基于动水法的流量过程线推移法在渠道渗漏计算中的应用

动水法观测渠道渗漏较静水法便捷,但由于动水法观测条件苛刻,通常使得动水法定义下的计算结果可靠性较差。该文通过对动水法观测问题及特点分析,建立了流量过程线推移法,通过数据平行检验,绘制有效数据的流量过程线,并对流量过程线进行顺流推移和逆流推移,从而获得某观测时段内上、下游观测断面的流量过程线差,进而算得损失流量。该文以石津灌区四干三分干南四支梯形混凝土衬砌渠道为例进行了分析,对该段渠道上6种衬砌形式进行静水法和流量过程线推移法观测。静水法分析得6种衬砌形式的渗漏量与渠道水深之间均表现为幂函数形式。流量过程线推移法通过平行检验得到19组数据,计算得到渗漏量,将其与静水法得到结果进行比较,得到有12组数据绝对误差小于10 m3/(km·h)。两种方法的渗漏量与水深相关分析呈现相同的变化趋势,即渗漏量随水深的增加而增加。该研究初步验证了流量过程线推移法在渗漏量计算上的可行性。

Flow hydrograph moving method based on inflow-outflow tests and its application on canal seepage calculation

Abstract: Inflow-outflow test and ponding test are both common ways to measure canal seepage and have their own advantages and disadvantages and respective applicable conditions. Inflow-outflow test is more convenient than ponding test, while less accuracy. Inflow-outflow test is conducted in irrigation period, and its calculation accuracy mainly depends on stability of canal flow. The evidence shows that stable flow volume is extremely rare in the measure data from Shijin Irrigation District. Since canal flow volume is controlled by sluice gate commonly, and calculation accuracy is sensitive to flow changes, inflow-outflow test is difficult to apply widely and effectively. Generally, a series of continuous inflow-outflow tests will get a group of data and draw a flow hydrograph. Theoretically, the 2 hydrographs have the same or close shape and parallel nearly when upstream hydrograph flows down to downstream section, and seepage quantity would be revealed by flow difference of the hydrographs between upstream and downstream section. This paper establishes the flow hydrograph moving (FHM) method, by which seepage quantity can be calculated. The FHM method has 3 factors: hydrograph flowing velocity, length between upstream and downstream section and time consumption, and needs 3 steps: drawing hydrographs (according to measure data for 2 times, calculate and line the 2 quantities with X-axis as time and Y-axis as quantity), moving hydrographs (time consumption of moving hydrograph from upstream to downstream section depends on the maximum hydrograph flowing velocity) and measuring flow difference (the moved hydrograph of one section will parallel with the other one, and measure the difference between the Y values of those 2 parallels). However, the measured flows by instruments contain potential errors, which will lead to the intersecting between the 2 hydrographs. Therefore, the moved upstream hydrograph should parallel the downstream one when the 2nd step is finished, which will decide whether data are effective or not. Basically, 5 hypotheses are providing supports to the FHM method: 1) One measure process is regarded as an average flow characteristic to the whole measuring process; 2) Hydrograph flowing velocity value takes the maximum velocity; 3) Seepage characteristics of canal are homogenized, such as longitudinal slope, roughness and cross-sectional shape; 4) Difference in seepage quantity caused by flow variation and seepage is ignored; 5) Hydrograph shape is linear between 2 measurements. However, the maximum velocity of upstream section will be decreased gradually with flow loss, which will influence time consumption, so the difference of the maximum velocity between upstream and downstream section is calculated and averaged by upstream moving and downstream moving in the 2nd step. The FHM method is applied in Shijin Irrigation District. In the case study, 6 kinds of concrete lining forms are designed and constructed, and inflow-outflow tests and ponding tests are both conducted successively. According to the analysis of the ponding test data by non-linear regression on 6 kinds of concrete lining, seepage characteristics showed exponential function between water depth and seepage quantity, and the correlation coefficients of 6 functions are 0.884 (P<0.1), 0.852 (P<0.1), 0.992 (P<0.001), 0.988 (P<0.0001), 0.964 (P<0.01) and 0.991 (P<0.01), respectively. There are 19 couples of hydrographs matching the parallel conditions in inflow-outflow tests data. Taking exponential function simulation results as benchmark, seepage calculation results by the FHM show that the errors from 12 groups are less than 10 m3/(km·h) (63.16% of total data), 6 groups fall in 10-50 m3/(km·h) (31.58% of total data), and the maximum error is 74.08 m3/(km·h). Furthermore, the linear regression for the FHM and exponential functions both revealed that seepage rate increased with water deepening. The possible cause of errors is potential flow fluctuation between 2 measurements. After all, time interval is almost inevitable between them. Seepage calculation using the FHM is more suitable under canal's measuring conditions and makes the application of inflow-outflow tests more effectively.