel in the channel is divided into several channel segments, and the historical channel erosion rate of each channel segment is calculated respectively. Based on the historical channel erosion rate, the historical period T is calculated. j Small watershed B i The amount of channel erosion (E g ) ij , and obtain the historical gully erosion amount; establish a multiple regression relationship between the historical gully erosion amount and the average annual rainfall, slope and gully width, and calculate the gully erosion rate under the rainfall conditions of the future climate model based on this multiple regression relationship, so as to obtain the future gully erosion amount (E g ) if ;

[0024] The slope erosion prediction includes: using the modified universal soil loss equation (RUSLE) to calculate the soil erosion modulus of each grid in the future period based on the rainfall and vegetation data under the future climate model, and then multiplying it by the grid area to obtain the grid scale future period T f The amount of soil erosion; the small watershed B i The soil erosion amount of each grid in the future period is accumulated to obtain the future period T f Small watershed B i The amount of slope erosion (E S ) if ;

[0025] The sum of the predicted four types of erosion amounts is used to obtain the future period T f Inner small watershed B i Total erosion (E) if .

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

[0027]

[0028] Where, ρ G is the density of the collapse and landslide material; (V G ) k is the historical period T j Small watershed B i The volume of material released by the kth collapse and landslide in the period T j Small watershed B i The total number of internal collapse and landslides; the volume of material released by a single collapse and landslide V G Calculate according to the following formula:

[0029]

[0030] Where 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 soil landslide, and γ is 1.3~1.6 for rock landslide;

[0031] The small watershed B i In the future period T f All valid rainfall events in the data are obtained by following the steps below:

[0032] First, the rainfall data under the future climate model after spatial division is calculated according to the following formula: τ Average rainfall in:

[0033]

[0034] Where, Small watershed B i In the future time period t τ Average rainfall in t τ is the temporal resolution of future rainfall data, M is the temporal resolution of the small watershed B i The total number of grids within Small watershed B i The mth grid in the future time period t τ of rainfall;

[0035] Small watershed B i In time period t τ Average rainfall Divide by time period t τ As a small watershed B i In time period t τ Average rainfall intensity;

[0036] Traverse each future period T f Obtain the rainfall intensity time series matrix of each small watershed, and judge the rainfall intensity of each small watershed in each future period T in chronological order. f When the rainfall intensity is greater than the first set value, it is considered that a valid rainfall event has started. When the rainfall intensity is less than the first set value and continues for not less than the second set value, it is considered that the valid rainfall event has stopped. The period of time when the rainfall intensity is continuously greater than the first set value is considered as a valid rainfall event, and the rainfall duration D and average rainfall intensity of the valid rainfall event are recorded. Thus, we can obtain the small watershed B i In the future period T f All valid rainfall events information within;

[0037] The rainfall threshold trigger condition set by historical rainfall data determines whether each effective rainfall event in the future period will trigger a debris flow, specifically:

[0038] Assume that the rainfall threshold is I c , according to the following formula with small watershed as the unit:

[0039] I c =α D D -β

[0040] Where, α D and β are constants set based on historical rainfall data;

[0041] When the average rainfall intensity of an effective rainfall event When , it is considered that no debris flow is triggered;

[0042] When the average rainfall intensity of an effective rainfall event When the debris flow is triggered, the statistics of small watershed B i In the future period T f Rainfall data for each event that will trigger mudslides Where l is the number of rainfall events that will trigger debris flow, the total number is L events, D l and Small watershed B i In the future period T f The duration and average rainfall intensity of the first rainfall event that will trigger a debris flow are calculated, and the volume of debris flow outflow V of each event is calculated using the following formula: D :

[0043]

[0044] Where Q D is the peak flow rate of debris flow; γ D is the bulk density of debris flow; γ W is the bulk density of clean water; S is the bulk density of solid matter in debris flow; Q P is the storm flood flow; K P is the confluence coefficient; F i Small watershed B i The drainage area; D C is the congestion coefficient; T is the duration of a debris flow; L D is the length of the main ditch of debris flow; U D is the speed of debris flow; S is the slope of gully bed;

[0045] The future period T f Small watershed B i The amount of debris flow erosion (E D ) if Calculate according to the following formula:

[0046]

[0047] Where, ρ D is the density of debris flow outflow material; (V D ) l For the future period T f Small watershed B i The volume of debris discharged from the first debris flow;

[0048] The historical period T j Small watershed B i The amount of channel erosion (E g ) ij Calculate according to the following formula:

[0049] (E g ) ij =(G g ) ij ΔT

[0050]

[0051] Where, L s is the length of the s-th channel; r s is the annual average erosion rate of the slope of the channel section, which is taken as the annual average change rate of the cross section of the channel section; ρ is the density of eroded sediment; ΔT is the historical period T j duration;

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

[0053]

[0054] Where A g is the area of ​​a single grid; A m Small watershed B i The future soil erosion modulus of the mth grid within the range. In 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. The dimensionless soil and water conservation measure factor P is assigned based on the historical slope and current land use type. M is 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 collapse and landslide location is not connected to the river system, the sediment yield and sedimentation caused by the gravity erosion of the collapse and landslide are both 0. If the collapse and landslide location is connected to the river system, the historical period T j Small watershed B i Sediment yield T′ corresponding to 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] Where p and P are the historical period T j Small watershed B i Number and total number of collapse and landslides connected to the river system; G The mass of material input to the river for a single landslide; w G is the average distance that a single landslide extends from the river bank into the water, based on historical orthophotos or field surveys; L G is the length of the river section affected by a single collapse and landslide; k G is the correction coefficient; ρ is the density of eroded sediment; h is L G is the average water depth of the corresponding river section; Q is the flow rate of the main river at the location of a single collapse and landslide; c and f are coefficients;

[0062] For the future sediment yield and deposition of debris flow erosion, first calculate the future period T according to the following formula: f Small watershed B i Sediment transport ratio of internal debris flow erosion (SD R D ) if :

[0063]

[0064] Where, θ is the small watershed B i The angle at which the inner main ditch joins the main river, obtained based on current or historical river system data; γ m and γ D are the future time periods T f Small watershed B i The bulk density of the main river and debris flow; q m and q D are the future time periods T f Small watershed B i The unit-width flow of the main river and debris flow is obtained based on the hydrological data, and the unit-width flow of the debris flow is calculated as q D =Q D / w D , w D For the future period T f Small watershed B i The width of the debris flow channel, Q D For the future period T f Small watershed B i Peak debris flow discharge;

[0065] Then based on the sediment delivery ratio (SDR D ) if Calculate the future period T f Small watershed Bi Sediment yield and sedimentation caused by debris flow erosion:

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

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

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

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

[0070]

[0071] Where, (SDR max ) if is the future period T f Small watershed B i The theoretical maximum sediment transport ratio is related to the surface soil texture; IC if is the future period T calculated based on historical terrain data and future vegetation data f Small watershed B i The average sediment connectivity index of the future period T f Small watershed B i The mean value of the sediment connectivity index at each grid scale; IC0 and k are the correction coefficients for calculating the sediment transport ratio;

[0072] Then based on the sediment delivery ratio (SDR IC ) if Calculate the future period T f Small watershed Bi The sediment yield and deposition corresponding to the gully erosion, and the sediment yield and deposition corresponding to the slope erosion:

[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] Where, (E g ) if For the future period T f Small watershed B i The amount of channel erosion, (T g ) if and (D g ) if are the future time periods T f Small watershed B i The amount of sediment production and deposition corresponding to the amount of gully erosion; (E S ) if For the future period T f Small watershed B i The amount of slope erosion, (T S ) if and (D S ) if are the future time periods T f Small watershed B i The amount of sediment production and deposition corresponding to the amount of slope erosion.

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

[0079]

[0080] IS m =RI m +C·P

[0081]

[0082] Where D up is the upslope component of a small watershed, reflecting the sediment production potential of the upstream; is the average impedance factor of the upslope catchment area of ​​a small watershed, representing the resistance of surface roughness to the flow of water and sediment; is the average slope of the upslope catchment area of ​​a small watershed; A up is the upslope catchment area of ​​a small watershed; D dn is the downslope component of a small watershed, reflecting the path resistance of sediment to the target; d m is the length of the flow path of the mth grid in a small watershed along the steepest downslope direction; W m is the impedance factor of the mth grid in a small watershed; SS m IS is the slope gradient of the mth grid in a small watershed; max IS is the maximum surface index of the small watershed where the grid is located; m is the surface index of the mth grid in a small watershed; RI m is the roughness index of the mth grid in a small watershed; To calculate RI m Used in Grid moving scanning pane, x m is the elevation of a grid, x s For the surrounding of a certain grille The average elevation of each grid; C is the dimensionless vegetation cover factor obtained based on vegetation data under the future climate model; P is the dimensionless soil and water conservation measure factor obtained based on the historical slope and current land use type.

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

[0084] According to the distribution of slope, river width and river type along the river, the river in the target basin is divided into X river sections R1, R2, ... R x ,…R X , stipulating that each river section shall have at most one reservoir or lake, and that the reservoir or lake shall be located at the entrance of the river section;

[0085] Calculate the suspended sediment load of the river in the target basin by river section, for the period T f Any river section within R x The amount of suspended sediment output (SSout )x f for:

[0086]

[0087] Where, (SS in )x f For the future period T f River section R x The amount of suspended sediment input from upstream to the main river; (I T ) n For river section R x The amount of suspended sediment input from the nth tributary into the main river, n and N are the x The number and total number of internal tributaries, then represents the future period T f River section R x The amount of suspended sediment input from all tributaries into the main river is x The amount of suspended sediment that a tributary inputs into the main river I T , calculated based on the future sediment yield of the small watershed obtained in step S3; (E B ) xf For the future period T f River section R x The particle size of the riverbank erosion is consistent with the mass of the suspended sediment, which is calculated based on the water flow work. f River section R x The amount of riverbank erosion is calculated based on runoff data under future climate models; (O F ) xf For the future period T f River section R x The amount of suspended sediment deposited on the floodplain is calculated based on the runoff data for the future period T under the future climate model. f River section R x The average flow rate through the floodplain, the average settling velocity of suspended sediment and the average area of ​​the floodplain are calculated; (O D ) xf For the future period T f River section R x The amount of suspended sediment transported in irrigation or water diversion projects is taken as the x The annual average of the amount of suspended sediment transported by irrigation or water diversion projects over the years and the amount of artificial dredging; (O R ) xf For the future period T f River section R x The amount of suspended sediment deposited 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 input from a tributary 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] Where, T Gf ′ is the future period T f Small watershed B i The amount of sediment produced corresponds to the amount of gravity erosion; T D For the future period T f The sediment yield corresponding to the debris flow erosion of a small watershed corresponding to a tributary within a single river reach; T g For the future period T f The sediment yield corresponding to the channel erosion of a small watershed corresponding to a tributary within a single river reach; T S For the future period T f The sediment yield corresponding to the slope erosion of a small watershed corresponding to a tributary within a single river reach; (Δ s ) G 、(Δ s ) D 、(Δ s ) g T Gf ′、T D and T g The proportion of suspended sediment is obtained by extracting the characteristic particle size proportion of suspended sediment in the target watershed from the gradation curves of collapse and landslide deposits, debris flow fans and channel slope materials in the current period;

[0091] Calculate the future period T according to the following formula f River section R x The particle size of the riverbank erosion is consistent with the mass of the suspended sediment (E B ) 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 the adjustment parameter; ρ w is the density of pure water; g is the acceleration due to gravity; Q B is the flow rate on the flat land of the river section; S is the slope of the river section; h B is the river bank height; L B is the length of the river section; ρ B is the density of the shore material; (Δ s ) B is the proportion of suspended sediment in the bank material; except for the flow on the flat beach of the river section, Q B Except for the runoff data based on the future climate model, the other parameters were obtained using historical data;

[0094] Calculate the future period T according to the following formula f River section R x The amount of suspended sediment deposited on the floodplain (O F ) xf :

[0095]

[0096] Where, (Q f ) xf For the future period T f River section R x The average flow of inland water through the floodplain is calculated based on runoff data under future climate models; xf For the future period T f River section R x Average settling velocity of suspended sediment; (A f ) xf For the future period T f River section R x Average floodplain area within the

[0097] In calculating river section R x The annual average of the amount of suspended sediment transported by irrigation or water diversion projects and the amount of artificial dredging is calculated according to the following formula for the historical period T j River section R x The amount of suspended sediment transported in irrigation or water diversion projects (O D ) xj :

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

[0099] Where, (Q D ) xj is the historical period T j River section R x The average output flow in irrigation or water diversion projects, (C D ) xj is the historical period T j River section R x Average sediment content of output water from irrigation or water diversion projects;

[0100] The future period T is estimated year by year based on the runoff data in the future climate model. f River section R x The amount of suspended sediment in the reservoir or lake (O R ) xf Specifically: take the current period as the starting point, and change the current period river section R x The amount of suspended sediment input from upstream to the main river and the current period of river section R x The product of the average sediment interception rate of the reservoir or lake is taken as the current period of river section R x The amount of suspended sediment deposition in the reservoir or lake is calculated based on the effective storage capacity of the reservoir or lake and the multi-year average runoff. In the next year, the amount of suspended sediment deposition is subtracted from the effective storage capacity of the reservoir or lake, and the multi-year average runoff is added to update the multi-year average runoff, and the average sediment retention rate of the reservoir or lake in the next year is further calculated. Then, the average sediment retention rate of the reservoir or lake in the target basin for all future years is calculated by analogy. On this basis, the future period T is calculated. f River section R x The average sediment retention rate and suspended sediment deposition of reservoirs or lakes.

[0101] In some embodiments, the river section R in a certain year x The average sediment retention rate of a reservoir or lake is calculated as follows:

[0102]

[0103] Where C R is the effective storage capacity of the reservoir or lake; I R It is the average multi-year runoff of a reservoir or lake.

[0104] A second aspect of the present invention provides a watershed sediment prediction device, comprising:

[0105] The basic data acquisition module is configured to collect basic data of the target watershed, including rainfall, soil, vegetation, topography, orthophotos, and hydrological data. The rainfall, vegetation, and hydrological data are future time period data obtained by collating future climate model data of the target watershed, and the soil, topography, and orthophotos data are historical data of the target watershed. The various basic data are organized into a grid format and uniformly spatially aligned. The boundaries of small watersheds are set as the spatial units for sediment prediction. The various basic data are spatially divided based on the boundaries of the small watersheds. The various basic data at the small watershed scale are divided into time periods based on the time scale requirements of sediment prediction.

[0106] The erosion prediction module is configured to predict the erosion amount for each small watershed according to different erosion types, namely gravity erosion, debris flow erosion, gully erosion, and slope erosion, and obtain the future temporal and spatial distribution of each type of erosion amount and the total erosion amount in the target watershed;

[0107] For gravity erosion, the historical spatiotemporal distribution of gravity erosion is obtained using multi-period historical orthophotos of the target watershed and the area-volume relationship of collapse and landslides. Based on this historical spatiotemporal distribution, the statistical characteristic values ​​of gravity erosion at the small watershed scale within the historical period are obtained. The corresponding statistical characteristic values ​​are selected as the future gravity erosion at the small watershed scale according to risk management requirements.

[0108] For debris flow erosion, all effective rainfall events in the small watershed in the future period are obtained based on future rainfall data, and the future debris flow erosion amount at the small watershed scale is obtained based on this effective rainfall event information;

[0109] To address gully erosion, the gullies within the small watershed were divided into several equal segments. The historical gully erosion rate was calculated for each segment based on historical topographic data. The historical gully erosion amount at the small watershed scale was calculated based on the historical gully erosion rate. A multiple regression relationship was established between the historical gully erosion amount and rainfall and topographic parameters. Based on this multiple regression relationship, the gully erosion rate under rainfall conditions of the future climate model was calculated, thereby obtaining the future gully erosion amount at the small watershed scale.

[0110] For slope erosion, the modified universal soil loss equation (RUSLE) is used to calculate the soil erosion amount at the grid scale in the future period based on the rainfall and vegetation data under the future climate model, thereby obtaining the future slope erosion amount at the small watershed scale.

[0111] The sediment yield and deposition prediction module is configured to predict the future sediment yield and deposition corresponding to each type of erosion, and obtain the future spatiotemporal distribution of sediment yield and deposition in the target basin based on the future sediment yield and deposition of each type of erosion at the small basin scale;

[0112] For gravity erosion, the historical sediment yield and deposition of gravity erosion at the small watershed scale were first calculated. Specifically, the historical sediment yield of gravity erosion was calculated based on multiple historical orthophotos and the area-volume relationship of collapses and landslides, and according to the volume of river material input from collapses and landslides connected to the water system. The ratio of gravity erosion sediment yield to gravity erosion volume was defined as the gravity erosion sediment transport ratio. The historical gravity erosion sediment transport ratio of each small watershed was statistically calculated based on the historical spatiotemporal distribution of gravity erosion volume. A multivariate regression relationship was established between the historical gravity erosion sediment transport ratio and the main river flow, main river water depth, and collapse and landslide volume. The future gravity erosion sediment transport ratio was calculated based on this multivariate regression relationship and runoff data under future climate models. The future gravity erosion sediment yield at the small watershed scale was calculated using the future gravity erosion volume at the small watershed scale and the future gravity erosion sediment transport ratio. The future gravity erosion sedimentation at the small watershed scale was obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion volume at the small watershed scale.

[0113] For debris flow erosion, assuming that the geometric structure of the river system does not change over time within a century, the main river flow is extracted based on runoff data under future climate models. The sediment transport ratio of future debris flow erosion at the small watershed scale is calculated based on the bulk density and flow of debris flows and main rivers in the future period, as well as the inflow angle. Based on this sediment transport ratio, the sediment yield and deposition of future debris flow erosion at the small watershed scale are calculated.

[0114] For gully erosion and slope erosion, the grid-scale sediment connectivity index is first calculated within the small watershed based on historical topographic data and future vegetation data. The future sediment transport ratio at the small watershed scale is then calculated based on this sediment connectivity index. The future sediment yield and deposition of gully erosion, as well as the future sediment yield and deposition of slope erosion at the small watershed scale, are then calculated based on this future sediment transport ratio.

[0115] The suspended sediment transport prediction module is configured to calculate the suspended sediment transport of small basins in the main river system section by section based on the predicted future sediment yield of all small basins in the target basin in each time period according to the upstream and downstream relationship of the location of each small basin in the target basin where it flows into the river, and to obtain the distribution of suspended sediment transport along the flow direction of the main river system by combining dredging, reservoir siltation and the input and output of suspended sediment in the river section; among them, the suspended sediment output caused by dredging is obtained based on the average value of historical dredging data; the suspended sediment output in the river section caused by reservoir siltation is estimated based on the effective storage capacity of the reservoir and future runoff data.

[0116] The beneficial effects of the present invention are:

[0117] 1. The method comprehensively considers and quantifies the contribution of various erosion types to watershed erosion, especially gravity erosion and debris flow erosion, two erosion types with high erosion intensity but often overlooked. This method has fewer limitations when applied in areas where collapses, landslides and debris flows are frequent.

[0118] 2. Correlating the physical processes of erosion, sediment production, and sediment deposition at the small watershed scale, and correlating the physical processes of sediment production in small watersheds with sediment transport in the main river at the river system scale, quantitatively describe the number of erosion, sediment production, and sediment transport processes in the entire target watershed, and provide the temporal and spatial distribution within the target watershed. This allows for rapid and precise location of the main erosion areas and sediment source areas within the watershed, providing a powerful tool for precise prevention, control, and restoration.

[0119] 3. The method system mainly relies on satellite images and hydrological data, has low requirements for on-site measurement and sampling, and is easy to control in cost. It is suitable for larger watersheds and provides technical support for rapid assessment and decision-making on erosion and sediment management in large watersheds. BRIEF DESCRIPTION OF THE DRAWINGS

[0120] Figure 1 This is an overall flow chart of a basin sediment prediction method provided by an embodiment of the first aspect of the present invention;

[0121] Figure 2 Schematic diagram of small watershed erosion and sediment transport involved in the embodiment of the first aspect of the present invention;

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

[0123] In order to make the purpose, technical solutions and advantages of this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0124] On the contrary, this application covers any alternatives, modifications, equivalents, and solutions made within the spirit and scope of this application as defined by the claims. Furthermore, to facilitate a better understanding of this application, certain specific details are described in detail below in the detailed description of this application. Those skilled in the art will be able to fully understand this application without these details.

[0125] See also Figure 1 、 Figure 2 The first embodiment of the present invention provides a method for predicting sediment in a watershed, comprising the following steps:

[0126] Step S1: Collect basic data of the target watershed, including rainfall, soil, vegetation, topography, orthophotos, and hydrological data. The rainfall, vegetation, and hydrological data are current data and / or future data compiled based on future climate model data of the target watershed (the current future climate model is generally for the year 2100, i.e., the next 75 years). The soil, topography, and orthophoto data are all historical data of the target watershed. Organize various basic data into a grid format and perform unified spatial registration. Set the boundaries of small watersheds as the spatial units for sediment prediction. Based on the boundaries of small watersheds, perform spatial division of various basic data. Based on the time scale requirements of sediment prediction, divide various basic data at the small watershed scale into time periods.

[0127] Step S2: For each small watershed, the erosion amount is predicted according to different erosion types, namely gravity erosion, debris flow erosion, gully erosion, and slope erosion, and the future spatiotemporal distribution of each type of erosion amount and the total erosion amount in the target watershed is obtained; wherein,

[0128] For gravity erosion, the historical spatiotemporal distribution of gravity erosion is obtained using multi-period historical orthophotos of the target watershed and the area-volume relationship of collapse and landslides. Based on this historical spatiotemporal distribution, the statistical characteristic values ​​of gravity erosion at the small watershed scale within the historical period are obtained. The corresponding statistical characteristic values ​​are selected as the future gravity erosion at the small watershed scale according to risk management requirements.

[0129] For debris flow erosion, all effective rainfall events in the small watershed in the future period are obtained based on future rainfall data, and the future debris flow erosion amount at the small watershed scale is obtained based on this effective rainfall event information;

[0130] To address gully erosion, the gullies within the small watershed were divided into several equal segments. The historical gully erosion rate was calculated for each segment based on historical topographic data. The historical gully erosion amount at the small watershed scale was calculated based on the historical gully erosion rate. A multiple regression relationship was established between the historical gully erosion amount and rainfall and topographic parameters. Based on this multiple regression relationship, the gully erosion rate under rainfall conditions of the future climate model was calculated, thereby obtaining the future gully erosion amount at the small watershed scale.

[0131] For slope erosion, the modified universal soil loss equation (RUSLE) is used to calculate the soil erosion amount at the grid scale in the future period based on the rainfall and vegetation data under the future climate model, thereby obtaining the future slope erosion amount at the small watershed scale.

[0132] Step S3: predict the future sediment yield and future sedimentation corresponding to each type of erosion respectively, and obtain the future spatiotemporal distribution of sediment yield and sedimentation in the target watershed based on the future sediment yield and future sedimentation of each type of erosion at the small watershed scale; wherein,

[0133] For gravity erosion, the historical sediment yield and deposition of gravity erosion at the small watershed scale were first calculated. Specifically, the historical sediment yield of gravity erosion was calculated based on multiple historical orthophotos and the area-volume relationship of collapses and landslides, and according to the volume of river material input from collapses and landslides connected to the water system. The ratio of gravity erosion sediment yield to gravity erosion volume was defined as the gravity erosion sediment transport ratio. The historical gravity erosion sediment transport ratio of each small watershed was statistically calculated based on the historical spatiotemporal distribution of gravity erosion volume. A multivariate regression relationship was established between the historical gravity erosion sediment transport ratio and the main river flow, main river water depth, and collapse and landslide volume. The future gravity erosion sediment transport ratio was calculated based on this multivariate regression relationship and runoff data under future climate models. The future gravity erosion sediment yield at the small watershed scale was calculated using the future gravity erosion volume at the small watershed scale and the future gravity erosion sediment transport ratio. The future gravity erosion sedimentation at the small watershed scale was obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion volume at the small watershed scale.

[0134] For debris flow erosion, assuming that the geometric structure of the river system does not change over time within a century, the main river flow is extracted based on runoff data under future climate models. The sediment transport ratio of future debris flow erosion at the small watershed scale is calculated based on the bulk density and flow of debris flows and main rivers in the future period, as well as the inflow angle. Based on this sediment transport ratio, the sediment yield and deposition of future debris flow erosion at the small watershed scale are calculated.

[0135] For gully erosion and slope erosion, the grid-scale sediment connectivity index is first calculated within the small watershed based on historical topographic data and future vegetation data. The future sediment transport ratio at the small watershed scale is then calculated based on this sediment connectivity index. The future sediment yield and deposition of gully erosion, as well as the future sediment yield and deposition of slope erosion at the small watershed scale, are then calculated based on this future sediment transport ratio.

[0136] Step S4: Based on the future sediment yields of all small watersheds in the target watershed in each time period predicted in step S3, the suspended sediment transport of the small watersheds in the main river system is calculated section by section according to the upstream and downstream relationship of the locations where each small watershed in the target watershed flows into the river. The distribution of the suspended sediment transport along the flow direction of the main river system is predicted in combination with dredging, reservoir siltation, and the input and output of suspended sediment in the river section. The output of suspended sediment caused by dredging is obtained based on the average value of historical dredging data; the output of suspended sediment in the river section caused by reservoir siltation is calculated based on the effective storage capacity of the reservoir and future runoff data.

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

[0138] Step S11: basic data collection.

[0139] Collect basic data for the target watershed, including rainfall, soil, vegetation, topography, and orthophotos. Precipitation data is raster data with a temporal resolution of 3 hours or higher, representing current rainfall data and / or rainfall data under future climate models (hereinafter referred to as future rainfall data, the same applies to the rest of the data). Soil data, primarily the organic matter content of sand, silt, and clay in the topsoil, is raster data and represents historical data for the target watershed. Vegetation data is raster data, representing the Normalized Difference Vegetation Index (NDVI) and vegetation types (trees, shrubs, etc.), and represents current and / or future data. Topography data uses a historical digital elevation model (DEM) with a spatial resolution of at least 30 meters. Furthermore, basic data includes historical land use types for the calculation of dimensionless soil and water conservation measures. All of these basic data are spatially registered and aligned to the same resolution as the DEM. Historical orthophotos of the target area must be collected from multiple periods, with consistent spatial resolution and consistent registration.

[0140] Collect hydrological data for the target basin, including river system data within the target basin (this river system data can be extracted using a DEM and is historical data), as well as flow, runoff, and sediment transport information from hydrological stations (the latter three being current and / or future data). The temporal resolution should be as close as possible to the daily scale. If there are no hydrological stations within the target basin, find water and sediment data from the nearest hydrological station downstream. If hydrological data such as flow and depth are available for the target area, or data obtained from distributed hydrological model simulations, these should also be collected.

[0141] Step S12: basic data preprocessing.

[0142] Spatial scale division: The basin corresponding to the smallest level river in Horton's law is set as a small basin, which is used as the spatial unit for sediment prediction. Based on the DEM, the target basin is divided into I small basins B1, B2, ... B i ,…B I , and statistics were collected on the area, terrain elevation difference, average slope, channel length, channel width and channel slope of each small watershed.

[0143] Time scale division: Determine the time scale of the final output data (such as one year or two years) according to the sediment forecast requirements, and divide the historical basic data with time series characteristics of the target basin collected in step S11 into J historical periods T1, T2, ...T according to the time scale. j ,…,T J Similarly, each future basic data is divided into F future time periods T1, T2, ...T f ,…,T F , the duration of each period is ΔT, and the current period data only contains data of one time unit ΔT.

[0144] Preprocessing of future rainfall data: First, use GIS analysis tools to obtain the B i The vector data file of the range is used to establish the mapping relationship between the small watershed and the future rainfall data in raster form, and the spatial weighted average method is used to calculate the B of the small watershed. i In each time period t τ The average rainfall in the area is calculated as follows:

[0145]

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

[0147] Small watershed B i In the future time period t τ The average rainfall divided by t τ This is the average rainfall intensity of the small watershed during this period. Traverse each future period T f Obtain the rainfall intensity time series matrix of each small watershed, and judge the rainfall intensity of each small watershed in each future period T in chronological order. f When the rainfall intensity is greater than 1 mm / h, it is considered that an effective rainfall begins. When the rainfall intensity is less than 1 mm / h and continues for at least 6 hours, it is considered that the effective rainfall stops. The period of time when the rainfall intensity is continuously greater than 1 mm / h is considered as an effective rainfall, and its rainfall duration D (unit: h) and average rainfall intensity are recorded. (Unit: mm / h) and other indicators to obtain small watershed B i In the future period T f All valid rainfall events information within.

[0148] In some embodiments, step S2 is to predict the erosion amount of the small watershed according to different erosion types, and to calculate the future time period T f The erosion of the watershed in the basin is divided into four categories: gravity erosion, debris flow erosion, gully erosion and slope erosion. Figure 2 , the prediction process of each type of erosion amount is described as follows:

[0149] Step S21: Gravity erosion amount

[0150] First, the historical spatiotemporal distribution of gravity erosion is determined based on multiple historical orthophotos. Specifically:

[0151] Gravity erosion is mainly caused by collapse and landslides in the basin. The historical period T is identified by visual recognition or deep neural network method through the multi-period historical orthophotos of the basin. j The newly added landslide area is calculated, and then the volume of materials released by the landslides in this historical period is estimated based on the relationship between the landslide area and volume. For a single landslide, the volume of materials released is calculated as:

[0152]

[0153] Where V G A is the volume of material released by a single collapse landslide, G is the area of ​​a single collapse landslide, α and γ are coefficients, α is generally taken as 0.05±0.02, γ is taken as 1.1~1.3 for soil landslide, and γ is taken as 1.3~1.6 for rock landslide.

[0154] Statistical historical period T j Small watershed B i The total volume of materials released by collapse and landslide in the historical period T j Small watershed B i Gravity erosion (E G ) ij :

[0155]

[0156] Where, ρ G The density of the collapse and landslide material is generally 2.0 to 2.5 t / m 3 For soil landslide, the value is generally 1.6~2.3t / m 3 ; K is the historical period T j Small watershed B i The total number of collapses and landslides; k is the historical period T j Small watershed B i Number of internal collapse and landslide materials, (V G ) k is the historical period T j Small watershed B i The volume of material released by the kth collapse and landslide.

[0157] Subsequently, based on the historical spatiotemporal distribution of gravity erosion, a cumulative probability distribution curve of the historical gravity erosion of each small watershed was constructed. According to the risk management requirements, the corresponding statistical characteristic values ​​(corresponding to 1%, 10%, 50%, 90%, 99%, etc. of the cumulative probability distribution curve, with 50% being the median) were selected from the cumulative probability distribution curve as the future time period Tf Small watershed B i Gravity erosion (E G ) if If the risk management requirements are too high, a relatively large statistical characteristic value is selected (such as 90% (meaning that the volume of landslide materials exceeds 90% of the historical volume value), 99%, etc.), and vice versa.

[0158] Step S22: Debris flow erosion amount

[0159] The debris flow process strongly transports the material source in the small watershed, causing the channel to cut down and transporting a large amount of material to the gully mouth accumulation fan. Calculating the volume of debris flow outflow can approximate the amount of debris flow erosion in the small watershed. Since debris flow gullies are mostly narrow and deep, it is difficult to directly determine whether they have occurred through orthophotos, and the time cost of on-site investigation is too high. Considering that most debris flows are triggered by rainfall, the rainfall threshold trigger condition set by historical rainfall data is used to determine whether debris flows will occur in the future. The rainfall threshold is set to I c , calculated based on formula (4) with small watershed as the unit:

[0160] I c =α D D -β (4)

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

[0162] Based on the set rainfall threshold I c Determine the future period T f Small watershed B i Whether each effective rainfall event triggers a debris flow:

[0163] like It is considered that no debris flow is triggered and the volume of the discharged material is 0.

[0164] like It is considered that debris flow is triggered, and the statistics of small watershed B i In the future period T f Rainfall data for each event that can trigger debris flows Where l is the number of rainfall events that can trigger debris flow, the total number is L events, D l and Small watershed B i In the future period T fThe duration and average rainfall intensity of the first rainfall event that can trigger a debris flow are calculated using equations (5) to (9) to calculate the volume of debris flow outflow V: D :

[0165]

[0166] Where Q D is the peak flow rate of debris flow (unit: m 3 / s); the coefficient 19 / 72 in formula (5) is the empirical coefficient given by the "Design Code for Investigation and Prevention of Debris Flows in Hydropower Projects" (NB / T 10139-2019); γ D is the bulk density of debris flow, which is determined through on-site investigation or regional debris flow characteristics; γ W γ is the clear water density. Generally, except for extremely strong sediment transport under extreme conditions, the main river density is unlikely to change significantly compared with the clear water density. Therefore, the main river density can be approximately determined by the clear water density, and the debris flow density can be determined by the regional debris flow density. S is the bulk density of solid matter in debris flow; Q P is the storm flood flow; K P is the confluence coefficient, and K is generally used for steep slopes in mountainous areas. P =0.7~0.9 (weak surface permeability, fast convergence speed), K is generally used in hilly areas P = 0.5~0.7 (medium infiltration and confluence conditions), plain or vegetation covered area K P =0.3~0.5 (strong penetration, slow convergence speed); F i Small watershed B i The drainage area; D C is the congestion coefficient, which can be obtained by referring to the Code for Calculation of Floods in Design of Water Conservancy and Hydropower Projects (Ministry of Water Resources of the People's Republic of China, 2006) (SL44-2006) in combination with on-site inspection; T is the duration of the debris flow (unit: s); L D is the length of the main ditch of debris flow; U D is the speed of debris flow; S is the slope of the gully bed.

[0167] Finally, statistics of the future period T f Small watershed B i The total volume of debris flow outflow is used as the future period T f Small watershed B i The amount of debris flow erosion (E D ) if :

[0168]

[0169] Where, ρ Dis the density of debris flow discharge, which is 1.3-1.8t / m for the area dominated by rare debris flow. 3 , in the area dominated by viscous debris flow, the rate is 2.0~2.4t / m 3 , the transitional debris flow dominant area takes 1.8~2.0t / m 3 ;(V D ) l For the future period T f Small watershed B i The volume of discharge from the first debris flow.

[0170] Step S23: Channel erosion amount

[0171] Gully erosion refers to the downcutting, lateral erosion and headward erosion of the gully under the action of the water flow of rainfall runoff.

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

[0173]

[0174] Where, L s is the length of the sth channel, r s is the historical average annual erosion rate of the slope of the channel section (m 2 / y), which is the historical average annual change rate of the cross section of the channel section; ρ is the density of eroded sediment, which is generally taken as 1.6t / m 3 .

[0175] The historical average annual change rate of the channel section cross section in formula (11) is r s Generally, channel cross sections at different locations are extracted and calculated after unified georeferencing of multiple historical DEMs. If conditions permit, they can also be obtained through long-term on-site monitoring. The historical average annual 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 mountain torrent gullies, debris flow gullies, etc., and no major collapse, landslide, and debris flow events occurred within the time range of interest), the historical average annual erosion rate of the gully section slope is r s The value can be approximated as a constant, that is, whether the historical average annual erosion rate of the channel section slope is obtained through DEM or on-site monitoring, only data with a shorter time span are needed.

[0177] Calculate the historical period T according to the following formula jSmall watershed B i The amount of channel erosion (E g ) ij :

[0178] (E g ) ij =(G g ) ij ·ΔT (12)

[0179] Thus, the historical gully erosion amount at the small watershed scale is obtained;

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

[0181] Step S24: Slope erosion amount

[0182] The slope erosion amount of the target watershed is predicted by using the modified universal soil loss equation (RUSLE) to calculate the future time period T for each grid using rainfall and vegetation data under the future climate model. f The soil erosion modulus in the future period T is then multiplied by the grid area to obtain the grid scale f The amount of soil erosion. 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 The amount of slope erosion (E S ) if . Specifically:

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

[0184] A=R·S·L·K·C·P (13)

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

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

[0187]

[0188] Where A g is the area of ​​a single grid, A m is the small watershed B calculated by the modified universal soil loss equation RUSLE i The future soil erosion modulus of the mth grid within the range, M is B i The total number of grids within the small watershed.

[0189] Step S25: Total erosion amount and basin erosion distribution

[0190] Future period T f Inner small watershed B i Total erosion (E) if is the sum of the above four erosion amounts, that is:

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

[0192] This also gives the future time period T f The spatial distribution of total erosion, gravity erosion, gully erosion and slope erosion in the watershed with small watersheds as units is calculated. The above calculations are performed for different future time periods to obtain the future spatial and temporal distribution of various types of erosion and total erosion in the target watershed.

[0193] The target basin will be in the future period T f The total erosion amount in is:

[0194]

[0195] This can be used to obtain the change of the total erosion amount in the target area over time.

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

[0197] In some embodiments, step S3 predicts the future sediment yield in the target watershed. Similar to step S2, step S3 also predicts the future sediment yield and future sedimentation at the small watershed scale for each of the four erosion types, which are described as follows:

[0198] Step S31: Future sand production and future sedimentation due to gravity erosion

[0199] First, the historical sediment yield of 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 situations are considered here: 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. Subsequently, gully erosion and slope erosion will continue. These 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 by a single landslide is calculated as follows:

[0200] T G =k G ·ρ·w G ·L G ·h (17)

[0201] h=cQ f (18)

[0202] Where, T G The mass of material input to the river for a single landslide; w G is the average distance that the landslide extends from the river bank to the water, L G is the length of the river section affected by the collapse and landslide. Both parameters can be obtained by extracting multiple historical orthophotos of the landslide area; k G is the correction coefficient, which is generally 0.7-0.8; ρ is the density of eroded sediment; h is the difference between the main river and L G The average water depth of the corresponding river section; Q is the flow of the main river at the collapse and landslide location, obtained through historical hydrological data; c and f are coefficients, generally c = 0.25 ~ 0.55, f = 0.3 ~ 0.4.

[0203] Then the historical period T j Small watershed B i Sediment yield from internal gravity erosion T′ G for:

[0204]

[0205] Where, T G ′ is the historical period T j Small watershed B i The sediment yield corresponding to the gravity erosion; p and P are the historical period T j Small watershed B i The numbers and total number of collapses and landslides connected to the river system.

[0206] Based on the sediment yield corresponding to the gravity erosion at the small watershed scale in each historical period, the historical temporal and spatial distribution of gravity erosion was obtained.

[0207] Then, the ratio of gravity erosion sediment yield to gravity erosion volume is defined as the gravity erosion sediment transport ratio. Based on the historical spatiotemporal distribution of gravity erosion volume, the historical gravity erosion sediment transport ratio of each small watershed is statistically analyzed. A multiple regression relationship is established between the historical gravity erosion sediment transport ratio and the main river flow, main river depth, and collapse and landslide volume. Based on this multiple regression relationship and the runoff data under the future climate model, the future gravity erosion sediment transport ratio is calculated. Suppose the future period T f Small watershed B i The gravity erosion sediment transport ratio is (SDR D ) if , the future period T obtained in step S21 f Small watershed B i Gravity erosion (E G ) if and the future period T f Small watershed B i The gravity erosion sediment transport ratio is (SDR D ) if Multiply to get the future period T f Small watershed B i The sediment yield corresponding to the gravity erosion amount T Gf ′, and the future gravity erosion sediment yield of the small watershed scale is obtained; 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 sediment yield of the small watershed scale, that is, (D G ) if =(E G ) if -T′ Gf ,(D G ) if For the future period T f Small watershed B iThe amount of sedimentation corresponding to the amount of gravitational erosion.

[0208] Step S32: Future sand production and future sedimentation of debris flow erosion

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

[0210]

[0211] Where, (SDR D ) if For the future period T f Small watershed B i The sediment transport ratio of internal debris flow erosion; θ is the future period T f Small watershed B i The angle at which the main ditch flows into the main river is obtained by the current river system distribution in the target basin. The river system distribution within the century scale is generally considered to be unchanged; γ m and γ D are the future time periods T f Small watershed B i The bulk density of the main river and debris flow. The bulk density of the main river changes little with different time periods and small watersheds. It is obtained based on historical or current river system data and is generally taken as a fixed value; q m and q D are the future time periods T f Small watershed B i The unit-width flow of the main river and debris flow is obtained based on the hydrological data under the future climate model, and the unit-width flow of the debris flow is calculated as q D =Q D / w D , w D For the future period T f Small watershed B i The width of the debris flow channel, Q D For the future period T f Small watershed B i Peak flow rate of debris flow.

[0212] Then, based on the above sediment transport ratio, the future time period T is calculated. f Small watershed B i The sediment yield corresponding to the debris flow erosion (T D ) if and sedimentation (D D ) if :

[0213] (T D )if =(E D ) if (SDR D ) if (twenty one)

[0214] (D D ) if =(E D ) if -(T D ) if (twenty two)

[0215] Step S33: Future sediment production and future deposition of gully erosion and slope erosion

[0216] Step S331: Calculate the grid-scale sediment connectivity index of each small watershed in the future period:

[0217]

[0218] Where IC is the grid-scale sediment connectivity index within a small watershed. A larger value indicates higher sediment connectivity. up is the upslope component of a small watershed, reflecting the sediment production potential of the upstream, and is obtained using data from the current period; is the average impedance factor of the upslope catchment area of ​​a small watershed in the current period, representing the obstruction of surface roughness to the flow of water and sediment; is the average slope of the upslope catchment area of ​​a small watershed in the current period (m / m); A up is the upslope catchment area of ​​a small watershed in the current period (m 2 );D dn is the downslope component of a small watershed in the current period, reflecting the path resistance of sediment to the target; d m W is the length of the flow path along the steepest downslope direction of the mth grid in a small watershed in the current period (m); m is the impedance factor (local surface roughness) of the mth grid in a small watershed; SS m is the slope gradient of the mth grid in a small watershed in the current period (m / m); the above D up 、 A up 、D dn , SS m All calculations are based on data from the current period.

[0219] Impedance factor W in uphill and downhill component calculations m Based on the roughness index RI m , vegetation cover factor C and soil and water conservation measures factor P to obtain the surface index IS m calculate:

[0220]

[0221] Where IS max is the maximum surface index of the small watershed where the grid is located; the surface index IS of each grid m Calculated as:

[0222] IS m =RI m +C·P (27)

[0223] Roughness index RI of the mth grid m Calculated as:

[0224]

[0225] Where, Used in calculations Grid moving scanning pane, x m is the elevation of a grid, x s For the surrounding of a certain grille The vegetation factors C and P are the same as the C and P factors calculated in the RUSLE method when calculating slope erosion (Equation 13).

[0226] Step S332: Calculate sediment transport ratio

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

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

[0229]

[0230] Where, (SDR IC ) ij is the future period T f Small watershed B i Sediment transport ratio of gully erosion or slope erosion; (SDR max ) ij is the future period T f Small watershed B i Theoretically, the maximum sediment transport ratio that can occur is related to the texture of the surface soil and can generally be taken as 1; IC if is the future period T calculated based on historical terrain data and future vegetation data f Small watershed B i The average sediment connectivity index of the future period Tf Small watershed B i The mean value of the sediment connectivity index at each grid scale within the grid; IC0 and k are correction coefficients for calculating the sediment transport ratio and need to be calibrated. if =IC0, there is (SDR IC ) if =0.5(SDR max ) if , therefore, IC0 is (SDR max ) if The sediment connectivity index value corresponding to half of the value is generally taken as (SDR max ) if =1, then IC0 is (SDR max ) if =0.5, 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, and then substitute it in to determine the specific value by trial calculation.

[0231] Step S333: Calculate future sand production and future sedimentation

[0232] Based on the above sediment transport ratio, calculate the future period T f Small watershed B i The amount of channel erosion (E g ) if The corresponding sediment yield (T g ) if and sedimentation (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, based on the above sediment transport ratio, the future period T is calculated f Small watershed B i The amount of slope erosion (E S ) if The corresponding sediment yield (T S ) if and sedimentation (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, we get the future time period T f The spatial distribution of sediment yield and deposition corresponding to gravity erosion, debris flow erosion, gully erosion and slope erosion in a watershed with small watersheds as units is calculated. The above calculations are performed for different future time periods to obtain the future spatial and temporal distribution of various types of sediment yield and deposition in the target watershed.

[0239] It can be understood that step S3 quantifies the future sediment yield and future deposition corresponding to various erosion types in small watersheds, and obtains the future spatiotemporal distribution characteristics of sediment yield and deposition in the target watershed, thereby providing a prediction of the future evolution of sediment sources in the watershed.

[0240] In some embodiments, step S4 is to predict the amount of river sediment transport. After calculating the erosion, sediment transport, and deposition in each future period for all small watersheds within the target basin, the sediment transport in the main river system is calculated section by section according to the upstream and downstream relationship of the location where the small watersheds flow into the river. Considering that the coarse bedload has a limited transport distance in the river system, step S4 mainly predicts the sediment transport of fine suspended load, see Figure 3 , specifically including the following steps:

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

[0242] Calculate the suspended sediment load of the target river basin in each river section. f Any river section within R x The amount of suspended sediment output (SS out ) xf for:

[0243]

[0244] Where, (SS in ) xf For the future period T f River section R x The amount of suspended sediment input from upstream to the main river; (I T ) n For river section R x The amount of suspended sediment input from the nth tributary into the main river, n and N are the x The number and total number of internal tributaries, then represents the future period T f River section R x The amount of suspended sediment input into the main river by all tributaries within the river; (E B ) xf For the future period T f River section R x The particle size of the riverbank erosion is consistent with the mass of the suspended sediment; (O F ) xf For the future period T f River section R x The amount of suspended sediment deposited on the floodplain; (O M ) xf For the future period T f River section R x The amount of artificial dredging shall be determined according to the actual scale of dredging in the river; (O D ) xf For the future period T f River section R x The amount of suspended sediment transported in irrigation or water diversion projects; (O R ) xf For the future period T f River section R x The amount of suspended sediment deposited in a reservoir or lake.

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

[0246] Among them, combined with the calculation of the future sediment yield of the small watershed in step S3, the amount of suspended sediment input from a tributary into the main river in a single river section is I T Calculated as:

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

[0248] Where, T Gf ′ is the future period T f A small watershed B corresponding to a tributary within a single river reach i The sediment yield corresponding to the gravity erosion is taken as the future period T f A small watershed B i The total mass of materials input into the river by all collapses and landslides connected to the river system; T D For the future period T f The sediment yield corresponding to the debris flow erosion of a small watershed corresponding to a tributary within a single river reach; T g For the future period T f The sediment yield corresponding to the channel erosion of a small watershed corresponding to a tributary within a single river reach; T S For the future period T f The sediment yield corresponding to the slope erosion of a small watershed corresponding to a tributary within a single river reach; (Δ s ) G 、(Δ s ) D 、(Δ s ) g T G ′、T D and T g The proportion of suspended sediment is obtained by extracting the proportion of characteristic particle size of suspended sediment (such as 0.05 mm) in the target watershed from the gradation curves of collapse and landslide deposits, debris flow fans and channel slope materials. It can be obtained through field sampling or literature research.

[0249] Future period T f River section R x The particle size of the riverbank erosion is consistent with the mass of the suspended sediment (E B ) xf The calculation based on water flow work is:

[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 the adjustment parameter used to adjust the calculation results to suit the actual situation; ρ w is the density of pure water; g is the acceleration due to gravity; Q B is the flow rate on the flat land of the river section. In the absence of measured data, the flood flow rate with a return period of 1 to 2 years can be used as an approximation; S is the slope of the river section, ρ wg (Q B ) xf S xf That is the future period T f River section R x The water flow work; h B is the river bank height, L B is the length of the river section, ρ B is the density of the shore material, (Δ s ) B is the proportion of suspended sediment in the bank material; among the above parameters, except for the river flat flow Q B Except for the runoff data based on future climate models, the remaining parameters are obtained using historical data.

[0252] Future period T f River section R x The amount of suspended sediment deposited on the floodplain (O F ) xf Calculated as:

[0253]

[0254] Where, (Q f ) xf For the future period T f River section R x The average flow of inland water through the floodplain is calculated based on runoff data under future climate models; xf For the future period T f River section R x Average settling velocity of suspended sediment; (A f ) xf For the future period T f River section R x Average floodplain area within the river; v xf and (A f ) xf The corresponding values ​​for future time periods are predicted using the changing trends of their respective historical data. If the historical data shows no trend of increase or decrease, the predicted value is taken as the value of the current time period.

[0255] In calculating river section R xThe annual average of the amount of suspended sediment transported by irrigation or water diversion projects and the amount of artificial dredging is calculated according to the following formula for the historical period T j River section R x The amount of suspended sediment transported in irrigation or water diversion projects (O D ) xj Calculated as:

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

[0257] Where, (Q D ) xj is the historical period T j River section R x The average output flow in irrigation or water diversion projects, (C D ) xj is the historical period T j River section R x The average sediment content of the output water in the irrigation or water diversion project. Both values ​​are obtained through the actual operation of the irrigation or water diversion project.

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

[0259] Taking the current period as the starting point, the river section R x The amount of suspended sediment input from upstream to the main river and the current period of river section R x The product of the average sediment interception rate of the reservoir or lake is taken as the current period of river section R x The amount of suspended sediment deposition in the reservoir or lake is calculated based on the effective storage capacity of the reservoir or lake and the multi-year average runoff. In the next year, the amount of suspended sediment deposition is subtracted from the effective storage capacity of the reservoir or lake, and the multi-year average runoff is added to update the multi-year average runoff, and the average sediment retention rate of the reservoir or lake in the next year is further calculated. Then, the average sediment retention rate of the reservoir or lake in the target basin for all future years is calculated by analogy. On this basis, the future period T is calculated. f River section R x The average sediment retention rate and suspended sediment deposition of reservoirs or lakes.

[0260] Furthermore, in a certain year, the river section Rx The average sediment retention rate of a reservoir or lake is calculated as follows:

[0261]

[0262] Where C R is the effective storage capacity of the reservoir or lake (10 3 *m 3 ), I R is the average annual runoff of the reservoir or lake (10 3 *m 3 ).

[0263] It can be understood that the embodiments of the present invention can obtain future predictions of the distribution of suspended sediment transport along the river system in the target basin, and specifically depict the future impact of the natural process of erosion and sand production and artificial facilities such as dredging, irrigation, and reservoirs on suspended sediment transport.

[0264] A second embodiment of the present invention provides a watershed sediment prediction device, comprising:

[0265] The basic data acquisition module is configured to collect basic data of the target watershed, including rainfall, soil, vegetation, topography, orthophotos, and hydrological data, wherein the rainfall, vegetation, and hydrological data are current data and / or future time period data obtained by collating future climate model data of the target watershed, and the soil, topography, and orthophotos data are historical data of the target watershed; various basic data are organized into a grid format and uniformly spatially aligned; small watershed boundaries are set as spatial units for sediment prediction; various basic data are spatially divided based on the small watershed boundaries; and various basic data at the small watershed scale are time-divided based on the time scale requirements of sediment prediction;

[0266] The erosion prediction module is configured to predict the erosion amount for each small watershed according to different erosion types, namely gravity erosion, debris flow erosion, gully erosion, and slope erosion, and obtain the future temporal and spatial distribution of each type of erosion amount and the total erosion amount in the target watershed;

[0267] For gravity erosion, the historical spatiotemporal distribution of gravity erosion is obtained using multi-period historical orthophotos of the target watershed and the area-volume relationship of collapse and landslides. Based on this historical spatiotemporal distribution, the statistical characteristic values ​​of gravity erosion at the small watershed scale within the historical period are obtained. The corresponding statistical characteristic values ​​are selected as the future gravity erosion at the small watershed scale according to risk management requirements.

[0268] For debris flow erosion, all effective rainfall events in the small watershed in the future period are obtained based on future rainfall data, and the future debris flow erosion amount at the small watershed scale is obtained based on this effective rainfall event information;

[0269] To address gully erosion, the gullies within the small watershed were divided into several equal segments. The historical gully erosion rate was calculated for each segment based on historical topographic data. The historical gully erosion amount at the small watershed scale was calculated based on the historical gully erosion rate. A multiple regression relationship was established between the historical gully erosion amount and rainfall and topographic parameters. Based on this multiple regression relationship, the gully erosion rate under rainfall conditions of the future climate model was calculated, thereby obtaining the future gully erosion amount at the small watershed scale.

[0270] For slope erosion, the modified universal soil loss equation (RUSLE) is used to calculate the soil erosion amount at the grid scale in the future period based on the rainfall and vegetation data under the future climate model, thereby obtaining the future slope erosion amount at the small watershed scale.

[0271] The sediment yield and deposition prediction module is configured to predict the future sediment yield and deposition corresponding to each type of erosion, and obtain the future spatiotemporal distribution of sediment yield and deposition in the target basin based on the future sediment yield and deposition of each type of erosion at the small basin scale.

[0272] For gravity erosion, the historical sediment yield and deposition of gravity erosion at the small watershed scale were first calculated. Specifically, the historical sediment yield of gravity erosion was calculated based on multiple historical orthophotos and the area-volume relationship of collapses and landslides, and according to the volume of river material input from collapses and landslides connected to the water system. The ratio of gravity erosion sediment yield to gravity erosion volume was defined as the gravity erosion sediment transport ratio. The historical gravity erosion sediment transport ratio of each small watershed was statistically calculated based on the historical spatiotemporal distribution of gravity erosion volume. A multivariate regression relationship was established between the historical gravity erosion sediment transport ratio and the main river flow, main river water depth, and collapse and landslide volume. The future gravity erosion sediment transport ratio was calculated based on this multivariate regression relationship and runoff data under future climate models. The future gravity erosion sediment yield at the small watershed scale was calculated using the future gravity erosion volume at the small watershed scale and the future gravity erosion sediment transport ratio. The future gravity erosion sedimentation at the small watershed scale was obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion volume at the small watershed scale.

[0273] For debris flow erosion, assuming that the geometric structure of the river system does not change over time within a century, the main river flow is extracted based on runoff data under future climate models. The sediment transport ratio of future debris flow erosion at the small watershed scale is calculated based on the bulk density and flow of debris flows and main rivers in the future period, as well as the inflow angle. Based on this sediment transport ratio, the sediment yield and deposition of future debris flow erosion at the small watershed scale are calculated.

[0274] For gully erosion and slope erosion, the grid-scale sediment connectivity index is first calculated within the small watershed based on historical topographic data and future vegetation data. The future sediment transport ratio at the small watershed scale is then calculated based on this sediment connectivity index. The future sediment yield and deposition of gully erosion, as well as the future sediment yield and deposition of slope erosion at the small watershed scale, are then calculated based on this future sediment transport ratio.

[0275] The suspended sediment transport prediction module is configured to calculate the suspended sediment transport of small basins in the main river system section by section based on the predicted future sediment yield of all small basins in the target basin in each time period according to the upstream and downstream relationship of the location of each small basin in the target basin where it flows into the river, and to obtain the distribution of suspended sediment transport along the flow direction of the main river system by combining dredging, reservoir siltation and the input and output of suspended sediment in the river section; among them, the suspended sediment output caused by dredging is obtained based on the average value of historical dredging data; the suspended sediment output in the river section caused by reservoir siltation is estimated based on the effective storage capacity of the reservoir and future runoff data.

[0276] It should be noted that the above explanations of the embodiment of the watershed sediment prediction method are also applicable to the watershed sediment prediction device of this embodiment, and will not be repeated here.

[0277] In the description of this specification, the reference terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean 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 invention. In this specification, the schematic expressions of the above terms must refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0278] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for predicting watershed sediment, characterized in that: include: Step S1: Collect basic data of the target watershed, including rainfall, soil, vegetation, topography, orthophotos, and hydrological data. The rainfall, vegetation, and hydrological data are current data and / or future data compiled based on future climate model data of the target watershed, and the soil, topography, and orthophotos are historical data of the target watershed. Organize the various basic data into a grid format and perform unified spatial registration. Set the boundaries of small watersheds as the spatial units for sediment prediction. Based on the boundaries of the small watersheds, spatially divide the various basic data. Based on the time scale requirements for sediment prediction, divide the various basic data at the small watershed scale into time periods. Step S2: For each small watershed, the erosion amount is predicted according to different erosion types, namely gravity erosion, debris flow erosion, gully erosion, and slope erosion, and the future spatiotemporal distribution of each type of erosion amount and the total erosion amount in the target watershed is obtained; wherein, For gravity erosion, the historical spatiotemporal distribution of gravity erosion is obtained using multi-period historical orthophotos of the target watershed and the area-volume relationship of collapse and landslides. Based on this historical spatiotemporal distribution, the statistical characteristic values ​​of gravity erosion at the small watershed scale within the historical period are obtained. The corresponding statistical characteristic values ​​are selected as the future gravity erosion at the small watershed scale according to risk management requirements. For debris flow erosion, all effective rainfall events in the small watershed in the future period are obtained based on future rainfall data, and the future debris flow erosion amount at the small watershed scale is obtained based on this effective rainfall event information; To address gully erosion, the gullies within the small watershed were divided into several equal segments. The historical gully erosion rate was calculated for each segment based on historical topographic data. The historical gully erosion amount at the small watershed scale was calculated based on the historical gully erosion rate. A multiple regression relationship was established between the historical gully erosion amount and rainfall and topographic parameters. Based on this multiple regression relationship, the gully erosion rate under rainfall conditions of the future climate model was calculated, thereby obtaining the future gully erosion amount at the small watershed scale. For slope erosion, the modified universal soil loss equation (RUSLE) is used to calculate the soil erosion amount at the grid scale in the future period based on the rainfall and vegetation data under the future climate model, thereby obtaining the future slope erosion amount at the small watershed scale. Step S3: predict the future sediment yield and future sedimentation corresponding to each type of erosion respectively, and obtain the future spatiotemporal distribution of sediment yield and sedimentation in the target watershed based on the future sediment yield and future sedimentation of each type of erosion at the small watershed scale; wherein, For gravity erosion, the historical sediment yield and deposition of gravity erosion at the small watershed scale were first calculated. Specifically, the historical sediment yield of gravity erosion was calculated based on multiple historical orthophotos and the area-volume relationship of collapses and landslides, and according to the volume of river material input from collapses and landslides connected to the water system. The ratio of gravity erosion sediment yield to gravity erosion volume was defined as the gravity erosion sediment transport ratio. The historical gravity erosion sediment transport ratio of each small watershed was statistically calculated based on the historical spatiotemporal distribution of gravity erosion volume. A multivariate regression relationship was established between the historical gravity erosion sediment transport ratio and the main river flow, main river water depth, and collapse and landslide volume. The future gravity erosion sediment transport ratio was calculated based on this multivariate regression relationship and runoff data under future climate models. The future gravity erosion sediment yield at the small watershed scale was calculated using the future gravity erosion volume at the small watershed scale and the future gravity erosion sediment transport ratio. The future gravity erosion sedimentation at the small watershed scale was obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion volume at the small watershed scale. For debris flow erosion, assuming that the geometric structure of the river system does not change over time within a century, the main river flow is extracted based on runoff data under future climate models. The sediment transport ratio of future debris flow erosion at the small watershed scale is calculated based on the bulk density and flow of debris flows and main rivers in the future period, as well as the inflow angle. Based on this sediment transport ratio, the sediment yield and deposition of future debris flow erosion at the small watershed scale are calculated. For gully erosion and slope erosion, the grid-scale sediment connectivity index is first calculated within the small watershed based on historical topographic data and future vegetation data. The future sediment transport ratio at the small watershed scale is then calculated based on this sediment connectivity index. The future sediment yield and deposition of gully erosion, as well as the future sediment yield and deposition of slope erosion at the small watershed scale, are then calculated based on this future sediment transport ratio. Step S4: Based on the future sediment yields of all small watersheds in the target watershed in each time period predicted in step S3, the suspended sediment transport of the small watersheds in the main river system is calculated section by section according to the upstream and downstream relationship of the locations where each small watershed in the target watershed flows into the river. The distribution of the suspended sediment transport along the flow direction of the main river system is predicted in combination with dredging, reservoir siltation, and the input and output of suspended sediment in the river section. The output of suspended sediment caused by dredging is obtained based on the average value of historical dredging data; the output of suspended sediment in the river section caused by reservoir siltation is calculated based on the effective storage capacity of the reservoir and future runoff data.

2. The basin sediment prediction method according to claim 1, characterized in that: Among the basic data collected in step S1, the temporal resolution of rainfall data is not less than 3 hours; the soil data includes the organic matter content in sand, silt, and clay in the surface soil; the vegetation data includes the normalized vegetation index and vegetation type; the terrain data uses a digital elevation model with a spatial resolution of not less than 30 meters; the hydrological data includes river system data, flow, and runoff within the target watershed; the basic data also includes the current land use type, which is used to calculate the dimensionless soil and water conservation measure factor; the spatial resolution used when performing unified spatial registration on the basic data in various grid forms is consistent with the spatial resolution of the digital elevation model; The small watershed is the watershed corresponding to the smallest level river in Horton's law. Based on the digital elevation model, the target watershed is divided into I small watersheds B1, B2, ... B i ,…B I , count the area, terrain height difference, average slope, channel length, channel width and channel slope of each small watershed; the time length used to divide various basic data into time periods is equal.

3. The basin sediment prediction method according to claim 1, characterized in that: In step S2, For the prediction of gravity erosion, it specifically includes: identifying the historical period T through the multi-period historical orthophotos of the target watershed j The newly added collapse and landslide area in the historical period T is calculated based on the collapse and landslide area and the collapse and landslide area-volume relationship. j Small watershed B i The total volume of materials released by collapse and landslide in the historical period T j Small watershed B i Gravity erosion (E G ) ij , based on the gravity erosion amount (E G ) ij Obtain the historical spatiotemporal distribution of gravity erosion; construct the cumulative probability distribution curve of the historical gravity erosion of each small watershed based on the historical spatiotemporal distribution of gravity erosion; select the corresponding statistical characteristic value from the cumulative probability distribution curve as the future time period T according to the risk management requirements f Small watershed B i Gravity erosion (E G ) if ; For debris flow erosion prediction, it specifically includes: obtaining small watershed B according to rainfall data under future climate model i In the future period T f All effective rainfall event information in the period, including the rainfall duration and average rainfall intensity of each effective rainfall event, is used to determine whether each effective rainfall event in the future period will trigger a debris flow through the rainfall threshold trigger condition set by the historical rainfall data; when it is determined that an effective rainfall event does not trigger a debris flow, the volume of the flushing material of the effective rainfall event is 0; when it is determined that an effective rainfall event triggers a debris flow, the volume of the flushing material of the effective rainfall event is calculated; statistics of the future period T f Small watershed B i The total volume of debris flow outflow is used as the future period T f Small watershed B i The amount of debris flow erosion (E D ) if ; The prediction of gully erosion includes: according to the historical topographic data, the historical period T j Small watershed B i The channel in the channel is divided into several channel segments, and the historical channel erosion rate of each channel segment is calculated respectively. Based on the historical channel erosion rate, the historical period T is calculated. j Small watershed B i The amount of channel erosion (E g ) ij , and obtain the historical gully erosion amount; establish a multiple regression relationship between the historical gully erosion amount and the average annual rainfall, slope and gully width, and calculate the gully erosion rate under the rainfall conditions of the future climate model based on this multiple regression relationship, so as to obtain the future gully erosion amount (E g ) if ; The slope erosion prediction includes: using the modified universal soil loss equation (RUSLE) to calculate the soil erosion modulus of each grid in the future period based on the rainfall and vegetation data under the future climate model, and then multiplying it by the grid area to obtain the grid scale future period T f The amount of soil erosion; the small watershed B i The soil erosion amount of each grid in the future period is accumulated to obtain the future period T f Small watershed B i The amount of slope erosion (E S ) if ; The sum of the predicted four types of erosion amounts is used to obtain the future period T f Inner small watershed B i Total erosion (E) if .

4. The basin sediment prediction method according to claim 3, characterized in that: In step S2, the historical period T is calculated according to the following formula: j Small watershed B i Gravity erosion (E G ) ij : Where, ρ G is the density of the collapse and landslide material; (V G ) k is the historical period T j Small watershed B i The volume of material released by the kth collapse and landslide in the period T j Small watershed B i The total number of internal collapse and landslides; the volume of material released by a single collapse and landslide V G Calculate according to the following formula: Where 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 soil landslide, and γ is 1.3~1.6 for rock landslide; The small watershed B i In the future period T f All valid rainfall events in the data are obtained by following the steps below: First, the rainfall data under the future climate model after spatial division is calculated according to the following formula: τ Average rainfall in: Where, Small watershed B i In the future time period t τ Average rainfall in t τ is the temporal resolution of future rainfall data, M is the temporal resolution of the small watershed B i The total number of grids within Small watershed B i The mth grid in the future time period t τ of rainfall; Small watershed B i In time period t τ Average rainfall Divide by time period t τ As a small watershed B i In time period t τ Average rainfall intensity; Traverse each future period T f Obtain the rainfall intensity time series matrix of each small watershed, and judge the rainfall intensity of each small watershed in each future period T in chronological order. f When the rainfall intensity is greater than the first set value, it is considered that a valid rainfall event has started. When the rainfall intensity is less than the first set value and continues for not less than the second set value, it is considered that the valid rainfall event has stopped. The period of time when the rainfall intensity is continuously greater than the first set value is considered as a valid rainfall event, and the rainfall duration D and average rainfall intensity of the valid rainfall event are recorded. Thus, we can obtain the small watershed B i In the future period T f All valid rainfall events information within; The rainfall threshold trigger condition set by historical rainfall data determines whether each effective rainfall event in the future period will trigger a debris flow, specifically: Assume that the rainfall threshold is I c , according to the following formula with small watershed as the unit: I c =a D D -β Where, α D and β are constants set based on historical rainfall data; When the average rainfall intensity of an effective rainfall event When , it is considered that no debris flow is triggered; When the average rainfall intensity of an effective rainfall event When the debris flow is triggered, the statistics of small watershed B i In the future period T f The rainfall data of each event that will trigger debris flow P l (D l , ), where l is the number of rainfall events that will trigger debris flow, the total number is L events, D l and Small watershed B i In the future period T f The duration and average rainfall intensity of the first rainfall event that will trigger a debris flow are calculated, and the volume of debris flow outflow V of each event is calculated using the following formula: D : Where Q D is the peak flow rate of debris flow; γ D is the bulk density of debris flow; γ W is the bulk density of clean water; S is the bulk density of solid matter in debris flow; Q P is the storm flood flow; K P is the confluence coefficient; F i Small watershed B i The drainage area; D C is the congestion coefficient; T is the duration of a debris flow; L D is the length of the main ditch of debris flow; U D is the speed of debris flow; S is the slope of gully bed; The future period T f Small watershed B i The amount of debris flow erosion (E D ) if Calculate according to the following formula: Where, ρ D is the density of debris flow outflow material; (V D ) l For the future period T f Small watershed B i The volume of debris discharged from the first debris flow; The historical period T j Small watershed B i The amount of channel erosion (E g ) ij Calculate according to the following formula: Where, L s is the length of the s-th channel; r s is the annual average erosion rate of the slope of the channel section, which is taken as the annual average change rate of the cross section of the channel section; ρ is the density of eroded sediment; ΔT is the historical period T j duration; The future period T f Small watershed B i The amount of slope erosion (E S ) if Calculate according to the following formula: Where A g is the area of ​​a single grid; A m Small watershed B i The future soil erosion modulus of the mth grid within the range. In 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. The dimensionless soil and water conservation measure factor P is assigned based on the historical slope and current land use type. M is the small watershed B i The total number of grid cells within.

5. The basin sediment prediction method according to claim 1, characterized in that: In step S3, The historical sediment yield of gravity erosion at the small watershed scale is calculated according to the following steps: If the collapse and landslide location is not connected to the river system, the sediment yield and sedimentation caused by the gravity erosion of the collapse and landslide are both 0. If the collapse and landslide location is connected to the river system, the historical period T j Small watershed B i Sediment yield T′ corresponding to internal gravity erosion G Calculate according to the following formula: T G =k G ·ρ·w G ·L G ·h h=cQ f Where p and P are the historical period T j Small watershed B i Number and total number of collapses and landslides connected to river systems; T G The mass of material input to the river for a single landslide; w G is the average distance that a single landslide extends from the river bank into the water, based on historical orthophotos or field surveys; L G is the length of the river section affected by a single collapse and landslide; k G is the correction coefficient; ρ is the density of eroded sediment; h is L G is the average water depth of the corresponding river section; Q is the flow rate of the main river at the location of a single collapse and landslide; c and f are coefficients; For the future sediment yield and deposition of debris flow erosion, first calculate the future period T according to the following formula: f Small watershed B i Sediment transport ratio (SDR) of internal debris flow erosion D ) if : Where, θ is the small watershed B i The angle at which the inner main ditch joins the main river, obtained based on current or historical river system data; γ m and γ D are the future time periods T f Small watershed B i The bulk density of the main river and debris flow; q m and q D are the future time periods T f Small watershed B i The unit-width flow of the main river and debris flow is obtained based on the hydrological data, and the unit-width flow of the debris flow is calculated as q D =Q D / w D , w D For the future period T f Small watershed B i The width of the debris flow channel, Q D For the future period T f Small watershed B i Peak debris flow discharge; Then based on the sediment delivery ratio (SDR D ) if Calculate the future period T f Small watershed B i Sediment yield and sedimentation caused by debris flow erosion: (T D ) if =(E D ) if ·(SDR D ) if (DD) if =(ED) if -(T D ) if Where, (T D ) if For the future period T f Small watershed B i The amount of sediment produced by debris flow erosion (D D ) if For the future period T f Small watershed B i the amount of sediment eroded by debris flows; In terms of the future sediment yield and deposition of gully erosion and slope erosion, the future period T is first calculated based on the grid-scale sediment connectivity index of each small watershed. f Small watershed B i Sediment transport ratio (SDR) of gully erosion or slope erosion IC ) if : Where, (SDR max ) if is the future period T f Small watershed B i The theoretical maximum sediment transport ratio is related to the surface soil texture; IC if is the future period T calculated based on historical terrain data and future vegetation data f Small watershed B i The average sediment connectivity index of the future period T f Small watershed B i The mean value of sediment connectivity index at each grid scale; IC0 and k are correction factors for calculating sediment transport ratio; Then based on the sediment delivery ratio (SDR IC ) if Calculate the future period T f Small watershed B i The sediment yield and deposition corresponding to the gully erosion, and the sediment yield and deposition corresponding to the slope erosion: (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 Where, (E g ) if For the future period T f Small watershed B i The amount of channel erosion, (T g ) if and (D g ) if are the future time periods T f Small watershed B i The amount of sediment production and deposition corresponding to the amount of gully erosion; (E S ) if For the future period T f Small watershed B i The amount of slope erosion, (T S ) if and (D S ) if are the future time periods T f Small watershed B i The amount of sediment production and deposition corresponding to the amount of slope erosion.

6. The basin sediment prediction method according to claim 5, characterized in that: Assume that the grid-scale sediment connectivity index of a small watershed in the future period is IC, which is calculated according to the following formula: IS m =RI m +C·P Where D up is the upslope component of a small watershed, reflecting the sediment production potential of the upstream; is the average impedance factor of the upslope catchment area of ​​a small watershed, representing the resistance of surface roughness to the flow of water and sediment; is the average slope of the upslope catchment area of ​​a small watershed; A up is the upslope catchment area of ​​a small watershed; D dn is the downslope component of a small watershed, reflecting the path resistance of sediment to the target; d m is the length of the flow path of the mth grid in a small watershed along the steepest downslope direction; W m is the impedance factor of the mth grid in a small watershed; SS m IS is the slope gradient of the mth grid in a small watershed; max IS is the maximum surface index of the small watershed where the grid is located; m is the surface index of the mth grid in a small watershed; RI m is the roughness index of the mth grid in a small watershed; To calculate RI m Used in Grid moving scanning pane, x m is the elevation of a grid, x s For the surrounding of a certain grille The average elevation of each grid; C is the dimensionless vegetation cover factor obtained based on vegetation data under the future climate model; P is the dimensionless soil and water conservation measure factor obtained based on the historical slope and current land use type.

7. The basin sediment prediction method according to claim 1, characterized in that: Step S4 specifically includes: According to the distribution of slope, river width and river type along the river, the river in the target basin is divided into X river sections R1, R2, ... R x ,…R X , stipulating that each river section shall have at most one reservoir or lake, and that the reservoir or lake shall be located at the entrance of the river section; Calculate the suspended sediment load of the river in the target basin by river section, for the period T f Any river section within R x The amount of suspended sediment output (SS out ) xf for: Where, (SS in ) xf For the future period T f River section R x The amount of suspended sediment input from upstream to the main river; (I T ) n For river section R x The amount of suspended sediment input from the nth tributary into the main river, n and N are the x The number and total number of internal tributaries, then represents the future period T f River section R x The amount of suspended sediment input from all tributaries into the main river is x The amount of suspended sediment that a tributary inputs into the main river I T , calculated based on the future sediment yield of the small watershed obtained in step S3; (E B ) xf For the future period T f River section R x The particle size of the riverbank erosion is consistent with the mass of the suspended sediment, which is calculated based on the water flow work. f River section R x The amount of riverbank erosion is calculated based on runoff data under future climate models; (O F ) xf For the future period T f River section R x The amount of suspended sediment deposited on the floodplain is calculated based on the runoff data for the future period T under the future climate model. f River section R x The average flow rate through the floodplain, the average settling velocity of suspended sediment and the average area of ​​the floodplain are calculated; (O D ) xf For the future period T f River section R x The amount of suspended sediment transported in irrigation or water diversion projects is taken as the x The annual average of the amount of suspended sediment transported by irrigation or water diversion projects over the years and the amount of artificial dredging; (O R ) xf For the future period T f River section R x The amount of suspended sediment deposited in reservoirs or lakes is estimated year by year based on runoff data under future climate models.

8. The basin sediment prediction method according to claim 7, characterized in that: The amount of suspended sediment input from a tributary into the 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 Where, T Gf ′ is the future period T f Small watershed B i The amount of sediment produced corresponds to the amount of gravity erosion; T D For the future period T f The sediment yield corresponding to the debris flow erosion of a small watershed corresponding to a tributary within a single river reach; T g For the future period T f The sediment yield corresponding to the channel erosion of a small watershed corresponding to a tributary within a single river reach; T S For the future period T f The sediment yield corresponding to the slope erosion of a small watershed corresponding to a tributary within a single river reach; (Δ s ) G 、(Δ s ) D 、(Δ s ) g T Gf ′、T D and T g The proportion of suspended sediment is obtained by extracting the characteristic particle size proportion of suspended sediment in the target watershed from the gradation curves of collapse and landslide deposits, debris flow fans and channel slope materials in the current period; Calculate the future period T according to the following formula f River section R x The particle size of the riverbank erosion is consistent with the mass of the suspended sediment (E B ) xf : (E B ) xf =b(ρ w g(Q B ) xf S xf )(h B ) xf (L B ) xf (r B ) xf ((D s ) B ) xf Where b is the adjustment parameter; ρ w is the density of pure water; g is the acceleration due to gravity; Q B is the flow rate on the flat land of the river section; S is the slope of the river section; h B is the river bank height; L B is the length of the river section; ρ B is the density of the shore material; (Δ s ) B is the proportion of suspended sediment in the bank material; except for the flow on the flat beach of the river section, Q B Except for the runoff data based on the future climate model, the other parameters were obtained using historical data; Calculate the future period T according to the following formula f River section R x The amount of suspended sediment deposited on the floodplain (O F ) xf : Where, (Q f ) xf For the future period T f River section R x The average flow of inland water through the floodplain is calculated based on runoff data under future climate models; xf For the future period T f River section R x Average settling velocity of suspended sediment; (A f ) xf For the future period T f River section R x Average floodplain area within the In calculating river section R x The annual average of the amount of suspended sediment transported by irrigation or water diversion projects and the amount of artificial dredging is calculated according to the following formula for the historical period T j River section R x The amount of suspended sediment transported in irrigation or water diversion projects (O D ) xj : (Oh D ) xj =(Q D ) xj ·ΔT·(C D ) xj Where, (Q D ) xj is the historical period T j River section R x The average output flow in irrigation or water diversion projects, (C D ) xj is the historical period T j River section R x Average sediment content of output water from irrigation or water diversion projects; The future period T is estimated year by year based on the runoff data in the future climate model. f River section R x The amount of suspended sediment in the reservoir or lake (O R ) xf Specifically: take the current period as the starting point, and change the current period river section R x The amount of suspended sediment input from upstream to the main river and the current period of river section R x The product of the average sediment interception rate of the reservoir or lake is taken as the current period of river section R x The amount of suspended sediment deposition in the reservoir or lake is calculated based on the effective storage capacity of the reservoir or lake and the multi-year average runoff. In the next year, the amount of suspended sediment deposition is subtracted from the effective storage capacity of the reservoir or lake, and the multi-year average runoff is added to update the multi-year average runoff, and the average sediment retention rate of the reservoir or lake in the next year is further calculated. Then, the average sediment retention rate of the reservoir or lake in the target basin for all future years is calculated by analogy. On this basis, the future period T is calculated. f River section R x The average sediment retention rate and suspended sediment deposition of reservoirs or lakes.

9. The basin sediment prediction method according to claim 8, characterized in that: River section R in a certain year x The average sediment retention rate of a reservoir or lake is calculated as follows: Where C R is the effective storage capacity of the reservoir or lake; I R It is the average multi-year runoff of a reservoir or lake.

10. A watershed sediment prediction device, characterized in that: include: The basic data acquisition module is configured to collect basic data of the target watershed, including rainfall, soil, vegetation, topography, orthophotos, and hydrological data. The rainfall, vegetation, and hydrological data are future time period data obtained by collating future climate model data of the target watershed, and the soil, topography, and orthophotos data are historical data of the target watershed. The various basic data are organized into a grid format and uniformly spatially aligned. The boundaries of small watersheds are set as the spatial units for sediment prediction. The various basic data are spatially divided based on the boundaries of the small watersheds. The various basic data at the small watershed scale are divided into time periods based on the time scale requirements of sediment prediction. The erosion prediction module is configured to predict the erosion amount for each small watershed according to different erosion types, namely gravity erosion, debris flow erosion, gully erosion, and slope erosion, and obtain the future temporal and spatial distribution of each type of erosion amount and the total erosion amount in the target watershed; For gravity erosion, the historical spatiotemporal distribution of gravity erosion is obtained using multi-period historical orthophotos of the target watershed and the area-volume relationship of collapse and landslides. Based on this historical spatiotemporal distribution, the statistical characteristic values ​​of gravity erosion at the small watershed scale within the historical period are obtained. The corresponding statistical characteristic values ​​are selected as the future gravity erosion at the small watershed scale according to risk management requirements. For debris flow erosion, all effective rainfall events in the small watershed in the future period are obtained based on future rainfall data, and the future debris flow erosion amount at the small watershed scale is obtained based on this effective rainfall event information; To address gully erosion, the gullies within the small watershed were divided into several equal segments. The historical gully erosion rate was calculated for each segment based on historical topographic data. The historical gully erosion amount at the small watershed scale was calculated based on the historical gully erosion rate. A multiple regression relationship was established between the historical gully erosion amount and rainfall and topographic parameters. Based on this multiple regression relationship, the gully erosion rate under rainfall conditions of the future climate model was calculated, thereby obtaining the future gully erosion amount at the small watershed scale. For slope erosion, the modified universal soil loss equation (RUSLE) is used to calculate the soil erosion amount at the grid scale in the future period based on the rainfall and vegetation data under the future climate model, thereby obtaining the future slope erosion amount at the small watershed scale. The sediment yield and deposition prediction module is configured to predict the future sediment yield and deposition corresponding to each type of erosion, and obtain the future spatiotemporal distribution of sediment yield and deposition in the target basin based on the future sediment yield and deposition of each type of erosion at the small basin scale; For gravity erosion, the historical sediment yield and deposition of gravity erosion at the small watershed scale were first calculated. Specifically, the historical sediment yield of gravity erosion was calculated based on multiple historical orthophotos and the area-volume relationship of collapses and landslides, and according to the volume of river material input from collapses and landslides connected to the water system. The ratio of gravity erosion sediment yield to gravity erosion volume was defined as the gravity erosion sediment transport ratio. The historical gravity erosion sediment transport ratio of each small watershed was statistically calculated based on the historical spatiotemporal distribution of gravity erosion volume. A multivariate regression relationship was established between the historical gravity erosion sediment transport ratio and the main river flow, main river water depth, and collapse and landslide volume. The future gravity erosion sediment transport ratio was calculated based on this multivariate regression relationship and runoff data under future climate models. The future gravity erosion sediment yield at the small watershed scale was calculated using the future gravity erosion volume at the small watershed scale and the future gravity erosion sediment transport ratio. The future gravity erosion sedimentation at the small watershed scale was obtained by subtracting the future gravity erosion sediment yield from the future gravity erosion volume at the small watershed scale. For debris flow erosion, assuming that the geometric structure of the river system does not change over time within a century, the main river flow is extracted based on runoff data under future climate models. The sediment transport ratio of future debris flow erosion at the small watershed scale is calculated based on the bulk density and flow of debris flows and main rivers in the future period, as well as the inflow angle. Based on this sediment transport ratio, the sediment yield and deposition of future debris flow erosion at the small watershed scale are calculated. For gully erosion and slope erosion, the grid-scale sediment connectivity index is first calculated within the small watershed based on historical topographic data and future vegetation data. The future sediment transport ratio at the small watershed scale is then calculated based on this sediment connectivity index. The future sediment yield and deposition of gully erosion, as well as the future sediment yield and deposition of slope erosion at the small watershed scale, are then calculated based on this future sediment transport ratio. The suspended sediment transport prediction module is configured to calculate the suspended sediment transport of small basins in the main river system section by section based on the predicted future sediment yield of all small basins in the target basin in each time period according to the upstream and downstream relationship of the location of each small basin in the target basin where it flows into the river, and to obtain the distribution of suspended sediment transport along the flow direction of the main river system by combining dredging, reservoir siltation and the input and output of suspended sediment in the river section; among them, the suspended sediment output caused by dredging is obtained based on the average value of historical dredging data; the suspended sediment output in the river section caused by reservoir siltation is estimated based on the effective storage capacity of the reservoir and future runoff data.

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