Method and system for determining flow of plain river channel based on water and sediment process

Abstract

The application discloses a plain river channel shaping flow determination method and system based on water and sediment process, comprising: obtaining water and sediment sequence representing hydrological station, determining annual periodicity and flood and dry season difference of water and sediment process through autocorrelation analysis, and determining flood and dry season junction flow according to the same; determining critical flow of the worst flow process stability and critical flow of the worst sediment transport rate process stability based on variation characteristics of relative standard deviation of flow sequence and sediment transport rate sequence with flow level respectively; comprehensively determining channel shaping flow and checking by combining flood and dry season junction flow, critical flow of the worst flow process stability and critical flow of the worst sediment transport rate process stability; and finally determining channel shaping flow. The application can not only solve the technical problem that traditional Markov method cannot obtain dry water bed forming flow, but also quantitatively determine shoal regulation water level according to water and sediment observation data of the hydrological station under the condition of missing side beach.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and waterway engineering technology, and in particular relates to a method and system for determining the flow rate of a channel in a plain river based on water and sediment processes. Background Technology

[0002] Shallows are a key target for waterway improvement in plain rivers. Shallows improvement requires the use of structures of a certain height to regulate water flow and increase the scouring force during the post-flood recession period, thereby increasing the water depth during the dry season. According to relevant specifications, the elevation of shallows improvement structures needs to be determined using the channel shaping flow rate or the shallows improvement water level; these are crucial parameters in waterway improvement engineering design. If these parameters are set too high, the project cost will increase exponentially, and the increased flood level will negatively impact flood control; if they are set too low, the project will fail to effectively increase the channel depth.

[0003] In quasi-equilibrium rivers with stable level-discharge relationships, channel shaping flow and shoal regulation water level are equivalent. In engineering practice, the channel shaping flow can be determined first, and then the shoal regulation water level can be determined based on the channel shaping flow. Alternatively, the shoal regulation water level can be directly determined by referring to the shoal elevation of favorable river sections and using empirical methods. However, both methods have some limitations in engineering applications: First, the channel shaping flow is theoretically considered equivalent to the low-water bed-forming flow, but the low-water bed-forming flow itself lacks a method for determination. For example, the traditional Makaveev method can only obtain the flood bed-forming flow on many rivers, but not the low-water bed-forming flow, making it difficult to quantify the channel shaping flow. Second, many shoal sections lack obvious shoals or have incompletely developed shoals, making it difficult to determine the shoal regulation water level using shoal elevation. These technical deficiencies bring many difficulties to waterway regulation engineering practice, necessitating the development of more objective and operational new methods.

[0004] On the other hand, with the construction of large reservoirs upstream of more and more rivers, the river's water and sediment processes are being artificially regulated. This not only disrupts the adaptability between the bank elevation and the water and sediment processes, but also makes the water level-discharge relationship unstable. The empirical methods for determining the water level in shallow river regulation, originally applicable to naturally balanced rivers, are no longer usable. Under these circumstances, there is an urgent need to propose a new method that can determine the channel shaping flow based on the new water and sediment processes downstream of the dam. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to propose a method for determining the channel shaping flow rate in plain rivers based on water and sediment processes. This method takes the self-adjusting and self-adapting relationship between alluvial channels and water and sediment processes as its starting point. It utilizes long-term series of flow, sediment concentration, and water level observation data from hydrological stations to identify the critical flow rate at which flood and dry seasons transition into channel shaping effects from the statistical characteristics of the water and sediment processes. This characteristic flow rate is used as the channel shaping flow rate, and the shallow water level is determined based on this. This method is applicable to both balanced and non-balanced rivers, and its advantages include readily available data, simple application, high reliability, and ease of promotion.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for determining the channel shaping flow of plain rivers based on water and sediment processes includes the following steps: Obtain water and sediment sequences representing hydrological stations, determine the annual periodicity and flood-dry difference of the water and sediment inflow process, and determine the flood-dry boundary flow accordingly. Based on the variation characteristics of the relative standard deviation of the flow series amplitude with the flow level, the flow level with the worst stability of the flow process is determined; Based on the variation characteristics of the relative standard deviation of the sediment transport rate sequence with the flow level, the flow level with the worst stability of the sediment transport rate process is determined. The channel shaping flow rate is determined by combining the flood-dry transition flow rate, the flow rate level with the worst flow process stability, and the flow rate level with the worst sediment transport rate stability. By utilizing the relationship between the topography and water level-discharge of the target river section, and based on the inflection point flow of the river width-water depth relationship curve, the channel shaping flow is checked to determine the final channel shaping flow.

[0007] Furthermore, the steps for determining the annual periodicity and flood-dry season differences of the water and sediment inflow process include: Hydrological stations with tributary confluence or diversion ratios not exceeding 1% between the target river section and the tributary confluence or diversion ratio were selected as representative hydrological stations. Collect the daily average flow, sediment concentration, or sediment transport rate observation data of the representative hydrological stations over several consecutive years to obtain flow sequence and sediment transport rate sequence; Autocorrelation analysis was performed on the flow rate series and sediment transport rate series respectively, and the autocorrelation coefficients were calculated for successive lags on a daily basis. Plot the relationship curve between lag days and autocorrelation coefficient. If the curve shows an annual periodicity of first decreasing and then increasing, and the lag days corresponding to the minimum autocorrelation coefficient are within the range of 182±10 days and the minimum autocorrelation coefficient is less than 0, then it is determined to have annual periodicity and flood-dry season differences.

[0008] Furthermore, the step of determining the flow rate at the boundary between flood and dry seasons includes: For the lag days and autocorrelation coefficient curve of the flow series, calculate the rate of change of each point on the autocorrelation coefficient curve, and take the lag days corresponding to the minimum rate of change as the characteristic lag days. Calculate the multi-year average daily flow series of representative hydrological stations and plot the process line of daily flow change throughout the year; The flow rate corresponding to the characteristic lag days is retrieved from the process line and used as the flow rate at the boundary between flood and dry seasons.

[0009] Furthermore, the step of determining the flow level with the worst flow process stability based on the relative standard deviation of the flow series amplitude includes: Using a fixed number of days as the time window, the long series of daily flow patterns are divided into multiple consecutive time periods on average; Calculate the average flow rate and the standard deviation of flow rate variation for each time period; Taking the average flow rate of each time period as the object, several flow rate intervals are divided between the minimum flow rate and the maximum flow rate. The number of occurrences of average flow rate in each flow rate interval is counted, and the representative flow rate, average amplitude standard deviation, and relative standard deviation of flow amplitude for each flow rate interval are calculated. Plot the curve showing the relationship between the relative standard deviation of the flow rate variation and the representative flow rate. Take the flow rate corresponding to the turning point where the curve changes from an upward trend to a stable or downward trend as the flow rate level with the worst flow process stability.

[0010] Furthermore, the step of determining the flow level with the worst stability in the sediment transport rate process based on the relative standard deviation of the amplitude of the sediment transport rate sequence includes: Using the same fixed-day time window as the flow series, the long series of daily sediment transport rate sequences are divided into multiple consecutive time periods; the average sediment transport rate and the standard deviation of sediment transport rate variation within each time period are calculated. According to the same flow level interval as the flow sequence, the average sediment transport rate, the standard deviation of the average sediment transport rate range, and the relative standard deviation of the sediment transport rate range are statistically analyzed within each flow level interval. Plot the relationship curve between the relative standard deviation of the sediment transport rate and the representative flow rate. Take the flow rate corresponding to the turning point where the relative standard deviation of the sediment transport rate changes from an upward trend to a stable or downward trend as the flow rate level with the worst stability of the sediment transport rate process.

[0011] Furthermore, the step of comprehensively determining the channel shaping flow rate includes: The same relative fluctuation range is assigned to the flow rate at the boundary between flood and dry seasons, the flow rate level with the worst flow process stability, and the flow rate level with the worst sediment transport rate stability, thereby expanding the three flow rates into three flow variation ranges. If the three flow variation intervals have a common overlapping interval, the average flow of the overlapping interval is taken as the channel shaping flow. If there are two overlapping intervals, the average flow of the overlapping interval on the side with the smaller flow is taken as the channel shaping flow.

[0012] Furthermore, the verification step includes: Within the target river section, select several characteristic cross-sections with side beaches or mid-river beaches, and determine the distance of each characteristic cross-section from the representative hydrological station; Multiple representative flow levels were selected at equal intervals between the minimum and maximum flow rates over the years. The water level of the representative hydrological station at each representative flow level was calculated. Combined with the average gradient of the river section and the distance of each characteristic section from the representative hydrological station, the corresponding water level of each characteristic section at each flow level was estimated. Based on the measured topography of each cross section, calculate the average water depth and river width of each characteristic cross section under each flow level; The average water depth and river width of all cross sections under the same flow level are taken to obtain the average water depth and average river width of the river section under each representative flow level.

[0013] Furthermore, the verification step also includes: Plot the relationship between the average river width and the average water depth of the river section under each representative flow level. Take the inflection point flow when the river width first increases continuously while the water depth remains basically unchanged as the critical flow for flooding of the low-lying shoals.

[0014] Furthermore, the verification step also includes: Compare the critical flow rate for flooding the low shoal with the channel shaping flow rate. If the difference between the two is within a reasonable range of the channel shaping flow rate, the channel shaping flow rate is determined to be reasonable and is set as the final channel shaping flow rate. Otherwise, the channel shaping flow rate is determined to be unreasonable, and the calculation or parameters need to be readjusted or reselected.

[0015] On the other hand, the present invention provides a system for determining the flow rate of a channel shaping in a plain river based on water and sediment processes, comprising: The flood-dry season boundary flow determination module is used to obtain the water and sediment sequence of representative hydrological stations, determine the annual periodicity and flood-dry season differences of the water and sediment inflow process, and determine the flood-dry season boundary flow accordingly. The module for determining the flow level with the worst flow process stability is used to determine the flow level with the worst flow process stability based on the variation characteristics of the relative standard deviation of the flow sequence amplitude with the flow level. The module for determining the flow level with the worst stability in the sediment transport rate process is used to determine the flow level with the worst stability in the sediment transport rate process based on the variation characteristics of the relative standard deviation of the flow sediment transport rate sequence with the flow level. The channel shaping flow integration module is used to determine the channel shaping flow by integrating the flood-dry season boundary flow, the flow level with the worst flow process stability, and the flow level with the worst sediment transport rate stability. The channel shaping flow verification module is used to verify the channel shaping flow by utilizing the topography and water level-flow relationship of the target river section and the inflection point flow of the river width-water depth relationship curve, so as to determine the final channel shaping flow.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes a method for determining the channel shaping flow of plain rivers based on hydrological data. Specifically, during the scour-deposition equilibrium period of the target river section, the annual periodicity and flood-dry season differences of the water and sediment process are identified through autocorrelation analysis using long-series daily average flow and daily average sediment transport rate observation data from hydrological stations. Based on this, the relationship between the autocorrelation coefficient and the time series lag time is established, and the feature point with the largest rate of change of the autocorrelation coefficient is extracted and mapped to the multi-year average flow process line to obtain the critical flow for the transition between flood and dry seasons. Furthermore, a segmented statistical method for the time series is used to calculate the relative standard deviation of the flow amplitude and the relative standard deviation of the sediment transport rate within a fixed time period. From the two dimensions of runoff fluctuation intensity and sediment transport fluctuation intensity under different flow levels, the characteristic flow levels with the most unstable water and sediment transport, the most drastic river channel adjustments, and the most frequent mainstream oscillations are identified. Finally, by combining the results of the flow indicators from multiple perspectives, the channel shaping flow and the shoal regulation water level are determined. Simultaneously, for rivers in a quasi-equilibrium state, the rationality of the flow is verified through river width-depth curves, combined with measured topographic data of the river section. This method not only solves the technical problem of obtaining low-water bed-forming flow rates in the traditional Makaveev method, but also quantitatively determines the shoal regulation water level based on hydrological station data when side shoals are missing. This method is also applicable to non-equilibrium rivers where water and sediment processes are regulated after the construction of upstream reservoirs. This method overcomes the limitations of traditional empirical methods, offering advantages such as clear physical meaning, simple operation, low cost, and high efficiency. Furthermore, multiple indicators corroborate each other, resulting in objective and reliable results, providing a new technical tool for the design of waterway regulation projects in plain rivers. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 is a graph showing the autocorrelation coefficients of the flow rate sequence and sediment transport rate sequence in an embodiment of the present invention; Figure 2 shows the multi-year average flow rate process curve and the autocorrelation coefficient derivative curve in an embodiment of the present invention; Figure 3 is a graph showing the relationship between flow rate and the relative standard deviation of flow rate variation in an embodiment of the present invention. Figure 4 is a graph showing the relative standard deviation of the flow rate versus sediment transport rate in an embodiment of the present invention. Figure 5 is a diagram of overlapping traffic intervals in an embodiment of the present invention; Figure 6 shows the location of each feature section in an embodiment of the present invention; Figure 7 is a curve showing the relationship between the average river width and average water depth of the target river section in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] Example 1 like Figure 1 As shown in the figure, this embodiment provides a method for determining the channel shaping flow of plain rivers based on water and sediment processes, including the following steps: Step 1: Obtain the water and sediment sequence representing the hydrological station, determine the annual periodicity and flood-dry season differences of the water and sediment inflow process, and determine the flood-dry season boundary discharge accordingly; including the following sub-steps: Step 1.1 For the target river section, select a representative hydrological station upstream or downstream. A representative hydrological station is one where there are no large tributaries converging or branching off between the station and the target river section; "large" refers to a branching or confluence ratio exceeding 1%. Collect data from the representative hydrological station. a ( a Hydrological observation data for ≥11 years, including average daily flow. Q and sand content S (or sediment transport rate) QS ) Observational data; if there are large reservoirs or other man-made projects built upstream of this river section, the selected area should be avoided. a The annual timeframe spans the period before and after project construction to ensure the consistency of the hydrological sequence; Step 1.2 Targeting representative hydrological stations a Using annual average daily flow and average daily sediment transport rate data, autocorrelation analysis was performed on the flow and sediment transport rate series using the autocorrelation function, and the lag of the flow and sediment transport rate series was calculated. b autocorrelation coefficient of days r b (b =1,2,...,365), where the average daily sediment transport rate is... QS = Q · S ; Step 1.3 Plot the two hydrological series on the coordinate plane with the lag days as the horizontal axis and the autocorrelation coefficient as the vertical axis. b ~ r b Relationship curve graph, if the curve is on The value exhibits an annual cyclical characteristic of first decreasing and then increasing, and Minimum value corresponding to b The value is within the range of 182 ± 10 days, and If the difference is significant, it indicates that the water and sediment inflow during the flood and dry seasons are significant, and subsequent operations can continue. Conversely, if the difference is not significant, it indicates that the water and sediment inflow process of the target river section does not have an annual periodicity and a difference between the flood and dry seasons, and this method is not applicable. Step 1.4 For the flow sequence b ~ r b Relationship curve, calculate the slope at each point on the curve. (in This represents the difference between the autocorrelation coefficients of the two points before and after the point; Set it to 1; i =2~365), drawing The minimum slope of the curve. The corresponding number of lag days is denoted as b min ; Step 1.5 Calculate and construct the multi-year average daily flow series for representative hydrological stations. ( i =1~365), sorted by the number of days in the year. i Plot the graph with the horizontal axis representing flow rate and the vertical axis representing volume. The timing process line diagram can be retrieved from this process line. b min The corresponding flow rate is the flow rate at the boundary between flood and dry seasons, denoted as Q c1 .

[0021] Step 2: Based on the variation characteristics of the relative standard deviation of the flow rate series with the flow rate level, determine the flow rate level with the worst stability of the flow process; including the following sub-steps: Step 2.1 Taking the daily average flow process of the representative hydrological station series as the object, the time window is set as... t day( t It can be a fixed value of 7 or 15, depending on the size of the river. t The larger the value, the better (in each case). t Each day is a segment, with a total length of 365.a Hydrological sequences are divided into y Segment; for each time period, calculate the segment within the segment. t Daily average flow Based on this, the standard deviation of the flow rate variation within each time period is calculated. ( o =1~ y ); Step 2.2 Calculate the average flow rate over each time period. ( o =1~ y ) as the object, at maximum flow and minimum flow Divide between m Each traffic interval is statistically analyzed, and the data belonging to each traffic interval is... ( o =1~ y The number of data points is denoted as . N j ( j =1~ m ); Step 2.3 Targeting m For each flow interval, calculate the representative flow for that interval and denot it as . ( j =1~ m ), calculate the standard deviation of the average flow rate variation within each flow range. Based on this, the relative standard deviation of flow rate variation within each flow range is calculated. ,in For the first j The sum of the standard deviations of all flow rate variations within a flow range; Step 2.4 Using flow rate The horizontal axis represents the relative standard deviation of flow rate variation. Plot on the coordinate plane with the vertical axis as the ordinate. The relationship curve shows a trend of first increasing and then stabilizing or decreasing. The inflection point where the trend changes from increasing to stabilizing (or decreasing) corresponds to the flow level with the worst flow process stability, and is denoted as... Q c2 .

[0022] Step 3: Based on the variation characteristics of the relative standard deviation of the sediment transport rate sequence with flow rate level, determine the flow rate level with the worst stability of the sediment transport rate process; including the following sub-steps: Step 3.1 Using the average daily sediment transport rate of the representative hydrological station series as the object, and following the same segmented time length as in Step 2.1. t The total length is 365 a The sediment transport rate sequence is divided into ySegment, calculate the average sediment transport rate within each time period. ( o =1~ y ) and standard deviation of sediment transport rate ; Step 3.2 Following the steps determined in Step 2.2 m For each flow interval, calculate the average sediment transport rate within that interval. ( j =1~ m ), standard deviation of average sediment transport rate and the relative standard deviation of sediment transport rate ; Step 3.3 Using traffic The horizontal axis represents the relative standard deviation of the sediment transport rate. Plot on the coordinate plane with the vertical axis as the ordinate. The relationship curve shows a trend of first increasing and then stabilizing or decreasing. The inflection point where the trend changes from increasing to stabilizing (or decreasing) corresponds to the flow rate level with the worst stability in the sediment transport process, denoted as . Q c3 .

[0023] Step 4: Determine the channel shaping flow rate by combining the flood-dry season boundary flow rate, the flow rate level with the worst flow process stability, and the flow rate level with the worst sediment transport rate stability; this includes the following sub-steps: Step 4.1 Calculate the results from steps 1, 2, and 3. Q c1 , Q c2 and Q c3 Each of the three flow rates is given a certain margin of ±0.1 times to reflect possible statistical errors in the calculation process, thereby converting the three flow rate values ​​into three flow rate amplitudes [0.9]. Q c1 1.1 Q c1 ]、[0.9 Q c2 1.1 Q c2 ] and [0.9 Q c3 1.1 Q c3 ]; Step 4.2 Observe the overlapping areas of the three flow rate variations. If there is a common overlapping interval among the three, take the average flow rate of the overlapping area as the target channel shaping flow rate. Q cIf there are two overlapping areas, the average flow rate within the overlapping interval on the side with the smaller flow rate should be taken as the target channel shaping flow rate for the river section. Q c ; Step 4.3 For representative hydrological stations in the target river section, use... a Annual average daily flow and water level observation data were used to fit a water level-flow function relationship in polynomial form. Q c Find the corresponding water level on the curve. Z c This refers to the water level at the shallow water level near the hydrological station.

[0024] Step 5: Utilizing the topography and water level-discharge relationship of the target river section, and based on the inflection point discharge of the river width-water depth relationship curve, verify the channel shaping discharge to determine the final channel shaping discharge; this includes the following sub-steps: Step 5.1 Collect measured topographic observation data within the target river section and select... G Each characteristic cross-section should be located within an area with side bars or mid-channel bars. The distance of each characteristic cross-section from a representative hydrological station should be determined. S k ( k =1~ G ); Step 5.2 Based on the representative hydrological station of the target river section a Annual flow data, selected at equal intervals between the historical maximum and minimum flows. n indivual( n ≥10) represents the flow rate level ( l =1~ n ), respectively n Substituting each representative flow level into the hydrological station's level-flow function relationship, the water level at each representative flow level is calculated. ( l =1~ n ); Step 5.3 Based on the average gradient within the target river section J and distance S k The corresponding water levels at each characteristic cross-section under representative flow rates were calculated. ( k =1~ G , l =1~ n Then, by combining the water level at each cross-section with the measured topography, the average water depth at each characteristic cross-section under each flow rate is calculated. and the width of the river at each characteristic cross-section ( k =1~ G ,l =1~ n ); Step 5.4 Taking the river width and average water depth of each characteristic cross-section under different flow levels as the object, the arithmetic mean is taken to obtain the average river width of the river segment under each flow level. with average water depth of the river section ( l =1~ n Step 5.5: Plot the average river width of the river section under each flow level on the coordinate plane as the horizontal axis and the average water depth of the river section as the vertical axis. B ~ H A line graph, the first appearance of a line graph. B While increasing H The essentially constant inflection point flow is the critical flow for flooding of the low-lying shoals. Q d ,contrast Q d With the shaping of flow in the channel Q c If the absolute value of the difference between the two is 15% Q c Within this range, it indicates the flow rate of the channel shaping. Q c Reasonable.

[0025] Preferably, in step 1.1, since there are leap years and common years, February has 28 days in a common year and 29 days in a leap year, for ease of statistics, the hydrological data for February 28th and 29th are taken as an arithmetic mean in leap years. a Hydrological data for 365 years, with a sequence length of 365. a Meanwhile, in order to ensure the consistency of the hydrological series, the double cumulative curve method can be used to check whether there are trend change points in the series to judge the consistency. The basic idea is to continuously accumulate the hydrological series and transform the discrete and highly fluctuating original data into a relatively smooth cumulative curve. If the cumulative curve is linear and the slope is stable, it indicates that the hydrological series is consistent. If the slope of the cumulative curve shows segmented differences, it usually indicates that the water-sediment relationship has changed trend. At this time, the hydrological series should be reselected.

[0026] Preferably, in step 1.2, the time series of long-term daily average flow or daily average sediment transport rate data is set as follows: X d (d=1,2,...,365) a ), its lag b Natural correlation coefficient r b The calculation formula is:

[0027] In the formula, The sample mean. b Lag days ( b =1,…,365); Lagging b Time series of daily average flow or daily average sediment transport rate data.

[0028] Preferably, in step 1.3, whether the hydrological sequence has annual periodicity and whether there are significant differences between the flood and dry seasons can be determined by... b ~ r b The following characteristics are characteristic of the relationship curve: (1) r 365 When the value is ≥0.5, the hydrological series is considered to have obvious annual periodicity; (2) if the autocorrelation coefficient of the hydrological series has the characteristic of first decreasing and then increasing, the minimum value is... The corresponding lag days are in the range of 182 ± 10 days, and It can be assumed that the hydrological sequence has obvious differences between flood and dry seasons.

[0029] Preferably, in step 1.4, due to the annual periodicity and flood-dry season differences in the flow sequence, its autocorrelation coefficient... r b With lag time b The correlation coefficient exhibits a non-monotonic change characteristic, first decreasing and then increasing. The decreasing process corresponds to the transition from the dry season to the flood season in the first half of the year, while the point where the correlation coefficient decreases most rapidly corresponds to the critical flow transition from the dry season to the flood season. This invention calculates the first derivative... We extract the point where the correlation coefficient decreases the most and use that point to determine the critical flow rate at the end of the dry season.

[0030] Preferably, in step 1.5, the multi-year average daily flow rate Calculate using the following formula:

[0031] In the formula, a For the total number of years in the traffic series, For the first p Year i Daily traffic.

[0032] Preferably, in step 2.1, a time period length is introduced to examine the continuous stability of the flow rate over a certain period of time. t Divide the total duration into y part, That is, the tail of the flow sequence is insufficient. t Data from day one was discarded; for day two... o Time period ( o =1~ y Average flow and standard deviation of flow rate Calculate using the following formulas respectively:

[0033]

[0034] In the formula, t The length of a period is measured in days. The first in the original flow sequence o Within the time period, the first k Daily average traffic volume Characterizing the first o The intensity of runoff fluctuations within a given time period.

[0035] Preferably, in step 2.2, the specific process for dividing the flow range is as follows: A logarithmic equal-interval grading method is adopted, and the first... j left endpoint of the interval ( j =1~ m ) is calculated using the following formula:

[0036] The interval represents the flow rate. It is obtained by the geometric mean of the values ​​at the left and right endpoints of the interval. Calculated by the following formula:

[0037] in, and These represent the minimum and maximum average flow rates within each time period.

[0038] Preferably, in step 3.1, for the first o Time period ( o =1~ y Average sediment transport rate and standard deviation of sediment transport rate Calculate using the following formulas respectively:

[0039]

[0040] In the formula, t For the number of days in the time period, The first in the original sediment transport rate sequence o Within the time period, the first k The average daily sediment transport rate per day Characterizing the first o The intensity of fluctuations in the sediment transport process within a given time period.

[0041] Preferably, in step 3.2, for the first j Average sediment transport rate within each flow range QS j Standard deviation of average sediment transport rate and relative standard deviation Calculated by the following formula:

[0042]

[0043]

[0044] The summation in the formula represents the summation of the first... j Summing a variable within a flow range, for example For the first j The sum of the standard deviations of all sediment transport rate variations within a given flow range.

[0045] The hydrological observation data used in this embodiment are the daily average flow and daily average sediment transport rate data from a hydrological station near a certain river section, spanning 17 years from January 1, 1986 to December 31, 2002. During this period, the river section was in a state of scour-deposition equilibrium. The topographic data used is the cross-sectional topographic data of this river section in 2002. Specifically, the following steps are included: Determining the annual periodicity of water and sediment processes in the S1 river section, the difference between flood and dry seasons, and the determination of the boundary flow between flood and dry seasons. First, using measured flow and sediment concentration data from hydrological stations over 17 consecutive years, the daily average sediment transport rate was calculated in Excel. Then, the autocorrelation coefficients of the flow and sediment transport rate sequences under different lag days were calculated using the autocorrelation function. Figure 1 As shown in the figure, with the increase of the lag days, the autocorrelation coefficients of each series show a pattern of first decreasing and then rebounding, with a significant peak at 365 days. 365 The values ​​are above 0.6. This indicates that all sequences exhibit a clear annual cycle, and the minimum value at 180 days is negative, suggesting significant differences in the hydrological characteristics of the dry and flood seasons for each sequence. To further analyze the differences in the dry and flood season characteristics of the sequences, [further analysis is needed]. Figure 1 The series corresponding to the period of minimum autocorrelation coefficient (July 2, 1986 to December 31, 2002) was reconstructed, and the autocorrelation coefficients of the flow and sediment transport series with the same lag days were calculated. As shown in the figure, each series still exhibits a stable annual cycle, showing a periodic structure of initial decline followed by recovery. This characteristic further reflects the significant differences in hydrological characteristics between the flood and dry seasons. Therefore, further steps can be taken.

[0046] Calculate the derivative value corresponding to each lag day within the annual cycle. ( i=2~365), based on the number of days of lag. Using as the independent variable, we obtain Data pair; Calculate the average daily flow over many years ( i =1~365), obtained Data pairs. Within the same graph, respectively using... and Plot the primary and secondary ordinate axes. Process line and Process line as Figure 2 As shown, positioning Q c1 16500m 3 / s.

[0047] Calculation of the relative standard deviation of S2 flow rate variation In this embodiment, the statistical period is set at 15 days, dividing the total hydrological sequence of 6209 into 413 time periods. The average flow and standard deviation of flow variation within each time period are calculated. Based on this, 40 flow levels are defined between the maximum and minimum flow, and the relative standard deviation of flow variation for each flow level is calculated. A semi-logarithmic coordinate system is used to plot the data with flow as the horizontal axis and relative standard deviation of flow variation as the vertical axis. Curve graph as Figure 3 As shown. By Figure 3 It can be seen that the relative standard deviation exhibits a significant nonlinear characteristic with flow rate variation. In the low flow range, the relative standard deviation is generally small, indicating that the runoff process during the dry season is mainly controlled by baseflow, with limited fluctuations and relatively stable flow. As the flow rate increases, the relative standard deviation gradually rises, reaching a maximum value in a certain mid-dry flow range, corresponding to a flow rate of 15000 m³ / h. 3 / s. This indicates that when the flow rate is 15000m³ / s. 3 After a flow rate of approximately / s, the inflow process becomes difficult to maintain a stable state, and large fluctuations are prone to occur, leading to frequent swings in the main flow and making it difficult for the floodplains in the low-flow channel to continue to silt up. When the flow rate continues to increase to the level of flood flow, the relative standard deviation shows a decreasing trend, indicating that under high flow conditions, the relative fluctuation of runoff is weakened. This leads to the determination... Q c2 15000m 3 Approximately / s.

[0048] Calculation of the relative standard deviation of S3 sediment transport rate variation Based on S2, the relative standard deviation of sediment transport rate variation for each flow rate stage was calculated. A semi-logarithmic coordinate system was used to plot the data, with flow rate on the horizontal axis and relative standard deviation of sediment transport rate variation on the vertical axis. Curve graph as Figure 4 As shown. By Figure 4It can be seen that the relative standard deviation of sediment transport rate also exhibits phased characteristics with changes in flow rate. During periods of low flow, the sediment transport rate fluctuates less, indicating that the sediment transport rate is relatively stable during the dry season. The value increases rapidly in the mid-dry season and reaches 15000 m³. 3 The sediment transport rate reaches a relatively high value near 15000m / s, and then remains relatively high within a certain flow range until the fluctuation of sediment transport rate gradually decreases during the major flood season. Therefore, from the perspective of sediment transport, this is also evident at 15000m. 3 Significant fluctuations occur after / s, which will also make the beach area above this flow rate less stable. Therefore, it is determined that... Q c3 15000m 3 Approximately / s.

[0049] S4 determines the channel shaping flow rate. Q c Comparison of flow levels of various characteristics Q c1 , Q c2 and Q c3 Flow range such as Figure 5 As shown. By Figure 5 It can be seen that the overlapping range is 14850~16500m. 3 / s, in this embodiment, the average value is taken as 15675m. 3 / s represents the channel shaping flow rate for this section of the river. Q c .

[0050] Channel shaping flow verification for the target river section during the S5 scour-deposition balance period In this embodiment, 10 characteristic cross-sections were selected for the target river section. The locations of each selected characteristic cross-section are as follows: Figure 6 As shown. The measured minimum and maximum flow rates at the representative hydrological station between 1986 and 2002 were 7040 m³ / h. 3 / s and 84300m 3 Based on this, 30 flow rates are divided. After fitting the water level-flow relationship curves representing the hydrological stations, the average water depth and average river width of the river section under each flow rate are calculated according to steps 5.3 and 5.4. A coordinate plane is plotted with the river width at each flow rate as the horizontal axis and the water depth as the vertical axis. B ~ H Curve graph as Figure 7 As shown in the figure, the curve exhibits a "bench" shaped feature twice, namely... B While increasing H The flow rate remains essentially unchanged; these two processes correspond to the low-shoal inundation process and the high-shoal inundation process, respectively. The low-shoal inundation flow rate... Qd 14000m 3 / s, compared to the channel shaping flow rate in S4 Q c =15675m 3 The flow rate is basically the same as that of a channel in a plain river, which shows that the method for determining the flow rate of a channel based on the water-sediment process proposed in this invention is reasonable.

[0051] Example 2 This embodiment provides a system for determining the flow rate of a channel in a plain river based on water and sediment processes, including: The flood-dry season boundary flow determination module is used to obtain the water and sediment sequence of representative hydrological stations, determine the annual periodicity and flood-dry season differences of the water and sediment inflow process, and determine the flood-dry season boundary flow accordingly. The module for determining the flow level with the worst flow process stability is used to determine the flow level with the worst flow process stability based on the variation characteristics of the relative standard deviation of the flow sequence amplitude with the flow level. The module for determining the flow level with the worst stability in the sediment transport rate process is used to determine the flow level with the worst stability in the sediment transport rate process based on the variation characteristics of the relative standard deviation of the flow sediment transport rate sequence with the flow level. The channel shaping flow integration module is used to determine the channel shaping flow by integrating the flood-dry season boundary flow, the flow level with the worst flow process stability, and the flow level with the worst sediment transport rate stability. The channel shaping flow verification module is used to verify the channel shaping flow by utilizing the topography and water level-flow relationship of the target river section and the inflection point flow of the river width-water depth relationship curve, so as to determine the final channel shaping flow.

[0052] It should be understood that any parts not described in detail in this specification belong to the prior art.

[0053] It should be understood that the above description of the preferred embodiments is quite detailed, but this should not be construed as limiting the scope of protection of this invention. It is neither necessary nor possible to exhaustively describe all possible implementations. Those skilled in the art, guided by this invention, can make substitutions or modifications without departing from the scope of the claims, all of which fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for determining the channel shaping flow rate of plain rivers based on water and sediment processes, characterized in that, Includes the following steps: Obtain water and sediment sequences representing hydrological stations, determine the annual periodicity of water and sediment inflow processes and the difference between flood and dry seasons, and determine the boundary flow between flood and dry seasons accordingly; Based on the variation characteristics of the relative standard deviation of the flow series amplitude with the flow level, the flow level with the worst stability of the flow process is determined; Based on the variation characteristics of the relative standard deviation of the sediment transport rate sequence with the flow level, the flow level with the worst stability of the sediment transport rate process is determined. The channel shaping flow rate is determined by combining the flood-dry transition flow rate, the flow rate level with the worst flow process stability, and the flow rate level with the worst sediment transport rate stability. By utilizing the relationship between the topography and water level-discharge of the target river section, and based on the inflection point flow of the river width-water depth relationship curve, the channel shaping flow is checked to determine the final channel shaping flow.

2. The method for determining the channel shaping flow rate of a plain river based on water and sediment processes according to claim 1, characterized in that, The steps for determining the annual periodicity and the difference between flood and dry seasons in the process of water and sediment inflow include: Hydrological stations with tributary confluence or diversion ratios not exceeding 1% between the target river section and the tributary confluence or diversion ratio were selected as representative hydrological stations. Collect the daily average flow, sediment concentration, or sediment transport rate observation data of the representative hydrological stations over several consecutive years to obtain flow sequence and sediment transport rate sequence; Autocorrelation analysis was performed on the flow rate series and sediment transport rate series respectively, and the autocorrelation coefficients were calculated for successive lags on a daily basis. Plot the relationship curve between lag days and autocorrelation coefficient. If the curve shows an annual periodicity of first decreasing and then increasing, and the lag days corresponding to the minimum autocorrelation coefficient are within the range of 182±10 days and the minimum autocorrelation coefficient is less than 0, then it is determined to have annual periodicity and flood-dry season differences.

3. The method for determining the channel shaping flow rate of a plain river based on water and sediment processes according to claim 1, characterized in that, The steps for determining the flow at the boundary between flood and dry seasons include: For the lag days and autocorrelation coefficient curve of the flow series, calculate the rate of change of each point on the autocorrelation coefficient curve, and take the lag days corresponding to the minimum rate of change as the characteristic lag days. Calculate the multi-year average daily flow series of representative hydrological stations and plot the process line of daily flow change throughout the year; The flow rate corresponding to the characteristic lag days is retrieved from the process line and used as the flow rate at the boundary between flood and dry seasons.

4. The method for determining the channel shaping flow rate of a plain river based on water and sediment processes according to claim 1, characterized in that, The steps for determining the flow level with the worst stability in the flow process based on the relative standard deviation of the flow series amplitude include: Using a fixed number of days as the time window, the long series of daily flow patterns are divided into multiple consecutive time periods on average; Calculate the average flow rate and the standard deviation of flow rate variation for each time period; Taking the average flow rate of each time period as the object, several flow rate intervals are divided between the minimum flow rate and the maximum flow rate. The number of occurrences of average flow rate in each flow rate interval is counted, and the representative flow rate, average amplitude standard deviation, and relative standard deviation of flow amplitude for each flow rate interval are calculated. Plot the curve showing the relationship between the relative standard deviation of the flow rate variation and the representative flow rate. Take the flow rate corresponding to the turning point where the curve changes from an upward trend to a stable or downward trend as the flow rate level with the worst flow process stability.

5. The method for determining the channel shaping flow rate of a plain river based on water and sediment processes according to claim 4, characterized in that, The steps for determining the flow stage with the worst stability in the sediment transport process based on the relative standard deviation of the amplitude of the sediment transport rate sequence include: Using the same fixed-day time window as the flow series, the long series of daily sediment transport rate sequences are divided into multiple consecutive time periods; the average sediment transport rate and the standard deviation of sediment transport rate variation within each time period are calculated. According to the same flow level interval as the flow sequence, the average sediment transport rate, the standard deviation of the average sediment transport rate range, and the relative standard deviation of the sediment transport rate range are statistically analyzed within each flow level interval. Plot the relationship curve between the relative standard deviation of the sediment transport rate and the representative flow rate. Take the flow rate corresponding to the turning point where the relative standard deviation of the sediment transport rate changes from an upward trend to a stable or downward trend as the flow rate level with the worst stability of the sediment transport rate process.

6. The method for determining the channel shaping flow rate of a plain river based on water and sediment processes according to claim 1, characterized in that, The steps for comprehensively determining the channel shaping flow rate include: The same relative fluctuation range is assigned to the flow rate at the boundary between flood and dry seasons, the flow rate level with the worst flow process stability, and the flow rate level with the worst sediment transport rate stability, thereby expanding the three flow rates into three flow variation ranges. If the three flow variation intervals have a common overlapping interval, the average flow of the overlapping interval is taken as the channel shaping flow. If there are two overlapping intervals, the average flow of the overlapping interval on the side with the smaller flow is taken as the channel shaping flow.

7. The method for determining the channel shaping flow rate of a plain river based on water and sediment processes according to claim 1, characterized in that, The verification steps include: Select several characteristic cross sections with side beaches or mid-river beaches within the target river section, and determine the distance of each characteristic cross section from the representative hydrological station; Multiple representative flow levels were selected at equal intervals between the minimum and maximum flow rates over the years. The water level of the representative hydrological station at each representative flow level was calculated. Combined with the average gradient of the river section and the distance of each characteristic section from the representative hydrological station, the corresponding water level of each characteristic section at each flow level was estimated. Based on the measured topography of each cross section, calculate the average water depth and river width of each characteristic cross section under each flow level; The average water depth and river width of all cross sections under the same flow level are taken to obtain the average water depth and average river width of the river section under each representative flow level.

8. The method for determining the channel shaping flow rate of a plain river based on water and sediment processes according to claim 7, characterized in that, The verification steps also include: Plot the relationship between the average river width and the average water depth of the river section under each representative flow level. Take the inflection point flow when the river width first increases continuously while the water depth remains basically unchanged as the critical flow for flooding of the low-lying shoals.

9. The method for determining the channel shaping flow rate of a plain river based on water and sediment processes according to claim 8, characterized in that, The verification steps also include: Compare the critical flow rate for flooding the low shoal with the channel shaping flow rate. If the difference between the two is within a reasonable range of the channel shaping flow rate, the channel shaping flow rate is determined to be reasonable and is set as the final channel shaping flow rate. Otherwise, the channel shaping flow rate is determined to be unreasonable, and the calculation or parameters need to be readjusted or reselected.

10. A system for determining the flow rate of a channel shaping in a plain river based on water and sediment processes, characterized in that, include: The flood-dry transition flow determination module is used to obtain the water and sediment sequence of representative hydrological stations, determine the annual periodicity and flood-dry difference of the water and sediment inflow process, and determine the flood-dry transition flow accordingly. The module for determining the flow level with the worst flow process stability is used to determine the flow level with the worst flow process stability based on the variation characteristics of the relative standard deviation of the flow sequence amplitude with the flow level. The module for determining the flow level with the worst stability in the sediment transport rate process is used to determine the flow level with the worst stability in the sediment transport rate process based on the variation characteristics of the relative standard deviation of the flow sediment transport rate sequence with the flow level. The channel shaping flow integration module is used to determine the channel shaping flow by integrating the flood-dry season boundary flow, the flow level with the worst flow process stability, and the flow level with the worst sediment transport rate stability. The channel shaping flow verification module is used to verify the channel shaping flow by utilizing the topography and water level-flow relationship of the target river section and the inflection point flow of the river width-water depth relationship curve, so as to determine the final channel shaping flow. The system for determining the flow rate of a channel for shaping a plain river based on water and sediment processes is used to perform the steps in the method for determining the flow rate of a channel for shaping a plain river based on water and sediment processes as described in any one of claims 1-9.

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