A distributed expression method for flash flood risk in a river basin based on flow return period

Abstract

The present invention provides a distributed expression method for flash flood risk in a watershed based on flow recurrence period, constructs a distributed Xin'anjiang model of the watershed, and obtains a distributed grid flow sequence; performs hydrological analysis and calculation based on DEM to obtain the spatial distribution of the basin runoff accumulation, normalizes the basin runoff accumulation, and produces the spatial distribution of the contribution of individual spatial grids to the basin outlet flow; focuses on the contribution of each grid in the basin to the empty station flow process at the basin outlet, combines the design flow of the outlet control station, determines the grid risk tolerance, that is, the design flow of each grid, combines the distributed simulation results, and more clearly expresses the spatiotemporal distribution of flash flood risk through spatial differentiation and fusion.

Description

Technical Field

[0001] The present invention relates to the field of hydrology, and in particular to a method for distributed expression of flash flood risk in a river basin based on flow recurrence period. Background Art

[0002] Flash flood disaster forecasting and warning mostly use critical rainfall and hydrological simulation methods. Critical rainfall is determined by observed rainfall and multi-year disaster statistics, and it is difficult to be universally applied in areas with insufficient data. In the distributed hydrological simulation method, model parameters can be determined according to their physical meaning, and the requirements for hydrological monitoring data are relatively low, and more reasonable simulation prediction results can be obtained.

[0003] Distributed hydrological simulation can give the temporal and spatial distribution of hydrological elements (usually flow) in the basin, and has a good flood indication effect. However, in actual use, it is difficult to determine whether the design standard is exceeded only by the simulated temporal and spatial distribution of flow, so it is difficult to judge the risk of flash flood disasters. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and provide a method for distributed expression of flash flood risk in a river basin based on flow recurrence period, so as to solve the technical problem of difficulty in judging the size of flash flood risk during flash flood disaster prevention.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for expressing the risk of flash floods in a river basin based on the flow return period, comprising the following steps:

[0007] S1, construct the basin distributed Xin'anjiang model and obtain the distributed grid flow sequence;

[0008] S2. Perform hydrological analysis and calculation based on the digital elevation model (DEM) to obtain the spatial distribution of the basin runoff accumulation, normalize the basin runoff accumulation, and produce the spatial distribution of the contribution of the individual spatial grids to the basin outlet flow;

[0009] S3, perform spatial matrix calculation on the design flow value of the basin outlet control station and the spatial distribution of basin outlet flow contribution to obtain the basin spatial grid design flow;

[0010] S4. Differentiate, overlay and fuse the distributed grid flow sequence calculated by the distributed model with the basin spatial grid design flow to obtain a spatiotemporal distribution atlas of flash flood risk in the basin.

[0011] Further, the S2 is specifically:

[0012] S201, normalize the accumulated flow of the watershed, specifically:

[0013] Calculate the normalized basin runoff accumulation of grid (i, j), that is, the basin outlet flow contribution ACC i,j , dimensionless; i, j represent the row and column numbers of the computational grid respectively;

[0014] If ACC max =ACC min , then ACC i,j =1;

[0015] If ACC max ≠ACC min ,

[0016] ACC i,j =(ACC i,j -ACC min ) / (ACC max -ACC min );

[0017] S202, traverse all grids within the basin to obtain the spatial distribution of the contribution of individual grids to the basin outlet flow ACC con ;

[0018]

[0019] Among them, m is the number of rows after gridding of the study area; n is the number of columns after gridding of the study area.

[0020] Further, the specific steps of S3 are:

[0021] S301, obtaining the design flow value of the basin outlet control station;

[0022] If the basin outlet control station has the design flow results, use them directly;

[0023] If there is no existing design flow result at the basin outlet control station, but there are long-term flow observation values, the P-III frequency curve is used for frequency analysis to obtain the design flow value of the basin outlet control station at the corresponding frequency;

[0024] If there is no design flow result at the basin outlet control station and no long-term flow observation, the design flow value of the basin outlet control station with the corresponding frequency is obtained by using the similar basin scaling method;

[0025] S302, according to the spatial distribution of the basin outlet flow contribution and the basin spatial grid design flow value, through matrix operation, the design flow QGrid of each basin spatial grid is obtained, in units of cubic meters per second;

[0026]

[0027]

[0028] Among them, Q P＝0.01 , Q P＝0.02 , Q P＝0.05 , Q P＝0.1 Indicates the design flow value of the export control station once in 100 years, once in 50 years, once in 20 years, and once in 10 years; unit: cubic meter / second.

[0029] Further, the specific steps of S4 are:

[0030] S401, set the start time and end time, input the driving data, the driving data includes: rainfall, evaporation capacity, run the calibrated distributed Xinanjiang model, and obtain the distributed grid flow sequence:

[0031]

[0032] Where Qt is the distributed grid flow sequence in the basin at time t, unit: cubic meter / second;

[0033] S402, perform difference, superposition and fusion calculation on the distributed grid flow sequence Qt at a certain moment and the basin spatial grid design flow QGrid of each return period to obtain the grid differential flow Qdis:

[0034]

[0035] Among them, Qt dis is the network differential flow in the basin at time t, unit: cubic meter / second;

[0036] S403, conditionally operate the network differential flow to obtain a matrix of whether each grid exceeds a given design flow standard, i.e., a spatiotemporal atlas of flash flood risk in the watershed Rt, dimensionless;

[0037]

[0038] If Qt dis >=0,Rt=1; there is a flash flood risk with a given return period;

[0039] If Qt dis <0, Rt = 0; no flash flood risk with a given return period;

[0040] S404, repeat S402 and S403 to obtain the time series risk matrix R:

[0041] R=[R1,R2,...,Rn];

[0042] S405 , color rendering is performed on the time series risk matrix R to generate a temporal and spatial distribution atlas of flash flood risk in the river basin.

[0043] Beneficial effects: Focus on the contribution of each grid in the basin to the empty station flow process at the basin outlet, determine the risk tolerance, that is, the design flow of each grid, combine with distributed simulation, and express the spatiotemporal distribution of flash flood risks more clearly through spatial differentiation and fusion. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a flow chart of a method for distributed expression of flash flood risk in a watershed based on flow return period of the present invention;

[0045] Figure 2 It is the cumulative amount of grid runoff in a small watershed in Anhui Province; Figure 3 This is a simulation diagram of the outlet flow of a small watershed in Anhui Province;

[0046] Figure 4 The contribution of the export flow of a small watershed in Anhui Province;

[0047] Figure 5 Design flow for a small watershed grid in Anhui Province;

[0048] Figure 6 This is the difference result at 8:00 on July 19, 2020;

[0049] Figure 7 This is the space-time risk map from 03:00 on July 19, 2020 to 09:00 on July 19. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] See also Figure 1 , a distributed expression method of flash flood risk in a river basin based on flow return period, including the following steps:

[0052] S1, construct the basin distributed Xin'anjiang model and obtain the distributed grid flow sequence;

[0053] Among them, the distributed Xinanjiang model is formed based on grids.

[0054] S2. Perform hydrological analysis and calculation based on the digital elevation model (DEM) to obtain the spatial distribution of the basin runoff accumulation, normalize the basin runoff accumulation, and produce the spatial distribution of the contribution of the individual spatial grids to the basin outlet flow;

[0055] Among them, the darker the grid color, the greater the contribution to the basin outlet flow.

[0056] S3, perform spatial matrix calculation on the design flow value of the basin outlet control station and the spatial distribution of basin outlet flow contribution to obtain the basin spatial grid design flow;

[0057] S4. Differentiate, overlay and fuse the distributed grid flow sequence calculated by the distributed model with the basin spatial grid design flow to obtain a spatiotemporal distribution atlas of flash flood risk in the basin.

[0058] The S2 is specifically:

[0059] S201, normalize the accumulated flow of the watershed, specifically:

[0060] Calculate the normalized basin runoff accumulation of grid (i, j), that is, the basin outlet flow contribution ACC i,j , dimensionless; i, j represent the row and column numbers of the computational grid respectively;

[0061] If ACC max =ACC min , then ACC i,j =1;

[0062] If ACC max ≠ACC min ,

[0063] ACC i,j =(ACC i,j -ACC min ) / (ACC max -ACC min );

[0064] S202, traverse all grids within the basin to obtain the spatial distribution of the contribution of individual grids to the basin outlet flow ACC con ;

[0065]

[0066] Among them, m is the number of rows after gridding of the study area; n is the number of columns after gridding of the study area.

[0067] The specific steps of S3 are:

[0068] S301, obtaining the design flow value of the basin outlet control station;

[0069] If the basin outlet control station has the design flow results, use them directly;

[0070] If there is no existing design flow result at the basin outlet control station, but there are long-term flow observation values, the P-III frequency curve is used for frequency analysis to obtain the design flow value of the basin outlet control station at the corresponding frequency;

[0071] If there is no design flow result at the basin outlet control station and no long-term flow observation, the design flow value of the basin outlet control station with the corresponding frequency is obtained by using the similar basin scaling method;

[0072] S302, according to the spatial distribution of the basin outlet flow contribution and the basin spatial grid design flow value, through matrix operation, the design flow QGrid of each basin spatial grid is obtained, in units of cubic meters per second;

[0073]

[0074] Among them, Q P＝0.01 , Q P＝0.02 , Q P＝0.05 , Q P＝0.1 Indicates the design flow value of the export control station once in 100 years, once in 50 years, once in 20 years, and once in 10 years; unit: cubic meter / second.

[0075] The specific steps of S4 are:

[0076] S401, set the start time and end time, input the driving data, the driving data includes: rainfall, evaporation capacity, run the calibrated distributed Xinanjiang model, and obtain the distributed grid flow sequence:

[0077]

[0078] Where Qt is the distributed grid flow sequence in the basin at time t, unit: cubic meter / second;

[0079] S402, perform difference, superposition and fusion calculation on the distributed grid flow sequence Qt at a certain moment and the basin spatial grid design flow QGrid of each return period to obtain the grid differential flow Qdis:

[0080]

[0081] Among them, Qt dis is the network differential flow in the basin at time t, unit: cubic meter / second;

[0082] S403, conditionally operate the network differential flow to obtain a matrix of whether each grid exceeds a given design flow standard, i.e., a spatiotemporal atlas of flash flood risk in the watershed Rt, dimensionless;

[0083]

[0084] If Qt dis >=0,Rt=1; there is a flash flood risk with a given return period;

[0085] If Qt dis <0, Rt = 0; no flash flood risk with a given return period;

[0086] S404, repeat S402 and S403 to obtain the time series risk matrix R:

[0087] R=[R1,R2,...,Rn];

[0088] S405 , color rendering is performed on the time series risk matrix R to generate a temporal and spatial distribution atlas of flash flood risk in the river basin.

[0089] Embodiment 1

[0090] This article uses the July 2020 flood in a river basin in Anhui Province as an example to illustrate;

[0091] The basin DEM can be downloaded for free on the Internet. The basin DEM map represents the ups and downs of the basin terrain. It is a grid matrix. The darker the color, the lower the elevation, and the lighter the color, the higher the elevation.

[0092] Based on the hydrological analysis function of ArcGIS software, the DEM data is processed to obtain the flow direction of the watershed. The flow direction is the classic D8 algorithm, which represents the direction of the water flow in the grid to the next level grid;

[0093] Based on the hydrological analysis function of ArcGIS software and combined with the flow direction file, the cumulative flow is obtained. The results are as follows: Figure 2 The grid flow accumulation value represents the sum of all grid points flowing upstream of the grid. The value of the flow accumulation can be obtained.

[0094] Other data required for the distributed hydrological model, such as land use and soil composition, can be downloaded from the Internet. In order to match the DEM data, it needs to be resampled to the same spatial resolution. This is a conventional existing technology and will not be described here.

[0095] According to the physical meaning of the parameters of the Xin'anjiang model in the basin distribution, combined with the underlying surface information of soil composition and land use, the values ​​of each grid parameter are calculated, such as the maximum tension water storage capacity WMM, the soil outflow coefficient KI, the groundwater outflow coefficient KG, and the surface runoff recession coefficient CS;

[0096] The data of rainfall stations and evaporation stations in the basin are interpolated into grid rainfall and evaporation series with the same spatial resolution, which are used as input to drive the basin distributed Xin'anjiang model together with the static parameter set to output grid flow.

[0097] The designed flow process of the basin outlet control station is taken as the actual value, the output flow of the basin distributed Xin'anjiang model is taken as the simulated value, and the relative error and Nash efficiency coefficient are used to calibrate other parameters of the basin distributed Xin'anjiang model. The calibration results are shown in Figure 3 ;

[0098] Based on DEM, hydrological analysis and calculation are performed to obtain the spatial distribution of the basin runoff accumulation, which is then normalized to generate the contribution distribution of the spatial individual grids to the basin outlet flow. Figure 4 , the contribution of the basin outlet flow can be obtained.

[0099] Taking the 20-year design flood as an example, the peak flow of the 20-year flood at the small basin outflow control station is 3150 cubic meters per second. By performing matrix calculation with the spatial distribution of flow contribution, the design flow of the basin space grid is obtained. Figure 5 The design flow value of the spatial grid for a 20-year flood means that when the simulated or actual flow of the grid is greater than this value, the simulated or actual flow of the grid exceeds the 20-year flood.

[0100] For example, the difference results at 8:00 on July 19, 2020 are shown in Figure 6 When the value is positive, it means that the network simulation or actual traffic is greater than the design value. When it is negative, it means that the network simulation or actual traffic is less than the design value.

[0101] For example, at 8:00 on July 19, 2020, the risk value obtained after conditional operation is 0, indicating no risk, and 1, indicating the risk of a flood that occurs more than once in 20 years.

[0102] Arrange the risk maps in chronological order to obtain a temporal and spatial distribution risk atlas Figure 7 ,Depend on Figure 7 It can be seen that at 03:00 on 19th, 2020, there was no risk in the entire basin; at 04:00, a small-scale risk appeared; at 06:00 the risk expanded to the maximum range, and then the risk range gradually decreased until it disappeared.

[0103] The above-mentioned embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be based on the attached claims.

Claims

1. A method for expressing the risk of flash floods in a river basin based on the flow return period, characterized by: The following steps are involved: S1, construct the basin distributed Xin'anjiang model and obtain the distributed grid flow sequence; S2. Perform hydrological analysis and calculation based on the digital elevation model (DEM) to obtain the spatial distribution of the basin runoff accumulation, normalize the basin runoff accumulation, and produce the spatial distribution of the contribution of the individual spatial grids to the basin outlet flow; The basin runoff accumulation is normalized as follows: Calculate the normalized basin runoff accumulation of grid (i, j), that is, the basin outlet flow contribution ACC i,j , dimensionless; i, j represent the row and column number of the computational grid respectively; If ACC max =ACC min , then ACC i,j =1; If ACC max ≠ACC min , Then ACC i,j =(ACC i,j -ACC min ) / (ACC max -ACC min ); Traverse all grids within the basin to obtain the spatial distribution of the contribution of individual grids to the basin outlet flow ACC con ; Among them, m is the number of rows after gridding of the study area; n is the number of columns after gridding of the study area; S3, perform spatial matrix calculation on the design flow value of the basin outlet control station and the spatial distribution of basin outlet flow contribution to obtain the basin spatial grid design flow; According to the spatial distribution of basin outlet flow contribution and the design flow value of the basin outlet control station, the design flow QGrid of each basin spatial grid is obtained through matrix operation, unit: cubic meter / second; Among them, Q P＝0.01 , Q P＝0.02 , Q P＝0.05 , Q P＝0.1 It indicates the design flow value of the export control station for 100-year, 50-year, 20-year and 10-year return periods; unit: cubic meter / second; S4, performing difference, superposition and fusion calculation on the distributed grid flow sequence obtained by the distributed model and the basin spatial grid design flow to obtain a spatiotemporal distribution atlas of the basin flash flood risk; S401, set the start time and end time, input the driving data, the driving data includes: rainfall, evaporation capacity, run the calibrated distributed Xinanjiang model, and obtain the distributed grid flow sequence: Where Qt is the distributed grid flow sequence in the basin at time t, unit: cubic meter / second; S402: Differentiate, overlay and fuse the distributed grid flow sequence Qt at a certain moment with the basin spatial grid design flow QGrid of each return period to obtain the grid differential flow Qt dis : Among them, Qt dis is the network differential flow in the basin at time t, unit: cubic meter / second; S403, conditionally operate the network differential flow to obtain a matrix of whether each grid exceeds a given design flow standard, i.e., a spatiotemporal atlas of flash flood risk in the watershed Rt, dimensionless; If Qt dis >=0,Rt=1; there is a flash flood risk with a given return period; If Qt dis <0, Rt = 0; no flash flood risk with a given return period; S404, repeat S402 and S403 to obtain the time series risk matrix R: R=[R1,R2,...,Rn]; S405 , color rendering is performed on the time series risk matrix R to generate a temporal and spatial distribution atlas of flash flood risk in the river basin.

2. According to claim 1, a method for expressing the risk of flash floods in a river basin based on the flow return period is characterized in that: The specific steps of S3 are: S301, obtaining the design flow value of the basin outlet control station; If the basin outlet control station has the design flow results, use them directly; If there is no existing design flow result at the basin outlet control station, but there are long-term flow observation values, the P-III frequency curve is used for frequency analysis to obtain the design flow value of the basin outlet control station at the corresponding frequency; If there is no design flow result at the basin outlet control station and no long-term flow observation, the similar basin scaling method is used to obtain the design flow value of the basin outlet control station with the corresponding frequency.

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