CN110555248A - combined determination method for tidal river reach bed building flow and beach water level - Google Patents
combined determination method for tidal river reach bed building flow and beach water level Download PDFInfo
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- CN110555248A CN110555248A CN201910759956.2A CN201910759956A CN110555248A CN 110555248 A CN110555248 A CN 110555248A CN 201910759956 A CN201910759956 A CN 201910759956A CN 110555248 A CN110555248 A CN 110555248A
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02B—HYDRAULIC ENGINEERING
- E02B3/00—Engineering works in connection with control or use of streams, rivers, coasts, or other marine sites; Sealings or joints for engineering works in general
- E02B3/02—Stream regulation, e.g. breaking up subaqueous rock, cleaning the beds of waterways, directing the water flow
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Abstract
The invention provides a method for jointly determining the bed-building flow and the beach water level of a tidal river reach, which comprises the following steps: step 1, calculating a time-by-time flow, a tide level and a sand content process of a target section by using a one-dimensional non-constant water sand mathematical model; step 2, determining a sand content-flow lag response relation and a sand transportation equivalent flow series of the target section; step 3, carrying out statistics on the combined frequency of the equivalent flow of sand transportation and the tidal level of the target section; and 4, calculating the bed forming strength of the target section, and solving the bed forming flow and the flat water level of the target section by using a graphical method. The method comprehensively considers the sand content lag characteristic under the tidal action, considers various combination frequencies of the flow and the tidal level and the influence of the combination frequencies on the bed-making action, and can simultaneously obtain the bed-making flow and the flat beach water level of the target section.
Description
Technical Field
The invention belongs to the technical field of water conservancy and water transport engineering, and particularly relates to a combined determination method for tidal river reach bed building flow and beach water level.
Technical Field
the tidal river reach is close to the mouth of the river, is a channel for conveying flood and silt into the sea, is also a water transportation channel for connecting inland and ocean, and is often required to implement large-scale river regulation. In the practice of river regulation engineering, the bed making flow and the flat water level are important parameters widely applied in the links of river bed evolution analysis, river regulation planning, regulation engineering design and the like, and whether the numerical value is determined to be reasonable or not can directly influence the cost, effect and even success or failure of river regulation.
the bed forming flow is a certain flow range with the strongest molding effect on the basic form of the alluvial river or the largest sand conveying effect, and the wide and deep scale and the volume of the cross section of the river channel are determined by the average value of the flow range; the beach water level is a certain elevation level flush with the heart shoal or the flood beach, and the elevation will determine the elevation of the top of the basic river channel and the height difference of the beach channel. The bed-building flow and the flat water level jointly determine the basic form of the alluvial river, and the bed-building flow and the flat water level are connected and have difference.
For the runoff type alluvial river channel, the upstream incoming water and sand process is the only factor for modeling the shape of the river channel, and the bed-building flow can be calculated by counting incoming water and sand features through mature methods such as the Makavyjeff method and the like. In the river reach, water and sand transportation has two characteristics, namely, the phase difference between the sand content and the flow change is not large, and the sand transportation rate and the bed building strength at a certain moment can be calculated by the flow at the same moment; secondly, the water level and flow relation is single and stable, the water level corresponding to the bed building flow is generally flush with the elevation of the edge of the beach, only one item of the bed building flow or the beach water level needs to be determined in engineering practice, and the rest item can be obtained through conversion of the water level and flow relation. However, in a tidal river section near the sea entrance at the downstream of the river, the river form is simultaneously influenced by the incoming water and sand at the upstream and the river tide at the river entrance, the two factors of the diameter and the tide have certain independence, the direct conversion relation between the sand content and the flow and between the flow and the water level is not established any more, and the method for estimating the bed-building flow of the runoff river section cannot be applied.
Aiming at the actual conditions that the water flow is not constant and the flow and the sand content are difficult to observe, a water flow mathematical model is adopted to simulate the flow process in the past engineering practice, the average falling tide flow is used as the flow of a bed, or the sand conveying capacity is directly calculated by the hourly flow along with a runoff river reach method, and then the flow with the largest sand conveying amount is selected as the flow of the bed. However, the methods still do not consider the characteristic that the change of the sand content is obviously lagged behind the change of the flow, and also do not consider the influence of the fluctuation of the tidal level on the bed building effect, the factors are not comprehensive enough, the parameter experience is strong, especially the flat beach water level cannot be obtained, and the requirements of river regulation planning and engineering design cannot be met in the section with strong tidal fluctuation.
Disclosure of Invention
The present invention is made to solve the above problems, and an object of the present invention is to provide a method for jointly determining a bed building flow rate and a flat water level of a tidal river reach, which can give consideration to both runoff influence and tidal fluctuation influence, and is suitable for tidal rivers, and the result is more objective and accurate.
In order to achieve the purpose, the invention adopts the following scheme:
The invention provides a method for jointly determining the bed-building flow and the beach water level of a tidal river reach, which is characterized by comprising the following steps of:
Step 1, calculating the time-by-time flow, the tide level and the sand content of a target section by using a one-dimensional non-constant water sand mathematical model, wherein the process comprises the following steps:
Step 1.1, if a hydrological site is arranged near the target section, determining whether the site has M-year (M is more than or equal to 10) long-series hourly flow Q, tide level (water level) Z and sand content S observation data, if the data is complete, entering step 2, otherwise, executing step 1.2;
Step 1.2, a one-dimensional unsteady flow water sand mathematical model is established, the calculation range of the model comprises a target section, a hydrological station at the entrance of a tidal river section is taken at the upper boundary of the model, the station is provided with M-year (M is more than or equal to 10) long-series hourly flow Q and sand content S observation data, a tidal station at the entrance of the tidal river section is taken at the lower boundary of the model, the station is provided with M-year (M is more than or equal to 10 and is the same time with the hydrological station data at the entrance) hourly tidal level data, and a small amount of hourly tidal level and sand content observation data for model calibration are also arranged in a simulated river section;
Step 1.3, the boundary condition of the model is processed, the time-by-time flow and sand content data are given by the inlet of the model, the time-by-time tide level data are given by the lower boundary of the model, and the modelConsidering the sand content of the lower boundary tidal current, and the formula S in the case of lack of observation datai＝βS*i+(1-β)Si-1calculation of where S*i、Sithe sand holding force and the sand content of the ith time step of the outlet section are respectively, and beta is a lagging parameter of the sand content to be determined;
Step 1.4, carrying out numerical simulation on the water flow sand conveying process of the tidal river reach, and calibrating a roughness parameter and an outlet sand content lag parameter beta in a mathematical model according to measured data to ensure the accuracy of a numerical simulation calculation result;
step 1.5, on the basis of parameter calibration, calculating a long-series water flow sand conveying process of the target river reach within M years, and outputting a time-by-time flow Q of the target section within M years by taking hours as a time stepiTidal level ZiSand content SiData;
Step 2, determining a sand content-flow lag response relation and a sand transportation equivalent flow series of the target section, comprising the following steps of:
Step 2.1, according to the one-dimensional non-constant water sand model calculation result obtained in the step 1, the hourly flow Q of the target section is obtainediCalculating a moving average absolute flowis the average value of the flow absolute values of the ith time step and the n previous time steps,n is a sliding period, and the first calculation can assume that n is 2;
Step 2.2 calculationAfter the series, the sand content S corresponding to the ith time step is takeniIn a power functionfitting SiAndThe relation between the coefficients of determination R of curve fitting is obtained in the process2；
Step 2.3 gradually increasing the sliding period n, repeating step 2.2 to obtain the curve fitting determination coefficient R under different sliding period conditions2with the gradual increase of n, the decision coefficient of curve fitting is increased first and then reduced, when the decision coefficient has an inflection point, the optimal sliding period n is obtained, and the optimal fitting relation is obtained at the same timeParameter k, a in (1), functional relationship at this timeA hysteresis response function called sand content-flow, corresponding to the decision coefficient R2should be above 0.5, otherwise not meet the implementation conditions of this method;
step 2.4 if the implementation conditions in step 2.3 are met, Q is usediAndCalculating the equivalent flow of sand transportation time by time based on the seriesWherein sign represents taking a positive or negative sign, when Qiwhen positive, sign takes +1, QiWhen the sign is negative, sign takes-1, otherwise, sign takes 0;
Step 3, the statistics of the combined frequency of the equivalent flow of sand transportation and the tidal level of the target section comprises the following steps:
Step 3.1 hour-by-hour sand transportation equivalent flow rate of the target section obtained in step 2 for M yearsWill be provided withSorting from high to low, dividing into several grade intervals by arithmetic equal interval, and calculating representative flow in each grade intervalrepresenting the total number of the flow grade intervals;
step 3.2 aiming at the hourly tide data Z of the target section M years obtained in the step 1iSorting tide level data from high to low, dividing into several grade intervals by arithmetic equal interval, and calculating representative tide level value in each grade intervalNZThe total number of tide level intervals);
Step 3.3 taking M years series sand conveying equivalent flow series of target sectionChronological tide level series ZiUsing division in steps 3.1 and 3.2Stage flow interval and NZThe interval of the grade tide level and the flow of the sand transporting equivalent are countedTidal level Zinumber of occurrences of combinationcalculating its frequency of occurrence Pm,j＝Nm,j/TM，Pm,jEquivalent flow rate of target cross sectionIn the mth flow interval and corresponding tide level ZiFrequency of occurrence of hydrological conditions in the jth tidal space, TMData series length of M years;
Step 4, calculating the bed forming strength of the target section, and solving the bed forming flow and the flat water level of the target section by using a graphical method, wherein the method comprises the following steps:
Step 4.1 representing flow rate according to each flow rate intervalRepresentative tide level of each tide level intervalFrequency P calculated in step 3.3m,jCalculating the bed-making strength F of the flow-tide level combination interval according to the geomorphic work principle and the sand content lag characteristic of the tidal river reachm,jwhich is calculated as
Step 4.2 with the representative flow as x-axis and the representative tidal level as y-axis, the bed forming intensity F obtained in step 4.1m,jAs coordinate z valueDrawing in a coordinate plane (Fm,j) Scatter points, on the basis of which a bed intensity contour map is drawn; if it is notIf the values are all positive values, the contour map is located in the first quadrant, 1 extreme point exists, and the x and y coordinates corresponding to the extreme point are the bed-making flow and the flat water level of the target section; if it is notMeanwhile, if the target cross section has positive and negative values, 2 extreme points exist in a first quadrant and a second quadrant in the coordinate plane, wherein the x coordinate and the y coordinate corresponding to the larger extreme point are the modeling flow and the flat water level of the target cross section.
Preferably, the method for jointly determining the bed-making flow and the flat beach water level of the tidal river reach provided by the invention can also have the following characteristics: in step 3.1, letIs composed ofstandard deviation of data series, traffic class interval valueIn thatOrChoose between by trying to get the differenceSo that the number of sectionsis between 20 and 30, and ensures that each interval is provided withThe data of (a); determining the number of the flow grade intervalsAnd size of the spaceThen, the average value of the upper and lower boundaries of each section is used as the representative flow rate of the section
Preferably, the method for jointly determining the bed-making flow and the flat beach water level of the tidal river reach provided by the invention can also have the following characteristics: in step 3.2, let SZas tidal level data series ZiStandard deviation of (2), tidal level grade interval value Δ Z at 0.25SZ、0.50SZ、0.75SZOr SZSelecting the interval, namely obtaining different delta Z by trial to ensure that the number of the divided intervals is between 15 and 25 and ensure that Z exists in each intervaliThe data of (a); determining the number N of tidal level intervalsZAnd after the interval size delta Z, taking the average value of the upper and lower boundaries of each interval as the representative tide level of the interval
preferably, the method for jointly determining the bed-making flow and the flat beach water level of the tidal river reach provided by the invention can also have the following characteristics: and (4) executing the steps 1 to 4 by adopting a computer to finally obtain the bed-making flow and the beach water level.
Action and Effect of the invention
Aiming at the unsteady movement of water flow and sediment in a tidal river reach under the influence of diameter and tide factors, the invention implements long-series unsteady flow water-sand numerical calculation on the tidal river reach, calculates the time-by-time flow, water level and sand content data of each target section, thereby determining the hysteresis response function relationship between the sand content and the flow of the target section, obtains the probability distribution of the bed-building strength under the joint influence of flow and tide level bivariate, obtains the water flow condition with the maximum bed-building effect by using a graphical method, further determines the bed-building flow and the beach water level simultaneously, and provides a convenient and reliable way for the estimation of the bed-building flow and the beach water level of the tidal river reach.
In engineering practice, methods adopted in tidal river reach are basically based on experience, for example, average falling tide in a tidal cycle is taken as a bed making flow, and average middle tide level is taken as a flat water level. The method provided by the invention can realize quantitative calculation on a computer for a large amount of data of a long time series through the provided calculation process, improves the utilization rate of original observation data, considers various combination frequencies of flow and tide level, can simultaneously obtain the bedmaking flow and the beach water level of a target section, enhances the objectivity of the result and has higher precision.
Drawings
FIG. 1 is a flow chart of a method for jointly determining a tidal river reach bed building flow and a beach water level according to an embodiment of the present invention;
FIG. 2 is a diagram showing the optimal sliding period n of the target section according to an embodiment of the present invention;
FIG. 3 is a graph showing the relationship between the sand content of the target cross section and the moving average flow rate according to the embodiment of the present invention;
FIG. 4 is a graph of the target cross-sectional modeling intensity distribution in an embodiment of the present invention;
FIG. 5(a) is a graph showing the estimation result of the conventional empirical method, and FIG. 5(b) is a graph showing the comparison between the estimation result of the conventional empirical method and the actual beach elevation.
Detailed Description
The following describes in detail a specific embodiment of the method for jointly determining the tidal river reach bed building flow and the beach water level according to the present invention with reference to the accompanying drawings.
< example >
the water level observation data adopted by the embodiment is downstream tidal river reach, long-distance cross section topographic data are arranged in the river reach, the adopted hydrological data comprise 10-year daily average flow and sand content data of a hydrological station (station A) at the river reach, 10-year same-time tide level observation data of a tide station (station B) near the sea entrance, and a C cross section near the river reach in the river reach is a target cross section. In addition, E, F two sections in the river reach have time-by-time flow and sand content observation data about 1 month for the parameter calibration of mathematical model.
As shown in fig. 1, the method for jointly determining the bed-building flow rate and the flat water level of the tidal river reach provided by this embodiment includes the following steps:
Step 1, simulating and calculating time-by-time flow, tide level and sand content data of a target section (C section);
Step 1.1, no hydrological station is arranged near the C section, and actual measurement data of hourly flow, tidal level and sand content are lacked, so that the step 1.2 is carried out;
Step 1.2, establishing a one-dimensional non-constant water-sand mathematical model aiming at the river reach, wherein the water flow calculation is according to the Saint Vietnam equation set, the sediment calculation is according to the sediment transport equation of the non-constant non-saturated suspended load, and the solution is solved by adopting a Prussian implicit differential format;
Step 1.3, processing the boundary conditions of the model, taking observation data of the average daily flow Q and the sand content S of the 10-year-old series of the station A, carrying out linear interpolation on the average daily data according to 1 day and 24 hours to obtain hourly data serving as an upper boundary, taking hourly tide position data of the station B in the same time period of 10 years serving as a lower boundary of the mathematical model, and adopting S for the sand content of the lower boundary at the flood tide time in the mathematical modeli＝βS*i+(1-β)Si-1Calculating beta as a undetermined parameter;
Step 1.4, carrying out long-series water-sand numerical simulation on the river reach, repeatedly adjusting model parameters according to comparison of actual measurement flow and sand content data of E, F two sections in the river reach and calculation data, ensuring that the calculation values are consistent with the actual measurement values, and finally determining a beta parameter to be 0.15;
Step 1.5, after parameter calibration, calculating the water flow sand conveying process of the river reach within 10 years, taking hours as time step, and outputting the hourly flow Q of the C section for 10 yearsiTidal level ZiSand content SiThe number of each kind of data is 88080 according to the calculation result.
Step 2, determining a sand content-flow lag response relation and a sand transportation equivalent flow series of the target section, and specifically comprising the following steps:
Step 2.1, based on the step 1, 88080 hourly flow rates Q of the target section are takenicalculating a moving average absolute flowIs the average value of the flow absolute values of the ith time step and the n previous time steps,n is the sliding period, the first calculation assumes n is 2, and 88078 resultData;
step 2.2, calculateafter the series, according to 88078 data at and after 3 hours, the corresponding sand content S at each time stepiIn a power functionFitting SiandThe relation between the two coefficients is obtained to obtain the determining coefficient R of curve fitting2is 0.28;
step 2.3, gradually increasing the sliding period n, repeating the step 2.2, and obtaining the curve fitting determination coefficient R under different sliding period conditions2the decision coefficient of curve fitting is increased and then decreased along with the gradual increase of n, and when n is 17, R is2The maximum value of 0.599 is reached, as shown in figure 2, the optimal fitting relation is obtained at the moment, namely, the hysteresis response function of the sand content to the flowReferring to FIG. 3, the corresponding coefficient of determination R2Above 0.5, thus satisfying the implementation conditions of the method;
step 2.4, after determining that the slip period n is 17, starting from the 18 th data, with QiAndCalculating the equivalent flow rate series of sand transportation time by time based on the data seriesWherein sign represents the flow rate QiThereby obtaining 88063data;
Step 3, carrying out statistics on the combined frequency of the equivalent flow of sand transportation and the tidal level of the target section, wherein the statistics specifically comprises the following steps:
Step 3.1, 88063 time-by-time equivalent flow data of 10 years of C section obtained in step 1sorting the flow rate values from high to low, dividing the flow rate values into a plurality of grade intervals at equal intervals by adopting arithmetic, and calculating a representative flow rate value in each grade interval;
Flow rate class interval valueCan try to getor(Is composed ofStandard deviation of data), in this example, C-section is time-by-timemaximum valueMinimum value (flow is negative for flood tide), flowStandard deviation of data Approximate interval valueBonding ofThe maximum value and the minimum value of the interval can be determined22 in number;
Obtaining the number of flow intervalsand size of the spaceThen, the lower limit value is taken to-1100003S, the flow rate can be determinedThe interval boundaries of (a) are in turn: -110000m3/s，-90000m3/s…，110000m3And/s, taking the average value of the upper and lower boundaries of each interval as the representative flow rate of the interval
step 3.2, aiming at the hourly tide data Z of the C section obtained in the step 1 for 10 yearsiIs a reaction of ZiSorting the data from high to low, dividing the data into a plurality of grade intervals at equal intervals by adopting arithmetic, and calculating a representative water level (tide level) value in each grade interval;
the water level interval value may be 0.25SZ、0.50SZ、0.75SZOr SZ(SZStandard deviation of tide level data), maximum tide level value Z of C sectionmax3.12m, minimum tidal level value Zmin＝-0.94m，SZThe number of the divided regions is between 15 and 25 and is calculated to be 0.25S when the number is 0.81mZ0.2025m, in order to ensure that the interval division is fine, the interval value is 0.2m, and the number N of intervals is calculatedZIs 21;
DeterminingNZThen, the section boundaries of the obtained water level are as follows in sequence: -0.94m, -0.74m, …,3.26m, the average value of the upper and lower boundaries of each interval being used as the representative water level of the interval
Step 3.3, taking the sand transportation equivalent flow series of the C section obtained in the step 2 for 10 yearsAnd corresponding chronological tide level series ZiUsing division in steps 3.1 and 3.2stage flow interval and NZStep tidal level interval, statistical flowWater level Zinumber of occurrences of combination Nm,j(m 1, 2.., 22, j 1, 2.., 21), the frequency of occurrence P thereof is calculatedm,j＝Nm,j/TM，Pm,jEquivalent flow rate of target cross sectionIn the mth flow interval, and corresponding tide level ZiFrequency of occurrence of hydrological conditions in the jth tidal space, TMfor the length 88063 of the 10-year data series after the sliding average, 462 frequency data are obtained because the number of flow and tide level intervals are 22 and 21 respectively;
Step 4, calculating the bed forming strength of the target section of the river reach, and solving the bed forming flow and the flat water level of the target section by using a graphical method, wherein the method specifically comprises the following steps:
Step 4.1, according to the representative flow of each flow intervalRepresentative tide level of each tide level intervalFrequency P calculated in step 3.3m,jCalculating the bed-making intensity F of the flow-tide level combination intervalm,jWhich is calculated asObtaining 462 pieces of bed making strength data in total;
Step 4.2, using the representative flow as x axis and the representative tide level as y axis, and using the bed forming intensity F obtained in the step 4.1m,jFor the z value (i 1, 2.., 22, j 1, 2.., 21), the drawing(s) are plottedFm,j) Scatter plot, based on which a contour plot of bed intensity is produced, is shown in FIG. 4. As can be seen from FIG. 4, there are two peak areas of the bed strength, but the peak area around (78000, 0.42) is the largest, and the peak point corresponds to a flow rate of 78000m3The water level of 0.42m and the water level of s are respectively the bed-making flow rate and the flat water level of the C section.
The tidal river reach water flow bed building action is subjected to the dual actions of runoff, incoming water, incoming sand and tidal fluctuation, the maximum flow magnitude of the bed building action is obtained in the graph 4, and meanwhile, the corresponding water level is obtained. In contrast, the average variation range of the tidal cycle falling current of the target section is shown in FIG. 5(a), and if an empirical method using the average falling current as the bed-making flow is adopted, the determined bed-making flow may be 25000m due to different data segments selected by the operator3/s～100000m3Any value in a larger interval of/s and stronger randomness. Even if the data samples adopted by the operator are enough to ensure that the determined bed-making flow is close to the perennial median of 60000m3s, which is also greater than 78000m determined by the method of the invention3The/s is far smaller. According to river dynamics theory, the flow rate of the bed-making is close to the maximum flow rate but less than the maximum flow rate, and obviously, the determined value of the method is more reasonable. Meanwhile, the average mean tide level variation range of the target section is also shown in FIG. 5(a), if an empirical method using the average tide level of the tide cycle as the beach water level is adopted, only the approximate interval of the beach water level can be determined to be-0.3 m-2.5 m, even if the average tide level is taken on the basisThe median probability corresponds to a tide level of 0.92m, which is also higher than the 0.42m determined by the method of the present invention. The actual river cross section form of the C cross section is drawn as shown in fig. 5(b), and it can be seen that the actually measured beach lip elevation is closer to the calculated beach water level of the method.
therefore, the method for jointly determining the bed-building flow and the flat water level of the tidal river reach is accurate and reliable, has a clear physical mechanism, and avoids experience and subjectivity. The application of the method in the embodiment also shows that in engineering practices such as tidal river bank design, riverway and waterway regulation and the like, the maximum water flow condition of the bed making effect is determined by the bed making flow and the flat water level, and the bed making flow and the flat water level are determined and used together.
The above embodiments are merely illustrative of the technical solutions of the present invention. The method for jointly determining the bed-making flow rate and the beach water level of the tidal river reach according to the present invention is not limited to the contents described in the above embodiments, but is subject to the scope defined by the following claims. Any modification or supplement or equivalent replacement made by a person skilled in the art on the basis of this embodiment is within the scope of the invention as claimed in the claims.
Claims (3)
1. a method for jointly determining the bed-building flow and the beach water level of a tidal river reach is characterized by comprising the following steps:
Step 1, calculating the time-by-time flow, the tide level and the sand content of a target section by using a one-dimensional non-constant water sand mathematical model, wherein the process comprises the following steps:
Step 1.1, if a hydrological site is arranged near the target section, determining whether the site has M-year (M is more than or equal to 10) long-series hourly flow Q, tide level (water level) Z and sand content S observation data, if the data is complete, entering step 2, otherwise, executing step 1.2;
Step 1.2, a one-dimensional unsteady flow water-sand mathematical model is established, the calculation range of the model comprises a target section, a hydrological station at the entrance of a tidal river section is taken at the upper boundary of the model, the station is provided with M-year (M is more than or equal to 10) long series hourly flow Q and sand content S observation data, a tidal level station at the entrance of the tidal river section is taken at the lower boundary of the model, the station is provided with M-year hourly tidal level data, and the interior of a simulated river section is also provided with hourly tidal level and sand content observation data for model rate determination;
Step 1.3, the boundary condition of the model is processed, the inlet of the model gives time-by-time flow and sand content data, the lower boundary of the model gives time-by-time tide level data, the sand content of lower boundary tidal current needs to be considered in the model, and the formula S is used under the condition of lack of observation datai＝βS*i+(1-β)Si-1calculation of where S*i、SiThe sand holding force and the sand content of the ith time step of the outlet section are respectively, and beta is a lagging parameter of the sand content to be determined;
Step 1.4, carrying out numerical simulation of a water flow sand conveying process on the tidal river reach, and calibrating a roughness parameter and an outlet sand content lag parameter beta in a mathematical model according to measured data;
Step 1.5, on the basis of parameter calibration, calculating a long-series water flow sand conveying process of the target river reach within M years, and outputting a time-by-time flow Q of the target section within M years by taking hours as a time stepiTidal level ZiSand content Sidata;
Step 2, determining a sand content-flow lag response relation and a sand transportation equivalent flow series of the target section, comprising the following steps of:
step 2.1, according to the one-dimensional non-constant water sand model calculation result obtained in the step 1, the hourly flow Q of the target section is obtainediCalculating a moving average absolute flowIs the average value of the flow absolute values of the ith time step and the n previous time steps,n is a sliding period, and the first calculation can assume that n is 2;
Step 2.2 calculationAfter the series, take the i time stepsand content SiIn a power functionFitting SiAndthe relation between the coefficients of determination R of curve fitting is obtained in the process2；
Step 2.3 gradually increasing the sliding period n, repeating step 2.2 to obtain the curve fitting determination coefficient R under different sliding period conditions2With the gradual increase of n, the decision coefficient of curve fitting is increased first and then reduced, when the decision coefficient has an inflection point, the optimal sliding period n is obtained, and the optimal fitting relation is obtained at the same timeParameter k, a in (1), functional relationship at this timeA hysteresis response function called sand content-flow, corresponding to the decision coefficient R2Should be above 0.5, otherwise not meet the implementation conditions of this method;
Step 2.4 if the implementation conditions in step 2.3 are met, Q is usediAndCalculating the equivalent flow of sand transportation time by time based on the series wherein sign represents taking a positive or negative sign, when Qiwhen positive, sign takes +1, QiWhen the sign is negative, sign takes-1, otherwise, sign takes 0;
Step 3, the statistics of the combined frequency of the equivalent flow of sand transportation and the tidal level of the target section comprises the following steps:
Step 3.1 hour-by-hour sand transportation equivalent flow rate of the target section obtained in step 2 for M yearswill be provided withsorting from high to low, dividing into several grade intervals by arithmetic equal interval, and calculating representative flow in each grade interval Representing the total number of the flow grade intervals;
Step 3.2 aiming at the hourly tide data Z of the target section M years obtained in the step 1iSorting tide level data from high to low, dividing into several grade intervals by arithmetic equal interval, and calculating representative tide level value in each grade intervalNZThe total number of tide level intervals);
step 3.3 taking M years series sand conveying equivalent flow series of target sectionChronological tide level series ZiUsing division in steps 3.1 and 3.2stage flow interval and NZThe interval of the grade tide level and the flow of the sand transporting equivalent are countedTidal level ZiNumber of occurrences of combinationCalculating its frequency of occurrence Pm,j＝Nm,j/TM，Pm,jEquivalent flow rate of target cross sectionIn the mth flow interval and corresponding tide level ZiFrequency of occurrence of hydrological conditions in the jth tidal space, TMData series length of M years;
Step 4, calculating the bed forming strength of the target section, and solving the bed forming flow and the flat water level of the target section by using a graphical method, wherein the method comprises the following steps:
Step 4.1 representing flow rate according to each flow rate intervalRepresentative tide level of each tide level intervalFrequency P calculated in step 3.3m,jCalculating the bed-making intensity F of the flow-tide level combination intervalm,jWhich is calculated as
Step 4.2 with the representative flow as x-axis and the representative tidal level as y-axis, the bed forming intensity F obtained in step 4.1m,jAs coordinate z valueDrawing in a coordinate plane scatter points, on the basis of which a bed intensity contour map is drawn; if it is notif the values are all positive values, the contour map is located in the first quadrant, 1 extreme point exists, and the x and y coordinates corresponding to the extreme point are the bed-making flow and the flat water level of the target section; if it is notMeanwhile, if the target cross section has positive and negative values, 2 extreme points exist in a first quadrant and a second quadrant in the coordinate plane, wherein the x coordinate and the y coordinate corresponding to the larger extreme point are the modeling flow and the flat water level of the target cross section.
2. the method of claim 1, wherein the method comprises the steps of:
Wherein, in step 3.1, letIs composed ofStandard deviation of data series, traffic class interval valueIn thatOrChoose between by trying to get the differenceso that the number of sectionsis between 20 and 30, and ensures that each interval is provided withthe data of (a);
Determining the number of the flow grade intervalsAnd size of the spaceThen, the average value of the upper and lower boundaries of each section is used as the representative flow rate of the section
3. The method of claim 1, wherein the method comprises the steps of:
Wherein, in step 3.2, S is setZAs tidal level data series ZiStandard deviation of (2), tidal level grade interval value Δ Z at 0.25SZ、0.50SZ、0.75SZOr SZSelecting the interval, namely obtaining different delta Z by trial to ensure that the number of the divided intervals is between 15 and 25 and ensure that Z exists in each intervaliThe data of (a);
determining the number N of tidal level intervalsZAnd after the interval size delta Z, taking the average value of the upper and lower boundaries of each interval as the representative tide level of the interval
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