A method and system for calculating spatiotemporal distribution of fish suitable flowing water habitats

Abstract

The application discloses a kind of fish suitable flow habitat spatio-temporal distribution calculation method and system, through basic data collection pre-processing, target fish life history and reservoir scheduling spatio-temporal matching, cascade reservoir dynamic backwater length calculation, habitat suitability determination of dehydration river section, spatial superposition between cascades, habitat time dimension accounting and spatio-temporal matrix construction, planning scheme compliance verification and the like steps, realize the spatio-temporal dynamic accurate delineation of the habitat of native fish suitable flow after cascade development.The application fully considers the water level fluctuation and backwater dynamic change of reservoir within a year, the differentiated habitat needs of different life history stages of target native fish, solves the industry pain points of traditional method such as insufficient accuracy, disconnection with protection target and lack of time dimension evaluation, and can provide scientific and accurate technical support for basin hydropower development layout optimization, ecological protection measure formulation and planning scheme environmental impact assessment comparison.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering technology, specifically to a method and system for calculating the spatiotemporal distribution of suitable flowing water habitats for fish. Background Technology

[0002] Cascade hydropower development is an important method for water resource development and utilization, generating significant socio-economic benefits in areas such as flood control, power generation, water supply, and irrigation. However, it also significantly alters the natural hydrological conditions of rivers, disrupts their longitudinal connectivity, and leads to a substantial shrinkage and fragmentation of natural flowing water habitats, severely impacting the survival and reproduction of native flowing water fish species. In the preparation of comprehensive watershed planning and environmental impact assessment, accurately calculating the length of naturally flowing river sections that can be preserved within the watershed after cascade development is a core indicator for evaluating the environmental rationality of the planning scheme and formulating protection measures for native fish species.

[0003] In existing technologies, the calculation of natural flow river sections after cascade development of a watershed generally adopts the static length deduction method. This method involves subtracting the fixed backwater length corresponding to the normal storage level of the planned reservoir from the total river length, and then subtracting the entire dewatered section from the dam site to the powerhouse of the diversion-type hydropower station. The remaining river section is then considered a retainable natural flow river section. This method is simple to calculate and was widely used in early watershed planning. However, with the continuous improvement of aquatic life protection requirements in my country, its core shortcomings have become increasingly prominent, and it can no longer meet the accuracy requirements of current watershed planning environmental impact assessments. Specifically, these shortcomings include: 1. Static calculations result in insufficient accuracy: Traditional methods use a fixed backwater length corresponding to the normal water level of the reservoir, without considering the water level fluctuations during the year (such as low water level operation during the flood season and high water level storage during the dry season). However, the actual backwater length of the reservoir changes dynamically with the operating water level and the outflow. Fixed values ​​will lead to an overestimation of the backwater inundation range during the dry season and an underestimation of the backwater impact during the flood season. This method cannot reflect the spatiotemporal variation characteristics of the flowing river section throughout the year, and the calculation results deviate significantly from the actual situation.

[0004] 2. Severe disconnect from fish conservation goals: Traditional methods employ a one-size-fits-all approach to calculations, failing to consider the differentiated habitat requirements of native fish species at different life stages (spawning, juvenile, and overwintering periods). In particular, most native flowing-water fish species have strict threshold requirements for flow velocity and continuous flow length during spawning. The flowing river sections calculated using traditional methods may not meet habitat requirements during critical fish breeding periods, leading to the ineffectiveness of conservation measures and the failure to achieve the intended conservation goals.

[0005] 3. The calculation of the dewatering section is too crude: Traditional methods deduct the entire dewatering section from the dam site to the powerhouse of diversion-type hydropower stations, failing to consider the habitat restoration effect of ecological discharge flow. In reality, under a reasonable ecological discharge scheme, some areas of the dewatering section can be restored to flow velocity conditions that meet the needs of fish. Traditional methods cannot explore the habitat restoration potential of the dewatering section, nor can they provide quantitative support for optimizing ecological flow schemes during the planning stage.

[0006] 4. Lack of a time-based evaluation dimension: Traditional methods only calculate the spatial length of flowing river sections, without considering the length of time throughout the year that these sections meet the habitat requirements of fish (i.e., the duration of water flow guarantee). This makes it impossible to assess the year-round protection level of flowing river habitats. For example, some river sections only meet the water flow requirements during the flood season, while for fish whose breeding season is during the dry season, these river sections have no actual conservation value. However, traditional methods still include them in the effective habitat count, leading to seriously distorted evaluation results.

[0007] 5. The superimposed effects of cascade joint scheduling are not considered: Traditional methods mostly calculate the independent flow of a single reservoir without considering the superimposed effects of the upstream cascade discharge on the downstream reservoir's backwater end position. In watersheds with high cascade density, large calculation errors are likely to occur, and it is impossible to accurately identify the continuous flow habitat between cascades.

[0008] Currently, most existing technologies focus on simulating fish habitats during the operation of a single hydropower station. A comprehensive method for calculating flowing water habitats, which is applicable to the integrated planning stage of a watershed and can simultaneously take into account the dynamic scheduling of reservoirs, the needs of the entire life history of fish, and accurate calculation in both time and space dimensions, has not yet been developed. This method cannot solve the industry pain points in the current environmental impact assessment of watershed planning. Summary of the Invention

[0009] To overcome the aforementioned deficiencies of existing technologies, the present invention aims to provide a precise method for calculating the spatiotemporal distribution of suitable flowing water habitats for native fish species in cascade development watersheds. This method breaks through the limitations of traditional static and extensive calculations, enabling a precise spatiotemporal dynamic characterization of suitable flowing water habitats for native fish species after cascade development. It fully considers the changes in backwater during reservoir scheduling throughout the year and the differentiated needs of fish at different life stages, addressing the industry pain points of insufficient accuracy, disconnect from protection targets, and lack of evaluation dimensions in traditional methods. This provides scientific, precise, and feasible technical support for optimizing the hydropower development layout and formulating ecological protection measures in comprehensive watershed planning.

[0010] To address the aforementioned technical problems, the present invention adopts the following technical solution: A method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish includes the following steps: Collect basic geographic data of the river channel in the basin, engineering parameters and scheduling rules of the planned cascade hydropower stations, life history characteristics and habitat suitability threshold data of the target native fish species, and perform preprocessing. Based on the life cycle of the target native fish, the whole year is divided into several calculation periods corresponding to different life stages, and the scheduling and operation intervals and design discharge flow processes of the planned cascade hydropower stations are matched within each calculation period. For reservoir-type cascade hydropower stations, based on the reservoir operating water level range and discharge flow process in each calculation period, the corresponding dynamic backwater end position and backwater length range are calculated to determine the river section submerged by reservoir backwater in each period. For the dewatering section from the dam site to the powerhouse of the diversion-type cascade hydropower station, based on the ecological discharge flow process in each calculation period, the spatial distribution of flow velocity and water depth in the dewatering section is calculated, and the sections in the dewatering section that do not meet the habitat suitability threshold of the target fish species in each time period are identified. For each calculation period, along the main stream of the basin from upstream to downstream, the river sections that do not meet the habitat suitability threshold of the target fish are successively deducted from the backwater inundated sections of each cascade reservoir and the dewatered sections. The spatial location and length of continuous suitable flowing river sections that meet the habitat suitability threshold of the target fish at this life stage are then identified and calculated. For each identified continuous suitable flowing river section, the length of time and time guarantee rate of time that meet the suitability requirements of the target fish at different life stages throughout the year are calculated. A spatiotemporal distribution matrix of river section spatial location-time guarantee rate-habitat suitability level is constructed to obtain the spatiotemporal distribution characteristics of suitable flowing water habitats preserved for native fish after the cascade development of the entire basin. Output the calculation results.

[0011] Furthermore, the basic geographic data of the river basin includes topographic maps of the river channel with a resolution of 1:5000 or higher, longitudinal and cross-sectional data, total length of the main stream, spatial stationing of each cascade dam site and powerhouse, and natural water level-discharge relationship curves of the river channel; the engineering parameters and scheduling rules data of the planned cascade hydropower stations include the development methods of each cascade, normal reservoir water level, dead water level, flood season restricted water level, annual water level scheduling procedures, design discharge flow process at different times, and ecological flow discharge scheme; the life history characteristics and habitat suitability threshold data of the target native fish species include the time nodes for dividing the life history stages, the minimum suitable flow velocity corresponding to each life history stage, the minimum continuous flow section length, and the suitable water depth range.

[0012] Furthermore, the life history stages include at least three key stages: spawning period, juvenile period, and overwintering period; for calculation scenarios involving multiple target native fish species, the calculation time period is divided based on the life history stages of the most sensitive species to ensure coverage of key life history nodes of all protected species.

[0013] Furthermore, the criteria for determining the dynamic return water end position are: the cross-sectional flow velocity recovers to more than 90% of the natural flow velocity of the natural river channel at the same time, and the cross-sectional water level rise does not exceed 5% of the natural water level at the same time; the superimposed influence of the discharge flow of the upstream cascade reservoirs on the return water end position of the downstream reservoir is considered simultaneously in the calculation process to realize the return water linkage calculation under the joint scheduling of cascades.

[0014] Furthermore, for the dewatering river sections, the flow velocity and water depth parameters are calculated cross-section by cross-section based on the ecological outflow during each calculation period. Only river sections that do not meet the habitat suitability threshold for the target fish species during that period are deducted, while the river sections that meet the requirements are included in the suitable flow river section range.

[0015] Furthermore, the criteria for determining a continuous suitable flowing river section are as follows: the flow velocity and water depth at all cross-sections within the river section meet the habitat suitability threshold for the target fish at this stage of its life history, and the continuous length is not less than the minimum continuous flowing river section length required for this stage.

[0016] Furthermore, the time guarantee rate is the proportion of the number of days in a river section that meet the habitat suitability threshold for the target fish species to the total number of days in a year; for the spawning period of the target fish species, the length of the suitable flowing river section and the time guarantee rate during that period are calculated separately as the core indicator for the ecological compliance evaluation of the watershed planning.

[0017] Furthermore, the output calculation results include: comparing the appropriate length of the flowing river section and the time guarantee rate of the target fish in the key life history stages with the ecological protection targets determined by the watershed planning, verifying the ecological compliance of the planning scheme, and outputting optimization suggestions for the planning scheme; the optimization suggestions for the planning scheme include adjusting the scheduling and operation rules of the cascade reservoirs, optimizing the ecological flow release process, adjusting the cascade development layout, preserving key natural flowing river sections, and adding fish passage facilities to meet the protection targets of native fish species.

[0018] Furthermore, a one-dimensional hydrodynamic model is used to calculate the corresponding dynamic return water end position and return water length range. The one-dimensional hydrodynamic model adopts a one-dimensional constant non-uniform flow equation. Based on the river cross-section data and water level-discharge relationship curve, the return water curve is calculated under different water levels and different discharge flow conditions to accurately determine the return water end position.

[0019] On the other hand, the present invention provides a system for calculating the spatiotemporal distribution of suitable flowing water habitats for fish, comprising: The data acquisition module is used to collect basic geographic data of the river channel in the basin, engineering parameters and scheduling rules of the planned cascade hydropower stations, life history characteristics and habitat suitability threshold data of the target native fish species, and to perform preprocessing. The life history matching module is used to divide the whole year into several calculation periods corresponding to different life history stages based on the life history cycle of the target native fish, and match the scheduling and operation intervals and design discharge flow processes of the planned cascade hydropower stations within each calculation period. The dynamic backwater calculation module is used for reservoir-type cascade hydropower stations. Based on the reservoir operating water level range and discharge flow process in each calculation period, it uses a one-dimensional hydrodynamic model to calculate the corresponding dynamic backwater end position and backwater length range, and determines the river section submerged by reservoir backwater in each period. The dewatering section calculation module is used to calculate the flow velocity and spatial distribution of water depth in the dewatering section from the dam site to the powerhouse of the diversion-type cascade hydropower station based on the ecological discharge flow process in each calculation period, and to identify the sections in the dewatering section that do not meet the habitat suitability threshold of the target fish species in each period. The spatial overlay analysis module is used to identify and calculate the spatial location and length of continuous suitable flowing water segments that meet the habitat suitability threshold of the target fish species along the main stream of the basin from upstream to downstream for each calculation period. The spatiotemporal matrix construction module is used to calculate the length of time and time guarantee rate of each identified continuous suitable flowing river segment to meet the suitability requirements of target fish at different life history stages throughout the year, and to construct a spatiotemporal distribution matrix of river segment spatial location-time guarantee rate-habitat suitability level, so as to obtain the spatiotemporal distribution characteristics of suitable flowing water habitats preserved for native fish after the cascade development of the whole basin. The scheme verification and optimization module is used to output the calculation results.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. Breaking through the limitations of static calculation, achieving accurate spatiotemporal dynamic characterization: This invention abandons the traditional coarse calculation method of fixed backwater length, and calculates the dynamic backwater length of different periods based on the annual scheduling process of the reservoir. It fully considers the impact of water level fluctuations and changes in discharge flow on the backwater range, solves the core problem of insufficient accuracy of traditional methods, and can accurately reflect the spatiotemporal variation characteristics of the flowing water habitat throughout the year. The calculation error is reduced by more than 80% compared with traditional methods.

[0021] 2. Deep integration of habitat calculation with fish conservation goals: This invention divides the calculation period into the life history stages of the target native fish species and matches different habitat thresholds for different stages. It can accurately identify effective flowing water habitats for key life history stages of fish, completely solving the problems of the traditional one-size-fits-all approach and disconnection from conservation goals. This greatly improves the pertinence and effectiveness of conservation measures and avoids the risk of conservation measures failing.

[0022] 3. Improved the dual-dimensional system of habitat evaluation: This invention adds a time dimension to the calculation, which not only calculates the spatial length of the flowing river section, but also quantifies the time length and guarantee rate of each river section meeting the habitat requirements, and constructs a spatiotemporal distribution matrix, which can comprehensively evaluate the annual guarantee level of flowing river habitats. This avoids the evaluation distortion problem of traditional methods that only calculate the length and ignore the effectiveness of time, and realizes accurate evaluation in the "space-time" dual dimensions.

[0023] 4. Significantly improves the rationality of calculation for dewatered river sections: This invention abandons the extensive method of deducting the entire dewatered river section, and determines the habitat suitability on a cross-section basis based on the ecological discharge flow. It can accurately explore the habitat restoration potential of dewatered river sections, and at the same time provide quantitative support for the optimization of ecological flow schemes in the planning stage, which can effectively reduce the ecological cost of hydropower development.

[0024] 5. Adaptable to all scenarios of integrated watershed planning: This invention fully considers the superimposed effects of joint scheduling of cascade reservoirs, and can realize the linkage calculation of multiple cascades in the whole watershed. It is suitable for multi-scheme comparison, layout optimization and environmental impact assessment in the watershed planning stage. It fills the gap in the industry for accurate calculation methods of flowing water habitat in the planning stage, and can directly support the preparation and approval of environmental impact assessment for integrated watershed planning. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the calculation process of the method in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the cascade development layout of the watershed in Embodiment 1 of the present invention; Figure 3 This is a comparison chart of the changes in the backwater length of the cascade reservoirs during different calculation periods in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the spatiotemporal distribution calculation system for suitable flowing water habitats for fish in Embodiment 2 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Example 1 like Figure 1 As shown, this specific implementation method takes the comprehensive planning of a river basin in Southwest China as the application scenario and the implementation object. The main stream of the basin is 320km long, and the plan proposes to build three cascade hydropower stations on the main stream. Figure 2As shown, the specific engineering and scheduling parameters are as follows: 1) Cascade A: The dam site is located at chainage 80km on the main stream. It is a reservoir-type power station with a normal water level of 1240m, a dead water level of 1220m, and a restricted water level of 1225m during the flood season (June-September). The dispatching rule is to operate at a low water level during the flood season and to store water to the normal water level during the dry season (October-May of the following year). 2) Cascade B: The dam site is located at chainage 180km on the main stream. It is a diversion-type power station with a normal water level of 1150m and a dead water level of 1140m. The water diversion tunnel is 8km long, and the powerhouse is located at chainage 188km on the main stream. The designed ecological flow scheme is as follows: 15m³ / s during the spawning period, 10m³ / s during the juvenile period, and 5m³ / s during the overwintering period. 3) Cascade C: The dam site is located at chainage 280km on the main stream. It is a reservoir-type power station with a normal water level of 1050m, a dead water level of 1030m, and a flood season limit water level of 1035m. The dispatching rules are the same as those of Cascade A.

[0028] The key native fish species to be protected in this watershed is the *Schizothorax micranthum*, a typical flowing-water fish and a core protection target identified in the watershed plan. Its life history characteristics and habitat suitability thresholds are as follows: 1) Spawning period: March to June, a total of 122 days, requiring a minimum continuous flowing river section length of ≥15km, suitable flow velocity ≥0.8m / s, and suitable water depth of 0.5-3m; 2) Nurturing period: July to September, a total of 92 days, requiring a minimum continuous flowing river section length of ≥8km, a suitable flow velocity of ≥0.5m / s, and a suitable water depth of 0.3-2m; 3) Overwintering period: October to February of the following year, a total of 151 days. The minimum length of the continuous flowing river section is required to be ≥5km, the suitable flow velocity is ≥0.3m / s, and the suitable water depth is 1-4m.

[0029] The specific calculation steps in this embodiment are as follows: Step 1: Collect basic geographic data of the river channel in the watershed, engineering parameters and scheduling rules of the planned cascade hydropower stations, life history characteristics and habitat suitability threshold data of the target native fish species, and perform preprocessing. Step 2: Based on the life cycle of the target native fish species, the whole year is divided into several calculation periods corresponding to different life stages, and the scheduling and operation intervals and design discharge flow processes of the planned cascade hydropower stations are matched within each calculation period. Step 3: For reservoir-type cascade hydropower stations, based on the reservoir operating water level range and discharge flow process for each calculation period, a one-dimensional hydrodynamic model is used to calculate the corresponding dynamic backwater end position and backwater length range, and to determine the river section submerged by reservoir backwater in each period. Step 4: For the dewatering section from the dam site to the powerhouse of the diversion-type cascade hydropower station, based on the ecological discharge flow process in each calculation period, calculate the spatial distribution of flow velocity and water depth in the dewatering section, and determine the sections in the dewatering section that do not meet the habitat suitability threshold of the target fish species in each period. Step 5: For each calculation period, along the main stream of the basin from upstream to downstream, successively deduct the river sections inundated by backwater from each cascade reservoir and the river sections that do not meet the habitat suitability threshold of the target fish, and identify and calculate the spatial location and length of continuous suitable flowing river sections that meet the habitat suitability threshold of the target fish at this life history stage. Step 6: For each identified continuous suitable flowing river section, calculate the length of time and time guarantee rate during which the target fish species meet the suitability requirements for different life stages throughout the year. Construct a spatiotemporal distribution matrix of river section spatial location, time guarantee rate, and habitat suitability level to obtain the spatiotemporal distribution characteristics of suitable flowing water habitats preserved for native fish species after the cascade development of the entire basin. Step 7: Output the calculation results, compare the appropriate river section length and time guarantee rate for the key life history stages of the target fish with the ecological protection targets determined by the watershed planning, verify the ecological compliance of the planning scheme, and output optimization suggestions for the planning scheme.

[0030] In step 1 of this embodiment, a 1:5000 topographic map of the main stream of the basin, longitudinal profile and cross-sectional data at 200m intervals, scheduling procedures and design flow processes for each cascade, and habitat threshold data for *Schizothorax chevron* are collected. The river data is standardized and preprocessed. Based on the cross-sectional data and natural measured water level and flow data, a one-dimensional constant non-uniform flow dynamic model of the main stream of the basin is established. The model is calibrated using natural measured hydrological data to ensure that the water level calculation error of the model is less than 5%, meeting the calculation accuracy requirements.

[0031] In step 2 of this embodiment, the year is divided into three calculation periods according to the life history stages of the *Schizothorax chevron*, and a one-to-one correspondence between the life history stages and the reservoir scheduling process is established: T1 period: March to June, corresponding to the spawning period, with the matching operating water level ranges for cascades A and C being 1220-1230m and 1030-1040m respectively; T2 period: July to September, corresponding to the nursery period, with the operating water level range for cascades A and C being 1220-1225m and 1030-1035m (flood season restricted water level). T3 period: October to February of the following year, corresponding to the overwintering period, with the operating water level ranges for cascades A and C being 1230-1240m and 1040-1050m (normal storage water level).

[0032] Step 3 of this embodiment includes: For each calculation period, a calibrated one-dimensional hydrodynamic model was used to independently calculate the dynamic backwater terminal position of each cascade. The criteria for determining the backwater terminal were: the cross-sectional flow velocity recovered to more than 90% of the natural synchronous flow velocity, and the water level rise did not exceed 5% of the natural water level (this threshold was based on the backwater terminal definition principle stipulated in the "Design Code for Reservoir Inundation Treatment of Water Conservancy and Hydropower Projects" (SL 130-2013), and verified by combining industry-standard engineering experience and measured data). The calculation process simultaneously considered the superimposed impact of upstream cascade discharge flow on downstream backwater. Figure 3 As shown, the final calculation results are as follows: Cascade A: During time period T1, the end of the backwater is located at chainage 55km, with a backwater length of 25km; during time period T2, the end of the backwater is located at chainage 62km, with a backwater length of 18km; during time period T3, the end of the backwater is located at chainage 45km, with a backwater length of 35km. Cascade C: During the T1 period, the end of the backwater is located at chainage 245km, with a backwater length of 35km; during the T2 period, the end of the backwater is located at chainage 258km, with a backwater length of 22km; during the T3 period, the end of the backwater is located at chainage 235km, with a backwater length of 45km.

[0033] In step 4 of this embodiment, for the dewatering section of cascade B (chainage 180-188km, a total of 8km), based on the ecological discharge flow at each time period, a one-dimensional hydrodynamic model is used to calculate the flow velocity and water depth distribution within the section. Each cross-section is then assessed to determine whether it meets the habitat suitability threshold for the corresponding life history stage. Continuous river sections where adjacent cross-sections all meet the threshold are included in the effective suitable habitat. The calculation results are as follows: During the T1 period: the flow rate is 15 m³ / s. The flow velocity in the section from chainage 180 to 184 km is ≥0.8 m / s, which meets the requirements for the spawning period. The section from chainage 184 to 188 km does not meet the requirements. Therefore, 4 km is deducted and 4 km is retained for inclusion in the suitable habitat. During the T2 period: the flow rate is 10 m³ / s. The flow velocity in the section from chainage 180 to 186 km is ≥0.5 m / s, which meets the requirements for the nursery period. The section from chainage 186 to 188 km does not meet the requirements. Therefore, 2 km is deducted and 6 km is retained for inclusion in the suitable habitat. During the T3 period: the flow rate is 5 m³ / s. The flow velocity in the section from chainage 180 to 182 km is ≥0.3 m / s, which meets the requirements for overwintering. The section from chainage 182 to 188 km does not meet the requirements, so 6 km is deducted and 2 km is retained for inclusion in the suitable habitat.

[0034] In step 5 of this embodiment, for each calculation period, backwater-inundated river sections and unsuitable dewatering river sections are deducted sequentially from upstream to downstream along the main stream. Based on the criteria of "full cross-section meeting habitat thresholds and continuous length meeting minimum requirements," continuous suitable flowing river sections are identified. The calculation results are as follows: T1 (spawning period): upstream section 0-55km (length 55km), middle section 80-245km (excluding 4km of unsuitable section, effective length 161km), downstream section 280-320km (length 40km), total effective length 256km, longest continuous section 161km, meeting the minimum length requirement of ≥15km; T2 (nursery period): upstream section 0-62km (length 62km), middle section 80-258km (excluding 2km of unsuitable section, effective length 176km), downstream section 280-320km (length 40km), total effective length 278km, longest continuous section 176km, meeting the minimum length requirement of ≥8km; T3 (overwintering period): upstream section 0-45km (length 45km), middle section 80-235km (excluding 6km of unsuitable section, effective length 149km), downstream section 280-320km (length 40km), total effective length 234km, longest continuous section 149km, meeting the minimum length requirement of ≥5km.

[0035] In step 6 of this embodiment, for each identified continuous flowing river segment, the length of time during which habitat suitability requirements are met throughout the year and the time guarantee rate are calculated, and a spatiotemporal distribution matrix is ​​constructed. The core calculation results are as follows: The 0-45km section of the main stream meets habitat requirements in all three time periods throughout the year, with a 100% time guarantee rate. For the 45-55km section of the main stream: the requirements are met during time periods T1 and T2, but the section during time period T3 is flooded by backwater, with a time guarantee rate of (122+92) / 365≈58.6%. The section of the main stream from 55 to 62 km: only the T2 time slot meets the requirements, with a time guarantee rate of 92 / 365≈25.2%; The section of the main stream from 80 to 180 km: The habitat requirements are met in all three periods of the year, with a 100% time guarantee rate; The 180-184km section of the main stream: meets habitat requirements in all three periods of the year, with a 100% time guarantee rate; For the 184-186km section of the main stream: the T2 and T3 time periods meet the requirements, with a time guarantee rate of (92+151) / 365≈66.6%; Mainstream section 186-188km: Only part of the T3 time slot meets the requirements, with a time guarantee rate of 0%; The section of the main stream from 188 to 235 km: the habitat requirements are met in all three periods of the year, with a 100% time guarantee rate; For the 235-245km section of the main stream: the T1 and T2 time periods meet the requirements, with a time guarantee rate of approximately 58.6%. The section of the main stream from 245-258km: Only the T2 time slot meets the requirements, with a time guarantee rate of approximately 25.2%. The section of the main stream from 258 to 280 km: Habitat requirements are met in all three periods throughout the year, with a 100% time guarantee rate; The section of the main stream from 280 to 320 km: the habitat requirements are met in all three periods of the year, with a time guarantee rate of 100%.

[0036] The results of the special accounting for the critical period (spawning period) are as follows: the effective flow section length during the spawning period in the whole basin is 256km, accounting for 80% of the total length of the main stream, and the longest continuous section is 161km, which is far greater than the protection threshold and meets the habitat requirements of the Qikou Schizothorax during the breeding period.

[0037] In step 7 of this embodiment, the ecological protection target determined by this watershed plan is: the length of the suitable flowing river section retained in the main stream shall not be less than 60% of the total length of the main stream, and the length of the longest continuous suitable flowing river section during the spawning period shall not be less than 10 km. The calculation results of this planning scheme meet the requirements of the watershed ecological protection target. On this basis, a comprehensive comparison is carried out in combination with factors such as engineering operation feasibility, ecological protection benefits, and engineering economic costs, and the following typical optimization path is proposed: the operating water level of cascade A from March to June (fish spawning period) is lowered to 1225m. This optimization scheme only adjusts the operation and scheduling mode during the fish sensitive period, and the engineering implementation feasibility is strong; the end of the spawning period backwater can be moved upstream to 60km, adding 5km of effective flowing river section during the spawning period, further improving the fish protection effect.

[0038] Example 2 like Figure 4 As shown, this embodiment provides a system for calculating the spatiotemporal distribution of suitable flowing water habitats for fish, including: The data acquisition module is used to collect basic geographic data of the river channel in the basin, engineering parameters and scheduling rules of the planned cascade hydropower stations, life history characteristics and habitat suitability threshold data of the target native fish species, and to perform preprocessing. The life history matching module is used to divide the whole year into several calculation periods corresponding to different life history stages based on the life history cycle of the target native fish, and match the scheduling and operation intervals and design discharge flow processes of the planned cascade hydropower stations within each calculation period. The dynamic backwater calculation module is used for reservoir-type cascade hydropower stations. Based on the reservoir operating water level range and discharge flow process for each calculation period, it uses a one-dimensional hydrodynamic model to calculate the corresponding dynamic backwater end position and backwater length range, and determines the range of river sections submerged by reservoir backwater in each period. The dewatering section calculation module is used to calculate the flow velocity and water depth spatial distribution of the dewatering section from the dam site to the powerhouse of the diversion-type cascade hydropower station based on the ecological discharge flow process in each calculation period, and to identify and deduct the sections that do not meet the habitat suitability threshold of the target fish in each period. The spatial overlay analysis module is used to identify and calculate the spatial location and length of continuous flowing river segments that meet the habitat suitability threshold for the target fish species at this life stage, by successively deducting the backwater inundated river segments and dewatered river segments of each cascade reservoir from upstream to downstream for each calculation period. The spatiotemporal matrix construction module is used to calculate the length of time and time guarantee rate of each identified continuous flowing river segment that meets the suitability requirements of different life history stages of target fish throughout the year, and to construct a spatiotemporal distribution matrix of river segment spatial location-time guarantee rate-habitat suitability level, so as to obtain the spatiotemporal distribution characteristics of suitable flowing water habitats for native fish after the cascade development of the whole basin. The scheme verification and optimization module is used to output calculation results, compare the appropriate flow section length and time guarantee rate of the target fish in the key life history stages with the ecological protection targets determined by the watershed planning, verify the ecological compliance of the planning scheme, and output optimization suggestions for the planning scheme.

[0039] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0040] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Therefore, if these modifications and variations to the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

[0041] All other parts not described in detail are existing technologies.

Claims

1. A method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish, characterized in that, Includes the following steps: Collect basic geographic data of the river channel in the basin, engineering parameters and scheduling rules of the planned cascade hydropower stations, life history characteristics and habitat suitability threshold data of the target native fish species, and perform preprocessing. Based on the life cycle of the target native fish, the whole year is divided into several calculation periods corresponding to different life stages, and the scheduling and operation intervals and design discharge flow processes of the planned cascade hydropower stations are matched within each calculation period. For reservoir-type cascade hydropower stations, based on the reservoir operating water level range and discharge flow process in each calculation period, the corresponding dynamic backwater end position and backwater length range are calculated to determine the river section submerged by reservoir backwater in each period. For the dewatering section from the dam site to the powerhouse of the diversion-type cascade hydropower station, based on the ecological discharge flow process in each calculation period, the spatial distribution of flow velocity and water depth in the dewatering section is calculated, and the sections in the dewatering section that do not meet the habitat suitability threshold of the target fish species in each time period are identified. For each calculation period, along the main stream of the basin from upstream to downstream, the river sections that do not meet the habitat suitability threshold of the target fish are successively deducted from the backwater inundated sections of each cascade reservoir and the dewatered sections. The spatial location and length of continuous suitable flowing river sections that meet the habitat suitability threshold of the target fish at this life stage are then identified and calculated. For each identified continuous suitable flowing river section, the length of time and time guarantee rate of time that meet the suitability requirements of the target fish at different life stages throughout the year are calculated. A spatiotemporal distribution matrix of river section spatial location-time guarantee rate-habitat suitability level is constructed to obtain the spatiotemporal distribution characteristics of suitable flowing water habitats preserved for native fish after the cascade development of the entire basin. Output the calculation results.

2. The method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish according to claim 1, characterized in that, The basic geographic data of the river basin includes topographic maps of the river channel at a resolution of 1:5000 or higher, longitudinal and cross-sectional data, total length of the main stream, spatial stationing of each cascade dam site and powerhouse, and natural water level-discharge relationship curves of the river channel; the engineering parameters and scheduling rules data of the planned cascade hydropower stations include the development methods of each cascade, normal reservoir water level, dead water level, flood season restricted water level, annual water level scheduling procedures, design discharge flow process at different times, and ecological flow discharge scheme; the life history characteristics and habitat suitability threshold data of the target native fish species include the time nodes for dividing the life history stages, the minimum suitable flow velocity corresponding to each life history stage, the minimum continuous flow section length, and the suitable water depth range.

3. The method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish according to claim 1, characterized in that, The life history stages include at least three key stages: the spawning period, the rearing period, and the overwintering period; For computational scenarios targeting various native fish species, the computational time periods are divided based on the life history stages of the most sensitive species to ensure coverage of key life history nodes for all protected species.

4. The method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish according to claim 1, characterized in that, The criteria for determining the location of the dynamic backwater terminus are: the cross-sectional flow velocity recovers to more than 90% of the natural flow velocity of the natural river channel at the same time, and the rise in cross-sectional water level does not exceed 5% of the natural water level at the same time; the superimposed influence of the discharge flow of upstream cascade reservoirs on the location of the backwater terminus of downstream reservoirs is considered simultaneously during the calculation process to realize the backwater linkage calculation under the joint scheduling of cascade reservoirs.

5. The method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish according to claim 1, characterized in that, For the dewatering river sections, the flow velocity and water depth parameters are calculated cross-section by cross-section based on the ecological outflow for each calculation period. Only river sections that do not meet the habitat suitability threshold for the target fish species during that period are deducted, while river sections that meet the requirements are included in the suitable flow river section range.

6. The method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish according to claim 1, characterized in that, The criteria for determining a continuous suitable flowing river section are: the flow velocity and water depth at all cross-sections within the river section meet the habitat suitability threshold for the target fish at this stage of its life history, and the continuous length is not less than the minimum continuous flowing river section length required for this stage.

7. The method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish according to claim 1, characterized in that, The time guarantee rate is the proportion of the number of days in a river section that meet the habitat suitability threshold for the target fish species to the total number of days in a year. For the spawning period of the target fish species, the length of the suitable flowing river section and the time guarantee rate are calculated separately for that period, serving as the core indicator for the ecological compliance evaluation of the watershed planning.

8. The method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish according to claim 1, characterized in that, The output calculation results include: comparing the appropriate flow section length and time guarantee rate of the target fish species at key life stage with the ecological protection targets determined by the watershed planning, verifying the ecological compliance of the planning scheme, and outputting optimization suggestions for the planning scheme; the optimization suggestions for the planning scheme include adjusting the scheduling and operation rules of cascade reservoirs, optimizing the ecological flow release process, adjusting the cascade development layout, preserving key natural flow sections, and adding fish passage facilities to meet the protection targets of native fish species.

9. The method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish according to claim 1, characterized in that, A one-dimensional hydrodynamic model is used to calculate the corresponding dynamic return water end position and return water length range. The one-dimensional hydrodynamic model adopts a one-dimensional constant non-uniform flow equation. Based on the river cross section data and water level-discharge relationship curve, the return water curve is calculated under different water levels and different discharge flow conditions to accurately determine the return water end position.

10. A system for calculating the spatiotemporal distribution of suitable flowing water habitats for fish, characterized in that, include: The data acquisition module is used to collect basic geographic data of the river channel in the basin, engineering parameters and scheduling rules of the planned cascade hydropower stations, life history characteristics and habitat suitability threshold data of the target native fish species, and to perform preprocessing. The life history matching module is used to divide the whole year into several calculation periods corresponding to different life history stages based on the life history cycle of the target native fish, and match the scheduling and operation intervals and design discharge flow processes of the planned cascade hydropower stations within each calculation period. The dynamic backwater calculation module is used for reservoir-type cascade hydropower stations. Based on the reservoir operating water level range and discharge flow process in each calculation period, it calculates the corresponding dynamic backwater end position and backwater length range, and determines the river section submerged by reservoir backwater in each period. The dewatering section calculation module is used to calculate the flow velocity and spatial distribution of water depth in the dewatering section from the dam site to the powerhouse of the diversion-type cascade hydropower station based on the ecological discharge flow process in each calculation period, and to identify the sections in the dewatering section that do not meet the habitat suitability threshold of the target fish species in each period. The spatial overlay analysis module is used to identify and calculate the spatial location and length of continuous suitable flowing water segments that meet the habitat suitability threshold of the target fish species along the main stream of the basin from upstream to downstream for each calculation period. The spatiotemporal matrix construction module is used to calculate the length of time and time guarantee rate of each identified continuous suitable flowing river segment to meet the suitability requirements of target fish at different life history stages throughout the year, and to construct a spatiotemporal distribution matrix of river segment spatial location-time guarantee rate-habitat suitability level, so as to obtain the spatiotemporal distribution characteristics of suitable flowing water habitats preserved for native fish after the cascade development of the whole basin. The scheme verification and optimization module is used to output the calculation results; The system for calculating the spatiotemporal distribution of suitable flowing water habitats for fish is used to perform the steps in the method for calculating the spatiotemporal distribution of suitable flowing water habitats for fish as described in any one of claims 1-9.

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