Cause Analysis on Recent Sharp Decrease of Water and Sediment inthe Reach from Hekouzhen to Longmen of the Yellow River

摘要

From the variation of rainfall, water — soil conservation function and other effects of human activities, this study analyzed the recent sharp decrease of water and sediment in the reach from Hekouzhen to Longmen. The results showed that the reduced rainfall is one of the important reasons. In such rainfall conditions, human activities played another important role in storing water and retaining sediment , and each reason accounted for about a half. In the 50% that human accounted, about 37. 2% belongs to the impoundment of soil and water conservation measures, and 12. 8% or so to the effects of other human activities that changed the ground surface conditions, which is based on the analysis of the data of the 1980' s which is with high precision. With the rapid development of socio — economic and other human activities became significant factors which made runoff and sediment reduce sharply, and this change may have brought water and sediment to change slowly that might not be paid much attention to, may be an important reason for the sharp decrease of water and sediment especially in the period of low rainfall. Therewith, we have a suggestion that to strengthen the study of the recent change causes and development trend in the future on water and sediment.