宁南山区淤地坝泥沙淤积特征及其对流域输沙变化的贡献

Aiming at the serious soil erosion and the fragile ecological environment in the mountainous area of southern Ningxia, and based on the interpretation and classification of different ecological restoration modes and combination characteristics in the study area, the project will be executed in the typical check-dam controlled watersheds under different ecological restoration modes. According to the sediment sampling of check-dam, the deposition couplet identification and erosive rainfall events correspondence, the sediment deposition yield of different time scales will be estimated by combining with the high precision topographic survey and the capacity curves of check-dams, and then the characteristics of sediment yield of check-dam controlled watersheds will be deduced at the runoff event and the annual scales. The relationship between the catchment erosion sediment yield and the rainfall, the underlying surface conditions will be revealed. The sediment yield of typical check-dam controlled watershed in different years in terms of different ecological restoration modes, the sediment retention of small watersheds in different ecological restoration modes will be analyzed. And then the effect of sediment retention by check-dams on the contribution of sediment discharge variation will be clarified. This study will provide scientific basis for the sustainable development of ecological restoration and management in the mountainous area of southern Ningxia. The research has the theoretical value and guiding significance to the environmental restoration in ecological fragile areas, investment direction and decision of soil erosion control in the future, the landscape engineering realization and the ecological civilization construction on the Loess Plateau.

针对宁南山区水土流失严重、生态环境脆弱的现状，通过对研究区不同生态修复模式及组合特征进行解译与分类的基础上，以代表不同生态修复模式的典型坝控流域为研究对象，基于淤地坝泥沙样品采集、淤积层次甄别及与产流降雨事件的对应关系，结合高精度地形测量及库容曲线，估算淤地坝不同时间尺度的泥沙淤积量，反演坝控流域在径流事件尺度和年尺度上的产沙模数变化特征，揭示流域侵蚀产沙与降雨、下垫面条件的关系；依据不同生态修复模式的典型坝控流域不同年份的产沙模数，分析不同生态修复模式小流域的淤地坝拦沙量，进而阐明淤地坝拦沙作用对流域输沙变化的贡献，以期为宁南山区生态修复与治理的可持续发展提供科学依据，对黄土高原生态脆弱区环境修复、未来水土流失治理的投资方向与决策、实现山川秀美及生态文明建设具有理论价值和指导意义。

黄土高原的水土流失治理及其对黄河泥沙变化的影响一直是相关管理部门和学术界关心的热点问题。宁南山区水土流失严重、生态环境脆弱，各类水土保持生态修复措施快速发展，如何维持一个可持续的生态修复模式来有效缓解土壤侵蚀？对促进黄土高原地区的生态环境恢复与可持续发展具有理论价值和指导意义。本研究以宁南山区清水河流域为研究对象，根据流域内淤地坝的数量、分布、建成时间和运营等情况，选取了3个代表不同生态修复模式组合的典型坝控小流域，基于淤积泥沙样品采集、层次甄别及与产流降雨事件的对应关系，结合高精度地形测量及淤地坝库容曲线，获得不同时间尺度淤地坝泥沙淤积量，反演坝控流域产沙模数变化特征，定量分析淤地坝拦沙作用对流域输沙变化的贡献。主要取得以下进展：一是明确了不同生态修复模式组合淤地坝的泥沙淤积过程与变化特征，以植被恢复为主的犁尖沟流域多年平均淤积量小于退耕型的塌堡子流域，而混合型的白吉流域多年平均淤积量最大，这与该流域耕地面积较大且耕种大量的坡耕地有关；二是揭示了不同生态修复模式坝控小流域的产沙模数变化特征，3个坝控小流域的最大次产模数是最小次产沙模数的27~84倍左右，多年平均产沙模数分别为1030.95 t/(km2·a)、1117.12 t/(km2·a)和980.86 t/(km2·a)，分属于轻度、轻度和微度土壤侵蚀；三是阐明了淤地坝拦沙作用对清水河流域输沙变化的贡献，截止2012年清水河流域淤地坝的泥沙淤积总量约为2414万t，自上世纪70年代中期以来清水河流域淤地坝的拦沙作用很明显，但随着退耕还林（草）工程实施以后，该流域淤地坝拦沙量仅占人类活动影响的10.4%，淤地坝的拦沙作用对流域输沙减少的贡献在逐渐减小。研究成果可为无观测设施地区侵蚀产沙资料的获取及重建小流域侵蚀产沙强度的历史变化过程提供数据支撑，并为进一步揭示黄河水沙变化的归因及黄土高原淤地坝建设决策提供科学依据。