Method for simulating water-energy-sand and total phosphorus loads at event scale in a basin based on daily resolution

Abstract

This invention discloses a method for simulating watershed hydro-energy-sediment and total phosphorus loads at an event scale based on daily resolution. The method includes the following steps: collecting relevant hydrological, sediment, and total phosphorus data and watershed area from the control hydrological stations of the study watershed during the study period; calculating daily baseflow process data, identifying water-sediment events, and calculating the corresponding statistical indices of water-sediment and total phosphorus loads and runoff erosion power for each event; constructing a watershed watershed hydro-energy-sediment model, dividing the model into calibration and validation periods, and performing parameter calibration and validation; simulating watershed sediment load at an event scale and evaluating its accuracy; and constructing a watershed total phosphorus load model, dividing the model into calibration and validation periods, performing parameter calibration and validation, simulating watershed total phosphorus load at an event scale, and evaluating its accuracy. This method can accurately and efficiently identify water-sediment events based on daily resolution data, achieving the simulation of two important environmental factors: sediment transport and total phosphorus load.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of watershed water and sediment and pollutant simulation, and relates to a daily-resolution event-scale watershed water and sediment and total phosphorus load simulation method. BACKGROUND

[0002] Water resource management and environmental protection are major global concerns, and accurate simulation of hydrological processes and pollutant loads at the watershed scale is of great significance for protecting ecological system health and achieving sustainable development. Watershed sediment and total phosphorus load are key factors affecting the ecological environment and water quality. A large amount of watershed sediment reflects serious soil erosion and ecological conditions in the watershed. Phosphorus, as a common nutrient, can cause water quality deterioration and affect the survival environment of aquatic organisms when the load is excessive. Meanwhile, there is a close relationship between the two, and phosphorus elements are mostly transported by the movement of sediment. Therefore, high-precision simulation of watershed sediment is the key to accurate simulation of total phosphorus load.

[0003] Traditional sediment and total phosphorus load simulation methods mostly rely on empirical soil erosion models for sediment simulation, and then empirical formulas are established between the two to calculate the total phosphorus load, and the time resolution is mostly annual or multi-year. However, the traditional soil erosion model has poor precision in simulating sediment, which leads to poor precision in simulating total phosphorus load. 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 rain and snowmelt can cause rapid changes in sediment and total phosphorus load in a short period of time, which cannot be accurately captured by traditional methods and cannot meet the real needs. Since the essential process of soil erosion is driven by runoff erosion energy, its size directly affects the watershed sediment yield and soil erosion conditions. Therefore, it is of great practical significance and value to propose a daily-resolution event-scale watershed water and sediment and total phosphorus load simulation method. SUMMARY

[0004] The purpose of the present application is to provide a daily-resolution event-scale watershed water and sediment and total phosphorus load simulation method, which can efficiently and accurately identify and simulate the amount of watershed sediment and total phosphorus load within a short-term event scale.

[0005] The technical scheme adopted by the present application is a daily resolution-based event scale watershed water-sediment and total phosphorus load simulation method, specifically comprising the following processes: collecting relevant hydrological sediment total phosphorus data and watershed area of a watershed control hydrological station in a research period; calculating daily base flow process data, identifying water-sediment events, and calculating water-sediment and total phosphorus load statistical indicators and runoff erosion power corresponding to the water-sediment events; constructing a watershed water-sediment model, dividing the calibration period and the verification period of the model, and performing parameter calibration and verification; simulating the event scale watershed sediment amount and performing precision evaluation; constructing a watershed total phosphorus load model, dividing the calibration period and the verification period of the model, performing parameter calibration and verification, simulating the event scale watershed total phosphorus load amount, and performing precision evaluation.

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

[0007] Specifically comprising the following steps:

[0008] Step 1: determining a research period and a watershed, and collecting daily flow, sediment content and total phosphorus content data of a watershed control hydrological station in the research period, and a watershed area;

[0009] Step 2: using the daily flow data of the research watershed control hydrological station in the research period collected in step 1, calculating 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 watershed area of the watershed control hydrological station in the research period collected in step 1, identifying water-sediment events, and calculating water-sediment and total phosphorus load statistical indicators and runoff erosion power corresponding to the water-sediment events;

[0011] Step 4: constructing a watershed water-sediment model according to the runoff erosion power corresponding to the water-sediment events calculated in step 3; and dividing the calibration period and the verification period of the model according to the research period determined in step 1;

[0012] Step 5: performing parameter calibration and verification on the watershed water-sediment model constructed in step 4 according to the water-sediment statistical indicators corresponding to the water-sediment events calculated in step 3, simulating the event scale watershed sediment amount, and performing precision evaluation;

[0013] Step 6: constructing a watershed total phosphorus load model according to the event scale watershed sediment amount simulated in step 5; and dividing the calibration period and the verification period of the model according to the research period determined in step 1;

[0014] Step 7: performing parameter calibration and verification on the watershed total phosphorus load model constructed in step 6 according to the total phosphorus load statistical indicators corresponding to the water-sediment events extracted in step 3, simulating the event scale watershed total phosphorus load amount, and performing precision evaluation.

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

[0016] Step 2 is specifically implemented according to the following steps:

[0017] The daily runoff of the research basin control hydrological station in the research period is collected by step 1, the runoff process is segmented by Chapman method, and the daily base flow process of the basin is calculated, and the specific formula is as follows:

[0018]

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

[0020] The specific process of step 3 is as follows:

[0021] Step 3.1, using the daily base flow process data calculated by step 2 and the daily flow and sediment concentration data of the basin control hydrological station in the research period collected by step 1, the water and sediment event is identified, and 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 of the t day, m 3 / s; SSC t is the daily sediment concentration of the t day, kg / m 3 ; SSY t is the daily sediment discharge of the t day, kg;

[0025] After calculating the daily surface flow process according to formula (3), the event is identified from the beginning of the process, and the date with daily surface runoff not equal to 0 is taken as the starting date of an event, and the date with adjacent next daily surface runoff equal to 0 is taken as the ending date of an event, and the daily flow and sediment discharge process between the two daily surface runoff 0 values is regarded as a water and sediment event.

[0026] Step 3.2, on the basis of identifying the water and sediment events in step 3.1, calculate the water and sediment and total phosphorus load statistical indicators corresponding to the water and sediment events, including the sediment discharge and total phosphorus load of the water and sediment events, and the specific formula is as follows:

[0027]

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

[0029] Step 3.3, on the basis of identifying the water and sediment events in step 3.1, combined with the basin area data collected in step 1, calculate the runoff erosion power corresponding to the water and sediment events, quantify the size of the event scale runoff erosion energy, and 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 i-th water and sediment event, m 4 / (s·km 2 ); Q' m,i is the peak flow modulus of the i-th water and sediment event, m 3 / (s·km 2 ); H i is the runoff depth of the i-th water and sediment event, m; Q m,i is the maximum daily flow, i.e. peak flow, of the i-th water and sediment event, m 3 / s; A is the area of the basin controlled by the hydrological station, km 2 ;

[0033] The specific process of step 4 is as follows:

[0034] Step 4.1, according to the runoff erosion power corresponding to the water and sediment events calculated in step 3, construct a watershed water and sediment model, and the specific formula is as follows:

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

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

[0037] Step 4.2, according to the research period determined in step 1, divide the period into two parts as the calibration period and the verification period of the model.

[0038] The specific process of step 5 is as follows:

[0039] Step 5.1, based on the measured sediment transport value of the corresponding water and sediment event calculated in step 3.2 and the watershed water and sediment model constructed in step 4, establish an objective function of minimizing the square sum of the difference between the measured value and the simulation value, and use genetic algorithm for parameter calibration and verification to simulate the event scale watershed sediment, the specific formula is as follows:

[0040]

[0041] TSSY i is the measured sediment transport value of the i-th water and sediment event, kg; TSSY sim,i is the simulation value of the i-th water and sediment event, kg; N is the number of water and sediment events; f TSSY,min is the objective function of minimizing the square sum of the difference between the measured value and the simulation value, and the minimum value of the function can be obtained by using genetic algorithm to calibrate the parameters a and b of the watershed water and sediment model that meet the requirements;

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

[0043]

[0044] NSE TSSY is the Nash efficiency coefficient between the measured value and the simulation value of the water and sediment event, and the value is greater than 0.5 in the calibration period and the verification period, which indicates that the watershed water and sediment model meets the accuracy requirements of sediment simulation.

[0045] The specific process of step 6 is as follows:

[0046] Step 6.1, based on the simulation value of the water and sediment event obtained in step 5.2, construct a total phosphorus load model of the watershed, the specific formula is as follows:

[0047]

[0048] TTP simTTP is the total phosphorus load measured value of the i th water and sediment event, kg; TTP is the total phosphorus load simulation value of the i th water and sediment event, kg; f is the objective function of minimizing the square sum of the difference between the measured value and the simulation value, and the minimum value of the function can be obtained by using a genetic algorithm to rate the parameters c and d of the total phosphorus load model that meet the requirements;

[0049] Step 6.2, according to the research period determined in step 1, the period is divided into two parts as the calibration period and the verification period of the model.

[0050] The specific process of step 7 is as follows:

[0051] Step 7.1, based on the total phosphorus load measured value corresponding to the water and sediment event calculated in step 3.2 and the total phosphorus load model of the basin constructed in step 6, an objective function of minimizing the square sum of the difference between the measured value and the simulation value is established, and a genetic algorithm is used for parameter calibration and verification to simulate the total phosphorus load of the event scale basin, and the specific formula is as follows:

[0052]

[0053] In the formula, TTP i is the total phosphorus load measured value of the i th water and sediment event, kg; TTP sim,i is the total phosphorus load simulation value of the i th water and sediment event, kg; f TTP,min is the objective function of minimizing the square sum of the difference between the measured value and the simulation value, and the minimum value of the function can be obtained by using a genetic algorithm to rate the parameters c and d of the total phosphorus load model that meet the requirements;

[0054] Step 7.2, on the basis of step 7.1, the accuracy of the simulation results is evaluated by using the Nash efficiency coefficient NSE, and the specific formula is as follows:

[0055]

[0056] In the formula, NSE TTP is the Nash efficiency coefficient between the measured value and the simulation value of the total phosphorus load of the water and sediment event, and the value is greater than 0.5 in the calibration period and the verification period, which indicates that the total phosphorus load model of the basin meets the accuracy requirements of the total phosphorus load simulation.

[0057] The beneficial effects of the present application are that the event scale basin water and sediment and total phosphorus load simulation method based on daily resolution provided by the present application not only has a simple construction process, high calculation accuracy and efficiency, but also can accurately identify water and sediment events based on daily resolution data, realize the simulation of two important environmental factors of sediment discharge and total phosphorus load, and effectively support the scientific decision-making of event scale water and soil conservation and water ecological environment protection planning of the basin. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is the flow chart of the event scale basin water and sediment and total phosphorus load simulation method based on daily resolution of the present application;

[0059] Figure 2 is a schematic diagram of the results of the daily runoff and base flow process of observation station No. 04073468 in the event scale watershed water energy sediment and total phosphorus load simulation method based on daily resolution of the present application;

[0060] Figure 3 is a schematic diagram of the results of the event scale sediment load simulation values and measured values of the calibration period and the verification period of observation station No. 04073468 in the event scale watershed water energy sediment and total phosphorus load simulation method based on daily resolution of the present application;

[0061] Figure 4 is a schematic diagram of the results of the event scale total phosphorus load simulation values and measured values of the calibration period and the verification period of observation station No. 04073468 in the event scale watershed water energy sediment and total phosphorus load simulation method based on daily resolution of the present application. DETAILED DESCRIPTION

[0062] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0063] Embodiment 1

[0064] The event scale watershed water energy sediment and total phosphorus load simulation method based on daily resolution of the present application specifically comprises the following steps:

[0065] Step 1, determining the research period and the watershed, collecting the daily flow, sediment content and total phosphorus content data of the research period of the watershed control hydrological station, and the area of the watershed;

[0066] Step 2, using the daily flow data of the research period of the research watershed control hydrological station collected in step 1, calculating the daily base flow process data; specifically implementing according to the following steps:

[0067] Using the daily flow of the research period of the research watershed control hydrological station collected in step 1, using the Chapman method to divide the runoff flow process, calculating the daily base flow process of the watershed, and the specific formula is as follows:

[0068]

[0069] In the formula, Q b,t is the base flow of the tth day, m 3 / s; Q t is the runoff of the tth day, m 3 / s; Q t-1 is the runoff of the t-1th day, m 3 / s; α is the base flow division parameter, generally taking a value of 0.90-0.95; Q d,t-1 is the surface flow of the t-1th day, m 3 / s; is the base flow of the tth day, m 3 / s; Q t is the runoff of the tth day, m 3 / s; Q t-1 is the runoff of the t-1th day, m 3 / s; α is the base flow division parameter, generally taking a value of 0.90-0.95; Q d,t-1 is the surface flow of the t-1th day, m 3 / s;

[0070] Step 3, using the daily base flow process data calculated in step 2 and the daily flow, sediment concentration, total phosphorus content data and basin area collected by the basin control hydrological station in the study period, identify the water and sediment event, and calculate the water and sediment and total phosphorus load statistical indicators corresponding to the water and sediment event; 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, sediment concentration data collected by the basin control hydrological station in the study period, identify the water and sediment event, and 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 runoff of the t day, m 3 / s; SSC t is the daily sediment concentration of the t day, kg / m 3 ; SSY t is the daily sediment discharge of the t day, kg;

[0075] After calculating the daily surface runoff process according to formula (3), from the beginning of the process (i.e. the first day of the study period), identify each event, take the date with daily surface runoff not equal to 0 as the starting date of an event, and take the date with adjacent next daily surface runoff equal to 0 as the ending date of an event, and the daily runoff and sediment discharge process between the two daily surface runoff 0 values is regarded as a water and sediment event.

[0076] Step 3.2, on the basis of identifying the water and sediment event in step 3.1, calculate the water and sediment and total phosphorus load statistical indicators corresponding to the water and sediment event, including the sediment discharge and total phosphorus load of the water and sediment event, and the specific formula is as follows:

[0077]

[0078]

[0079] In the formula, TSSY i is the sediment discharge of the i water and sediment event, kg; SSY i,j is the sediment discharge of the j day in the i water and sediment event, kg; TTP i is the total phosphorus load of the i water and sediment event, kg; TP i,jTotal phosphorus content of the i-th water and sediment event on the j-th day, kg / m 3 ; M i Number of days of the i-th water and sediment event

[0080] Step 3.3, on the basis of the water and sediment event identified in step 3.1, combined with the watershed area data collected in step 1, calculate the runoff erosion power corresponding to the water and sediment event, quantify the size of the event scale runoff erosion energy, 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 i-th water and sediment event, m 4 / (s·km 2 ); Q' m,i is the peak flow modulus of the i-th water and sediment event, m 3 / (s·km 2 ); H i is the runoff depth of the i-th water and sediment event, m; Q m,i is the maximum daily flow (i.e. peak flow) in the i-th water and sediment event, m 3 / s; A is the watershed area controlled by the hydrological station, km 2 .

[0084] Step 4, according to the runoff erosion power of the corresponding water and sediment event calculated in step 3, construct the watershed water and sediment model; then according to the research period determined in step 1, divide the calibration period and the verification period of the model; the specific process is as follows:

[0085] Step 4.1, according to the runoff erosion power of the corresponding water and sediment event calculated in step 3, construct the watershed water and sediment model, the specific formula is as follows:

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

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

[0088] Step 4.2, according to the research period determined in step 1, divide the period into two parts as the calibration period and the verification period of the model.

[0089] Step 5, according to the water and sediment statistical indicators of the corresponding water and sediment events calculated in step 3, the parameters of the watershed water and sediment model constructed in step 4 are calibrated and verified, the event scale watershed sediment amount is simulated, and the accuracy is evaluated, the specific process is as follows:

[0090] Step 5.1, based on the measured value of sediment discharge corresponding to the water and sediment event calculated in step 3.2 and the watershed water and sediment model constructed in step 4, the objective function of minimizing the square sum of the difference between the measured value and the simulated value is established, and the genetic algorithm is used for parameter calibration and verification to simulate the event scale watershed sediment amount, the specific formula is as follows:

[0091]

[0092] In the formula, TSSY i is the measured value of sediment discharge of the i-th water and sediment event, kg; TSSY sim,i is the simulated value of sediment discharge of the i-th water and sediment event, kg; N is the number of water and sediment events; f TSSY,min is the objective function of minimizing the square sum of the difference between the measured value and the simulated value, and the minimum value of the function can be obtained by using the genetic algorithm to calibrate the parameters a and b of the watershed water and sediment model that meet 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] In the formula, NSE TSSY is the Nash efficiency coefficient between the measured value and the simulated value of the sediment discharge of the water and sediment event, and the value is greater than 0.5 in the calibration period and the verification period, which indicates that the watershed water and sediment model meets the accuracy requirements of sediment simulation. The runoff erosion work and the parameters (a and b) that meet the model accuracy requirements are substituted into the model to simulate the sediment discharge of the water and sediment event.

[0096] Step 6, according to the event scale watershed sediment amount simulated in step 5, a total phosphorus load model of the watershed is constructed; then according to the research period determined in step 1, the calibration period and the verification period of the model are divided; the specific process is as follows:

[0097] Step 6.1, based on the simulated value of sediment discharge of the water and 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] In the formula, TTP sim is the simulated value sequence of total phosphorus load of the water and sediment event, kg; c and d are the parameters of the model;

[0100] Step 6.2, according to the study period determined in step 1, the period is divided into 2 parts as the rate period and the verification period of the model.

[0101] Step 7, according to the total phosphorus load statistical indicators of corresponding water and sediment events extracted in step 3, the total phosphorus load model of the basin constructed in step 6 is parameterized and verified, the event scale total phosphorus load of the basin is simulated, and the precision is evaluated.

[0102] Example 2

[0103] On the basis of example 1, the specific process of step 7 is as follows:

[0104] Step 7.1, based on the total phosphorus load measured value of corresponding water and sediment events calculated in step 3.2 and the total phosphorus load model of the basin constructed in step 6, an objective function of minimizing the square sum of the difference between the measured value and the simulated value is established, and the genetic algorithm is used for parameterization and verification to simulate the event scale total phosphorus load of the basin, and the specific formula is as follows:

[0105]

[0106] In the formula, TTP i is the total phosphorus load measured value of the i th water and sediment event, kg; TTP sim,i is the total phosphorus load simulated value of the i th water and sediment event, kg; f TTP,min is the objective function of minimizing the square sum of the difference between the measured value and the simulated value, and the minimum value of the function can be obtained by using the genetic algorithm to rate the parameters c and d of the total phosphorus load model of the basin that meet the requirements.

[0107] Step 7.2, on the basis of step 7.1, the Nash efficiency coefficient NSE is used to evaluate the precision of the simulation result, and the specific formula is as follows:

[0108]

[0109] In the formula, NSE TTP is the Nash efficiency coefficient between the total phosphorus load measured value and the simulated value of the water and sediment event, and the value is greater than 0.5 in the rate period and the verification period, which indicates that the total phosphorus load model of the basin meets the precision requirements of the total phosphorus load simulation, and the sediment discharge simulated value and the parameters (c and d) that meet the model precision requirements are substituted into the model to finally simulate the total phosphorus load simulated value of the water and sediment event.

[0110] Example 3

[0111] As shown in the following table, the technical process is taken as an example of the control basin of the observation station of the United States 04073468. Figure 1 Figure 1 ​The following steps are shown:

[0112] Step 1, collect the daily flow, sediment concentration and total phosphorus content data of the US 04073468 observation station from February 1, 1987 to September 29, 2015, and its station control watershed area of 138.45km 2 ;

[0113] Step 2, using the daily flow data of the US 04073468 observation station control watershed collected in step 1 from February 1, 1987 to September 29, 2015, the runoff flow process is divided by Chapman method, the daily base flow process of the watershed is calculated, and the above formula (1) is used for calculation, and the calculation result is shown as Figure 2 .

[0114] Step 3, using the daily base flow process data calculated in step 2 and the daily flow, sediment concentration, total phosphorus content data and watershed area of the US 04073468 observation station control watershed collected in step 1 from February 1, 1987 to September 29, 2015, identify the water and sediment event, and calculate the water and sediment and total phosphorus load statistical index corresponding to the water and sediment event, and the runoff erosion power;

[0115] Step 3.1, using the daily base flow process data calculated in step 2 and the daily flow, sediment concentration and total phosphorus content data of the US 04073468 observation station control watershed collected in step 1 from February 1, 1987 to September 29, 2015, identify the water and sediment event, and calculate the water and sediment event using the above formula (2) and formula (3); After calculating the daily surface flow process according to formula (3), identify the event from the beginning of the process (i.e. February 1, 1987), the date of daily surface runoff is 0 is regarded as the starting date of an event, and the date of adjacent next daily surface runoff is 0 is regarded as the ending date of an event, the daily flow and sediment transport between the two daily surface runoff 0 values is regarded as a water and sediment event, a total of 270 water and sediment events are identified;

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

[0117] Step 3.3, based on the 270 water and sediment events identified in step 3.1, combined with the watershed area data collected in step 1, calculate the runoff erosion power corresponding to the water and sediment event, quantify the size of the event scale runoff erosion energy, and calculate using the above formula (6)-(8), wherein A is the area of the hydrological station control watershed, i.e. 138.45km 2 ;

[0118] Step 4, according to the runoff erosion power of the corresponding water and sand event calculated in step 3, the watershed water and sand model is constructed; and according to the research period determined in step 1, the calibration period and the verification period of the model are divided;

[0119] Step 4.1, according to the runoff erosion power of the corresponding water and sand event calculated in step 3, the watershed water and sand model is constructed, TSSY sim The simulation value sequence of the sediment discharge of the water and sand event is shown in the above formula (9);

[0120] Step 4.2, according to the research period determined in step 1, the period from February 1, 1987 to September 29, 2015 is divided into two parts, the first two-thirds as the calibration period of the model, and the last one-third as the verification period.

[0121] Step 5, according to the water and sand statistical index of the corresponding water and sand event calculated in step 3, the parameters of the watershed water and sand model constructed in step 4 are calibrated and verified, the event scale watershed sediment is simulated, and the precision is evaluated.

[0122] Step 5.1, based on the measured value of the sediment discharge of the corresponding water and sand event calculated in step 3.2 and the watershed water and sand model constructed in step 4, the objective function of minimizing the square sum of the difference between the measured value and the simulation value is established, and the genetic algorithm is used for parameter calibration and verification to simulate the event scale watershed sediment. The objective function f of minimizing the square sum of the difference between the measured value and the simulation value is established, and the genetic algorithm is used for parameter calibration and verification to simulate the event scale watershed sediment. TSSY,min As shown in the above formula (10), the minimum value of the function is obtained by using the genetic algorithm, that is, the parameters a and b of the watershed water and sand model meeting the requirements are calibrated, and the results of a and b are 11278750 and 0.58 respectively.

[0123] Step 5.2, on the basis of step 5.1, the accuracy of the simulation results is evaluated by using Nash efficiency coefficient NSE, NSE TSSY The Nash efficiency coefficient between the measured value and the simulation value of the sediment discharge of the water and sand event is calculated by using the above formula (11); the value is greater than 0.5 in the calibration period and the verification period, which indicates that the watershed water and sand model meets the precision requirements of sediment simulation, and the runoff erosion power and the parameters meeting the model precision requirements are substituted into the model to simulate the sediment discharge simulation value of the water and sand event. The evaluation results of the watershed water and sand model show that the NSE TSSY in the calibration period and the verification period are 0.8 and 0.78 respectively, which meet the model precision requirements, and the simulation results of the event scale sediment discharge are shown in Figure 3 .

[0124] Step 6, according to the event scale watershed sediment simulated in step 5, the total phosphorus load model of the watershed is constructed; and according to the research period determined in step 1, the calibration period and the verification period of the model are divided;

[0125] Step 6.1, based on the sediment transport simulation value of the water and sediment event obtained in step 5.2, a total phosphorus load model of the watershed is constructed, TTP sim The total phosphorus load simulation value sequence of the water and sediment event is represented by the above formula (12);

[0126] Step 6.2, according to the research period determined in step 1, February 1, 1987 to September 29, 2015 is divided into two parts, the first two-thirds as the calibration period of the model, and the last one-third as the verification period.

[0127] Step 7, according to the total phosphorus load statistical indicators corresponding to the water and sediment event extracted in step 3, the total phosphorus load model constructed in step 6 is parameterized and verified, the event scale total phosphorus load is simulated, and the accuracy is evaluated.

[0128] Step 7.1, based on the total phosphorus load measured value corresponding to the water and sediment event calculated in step 3.2 and the total phosphorus load model constructed in step 6, an objective function of minimizing the square sum of the difference between the measured value and the simulation value is established, and genetic algorithm is used for parameter calibration and verification, the event scale total phosphorus load is simulated, and the objective function f of minimizing the square sum of the difference between the measured value and the simulation value is established. TTP,min The minimum value of the function is calculated by using the above formula (13), and the parameters c and d of the total phosphorus load model that meet the requirements can be calibrated, and the results of c and d are 0.09 and 0.78 respectively.

[0129] Step 7.2, based on step 7.1, the accuracy of the simulation results is evaluated by using Nash efficiency coefficient NSE, NSE TTP The Nash efficiency coefficient between the measured value and the simulation value of the total phosphorus load of the water and sediment event, the value is greater than 0.5 in the calibration period and the verification period, which indicates that the total phosphorus load model of the watershed meets the accuracy requirements of the total phosphorus load simulation, and the sediment transport simulation value and the parameters that meet the model accuracy requirements are substituted into the model to simulate the total phosphorus load simulation value of the water and sediment event. The evaluation results of the total phosphorus load model of the watershed show that the NSE TTP in the calibration period and the verification period are 0.85 and 0.75 respectively, which meet the model accuracy requirements, and the simulation results of the event scale total phosphorus load are shown in Figure 4 .

Claims

1. A method for simulating the event-scale watershed water-energy-sand and total phosphorus loadings based on daily resolution, characterized in that, Specifically comprising the following processes: collecting the relevant hydrological sediment total phosphorus data of the basin control hydrological station in the research period and the basin area; calculating the daily base flow process data, identifying the water and sediment event, and calculating the water and sediment and total phosphorus load statistical indicators corresponding to the water and sediment event, and the runoff erosion power; constructing the basin water and sediment model, dividing the calibration period and the verification period of the model, and performing parameter calibration and verification; Simulate the event scale basin sediment load, and perform precision evaluation; construct the basin total phosphorus load model, divide the calibration period and the verification period of the model, perform parameter calibration and verification, simulate the event scale basin total phosphorus load, and perform precision evaluation; specifically comprising the following steps: Step 1, determine the research period and the basin, and collect the daily flow, sediment concentration and total phosphorus content data of the basin control hydrological station in the research period, and the basin area; Step 2, using the daily flow data of the research basin control hydrological station in the research period collected in step 1, calculate the daily base flow process data; the specific process of step 2 is as follows: Using the daily flow of the research basin control hydrological station in the research period collected in step 1, using Chapman method to divide the runoff flow process, the daily base flow process of the basin is calculated, the specific formula is as follows: （1） In the formula, For the first t Daily base flow rate, m 3 / s; For the first t Daily runoff, m 3 / s; For the first t -1 day runoff, m 3 / s; These are the base current segmentation parameters; For the first t Surface flow on day -1, m 3 / s; Step 3, using the daily base flow process data calculated in step 2 and the daily flow, sediment concentration, total phosphorus content data and basin area of the basin control hydrological station in the research period collected in step 1, identify the water and sediment event, and calculate the water and sediment and total phosphorus load statistical indicators corresponding to the water and sediment event, and the runoff erosion power; 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 concentration data of the basin control hydrological station in the research period collected in step 1, identify the water and sediment event, the specific calculation formula is as follows: （2） In the formula, For the first t Daily surface flow, m 3 / s; For the first t Daily sediment content, kg / m³ 3 ; For the first t Daily sediment transport volume, kg; After calculating the daily surface flow process according to formula (3), the event is identified from the beginning of the process, the date of daily surface flow not being 0 is taken as the starting date of an event, and the date of adjacent next daily surface runoff being 0 is taken as the ending date of an event, and the daily flow and sediment transport between the two daily surface runoff 0 values are regarded as a water and sediment event; Step 3.2, on the basis of identifying the water and sediment event in step 3.1, calculate the water and sediment and total phosphorus load statistical indicators corresponding to the water and sediment event, including the sediment transport and total phosphorus load of the water and sediment event, the specific formula is as follows: （4） wherein is the sediment load of the nth water-sediment event, kg; i is the sediment load of the nth day within the mth water-sediment event, kg; is the total phosphorus load of the nth water-sediment event, kg; i is the total phosphorus content of the nth day within the mth water-sediment event, kg / m2; j is the total phosphorus content of the nth day within the mth water-sediment event, kg / m2; is the total phosphorus load of the nth water-sediment event, kg; i is the total phosphorus content of the nth day within the mth water-sediment event, kg / m2; is the total phosphorus content of the nth day within the mth water-sediment event, kg / m2; 3 ; i is the total phosphorus content of the nth day within the mth water-sediment event, kg / m2; j is the total phosphorus content of the nth day within the mth water-sediment event, kg / m2; is the total phosphorus content of the nth day within the mth water-sediment event, kg / m2; i ​ Step 3.3, on the basis of identifying the water and sediment event in step 3.1, combined with the basin area data collected in step 1, calculate the runoff erosion power corresponding to the water and sediment event, quantify the size of the event scale runoff erosion energy, the specific calculation formula is as follows: wherein is the runoff erosive power of the i-th water-sediment event, m4 / (s·km2); is the peak flow modulus within the i-th water-sediment event, m3 / (s·km2); is the runoff depth of the i-th water-sediment event, m; is the maximum daily flow, i.e. the peak flow, within the i-th water-sediment event, m3 / s; is the area of the hydrological station control basin, km2; Step 4, according to the runoff erosion power corresponding to the water and sediment event calculated in step 3, construct the basin water and sediment model; then, according to the research period determined in step 1, divide the calibration period and the verification period of the model; Step 5, according to the water and sediment statistical indicators corresponding to the water and sediment event calculated in step 3, perform parameter calibration and verification on the basin water and sediment model constructed in step 4, simulate the event scale basin sediment load, and perform precision evaluation; Step 6, according to the event scale of the simulated sediment amount in step 5, a total phosphorus load model of the basin is constructed; and according to the research period determined in step 1, a calibration period and a verification period of the model are divided; Step 7, according to the total phosphorus load statistical index corresponding to the water and sediment event extracted in step 3, the total phosphorus load model constructed in step 6 is parameterized and verified, the event scale of the total phosphorus load of the basin is simulated, and the accuracy is evaluated.

2. The method according to claim 1, wherein, The specific process of step 4 is: Step 4.1, according to the runoff erosion power corresponding to the water and sediment event calculated in step 3, a water and sediment model of the basin is constructed, and the specific formula is as follows: （9）； wherein is the sediment transport simulation value sequence of the water and sediment event, kg; is the runoff erosion power sequence of the water and sediment event, m 4 / s·km 2 ; and are the model parameters; Step 4.2, according to the research period determined in step 1, the period is divided into two parts as the calibration period and the verification period of the model.

3. The method according to claim 2, wherein, The specific process of step 5 is: Step 5.1, based on the measured sediment discharge corresponding to the water and sediment event calculated in step 3.2 and the water and sediment model of the basin constructed in step 4, an objective function of minimizing the square sum of the difference between the measured value and the simulated value is established, and the genetic algorithm is used for parameterization and verification, the event scale of the sediment amount of the basin is simulated, and the specific formula is as follows: （10）； In the formula, is the measured value of sediment discharge of the nth water-sediment event, kg; i is the simulated value of sediment discharge of the nth water-sediment event, kg; i is the number of water-sediment events; is the objective function of minimizing the square sum of the difference between the measured value and the simulated value, and the minimum value of the function is obtained by using a genetic algorithm to calibrate the parameters of the watershed water-sediment model that meets the requirements and ;​​ Step 5.2, based on step 5.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results, and the specific formula is as follows: （11）； In the formula, Nash efficiency coefficient between the measured value and the simulated value of sediment discharge of water and sediment event, the value is greater than 0.5 in the calibration period and the verification period, which indicates that the watershed water and sediment model meets the accuracy requirements of sediment simulation.

4. The method according to claim 3, wherein, The specific process of step 6 is: Step 6.1, based on the simulated sediment discharge of the water and sediment event obtained in step 5.2, a total phosphorus load model of the basin is constructed, and the specific formula is as follows: （12）； wherein is the total phosphorus load simulation value sequence of the water and sediment event, kg; and is the model parameter; Step 6.2, according to the research period determined in step 1, the period is divided into two parts as the calibration period and the verification period of the model.

5. The method according to claim 4, wherein, The specific process of step 7 is: Step 7.1, based on the measured total phosphorus load corresponding to the water and sediment event calculated in step 3.2 and the total phosphorus load model of the basin constructed in step 6, an objective function of minimizing the square sum of the difference between the measured value and the simulated value is established, and the genetic algorithm is used for parameterization and verification, the event scale of the total phosphorus load of the basin is simulated, and the specific formula is as follows: （13）； In the formula, is the measured value of total phosphorus load of the nth water-sediment event, kg; i is the measured value of total phosphorus load of the nth water-sediment event, kg; is the simulated value of total phosphorus load of the nth water-sediment event, kg; i is the simulated value of total phosphorus load of the nth water-sediment event, kg; is the objective function of minimizing the square sum of the difference between the measured value and the simulated value, and the minimum value of the function is obtained by using a genetic algorithm to calibrate the parameters of the total phosphorus load model of the basin that meets the requirements and ; Step 7.2, based on step 7.1, the Nash efficiency coefficient NSE is used to evaluate the accuracy of the simulation results, and the specific formula is as follows: （14）； In the formula, Nash efficiency coefficient between the measured value and the simulated value of total phosphorus load of water and sediment events, the value is greater than 0.5 in the calibration period and the verification period, which indicates that the total phosphorus load model of the basin meets the accuracy requirements of total phosphorus load simulation.

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