Water balance-based daily average flow calculation method

Abstract

The invention discloses a water balance-based daily average flow calculation method, which comprises the following steps of: obtaining a drainage basin rainfall observation value, a runoff observation value and a reservoir water storage variable quantity, and calculating a drainage basin water content change and an evaporation value in combination with water balance; calculating to obtain the flow of regression and rainfall supplementation based on the flow increment caused by rainfall, and calculating to obtain the reference flow based on the change of the water content of the drainage basin; calculating the daily average flow according to the fading and rainfall supplementing flow and the reference flow; and obtaining a continuous rainfall observation value and a reservoir water storage variable quantity of the drainage basin in a set T day, calculating the evaporation capacity of the T day and the change of the water content of the drainage basin in the Tth day, and calculating the daily average flow of the future T day. The initial water content of the watershed is calculated according to rainfall, evaporation, reservoir water storage variation and other data in combination with water balance, the model applicability and precision are improved, the model uncertainty is reduced, and a solid support is provided for medium and small river hydrological forecasting.

Description

Technical Field

[0001] This invention relates to the field of flow estimation technology, and specifically to a method for estimating daily average flow based on water balance. Background Technology

[0002] Daily average flow estimation, a crucial component of hydrological forecasting, is a key parameter for assessing water flowability and hydrological periodicity, playing a vital role in water resource management, flood control design, and ecological protection. Currently, daily average flow is typically calculated based on statistical analysis of flow data over a period of time, using either average values ​​or complex hydrological models. While average value calculations offer lower accuracy, and models can simulate actual hydrological conditions more effectively, they suffer from drawbacks such as model complexity, computational burden, and significant uncertainties. Summary of the Invention

[0003] To overcome the defects and shortcomings of existing technologies, this invention provides a method for estimating daily average flow based on water balance. This invention uses data such as rainfall, evaporation, and reservoir water storage changes, and combines water balance calculations to determine the initial water content of the watershed, thereby improving the applicability and accuracy of the model, reducing model uncertainty, and providing solid support for hydrological forecasting of small and medium-sized rivers.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention provides a method for estimating daily average flow rate based on water balance, comprising the following steps:

[0006] Obtain watershed rainfall observations, runoff observations, and reservoir water storage changes, and combine these with water balance calculations to determine watershed water content changes and evaporation values.

[0007] The flow rate due to receding and replenishment is calculated based on the flow increment caused by rainfall, and the baseline flow rate is calculated based on the change in watershed water content.

[0008] The daily average flow rate is calculated based on the flow rate of receding water and rainfall replenishment, and the baseline flow rate.

[0009] Obtain continuous rainfall observations and reservoir water storage changes within a set period of T days in the watershed, calculate the evaporation on day T and the watershed water content change on day T, and estimate the average daily flow for the next T days.

[0010] As a preferred technical solution, the formula for calculating the change in watershed water content is expressed as follows:

[0011]

[0012] Among them, W T P represents the water content of the basin on day T. T-1R represents the observed rainfall value of the previous day in the watershed. T W represents the observed runoff value on day T. T-1 This indicates the water content of the basin on the previous day. E represents the change in reservoir water storage. T This indicates the amount of evaporation.

[0013] As a preferred technical solution, the evaporation rate is specifically expressed as follows:

[0014]

[0015] Among them, E T This represents the evaporation rate of the basin on day T. This represents the measured evaporation amount. E′ represents the amount of rainfall that affected the preceding period. T This indicates the assumed evaporation rate.

[0016] As the preferred technical solution, the initial impact on rainfall is specifically represented as follows:

[0017]

[0018] in, This indicates the amount of rainfall that affected the initial rainfall. Let P be the initial rainfall amount at the beginning of day T-1, where a is the recession coefficient. T This represents the rainfall on day T in the basin.

[0019] As a preferred technical solution, let's assume the evaporation rate is specifically expressed as:

[0020]

[0021] Among them, E′ T Assuming evaporation rate, b is W. T-1 / W m The index, W m W is the maximum water storage capacity of the basin. T-1 This indicates the water content of the basin on the previous day.

[0022] As a preferred technical solution, the flow rate due to receding rainfall and replenishment is calculated based on the flow rate increment caused by rainfall, specifically expressed as follows:

[0023]

[0024] in, The flow rate on day T represents the receding water level and the replenishment of rainfall. e is the flow rate for the receding water and replenishment of rainfall on day T-1. T Q is the extinction coefficient. PT This represents the increase in flow on day T due to rainfall on day T-1.

[0025] As a preferred technical solution, the increase in flow on day T due to rainfall on day T-1 is specifically expressed as follows:

[0026]

[0027] Among them, W T W represents the water content of the basin on day T. w W represents the upper limit of water content in the basin. m W represents the maximum upper limit of water storage in the basin. c To estimate the maximum amount that can be exceeded above the maximum upper limit of watershed storage, f is the exponential upper limit, g is the minimum rainfall-runoff coefficient, and h is W. T The change in rainfall-runoff coefficient for each increase of daily water content W1 in the basin, where A is the catchment area of ​​the basin and P represents the rainfall in the basin.

[0028] As a preferred technical solution, the fading coefficient is expressed as:

[0029]

[0030] Among them, e max A threshold is set for the fading coefficient, where i is a constant and W T-1 W represents the watershed water content status of the previous day. ava Let W2 be the average water content of the watershed, and j be the coefficient of the ratio of the watershed's water content on the previous day to the watershed's water content on the second day. The flow rate for the receding water and replenishment of rainfall on day T-1.

[0031] As a preferred technical solution, the baseline flow rate is calculated based on the change in watershed water content, specifically expressed as follows:

[0032]

[0033] in, W represents the baseline flow rate. T-1 The water content of the basin is represented by C, the baseflow coefficient is represented by A, the catchment area of ​​the basin is represented by d, and the minimum baseline flow rate is represented by d.

[0034] As a preferred technical solution, the daily average flow is calculated based on the flow rate of receding water and rainfall replenishment, and the baseline flow rate, specifically expressed as follows:

[0035]

[0036] in, Indicates average daily traffic. Indicates the baseline flow rate. This indicates the flow rate during the receding of water and the replenishment of rainfall.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] (1) This invention improves the applicability and accuracy of the model and reduces the uncertainty of the model by using data such as rainfall, evaporation, and reservoir water storage changes, and by combining water balance calculations to calculate the initial water content of the watershed, thus providing solid support for hydrological forecasting of small and medium-sized rivers.

[0039] (2) Based on a large number of hydrological analysis and calculations, this invention obtains the daily average flow estimation results by analyzing and calculating the runoff generation of the basin. Unlike complex hydrological models, it reduces the number of model parameters, makes the specific meaning of the parameters simpler and more intuitive, and has high forecast accuracy. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the daily average flow estimation method based on water balance according to the present invention.

[0041] Figure 2 This is a schematic diagram illustrating the changes in rainfall and reservoir water storage according to the present invention;

[0042] Figure 3 This is a schematic diagram illustrating the calculation results of evaporation according to the present invention;

[0043] Figure 4 This invention calculates the watershed water content variation diagram;

[0044] Figure 5 This is a schematic diagram comparing the calculated flow rate with the measured average flow rate of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] Example

[0047] This embodiment uses a certain watershed as an example, with a catchment area of ​​12,954 km². 2 ;

[0048] like Figure 1 As shown in the figure, this embodiment provides a method for estimating the average daily flow rate based on water balance, including the following steps:

[0049] S1: Taking a historical period of the basin as an example, the starting date for the calculation is selected as 150 days from the initial time interval of the flood calculation, with P0 = 0 and W0 = 70. Based on daily monitoring changes in rainfall and reservoir storage, such as... Figure 2 As shown, combining the water balance calculation of watershed water content changes and evaporation values, the runoff on the first day is expressed as:

[0050]

[0051] Among them, R1 and E1 is an observed value, and P0 and W0 have given initial values, so W1 can be determined. Similarly, the formula for the watershed water content on day T is as follows:

[0052]

[0053] Among them, R T The daily runoff (observed value) is T, in mm; P T-1 The rainfall in the basin the previous day (from 8:00 AM on day T to 8:00 AM the previous day) is measured in mm; W T Water content of the basin on day T (continuously calculated value), unit: mm; W T-1 E represents the water content of the watershed the previous day, in mm. T This is the evaporation rate; the calculated value is not the measured value, and the unit is mm. This represents the change in reservoir water storage, in mm. The change in reservoir storage volume is expressed in meters (m). 3 A represents the catchment area of ​​the watershed, in km². 2 .

[0054] Specifically, the implementation process of step S1 includes:

[0055] S11: Daily evaporation in the basin (E) T Calculation is a prerequisite for ensuring water balance using the above formula. Calibration should be performed using long-term daily monitoring data to ensure water balance, when measured evaporation is greater than or equal to the preceding influencing rainfall. At that time, E T Take the measured value; otherwise, E T Then it needs to be recalculated, and the calculation result is as follows: Figure 3 As shown, specifically:

[0056]

[0057] in, The measured evaporation rate is in mm. Rainfall amounts in the preceding period, in mm;

[0058] In this embodiment, the initial impact of rainfall The calculation formula is:

[0059]

[0060] in, denoted as the initial rainfall at the start of day T-1, in mm; 'a' is the recession coefficient, a calibration parameter, preferably 0.7 in this embodiment; P TThis represents the rainfall on day T in the watershed, in mm.

[0061] In this embodiment, it is assumed that the evaporation amount E′ T The calculation formula is:

[0062]

[0063] Among them, E′ T The assumed evaporation rate is in mm; b represents W. T-1 / W m The index, a calibration parameter, is set to 0.8 for the watershed in this embodiment; W m The maximum water storage capacity of the basin is expressed in mm, and is preferably 500 mm in this embodiment.

[0064] S12: Combining the evaporation calculation results from step S11, the change in watershed water content ΔW can be calculated. T Calculation, the calculation result is as follows Figure 4 As shown, specifically:

[0065] W T -W T-1 =ΔW T

[0066] Among them, △W T The change in water content in the basin on day T is divided at 0:00, and the unit is mm.

[0067] The formula for calculating daily runoff T has been updated to:

[0068]

[0069] S2: After calculating the changes in evaporation and watershed moisture content, calculate the average daily flow rate, specifically as follows:

[0070]

[0071] in, This represents the average daily flow rate, in cubic meters (m³). 3 / s; This represents the baseline flow rate, in cubic meters (m³). 3 / s; The flow rate represents the rate of precipitation receding and replenishing, measured in cubic meters per second (m³). 3 / s;

[0072] Specifically, the implementation process of step S2 includes:

[0073] S21: Calculate the baseline flow rate Specifically, it is expressed as follows:

[0074]

[0075] Where C is the baseflow generation coefficient, which is a calibration coefficient, preferably 0.002 in this embodiment; A is the catchment area of ​​the watershed, in km². 2 In this embodiment, the preferred mileage is 12954 km. 2 d is the minimum baseline flow rate, m 3 / s, preferably 20m in this embodiment. 3 / s;

[0076] S22: Calculate the flow rate of dissipation and rainfall replenishment, specifically expressed as:

[0077]

[0078] in, The flow rate (m) is the flow rate of the receding water and replenishment of rainfall on day T. 3 / s; The flow rate (m) is the flow rate of the receding water and replenishment of rainfall on day T-1. 3 / s;e T Here, is the fading coefficient, and is the calibration parameter; in this embodiment, it is preferably 1.8; Q PT m represents the increase in flow rate on day T due to rainfall on day T-1. 3 / s.

[0079] S23: The increase in flow rate Q on day T due to rainfall on day T-1. PT Specifically, it is expressed as:

[0080]

[0081] Among them, W w The upper limit of water content for stable runoff generation in the basin without significant free water is typically slightly lower than the multi-year average flow rate, expressed in mm. In this embodiment, it is preferably 300 mm. f is the upper limit of the exponent, a calibration parameter, preferably 1.8 in this embodiment. W m The maximum water storage capacity of the basin is expressed in mm; in this embodiment, it is preferably 500 mm. c To estimate the maximum amount that can be exceeded above the upper limit, the unit is mm, and in this embodiment, it is preferably 100 mm; g is the minimum rainfall-runoff coefficient under the driest condition, and in this embodiment, it is preferably 0.1; h is W T The change in rainfall-runoff coefficient for each increase of W1 is preferably 0.009 in this embodiment;

[0082] S24: Extinction coefficient e T It is a daily changing value, specifically expressed as:

[0083]

[0084] Where i is a constant, preferably 1 in this embodiment; W T-1The watershed water content status for the previous day, in mm; W ava W2 is the average water content of the watershed, in mm, and is preferably 350 mm in this embodiment; j is the coefficient of the ratio of the watershed water content of the previous day to the watershed water content of the second day, which is a calibration parameter, and is preferably 0.6 in this embodiment;

[0085] S3: Input the continuous rainfall P1, P2, ..., P1 over a future period. n (T = 1, 2, ..., n days), changes in reservoir water storage, and water content in the basin. (T = 1, 2, ..., n days), continuously cycle through steps S1 and S2, and calculate the daily evaporation E thereafter. T Change in water content in the basin on day T, △W T The average daily traffic Q on the next T day T .

[0086] In this embodiment, after calculating the baseline flow, the receding flow, and the replenishment flow, the daily average flow can be calculated. Figure 5 As shown, the calculated and measured daily average flow rate are compared, and the Nash coefficient is 0.94, indicating that the method in this embodiment has a certain degree of accuracy.

[0087] The Nash efficiency coefficient (NSE) is commonly used to verify the quality of hydrological model simulation results. E ranges from negative infinity to 1. An E close to 1 indicates good model quality and high reliability; an E close to 0 indicates that the simulation results are close to the average level of the observed values, meaning the overall results are reliable, but the process simulation error is large; an E far less than 0 indicates that the model is unreliable.

[0088]

[0089] in, Observed values The simulated value represents a value at time t. It represents the overall average of the observed values.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for estimating daily average flow rate based on water balance, characterized in that, Includes the following steps: Obtain watershed rainfall observations, runoff observations, and reservoir water storage changes, and combine these with water balance calculations to determine watershed water content changes and evaporation values. The flow rate due to receding and replenishment is calculated based on the flow increment caused by rainfall, and the baseline flow rate is calculated based on the change in watershed water content. The daily average flow rate is calculated based on the flow rate of receding water and rainfall replenishment, and the baseline flow rate. Obtain continuous rainfall observations and reservoir water storage changes within a set period of T days in the watershed, calculate the evaporation on day T and the watershed water content change on day T, and estimate the average daily flow for the next T days.

2. The method for estimating daily average flow rate based on water balance according to claim 1, characterized in that, The formula for calculating the change in watershed water content is as follows: Among them, W T P represents the water content of the basin on day T. T-1 R represents the observed rainfall value of the previous day in the watershed. T W represents the observed runoff value on day T. T-1 This indicates the water content of the basin on the previous day. E represents the change in reservoir water storage. T This indicates the amount of evaporation.

3. The method for estimating daily average flow rate based on water balance according to claim 1, characterized in that, Evaporation is specifically expressed as: Among them, E T This represents the evaporation rate of the basin on day T. This represents the measured evaporation amount. E indicates the amount of rainfall that affected the initial period. ′ T This indicates the assumed evaporation rate.

4. The method for estimating daily average flow rate based on water balance according to claim 3, characterized in that, The specific amounts of rainfall that affected the initial stage are as follows: in, This indicates the amount of rainfall that affected the initial rainfall. Let P be the initial rainfall amount at the beginning of day T-1, where a is the recession coefficient. T This represents the rainfall on day T in the basin.

5. The method for estimating daily average flow rate based on water balance according to claim 3, characterized in that, Assume the evaporation rate is specifically expressed as: Among them, E ′ T Assuming evaporation rate, b is W. T-1 / W m The index, W m W is the maximum water storage capacity of the basin. T-1 This indicates the water content of the basin on the previous day.

6. The method for estimating daily average flow rate based on water balance according to claim 1, characterized in that, The flow rate resulting from the increase in flow rate due to rainfall is calculated as follows: in, The flow rate on day T represents the receding water level and the replenishment of rainfall. e is the flow rate for the receding water and replenishment of rainfall on day T-1. T Q is the extinction coefficient. PT This represents the increase in flow on day T due to rainfall on day T-1.

7. The method for estimating daily average flow rate based on water balance according to claim 6, characterized in that, The increase in flow on day T due to rainfall on day T-1 is specifically expressed as follows: Among them, W T W represents the water content of the basin on day T. w W represents the upper limit of water content in the basin. m W represents the maximum upper limit of water storage in the basin. c To estimate the maximum amount that can be exceeded above the maximum upper limit of watershed storage, f is the exponential upper limit, g is the minimum rainfall-runoff coefficient, and h is W. T The change in rainfall-runoff coefficient for each increase of daily water content W1 in the basin, where A is the catchment area of ​​the basin and P represents the rainfall in the basin.

8. The method for estimating daily average flow rate based on water balance according to claim 6, characterized in that, The fading coefficient is expressed as: Among them, e max A threshold is set for the fading coefficient, where i is a constant and W T-1 W represents the watershed water content status of the previous day. ava Let W2 be the average water content of the watershed, and j be the coefficient of the ratio of the watershed's water content on the previous day to the watershed's water content on the second day. The flow rate for the receding water and replenishment of rainfall on day T-1.

9. The method for estimating daily average flow rate based on water balance according to claim 1, characterized in that, The baseline flow rate is calculated based on the changes in watershed water content, and is specifically expressed as follows: in, W represents the baseline flow rate. T-1 The water content of the basin is represented by C, the baseflow coefficient is represented by A, the catchment area of ​​the basin is represented by d, and the minimum baseline flow rate is represented by d.

10. The method for estimating daily average flow rate based on water balance according to claim 1, characterized in that, The daily average flow rate is calculated based on the flow rate from receding water and rainfall replenishment, and the baseline flow rate, and is specifically expressed as follows: in, Indicates average daily traffic. Indicates the baseline flow rate. This indicates the flow rate during the receding of water and the replenishment of rainfall.

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