渭河下游河流输沙需水量计算

基于对河流输沙运动特性的分析,认为最小河流输沙需水量是当河流输沙基本上处于冲淤平衡状态时输送单位重量的泥沙所需要的水的体积,通过河段进口即上游断面水流挟沙力(Su*)与含沙量(Su)比较,分Su≤Su*和Su>Su*两种情况,分别建立了最小河段输沙需水量的计算方法。并应用该方法对渭河下游输沙需水量做了计算。计算的空间尺度为渭河下游的咸阳、临潼、华县三个断面,时间尺度为四个代表年的年内月均需水量,分p=25%(1963年)、p=50%(1990年)、p=75%(1982年)、p=90%(1979年)。计算结果分析表明:渭河各断面汛期月均输沙需水量大于非汛期月均输沙需水量。相较而言,在不同代表年的汛期和非汛期,从咸阳断面至华县断面输沙需水量在增加。在丰水年(p=25%),渭河下游咸阳、临潼、华县等3个断面年输沙需水量分别为63.67亿m3、97.95亿m3和103.25亿m3;在平水年(p=50%),渭河下游咸阳、临潼、华县等3个断面年输沙需水量分别为49.71亿m3、83.27亿m3和85.08亿m3;在枯水年(p=75%),渭河下游咸阳、临潼、华县等3个断面年输沙需水量分别为30.17亿m3、55.14亿m3和65.32亿m3;在特枯水年(p=90%),渭河下游咸阳、临潼、华县等3个断面年输沙需水量分别为23.96亿m3、37.91亿m3和38.92亿m3。由丰水年到枯水年,渭河下游各断面年输沙需水量变小。

Estimation of Instream Flow Requirements for Transporting Sediment in the Lower Reach of the Weihe River

On the basis of the characteristic analysis for river load movement, the minimum instream flow requirements for transporting sediment was considered as a certain volume of intream flow required to transport per weight sediment when the sediment transportation is at balanced state of erosion and deposition. Through the analysis of sediment carrying capacity (S_u^*) and a comparison with the sediment concentration (S_u) at the upper reach, a method to estimate minimum sectional instream flow requirements for transporting sediment of river was proposed according to S_u ≤ S_u^* and S_u > S_u^* respectively. Then, this method was applied to estimate the monthly instream flow requirements for transporting sediment in the lower Weihe River. The temporal scale of typical years included p = 25% (1963), p = 50% (1990), p = 75% (1982) and p = 90% (1979), and the spatial scale of the study areas included Xianyang section, Lintong section and Huaxian section. The results show that the average monthly instream flow requirements for transporting sediment in flood seasons are higher than those in non-flood seasons. Generally speaking, from Xianyang section to Huaxian section, the sectional instream flow requirements for transporting sediment in both flood seasons and non-flood seasons of each typical year increase. Estimated for a wet year (p = 25%), the annual instream flow requirements for transporting sediment of Xianyang section, Lintong section and Huanxian section are 63.67×10⁸ m³, 97.95×10⁸ m³ and 103.25×10⁸ m³ respectively; estimated for normal year (p = 50%), the instream flow requirements for transporting sediment of Xianyang section, Lintong section and Huanxian section are 49.71×10⁸ m³, 83.27×10⁸ m³ and 85.08×10⁸ m³ respectively; estimated for a dry year (p = 75%), the instream flow requirements for transporting sediment of Xianyang section, Lintong section and Huanxian section are 30.17×10⁸ m³, 55.14×10⁸ m³ and 65.32×10⁸ m³ respectively; and estimated for a much drier year (p = 90%), the instream flow requirements for transporting sediment of Xianyang section, Lintong section and Huanxian section are 23.96×10⁸ m³, 37.91×10⁸ m³ and 38.92×10⁸ m³ respectively. It can be found that from wet year to dry year, the instream flow requirements for transporting sediment of each section decrease.