CN116542459A - An ecological scheduling method for habitat remodeling of fish spawning grounds in changing backwater areas - Google Patents

Abstract

The invention discloses an ecological scheduling method for remodeling spawning sites of fishes in a fluctuation water return area, which comprises the steps of establishing a depth two-dimensional plane numerical model of the fluctuation water return area of a reservoir, and recording the model as a two-dimensional hydrodynamic model; the effective habitat area (WUA) of fish under the average flow for years when the natural river channel of the water return area is changed is simulated, the target WUA value is determined, WUA under the working conditions of different flow and water level after the reservoir is built is simulated, the working condition that the spawning ground of the water return area is changed to meet the target WUA value is further clearly made, and the water level interval meeting the building requirement is selected according to the incoming flow condition to perform water level scheduling. According to the method, the relationship between reservoir flow, water level and effective fish habitat area is established by integrating the two-dimensional hydrodynamic model and the fish habitat model, so that reservoir ecological dispatching measures are defined. The ecological dispatching method provided by the invention can effectively improve river ecology and provide effective reference for maintaining and rebuilding reservoirs of the spawning sites of the fluctuation water return areas.

Description

An ecological scheduling method for habitat remodeling of fish spawning grounds in changing backwater areas

technical field

The invention belongs to the technical field of reservoir management, relates to ecological scheduling of fish spawning grounds, and in particular relates to an ecological scheduling method for habitat remodeling of fish spawning grounds in changing backwater areas.

Background technique

While performing their beneficial functions such as flood control, power generation, and irrigation, the reservoir group has also changed the natural hydrological regime of the river, resulting in changes in the river's topography, hydrodynamics, and water temperature, thereby destroying the original environment of aquatic organisms. reproductive growth conditions. The stronger the regulation performance of the reservoir, the greater the impact on the natural hydrological situation of the river, and the living habits of aquatic organisms represented by fish will also be changed accordingly. In order to reduce this adverse impact of the reservoir, ecological regulation research is needed. However, current studies on the impact of reservoir construction on fish spawning grounds are mostly focused on the downstream reaches of the dam site, and little attention has been paid to the backwater areas of reservoir changes, resulting in the abandonment of spawning grounds in the backwater areas of reservoir changes. Due to the particularity of the regulation of the reservoir, the spawning grounds in the changing backwater areas of the reservoirs will not disappear completely. The most representative is the research on the habitat of fish spawning grounds in the changing backwater areas of the Three Gorges Reservoir of the Yangtze River. During the observation, fish eggs were found near the original natural river spawning ground, which indicated that fish would still breed in the variable backwater area suitable for their spawning.

The current research on fish spawning ground habitats in variable backwater areas only focuses on the four major domestic carps in reservoirs in plain areas, but the four major domestic carps have a wide range of suitability for hydrodynamic conditions, and mainly analyze the fish before and after the establishment of the dam. For changes in Weighted Usable Area (hereinafter referred to as WUA), the qualitative evaluation of reservoir operation and management should take into account changes in the spawning grounds in the backwater area. These research methods are difficult to meet the quantitative ecological regulation of the fluctuating backwater areas of mountainous river-type reservoirs and the spawning grounds of bottom-dwelling cold-water fishes such as Schizothorax.

Contents of the invention

In view of the lack of ecological regulation in the changing backwater area of river channel reservoirs in mountainous areas, especially the lack of quantitative ecological regulation for the spawning grounds of bottom-dwelling cold-water fish, the present invention aims to provide a method for determining fish spawning grounds based on reservoir changing backwater areas. The method of ecological regulation of the reservoir can predict the effective habitat area of fish under different working conditions, and then obtain the relationship between the effective habitat area (WUA) of the fish in the backwater area of the reservoir change and the reservoir regulation, so as to provide information for the operation and regulation of the reservoir. Technical support is conducive to reservoir management and protection of fish spawning grounds in changing backwater areas.

The inventive idea of the present invention is to firstly establish a reservoir model, simulate the WUA of the natural river, and then determine the target WUA value, and then simulate the WUA under different working conditions after the reservoir is built, and then determine that the spawning ground in the variable backwater area can meet the target According to the working conditions of WUA value, the reservoir dispatching is carried out according to the selected working conditions.

Based on the idea of the above invention, the present invention provides an ecological scheduling method for habitat remodeling of fish spawning grounds in changing backwater areas, which includes the following steps:

Step 1: Establish a two-dimensional planar numerical model of reservoir depth including the variable backwater area of the reservoir, which is denoted as a two-dimensional hydrodynamic model;

Step 2, use the two-dimensional hydrodynamic model to calculate the effective habitat area WUA of benthic cold-water fish in the changing backwater area under different percentages of the annual average flow of the natural river, so as to determine the target WUA value;

Step 3, based on historical hydrological data, determine the flow and water level conditions that occurred during the spawning period of benthic cold-water fish;

Step 4, use the two-dimensional hydrodynamic model to calculate the hydrodynamic conditions of the variable backwater area under different flow and water level conditions in step 3, and calculate the WUA value of the variable backwater area according to the suitability curve of fish flow rate and water depth;

Step 5: Determine the reservoir water level regulation scheme according to the flow and water level conditions that meet the target WUA value or more.

The first step above is to collect reservoir topographical data, hydrological data and fish flow depth suitability curve. curves and water depth suitability curves. The collected hydrological data are used for model verification and statistics of the flow and water level of the reservoir during the spawning period. Statistical flow and water level conditions during the spawning period will be used for subsequent clear calculation conditions, so as much hydrological data as possible should be collected to fully reflect the response of fish WUA to hydrological data in the backwater area of reservoir changes.

The collected topographic data is used to establish a two-dimensional plane numerical model of the reservoir depth; the collected hydrological data is used to calibrate the parameters of the established numerical model to ensure that the hydrodynamic conditions simulated by the model are reliable.

The specific operation is: use Notepad to convert the terrain data and boundary data into XYZ format files, import the XYZ format files into the Mesh Generator module in MIKE Zero to generate calculation grids and terrain interpolation, generate mesh files and import them. Select the Flow Mode module in MIKE21, import the mesh file, set the simulation time, simulation step size, dry-wet boundary, density, eddy viscosity coefficient, bed roughness, wind field, rainfall, evaporation, flow and water level data, and run The file in m21fm format is generated to complete the construction of the hydrodynamic model; the number of grids in the variable backwater area in the generated two-dimensional hydrodynamic model accounts for 70-98% of the grids in the entire reservoir. The hydrodynamic model is calibrated according to the collected hydrological data, and the error between the simulated value and the measured value is controlled within 10%.

The second step above is to simulate the WUA value of the changing backwater area under the condition of the natural channel of the changing backwater area of the reservoir under different percentages of the annual average flow rate, obtain the flow-WUA curve, determine the maximum WUA value according to the curve, and set 60% of the maximum value of WUA as the target WUA value, the specific steps are as follows:

(1) Utilize the two-dimensional hydrodynamic model to simulate the hydrodynamic conditions under the different percentages of the multi-year average flow rate under the natural channel of the reservoir including the variable backwater area of the reservoir; the hydrodynamic conditions include flow velocity and water depth;

(2) Extract the flow velocity and water depth data under different percentages of each calculation unit;

(3) Find the corresponding suitability of each flow rate and depth data from the suitability curve of flow rate and water depth, and use the geometric mean method to calculate the comprehensive habitat suitability index HSI of each calculation unit; the calculation formula of HSI is:

Among them, HSI _i is the comprehensive habitat suitability index of the calculation unit, which is composed of SI _vi , SI _di and SI _ci (namely, flow velocity, water depth, channel suitability (SI _ci comprehensively considers the substrate and cover conditions)) , these three are the most representative variables of the physical habitat of the river, and the value range of the three is 0 to 1; for the variable backwater area of the reservoir that has been clearly used as a fish spawning ground, the river channel suitability index in the calculation SI _ci are all 1;

(4) Calculate the fish effective habitat area WUA in the changing backwater area; WUA refers to the effective habitat area that fish can survive in the river, which is defined as the product of the habitat suitability index of the calculation unit and the unit area, The calculation formula is:

Among them, n is the number of calculation units in the variable backwater area of the reservoir; A _i is the area of the calculation unit; thus, the effective habitat area WUA of fish in the variable backwater area is calculated under each working condition;

(5) Determine the flow-WUA curve according to the flow rate corresponding to different percentages of the annual average flow rate and the corresponding fish effective habitat area WUA, and obtain the maximum WUA value according to the curve, and set 60% of the maximum WUA value as the target WUA value.

The bottom-dwelling cold-water fishes targeted by the present invention refer to schizothorax, which are special products in plateau areas and often live in torrents, such as schizothorax full-mouth, schizothorax heavy-mouth and the like.

In the third step above, according to the collected hydrological data, the inflow flow and the water level of the reservoir during the spawning period of benthic cold-water fishes are counted, including the flow threshold range and the water level threshold range. For flow, start from the lowest flow, set a flow condition at intervals of 20-100m ³ /s until the highest flow; for water level, start from the lowest water level, set a water level condition at intervals of 2-5 meters, Up to the highest water level; use the flow and water level conditions to construct several flow and water level combinations.

In the above step 4, use the two-dimensional hydrodynamic model to calculate the hydrodynamic conditions in the variable backwater area in step 3 under different inflow flows and reservoir water level conditions, and determine the effective habitat area WUA value for fish in the variable backwater area of the reservoir , see (2)-(4) in Step 2 for specific steps.

The above step five, combined with the working conditions above the target WUA value, screen out the combination of flow and water levels that meet the target WUA and above; determine the water level range of the reservoir according to the inflow of fish during the spawning period (that is, the inflow flow of the reservoir), and then adjust the water level of the reservoir In order to make the WUA of the variable backwater area above the target value.

Compared with the prior art, the ecological scheduling method for fish spawning ground remodeling in the changing backwater area provided by the present invention has the following beneficial effects:

The present invention integrates the two-dimensional hydrodynamic model and the fish habitat model, establishes the relationship between reservoir flow-water level-fish effective habitat area, and clarifies the ecological regulation measures of the reservoir; the ecological regulation method provided by the present invention can effectively Improve river ecology and provide effective reference for maintaining and rebuilding reservoirs in spawning grounds in changing backwater areas.

Description of drawings

Figure 1 is a schematic flow chart of the ecological scheduling method for habitat remodeling of fish spawning grounds in changing backwater areas.

Fig. 2 is the suitability curve of flow velocity and water depth of the Minjiang schizothorax selected in the embodiment of the present invention during the spawning period.

Fig. 3 is the WUA diagram of the variable backwater area under different working conditions in the embodiment of the present invention; wherein, (a) is the WUA variation diagram under different flow and water level situations; (b) is the flow-water level relationship diagram satisfying the target WUA or above.

In the present invention, the water level refers to the elevation of the water surface higher than the characteristic sea level (commonly used as the base of the Yellow Sea); the water depth refers to the distance from the water surface to the bottom of the river.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

Example 1

The Minjiang River is a secondary tributary of the middle and upper reaches of the Yangtze River. It has the same characteristics as many rivers in the mountainous areas of Southwest China, such as turbulent water flow and steep slope. The main stream of the Minjiang River has also undergone cascade hydropower development. Spawning grounds are flooded. Zipingpu Reservoir is the largest water conservancy project in the main stream of Minjiang River. The normal storage level of the reservoir is 877m, the stagnant water level is 817m, and the water level varies by 60m. The backwater area of the Zipingpu Reservoir is 12km long. According to the survey, there was a spawning ground for Schizothorax (belonging to bottom-dwelling cold-water fish) near Guxigou Village in the reservoir area before the reservoir was impounded. The submersion of the backwater and the impact of water level fluctuation caused the rapids habitat to disappear, which greatly reduced the survival opportunities and living space of the original Schizothorax and other rapids fish. Schizothorax is a typical dominant fish in the mountainous rivers of Southwest China, and it is also a provincial-level protected animal in Sichuan Province. The above-mentioned habits are not in line with the environment of the reservoir area, so people pay little attention to their living dynamics. In May 2022, during the field observation of Zipingpu Reservoir, it was found that there were signs of fish spawning and reproduction in the original spawning ground, which indicated that there were still suitable habitats for fish spawning in the changed backwater area. Example Taking the Zipingpu Reservoir as an example, the ecological regulation method provided by the present invention remodels the spawning habitat of Schizothorax in the variable backwater area of the reservoir.

The ecological scheduling method for fish spawning ground habitat remodeling in the changing backwater area provided by this embodiment, as shown in Figure 1, includes the following steps:

Step 1: Establish a two-dimensional planar numerical model of the reservoir depth including the variable backwater area of the reservoir, which is denoted as a two-dimensional hydrodynamic model.

In this step, the reservoir topographic data, hydrological data and fish flow velocity water depth suitability curve are collected. The hydrological data include inflow flow, outflow flow, water level in front of the dam, and the suitability curve of flow velocity and water depth is obtained from the literature.

The collected topographic data is used to establish a two-dimensional plane numerical model of the reservoir depth; the collected hydrological data is used to calibrate the parameters of the established numerical model to ensure that the hydrodynamic conditions simulated by the model are reliable. The specific operation is:

(1) Use notepad to convert terrain data and boundary data into XYZ format files, import the XYZ format files into the Mesh Generator module in MIKE Zero to generate calculation grids and terrain interpolation, generate mesh files and import them; select Flow Mode in MIKE21 module, import the mesh file, set the simulation time, simulation step size, dry-wet boundary, density, eddy viscosity coefficient, bed roughness, wind field, rainfall, evaporation, flow and water level data, run to generate the m21fm format file, Complete the hydrodynamic model construction;

(2) The hydrodynamic model is calibrated according to the collected hydrological data, and the error between the simulated value and the measured value is controlled within 10%.

In this example, the Zipingpu Reservoir is a typical river-type reservoir in the southwest mountainous area, and the slope of the variable backwater area is large. According to the specific implementation method step 1, the terrain data, hydrological data and flow velocity in 2016 were collected from the management office of the Zipingpu Reservoir Water depth suitability curve and other basic data, hydrological data include the 50-year (1971-2020) period-by-day flow at the reservoir dam site and the 10-year (2011-2020) Zipingpu Reservoir Schizothorax spawning period ( March to May) measured daily flow and water level. The water depth suitability curve for the spawning period of the Minjiang Schizothorax adopts the results obtained by Chen Mingqian in the Minjiang River. The optimum range of the spawning flow velocity of the Schizothorax in the Minjiang River is 0.5-2.5m/s, of which 1.4-1.6m/s s is the optimum suitable interval, and the suitability is 1; for the water depth, the suitable interval is 0.5-1.5m, and the detailed flow velocity and water depth suitability are shown in Figure 2.

According to step 1, the hydrodynamic MIKE21 numerical model (ie two-dimensional hydrodynamic model) of Zipingpu Reservoir was constructed and calibrated. Firstly, the topographic data of Zipingpu Reservoir collected in 2016 were converted into plane coordinates and elevations, and imported into MIKE21 to generate 23,452 unstructured grids, among which 22,391 dense grids with an area of no more than ^700m2 were constructed in the variable backwater area (In the generated two-dimensional hydrodynamic model, the number of grids in the variable backwater area accounts for about 95% of the total number of grids in the reservoir), and the established Zipingpu reservoir depth-average two-dimensional MIKE21 numerical model ) is used to calculate and evaluate the hydrodynamic conditions. Using the inflow flow of the main reservoir Minjiang River, the inflow flow of the branch reservoir Shouxi River and the outflow flow of the reservoir to simulate the daily water level in front of the dam in March 2016, compare the simulated value of the water level in front of the dam calculated by the model with the measured value of the water level in front of the dam, the model The maximum absolute error between the simulated value and the measured value is 0.32m, which meets the error requirement.

The second step is to use the two-dimensional hydrodynamic model to calculate the effective habitat area WUA of benthic cold-water fish in the variable backwater area under different percentages of the annual average flow of the natural river to determine the target WUA value.

This step specifically includes the following sub-steps:

(1) Using a two-dimensional hydrodynamic model to simulate the hydrodynamic conditions of the natural channel of the reservoir including the variable backwater area of the reservoir under different percentages of the annual average flow rate; the hydrodynamic conditions include flow velocity and water depth.

The multi-year average discharge at the dam site of Zipingpu Reservoir is 469m ³ /s. During the process of the percentage gradually increasing from 15% to 100%, 10 working conditions were set up for calculation, namely 15%, 30%, 40%, and 50%. , 55%, 60%, 65%, 70%, 80%, and 100%.

Based on the set 10 different flow conditions, the two-dimensional hydrodynamic model is used for simulation to obtain the hydrodynamic conditions under the corresponding conditions.

(2) Extract the flow velocity and water depth data under different percentages of each calculation unit.

According to the simulation results of step (1), the flow velocity and water depth data under each flow condition are derived.

(3) Find the corresponding suitability of each flow rate and depth data from the suitability curve of flow rate and water depth, and use the geometric mean method to calculate the comprehensive habitat suitability index HSI of each calculation unit; the calculation formula of HSI is:

Among them, HSI _i is the comprehensive habitat suitability index of the calculation unit, which is composed of SI _vi , SI _di and SI _ci (namely, flow velocity, water depth, channel suitability, SI _ci comprehensively considers the status of substrate and cover), These three are the most representative variables of the physical habitat of the river, and the value range of the three is 0 to 1; for the variable backwater area of the reservoir that has been clearly used as a fish spawning ground, the river suitability index SI in the calculation _ci are all 1.

According to Figure 2, the suitability corresponding to the flow velocity and water depth of each calculation unit was found, and then the comprehensive habitat suitability index HSI of each calculation unit was calculated according to the above formula.

(4) Calculate the fish effective habitat area WUA in the changing backwater area; WUA refers to the effective habitat area that fish can survive in the river, which is defined as the product of the habitat suitability index of the calculation unit and the unit area, The calculation formula is:

Among them, n is the number of calculation units in the variable backwater area of the reservoir; A _i is the area of the calculation unit; thus, the effective habitat area WUA for fish in the variable backwater area is calculated under each working condition.

According to the WUA formula, the WUA value of the variable backwater area under each flow condition is calculated, and then the flow-WUA curve is obtained.

(5) Determine the flow-WUA curve according to the flow rate corresponding to different percentages of the annual average flow rate and the corresponding fish effective habitat area WUA, and obtain the maximum WUA value according to the curve, and set 60% of the maximum WUA value as the target WUA value.

According to the flow-WUA curve, when the percentage gradually increases from 15% to 100%, WUA first increases and then decreases. At 65% of the annual average discharge (ie 304.85m ³ /s), the WUA reaches a peak value of 634889m ² , so the target WUA of the variable backwater area of Zipingpu Reservoir is 60% of the WUA peak value, which is 380933m ² .

Step 3, based on historical hydrological data, determine the flow and water level conditions that occurred during the spawning period of benthic cold-water fish, including the flow threshold range and water level threshold range. For flow, start from the lowest flow, set a flow condition at intervals of 20-100m ³ /s until the highest flow; for water level, start from the lowest water level, set a water level condition at intervals of 3 meters until the highest Water level; use flow conditions and water level conditions to construct several flow and water level combinations.

The daily flow and water level of the Zipingpu Reservoir during the spawning period of Schizothorax schizothorax were collected statistically from 10 years from 2011 ^to 2020. When the flow rate is 900m3/s, because the flow velocity is too large, the WUA value in the variable backwater area is low, which is obviously not suitable for creating a spawning ground habitat; the design change range of water level is 817-856m, so 13 kinds of flow gradients and 14 kinds of water level gradients are determined as shown in the table 1. 13 kinds of discharge gradients and 14 kinds of water level gradients were combined into 182 groups of working conditions to simulate and calculate the hydrodynamic conditions in the changing backwater area.

Table 1 Flow and water level conditions

Step 4: Use the two-dimensional hydrodynamic model to calculate the hydrodynamic conditions in the variable backwater area under different flow and water level conditions in step 3, and calculate the WUA value in the variable backwater area according to the suitability curve for fish flow rate and water depth.

This step specifically includes the following sub-steps:

(1) Using a two-dimensional hydrodynamic model to simulate the hydrodynamic conditions of the natural river course of the reservoir including the variable backwater area of the reservoir under different flow and water level conditions in Step 3; the hydrodynamic conditions include flow velocity and water depth.

Based on the set 182 groups of different flow and water level working conditions, the two-dimensional hydrodynamic model is used to simulate and obtain the hydrodynamic conditions under the corresponding working conditions.

(2) Extract the flow velocity and water depth data under different percentages of each calculation unit.

According to the simulation results of step (1), the flow velocity under each flow and water level condition is derived.

(3) Find the corresponding suitability of each flow rate and depth data from the suitability curve of flow rate and water depth, and use the geometric mean method to calculate the comprehensive habitat suitability index HSI of each calculation unit; the calculation formula of HSI is:

Among them, HSI _i is the comprehensive habitat suitability index of the calculation unit, which is composed of SI _vi , SI _di and SI _ci (namely, flow velocity, water depth, channel suitability (SI _ci comprehensively considers the substrate and cover conditions)) , these three are the most representative variables of the physical habitat of the river, and the value range of the three is 0 to 1; for the variable backwater area of the reservoir that has been clearly used as a fish spawning ground, the river channel suitability index in the calculation SI _ci are all 1.

According to Figure 2, the suitability corresponding to the flow velocity and water depth of each calculation unit was found, and then the comprehensive habitat suitability index HSI of each calculation unit was calculated according to the above formula.

(4) Calculate the fish effective habitat area WUA in the changing backwater area according to the following formula:

Among them, n is the number of calculation units in the variable backwater area of the reservoir; A _i is the area of the calculation unit; thus, the effective habitat area WUA for fish in the variable backwater area is calculated under each working condition.

Taking the inflow flow of Zipingpu Reservoir as 300m ³ /s and the water level in front of the dam as 841m as an example, the corresponding adaptability of the calculation unit flow rate and water depth in the model part is shown in Table 2.

Table 2 The corresponding adaptability of calculation unit velocity and water depth

For the fluctuating backwater areas of reservoirs that have been clearly used as fish spawning grounds, the river channel suitability indexes in the calculation are all 1. Calculate the HSI _i of each calculation unit when the inflow flow is 300m ³ /s and the water level in front of the dam is 841m according to the HSI formula. The results are shown in Table 3. Then according to the WUA formula the effective habitat area of the reservoir (that is, the WUA value).

Table 3 Calculation unit HSI

The final calculation shows that the WUA of the variable backwater area is 414667.5185m ² when the inflow flow of Zipingpu Reservoir is 300m ³ /s and the water level in front of the dam is 841m.

Other working conditions are calculated according to the above working conditions, and the WUA results of Zipingpu variable backwater area under different working conditions are finally obtained, as shown in Figure 3.

Step 5: Determine the reservoir water level regulation scheme according to the flow and water level conditions that meet the target WUA value or more.

The specific implementation process of this step is as follows:

(1) Sorting out the WUA changes in the variable backwater area of the reservoir under different flow and water level combinations, and screening out the flow and water level combinations that meet the target WUA or higher;

(2) Determine the water level range of the reservoir according to the inflow flow of the reservoir, and adjust the water level of the reservoir so that the WUA of the variable backwater area of the reservoir meets the target WUA.

In this example, it can be seen from Figure 3(a) that when the water level of the reservoir is fixed, as the inflow flow increases from 50m ³ /s to 900m ³ /s, the WUA of the variable backwater area of the reservoir first increases to the peak value gradually decrease thereafter. Under different water level conditions, it is shown that the WUA in the fluctuating backwater area of the reservoir reaches the peak at the flow rate of 300m ³ /s, and then declines steadily after 300m ³ /s, which has a very high consistency. When the flow rate is fixed, as the water level rises from 817m to 856m, the WUA in the backwater area of the reservoir changes shows a significant monotonicity, and the higher the water level, the smaller the WUA. The white plane in the figure is the target WUA value of 380933m ² , above the white plane, the target WUA is met. When the water level of the reservoir is above 844m, the WUA values are all below the white plane, and the target WUA cannot be reached. Therefore, for the Zipingpu Reservoir, when the water level is higher than 844m, regardless of the inflow conditions, it is impossible to create a WUA above the target value. Therefore, during the spawning period of Schizothorax, the reservoir water level should be kept below 844m as much as possible. , but it should not be lower than the designed dead water level of Zipingpu Reservoir of 817m.

Extract the flow and water level conditions that meet the target WUA value (Fig. 3(b)). The darker the color in the figure, the higher the WUA in the variable backwater area of the reservoir. On the contrary, the lighter the color, the lower the WUA in the variable backwater area of the reservoir. The hatched area is above the target WUA value. It can be seen that the high value of WUA in the fluctuating backwater area of the reservoir is concentrated around the flow rate of 300m ³ /s, and the lower the water level, the greater the WUA. When the inflow flow is lower than 114.72m ³ /s or higher than 652.64m ³ /s, the target WUA value cannot be met by regulating the reservoir water level. When the inflow flow is between [260m ³ /s, 370m ³ /s], the reservoir water level below 844m can meet the target WUA, but it should not be lower than the designed dead water level of the reservoir 817m.

Zipingpu Reservoir can adjust the water level according to the inflow flow during the spawning period of Schizothorax so that the WUA value falls in the hatched area in Figure 3, so as to achieve the purpose of creating enough fish WUA in the variable backwater area.

Those skilled in the art will appreciate that the embodiments described here are to help readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical revelations disclosed in the present invention without departing from the essence of the present invention, and these modifications and combinations are still within the protection scope of the present invention.

Claims (5)

1. An ecological scheduling method for remodeling spawning ground habitat of fishes in a variable water return area is characterized by comprising the following steps of:

step one, establishing a reservoir depth two-dimensional plane numerical model comprising a reservoir fluctuation water return area, and recording the model as a two-dimensional hydrodynamic model;

calculating effective habitat area WUA of benthonic cold water fishes in a variable water return area under different percentages of the annual average flow of a natural river by utilizing a two-dimensional hydrodynamic model so as to determine a target WUA value;

step three, determining the flow and water level working conditions which occur during the spawning period of benthonic cold water fishes according to the historical hydrological data;

calculating hydrodynamic conditions of the fluctuation water return area under different flow and water level working conditions in the third step by using a two-dimensional hydrodynamic model, and calculating WUA values of the fluctuation water return area according to a fish flow velocity water depth suitability curve;

and fifthly, determining a reservoir water level scheduling scheme according to the flow and water level working conditions which meet the target WUA value.

2. The ecological scheduling method for remodeling spawning ground habitats of fish in a variable water return area according to claim 1, wherein the number of meshes in the variable water return area in the generated two-dimensional hydrodynamic model accounts for 70-98% of the number of meshes in the whole reservoir.

3. The ecological scheduling method for the remodeling of fish spawning ground habitat of a variable water return area according to claim 1 or 2, wherein in the second step, the WUA value of the variable water return area is simulated under the condition of a natural river channel of the variable water return area of a reservoir for a plurality of years at different percentages of average flow, a flow-WUA curve is obtained, a maximum WUA value is determined according to the curve, and 60% of the maximum WUA value is used as a target WUA value, and the specific steps are as follows:

(1) Simulating hydrodynamic conditions under different percentages of average annual flow under the condition of a natural river channel of a reservoir containing a reservoir fluctuation water return area by using a two-dimensional hydrodynamic model; the hydrodynamic conditions include flow rate and water depth;

(2) Extracting flow velocity and water depth data of each calculation unit under different percentage conditions;

(3) Searching the suitability degree corresponding to the water depth data of each flow rate from the water depth suitability curve of the flow rate, and calculating the comprehensive habitat suitability index HIS of each calculation unit by using a geometric average method; the HSI calculation formula is:

wherein HSI _i To calculate the comprehensive habitat suitability index, SI of the unit _vi ，SI _di And SI (information and information) _ci Respectively representing the flow rate, the water depth and the suitability of the river channel;

(4) Calculating the effective habitat area WUA of the fish in the changed water return area; WUA refers to the effective habitat area for fish to survive in a river, defined as the product of the habitat suitability index of a unit and the unit area, calculated as:

wherein n is the number of calculation units in the reservoir fluctuation water return area; a is that _i Is the area of the calculation unit; calculating the effective habitat area WUA of the fish in the variable water return area under each working condition;

(5) And determining a flow-WUA curve according to the corresponding flow of different percentages of the average flow for many years and the corresponding effective habitat area WUA of the fish, obtaining a maximum WUA value according to the curve, and taking 60% of the maximum WUA value as a target WUA value.

4. The ecological scheduling method for remodeling spawning ground and habitat of fish in variable water return area as recited in claim 3, wherein in step three, for the flow rate, starting from the lowest flow rate, each interval is 20-100m ³ Setting a flow condition until the flow is highest; for the water level, starting from the lowest water level, setting a water level working condition at intervals of 2-5 meters until the water level reaches the highest water level; and constructing a plurality of flow water level combinations by utilizing the flow working conditions and the water level working conditions.

5. The ecological scheduling method for remodeling spawning ground habitat of fishes in a variable water return area according to claim 3, wherein in the fifth step, the flow water level combination condition meeting the condition above a target WUA is screened out by combining the condition above the target WUA value; and determining a reservoir water level range according to the inflow condition of the spawning period of the fish, and further scheduling the reservoir water level so that the changed water return area WUA is above a target value.