Special Column:Celebration of the 70th Anniversary of IGSNRR, CAS
Ni Jinren, Han Peng, Zhang Ren
Special attention has been paid, in the present study, to the variations of suspended sediment size distributions in the tributaries as well as in the main stream within the middle reach of Yellow River with respect to regional water and soil conservations and the human activities. It is revealed that the conservations of water and soil in various catchments between Hekou and Longmen have significant impacts on the sediment size distributions in their corresponding rivers, and principally reduce median diameters of the grain groups. The sediment distribution functions in the study area are found to be controled by both the geomorphologic factors and the types of conservation activities in addition to the hydrological/hydraulic effects. For the hilly ground in Loess Plateau, the sediment size distributions in the rivers are fairly presented by the normal distribution with two important parameters, median grain diameter and the mean square deviation, which are altered by the specific mechanical practices and the landforms, respectively. For the sand gravel hilly ground, a Pearson Ⅲ type function is a good approximation for the sediment gradings, with three parameters altered by the conservation measures. The topic presented herein is of great value but is rarely approached in the previous studies. The applications of the findings are discussed in greater details in the companion paper.
