Method for predicting flow velocity along floating vegetation river course

Abstract

The application discloses a method for predicting the flow velocity along the course of a river with floating vegetation, and the river with floating vegetation is divided along the water flow direction of the river according to the flow regulation distance, and the water flow direction velocity prediction model of the river with floating vegetation is constructed to realize the prediction of the flow velocity along the course of the river, so as to provide a theoretical basis for further research on the water flow, sediment movement characteristics and riverbed evolution of the natural river and lake with floating vegetation.

Description

Technical Field

[0001] This invention belongs to the field of hydraulics and river dynamics, and relates to a method for predicting the velocity of water flow along its course, particularly for predicting the velocity of water flow along the course of rivers with floating vegetation. Background Technology

[0002] Floating vegetation is common in streams and wetlands, playing a vital role in river ecosystems. It impedes water flow, altering flow velocity and sediment transport along the river's course. Under suitable environmental and climatic conditions, floating vegetation expands and may cover the entire water surface, influencing the flow structure within and beneath the vegetation. Specifically, the flow velocity within floating vegetation decreases due to vegetation resistance; the flow velocity increases in the unvegetated areas between the riverbed and the vegetation due to the continuity of the flow. Because of the velocity difference between the vegetation and the area beneath it, a shear layer forms at the bottom of the vegetation. If the shear is strong enough, Kelvin-Helmholtz eddies (KH eddies) emerge, driving momentum exchange between the water flow within and beneath the vegetation layer. The complex flow structure within and beneath floating vegetation can affect the transport and diffusion of sediments, pollutants, and other substances in the river channel, thus influencing riverbed morphology.

[0003] Given this fact, it is crucial to study the changes in flow velocity along rivers with floating vegetation and to further investigate the interaction between floating vegetation and riverbed evolution. Therefore, it is essential to understand the velocity variations within and around floating vegetation. However, under natural conditions, it is difficult to continuously measure flow velocity along vegetated rivers over extended periods. This is because, firstly, flow conditions in natural rivers are not constant; variations in upstream flow directly affect the measurement results, potentially leading to unrepresentative findings. Secondly, measuring and collecting velocity data requires a significant amount of time. While constant, uniform flow can be obtained under laboratory conditions, allowing for detailed measurement of flow velocity in rivers with floating vegetation, the measurement, collection, and analysis of this data still require substantial time, manpower, and financial investment. Typically, a vegetation community 0.5 meters wide and 4 meters long is constructed in a test water tank that is 1 meter wide and 16 meters long. ADV (Doppler velocity measurement) is used, with a sampling frequency of 50 Hz. The sampling time at each point must be set to at least 2 minutes and 30 seconds. Under the condition of measuring for 8 hours a day, it takes a month or even longer to measure the flow velocity along the river with floating vegetation in detail.

[0004] Therefore, there is an urgent need for a simple and practical method to predict the flow velocity along rivers with floating vegetation, so as to provide a theoretical basis for further research on vegetation community evolution. Summary of the Invention

[0005] In view of the current situation where existing technologies are difficult to effectively predict the flow velocity along rivers with floating vegetation, the purpose of this invention is to provide a method for predicting river flow velocity, which is based on the continuity equation and momentum equation model to predict the flow velocity in vegetated areas and adjacent areas without vegetation.

[0006] This invention is applicable to river conditions with floating vegetation where the water flow velocity is greater than 0 cm / s. Therefore, the water flow variation can be considered two-dimensional, that is, only in the direction of water flow and the transverse direction (perpendicular to the direction of water flow). In this invention, x and z represent the direction of water flow and the vertical direction, respectively. The point x = 0 is the leading edge of the floating vegetation.

[0007] The invention concept is to analyze the water flow velocity in the floating vegetation area and the area below the vegetation to obtain a prediction model for the water flow velocity along the floating vegetation in a river channel with floating vegetation.

[0008] Research has shown that in river channels, due to vegetation resistance, the water flow entering the floating vegetation area shifts from the vegetated area to the area below the vegetation. As the distance the water flows over the floating vegetation increases (the distance between the water flow and the vegetation front at x=0 increases), the vegetation area (H≥z>h) becomes more densely populated. g The water flow velocity decreases, below the canopy (h) g The velocity of (≥z≥0) increases until a new flow equilibrium is reached. Within and around the suspended vegetation, initial adjustments occur in both the x-direction and the perpendicular direction of the flow (z-direction), forming a secondary circulation. Figure 1 (a) and 1(b)), where it is assumed that the average flow velocity U in the vegetated area is... c (x) and the average flow velocity U below the vegetation b (x) is uniform in the vertical direction.

[0009] The water flow velocity decreases inside the floating vegetation, while the water flow velocity increases below the vegetation. The flow regulation distance X D Defined as the distance from the vegetation front to the point where the water flow velocity inside the vegetation decreases to a constant value (Chen et al., 2013; Huthoff et al., 2007; Lei and Nepf, 2021; Huai et al., 2021):

[0010]

[0011] Among them, h c C represents the height of the floating vegetation. D ah c C is the vegetation density coefficient. D denoted as the drag coefficient, a as the area of ​​the floating vegetation blocking water, and H as the river depth.

[0012] In X DIn addition, if the shear layer at the base of the vegetation is strong enough, KH eddies begin to form, and the local Reynolds shear stress is significantly enhanced. Here, this is set in a region with fully developed water flow (X). D (<x≤L), the water flow within and beneath the vegetation remains constant. L is the length of the floating vegetation.

[0013] Based on the above-mentioned inventive concept, the present invention provides a method for predicting the flow velocity along a river with floating vegetation, comprising the following steps:

[0014] S1 obtains the flow adjustment distance X D ;

[0015] S2 when 0 < x ≤ X D At that time, determine the direction and velocity of water flow within the floating vegetation by following these steps:

[0016] S21 obtains the floating vegetation front velocity prediction function f(U0) at x=0 using the following formula:

[0017]

[0018] Where U0 is the water flow velocity at the leading edge of floating vegetation, and A', B' and C' are defining coefficients;

[0019] S22 obtains the prediction function f(U) for the average flow velocity within the vegetation at the leading edge of non-floating vegetation using the following formula. c (x)):

[0020]

[0021] Where α and β are defined coefficients;

[0022] S23 predicts the average flow velocity within the vegetation based on the obtained function f(U). c (x)), the flow velocity in the direction of water flow in the floating vegetation is calculated according to the above formula (1a);

[0023] S3 X D When x ≤ L, the flow velocity in the direction of water flow within the floating vegetation is determined according to the following formula:

[0024]

[0025] Where φ is the solid volume fraction, h c C is the height of the floating vegetation, and C is the shear parameter. b C is the coefficient of friction of the riverbed. D Here, denoted as the drag coefficient, a is the water-blocking area of ​​the floating vegetation (a = nd), n is the number of plants per unit area in the floating vegetation zone, d is the diameter of a single floating plant, and H is the river depth.

[0026] The following explanation details the method for predicting the flow velocity along the course of rivers with floating vegetation.

[0027] For 0 < x ≤ X D To obtain the above formulas (1a) and (1b), it is first necessary to obtain the average flow velocity U within the vegetated area. c (x) and the average flow velocity U below the vegetation b (x) direct relationship.

[0028] The river channel with floating vegetation will flow along the z-direction at z = h g The area is divided into two regions: Region 1, the interior region of floating vegetation (H≥z>h) g ), and area 2, the area below the floating vegetation (h g ≥z≥0).

[0029] In waterways with floating vegetation, a flow continuity equation is introduced:

[0030] U c (x)h c (1-φ)+U b (x)(Hh c )=U0H (3)

[0031] Combining the momentum equations inside and below the vegetation, we get equations (3) and (4) respectively:

[0032]

[0033]

[0034] Where φ is the vegetation volume fraction per unit water body, U0 is the flow velocity at the floating vegetation front, taken as the average velocity in the upper reaches of the river, ρ is the density of water, and W c (x), W b (x) represents the vertical flow velocity of water within the vegetated area and below the vegetation, respectively. and Here, represents the vertical acceleration of water flow within and below the vegetation area, respectively; g is the acceleration due to gravity; and C (=0.04) is the shear parameter (Plew, 2010). b Let be the riverbed friction coefficient. Compared with the momentum equation for the region inside floating vegetation (Equation (4)), the momentum equation for the region below floating vegetation (Equation (5)) does not include the vegetation resistance term. However, it includes the riverbed resistance term (ρC). b [U b (x)] 2 ).

[0035] In the area of ​​floating vegetation and the area beneath the vegetation (z = h) gAt the interface, due to the continuity of water flow, the vertical velocity and vertical velocity gradient of the water flow are the same in both regions. That is, W c (x)=W b (x) and By combining formula (4) with formula (5) × h c / (Hh c By combining these methods, both the vertical advection term and the pressure term can be eliminated simultaneously.

[0036]

[0037] Combining formulas (3) and (6), we obtain U c (x) expression:

[0038]

[0039] To solve U c (x), defining coefficients α, β, A', B' and C':

[0040]

[0041] In summary, formula (7) can be simplified to:

[0042]

[0043] Integrating equation (9), we obtain the equation that satisfies 0 < x ≤ X. D Predictive models for water flow direction and velocity within floating vegetation under certain conditions:

[0044]

[0045]

[0046] Where f(U) is the water flow velocity prediction function.

[0047] Based on equations (1a) and (1b), the Euler method is used to predict U. c (x). The initial condition is that the water flow velocity at the leading edge of the floating vegetation is the same as the average flow velocity of the river channel, i.e., U. c (x=0)=U0.

[0048] In areas where water flow is fully developed (X) D <x≤L), the water flow inside and below the floating vegetation remains constant. Therefore, the momentum equations inside the floating vegetation (Equation (4)) and below the floating vegetation (Equation (5)) can be used to determine the momentum equations.

[0049] Simplified as follows:

[0050]

[0051]

[0052] Among them, U cf and U bf Let be the average water depth velocity inside and below the floating vegetation within the fully developed flow region, respectively. The flow continuity equation for the fully developed region simplifies to:

[0053] U cf h c (1-φ)+U bf (Hh c )=U0H (12)

[0054] By combining formulas (10), (11), and (12), the region of fully developed water flow (x>X) is obtained. D ) Floating vegetation internal water depth average velocity prediction model U cf :

[0055]

[0056] Currently, there is no model capable of predicting the flow velocity along the course of a river with floating vegetation. The method for predicting the flow velocity along the course of a river with floating vegetation provided by this invention has the following beneficial effects:

[0057] 1. This invention divides the floating vegetation area along the river flow direction based on the flow regulation distance, and can predict the river flow velocity along the course based on the constructed flow velocity prediction model in the river with floating vegetation, providing a theoretical basis for further research on the flow, sediment movement characteristics and riverbed evolution of natural rivers and lakes with floating vegetation.

[0058] 2. The velocity prediction model for floating vegetation areas constructed in this invention combines the momentum equation and the flow continuity equation, which satisfies the physical laws of fluid dynamics. The velocity of the river with floating vegetation obtained by this prediction model is closer to the actual velocity along the river, and the prediction accuracy is high.

[0059] 3. This invention does not require flow velocity measurement. It only requires the prediction of the flow velocity along the course of a river with floating vegetation based on the basic parameters of the river channel and vegetation community (including river channel width, vegetation community width, vegetation community density, vegetation drag coefficient, riverbed resistance coefficient, etc.).

[0060] The method for predicting the flow velocity along the course of rivers with floating vegetation provided by this invention not only reduces research costs but is also applicable to natural rivers (including river areas where on-site measurements are not convenient). Therefore, this invention has very wide applicability. Attached Figure Description

[0061] Figure 1(a) is a schematic diagram of a river channel with floating vegetation. Circles indicate the positions of individual floating vegetation plants, U0 is the average flow velocity of the river channel, B is the width of the channel (vegetation), and L is the length of the floating vegetation. For each measurement point x, the water flow velocity is measured at the corresponding y = 0, y = -dy / 8, and y = dy / 8, where dy is the distance between two adjacent individual vegetation plants in the horizontal direction; (b) is a two-dimensional generalized diagram of the water flow regulation mechanism of floating vegetation. Vertical lines represent floating vegetation communities composed of rigid individual vegetation plants, X D H represents the water flow regulation distance within the vegetation, where H is the water depth and h is the water depth. c It refers to the height of the floating vegetation.

[0062] Figure 2 U represents the ratio of the internal water flow velocity of floating vegetation to the average flow velocity of the river channel under different conditions. c (x) / U0 longitudinal distribution; (a) corresponding to different average flow velocities U0 in different river channels, (b) corresponding to different floating vegetation blocking areas a, (c) corresponding to different relative flow depths h g / H.

[0063] Figure 3 The measured water flow velocity within floating vegetation and the method proposed in this invention for predicting flow velocity U. c (x) is a comparison diagram; where the measured velocity values ​​are represented by hollow rhombuses, the predicted velocity values ​​are represented by solid lines, and the dashed lines represent the uncertainty range of the velocity prediction caused by parameters C and U0, where C = 0.076 ± 0.025 and U0 = 16.8 ± 0.3 cm / s. Detailed Implementation

[0064] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are part of the present invention.

[0065] Example 1

[0066] This embodiment provides a detailed description of the velocity prediction results along the course of a river with floating vegetation, obtained through flume testing.

[0067] ① Experimental Objective

[0068] The flow velocity along the course of a river with floating vegetation was measured using a flume test, and detailed velocity measurements were taken under selected operating conditions. The flow velocity in the floating vegetation area under different vegetation densities was determined, and the obtained flow velocity along the course of the river in the floating vegetation area was compared with the flow velocity along the course obtained using a prediction method to verify the accuracy of the flow velocity prediction method along the course of a river with floating vegetation provided by this invention.

[0069] ② Test equipment

[0070] The main equipment is shown in Table 1 below.

[0071] Table 1 shows the experimental setup with floating vegetation in a water tank.

[0072]

[0073]

[0074] ③ Test conditions

[0075] The experiment was conducted in a test flume measuring 16 meters long, 1 meter wide, and 0.5 meters high. The test section of the flume was 4 meters long. In this experiment, the water depth ranged from 22.5 to 33.0 cm. The average channel velocity U0 varied from 9.3 to 17.3 cm / s, which is consistent with common flow velocities in natural streams and wetlands (2–20 cm / s, Downing-Kunz and Stacey, 2011, 2012; Wilkie et al., 2012). Under all experimental conditions, the flow was turbulent, but had fully developed into a steady flow before entering the test section of the flume.

[0076] The model of floating vegetation was fixed to a polyvinyl chloride (PVC) board, which was positioned above the water surface. The model of floating vegetation was placed upside down below the water surface to simulate suspended vegetation. The diameter of a single model of floating vegetation was d = 0.8 cm, which is consistent with the observed range of natural floating vegetation (d = 0.1-1.5 cm, Tanner and Headley, 2011; Zhao et al., 2017). The simulated floating vegetation conforms to the morphology of floating vegetation in natural rivers and lakes, but does not represent a specific type of vegetation. Two vegetation densities were considered in the experiment of this invention: n = 0.020-0.035 plants / cm². 2 The water-blocking areas a (=nd) of the floating vegetation are 1.6 and 2.8 m², respectively. -1 This is consistent with the range of water-blocking area of ​​floating vegetation observed in the field (a = 1.0 to 3.2 m). -1 (Downing-Kunz and Stacey, 2012; Plew, 2010; Tseung et al., 2016; Zhao et al., 2017). In this invention, the floating vegetation in the model is 4 meters long and 1 meter wide, and the width of the vegetation is the same as that of the water tank, so there is no lateral water flow regulation. It is worth noting that flow regulation occurs in the vertical direction, and the regulation area is the leading edge of the vegetation area (0 < x ≤ X). D The 4-meter-long vegetation consisted of eight sections, each 0.5 meters wide and 1 meter long. The submersion height of the floating vegetation remained constant (h) across all operating conditions.c =14cm). Height h of the area below the floating vegetation. g Defined as the distance from the riverbed (z=0) to the bottom of the floating vegetation (z=h) g The distance of h) g =H–h c The calculations were performed. The experimental parameters are summarized in Table 2.

[0077] The coordinate system used in the experiment of this invention is as follows: Figure 1 As shown in the diagram, x, y, and z represent the directions along, lateral, and perpendicular to the water flow, respectively. x = 0 represents the leading edge of the floating vegetation, y = 0 represents the centerline of the vegetation and the channel, and z = 0 represents the riverbed surface. Accordingly, the components of the water flow velocity in the three coordinate directions are defined as u(x,y,z) = (U,V,W). Velocity was measured using a Nortek Acoustic Doppler Velocimetry (ADV) meter. For each operating condition, the vertical velocity distribution was measured at x = -300, 0, 50, 100, 150, 200, 250, 300, and 350 cm.

[0078] Measurement results confirm that the flow velocity at the mid-height of the floating vegetation is similar to the average vertical flow velocity of the vegetation. The difference between the values ​​is less than 8%, indicating that the flow velocity at the middle height of the floating vegetation is the same as the average water depth flow velocity in the vegetation area. Based on this, the experiment was conducted along the middle height of the floating vegetation (z = h). g +h c / 2) Measure the water flow velocity. In the water flow regulation region (x = 0 ~ X...), measure the water flow velocity. D ), measure the flow velocity at intervals of 20-30 cm along the x-direction; in the region where the water flow is fully developed (x=X D -L), flow velocity was measured at 50 cm intervals along the x-direction. For each measurement point x, the flow velocity was measured at y = 0, y = -dy / 8, and y = dy / 8 using an ADV measuring instrument (see...). Figure 1 (a) The average of the three velocities is considered as the average flow velocity. At each location, the velocity is recorded for 120 seconds at a frequency of 50 Hz. The instantaneous flow velocity data in the three directions are processed using the data processing software provided with ADV to obtain the time-averaged flow velocities (U, V, W) and flow velocity fluctuation components (u′, v′, w′) in the three directions (x, y, z).

[0079] Based on previous methods for estimating the drag coefficient and considering the influence of porosity in adjacent cylinders, the average velocity within the floating vegetation area is defined as... (Etminan et al., 2017). Based on formula R ec =U c 'd / ν (White, 1991) yields the drag coefficient C. D :

[0080] C D =1+10R ec -2 / 3 (13)

[0081] The range of the obtained drag coefficient C under all operating conditions D =1.0-1.2, indicating that C is assumed in the following predictions. D =1 is reasonable.

[0082] The riverbed friction coefficient C was determined according to the method proposed by Liu and Shan (2019). b =0.003±0.001. Riverbed shear stress τ b Near-bottom Reynolds shear stress Very similar (Yang et al., 2015).

[0083] To quantitatively compare the predicted water flow velocity values ​​obtained by the prediction method proposed in this invention with the actual measured values, the root mean square error (RMSE) is defined:

[0084]

[0085] Where N is the number of measured and predicted values, U c(x) (m) and U c(x) (p) represents the measured water flow velocity and the predicted flow velocity at the corresponding location, respectively.

[0086] ④ Analysis of Experimental Results

[0087] When water enters floating vegetation, the flow is vertically deflected from inside the vegetation to the area below, causing the flow velocity in the flow regulation zone within the vegetation to continuously decrease. Flow regulation distance X D Defined as the distance from the vegetation front to the point where the water flow velocity within the vegetation decreases to a constant value. Figure 1 (b) If the length L of the floating vegetation is less than X D The water flow velocity continuously decreases throughout the vegetation. For submerged vegetation, Lei and Nepf (2021) indicated that the ratio X of the length of the water flow regulation zone to the vegetation height... D / h c With vegetation density (1 / C) D (ah) and relative water depth ((Hh) c () / H) related. X obtained from 8 operating condition experiments. D Measured values ​​(see Table 2), for X D Perform linear fitting (R) 2 =0.91) yields:

[0088]

[0089] Combining formulas (15), (1), and (2), the velocity distribution along the flow direction in rivers with floating vegetation is predicted according to the following steps:

[0090] S1 obtains the flow adjustment distance X D .

[0091] Here, the internal water flow regulation distance X of the floating vegetation is calculated according to the above formula (15) for each working condition. D This determines the water flow regulation zone (0 < x ≤ X). D ) and areas with fully developed water flow (X) D <x≤L).

[0092] S2 when 0 < x ≤ X D At that time, determine the direction and velocity of water flow within the floating vegetation by following these steps:

[0093] S21 obtains the floating vegetation front velocity prediction function f(U0) at x=0 using the following formula:

[0094]

[0095] Where U0 is the water flow velocity at the leading edge of the floating vegetation, and A', B' and C' are the coefficients defined above.

[0096] S22 obtains the prediction function f(U) for the average flow velocity within the vegetation at the leading edge of non-floating vegetation using the following formula. c (x)):

[0097]

[0098] Where α and β are the coefficients defined above.

[0099] S23 predicts the average flow velocity within the vegetation based on the obtained function f(U). c (x)) The predicted flow velocity in the direction of water flow within the floating vegetation is calculated according to the above formula (1a).

[0100] S3 X D When x ≤ L, the predicted flow velocity within the floating vegetation is determined using the following formula:

[0101]

[0102] Where φ is the vegetation volume fraction per unit water body, h c C is the height of the floating vegetation, and C is the shear parameter. b C is the coefficient of friction of the riverbed. D denoted as the drag coefficient, a as the area of ​​the floating vegetation blocking water, and H as the river depth.

[0103] Table 2 shows the parameters for various operating conditions in the floating vegetation flume test.

[0104]

[0105] In the table: U0 is the average river flow velocity; H is the water depth; h g h is the height of the area where the water flows freely beneath the floating vegetation. g / H represents the relative flowing water depth, h g =Hh c n is the amount of vegetation per unit area within the floating vegetation; a (=nd) is the water-blocking area of ​​the vegetation; φ is the volume fraction of vegetation per unit water body; X D(m) The length of the water flow regulation zone to be measured; U cf The measured flow velocity is in the fully developed flow zone; the root mean square error (RMSE) is calculated by equation (14).

[0106] like Figure 2 As shown, the ratio U of the internal water flow velocity of floating vegetation to the average flow velocity of the river channel under different conditions... c The longitudinal distribution experiment of (x) / U0 verified the mean channel velocity (U0) and relative flow depth (h). g The influence of / H) and the water-blocking area (a) of floating vegetation on the flow velocity along the path of floating vegetation:

[0107] (1) At a relative water depth (h) g When the obstruction area (a) of the floating vegetation (H) is the same, the effect of the average river velocity (U0) on the flow velocity along the vegetation can be ignored. Specifically, when the average river velocity is U0 = 16.8 ± 0.3 cm / s (condition: Case 1) and 13.3 ± 0.2 cm / s (condition: Case 2), the ratio of the measured flow velocity along the vegetation to the average river velocity is U c The (x) / U0 curves are very similar, such as Figure 2 As shown in (a).

[0108] (2) At a relative water depth (h) g At the same / H), a larger floating vegetation water-blocking area (a) provides greater vegetation resistance, thus the water flow velocity within the vegetation is lower, such as Figure 2 As shown in (b).

[0109] (3) When the water-blocking area (a) of floating vegetation is the same, the relative water depth (h) g / H) affects the velocity of water flow along the vegetation: lower relative flow depth (h) g / H) leads to a larger water flow velocity within vegetation (e.g. Figure 2 (as shown in (c)). For example, in Case 4, h gThe mean value of the dimensionless water flow velocity / H=0.4 (square) is compared with h in working condition Case 2. g The mean dimensionless water flow velocity in the triangle with / H=0.6 is 25% greater. This is because h g The larger the / H value, the larger the free-flowing area under the floating vegetation. Therefore, there is more water under the floating vegetation and less water passing through the floating vegetation, resulting in a lower water flow velocity within the floating vegetation area.

[0110] The effectiveness of the prediction method proposed in this invention was verified using the experimental data (Table 2) of this invention. Figure 3 The measured velocity within vegetation and the predicted velocity (U0 = 9.3–17.3 cm / s, h) using the prediction method provided in this invention were compared. g / H=0.4~0.6,a=1.6 and 2.8m -1 The dashed line represents the velocity uncertainty caused by parameters C and U0. From Figure 3 As can be seen, the predicted water flow velocity in the floating vegetation area using the method proposed in this invention is highly consistent with the measured value. In all operating conditions, the root mean square error (RMSE / U0) between the predicted and measured velocity values ​​is less than 6%.

[0111] In summary, the method for predicting the flow velocity along the path in floating vegetation areas proposed in this invention has a very good match between the predicted and measured flow velocities, high prediction accuracy, and strong applicability. The prediction model (formulas (1) and (2)) proposed in this invention can effectively predict the flow velocity along the path in suspended vegetation.

[0112] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for predicting the streamwise flow velocity of a river with floating vegetation, characterized in that, The method comprises the following steps: S1 determines the flow regulating distance X according to the following formula D : ； S2 When 0 < x < X D The direction of the water flow within the floating vegetation is determined according to the following steps: S21: obtaining a floating vegetation front flow velocity prediction function f(U0) at the floating vegetation front x = 0 according to the following formula: (1a)； wherein U0 is the flow velocity of the floating vegetation front, , and are defined coefficients; , and was determined according to the following formula: ； ； ； S22 The vegetation internal mean flow velocity prediction function f(U c (x)) is obtained according to the following formula (1b)； Wherein, α and β are definition coefficients; α and β are determined according to the following formula: ； ； S23 predicting the function f(U c (x)) according to the above formula (1a) to calculate the water flow direction velocity in the floating vegetation. S3 X D When x≤L, L is the length of the floating vegetation, and the flow direction velocity in the floating vegetation is determined according to the following formula: (2)； where φ is the volume fraction of vegetation in the unit water body, h c is the height of floating vegetation, C is the shear parameter, C b is the bed friction coefficient, C D is the resistance coefficient, a is the water resistance area of floating vegetation, and H is the water depth of the river channel.

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