中文摘要：

至2010年10月，小浪底水库干流三角洲顶点推进到距坝18．75km的HH12断面，库区淤积量达到28．23亿m3。本文通过分析小浪底水库运用以来库区干流淤积形态，研究了水库三角洲淤积形态对水沙输移的影响机理与作用，结果表明：三角洲淤积形态与锥体淤积形态相比，相同淤积量与相同蓄水量条件下，前者回水长度明显缩短，坝前蓄水位明显降低；发挥水库拦粗排细减淤效果及优化出库水沙过程等方面，三角洲淤积明显优于锥体淤积。三角洲淤积更有利于塑造异重流，异重流排沙效果优于壅水明流排沙。小浪底水库降水冲刷实体模型试验结果表明，河槽溯源冲刷下切的同时水位下降，两岸尚未固结且处于饱和状态的淤积物失去稳定，在重力及渗透水压力的共同作用下向主槽内滑塌，库容得到恢复。当前在水库运用过程中，若遇洪水入库，通过降低水库坝前水位，可在坝前段及三角洲洲面形成溯源冲刷，从而尽可能延长库区由三角洲淤积转化为锥体淤积的时间。

英文摘要：

By October 2010, the mainstream delta vertex of Xiaolangdi Reservoir had moved up to cross section HH12 which is 18.75km to dam, and the amount of sediment reached 2.823 billion m3. The re- suits show that under the same amount of sediment and water storage, compared with cone deposition mor- phology, the backwater length of delta deposition morphology is obviously shorter and the water lever be- fore dam is obviously lower. The delta deposition morphology is obviously superior to cone deposition mor- phology in the aspects of trapping the coarse sand, discharging the fine sand, and reducing deposition and optimizing the process of outlet water and sediment, and so on. The delta deposition morphology is benefi- cial to shape density current, and the sediment ejection effect of density current is superior to backwater free flow. Physical model tests of Xiaolangdi Reservoir show that when channel suffers from retrogressive erosion and water level drops, the unconsolidated deposits in saturation state on both bank beaches will lost stability and slump into the channel and the storage capacity may recovery under the combined action of gravity and seepage water pressure. Therefore, in the current process of reservoir operation, retrogressive erosion can be shaped in river reach before dam and delta continent surface by controlling water level of inflow floods, so as to delay the transformation from delta deposition morphology into cone deposition mor- phology as long as possible.