Data-free area distributed flood forecasting method considering dam break influence of small and medium-sized reservoirs

Abstract

The invention belongs to the technical field of distributed flood forecasting, and discloses a data-free area distributed flood forecasting method considering dam break influence of small and medium-sized reservoirs. Aiming at the problem that a hydrological model specially considering the dam break condition of a reservoir is lacked in a region without data at the present stage, the invention constructs a distributed hydrological model taking a grid as a unit, and the distributed hydrological model comprises a data processing module, a reservoir module, a runoff production module and a confluence module. The reservoir module judges a dam break or impounding state through the rain receiving capacity of the virtual reservoir; the runoff production module calculates surface runoff and underground runoff based on a mixed runoff production principle, and whether regulation and storage effects of small and medium-sized reservoirs are considered or not is judged according to results of the reservoir module; and the confluence module takes the result of the runoff generation module as input, and further obtains the flow process of each grid and outlet of the drainage basin according to the result of the reservoir module whether dam break of small and medium-sized reservoirs is considered. The flood forecasting method considering the dam break of the medium and small reservoirs is provided for areas without data, and the uncertainty of flood forecasting is expected to be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of distributed flood forecasting, and in particular to a distributed flood forecasting method for data-free areas taking into account the impact of dam breaches of small and medium-sized reservoirs. Background Art

[0002] Floods are one of the most common and destructive natural disasters in the world. Especially in areas without data, their prediction and management face huge challenges. Small and medium-sized reservoirs are important facilities for flood regulation in these areas. Once the risk of dam failure occurs, it will not only pose a serious threat to downstream areas, but also increase the uncertainty of flood forecasting. Therefore, there is an urgent need for a distributed flood forecasting method that can effectively consider the dam failure effect of small and medium-sized reservoirs in areas without data.

[0003] Distributed flood forecasting models have significant advantages in simulating the rainfall-runoff process in a watershed. They can divide the watershed into several sub-regions and consider the influence of spatial heterogeneity factors such as rainfall, topography, and soil in each sub-region. By introducing the dam-breaking behavior of small and medium-sized reservoirs into the distributed flood forecasting model, not only can the spatial resolution of the model be improved, but also the nonlinear characteristics of the dam-breaking flood propagation process can be more accurately captured, thereby significantly improving the accuracy of flood forecasting.

[0004] Therefore, the present invention aims to develop a distributed flood forecasting method for data-free areas that takes into account the impact of dam breaches of small and medium-sized reservoirs. By comprehensively applying distributed modeling technology and simulation methods for storage and discharge of small and medium-sized reservoirs and dam breach effects, high-precision flood forecasting under the influence of small and medium-sized reservoirs can be achieved in data-free areas. This method can not only provide important technical support for flood prevention and disaster reduction in data-free areas, but also provide a scientific basis for the safety management of small and medium-sized reservoirs. Summary of the invention

[0005] In view of the problems in the prior art, the present invention provides a distributed flood forecasting method for data-free areas taking into account the impact of dam breaches of small and medium-sized reservoirs.

[0006] The technical solution of the present invention is as follows: a distributed flood forecasting method for data-free areas taking into account the impact of dam breaches of small and medium-sized reservoirs, constructing and training a grid-based distributed flood forecasting model to perform distributed flood forecasting; the grid-based distributed flood forecasting model includes a data processing module, a reservoir module, a flow generation module and a confluence module;

[0007] The data processing module divides the watershed into a number of grid units, and the data recorded by each station in the watershed is divided into a grid format corresponding to the grid units;

[0008] The reservoir module aggregates a number of small and medium-sized reservoirs into a virtual reservoir by means of aggregated reservoirs and generalizes their spatial positions, and uses the rain-receiving capacity of the virtual reservoir as a dam-break judgment index; if the current rain-receiving capacity of the virtual reservoir exceeds its design standard, the confluence module starts the dam-break calculation; otherwise, if the reservoir operates normally, the flow generation module starts the flood interception and storage calculation;

[0009] The flow generation module adopts the mixed flow generation principle to calculate and obtain the surface runoff and underground runoff of each grid unit. If the flood interception calculation is started, the regulation and storage effect of small and medium-sized reservoirs in the basin on the flood process needs to be considered to obtain the actual flow generation of each grid; the actual flow generation is the sum of surface runoff and underground runoff;

[0010] The confluence module uses the actual flow generation calculated by the flow generation module as input to perform confluence calculations. If the dam break calculation is started, the impact of dam breaks of small and medium-sized reservoirs in the basin on the flood process needs to be considered. The flow generation results of each grid unit are used to calculate the confluence according to the topological relationship of the water system. The confluence results are superimposed with the calculated dam break flow, and finally the flow process of all grids in the basin and the basin outlet is obtained.

[0011] The calculation process of the reservoir module is as follows:

[0012] Calculate the design rainstorm of the basin and simulate the runoff through the designated basin outlet under different design rainstorms; find the design rainstorm that is closest to the runoff according to the current water storage status of the virtual reservoir and the design standard, so as to determine the reservoir's rain-holding capacity and whether the dam-breaking conditions are met. The design rainstorm of the basin is calculated using the following formula;

[0013]

[0014] Among them, z is the observed value of the random variable, σ is the scale parameter, μ is the location parameter, and x is the shape parameter.

[0015] The runoff generation module includes four parts: evapotranspiration, surface runoff, underground runoff and reservoir storage, as follows:

[0016] (1) Evapotranspiration calculation

[0017] Evapotranspiration in the runoff module includes canopy wet evaporation, vegetation transpiration, and bare soil evaporation;

[0018] The canopy wet part evaporation E c Calculate according to the following formula;

[0019]

[0020] Where f is the time period required for the canopy to intercept water and evaporate; P2 is the rainfall intensity; △t is the calculation time step; is the maximum canopy wet part evaporation; W iis the total amount of canopy interception; W im is the maximum interception of the canopy; E p is the surface evaporation potential when the stomatal resistance of the leaf surface is set to zero; r w is the aerodynamic impedance of water transport; r0 is the surface evaporation impedance;

[0021] The vegetation transpiration E t The following formula is used for calculation;

[0022]

[0023] r c is the stomatal impedance of the leaf surface;

[0024] The bare soil evaporation E l The calculation formula is as follows;

[0025]

[0026] In the formula, A S is the proportion of bare soil saturated area; i0 is the water storage capacity of a certain point; A is the proportion of the area with water storage capacity less than i, b is the water storage shape parameter, E p for potential evaporation;

[0027] When the soil is not fully watered, the actual evaporation of the soil is βEp, and the Penman-Monteith formula is used to calculate the potential evaporation; β is a function of soil moisture; for water storage capacity, the water storage capacity distribution curve is used for calculation, and the formula is as follows;

[0028] i=i m [1-(1-A) 1 / b ] (5)

[0029] In the formula, i is the water storage capacity; m is the maximum water storage capacity; A is the proportion of the area with water storage capacity less than i; b is the water storage shape parameter.

[0030] The surface runoff is calculated using a water storage capacity distribution curve and an infiltration capacity distribution curve to obtain a surface runoff process to simultaneously consider the full storage runoff generation and over-infiltration runoff generation mechanisms as well as the influence of sub-grid heterogeneity of soil properties on runoff generation;

[0031] The water storage capacity distribution curve is described by formula (4), and the infiltration capacity distribution curve is described as follows;

[0032] f'=f m [1-(1-C) 1 / B ] (7)

[0033] Where f' is the infiltration capacity; f mis the maximum infiltration capacity; C is the area ratio with infiltration capacity less than or equal to f'; B is the infiltration capacity shape parameter;

[0034] The full flow R1 occurs in the initial saturated area As and the part that becomes saturated during the period (A s '-A s ) area, excess infiltration runoff R2 occurs on the remaining area (1-As) and is redistributed within the entire excess infiltration runoff calculation area; P represents the total rainfall over a period of time, including full storage runoff R1, excess infiltration runoff R2 and the total amount of water infiltrating into the soil △W. The relationship between the three is as follows;

[0035] P=R1(y)+R2(y)+△W(y) (8)

[0036] y=R1(y)+△W(y) (9)

[0037] Where y is the vertical depth shown by the water storage capacity distribution;

[0038] According to formula (5), the calculation formulas for full storage runoff R1 and soil moisture content change △W are as follows:

[0039]

[0040] According to formula (12), the water input rate W is obtained p , the calculation formula is as follows;

[0041]

[0042] The excess infiltration runoff R2 is determined by the time period length and infiltration capacity distribution curve, soil infiltration capacity and W p The product of the three enclosed areas is obtained by the following calculation formula:

[0043]

[0044] The vertical one-dimensional soil water movement is described by the ARNO model, and the water vapor flux between soil layers obeys Darcy's law, so the underground runoff is calculated, and the calculation formula is as follows;

[0045]

[0046] Where D m is the maximum base flow; D s is the current base flow and D m The ratio of is the initial moisture content of the underlying soil; is the maximum water content of the lower soil; W s It is the water content ratio of the lower soil.

[0047] The reservoir interception and storage constructs a nonlinear equation between soil moisture content and reservoir water storage capacity, thereby obtaining the reservoir water storage capacity in each period during the flood period. The specific formula is as follows:

[0048]

[0049] Where V(t) is the reservoir capacity in period t; m and n are linear and nonlinear parameters respectively; W(t) is the soil moisture content in period t; W m V is the soil water storage capacity; e To promote the storage capacity; V d For dead storage capacity;

[0050] After deducing the time series of reservoir water storage during the flood period, the storage capacity change value in each time period is deduced according to ΔV(t)=V(t)-V(t-1), which represents the impact of the reservoir on the flow generation in the basin. ΔV(t) is converted to the flow generation above the reservoir to simulate the reservoir interception and storage.

[0051] The confluence module includes three parts: slope confluence, river confluence and reservoir dam breach, and its calculation is as follows;

[0052] The slope runoff is calculated using a slope runoff unit line based on a two-parameter Gamma distribution. The shape of the unit line is controlled by a time scale parameter a and a shape parameter θ. The calculation formula of the Gamma distribution function is as follows:

[0053]

[0054] Where, t represents time; a is the time scale parameter of the distribution function; θ represents the shape parameter;

[0055] Taking the calculation results of the runoff module as input, the Gamma distribution function is used to calculate the slope runoff flow in each period. The calculation formula is as follows;

[0056]

[0057] Where q is the flow rate at time step t; y t ' represents the flow rate calculated by the flow generation module; t max Indicates the maximum time length of the Gamma distribution; s indicates the calculation period;

[0058] The impulse response function method is used to calculate the river confluence flow; IRF is a one-dimensional diffusion wave equation derived from the one-dimensional Saint-Venant equation, and the calculation equation is as follows;

[0059]

[0060] In the formula, q is the flow rate of the water section; x is the distance along the river; C represents the flow velocity; D represents the diffusion coefficient; the convolution integral of the equation is solved to obtain the river confluence flow rate, and the calculation formula is as follows;

[0061]

[0062] in,

[0063]

[0064] Where U(ts) is the runoff depth generated at time ts;

[0065] The following formula is used to calculate the dam-break flow of the reservoir;

[0066]

[0067] In the formula, H0 is the water level in front of the dam; Z is the dam length; g is the acceleration of gravity; Q M is the maximum dam-break discharge; h = H0-h', where h' is the residual height; L is the breach length;

[0068] The linear shape of the dam-break flood process is generalized as a fourth-order parabola, and the reservoir emptying time T is calculated as follows;

[0069]

[0070] In the formula, W is the dam-break reservoir capacity; Q M is the maximum dam-break flow; K is the coefficient;

[0071] The dam-break flow process takes t / T as the X-axis and Q / Q as the M is the vertical axis to approximate the parabola; when t / T is equal to 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, Q / Q M The corresponding values ​​are 1, 0.62, 0.48, 0.34, 0.26, 0.207, 0.168, 0.13, 0.094, 0.061, 0.03. When t / T is equal to 1, Q / Q M The corresponding value is Q0 / Q M , Q / Q M is 0.

[0072] The calculation formula of the breach length L is as follows:

[0073] 1) When the reservoir capacity is greater than 1 million m 3 hour;

[0074]

[0075] Where, k is the material coefficient of the dam body; for clay, clay core wall or inclined wall, soil, stone, and concrete, k is 1.19; for homogeneous loam material, k is 1.98;

[0076] 2) When the storage capacity is less than 1 million m 3 hour;

[0077]

[0078] In the formula, if the dam material is good, k is 6.6; otherwise, k is 9.1.

[0079] Beneficial effects of the invention: The invention proposes a flood forecasting method in view of the current situation of lack of measured data of reservoirs in areas without data. By establishing a distributed hydrological model with grids as units, the propagation process and spatiotemporal characteristics of dam-break floods are simulated, providing scientific support for risk assessment and emergency management, while effectively reducing the uncertainty of flood forecasting. While improving the flood forecasting capabilities in areas without data, this method promotes the application of distributed hydrological models in the simulation of complex hydrological processes, and has important theoretical innovation and practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 It is a flow chart of the present invention.

[0081] Figure 2 It is a schematic diagram of the runoff module of the distributed hydrological model; (a) is the water storage capacity curve, and (b) is the infiltration capacity curve.

[0082] Figure 3 It is a schematic diagram of rainfall stations and hydrological divisions in the study area.

[0083] Figure 4 It is a schematic diagram of the reservoir distribution in the study area.

[0084] Figure 5 This is a schematic diagram of land use in the study area.

[0085] Figure 6 It is a 12.5m resolution DEM elevation map of the study area.

[0086] Figure 7 This is a schematic diagram of vegetation utilization in the study area. DETAILED DESCRIPTION

[0087] Based on distributed hydrological modeling, the present invention proposes a distributed flood forecasting method for data-free areas taking into account the impact of dam breaches of small and medium-sized reservoirs.

[0088] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0089] Huanren Hydropower Station is the leader of the Hunjiang cascade power stations, located about 4km upstream of Huanren Town, Huanren Manchu Autonomous County, Liaoning Province. The dam site controls a basin area of ​​10,364km 2 , accounting for 67.2% of the Hunjiang River Basin area. The main task of the power station is to generate electricity, while taking into account the comprehensive utilization of downstream flood control, irrigation, aquaculture, etc., and playing the role of peak load regulation, frequency regulation, and emergency standby in the Northeast Power Grid.

[0090] The first step is data processing

[0091] The data required for the model construction of the present invention include basin rainfall, soil, vegetation utilization and DEM, as well as the location and storage capacity information of small and medium-sized water conservancy projects in the basin. Specifically: DEM, reservoir distribution, soil type, vegetation type, precipitation, temperature, wind speed and soil moisture content, etc. Download the DEM data of the study area with a resolution of 12.5m from the data download platform of 91 Weitu (https: / / www.91weitu.com / ); use the spatial distribution data of soil types with a resolution of 1km published by the Food and Agriculture Organization of the United Nations (FAO); use the global 1km resolution vegetation utilization data set published by the University of Maryland; the basin period rainfall, the location and storage capacity information of small and medium-sized water conservancy projects are obtained from the basin water conservancy management department. According to actual needs, the basin is divided into several orthogonal grids of equal size, and the underlying surface information such as soil properties, slope, river length and river section topological structure in the grid unit is extracted; the rainfall data of the rain gauge station is interpolated into 0.05° grid data using the inverse distance weighted method (IDW).

[0092] In the second step, based on the data collected in the first step, the basin above the Huanren Reservoir is divided into three parts: upper, middle and lower. The idea of ​​aggregated reservoirs is adopted to aggregate the numerous small and medium-sized reservoirs in each part into a virtual reservoir and generalize their spatial positions. The current rainfall receiving capacity of the reservoir is calculated, and it is determined whether it exceeds its design standard, and then the dam break is initiated in the confluence module or the flood is intercepted and stored in the flow generation module.

[0093] In the third step, the surface runoff is calculated using the soil water storage capacity distribution curve and the infiltration capacity distribution curve, and the underground runoff is calculated using the ARNO model. If the flood interception calculation is started, the interception capacity of small and medium-sized reservoirs for the flood process is calculated, and the actual flow production of each grid is obtained.

[0094] The fourth step is to use the results of the flow generation module as input, use the unit line based on the Gamma distribution to calculate the slope runoff, and use the IRF method to calculate the river runoff. If the dam break calculation is started, the dam break flow process of small and medium-sized reservoirs in the basin is calculated, and the calculation results of the upstream runoff of the reservoir are superimposed with the dam break flow process, and finally the flow process of all grids in the basin and the basin outlet is obtained.

[0095] The fifth step is to discuss the inflow of Huanren Reservoir under the conditions of virtual reservoir dam breach at different spatial locations, calculate the dam breach flow process of the three virtual reservoirs above Huanren Reservoir under the conditions of extreme precipitation, and superimpose it with the distributed flood forecast results of the specified sub-basin to obtain the flow process of all grids and basin outlets in the basin under different extreme conditions.

[0096] Table 1 Flood information of Huanren Reservoir under different schemes

[0097]

[0098] The above-described embodiments merely express the implementation methods of the present invention, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A distributed flood forecasting method for data-free areas considering the impact of dam failure of small and medium-sized reservoirs, characterized in that: Constructing and training a grid-based distributed flood forecasting model to perform distributed flood forecasting; the grid-based distributed flood forecasting model includes a data processing module, a reservoir module, a flow generation module and a confluence module; The data processing module divides the watershed into a number of grid units, and the data recorded by each station in the watershed is divided into a grid format corresponding to the grid units; The reservoir module aggregates a number of small and medium-sized reservoirs into a virtual reservoir by means of aggregated reservoirs and generalizes their spatial positions, and uses the rain-receiving capacity of the virtual reservoir as a dam-break judgment index; if the current rain-receiving capacity of the virtual reservoir exceeds its design standard, the confluence module starts the dam-break calculation; otherwise, if the reservoir operates normally, the flow generation module starts the flood interception and storage calculation; The flow generation module adopts the mixed flow generation principle to calculate and obtain the surface runoff and underground runoff of each grid unit. If the flood interception calculation is started, the regulation and storage effect of small and medium-sized reservoirs in the basin on the flood process needs to be considered to obtain the actual flow generation of each grid; The actual runoff is the sum of surface runoff and underground runoff; The confluence module uses the actual flow generation calculated by the flow generation module as input to perform confluence calculations. If the dam break calculation is started, the impact of dam breaks of small and medium-sized reservoirs in the basin on the flood process needs to be considered. The flow generation results of each grid unit are used to calculate the confluence according to the topological relationship of the water system. The confluence results are superimposed with the calculated dam break flow, and finally the flow process of all grids in the basin and the basin outlet is obtained.

2. A distributed flood forecasting method for data-free areas considering the impact of dam failure of small and medium-sized reservoirs according to claim 1, characterized in that: The calculation process of the reservoir module is as follows: Calculate the design rainstorm of the basin and simulate the runoff through the designated basin outlet under different design rainstorms; find the design rainstorm that is closest to the runoff according to the current water storage status of the virtual reservoir and the design standard, so as to determine the reservoir's rain-holding capacity and whether the dam-breaking conditions are met. The design rainstorm of the basin is calculated using the following formula; Among them, z is the observed value of the random variable, σ is the scale parameter, μ is the location parameter, and x is the shape parameter.

3. A distributed flood forecasting method for data-free areas considering the impact of dam breaches of small and medium-sized reservoirs according to claim 1 or 2, characterized in that: The runoff generation module includes four parts: evapotranspiration, surface runoff, underground runoff and reservoir storage, as follows: The evapotranspiration is calculated as follows; Evapotranspiration in the runoff module includes canopy wet evaporation, vegetation transpiration, and bare soil evaporation; The canopy wet part evaporation E c Calculate according to the following formula; Where f is the time period required for the canopy to intercept water and evaporate; P2 is the rainfall intensity; △t is the calculation time step; W is the maximum canopy wet part evaporation; i is the total amount of canopy interception; W im is the maximum interception of the canopy; E p is the surface evaporation potential when the stomatal resistance of the leaf surface is set to zero; r w is the aerodynamic impedance of water transport; r0 is the surface evaporation impedance; The vegetation transpiration E t The following formula is used for calculation; r c is the stomatal impedance of the leaf surface; The bare soil evaporation E l The calculation formula is as follows; In the formula, A S is the proportion of bare soil saturated area; i0 is the water storage capacity of a certain point; A is the proportion of the area with water storage capacity less than i, bb is the water storage shape parameter, E p for potential evaporation; When the soil is not fully watered, the actual evaporation of the soil is βEp, and the Penman-Monteith formula is used to calculate the potential evaporation; β is a function of soil moisture; for water storage capacity, the water storage capacity distribution curve is used for calculation, and the formula is as follows; i=i m [1-(1-A) 1 / b ] (5) In the formula, i is the water storage capacity; m is the maximum water storage capacity; A is the proportion of the area with water storage capacity less than i; b is the water storage shape parameter.

4. The distributed flood forecasting method for data-free areas considering the impact of dam failure of small and medium-sized reservoirs according to claim 3 is characterized in that: The surface runoff is calculated using a water storage capacity distribution curve and an infiltration capacity distribution curve to obtain a surface runoff process to simultaneously consider the full storage runoff generation and over-infiltration runoff generation mechanisms as well as the influence of sub-grid heterogeneity of soil properties on runoff generation; The water storage capacity distribution curve is described by formula (4), and the infiltration capacity distribution curve is described as follows; f'=f m [1-(1-C) 1 / B ] (7) Where f' is the infiltration capacity; f m is the maximum infiltration capacity; C is the area ratio with infiltration capacity less than or equal to f'; B is the infiltration capacity shape parameter; The full flow R1 occurs in the initial saturated area As and the part that becomes saturated during the period (A′ s -A s ) area, excess infiltration runoff R2 occurs on the remaining area (1-As) and is redistributed within the entire excess infiltration runoff calculation area; P represents the total rainfall over a period of time, including full storage runoff R1, excess infiltration runoff R2 and the total amount of water infiltrating into the soil △W. The relationship between the three is as follows; P=R1(y)+R2(y)+△W(y) (8) y=R1(y)+△W(y) (9) Where y is the vertical depth shown by the water storage capacity distribution; According to formula (5), the calculation formulas for full storage runoff R1 and soil moisture content change △W are as follows: According to formula (12), the water input rate W is obtained p , the calculation formula is as follows; The excess infiltration runoff R2 is determined by the time period length and infiltration capacity distribution curve, soil infiltration capacity and W p The product of the three enclosed areas is obtained by the following calculation formula:

5. The distributed flood forecasting method for data-free areas considering the impact of dam failure of small and medium-sized reservoirs according to claim 4 is characterized in that: The vertical one-dimensional soil water movement is described by the ARNO model, and the water vapor flux between soil layers obeys Darcy's law, so the underground runoff is calculated, and the calculation formula is as follows; Where D m is the maximum base flow; D s is the current base flow and D m The ratio of is the initial moisture content of the underlying soil; is the maximum water content of the lower soil; W s It is the water content ratio of the lower soil.

6. The distributed flood forecasting method for data-free areas considering the impact of dam failure of small and medium-sized reservoirs according to claim 5 is characterized in that: The reservoir interception and storage constructs a nonlinear equation between soil moisture content and reservoir water storage capacity, thereby obtaining the reservoir water storage capacity in each period during the flood period. The specific formula is as follows: Where V(t) is the reservoir capacity in period t; m and n are linear and nonlinear parameters respectively; W(t) is the soil moisture content in period t; W m V is the soil water storage capacity; e To promote the storage capacity; V d For dead storage capacity; After deducing the time series of reservoir water storage during the flood period, the storage capacity change value in each time period is deduced according to ΔV(t)=V(t)-V(t-1), which represents the impact of the reservoir on the flow generation in the basin. ΔV(t) is converted to the flow generation above the reservoir to simulate the reservoir interception and storage.

7. The distributed flood forecasting method for data-free areas considering the impact of dam failure of small and medium-sized reservoirs according to claim 1 is characterized in that: The confluence module includes three parts: slope confluence, river confluence and reservoir dam breach, and its calculation is as follows; The slope runoff is calculated using a slope runoff unit line based on a two-parameter Gamma distribution. The shape of the unit line is controlled by a time scale parameter a and a shape parameter θ. The calculation formula of the Gamma distribution function is as follows: In the formula, t represents time; a is the time scale parameter of the distribution function; θ represents the shape parameter; Taking the calculation results of the runoff module as input, the Gamma distribution function is used to calculate the slope runoff flow in each period. The calculation formula is as follows; Where q is the flow rate at time step t; y t ' represents the flow rate calculated by the flow generation module; t max Indicates the maximum time length of the Gamma distribution; s represents the calculation period.

8. The distributed flood forecasting method for data-free areas considering the impact of dam breach of small and medium-sized reservoirs according to claim 7 is characterized in that: The flow of the river confluence is calculated using the impulse response function method; IRF is a one-dimensional diffusion wave equation derived from the one-dimensional Saint-Venant equation, and the calculation equation is as follows; In the formula, q is the flow rate of the water section; x is the distance along the river; C represents the flow velocity; D represents the diffusion coefficient; the convolution integral of the equation is solved to obtain the river confluence flow rate, and the calculation formula is as follows: in, Where U(ts) is the runoff depth generated at time ts.

9. The distributed flood forecasting method for data-free areas considering the impact of dam failure of small and medium-sized reservoirs according to claim 7 is characterized in that: The flow rate of the reservoir dam break is calculated using the following formula: In the formula, H0 is the water level in front of the dam; Z is the dam length; g is the acceleration of gravity; Q M is the maximum dam-break discharge; h = H0-h', where h' is the residual height; L is the breach length; The linear shape of the dam-break flood process is generalized as a fourth-order parabola, and the reservoir emptying time T is calculated as follows; In the formula, W is the dam-break reservoir capacity; Q M is the maximum dam-break flow; K is the coefficient; The dam-break flow process takes t / T as the X-axis and Q / Q as the M is the vertical axis to approximate the parabola; when t / T is equal to 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, Q / Q M The corresponding values ​​are 1, 0.62, 0.48, 0.34, 0.26, 0.207, 0.168, 0.13, 0.094, 0.061, 0.

03. When t / T is equal to 1, Q / Q M The corresponding value is Q0 / Q M , Q / Q M is 0.

10. The distributed flood forecasting method for data-free areas considering the impact of dam failure of small and medium-sized reservoirs according to claim 9 is characterized in that: The calculation formula of the breach length L is as follows: 1) When the reservoir capacity is greater than 1 million m 3 hour; Where, k is the material coefficient of the dam body; for clay, clay core wall or inclined wall, soil, stone, and concrete, k is 1.19; for homogeneous loam material, k is 1.98; 2) When the storage capacity is less than 1 million m 3 hour; In the formula, if the dam material is good, k is 6.6; otherwise, k is 9.1.

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