Method for predicting riverbed siltation height and silt siltation range after silt supply change

Abstract

The invention discloses a method for predicting a riverbed siltation height and a sediment siltation range after sediment supply change, and the method comprises the following steps: S1, employing a variable rate equation to describe a dynamic adjustment process of a river channel characteristic variable under the sediment supply change, and the river channel characteristic variable comprises the riverbed siltation height and the sediment siltation range; s2, solving the variable rate equation to obtain a calculation expression of the characteristic variables; s3, determining a riverbed siltation height balance value and a sediment siltation range balance value of the sediment supply point position according to an incoming flow condition and an incoming sand condition of the target river channel; and S4, according to the balance value obtained in the step S3, in combination with the calculation expression of the characteristic variables, calculating and obtaining the riverbed siltation height and the sediment siltation range of the target river channel. The method can effectively predict the deposition height and the deposition range of the riverbed deposition area under different sediment supply conditions, provides key parameters for dangerous area division in flood control practice, and provides important theory and method support for mountain river water and sediment disaster prevention and control.

Description

Technical Field

[0001] The invention relates to the technical field of hydraulics and river dynamics, and in particular to a method for predicting riverbed siltation height and siltation range after silt replenishment changes. Background Art

[0002] In recent years, global climate change, frequent natural disasters and intensified human activities have significantly changed the sediment replenishment process of mountain rivers. In mountainous basins, natural factors (earthquakes, bank collapse, landslides and mountain torrents and debris flows, etc.) or human factors (dam demolition, engineering waste, etc.) cause a large amount of sediment to enter the river in a short period of time, resulting in riverbed siltation and water level rise in local river sections, which in turn triggers major water and sand disasters. After the river channel is silted up, it takes a long time for dynamic adjustment to return to a stable state. During the entire adjustment process, the riverbed siltation height and the siltation range are the key parameters for determining the flood level. Accurately predicting and calculating the riverbed siltation height and the siltation range play an important guiding role in determining flood control areas, designing flood control projects and flood forecasting and warning.

[0003] At present, there are relatively few research results on the response of riverbeds to sediment entering rivers. There is a lack of clear understanding of the evolution laws of riverbed scouring and silting under changes in sediment supply, and a lack of corresponding prediction and calculation methods for riverbed scouring and silting evolution, which seriously restricts the level of water and sand disaster prevention and control in mountainous rivers. Summary of the invention

[0004] In view of the above problems, the present invention aims to provide a method for predicting the riverbed siltation height and siltation range after the change of silt replenishment.

[0005] The technical solution of the present invention is as follows:

[0006] A method for predicting riverbed sedimentation height and sediment deposition range after sediment supply changes, comprising the following steps:

[0007] S1: The rate equation is used to describe the dynamic adjustment process of the channel characteristic variables under the change of sediment supply, and the channel characteristic variables include the riverbed siltation height and the sediment deposition range;

[0008] S2: solving the rate of change equation to obtain a calculation expression for the characteristic variable;

[0009] S3: Determine the riverbed sedimentation height balance value and sedimentation range balance value at the sediment recharge point location according to the inflow conditions and sediment inflow conditions of the target river channel;

[0010] S4: According to the riverbed siltation height balance value and the siltation range balance value, combined with the calculation expression of the characteristic variable, the riverbed siltation height and the siltation range of the target river channel are calculated.

[0011] Preferably, in step S1, the rate of change equation is:

[0012]

[0013] Where: dy / dt is the adjustment rate of the river channel characteristic variable; y is the river channel characteristic variable; t is time; β is the adjustment rate coefficient of the river channel characteristic variable; y e is the equilibrium value of the river channel characteristic variables.

[0014] Preferably, in step S2, the calculation expression of the characteristic variable is the calculation expression of mode 1 or the calculation expression of mode 2, the initial value of the characteristic variable in mode 1 is the measured value of the characteristic variable at the end of the previous period, and the initial value of the characteristic variable in mode 2 is the calculated value of the characteristic variable at the end of the previous period;

[0015] The calculation expression of the mode is:

[0016]

[0017] Where: ΔZ b,i is the riverbed sedimentation height at the end of the i-th period; β Z is the adjustment rate coefficient of the riverbed sedimentation height; Δt is the calculation step length; ΔZ b,ei is the equilibrium value of riverbed sedimentation height at the end of the i-th period; ΔZ b,i-1 is the riverbed sedimentation height at the end of the i-1th period; L i is the sedimentation range at the end of the i-th period; β L is the adjustment rate coefficient of the sediment deposition range; L ei is the sedimentation range equilibrium value at the end of the i-th period; L i-1 is the sedimentation range at the end of the i-1th period;

[0018] The calculation expression under the second mode is:

[0019]

[0020] Where: ΔZ b,n is the riverbed sedimentation height at the end of the nth period; n is the total number of calculation steps; ΔZ b,0 is the riverbed siltation height at the initial moment; L n is the sedimentation range at the end of the nth period; L0 is the sedimentation range at the initial moment.

[0021] Preferably, in step S3, the riverbed siltation height balance value and the siltation range balance value are calculated by the following formulae respectively:

[0022]

[0023]

[0024] Where: ΔZ be * is the dimensionless equilibrium value of riverbed sedimentation height; k, a and b are coefficients; is the dimensionless single-width flow rate; is the dimensionless single-width sediment replenishment rate; S be S is the balanced slope of the riverbed; b0 is the initial slope of the riverbed.

[0025] Preferably, the dimensionless single width flow is calculated by the following formula:

[0026]

[0027] Where: q w is the single-width flow rate; g is the acceleration due to gravity; D 84 It is the particle size corresponding to when the cumulative frequency distribution percentage of sediment reaches 84%;

[0028] The dimensionless single-width sediment replenishment rate is calculated by the following formula:

[0029]

[0030] Where: q bf is the sediment replenishment rate per unit width; ρ s is the density of sediment; ρ is the density of water; D 50 is the median particle size of sediment;

[0031] The riverbed equilibrium slope is calculated by the following formula:

[0032]

[0033] Where: m is the roughness; is the dimensionless sediment transport rate. When the river channel is in equilibrium, is the dimensionless critical starting shear stress; q w For single-width flow.

[0034] Preferably, the roughness is calculated by the following formula:

[0035]

[0036] Where: D is the sediment particle size.

[0037] As a preferred method, the riverbed siltation height at any section downstream of the river is calculated by the following formula:

[0038]

[0039] Where: Z bx Z is the riverbed siltation height at any section of the downstream river; b,x＝0 is the riverbed siltation height at the sediment recharge point; x is the distance from any section downstream of the river to the sediment recharge point; L is the sedimentation range.

[0040] The beneficial effects of the present invention are:

[0041] 1. The present invention constructs a generalized model for the scouring and silting adjustment of the river channel to reach a balanced state through the movement form of the riverbed silt deposits after silt replenishment, proposes a calculation method for the equilibrium value of the riverbed siltation height and the equilibrium value of the siltation range, reveals the scouring and silting adjustment law of mountain rivers under the change of silt replenishment, and significantly improves the understanding of the riverbed evolution law under the change of silt replenishment.

[0042] 2. Based on the rate-varying equation, the present invention derives a prediction formula for the riverbed siltation height and siltation range after the sediment supply changes. The formula can predict the non-equilibrium adjustment process of the riverbed of mountain rivers under different water and sediment supply conditions, and provide technical support for the delineation of flash flood and debris flow hazard zones in mountain rivers.

[0043] 3. The present invention only needs to determine the morphological parameters of the mountain river channel (such as river channel width, riverbed slope, etc.) and the water and sediment conditions (such as flow rate, sediment replenishment rate, etc.), and then determine the relevant parameters of the prediction calculation formula based on the measured data, so as to realize the prediction and calculation of the evolution of riverbed scouring and siltation under the change of sediment replenishment. It is easy to operate in actual conditions and has wide versatility in this field. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0045] Figure 1 This is a schematic diagram of the sediment supply conditions for the flume test; Figure 1 (a) is a schematic diagram of the conditions of group one of each group, 1(b) is a schematic diagram of the conditions of group two of each group, 1(c) is a schematic diagram of the conditions of group three of each group, and 1(d) is a schematic diagram of the conditions of group four of each group;

[0046] Figure 2 This is a schematic diagram of the longitudinal section of the riverbed sediment accumulation body after the sediment supply changes;

[0047] Figure 3It is a schematic diagram of the comparison results of the calculated value and the measured value of the riverbed sedimentation height at the sediment supply point in a specific embodiment of the flume test; Figure 3 (a) is a schematic diagram of the results of group one, 3(b) is a schematic diagram of the results of group two, and 3(c) is a schematic diagram of the results of group three;

[0048] Figure 4 This is a schematic diagram of the comparison between the calculated value and the measured value of the sediment deposition range in a flume test in another specific embodiment; Figure 4 (a) is a schematic diagram of the results of group one, 4(b) is a schematic diagram of the results of group two, and 4(c) is a schematic diagram of the results of group three. DETAILED DESCRIPTION

[0049] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0050] A method for predicting riverbed sedimentation height and sediment deposition range after sediment supply changes, comprising the following steps:

[0051] S1: The rate equation is used to describe the dynamic adjustment process of the channel characteristic variables under the change of sediment supply, and the channel characteristic variables include the riverbed siltation height and the sediment deposition range.

[0052] In a specific embodiment, the rate of change equation is:

[0053]

[0054] Where: dy / dt is the adjustment rate of the river channel characteristic variable; y is the river channel characteristic variable; t is time; β is the adjustment rate coefficient of the river channel characteristic variable; y e is the equilibrium value of the river channel characteristic variables.

[0055] S2: Solve the rate equation to obtain a calculation expression for the characteristic variable.

[0056] In a specific embodiment, the calculation expression of the characteristic variable is the calculation expression of mode 1 or the calculation expression of mode 2, the initial value of the characteristic variable in mode 1 is the measured value of the characteristic variable at the end of the previous period, and the initial value of the characteristic variable in mode 2 is the calculated value of the characteristic variable at the end of the previous period;

[0057] The calculation expression of the mode is:

[0058]

[0059] Where: ΔZ b,i is the riverbed sedimentation height at the end of the i-th period; β Z is the adjustment rate coefficient of the riverbed sedimentation height; Δt is the calculation step length; ΔZ b,ei is the equilibrium value of riverbed sedimentation height at the end of the i-th period; ΔZ b,i-1 is the riverbed sedimentation height at the end of the i-1th period; L i is the sedimentation range at the end of the i-th period; β L is the adjustment rate coefficient of the sediment deposition range; L ei is the sedimentation range equilibrium value at the end of the i-th period; L i-1 is the sedimentation range at the end of the i-1th period;

[0060] The calculation expression under the second mode is:

[0061]

[0062] Where: ΔZ b,n is the riverbed sedimentation height at the end of the nth period; n is the total number of calculation steps; ΔZ b,0 is the riverbed siltation height at the initial moment; L n is the sedimentation range at the end of the nth period; L0 is the sedimentation range at the initial moment.

[0063] In the above embodiment, the first mode is applicable to the case where there are measured values ​​for a river channel, and the second mode is applicable to the case where the initial value is known but the measured value at the end of each calculation period is unknown.

[0064] S3: Determine the riverbed sedimentation height balance value and sedimentation range balance value at the sediment recharge point location based on the inflow conditions and sediment inflow conditions of the target river channel.

[0065] In a specific embodiment, the riverbed siltation height balance value and the siltation range balance value are calculated by the following formulae respectively:

[0066]

[0067]

[0068] Where: ΔZ be * is the dimensionless equilibrium value of riverbed sedimentation height; k, a and b are coefficients; is the dimensionless single-width flow rate; is the dimensionless single-width sediment replenishment rate; S be S is the balanced slope of the riverbed; b0 is the initial slope of the riverbed.

[0069] In a specific embodiment, the dimensionless single width flow is calculated by the following formula:

[0070]

[0071] Where: q w is the single-width flow rate; g is the acceleration due to gravity; D 84 It is the particle size corresponding to when the cumulative frequency distribution percentage of sediment reaches 84%;

[0072] The dimensionless single-width sediment replenishment rate is calculated by the following formula:

[0073]

[0074] Where: q bf is the sediment replenishment rate per unit width; ρ s is the density of sediment; ρ is the density of water; D 50 is the median particle size of sediment;

[0075] The riverbed equilibrium slope is calculated by the following formula:

[0076]

[0077] Where: m is the roughness; is the dimensionless sediment transport rate. When the river channel is in equilibrium, is the dimensionless critical starting shear stress; q w For single-width flow.

[0078] In the above embodiment, the single-width flow rate and the single-width sediment replenishment rate are the inflow condition and the inflow sediment condition.

[0079] In a specific embodiment, the roughness is calculated by the following formula:

[0080]

[0081] Where: D is the sediment particle size.

[0082] S4: According to the riverbed siltation height balance value and the siltation range balance value, combined with the calculation expression of the characteristic variable, the riverbed siltation height and the siltation range of the target river channel are calculated.

[0083] In this step, the riverbed sedimentation height equilibrium value shown in formula (6) is substituted into formula (2) or formula (4) to obtain the final prediction calculation formula of the riverbed sedimentation height, namely:

[0084]

[0085] Where: K Z 、a Z and b Z It is the coefficient used to calculate the riverbed sedimentation height.

[0086] In the above embodiment, the present invention predicts the riverbed siltation height at the sediment supply location. In a specific embodiment, combined with the longitudinal profile of the riverbed siltation body, the riverbed siltation height at any section downstream of the river can be calculated by the following formula:

[0087]

[0088] Where: Z bx Z is the riverbed siltation height at any section of the downstream river; b,x＝0 is the riverbed siltation height at the sediment recharge point; x is the distance from any section downstream of the river to the sediment recharge point; L is the sedimentation range.

[0089] Substituting the sediment accumulation range balance value shown in formula (7) into formula (3) or formula (5) can obtain the final prediction calculation formula of the sediment accumulation range, namely:

[0090]

[0091] Where: K L 、a L and b L It is the coefficient used to calculate the range of silt deposition.

[0092] In a specific embodiment, the method for predicting the riverbed siltation height and siltation range after the change of sediment supply described in the present invention is used to predict the riverbed siltation height of a simulated river channel (water tank), which specifically includes the following steps:

[0093] The relevant parameters β of equations (13) and (14) are obtained by water tank test. Z , K Z 、a Z and b Z , specifically including the following sub-steps:

[0094] Prepare a test tank, silt and water. The test tank is 10.0m long, 0.6m wide and 0.8m high. The silt is uniform silt with a particle size of 3.6mm and a density of 2650kg / m 3 ; The density of the water is 1000kg / m3 The bed sand is laid from 1.0m away from the entrance of the water tank to the end of the water tank. The initial laying thickness is 0.2m and the initial laying slope of the bed surface is S b0 =0.5.

[0095] Conducting a water tank test is divided into three stages:

[0096] (i) Initial stage. In this stage, the sediment is replenished for a long enough time according to the sediment transport capacity of the water flow so that the riverbed reaches a balanced state. The duration of this stage is 180 minutes.

[0097] (II) Sediment replenishment stage. In this stage, sediment replenishment is carried out according to the test conditions. The river channel undergoes a significant riverbed scouring and silting evolution process accompanied by large-scale sediment transport. This stage lasts for 100 minutes.

[0098] (III) Continuous scouring stage. In this stage, the upstream stops the sediment supply, but the water flow continues. As the sediment is continuously transported out of the flume, the river channel is continuously scoured, and finally a new stable riverbed morphology is formed. This stage lasts for about 320 minutes.

[0099] All experiments were conducted under constant flow conditions, and the sediment recharge included one constant sediment recharge and three step-type sediment recharges, e.g. Figure 1 A total of three groups of experiments were carried out, and the test profile is shown in Table 1:

[0100] Table 1 Summary of experimental parameters of riverbed response under changing sediment supply

[0101]

[0102] In Table 1: Q is the flow rate; H0 is the initial water depth; U0 is the initial average flow velocity; U c is the initial sediment starting critical velocity; U0 / U c is the water flow intensity; q bf,low for Figure 1 The minimum single-width sediment recharge rate of the step-type sediment recharge shown; q bf,peak for Figure 1 The maximum single-width sediment recharge rate of the step-type sediment recharge shown; T r for Figure 1 The time from the beginning to the peak of the step-type sediment recharge rate shown; T f for Figure 1 The time from the peak to the end of the step-type sediment replenishment rate shown; M bf is the total amount of sediment supply.

[0103] The relative water flow intensities of the three groups of embodiments are 0.82, 0.98 and 1.16 respectively. Each group of embodiments is provided with one group of constant sediment supply and three groups of step-type variable sediment supply. The test results are shown in FIG. Figure 2 As shown. Figure 2 It can be seen that the riverbed sediment deposit presents a wedge-shaped sedimentation shape, and the longitudinal section is approximately triangular. The relevant parameter β is determined by multivariate linear regression analysis based on the measured experimental data. Z =2.23, K Z =367.02, a Z =-1.1, b Z =0.66.

[0104] According to the results of the relevant parameters and the parameters of the target river channel, the riverbed siltation height at the location of the simulated river channel sediment recharge point is predicted by equations (13)-(14). The results are as follows: Figure 3 shown.

[0105] In another specific embodiment, the method for predicting the riverbed siltation height and siltation range after the change of silt supply described in the present invention is used to predict the siltation range of a simulated river channel (water tank). In this embodiment, similar to the above embodiment, the relevant parameters β of formula (15)-formula (16) are obtained through the water tank test L , K L 、a L and b L , the result is β L =1.35, K L =1.5105, a L =-2.48, b L =1.12. Based on the results of the related parameters and the parameters of the target river, the siltation range of the target river is predicted by equations (15)-(16). The results are as follows: Figure 4 shown.

[0106] In summary, the present invention can accurately predict the riverbed sedimentation height and sedimentation range after the sediment supply changes. Compared with the prior art, the present invention has significant progress.

[0107] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for predicting the riverbed sedimentation height and sedimentation range after sediment supply changes, characterized in that: The following steps are involved: S1: The rate equation is used to describe the dynamic adjustment process of the channel characteristic variables under the change of sediment supply, and the channel characteristic variables include the riverbed siltation height and the sedimentation range; S2: solving the rate of change equation to obtain a calculation expression for the characteristic variable; S3: Determine the riverbed sedimentation height balance value and sedimentation range balance value at the sediment recharge point location according to the inflow conditions and sediment inflow conditions of the target river channel; S4: According to the riverbed siltation height balance value and the siltation range balance value, combined with the calculation expression of the characteristic variable, the riverbed siltation height and the siltation range of the target river channel are calculated.

2. The method for predicting riverbed siltation height and siltation range after sediment replenishment changes according to claim 1, characterized in that: In step S1, the rate of change equation is: Where: dy / dt is the adjustment rate of the river channel characteristic variable; y is the river channel characteristic variable; t is time; β is the adjustment rate coefficient of the river channel characteristic variable; y e is the equilibrium value of the river channel characteristic variables.

3. The method for predicting riverbed siltation height and siltation range after sediment replenishment changes according to claim 2, characterized in that: In step S2, the calculation expression of the characteristic variable is the calculation expression of mode 1 or the calculation expression of mode 2, the initial value of the characteristic variable in mode 1 is the measured value of the characteristic variable at the end of the previous period, and the initial value of the characteristic variable in mode 2 is the calculated value of the characteristic variable at the end of the previous period; The calculation expression of the mode is: Where: ΔZ b,i is the riverbed sedimentation height at the end of the i-th period; β Z is the adjustment rate coefficient of the riverbed sedimentation height; Δt is the calculation step length; ΔZ b,ei is the equilibrium value of riverbed sedimentation height at the end of the i-th period; ΔZ b,i-1 is the riverbed sedimentation height at the end of the i-1th period; L i is the sedimentation range at the end of the i-th period; β L is the adjustment rate coefficient of the sediment deposition range; L ei is the sedimentation range equilibrium value at the end of the i-th period; L i-1 is the sedimentation range at the end of the i-1th period; The calculation expression under the second mode is: Where: ΔZ b,n is the riverbed sedimentation height at the end of the nth period; n is the total number of calculation steps; ΔZ b,0 is the riverbed siltation height at the initial moment; L n is the sedimentation range at the end of the nth period; L0 is the sedimentation range at the initial moment.

4. The method for predicting riverbed siltation height and siltation range after sediment replenishment changes according to claim 3, characterized in that: In step S3, the riverbed siltation height balance value and the siltation range balance value are calculated by the following formulae respectively: Where: ΔZ be * is the dimensionless riverbed sedimentation height equilibrium value; k, a and b are coefficients; is the dimensionless single-width flow rate; is the dimensionless single-width sediment replenishment rate; S be S is the balanced slope of the riverbed; b0 is the initial slope of the riverbed.

5. The method for predicting riverbed siltation height and siltation range after sediment replenishment changes according to claim 4, characterized in that: The dimensionless single width flow is calculated by the following formula: Where: q w is the single-width flow rate; g is the acceleration due to gravity; D 84 It is the particle size corresponding to when the cumulative frequency distribution percentage of sediment reaches 84%; The dimensionless single-width sediment replenishment rate is calculated by the following formula: Where: q bf is the sediment replenishment rate per unit width; ρ s is the density of sediment; ρ is the density of water; D 50 is the median particle size of sediment; The riverbed equilibrium slope is calculated by the following formula: Where: m is the roughness; is the dimensionless sediment transport rate. When the river channel is in equilibrium, is the dimensionless critical starting shear stress; q w For single-width traffic.

6. The method for predicting riverbed siltation height and siltation range after sediment replenishment changes according to claim 5, characterized in that: The roughness is calculated by the following formula: Where: D is the sediment particle size.

7. The method for predicting riverbed sedimentation height and sedimentation range after sediment replenishment changes according to claim 3, characterized in that: The riverbed siltation height at any section downstream of the river is calculated by the following formula: Where: Z bx Z is the riverbed siltation height at any section of the downstream river; b,x＝0 is the riverbed siltation height at the sediment recharge point; x is the distance from any section downstream of the river to the sediment recharge point; L is the sedimentation range.

Images