Method, storage medium and system for judging the control effect of river channel on water level drop

Abstract

The present invention relates to a method, storage medium and system for judging the control effect of a river channel on a water level drop. The method comprises the following steps: S1. Differentiating a one-dimensional steady flow motion equation to obtain a corresponding gradient expression between adjacent discrete sections; S2. Assuming that the distance between two adjacent sections is small and the cross-sectional area does not change much, S1 is simplified; S3. The cross-sectional area, river width and water depth of the cross-sectional area along the river section under the low-water flow level Q of the river section are extracted along the river section, and the roughness is calculated; S4. When a specific water level drop occurs at the outlet of the river section, the ratio of the water level drop value of each cross-sectional area along the river section to the preset standard value is examined to judge the control effect of the water level drop of the river section. The advantage of the present invention is that the method approximately simplifies the one-dimensional implicit equation into an explicit calculation process, and can quickly judge the control effect of the river channel on the water level drop. If the control effect is weak, it is necessary to prevent the influence of the downstream water level drop, and then it can play a guiding role in the design of related projects on the river channel.

Description

Technical Field

[0001] The present invention belongs to the technical field of river water level control, and in particular relates to a method for determining the control effect of a river on water level drop, a storage medium and a system. Background Art

[0002] The construction of reservoirs or hubs has greatly changed the water and sediment conditions downstream, and the downstream river channel will inevitably face the problems of scouring, cutting and water level drop. Even if the river section below the dam has basically completed scouring and coarsening, and the riverbed remains basically stable, the low water level will still drop further due to the upstream transmission of the low water level drop at the far end. For navigation hubs, the continuous drop in the low water level below the dam may cause insufficient water depth at the threshold of the ship lock, affecting the navigation of the ship lock. Therefore, evaluating the control effect of the water level drop in the river section below the dam has a strong practical significance. Summary of the invention

[0003] The present invention provides a method, storage medium and system for determining the control effect of a river channel on a water level drop, aiming to quickly and conveniently determine the control effect of a low water level on a river section with a basically stable riverbed, in order to guide the design of related projects.

[0004] The technical solution of the present invention to solve the above technical problems is as follows: a method for determining the control effect of a river channel on water level drop, which is derived by differentiating a one-dimensional steady flow motion equation and appropriately simplifying it, and is briefly described as follows:

[0005] First, the water surface gradient between two adjacent discrete sections of the river channel is obtained by differentiating the one-dimensional steady flow motion equation. , velocity head gradient and energy loss ratio : (Formula 1)

[0006] (Formula 2) (Formula 3) Where Q is the flow rate, A is the cross-sectional area of ​​the water flow, z is the water level, n is the roughness, and R is the hydraulic radius. is the gradient between discrete sections, and the subscript j is the discrete section number. is the section spacing, is the weight factor, and the subscript j+1 represents downstream.

[0007] Secondly, by assuming that the distance between two adjacent discrete sections is small and the cross-sectional area of ​​the water flow does not change much, the unified A j and A j+1 , and then simplify formula 3 to get the following formula:

[0008] (Formula 4)

[0009] in , , are the average roughness, average river width and average water depth between two adjacent discrete sections.

[0010] Then, the water-passing area A of the section along the river under the low-water flow level Q of the assessed river section is extracted along the river. j 、River width B j 、Water depth H j , because the distance between two adjacent discrete sections is small, the roughness change is small, that is, =( + ) / 2= , substituting into formula 4, we can get , the specific calculation formula is as follows:

[0011] (Formula 5)

[0012] in is the energy loss ratio at discrete section j, which is obtained by combining formulas 1 and 2 with the extracted water flow area A. j 、River width B j 、Water depth H j The parameters including etc. are calculated.

[0013] S4. Finally, when a specific drop in water level occurs at the outlet of the assessed river section When the water level drops at each section along the way and Ratio With the preset standard value If the size relationship is reached until the entrance section of the assessed river section, Are greater than , it means that the entire assessed river section does not have a strong enough control effect on the water level drop at the outlet, otherwise it has a strong enough control effect; the water level drop values ​​of each section along the way Formulas 6 to 8 are used to calculate the interval from the downstream section to the upstream section: (Formula 6) (Formula 7) (Formula 8).

[0014] The present invention also provides a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the steps of the above method are implemented.

[0015] The present invention also provides a system for determining the control effect of a river channel on water level drop, which comprises the above-mentioned storage medium and a processor, and the processor implements the steps of the above-mentioned method when executing the computer program on the storage medium.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] According to the method provided by the present invention, it is only necessary to extract the water-passing area A of the section along the river under the low-water flow level Q of the river section to be evaluated. j 、River width B j and water depth H j Then, according to the corresponding formula, the water level drop of each section along the way can be obtained by calculating from the downstream section to the upstream section one by one. and 0.05 If the size of the river section is All greater than 0.05 , which means that the river section has a weaker control effect on the water level drop, otherwise it means that the river section has a stronger control effect on the water level drop; this method approximates the one-dimensional implicit equation into an explicit calculation process, which is convenient and efficient, and can quickly determine the control effect of the river channel on the water level drop. If the control effect is weak, it is necessary to guard against the impact of the downstream water level drop, which can then play a guiding role in the design of related projects on the river channel. DETAILED DESCRIPTION

[0018] The principles and features of the present invention are further described in detail below in conjunction with specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0019] The present invention provides a method for determining the control effect of a river channel on water level drop, which comprises the following steps:

[0020] S1. Obtain the water surface gradient between two adjacent discrete sections of the river by differentiating the one-dimensional steady flow motion equation , velocity head gradient and energy loss ratio :

[0021] The equation of motion for a one-dimensional steady flow (Saint-Venant equation) is as follows:

[0022] Differentiate the above equation to get the difference equation:

[0023] Note: The first difference ignores the In addition to the partial differential symbol, it is included together with the difference, and the difference is very small. .

[0024] The second term on the left side of the above differential equation is the gradient, which represents the ratio of the water level difference between any two end points to the horizontal distance between the two points, that is, the gradient between two adjacent discrete sections. The expression is as follows: , Increasing footnotes indicate going downstream, while decreasing footnotes indicate going downstream. It is the upstream water level minus the downstream water level divided by the distance. Combining the above differential equation, we know It can be calculated by formula 1: (Formula 1); (Formula 2); (Formula 3); where Q is the flow rate, A is the cross-sectional area of ​​the water flow, z is the water level, n is the roughness, and R is the hydraulic radius. is the gradient between discrete sections, and the subscript j is the discrete section number. is the section spacing, is the weight factor, and the subscript j+1 represents downstream;

[0025] S2. Assuming that the distance between two adjacent discrete sections is small and the cross-sectional area of ​​the water flow does not change much, Formula 3 can be simplified as follows: (Formula 4), where , , are the average roughness, average river width, and average water depth between two adjacent discrete sections;

[0026] When simplifying Formula 3, assuming that the discrete cross-section of the assessed river section is a rectangular cross-section, then , B is the river width, H is the water depth. For rivers on the plains, the width B is much greater than the depth H. , , S is the wetted perimeter, H and B are not in the same order of magnitude, that is, they are ignored In the formula, H is .

[0027] S3. Extract the water-passing area A of the section along the river under the low-water flow level Q of the river section j 、River width B j 、Water depth H j , because the distance between two adjacent discrete sections is small, the roughness change is small, that is, = , substituting into formula 4, we get (Formula 5), ​​where is the energy loss ratio at discrete section j, calculated by formulas 1 and 2;

[0028] In this step, the equation on the left side of Formula 1 Calculate the water surface gradient along the section , and then calculate the velocity head gradient using formula 2 , then the energy loss ratio of the discrete section numbered j along the path can be calculated , = - , that is, the parameters under the square root in formula 5 are all extracted or calculated through the previous steps, and are all known values, so the roughness at the discrete section can be calculated , can be calculated It can be used in the next step to calculate the gradient caused by the water level drop. .

[0029] In steps S2 and S3, for medium and large rivers, the cross-sectional spacing No more than 200m, split the discrete sections along the way and extract the water-passing area A along the way j 、River width B j and water depth H j .

[0030] S4. When a specific drop in water level occurs at the outlet of the assessed river section When the water level drops at each section along the way and Ratio With the preset standard value If the size relationship is reached until the entrance section of the assessed river section, Are greater than , it means that the entire assessed river section does not have a strong enough control effect on the water level drop at the outlet, which will cause the water level at the inlet section to drop to a certain extent. On the contrary, it has a strong enough control effect, and the water level at the outlet section will drop to a certain extent. When the water level at the inlet section does not drop or drops insignificantly, the water level drop at each section along the way Formulas 6 to 8 are used to calculate the interval from the downstream section to the upstream section: (Formula 6) In Formula 6, the actual , , Instead of the corresponding average value, an approximate process is performed. When the differential interval is small enough, the impact of the approximate process is very small. The advantage of this process is that it transforms the implicit iterative process into an explicit step-by-step calculation.

[0031] It should be noted here that = / , preset standard value It is an empirical value, ranging from 0.045 to 0.055, and is usually specified directly is 0.050, which is about to and 0.05 Because in general, the drop in downstream water level does not affect the upstream water level at all, and it takes a considerable amount of river reduction. If the water level drops at each section along the way All greater than 0.05 , indicating that there is an impact, while less than or equal to 0.05 , it can be determined that there is basically no impact. If there is a stronger requirement for the control effect, then A specific value smaller than 0.05 may also be selected.

[0032] (Formula 7) It should be noted that the right side of the equation in Formula 7 , , and is known, when a specific drop in water level is assumed at the outlet of the assessed river reach When Given, that is, Based on this, the inlet section of this interval can be calculated by formula 7. and , It can be substituted into the following formula 8 to calculate the previous interval .

[0033] (Formula 8) In other words, when the outlet section assumes a drop After that, the water level dropped. , Formula 6 is now used to derive the gradient of the section immediately upstream of the outlet section , together with Formula 7 and Formula 8, we can calculate one interval higher, and then keep calculating. Formula 6 assumes that the drop in water depth at the inlet of the section is equal to that at the outlet, and is used to estimate the gradient change; Formula 7 uses the gradient change to appropriately correct the assumption of Formula 6, which is equivalent to the gradient must increase after the water depth drops, so the drop in water level at the inlet of the section must be less than that at the outlet.

[0034] It should be noted that in the above method, the specific drop in the outlet water level When making assumptions, the assumed value should not be greater than the critical value of rapid and slow flow: ,in is the outlet water level, is the outlet cross-sectional area.

[0035] In summary, the method provided by the present invention can be used to simply and quickly identify the strength of the control effect of the low-water river section below the dam on the water level drop, which has certain guiding significance for the engineering design related to the river channel. When the river channel has a weak control effect on the water level drop, the drop in the water level at the downstream outlet will obviously affect the water level at the upstream river section inlet, and the navigation of ships depends on how much water depth is reserved for the threshold of the ship lock. When there is a lot of surplus, even if the control is weak, it does not matter if the water level drops. However, if there is little surplus, the water level control power of the downstream river section is very important. Once it drops, it will cause the problem of difficulty in normal navigation of the ship lock.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the control effect of a river channel on water level decline, characterized in that: The steps include: S1. Obtain the water surface gradient between two adjacent discrete sections of the river by differentiating the one-dimensional steady flow motion equation , velocity head gradient and energy loss ratio : (Formula 1); (Formula 2); (Formula 3); Among them, Q is the flow rate, A is the cross-sectional area of ​​the water flow, z is the water level, n is the roughness, and R is the hydraulic radius. is the gradient between discrete sections, and the subscript j is the discrete section number. is the section spacing, is the weight factor, and the subscript j+1 represents downstream; S2. Assuming that the distance between two adjacent discrete sections is small and the cross-sectional area of ​​the water flow does not change much, Formula 3 can be simplified as follows: (Formula 4), where , , are the average roughness, average river width, and average water depth between two adjacent discrete sections; S3. Extract the water-passing area A of the section along the river under the low-water flow level Q of the river section j 、River width B j 、Water depth H j , because the distance between two adjacent discrete sections is small, the roughness change is small, that is, = , substituting into formula 4, we get (Formula 5), ​​where is the energy loss gradient at discrete section j, calculated by formulas 1 and 2; in steps S2 and S3, the water surface gradient along the section is calculated by the equation on the left side of formula 1 , and then calculate the velocity head gradient using formula 2 , then the energy loss ratio of the discrete section numbered j along the path can be calculated , = - ; S4. When a specific drop in water level occurs at the outlet of the assessed river section When the water level drops at each section along the way and Ratio With the preset standard value The magnitude relationship is used to determine the water level drop control effect of the river section; the water level drop value of each section along the river Formulas 6 to 8 are used to perform interval-by-interval calculations from the downstream section to the upstream section: (Formula 6) (Formula 7) (Formula 8).

2. The method for determining the control effect of a river channel on water level drop according to claim 1, characterized in that: In step S2, when simplifying formula 3, it is assumed that the discrete cross-section of the assessed river section is a rectangular cross-section, then , B is the river width, H is the water depth. For rivers on the plains, the width B is much greater than the depth H. , , S is the wetted perimeter, if H and B are not in the same order of magnitude .

3. The method for determining the control effect of a river channel on water level drop according to claim 1, characterized in that: In step S3, for medium and large rivers, the cross-sectional spacing No more than 200m, split the discrete sections along the way and extract the water-passing area A along the way j 、River width B j and water depth H j .

4. The method for determining the control effect of a river channel on water level drop according to claim 1, characterized in that: Any specific value in the range of 0.045-0.

055.

5. The method for determining the control effect of a river channel on water level drop according to claim 4, characterized in that: The value of is 0.

050.

6. The method for determining the control effect of a river channel on water level drop according to claim 1, characterized in that: Specific drop in outlet water level in step S4 The assumed value of should not be greater than the critical value of rapid and slow flow: ,in is the outlet water level, is the outlet cross-sectional area.

7. The method for determining the control effect of a river channel on water level drop according to any one of claims 1 to 6, characterized in that: In step S4, if the evaluation reaches the river entrance section, Are greater than , it means that the entire assessed river section does not have a strong enough control effect on the water level drop at the outlet, otherwise it has a strong enough control effect.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

9. A system for determining the control effect of a river on water level decline, characterized in that: The method comprises the storage medium as claimed in claim 8 and a processor, wherein the processor implements the steps of the method as claimed in any one of claims 1 to 7 when executing the computer program on the storage medium.

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