A method for estimating unit flow of surface water in small watershed

Abstract

The present invention provides a method for estimating the unit flow of surface water in a small watershed, comprising the following steps: S1, determining the position of a monitoring section; S2, measuring the width of the section; S3, measuring the average height of the section; S4, determining the point where the average height of the section is located; S5, measuring the flow velocity of the water body in the section; S6, calculating the flow; S7, secondary measurement; S8, measuring the water layer height and flow velocity at the average height point; S9, calculating the unit flow during the secondary measurement. The present invention is scientifically and reasonably designed, simple and easy to implement, can use common equipment to complete the determination of the surface water flow in a small watershed, can effectively avoid a large amount of repetitive work, and greatly improve work efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental monitoring, and in particular relates to a method for estimating the unit flow of surface water in a small watershed. Background Art

[0002] Small watersheds are the basic units of environmental management, and the water environment within the watershed is an important indicator of the overall environment of the watershed. In the process of environmental assessment, collecting and analyzing surface water in small watersheds is a key link in conducting water resource surveys, conducting water quality testing, delineating water environment functional zones, and simulating ecological sensitivity. Among them, estimating the flow of water bodies within the watershed is an inevitable and necessary step in completing the above work.

[0003] Existing technical means can use ultrasonic level meters to measure water level height, and then combine the width of the water area and the flow meter to calculate the ditch flow, but in actual work, especially in areas lacking basic hydrological data, this method has at least the following shortcomings. First, because the cross-section of the ditch is often irregular, and is limited by objective factors such as different topography, direct light, interference from the surrounding environment, and changes in the width of the water area caused by the dynamic evolution of rainfall, it is difficult to fully and accurately reflect the average water layer thickness of a certain section by using ultrasonic level meters to locate and measure the water level height. Second, when carrying out mobile operations in the field, ultrasonic equipment is inconvenient to carry. In order to prevent loss, it is necessary to measure and install it once, which is a heavy repetitive work. Third, the cost of ultrasonic level meters is relatively high, there is a risk of failure, and the equipment maintenance requires a lot of effort. Therefore, it is very necessary to design a small ditch flow measurement method that is low-cost, easy to operate, can avoid repetitive work, improve work efficiency, and is suitable for different cross-sectional shapes. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for estimating the unit flow of surface water in a small watershed in view of the deficiencies of the above-mentioned prior art. The method is simple and easy to implement, has high measurement efficiency, accurate and reliable data results, a wide range of applications, and the measurement has both regularity and randomness, fits the actual situation, can effectively avoid a large amount of repetitive work, and can be promoted and used in the field of surface water environment monitoring.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for estimating the unit flow of surface water in a small watershed, characterized in that it includes the following steps:

[0006] S1. Determine the location of the monitoring section: In the surface water collection area of ​​the small watershed, select a location on the bank that is open, unobstructed, free of debris, and with gentle water flow as the vertical monitoring section location;

[0007] S2. Measure the width w1 of the monitoring section: set points p1 and p2 on both sides of the boundary of the water area where the monitoring section is located, mark the positioning points p1 and p2 with marking rods, and measure the straight-line distance w1 between p1 and p2 with a tape measure;

[0008] S3. Measure the average height of the monitoring section: along the stretching direction of the tape measure, use the steel tape measure to measure multiple water layer depths at equal intervals in the width direction of the monitoring section, i.e., in the direction of the connecting line between points p1 and p2. The average value of the multiple water layer depths is the average height H1 of the monitoring section.

[0009] S4. Determine the location of the average height of the monitoring section: lock the steel tape measure at the H1 scale along the stretching direction of the tape measure, determine the point where the water depth is H1 and record it as p, and mark the location with a column or a marking rod; if the water layer heights of multiple points measured on the monitoring section are the same as the average height H1, select the point closest to the center of the monitoring section as point p;

[0010] S5. Measure the water flow velocity of the monitoring section: Use a flow velocity measuring device to measure the water flow velocity v1 at a water depth H1 / 2 below point p;

[0011] S6, calculate the water flow rate of the monitoring section: obtain the unit flow rate S1 of the initial measurement according to the water flow velocities v1, w1 and H1 obtained in S5;

[0012] S7, secondary measurement: after a certain time interval, the width of the monitoring section changes, measure the distance y1 from p1 to the boundary of the water area on the same side, and the distance y2 from p2 to the boundary of the water area on the same side, and calculate the width w2 of the monitoring section again based on y1, y2 and w1. When the width of the water area of ​​the monitoring section becomes larger, y1 and y2 are recorded as positive values, otherwise they are recorded as negative values;

[0013] S8, measure the water layer height H2 at point p with a steel tape measure, repeat S5 and S6 to measure the water flow velocity v2 at a water depth H2 / 2 below point p again, and calculate the unit flow S2 of the second measurement based on H2, v2 and w2;

[0014] S9. Repeat the operations of S7-S8 to perform flow measurement of the monitoring section twice or more according to actual needs.

[0015] Preferably, the specific operation mode of S2 is: the connecting line between points p1 and p2 is perpendicular to the flow direction of water, and the length of the connecting line between points p1 and p2 is the width w1 of the monitoring section.

[0016] Preferably, the specific method of S3 is: determine n water depth measurement points equidistantly along the connecting line between points p1 and p2 and obtain n water layer depths h1, h2, h3, ..., h corresponding to the n water depth measurement points. n ,but When w1≤1m, n=5; when 1m<w1≤2m, n=7; when 2m<w1≤3m, n=9; when 3m<w1≤4m, n=11; when 4m<w1≤5m, n=13. The distance between adjacent measuring points is w1 / (n+1).

[0017] Preferably, the method for calculating the unit flow S1 in S6 is: S1 = w1 × H1 × v1.

[0018] Preferably, in S7, w2=w1+y1+y2, and in S8, S2=w2×H2×v2.

[0019] Preferably, w1 is measured by a tape measure, point p is determined by a steel tape measure, and p1, p2, and p are marked and positioned by a marking rod. The marking rod is a cylindrical rod with a diameter of 3-10 cm, eye-catching color, hard texture, wear resistance, and corrosion resistance. After the marking rod is set, it is more than 20 cm above the water surface, and the price rod is inserted into the soil layer more than 40 cm to ensure that the marking rod is firmly laid and will not be displaced or lost due to water erosion.

[0020] Preferably, in order to obtain a more accurate area of ​​irregular figures, it is necessary to measure the height of the water body at equal distances along the cross section. The specific interval distance is determined according to the change in the cross-section width and the angle of the bottom of the cross section. See the specific operation steps of S3 above for details. At the same time, if the height difference between adjacent water depth measurement points is greater than the horizontal distance between adjacent measurement points, an additional measurement is performed at the middle position to ensure that the measurement data is consistent with the actual situation as much as possible. The average of multiple water body heights multiplied by the cross-section width is the cross-sectional area, which is equivalent to converting irregular figures into rectangles. In theory, the smaller the interval between the water depth measurement points, the closer it is to reality, and the more accurate its mean value is. Therefore, in practical applications, additional measurements can be taken according to the actual situation of the measurement points to improve data accuracy.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The method of the present invention is simple and easy to implement, has high practical value, good use effect, can effectively reduce repetitive work, improve measurement efficiency, and the calculated data results are in line with reality, accurate and reliable, which ensures the continuity of monitoring work and lays a good foundation for subsequent comparative analysis of water flow in typical sections at different times and under different conditions.

[0023] 2. The devices and equipment used in the present invention, such as marking rods, tape measures and steel tape measures, are all common items, inexpensive, easy to carry and operate, and are particularly suitable for water environment monitoring work in the field environment, with low monitoring conditions.

[0024] 3. The present invention is more in line with the reality of the irregular bottom of the water body section in measuring the water layer thickness. At the same time, it reserves space for making appropriate manual adjustments according to the actual situation of the section, which is conducive to obtaining more accurate water layer thickness data.

[0025] 4. The present invention is a method for estimating water flow. The water environment is an indicative factor for characterizing the intensity of regional non-point source pollution. This method can also be widely used in scientific research on non-point source pollution, collection and census of environmental resources in areas with scarce data, field hydrological monitoring and early warning, and dynamic evaluation of water quality.

[0026] The present invention is further described in detail below in conjunction with embodiments. DETAILED DESCRIPTION

[0027] Example 1

[0028] The method for estimating the unit flow rate of surface water in a small watershed of this embodiment is applied to the Tanjiawan small watershed in Yunyang District, Shiyan City, Hubei Province to monitor the unit flow rate. A total of three monitoring tests are conducted, each with an interval of one week. The specific operation steps are as follows:

[0029] First monitoring:

[0030] S11. In the surface water collection area of ​​a small watershed, select a location on the bank that is open, unobstructed, free of debris, and with a gentle water flow as the vertical monitoring section location.

[0031] S12. In the direction perpendicular to the water flow, set an initial width point p1 and p2 on both sides of the water boundary and use fine wooden stakes to locate them. Use a tape measure to measure the distance between p1 and p2, which is the initial cross-sectional width of the water area w1 = 3.5m. 11 measuring points need to be set at equal distances, and the distance between each measuring point is about 3.5÷12 = 29cm.

[0032] S13. Place the steel tape measure vertically close to the tape measure, and measure multiple water layer depth data h1, h2, h3...h at equal intervals along the extension direction of the tape measure scale. 11 They are 0.08, 0.13, 0.27, 0.46, 0.84, 0.87, 0.73, 0.59, 0.24, 0.11 and 0.05m respectively. Since the height difference between h4 and h5, h8 and h9 exceeds the horizontal distance of 29cm between adjacent measuring points, additional measurement is made at the middle position between h4 and h5, h8 and h9, which are 0.62m and 0.37m respectively. The average value of all 13 points is calculated to obtain the average height of the water section H1≈0.41m.

[0033] S14. Lock the scale of the steel tape measure at 0.41m, make the 0.41m scale of the steel tape measure close to the measuring tape, determine the point p where the water layer thickness is 0.41m, and use a long bamboo pole as a significant marker for positioning.

[0034] S15. Using the XHW-1 signal-controlled current meter, the water flow velocity v1 = 0.33 m / s was measured at point p, 0.21 m underwater.

[0035] S16, S1=w1×H1×v1=3.5×0.41×0.33≈0.47m 3 / s.

[0036] Second monitoring:

[0037] S21. The water boundary changed during the secondary measurement. The distance between p1 and the water boundary on the same side was measured by a tape measure, and the distance between p2 and the water boundary on the same side was measured to be y1 = 0.20m, and the distance between p2 and the water boundary on the same side was y2 = 0.13m. Therefore, the width of the secondary water area is w2 = 3.5 + 0.20 + 0.13 = 3.83m.

[0038] S22. Use a steel tape measure to measure the water layer height H2 = 0.53m at point p again, and use a signal-controlled flow meter to measure the flow velocity v2 = 0.37m / s at a water depth of 0.27m below point p.

[0039] S23, S2=w2×H2×v2=3.83×0.53×0.37≈0.75m 3 / s.

[0040] The third monitoring:

[0041] S31, again using a tape measure to measure the distance y1 from p1 to the water boundary on the same side = -0.16m, and the distance y2 from p2 to the water boundary on the same side = -0.09m. Then the width of the water area monitored this time is w3 = 3.5-0.16-0.09 = 3.25m.

[0042] S32. Use a steel tape measure to measure the water layer height H3 = 0.36m at point p again, and use a signal-controlled flow meter to measure the flow velocity v3 = 0.31m / s at a water depth of 0.18m below point p.

[0043] S33, S3=w3×H3×v3=3.25×0.36×0.31≈0.36m 3 / s.

[0044] If long-term monitoring is required, the second and third monitoring methods can be followed to obtain continuous monitoring data on the unit flow of surface water in the small watershed.

[0045] In this embodiment, combined with the mass concentration detection data of total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (COD) in the water body, the load of different pollutants in the basin is estimated as shown in Table 1 below.

[0046]

[0047] The flow data obtained has the following uses: (1) Through annual continuous monitoring, the annual flow in the target basin can be calculated in detail, which helps to accumulate hydrological data in different seasons and time periods. (2) Combined with the concentration detection data of pollutants such as TN, TP, COD in the water body, it is the only way to obtain the actual loss of pollutants such as TN, TP, COD in the target basin. On this basis, the standard pollution load of different pollutants can be obtained according to the water function zoning of the target basin. This is of great guiding significance for quantitatively describing the pollution intensity of the target basin water body, correctly understanding the main pollutants and pollution sources, and environmental pollution risk assessment, and formulating basin pollution control strategies based on this, and promoting ecological environment improvement.

[0048] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for estimating the unit flow of surface water in a small watershed, characterized in that: The following steps are involved: S1. Determine the monitoring section: In the surface water collection area of ​​the small watershed, select a location with open, unobstructed, free of debris and gentle water flow on the bank as the monitoring section location; S2. Measure the width w1 of the monitoring section: set points p1 and p2 on both sides of the boundary of the water area where the monitoring section is located, and determine w1 according to the positions of p1 and p2; S3. Measure the average height of the monitoring section: measure multiple water layer depths at equal intervals in the width direction of the monitoring section, and the average value of the multiple water layer depths is the average height H1 of the monitoring section; S4, determine the position corresponding to the average height of the monitoring section, and record the point where the average height H1 is located as p; if the water layer heights of multiple points measured on the monitoring section are the same as the average height H1, select the point closest to the center of the monitoring section as point p; S5. Measure the water flow velocity of the monitoring section: Use a flow velocity measuring device to measure the water flow velocity v1 at half the water depth below point p; S6, calculate the water flow rate of the monitoring section: obtain the unit flow rate S1 of the initial measurement according to the water flow velocities v1, w1 and H1 obtained in S5; S7, secondary measurement: after a certain period of time, the width of the monitoring section changes, and the distance y1 from p1 to the boundary of the water area on the same side and the distance y2 from p2 to the boundary of the water area on the same side are measured, and the width w2 of the monitoring section is calculated again based on y1, y2 and w1; S8, measure the height H2 of the water layer at point p, repeat S5 and S6 to measure the water velocity v2 at half the water depth below point p again, and calculate the unit flow S2 of the second measurement based on H2, v2 and w2; S9. Repeat the operations of S7-S8 to perform flow measurement of the monitoring section twice or more according to actual needs.

2. A method for estimating unit flow of surface water in a small watershed according to claim 1, characterized in that: The specific operation mode of S2 is: the connecting line between points p1 and p2 is perpendicular to the flow direction of water, and the length of the connecting line between points p1 and p2 is the width w1 of the monitoring section.

3. A method for estimating unit flow of surface water in a small watershed according to claim 1, characterized in that: The specific method of S3 is: determine n water depth measurement points at equal intervals along the connecting line between points p1 and p2 and obtain n water layer depths h1, h2, h3, ..., h corresponding to the n water depth measurement points. n ,but ; when w1≤1m, n=5; when 1m<w1≤2m, n=7; when 2m<w1≤3m, n=9; when 3m<w1≤4m, n=11; when 4m<w1≤5m, n=13.

4. A method for estimating unit flow of surface water in a small watershed according to claim 1, characterized in that: The method for calculating the unit flow S1 in S6 is: .

5. A method for estimating unit flow of surface water in a small watershed according to claim 1, characterized in that: The S7 , the S8 .

6. A method for estimating unit flow of surface water in a small watershed according to claim 1, characterized in that: Measure w1 with a tape measure, determine point p with a steel tape measure, and mark and locate p1, p2, and p with a marking rod.

7. A method for estimating unit flow of surface water in a small watershed according to claim 3, characterized in that: When calculating the average height of the monitoring section, when the height difference between adjacent water depth measurement points is greater than the horizontal distance between adjacent measurement points, the water depth of the water depth measurement point is added to the midpoint between the two water depth measurement points.

8. A method for estimating unit flow of surface water in a small watershed according to claim 1, characterized in that: The width of the surface water in the small watershed is less than 5m and the maximum depth does not exceed 1m.

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