绵远河流域地震侵蚀与泥沙输移特征

汶川地震引发大量的崩塌滑坡、泥石流,为震区河流提供了丰富的泥沙来源。对处于地震极重灾区的绵远河流域进行了地震侵蚀与流域内的泥沙输移状况的调查统计。绵远河山区河段地震时产生了1.15×108 m3的松散堆积物,相当于正常年份土壤侵蚀量的约100倍。5a实地调查的结果显示,崩塌滑坡体绝大部分堆积在支沟中。在震后水文气候条件不变的情况下,松散堆积物中占多数的大粒径颗粒超过了河流输运能力,仅少量细颗粒物质以悬移质形式被输送到下游。研究表明,虽然绵远河上游地震侵蚀产沙总量巨大,但汶川地震后与震前进入绵远河平原河段的泥沙量变化不大,近期内对绵远河下游及沱江的泥沙输移没有明显影响。

Earthquake Erosion and Sediment Transportation of Mianyuan River Basin

A large number of the collapse, landslides and debris flows at different scales triggered by Wenchuan Earthquake are great sources of sediment for the river in earthquake area. To study effects of earthquake erosion on sediment transportation after Wenchuan Earthquake, field investigation and measurements were performed for the landslides and avalanches on the Mianyuan River. Based on the data for the past 5 years, 1.15×10⁸ m³ deposits were produced during this earthquake equivalent to about 100 times of the amount of soil erosion for a normal year, most of which were deposited and accumulated in the tributary ditches or channels. It indicated that only a few part of fine sediments were transported to the downstream as suspended load, as the dominant coarse particles were over the transportation capacity of the rivers without distinct change of hydrological conditions during the last five years. Although earthquake erosion resulted in a huge amount of sediment in the upstream Mianyuan River, the annual sediment discharge had no obvious difference from that before the earthquake, which showed that the effects of sediment from earthquake erosion on sediment transportation in the lower Mianyuan and Tuojiang Rivers are limited in the short term.