Method for calculating comprehensive roughness coefficient of riverway of vegetation-covered beach based on dynamic partition

Abstract

The invention discloses a method for calculating a comprehensive roughness coefficient of a riverway of a vegetation-covered beach based on dynamic partition. The method comprises the following steps: dividing the riverway into a river channel and a vegetation beach land according to actually measured topographic data of the riverway; obtaining a partition roughness coefficient of the vegetation beach land, a wetted weekly parameter of a river channel, a wetted weekly parameter of the vegetation beach land, a full wetted weekly parameter of a river channel and a roughness coefficient of the river channel under the overtopping beach scene, and calculating a comprehensive roughness coefficient of the river channel under the overtopping beach scene; when the vegetation type or the vegetation submerging degree changes, the partition roughness coefficient of the vegetation beach land changes to cause the change of the comprehensive roughness coefficient of the river channel, and the comprehensive roughness coefficient of the river channel is calculated by combining the comprehensive roughness coefficient of the river channel under the beach overtopping situation. According to the method, the calculation difficulty of the comprehensive roughness coefficient of the river channel is reduced, the problem of instantaneous change of the comprehensive roughness coefficient of the river channel under the condition that the vegetation submerging degree of the vegetation bottomland of the river mouth river channel region changes drastically is solved, and rapid inversion of the on-way resistance parameter of the river channel is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydraulic engineering, in particular to a river comprehensive roughness coefficient calculation method for vegetation-covered floodplain based on dynamic zoning. BACKGROUND

[0002] The hydrodynamic resistance of a vegetated river can be decomposed into two basic components: riverbed matrix resistance and vegetation additional resistance. The river comprehensive roughness coefficient, as a key parameter for integrating the representation of composite resistance, has significant advantages in the simulation of water and sediment transport processes by coupling the interaction mechanism of the two heterogeneous resistance sources, and provides a key theoretical parameter for revealing the coupling rules of water and sediment in rivers. However, due to the differences in physical properties of riverbed composition, such as vegetation diameter, density and distribution, sediment particle size, porosity, sand wave, sand grain and other bed surface morphology, the spatial heterogeneity of roughness distribution characteristics often occurs in natural rivers, resulting in significant spatial differentiation of resistance within a single section. Traditional methods often use average parameters such as river section average flow velocity and average water depth for section roughness calculation, and do not fully consider the influence of river section composition differences on roughness. Therefore, it is particularly necessary to propose a section comprehensive roughness coefficient zoning calculation method.

[0003] In the river-estuary transition zone dominated by strong tidal dynamics, the periodic wetting and drying effect causes the submergence state of the floodplain vegetation to present a high-frequency dynamic oscillation. During this process, the spatial and temporal heterogeneity of the hydrodynamic boundary layer causes the roughness parameter in the vegetation-covered area to respond in phase synchronization, resulting in the nonlinear evolution characteristics of the river comprehensive roughness on the scale of the tidal period. In order to achieve high-precision simulation of the water and sediment transport process in the tide-controlled estuary, a real-time dynamic roughness calculation framework needs to be constructed to respond to the transient changes in the vegetation submergence degree. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a river comprehensive roughness coefficient calculation method for vegetation-covered floodplain based on dynamic zoning, which divides the river section into two sub-units with uniform hydraulic characteristics, i.e. river channel and vegetation floodplain, and calculates the river comprehensive roughness coefficient by zoning integration, thereby realizing the rapid inversion of the river resistance parameter along the way.

[0005] To achieve the above technical purpose, the present application adopts the following technical solution: a river comprehensive roughness coefficient calculation method for vegetation-covered floodplain based on dynamic zoning, specifically comprising the following steps:

[0006] Step S1, dividing the river into a river channel and a vegetation floodplain according to the measured topographic data of the river;

[0007] Step S2, according to the state of vegetation submergence in the floodplain scenario, the zonal roughness coefficient of the vegetation floodplain in the floodplain scenario is derived by using the flow force balance equation of the river channel floodplain containing vegetation; the wet perimeter parameter of the river channel in the floodplain scenario, the wet perimeter parameter of the vegetation floodplain and the total wet perimeter parameter of the river channel are obtained according to the measured terrain data and water depth of the river channel; the roughness coefficient of the river channel in the floodplain scenario is obtained;

[0008] Step S3, according to the zonal roughness coefficient of the vegetation floodplain in the floodplain scenario, the roughness coefficient of the river channel, the wet perimeter parameter of the river channel, the wet perimeter parameter of the vegetation floodplain and the total wet perimeter parameter of the river channel, the comprehensive roughness coefficient of the river channel in the floodplain scenario is calculated.

[0009] Step S4, when the vegetation type or the vegetation submergence degree changes, the zonal roughness coefficient of the vegetation floodplain changes, causing the change of the comprehensive roughness coefficient of the river channel, and the comprehensive roughness coefficient of the river channel is calculated in combination with the comprehensive roughness coefficient of the river channel in the floodplain scenario.

[0010] Further, the calculation process of the comprehensive roughness coefficient of the river channel in the floodplain scenario in step S3 is:

[0011]

[0012] Wherein, n0 represents the comprehensive roughness coefficient of the river channel in the floodplain scenario, P0 represents the total wet perimeter parameter of the river channel in the floodplain scenario, P0=P1+P2, P1 represents the wet perimeter parameter of the vegetation floodplain in the floodplain scenario, P2 represents the wet perimeter parameter of the river channel in the floodplain scenario, n1 represents the zonal roughness coefficient of the vegetation floodplain in the floodplain scenario, n2 represents the roughness coefficient of the river channel in the floodplain scenario, and a represents the roughness calculation coefficient.

[0013] Further, the calculation process of the comprehensive roughness coefficient of the river channel in step S4 is:

[0014] n=n0+Δn0

[0015] Wherein, n represents the comprehensive roughness coefficient of the river channel after the change of the zonal roughness coefficient of the vegetation floodplain, and Δn0 represents the comprehensive roughness change coefficient of the river channel.

[0016] Further, the calculation process of the comprehensive roughness change coefficient Δn0 of the river channel is:

[0017]

[0018] Wherein, Δn1 represents the zonal roughness change coefficient of the vegetation floodplain.

[0019] Further, the roughness calculation coefficient a takes the value of 3 / 2 or 2.

[0020] Further, the roughness calculation coefficient a is substituted into the calculation expression of the river comprehensive roughness coefficient to perform trial calculation: when the width-depth ratio of the river channel is 20 < B / H≤ 60, the relative change rate of the river comprehensive roughness coefficient needs to satisfy 10% < Δn0 / n0≤ 20%; when the width-depth ratio of the river channel is 60 < B / H≤ 100, the relative change rate of the river comprehensive roughness coefficient needs to satisfy 7% < Δn0 / n0≤ 10%; when the width-depth ratio of the river channel is B / H > 100, the relative change rate of the river comprehensive roughness coefficient needs to satisfy Δn0 / n0≤ 7%; wherein B represents the width of the river channel, and H represents the depth of the river channel.

[0021] Compared with the prior art, the application has the following beneficial effects: the river comprehensive roughness coefficient calculation method based on dynamic zoning of vegetation-covered floodplain of the application divides the river section into two sub-units with uniform hydraulic characteristics of vegetation floodplain and river channel according to the spatial gradient change of the river channel, calculates the river comprehensive roughness coefficient under the floodplain scenario, and calculates the river comprehensive roughness coefficient according to the change of the zoning roughness coefficient of the vegetation floodplain, thereby reducing the calculation difficulty of the river comprehensive roughness coefficient, solving the problem of instantaneous change of the river comprehensive roughness coefficient under the condition of severe change of the vegetation submergence degree of the vegetation floodplain in the estuary river channel region, and realizing the rapid inversion of the resistance parameter along the river channel; the method effectively solves the problem of the characterization of the river comprehensive roughness coefficient under the heterogeneous resistance field, breaks through the limitation of the traditional static roughness assumption, significantly improves the simulation accuracy of the hydraulic model, and has double application values for the parameterization of the hydraulic design of the tidal estuary regulation project and the resistance optimization configuration of the ecological revetment project. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The flowchart of the river comprehensive roughness coefficient calculation method based on dynamic zoning of vegetation-covered floodplain of the application;

[0023] Figure 2 The local schematic view of the river section in the application. DETAILED DESCRIPTION

[0024] The technical scheme of the application will be further explained and described below in combination with the drawings.

[0025] As Figure 1 The flowchart of the river comprehensive roughness coefficient calculation method based on dynamic zoning of vegetation-covered floodplain of the application, and the river comprehensive roughness coefficient calculation method specifically includes the following steps:

[0026] Step S1, according to the river channel measured terrain data, the river channel is divided into a river channel and a vegetation floodplain, as shown in Figure 2 The river channel measured terrain data includes: terrain, typical section flow, average flow velocity, water surface gradient, water depth and the like.

[0027] Step S2, according to the state of vegetation inundation under the floodplain scenario, the zonal roughness coefficient of the vegetation floodplain under the floodplain scenario is derived by using the flow force balance equation of the river channel floodplain containing vegetation, for details, see the Chinese patent application with the publication number CN114896552A and the invention name of a method for measuring and calculating the roughness coefficient of a river channel floodplain containing vegetation, the calculation process of the zonal roughness coefficient of the vegetation floodplain under the floodplain scenario in the present application is the calculation process of the roughness coefficient of the river channel floodplain containing vegetation; according to the measured terrain data and water depth of the river channel, the wet perimeter parameter of the river channel under the floodplain scenario, the wet perimeter parameter of the vegetation floodplain and the full wet perimeter parameter of the river channel are obtained; by querying the Water Conservancy Design Manual (2nd edition), the roughness coefficient of the river channel under the floodplain scenario is obtained.

[0028] Step S3, according to the zonal roughness coefficient of the vegetation floodplain under the floodplain scenario, the roughness coefficient of the river channel, the wet perimeter parameter of the river channel, the wet perimeter parameter of the vegetation floodplain and the full wet perimeter parameter of the river channel, the comprehensive roughness coefficient of the river channel under the floodplain scenario is calculated; specifically: according to Pavlovskij Mothed (PM) formula and Einstein-Banks Mothed (EBM) formula, it can be concluded that: Thus, Wherein, n0 represents the comprehensive roughness coefficient of the river channel under the floodplain scenario, P0 represents the full wet perimeter parameter of the river channel under the floodplain scenario, P0=P1+P2, P1 represents the wet perimeter parameter of the vegetation floodplain under the floodplain scenario, P2 represents the wet perimeter parameter of the river channel under the floodplain scenario, n1 represents the zonal roughness coefficient of the vegetation floodplain under the floodplain scenario, n2 represents the roughness coefficient of the river channel under the floodplain scenario, and a represents the roughness calculation coefficient, when a=3 / 2, the formula is PM method, and when a=2, the formula is EBM method.

[0029] Step S4, when the vegetation type or the vegetation inundation degree changes, the zonal roughness coefficient of the vegetation floodplain changes, causing the change of the comprehensive roughness coefficient of the river channel, combined with the comprehensive roughness coefficient of the river channel under the floodplain scenario, the comprehensive roughness coefficient of the river channel is calculated:

[0030] n=n0+Δn0 (1)

[0031] Wherein, n represents the comprehensive roughness coefficient of the river channel after the zonal roughness coefficient of the vegetation floodplain changes, and Δn0 represents the comprehensive roughness change coefficient of the river channel.

[0032] When the vegetation type changes or the vegetation inundation degree changes, the zonal roughness coefficient of the vegetation floodplain changes, resulting in the change of the comprehensive roughness coefficient of the river channel, therefore, the calculation process of the comprehensive roughness change coefficient Δn0 of the river channel is:

[0033]

[0034] After sorting, we can get:

[0035]

[0036] Wherein, Δn1 represents the change coefficient of the roughness of the vegetation beach, ΔP1 represents the change value of the wet perimeter parameter of the vegetation beach, Δn2 represents the change coefficient of the roughness of the river channel, and ΔP2 represents the change value of the wet perimeter parameter of the river channel. When the submergence degree of the vegetation changes, the change of the wet perimeter parameter of the actual river channel is small, ΔP1 can be ignored, and ΔP1 is 0. Since the roughness coefficient and the wet perimeter parameter of the river channel do not change, Δn2 and ΔP2 are 0. When the vegetation type or coverage of the vegetation beach changes in different river sections of the same river, the wet perimeter parameter of the vegetation beach, the wet perimeter parameter of the river channel and the roughness coefficient of the river channel do not change, ΔP1, Δn2 and ΔP2 are 0. Therefore, formula (3) can be rewritten as:

[0037]

[0038] After formula (1) is substituted into formula (4), the following formula can be obtained:

[0039]

[0040] Therefore, the comprehensive roughness coefficient of the river channel is

[0041] In the present application, the roughness calculation coefficient α is 3 / 2 or 2. Specifically, the roughness calculation coefficient α is substituted into the calculation expression of the comprehensive roughness coefficient of the river channel to determine whether the relative change rate Δn0 / n0 of the comprehensive roughness coefficient meets the corresponding interval range, so as to determine the specific value of the roughness calculation coefficient α. When the width-depth ratio of the river channel is 20

[0042] The method for calculating the comprehensive roughness coefficient of the vegetation-covered beach of the river channel based on dynamic zoning in the present application reduces the calculation difficulty of the comprehensive roughness coefficient of the river channel according to the spatial gradient change of the river channel, solves the problem of the instantaneous change of the comprehensive roughness coefficient of the river channel under the condition that the submergence degree of the vegetation beach of the estuary river channel region changes dramatically, and realizes the rapid inversion of the resistance parameter along the river channel. The method effectively solves the problem of the characterization of the comprehensive roughness coefficient of the river channel under the heterogeneous resistance field, breaks through the limitation of the traditional static roughness assumption, significantly improves the simulation accuracy of the hydraulic model, and has double application values for the parameterization of the hydraulic design of the tidal estuary regulation project and the resistance optimization configuration of the ecological revetment project.

[0043] Embodiment

[0044] The method is used for calculating the comprehensive roughness coefficient of a river channel by the dynamic zoning vegetation cover beach channel comprehensive roughness coefficient calculation method of the application.

[0045] Step S1, collecting the measured terrain data and beach vegetation type data of a certain river channel, and dividing the river channel into a river channel and a vegetation beach.

[0046] Step S2, the B / H of the river channel is 50, the n1 above the gate is 0.03, the n1 below the gate is 0.08, the n2 is 0.0225, the P1 is 20 meters, and the P2 is 250 meters.

[0047] Step S3, calculating the comprehensive roughness coefficient of the river channel under the overbank scenario

[0048] Step S4, when the vegetation type or the vegetation submergence degree changes, the zoning roughness coefficient of the vegetation beach changes, causing the change of the comprehensive roughness coefficient of the river channel, and combining the comprehensive roughness coefficient of the river channel under the overbank scenario, the comprehensive roughness coefficient of the river channel is calculated:

[0049] When α is 3 / 2, the comprehensive roughness coefficient calculation formula of the river channel can be changed to:

[0050]

[0051] When α is 2, the comprehensive roughness coefficient calculation formula of the river channel can be changed to:

[0052]

[0053] When α is 3 / 2, according to the Pavlovskij (PM) method, the comprehensive roughness n0 of the river channel above the gate under the overbank scenario is 0.0231, the comprehensive roughness n of the river channel below the gate is 0.0285, the roughness difference Δn1 of the vegetation beach above and below the gate is 0.05, and the comprehensive roughness n of the river channel below the gate calculated by the method is 0.0273.

[0054] When α is 2, according to the Einstein-Banks (EBM) method, the comprehensive roughness n0 of the river channel above the gate under the overbank scenario is 0.0231, the comprehensive roughness n of the river channel below the gate is 0.0285, the roughness difference Δn1 of the vegetation beach above and below the gate is 0.05, and the comprehensive roughness n of the river channel below the gate calculated by the method is 0.0279.

[0055] According to the river channel width-depth ratio B / H=50, when α is 3 / 2, Δn0 / n0=18.28%, which is between 10% and 20%; when α is 2, Δn0 / n0=20.75%, which is not between 10% and 20%, at this time, α should be taken as 3 / 2, and the corresponding comprehensive roughness error is only 4.02%.

[0056] The above merely describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical scheme falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled in the art, some improvements and refinements without departing from the principles of the present application shall be considered as falling within the protection scope of the present application.

Claims

1. A method for calculating the integrated roughness coefficient of a river channel covered by vegetation and beach based on dynamic zoning, characterized in that, Specifically comprising the following steps: Step S1, dividing the river channel into a river channel and a vegetation beach according to the measured terrain data of the river channel; Step S2, deriving the zoned roughness coefficient of the vegetation beach in the overbank scenario according to the submerged state of the vegetation in the overbank scenario, using the flow power balance equation of the river channel with vegetation; obtaining the wet perimeter parameter of the river channel, the wet perimeter parameter of the vegetation beach and the total wet perimeter parameter of the river channel in the overbank scenario according to the measured terrain data and the water depth of the river channel; and obtaining the roughness coefficient of the river channel in the overbank scenario; Step S3, calculating the comprehensive roughness coefficient of the river channel in the overbank scenario according to the zoned roughness coefficient of the vegetation beach, the roughness coefficient of the river channel, the wet perimeter parameter of the river channel, the wet perimeter parameter of the vegetation beach and the total wet perimeter parameter of the river channel in the overbank scenario; Step S4, when the vegetation type or the submerged degree of the vegetation changes, the zoned roughness coefficient of the vegetation beach changes, causing the change of the comprehensive roughness coefficient of the river channel, and combining the comprehensive roughness coefficient of the river channel in the overbank scenario, the comprehensive roughness coefficient of the river channel is calculated.

2. The method according to claim 1, wherein, The calculation process of the comprehensive roughness coefficient of the river channel in the overbank scenario in step S3 is as follows: Wherein, n0 represents the comprehensive roughness coefficient of the river channel in the overbank scenario, P0 represents the total wet perimeter parameter of the river channel in the overbank scenario, P0=P1+P2, P1 represents the wet perimeter parameter of the vegetation beach in the overbank scenario, P2 represents the wet perimeter parameter of the river channel in the overbank scenario, n1 represents the zoned roughness coefficient of the vegetation beach in the overbank scenario, n2 represents the roughness coefficient of the river channel in the overbank scenario, and a represents the roughness calculation coefficient.

3. The method according to claim 2, wherein, The calculation process of the comprehensive roughness coefficient of the river channel in step S4 is as follows: n=n0+Δn0 Wherein, n represents the comprehensive roughness coefficient of the river channel after the change of the zoned roughness coefficient of the vegetation beach, and Δn0 represents the change coefficient of the comprehensive roughness of the river channel.

4. The method according to claim 3, wherein, The calculation process of the change coefficient of the comprehensive roughness of the river channel Δn0 is as follows: Wherein, Δn1 represents the change coefficient of the zoned roughness of the vegetation beach.

5. The method according to any one of claims 2-4, wherein the method is characterized in that, The value of the roughness calculation coefficient a is 3 / 2 or 2.

6. The method according to claim 5, wherein, The roughness calculation coefficient a is substituted into the calculation expression of the comprehensive roughness coefficient of the river channel for trial calculation: when the width-depth ratio of the river channel is 20 B / H≤60, the relative change rate of the comprehensive roughness coefficient of the river channel needs to satisfy 10%<Δn0 / n0≤20%; when the width-depth ratio of the river channel is 60 B / H≤100, the relative change rate of the comprehensive roughness coefficient of the river channel needs to satisfy 7%<Δn0 / n0≤10%; and when the width-depth ratio of the river channel is B / H>100, the relative change rate of the comprehensive roughness coefficient of the river channel needs to satisfy Δn0 / n0≤7%; wherein, B represents the width of the river channel, and H represents the depth of the river channel.

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