黄土丘陵区淤地坝建设后小流域泥沙拦蓄与输移特征

摘要

了解淤地坝建设后小流域泥沙拦蓄与输移的变化特征对正确认识和评价淤地坝的减蚀作用有重要意义.该文通过对黄土丘陵区王茂沟流域1953-2015年不同时段内淤地坝的拦沙量和流域出口输沙量的分析,研究了坝系建设后泥沙拦蓄、输移和侵蚀的变化过程与特征.研究表明,王茂沟流域年均拦沙模数呈减少-增加-再减少的波动变化趋势;流域年均输沙模数呈先增加后减少的变化趋势;1953-1986年期间,不同阶段的年均侵蚀模数变化不大,1987年后呈显著下降趋势.流域治理后期与初期相比,年均拦沙模数、输沙模数和侵蚀模数分别下降了79.3％、90.6％和83.9％.淤地坝建设初期,有效库容对流域拦沙模数和输沙模数的变化有重要影响,侵蚀性降雨频发和较低的水土流失治理度是侵蚀强烈的主要因素;流域治理后期,侵蚀性降雨及其发生频次的减少,水土流失治理度的提高与稳固,是流域拦沙、输沙和侵蚀产沙显著下降的主要原因.淤地坝在控制流域侵蚀产沙、减少泥沙输移方面作用显著,但要达到持续有效的作用,坡面治理不容忽视,两者兼顾是黄土丘陵区水土保持的必由之路.%Since the 1950s,as one of engineering measures for conserving soil and water,many check dams have been constructed on the Loess Plateau in China.Up to now,there is more than 110 thousand of check dams have been constructed,which play important roles in holding back eroded soil just like sediment ponds.Understanding the variance of sediment retention and transport in a small watershed after construction of check dams is very important for the correct evaluation on the sediment reducing benefit of check dams.As a typical watershed with check dam construction,many check dams have been constructed and played important role in blocking sediment and changing the transport process in the past six decades in the Wangmaogou watershed in the Loess Hilly Area.Based on the date of sediment retention in check dams and the sediment discharge in the Wangmaogou watershed during the period of 1953-2015,the variation in processes and characteristics of sediment yield,and retention and transport in different stages in the watershed were analyzed in this study.Results showed that the variation of average annual sediment retention in the check dams fluctuated with time.The sediment discharge increased firstly and then reduced.The variance of erosion intensity was very small in various stages during 1953-1986,but it decreased significantly after 1987 in the watershed.Compared to the initial stage after the check dam was constructed,in the present stage (1993-2015),the average annual sediment retention in the check dams,and the average annual sediment discharge and soil erosion intensity for the watershed decreased by 79.3％,90.6％ and 83.9％,respectively.In the initial stage,the usable capacity of check dams was a main influence factor for the variance of sediment retention and discharge,while more erosive rainfall and higher occurrence frequency had great effect on the erosion intensity,and the latter increased with the increase of the former.Since the year of 1987,the decrease of erosive rainfall and its occurrence frequency were the main factors for decreased erosion intensity.Meanwhile,the continuous increasing soil and water conservation ratio,particularly along with the quick increase of soil and water conservation measures on hill slopes,such as terrace,woodland,grassland and so on,has greatly reduced the runoff production and sediment yield from hill slopes and thus reduced the potential kinetic energy and gully erosion.Thus,the benefit of sediment reduction from the hill slope was gradually increasing,whereas the benefit from the check dams was gradually decreasing during the past six decades.When the soil and water conservation ratio reached a higher degree,its sediment reduction effect can work gradually.For high-intensity rainfall,check dams had a significant and irreplaceable role in controlling soil erosion and reducing the sediment transport,but these soil and water conservation measured on hill slopes cannot be ignored in order to achieve sustainable and effective role in the Loess Hilly Area.