Effects and Significance of Water and Sediment Regulation by Reservoirs in the Middle Yellow River

Abstract

This paper describes chiefly water and sediment regulation with different operational modes subsequent to the re-construction of Sanmenxia reservoir, and analyses sedimentation in the reservoir and the lower river course. Regulation of sediment must be taken into account together with regulation of runoff. A certain storage capacity has been maintained for long-term use for multi-purpose developments of flood control, irrigation and power generation and for sediment conveyance in the lower river course as well through rational regulation of water and sediment in reservoirs built on middle reaches of the Yellow River. Reservoir operational modes for water and sediment regulation are also discussed in the paper.

The total annual water runoff and sediment load at Sanmenxia is 42 billion cu.m and 1.6 billion tons respectively. More than 90% of the total sediment comes from the loess area of the middle Yellow River basin. This load causes severe deposition in the lower river course and brings about many problems in the development of the water resources of Yellow River. Since the founding of new China, a number of large and medium sized reservoirs have been built on the main stem and tributaries of the Yellow River for flood control, irrigation and power generation. Great benefits have been obtained and much experience gained in dealing with sedimentation problems in the reservoirs. Sanmenxia Reservoir was put into operation and commenced impoundment in Sept. 1960. The operational method of detaining floods and sluicing sediment was adopted in March 1962 due to serious siltation in the reservoir during its initial storage period. In 1964, a decision was made to reconstruct and enlarge the outlet discharge capacity to facilitate the disposal of sediment. By the end of 1973, reconstruction was complete and releases from the reservoir were controlled in such a way that relatively clear water was stored during the non-flood season and sediment retained during this season was flushed out of the reservoir during the flood season. This paper discusses the conditions of water and sediment regulation by reservoir operation to maintain effective storage capacity for long-term use. The influence of sedimentation on the lower Yellow River and the possible approaches to development of multi-purpose benefits and the control of hazards with reservoirs are also discussed.