Morphodynamics of the Shi-ting River after Wenchuan Earthquake: Effects of in-channel weirs and fine sediment supply on river incision

Since the 2008 Wenchuan (Ms. 8.0) earthquake, the Shi‑ting River in Sichuan Province, China has suffered massive bed incision, with the largest incision depth being more than 20 m in 7 years. Potential reasons include: breaks in sediment connectivity due to widespread in-channel weirs; the supply of fine sediment after the earthquake; intensive sand mining, etc. In this study, we simulate the combined role of in-channel weirs and fine sediment supply in determining the massive bed incision in the Shi-ting River. A one-dimensional river morphodynamic model is implemented. The simulated results show that the in-channel weirs can lead to bed incision and bed coarsening in the downstream channel. For a weir with a height of 5 m, the maximum incision depth is about 5 m, and the extent of downstream incision is no more than 20 km within 20 years. The supply of fine sediment can enhance the downstream channel incision, as the weir preferentially traps coarse sediment but passes the fine sediment downstream. However, a combination of in-channel weirs and the fine sediment supply cannot explain the dramatic incision (20 m in 7 years) as observed in the Shi-ting River. This suggests that the mining of gravel and sand had a significant role in driving channel degradation.