Event scale watershed hydroenergy sand and total phosphorus load simulation method based on daily resolution

Abstract

The invention discloses a daily resolution-based event scale watershed water power sediment and total phosphorus load simulation method. The method specifically comprises the following steps of collecting related hydrological sediment total phosphorus data and watershed area of a research watershed control hydrological station in a research period; day-by-day base flow process data are calculated, water and sediment events are identified, and water and sediment and total phosphorus load statistical indexes and runoff erosion power corresponding to the water and sediment events are calculated; constructing a watershed water power sand model, dividing a calibration period and a verification period of the model, and performing parameter calibration and verification; simulating the sediment volume of the event scale drainage basin, and performing precision evaluation; and constructing a drainage basin total phosphorus load model, dividing a calibration period and a verification period of the model, performing parameter calibration and verification, simulating an event scale drainage basin total phosphorus load, and performing precision evaluation. According to the method, the water and sediment events can be accurately and efficiently identified based on the daily resolution data, and simulation of two important environmental elements including the sediment transport capacity and the total phosphorus load capacity is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of watershed water, sediment and pollutant simulation, and relates to a method for simulating water, energy, sediment and total phosphorus load in a watershed at an event scale based on daily resolution. Background Art

[0002] Water resource management and environmental protection are major issues of global concern. In particular, accurate simulation of hydrological processes and pollutant loads at the watershed scale is of great significance for protecting the health of the ecosystem and achieving sustainable development. Basin sediment and total phosphorus load are key factors affecting the ecological environment and water quality. A large amount of basin sediment reflects the serious soil erosion and ecological conditions in the basin. As a common nutrient, excessive phosphorus load will lead to water quality deterioration and affect the living environment of aquatic organisms. At the same time, there is a close connection between the two, and most phosphorus elements migrate by attaching to the movement of sediment. Therefore, achieving high-precision simulation of basin sediment is the key to accurate simulation of total phosphorus load.

[0003] Traditional simulation methods for sediment and total phosphorus loads mostly rely on empirical soil erosion models for sediment simulation, and then establish empirical formulas between the two to calculate total phosphorus loads, and the time resolution is mostly annual or multi-year scales. However, the accuracy of sediment simulation by traditional soil erosion models is poor, resulting in poor accuracy in total phosphorus load simulation. At the same time, in watershed management and pollutant control, changes at the event scale are often more important. For example, extreme weather events such as heavy rains and snowmelt can cause drastic changes in sediment and total phosphorus loads in a short period of time. This change cannot be accurately captured by traditional methods and is difficult to meet actual needs. Since the essential process of soil erosion is driven by runoff erosion energy, its size directly affects the sediment yield and soil and water loss conditions in the basin. Therefore, the proposed method for simulating water-energy sediment and total phosphorus loads at the event scale based on daily resolution has important practical significance and value. Summary of the invention

[0004] The purpose of the present invention is to provide a method for simulating watershed water, energy, sediment and total phosphorus loads at an event scale based on daily resolution, which can efficiently and accurately identify and simulate the sediment and total phosphorus loads at a short-term event scale in a watershed.

[0005] The technical solution adopted by the present invention is a method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale with daily resolution, which specifically includes the following processes: collecting relevant hydrological, sediment, total phosphorus data and watershed area of ​​the watershed control hydrological station during the study period; calculating daily base flow process data, identifying water and sediment events, and calculating statistical indicators of water, sediment and total phosphorus loads and runoff erosion power of corresponding water and sediment events; constructing a watershed water, energy and sediment model, dividing the model into a rate period and a verification period, and performing parameter calibration and verification; simulating event-scale watershed sediment volume, and performing accuracy evaluation; constructing a watershed total phosphorus load model, dividing the model into a rate period and a verification period, and performing parameter calibration and verification, simulating event-scale watershed total phosphorus load, and performing accuracy evaluation.

[0006] The present invention is also characterized in that:

[0007] The specific steps include:

[0008] Step 1: determine the study period and watershed, collect daily flow, sediment content, total phosphorus content data and watershed area of ​​the watershed control hydrological station during the study period;

[0009] Step 2, using the daily flow data of the control hydrological station in the study basin collected in step 1 during the study period, calculate the daily base flow process data;

[0010] Step 3, using the daily base flow process data calculated in step 2 and the daily flow, sediment content, total phosphorus content data and basin area of ​​the basin control hydrological station collected in step 1 during the study period, identify water-sediment events, and calculate the statistical indicators of water-sediment and total phosphorus loads and runoff erosion power corresponding to the water-sediment events;

[0011] Step 4: construct a watershed water-energy-sediment model based on the runoff erosion power of the corresponding water-sediment event calculated in step 3; and divide the model into a rate period and a verification period according to the research period determined in step 1;

[0012] Step 5: calibrate and verify the parameters of the water-energy-sediment model of the watershed constructed in step 4 according to the water-sediment statistical indicators of the corresponding water-sediment event calculated in step 3, simulate the event-scale watershed sediment volume, and conduct accuracy evaluation;

[0013] Step 6: Based on the event-scale sediment load in the watershed simulated in step 5, a watershed total phosphorus load model is constructed; and based on the research period determined in step 1, the model is divided into a rate period and a verification period;

[0014] Step 7: Based on the total phosphorus load statistical indicators of the corresponding water and sediment events extracted in step 3, the total phosphorus load model of the watershed constructed in step 6 is calibrated and verified, the total phosphorus load of the watershed at the event scale is simulated, and the accuracy is evaluated.

[0015] The present invention is also characterized in that:

[0016] Step 2 is implemented as follows:

[0017] Using the daily flow of the control hydrological station in the study basin collected in step 1 during the study period, the Chapman method is used to segment the runoff flow process and calculate the daily base flow process of the basin. The specific formula is as follows:

[0018]

[0019] In the formula, Q b,t is the base flow on day t, m 3 / s;Q t is the runoff flow on day t, m 3 / s;Q t-1 is the runoff flow on day t-1, m 3 / s; α is the base flow segmentation parameter, which is generally 0.90 to 0.95; Q d,t-1 is the surface flow on day t-1, m 3 / s;

[0020] The specific process of step 3 is:

[0021] Step 3.1, using the daily base flow process data calculated in step 2 and the daily flow and sediment content data of the basin control hydrological station collected in step 1 during the study period, identify water and sediment events. The specific calculation formula is as follows:

[0022] Q d,t =Q t -Q b,t (2);

[0023] SSY t =24·60·60Q t ·SSC t (3);

[0024] In the formula, Q d,t is the surface flow on day t, m 3 / s;SSC t is the daily sediment content on day t, kg / m 3 ;SSY t is the daily sediment discharge on day t, kg;

[0025] After the daily surface flow process is calculated according to formula (3), the event identification is performed one by one from the beginning of the process. The date when the daily surface flow is not 0 is regarded as the start date of an event, and the date when the next daily surface runoff is 0 is regarded as the end date of an event. The daily flow and sediment transport process between two daily surface runoff 0 values ​​is regarded as a water-sediment event.

[0026] Step 3.2, based on the identification of water and sediment events in step 3.1, calculate the statistical indicators of water and sediment and total phosphorus load of the corresponding water and sediment events, including the sediment transport and total phosphorus load of the water and sediment events, respectively. The specific formula is as follows:

[0027]

[0028] In the formula, TSSY i is the sediment transport of the ith water-sediment event, kg; SSY i,j is the sediment transport on the jth day in the ith water-sediment event, kg; TTP i is the total phosphorus load of the ith water and sediment event, kg; TP i,j is the total phosphorus content on the jth day in the ith water and sediment event, kg / m 3 ;M i is the number of days of the ith water-sediment event;

[0029] Step 3.3, based on the identification of water and sediment events in step 3.1, combined with the basin area data collected in step 1, calculate the runoff erosion power of the corresponding water and sediment events and quantify the runoff erosion energy at the event scale. The specific calculation formula is as follows:

[0030] E i =Q' m,i ·H i (6);

[0031]

[0032] In the formula, E i is the runoff erosion power of the ith water and sediment event, m 4 / (s·km 2 );Q' m,i is the peak flow modulus in the ith water-sediment event, m 3 / (s·km 2 );H i is the runoff depth of the ith water and sediment event, m; Q m,i is the maximum daily flow rate in the ith water and sediment event, i.e., the peak flow rate, m 3 / s; A is the basin area controlled by the hydrological station, km 2 ;

[0033] The specific process of step 4 is:

[0034] Step 4.1: Based on the runoff erosion power of the corresponding water-sediment event calculated in step 3, a watershed water-energy-sediment model is constructed. The specific formula is as follows:

[0035] TSSY sim =aE b (9);

[0036] In the formula, TSSY sim is the simulated sediment transport value sequence of water and sediment events, kg; E is the runoff erosion power sequence of water and sediment events, m 4 / (s·km 2 ); a and b are the model parameters;

[0037] Step 4.2, based on the research period determined in step 1, divide the period into two parts, which serve as the rate period and the validation period of the model.

[0038] The specific process of step 5 is:

[0039] Step 5.1, based on the measured sediment transport value of the corresponding water-sediment event calculated in step 3.2 and the watershed water-energy-sediment model constructed in step 4, establish the objective function of minimizing the sum of squares of the difference between the measured value and the simulated value, use the genetic algorithm to calibrate and verify the parameters, and simulate the event-scale watershed sediment transport. The specific formula is as follows:

[0040]

[0041] In the formula, TSSY i is the measured value of sediment transport in the ith water-sediment event, kg; TSSY sim,i is the simulated value of sediment transport of the ith water-sediment event, kg; N is the number of water-sediment events; f TSSY,min The objective function is to minimize the sum of squares of the difference between the measured value and the simulated value. The genetic algorithm is used to find the minimum value of this function to calibrate the parameters a and b of the watershed water-energy-sediment model that meets the requirements.

[0042] Step 5.2: Based on step 5.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results. The specific formula is as follows:

[0043]

[0044] Where NSE TSSY It is the Nash efficiency coefficient between the measured value and the simulated value of the sediment transport of the water-sediment event. If the value is greater than 0.5 in both the rate period and the verification period, it indicates that the watershed water-energy-sediment model meets the accuracy requirements of sediment simulation.

[0045] The specific process of step 6 is:

[0046] Step 6.1: Based on the simulated sediment transport value of the water-sediment event obtained in step 5.2, a total phosphorus load model of the watershed is constructed. The specific formula is as follows:

[0047]

[0048] Where, TTP simis the simulated value sequence of total phosphorus load of water and sediment events, kg; c and d are the model parameters;

[0049] Step 6.2, based on the research period determined in step 1, divide the period into two parts, which serve as the rate period and the validation period of the model.

[0050] The specific process of step 7 is:

[0051] Step 7.1, based on the measured value of the total phosphorus load of the corresponding water and sediment event calculated in step 3.2 and the total phosphorus load model of the watershed constructed in step 6, establish the objective function of minimizing the sum of squares of the difference between the measured value and the simulated value, use the genetic algorithm to calibrate and verify the parameters, and simulate the total phosphorus load of the watershed at the event scale. The specific formula is as follows:

[0052]

[0053] Where, TTP i is the measured value of total phosphorus load of the ith water and sediment event, kg; TTP sim,i is the simulated value of total phosphorus load of the ith water and sediment event, kg; f TTP,min The objective function is to minimize the sum of squares of the difference between the measured value and the simulated value. The genetic algorithm is used to find the minimum value of this function to calibrate the parameters c and d of the total phosphorus load model of the watershed that meets the requirements.

[0054] Step 7.2: Based on step 7.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results. The specific formula is as follows:

[0055]

[0056] Where NSE TTP It is the Nash efficiency coefficient between the measured value and the simulated value of the total phosphorus load of water and sediment events. If the value is greater than 0.5 in both the rate period and the verification period, it indicates that the total phosphorus load model of the basin meets the accuracy requirements of the total phosphorus load simulation.

[0057] The beneficial effect of the present invention is that the method for simulating water-energy, sediment and total phosphorus loads in a watershed at an event scale based on daily resolution provided by the present invention not only has a simple construction process and high calculation accuracy and efficiency, but can also accurately identify water-sediment events based on daily resolution data, and realize the simulation of two important environmental factors, sediment transport and total phosphorus load, which can effectively support scientific decision-making on soil and water conservation and water ecological environment protection planning at the event scale of the watershed. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a flow chart of the method for simulating water-energy-sediment and total phosphorus loads in a watershed at an event scale based on daily resolution of the present invention;

[0059] Figure 2 It is a result schematic diagram of the daily runoff and base flow process of the observation station No. 04073468 in the United States in the embodiment of the method for simulating watershed water, energy, sediment and total phosphorus loads at an event scale based on daily resolution of the present invention;

[0060] Figure 3 It is a result schematic diagram of simulated values ​​and measured values ​​of sediment transport during the regular and verification periods of the event scale rate of the observation station No. 04073468 of the United States in the embodiment of the event scale watershed water energy sediment and total phosphorus load simulation method based on daily resolution of the present invention;

[0061] Figure 4 It is a result schematic diagram of the simulated values ​​and measured values ​​of the total phosphorus load during the event scale period and verification period of the United States 04073468 observation station in the embodiment of the event scale watershed water energy sediment and total phosphorus load simulation method based on daily resolution of the present invention. DETAILED DESCRIPTION

[0062] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0063] Example 1

[0064] The method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale with daily resolution in the present invention specifically comprises the following steps:

[0065] Step 1: determine the study period and watershed, collect daily flow, sediment content, total phosphorus content data and watershed area of ​​the watershed control hydrological station during the study period;

[0066] Step 2, using the daily flow data of the control hydrological station in the study basin collected in step 1 during the study period, calculate the daily base flow process data; specifically, follow the following steps:

[0067] Using the daily flow of the control hydrological station in the study basin collected in step 1 during the study period, the Chapman method is used to segment the runoff flow process and calculate the daily base flow process of the basin. The specific formula is as follows:

[0068]

[0069] In the formula, Q b,t is the base flow on day t, m 3 / s;Q t is the runoff flow on day t, m 3 / s;Q t-1 is the runoff flow on day t-1, m 3 / s; α is the base flow segmentation parameter, which is generally 0.90 to 0.95; Q d,t-1 is the surface flow on day t-1, m 3 / s;

[0070] Step 3: Use the daily base flow process data calculated in step 2 and the daily flow, sediment content, total phosphorus content data and basin area collected in step 1 at the basin control hydrological station during the study period to identify water and sediment events, and calculate the statistical indicators of water and sediment and total phosphorus loads and runoff erosion power corresponding to the water and sediment events. The specific process is as follows:

[0071] Step 3.1, using the daily base flow process data calculated in step 2 and the daily flow and sediment content data of the basin control hydrological station collected in step 1 during the study period, identify water and sediment events. The specific calculation formula is as follows:

[0072] Q d,t =Q t -Q b,t (2);

[0073] SSY t =24·60·60Q t ·SSC t (3);

[0074] In the formula, Q d,t is the surface flow on day t, m 3 / s;SSC t is the daily sediment content on day t, kg / m 3 ;SSY t is the daily sediment discharge on day t, kg;

[0075] After the daily surface flow process is calculated according to formula (3), the event identification is performed one by one from the beginning of the process (i.e. the first day of the study period). The date when the daily surface flow is not zero is taken as the start date of an event, and the date when the next daily surface runoff is zero is taken as the end date of an event. The daily flow and sediment transport process between two daily surface runoff zero values ​​is regarded as a water-sediment event.

[0076] Step 3.2, based on the identification of water and sediment events in step 3.1, calculate the statistical indicators of water and sediment and total phosphorus load of the corresponding water and sediment events, including the sediment transport and total phosphorus load of the water and sediment events, respectively. The specific formula is as follows:

[0077]

[0078]

[0079] In the formula, TSSY i is the sediment transport of the ith water-sediment event, kg; SSY i,j is the sediment transport on the jth day in the ith water-sediment event, kg; TTP i is the total phosphorus load of the ith water and sediment event, kg; TP i,jis the total phosphorus content on the jth day in the ith water and sediment event, kg / m 3 ;M i is the number of days of the ith water-sediment event;

[0080] Step 3.3, based on the identification of water and sediment events in step 3.1, combined with the basin area data collected in step 1, calculate the runoff erosion power of the corresponding water and sediment events and quantify the runoff erosion energy at the event scale. The specific calculation formula is as follows:

[0081] E i =Q' m,i ·H i (6);

[0082]

[0083] In the formula, E i is the runoff erosion power of the ith water and sediment event, m 4 / (s·km 2 );Q' m,i is the peak flow modulus in the ith water-sediment event, m 3 / (s·km 2 );H i is the runoff depth of the ith water and sediment event, m; Q m,i is the maximum daily flow (i.e. peak flow) in the ith water and sediment event, m 3 / s; A is the basin area controlled by the hydrological station, km 2 .

[0084] Step 4: Based on the runoff erosion power of the corresponding water-sediment event calculated in step 3, a watershed water-energy-sediment model is constructed; and based on the research period determined in step 1, the model is divided into a rate period and a verification period. The specific process is as follows:

[0085] Step 4.1: Based on the runoff erosion power of the corresponding water-sediment event calculated in step 3, a watershed water-energy-sediment model is constructed. The specific formula is as follows:

[0086] TSSY sim =aE b (9);

[0087] In the formula, TSSY sim is the simulated sediment transport value sequence of water and sediment events, kg; E is the runoff erosion power sequence of water and sediment events, m 4 / (s·km 2 ); a and b are the model parameters;

[0088] Step 4.2, based on the research period determined in step 1, divide the period into two parts, which serve as the rate period and the validation period of the model.

[0089] Step 5: According to the water-sediment statistical indicators of the corresponding water-sediment event calculated in step 3, the watershed water-energy-sediment model constructed in step 4 is calibrated and verified, the event-scale watershed sediment volume is simulated, and the accuracy is evaluated. The specific process is as follows:

[0090] Step 5.1, based on the measured sediment transport value of the corresponding water-sediment event calculated in step 3.2 and the watershed water-energy-sediment model constructed in step 4, establish the objective function of minimizing the sum of squares of the difference between the measured value and the simulated value, use the genetic algorithm to calibrate and verify the parameters, and simulate the event-scale watershed sediment transport. The specific formula is as follows:

[0091]

[0092] In the formula, TSSY i is the measured value of sediment transport in the ith water-sediment event, kg; TSSY sim,i is the simulated value of sediment transport of the ith water-sediment event, kg; N is the number of water-sediment events; f TSSY,min The objective function is to minimize the sum of squares of the differences between the measured values ​​and the simulated values. The genetic algorithm is used to find the minimum value of this function to calibrate the parameters a and b of the watershed water-energy-sediment model that meets the requirements.

[0093] Step 5.2: Based on step 5.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results. The specific formula is as follows:

[0094]

[0095] Where NSE TSSY It is the Nash efficiency coefficient between the measured value and the simulated value of the sediment transport of water-sediment events. If the value is greater than 0.5 in both the rate period and the verification period, it means that the watershed water-energy-sediment model meets the accuracy requirements of sediment simulation. By substituting the runoff erosion work and the parameters (a and b) that meet the accuracy requirements of the model into the model, the simulated sediment transport value of the water-sediment event can be finally simulated.

[0096] Step 6: Based on the event-scale basin sediment load simulated in step 5, a basin total phosphorus load model is constructed; and then, based on the research period determined in step 1, the model is divided into a rate period and a verification period. The specific process is as follows:

[0097] Step 6.1: Based on the simulated sediment transport value of the water-sediment event obtained in step 5.2, a total phosphorus load model of the watershed is constructed. The specific formula is as follows:

[0098]

[0099] Where, TTP sim is the simulated value sequence of total phosphorus load of water and sediment events, kg; c and d are the model parameters;

[0100] Step 6.2, based on the research period determined in step 1, divide the period into two parts, which serve as the rate period and the validation period of the model.

[0101] Step 7: Based on the total phosphorus load statistical indicators of the corresponding water and sediment events extracted in step 3, the total phosphorus load model of the watershed constructed in step 6 is calibrated and verified, the total phosphorus load of the watershed at the event scale is simulated, and the accuracy is evaluated.

[0102] Example 2

[0103] Based on Example 1, the specific process of step 7 is as follows:

[0104] Step 7.1, based on the measured value of the total phosphorus load of the corresponding water and sediment event calculated in step 3.2 and the total phosphorus load model of the watershed constructed in step 6, establish the objective function of minimizing the sum of squares of the difference between the measured value and the simulated value, use the genetic algorithm to calibrate and verify the parameters, and simulate the total phosphorus load of the watershed at the event scale. The specific formula is as follows:

[0105]

[0106] Where, TTP i is the measured value of total phosphorus load of the ith water and sediment event, kg; TTP sim,i is the simulated value of total phosphorus load of the ith water and sediment event, kg; f TTP,min The objective function is to minimize the sum of squares of the differences between the measured values ​​and the simulated values. The genetic algorithm is used to find the minimum value of this function to calibrate the parameters c and d of the basin total phosphorus load model that meets the requirements.

[0107] Step 7.2: Based on step 7.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results. The specific formula is as follows:

[0108]

[0109] Where NSE TTP is the Nash efficiency coefficient between the measured value and the simulated value of the total phosphorus load of water and sediment events. If the value is greater than 0.5 in both the rate period and the verification period, it means that the total phosphorus load model of the basin meets the accuracy requirements of the total phosphorus load simulation. By substituting the simulated value of the sediment discharge and the parameters (c and d) that meet the accuracy requirements of the model into the model, the simulated value of the total phosphorus load of the water and sediment events can be finally simulated.

[0110] Example 3

[0111] like Figure 1 As shown, taking the control basin of observation station No. 04073468 in the United States as an example, the technical process is as follows Figure 1As shown, the specific implementation steps are as follows:

[0112] Step 1: Collect daily flow, sediment content, and total phosphorus content data from the US 04073468 observation station from February 1, 1987 to September 29, 2015, and the control basin area of ​​the station is 138.45 km 2 ;

[0113] Step 2: Using the daily flow data of the control basin of the US 04073468 observation station from February 1, 1987 to September 29, 2015 collected in step 1, the Chapman method is used to segment the runoff flow process and calculate the daily base flow process of the basin. The above formula (1) is used for calculation. The calculation result is as follows: Figure 2 shown.

[0114] Step 3, using the daily base flow process data calculated in step 2 and the daily flow, sediment content, total phosphorus content data and basin area of ​​the control basin of the United States 04073468 observation station collected in step 1 from February 1, 1987 to September 29, 2015, identify water-sediment events, and calculate the statistical indicators of water-sediment and total phosphorus loads and runoff erosion power corresponding to the water-sediment events;

[0115] Step 3.1, using the daily base flow process data calculated in step 2 and the daily flow, sediment content and total phosphorus content data of the control basin of the US 04073468 observation station collected in step 1 from February 1, 1987 to September 29, 2015, identify water and sediment events, and use the above formula (2) and formula (3) for calculation; after the daily surface flow process is calculated according to formula (3), identify each event from the beginning of the process (i.e., February 1, 1987), and take the date when the daily surface flow is not 0 as the start date of an event, and the date when the next adjacent daily surface runoff is 0 as the end date of an event. The daily flow and sediment transport process between two daily surface runoff 0 values ​​is regarded as a water and sediment event, and a total of 270 water and sediment events are identified;

[0116] Step 3.2, based on the 270 water-sediment events identified in step 3.1, calculate the statistical indicators of water-sediment and total phosphorus load of the corresponding water-sediment events, including the sediment transport and total phosphorus load of the water-sediment events, respectively, using the above formula (4) and formula (5) for calculation;

[0117] Step 3.3: Based on the 270 water and sediment events identified in step 3.1, the runoff erosion power of the corresponding water and sediment events is calculated in combination with the watershed area data collected in step 1. The runoff erosion energy at the event scale is quantified using the above formulas (6) to (8), where A is the watershed area controlled by the hydrological station, i.e., 138.45 km 2 ;

[0118] Step 4: construct a watershed water-energy-sediment model based on the runoff erosion power of the corresponding water-sediment event calculated in step 3; and divide the model into a rate period and a verification period according to the research period determined in step 1;

[0119] Step 4.1: Based on the runoff erosion power of the corresponding water-sediment event calculated in step 3, a watershed water-energy-sediment model, TSSY sim The simulated value sequence of sediment transport for water-sediment events is shown in the above formula (9);

[0120] Step 4.2: Based on the research period determined in step 1, divide February 1, 1987 to September 29, 2015 into two parts, with the first two-thirds serving as the proving period of the model and the last one-third serving as the validation period.

[0121] Step 5: Based on the water-sediment statistical indicators of the corresponding water-sediment event calculated in step 3, the watershed water-energy-sediment model constructed in step 4 is calibrated and verified, the event-scale watershed sediment load is simulated, and the accuracy is evaluated.

[0122] Step 5.1: Based on the measured sediment transport value of the corresponding water-sediment event calculated in step 3.2 and the watershed water-energy-sediment model constructed in step 4, establish the objective function of minimizing the sum of squares of the difference between the measured value and the simulated value, use the genetic algorithm to calibrate and verify the parameters, simulate the event-scale watershed sediment transport, and minimize the objective function f of the sum of squares of the difference between the measured value and the simulated value. TSSY,min As shown in the above formula (10), the parameters a and b of the basin water-energy-sediment model that meet the requirements can be calibrated by using the genetic algorithm to find the minimum value of the function. The results of a and b are 11278750 and 0.58 respectively.

[0123] Step 5.2: Based on step 5.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results. TSSY The Nash efficiency coefficient between the measured value and the simulated value of the sediment transport of the water-sediment event is calculated using the above formula (11); this value is greater than 0.5 during the rate period and the verification period, indicating that the watershed water-energy-sediment model meets the accuracy requirements of sediment simulation. Substituting the runoff erosion work and the parameter rate that meets the model accuracy requirements into the model, the simulated sediment transport value of the water-sediment event can be finally simulated. The evaluation results of the watershed water-energy-sediment model show that during the rate period and the verification period, NSE TSSY They are 0.8 and 0.78 respectively, which meet the model accuracy requirements. The simulation results of event-scale sediment transport are shown in Figure 3 shown.

[0124] Step 6: Based on the event-scale sediment load in the watershed simulated in step 5, a watershed total phosphorus load model is constructed; and based on the research period determined in step 1, the model is divided into a rate period and a verification period;

[0125] Step 6.1: Based on the simulated sediment transport value of the water and sediment event obtained in step 5.2, a total phosphorus load model of the basin is constructed. sim The simulated value sequence of total phosphorus load for water and sediment events is expressed by the above formula (12);

[0126] Step 6.2: Based on the research period determined in step 1, divide February 1, 1987 to September 29, 2015 into two parts, with the first two-thirds serving as the proving period for the model and the last one-third serving as the validation period.

[0127] Step 7: Based on the total phosphorus load statistical indicators of the corresponding water and sediment events extracted in step 3, the total phosphorus load model of the watershed constructed in step 6 is calibrated and verified, the total phosphorus load of the watershed at the event scale is simulated, and the accuracy is evaluated.

[0128] Step 7.1, based on the measured value of the total phosphorus load of the corresponding water and sediment event calculated in step 3.2 and the basin total phosphorus load model constructed in step 6, establish the objective function of minimizing the sum of squares of the difference between the measured value and the simulated value, use genetic algorithm to calibrate and verify the parameters, simulate the total phosphorus load of the basin at the event scale, and minimize the objective function f of minimizing the sum of squares of the difference between the measured value and the simulated value TTP,min By using the above formula (13) to calculate and using the genetic algorithm to find the minimum value of the function, the parameters c and d of the basin total phosphorus load model that meet the requirements can be calibrated. The results of c and d are 0.09 and 0.78 respectively.

[0129] Step 7.2: Based on step 7.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results. TTP It is the Nash efficiency coefficient between the measured value and the simulated value of the total phosphorus load of the water and sediment event. If the value is greater than 0.5 during the rate period and the verification period, it means that the total phosphorus load model of the basin meets the accuracy requirements of the total phosphorus load simulation. Substituting the simulated value of the sediment transport and the parameters that meet the accuracy requirements of the model into the model, the simulated value of the total phosphorus load of the water and sediment event can be finally simulated. The evaluation results of the total phosphorus load model of the basin show that during the rate period and the verification period, NSE TTP are 0.85 and 0.75 respectively, which meet the model accuracy requirements. The simulation results of total phosphorus load at event scale are as follows: Figure 4 shown.

Claims

1. A method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale with daily resolution, characterized by: The specific process includes the following: collecting relevant hydrological sediment total phosphorus data and basin area at the basin control hydrological station during the study period; calculating daily base flow process data, identifying water and sediment events, and calculating statistical indicators of water, sediment and total phosphorus loads and runoff erosion power corresponding to water and sediment events; constructing a basin water-energy-sediment model, dividing the model into a calibration period and a verification period, and performing parameter calibration and verification; Simulate the event-scale basin sediment load and conduct accuracy evaluation; construct a basin total phosphorus load model, divide the model into a calibration period and a verification period, perform parameter calibration and verification, simulate the event-scale basin total phosphorus load, and conduct accuracy evaluation.

2. The method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale based on daily resolution according to claim 1 is characterized in that: The specific steps include: Step 1: determine the study period and watershed, collect daily flow, sediment content, total phosphorus content data and watershed area of ​​the watershed control hydrological station during the study period; Step 2, using the daily flow data of the control hydrological station in the study basin collected in step 1 during the study period, calculate the daily base flow process data; Step 3, using the daily base flow process data calculated in step 2 and the daily flow, sediment content, total phosphorus content data and basin area of ​​the basin control hydrological station collected in step 1 during the study period, identify water-sediment events, and calculate the statistical indicators of water-sediment and total phosphorus loads and runoff erosion power corresponding to the water-sediment events; Step 4: construct a watershed water-energy-sediment model based on the runoff erosion power of the corresponding water-sediment event calculated in step 3; and divide the model into a rate period and a verification period according to the research period determined in step 1; Step 5: calibrate and verify the parameters of the water-energy-sediment model of the watershed constructed in step 4 according to the water-sediment statistical indicators of the corresponding water-sediment event calculated in step 3, simulate the event-scale watershed sediment volume, and conduct accuracy evaluation; Step 6: Based on the event-scale sediment load in the watershed simulated in step 5, a watershed total phosphorus load model is constructed; and based on the research period determined in step 1, the model is divided into a rate period and a verification period; Step 7: Based on the total phosphorus load statistical indicators of the corresponding water and sediment events extracted in step 3, the total phosphorus load model of the watershed constructed in step 6 is calibrated and verified, the total phosphorus load of the watershed at the event scale is simulated, and the accuracy is evaluated.

3. The method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale based on daily resolution according to claim 2 is characterized in that: The specific process of step 2 is as follows: Using the daily flow of the control hydrological station in the study basin collected in step 1 during the study period, the Chapman method is used to segment the runoff flow process and calculate the daily base flow process of the basin. The specific formula is as follows: In the formula, Q b,t is the base flow on day t, m 3 / s;Q t is the runoff flow on day t, m 3 / s;Q t-1 is the runoff flow on day t-1, m 3 / s; α is the base flow segmentation parameter; Q d,t-1 is the surface flow on day t-1, m 3 / s.

4. The method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale based on daily resolution according to claim 3 is characterized in that: The specific process of step 3 is as follows: Step 3.1, using the daily base flow process data calculated in step 2 and the daily flow and sediment content data of the basin control hydrological station collected in step 1 during the study period, identify water and sediment events. The specific calculation formula is as follows: Q d,t =Q t -Q b,t (2); SSY t =24·60·60Q t ·SSC t (3); In the formula, Q d,t is the surface flow on day t, m 3 / s;SSC t is the daily sediment content on day t, kg / m 3 ;SSY t is the daily sediment discharge on day t, kg; After the daily surface flow process is calculated according to formula (3), the event identification is performed one by one from the beginning of the process. The date when the daily surface flow is not 0 is regarded as the start date of an event, and the date when the next daily surface runoff is 0 is regarded as the end date of an event. The daily flow and sediment transport process between two daily surface runoff 0 values ​​is regarded as a water-sediment event. Step 3.2, based on the identification of water and sediment events in step 3.1, calculate the statistical indicators of water and sediment and total phosphorus load of the corresponding water and sediment events, including the sediment transport and total phosphorus load of the water and sediment events, respectively. The specific formula is as follows: In the formula, TSSY i is the sediment transport of the ith water-sediment event, kg; SSY i,j is the sediment transport on the jth day in the ith water-sediment event, kg; TTP i is the total phosphorus load of the ith water and sediment event, kg; TP i,j is the total phosphorus content on the jth day in the ith water and sediment event, kg / m 3 ; M i is the number of days of the ith water-sediment event; Step 3.3, based on the identification of water and sediment events in step 3.1, combined with the basin area data collected in step 1, calculate the runoff erosion power of the corresponding water and sediment events and quantify the runoff erosion energy at the event scale. The specific calculation formula is as follows: E i =Q' m,i ·H i (6); In the formula, E i is the runoff erosion power of the ith water and sediment event, m 4 / (s·km 2 );Q' m,i is the peak flow modulus in the ith water-sediment event, m 3 / (s·km 2 );H i is the runoff depth of the ith water and sediment event, m; Q m,i is the maximum daily flow rate in the ith water and sediment event, i.e., the peak flow rate, m 3 / s; A is the basin area controlled by the hydrological station, km 2 .

5. The method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale based on daily resolution according to claim 4 is characterized in that: The specific process of step 4 is as follows: Step 4.1: Based on the runoff erosion power of the corresponding water-sediment event calculated in step 3, a watershed water-energy-sediment model is constructed. The specific formula is as follows: TSSY sim =aE b (9); In the formula, TSSY sim is the simulated sediment transport value sequence of water-sediment events, kg; E is the runoff erosion power sequence of water and sediment events, m 4 / (s·km 2 ); a and b are the model parameters; Step 4.2, based on the research period determined in step 1, divide the period into two parts, which serve as the rate period and the validation period of the model.

6. The method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale based on daily resolution according to claim 5, characterized in that: The specific process of step 5 is as follows: Step 5.1, based on the measured sediment transport value of the corresponding water-sediment event calculated in step 3.2 and the watershed water-energy-sediment model constructed in step 4, establish the objective function of minimizing the sum of squares of the difference between the measured value and the simulated value, use the genetic algorithm to calibrate and verify the parameters, and simulate the event-scale watershed sediment transport. The specific formula is as follows: In the formula, TSSY i is the measured value of sediment transport in the ith water-sediment event, kg; TSSY sim,i is the simulated value of sediment transport of the ith water-sediment event, kg; N is the number of water-sediment events; f TSSY,min The objective function is to minimize the sum of squares of the difference between the measured value and the simulated value. The genetic algorithm is used to find the minimum value of this function to calibrate the parameters a and b of the watershed water-energy-sediment model that meets the requirements. Step 5.2: Based on step 5.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results. The specific formula is as follows: Where NSE TSSY It is the Nash efficiency coefficient between the measured value and the simulated value of the sediment transport of the water-sediment event. If the value is greater than 0.5 in both the rate period and the verification period, it indicates that the watershed water-energy-sediment model meets the accuracy requirements of sediment simulation.

7. The method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale based on daily resolution according to claim 6, characterized in that: The specific process of step 6 is as follows: Step 6.1: Based on the simulated sediment transport value of the water-sediment event obtained in step 5.2, a total phosphorus load model of the watershed is constructed. The specific formula is as follows: Where, TTP sim is the simulated value sequence of total phosphorus load of water and sediment events, kg; c and d are the model parameters; Step 6.2, based on the research period determined in step 1, divide the period into two parts, which serve as the rate period and the validation period of the model.

8. The method for simulating water, energy, sediment and total phosphorus loads in a watershed at an event scale based on daily resolution according to claim 7, characterized in that: The specific process of step 7 is as follows: Step 7.1, based on the measured value of the total phosphorus load of the corresponding water and sediment event calculated in step 3.2 and the total phosphorus load model of the watershed constructed in step 6, establish the objective function of minimizing the sum of squares of the difference between the measured value and the simulated value, use the genetic algorithm to calibrate and verify the parameters, and simulate the total phosphorus load of the watershed at the event scale. The specific formula is as follows: Where, TTP i is the measured value of total phosphorus load of the ith water and sediment event, kg; TTP sim,i is the simulated value of total phosphorus load of the ith water and sediment event, kg; f TTP,min The objective function is to minimize the sum of squares of the difference between the measured value and the simulated value. The genetic algorithm is used to find the minimum value of this function to calibrate the parameters c and d of the total phosphorus load model of the watershed that meets the requirements. Step 7.2: Based on step 7.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results. The specific formula is as follows: Where NSE TTP It is the Nash efficiency coefficient between the measured value and the simulated value of the total phosphorus load of water and sediment events. If the value is greater than 0.5 in both the rate period and the verification period, it indicates that the total phosphorus load model of the basin meets the accuracy requirements of the total phosphorus load simulation.

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