北江干流中下游水沙特性变化及建库影响

定量研究水库的拦沙效应是揭示水库对河道泥沙输移影响的关键之一。在对北江干流中下游近60年水沙特性变化分析的基础上,运用干、支流主要控制水文站实测资料,估算梯级水库拦沙量;基于Brune拦沙率方法,提出北江干流梯级水库综合拦沙率修正式,研究水库拦沙对下游河道输沙量减少的影响。结果表明:(1)与1956—1999年相比,2000—2005年石角站年径流量仅减少6.16%,年输沙量则减少39.17%。其中,干支流水库拦沙合计约142.59万t/a,约占石角站减沙量的52.34%;水土流失工程措施减沙量约占18.83%;径流量减少引起的减沙量约占5.07%。(2)采用修正式计算,现状条件下(2012—2016年),干流梯级水库综合拦沙率约为12.81%,与实测值较为吻合。(3)2006年以来,库区泥沙淤积量与采砂量基本平衡,北江干流梯级枢纽水库拦沙率将在较长时间内维持现状水平。

Variations in runoff and sediment load in middle and lower Beijiang River and impacts of cascade reservoirs

Quantitative research on the reservoir sediment trapping effect is key in revealing the influence of cascade reservoirs on sediment transport. This paper estimates the trapping efficiency through an analysis on the variations in runoff and sediment load in the middle and lower Beijiang recorded at the hydrologic stations on the mainstream and tributaries in the past 60 years. We modify the formula of reservoir trapping efficiency using G. M. Brune’s trapping efficiency curves, and apply it to evaluating the influence of cascade reservoirs on sediment transport. The results show that (1) from the period of 1956-1999 to 2000-2005, Shijiao station manifested a reduction of 39.17% in sediment discharge while a reduction of only 6.16% in annual runoff. In 2000-2005, the total sediment trapped in the reservoirs was about 1.43 million tons per year, or 52.3% of the reduction at Shijiao. To the total sediment reduction, the contribution was 18.83% by the engineering measures for water and soil conservation, and 5.07% by runoff drop. (2) By the modified formula, the sediment trapping efficiency of cascade reservoirs in the 2012-2016 conditions is about 12.81%, which agrees well with the measurement. (3) Since 2006, the amounts of sedimentation and sand mining have nearly balanced in the cascade reservoir area, and we predict that the sediment trapping efficiency of reservoirs will be maintained at the existing level for long in future.