Estimation of Instream Flow Requirements for Transporting Sediment in the Lower Reach of the Weihe River
渭河下游河流输沙需水量计算

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 (Su*) and a comparison with the sediment concentration (Su) at the upper reach, a method to estimate minimum sectional instream flow requirements for transporting sediment of river was proposed according to Su ≤ Su* and Su > Su* 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.