The Impacts Of Initial Operation Stage Of Xiaolangdi Reservoir On Flood Control For Henan Reaches Of Yellow River And Countermeasures

This paper provides a systematic presentation of the influences of the initial operation stage of Xiaolangdi multi-purpose reservoir on Henan reaches of Yellow River, and of some new circumstances occurred after the operation of this reservoir. Some personal comments and countermeasures for the existing problems have been proposed by analyzing the influence on the incoming water and sediment in lower reaches and the flood control situation during the control operation of Sanmenxia pivot and other multi-purpose projects on Yellow River. At the same time, the current characteristics of Henan reaches and the features of flood and sediment are taken into account, and the new flood control situation of Henan reaches and the influence of the initial operation stage of Xiaolangdi reservoir are focused in this paper. The main achievements of this paper are as follows.1. By analyzing the characteristics of the incoming water and sediment before the operation of Xiaolangdi reservoir and after the operation of Sanmenxia reservoir, it is shown that the operation of reservoir influences the annual distribution of runoff in the lower reach. And the reservoir's regulation greatly reduces the occurrence frequency of large flood and makes middle or small floods occur more frequently. Because the probability of overflowing the main channel of middle and small floods decreases, which results in serious deposition in the main channel, the water level of middle and small floods appears higher. This lead to speeds up the formation of the second suspended river to a certain extent. All these phenomena are harmful to the safety of the flood control of Yellow River.2. During the initial operation stage of Xiaolangdi Reservoir, the incoming conditions of water and sediment for lower reaches ofYellow River are greatly changed, especially in the first decade since it is the period of sediment retention. In this period, the channel of Henan reaches will be influenced heavily, such as scouring, downcutting, and sloughing of strand. The dangerous situations maybe occur for flood control works. The down channel measurement after operation of Sanmenxia Reservoir and Xiaolangdi Reservoir shows that the operation of reservoir has notable impact on the stable of river regime. However, the situation of some control works were destroyed and the tremendous changes of river regime during the initial operation stage of Sanmenxia Reservoir, the water discharge with low sediment concentration, will not happen. The main reasons are: having much more control works which are relatively stable, less water amount to lower reaches in recent years, strict system of flood prevention responsibility, and improvement of ways of emergence flood fighting.3. Flood control situation of Henan reaches of Yellow River during the initial operation stage of Xiaolangdi reservoir: after the operation of Xiaolangdi reservoir, it is still possible for large flood to occur in Henan reaches, as there is 27000km2 watershed area from Xiaolangdi to Huayuankou which is non-project controlled area. Meanwhile, there will be negative impacts on flood control in Henan reaches as following aspects: 1) Since the changing of annual water volume distribution and water and sediment conditions in downstream, the Yellow River gradually loses its nature and the inherent natural rules, which haven't been realized completely, are gradually disappearing. These greatly influence the hydrological forecasting of Yellow River. 2) The occurrence frequency of middle or small floods is increasing. "Transversal river" and "lateral river" phenomenon will occur more frequently, resulting in great pressure on embankment prevention. 3) The changing of water and sediment conditions causes longitudinal and transverse variation of river-bed, as well as seriously floodplain bank collapse, and channel is easily to form bend. If bend continues to develop, the phenomena of "one bend changing results changing of many bends" will occur, inducing big changes in river regime and greatly increasing frequency of...