Analysis of the Characters of Recent Dynamic Variation of Runoff and Sediment in the Middle Yellow River Coarse Sediment Source Area

The middle Yellow River coarse sediment source area is the most serious soil and water loss area of the Yellow River basin, to strengthen soil and water loss controlling of this area is one of the most direct and effective ways which reduced the sand into the Yellow River and the harm of siltation in the lower reaches. Mastering runoff and sediment of this area in time, is the premise of correctly analysing the variation of runoff and sediment, and is the basic data for formulating soil and water loss prevention measures and analyzing soil and water conservation benefit. In this study, we take the middle Yellow River coarse sediment source area as object, the year of 1956 similar to 2004 is the basic period, 2005 similar to 2010 is the monitoring contrast period, areal precipitation is obtained by the way of drawing the isoline map of precipitation which based on collecting observed data of existing rain gauge station, considering the difference of geomorphic type and river basin management degree in this area, runoff and sediment discharge use zone plan for calculation, the flood change reacts according to the annual maximum peak discharge of hydrologic station in this study area, and the management degree of soil and water conservation reacts by means of changing of soil and water conservation measures. The outcomes show that comparing with the basic period, precipitation in the monitoring period increased by 3. 9%, runoff decreased by 48. 2%, the total sediment, coarse sediment of grain size larger than 0. 05 mm and 0. 1 mm are less than 85. 9%,90. 8% and 93.0%, respectively. It is an estimation that there is no great flood in the area according to the annual maximum peak discharge of hydrologic station, precipitation shows a weak increasing trend, and runoff and sediment decrease remarkably, It relates to that in the monitoring period there is no happen to a wide extent and great intensity rainstorm, precipitation intensity is smooth relatively although total precipitation has a little change. In ultra infiltration flow area, it goes against producing runoff and sediment. Additionally effective management of soil and water conservation has been condffcted in recent years, especially the implementation of "return farmland to forests or grassland" and banned for harness measures, the ecological environment in this area has improved evidently, appearing a sharp reduction of observed runoff and sediment in the monitoring period.