孔兑沙漠小流域高含沙洪水水沙关系特征及其指示意义——以毛布拉孔兑苏达尔沟为例

Characteristics of sediment-discharge relationship of hyper-concentrated flood and its implication in the Sudaer River of Maobula Kongdui

黄河上游十大孔兑流域是风水复合侵蚀十分严重的区域,以高含沙洪水为典型特征,水土流失严重,对区域生态与环境以及黄河干流造成严重威胁。因此,揭示孔兑小流域的暴雨洪水水沙关系,阐明高含沙洪水泥沙输移过程与特征,对防治区域泥沙灾害与整治水土流失具有指导意义。流量与含沙量(悬移质含量)滞后环(C-Q环)是研究水沙关系的重要工具和手段,是一种很有效的用来探讨泥沙输移动态变化的方法,能揭示泥沙输移的空间与时间上的联系,区分悬移质泥沙供给的时空来源。文中选择毛布拉孔兑支沟苏达尔沟作为孔兑沙漠小流域的典型观测对象,基于实地观测的暴雨洪水数据,研究探讨高含沙洪水的水沙关系。结果表明:砒砂岩与风沙是该区域高含沙洪水主要泥沙供给源,但两者对其洪水悬移质的供给方式不同。受砒砂岩沟道塌岸的滞后效应影响,洪水在上游砒砂岩段的水沙关系环表现为典型的逆时针滞后环,洪水涨水阶段泥沙含量约0. 2×10~3kg·m^(^(-3)),塌岸滞后效应使洪水退水阶段的最大含沙量约0. 8×10~3kg·m^(^(-3))。在下游沙漠段,风沙的大量横向供给直接导致水沙关系完全区别于上游砒砂岩段。由于沟岸沙丘的易侵蚀性与松散非粘滞性,洪水对沟岸沙丘的侵蚀过程并无滞后效应,所以洪水涨水阶段泥沙浓度急剧增大,形成超高含沙量的洪水,洪水泥沙浓度峰值平均约1. 2×10~3kg·m^(^(-3)),最大达1. 5×10~3kg·m^(^(-3));洪水退水阶段前期悬移质浓度无显著下降,直至洪水末期消退阶段悬移质浓度才急剧下降,水沙关系曲线呈现为"8"字形滞后环。因此,沙漠风沙的横向供给是该区域风水复合侵蚀与高含沙洪水的重要影响因素。

Ten Kongdui:is at the Upper Yellow River,and one of the typical regions of fluvial-aeolian interactions with serious water and soil loss,characterized by hyper-concentrated flood,which poses serious threats to local eco-environment system and the Yellow River.Thus,revealing sediment-discharge relationship and understanding suspended sediment dynamics in the small watershed of Kongduis can provide significant references for preventing sediment disaster and controlling water and soil loss in this area.Sediment-discharge hysteresis loop(C-Q loop),a useful method to explore suspended sediment dynamics,is an important means of studying discharge-sediment relationship,which can reveal temporal and spatial variation of sediment transport and distinguish sediment source origins.This paper has chosen the Sudaer river of Maobula Kongdui as the monitoring area of the small desert regions.Based on the monitored storm-flood data in the Sudaer river,we studied and explored the sediment-discharge relationship of the hyper-concentrated flood.The results show that"Pisha"sandstone sediment and aeolian sand are the two major suspended sediment origins,but they have different supply patterns for suspended sediments in the hyper-concentrated floods.In the upper reaches of the Sudaer river,owing to the hysteresis effect of bank collapse,anticlockwise hysteresis loops developed;there was mean 0.2×10^3 kg·m^-3 of suspended sediment concentration(SSC)on the rising limp,but 0.8×10^3 kg·m^-3 of SSC on the falling limp caused by the hysteresis effect of bank collapse.However,in the lower reaches of the Sudaer river,large lateral infusion of aeolian sand has a significant impact on sediment-discharge relationship,consequently,which is different from the"Pisha"sandstone area upstream.Owing to noncohesive and unconsolidated aeolian dunes with the hyper-erobility,there was no hysteresis effect on the contribution of dunes to suspended sediments.Therefore,in the rising stage of discharge,SSC sharply increased and developed hyper-concentrated flood,with the mean SSC of 1.2×10^3 kg·m^-3 and the maximum SSC of 1.5×10^3 kg·m^-3.In the early falling stage of discharge,there was no obvious reduction in SSC;whereas in the last falling stage of discharge,SSC tended to be a sharp decreasing trend.The sediment-discharge relationship developed figure-eight loops in lower reaches of the Sudaer river.Thus,lateral infusion of aeolian sand is the significant factor in the aeolian-fluvial interactions and hyper-concentrated floods in this area.