黄土高原典型支流淤地坝拦沙对输沙量减少的贡献

为探明淤地坝拦沙作用对河流输沙量变化的影响,依据淤地坝作用年限、坝控面积、坝控流域侵蚀产沙模数及淤地坝排沙率,确定淤地坝拦沙量的估算方法,并结合2009年淤地坝安全大检查数据,分析黄土高原典型支流淤地坝拦沙对输沙量减少的贡献.延河与皇甫川淤地坝在不同年代的拦沙量分别在92.48万～854.35万t/a与36.47万～1 138.75万t/a之间,淤地坝拦沙量占人类活动影响的比例在一级和二级突变后分别为29.1％、28.5％与8.4％、18.2％;2000年以后延河与皇甫川输沙量减幅均达到85％以上,而淤地坝拦沙量的贡献率分别小于10％和20％.淤地坝的拦沙作用已不是目前输沙量减少的主要因素,但由于土壤侵蚀环境的不同,淤地坝在皇甫川对输沙量减少的贡献比在延河要大.

Contribution of sediment retention by check-dams to sediment discharge reduction of typical tributaries on the Loess Plateau

Background] This work aims to ascertain the contribution of sediment retention by check-dams to sediment discharge reduction,and to further reveal the attribution of the water and sediment changes in the Yellow River and provide the decision-making basis of check-dam construction on the Loess Plateau.Methods] The typical tributaries of Yanhe River in the loess hilly-gully region and Huangfuchuan River in the weathered sandstone hilly-gully (pisha) region were selected.On the basis of the safety survey database of check-dams in 2009,the operation period of check-dams,dams-controlled area,erosion-sediment yield modulus of dams-controlled watershed and sediment delivery ratio,the estimation method of the sediment retention were determined,and the contribution of sediment retention by check-dams to sediment discharge reduction in the typical tributaries on the Loess Plateau was analyzed.Results] The average annual retained sediment amount by check-dams in different decades during 1960-2015 in the Yanhe watershed ranged from 0.92 million t/a to 8.54 million t/a,in which the maximum appeared in the 1980s,followed by the 1970s (7.89 million t/a),the minimum occurred in 2000-2009.While in the Huangfuchuan watershed,the average annual retained sediment amount in different decades varied from 0.36 million t/a to 11.39 million t/a,the maximum in 2010-2015,then 1990s (7.41 million t/a) and the minimum in 1960s.In addition,the results showed that the significant reduction of the annual sediment discharge in the Yanhe and Huangfuchuan watersheds (P ＜ 0.01) according to the Mann-Kendall trend test.On the basis of the Pettitt's abrupt test,the first transition year of the annual sediment discharge from 1955 to 2014 in the Yanhe and Huangfuchuan watersheds appeared in 1996 and 1984 (P ＜ 0.05),while the second transition year of the annual sediment discharge were in 2005 and 2003 (P ＜ 0.05),respectively.Meanwhile,the sediment discharge reduction after the abrupt change ranged from 18.25 million t/a to 42.20 million t/a in the Yanhe watershed and from 27.49 million t/a to 50.37 million t/a in the Huangfuchuan watershed,respectively.The influence of precipitation on sediment discharge reduction was weakened after abrupt change,while the effect of human activities was enhanced gradually.In addition,the contribution of sediment retention amount by check-dams to human activities in the Yanhe and Huangfuchuan tributaries were 29.1％ and 28.5％ after the first transition year,8.4％ and 18.2％ after the second transition year,respectively.After 2000,the decreased sediment discharge was more than 85％ in the Yanhe and Huangfuchuan tributaries,while the contribution of retained sediment amount by check-dams was less than 10％ and 20％,respectively.Conclusions] It showed that the effect of sediment retention by check-dams was not the main factor of sediment discharge reduction.Due to the different soil erosion environment,especially the differences in the vegetation restoration effect and proportion of dam-controlled area to watershed area,the contribution of check-dams on sediment discharge reduction in the Huangfuchuan tributary was greater than that in the Yanhe tributary.