Influence of Wind-Generated Wave Action on Mountain Reservoir Bank Collapse: A Case Study at the Lancang River, Western China

Xuan Zhang,Faming Zhang,Qingxiang Meng,Yonghui Wu

doi:10.2113/2022/6427717

Abstract

Abstract Slopes facing reservoir water often collapse, affecting reservoir capacity. It is important to understand the factors affecting such collapses and predict the locations of collapse after impoundment for practical purposes. However, the mechanism of bank collapse in mountainous areas after reservoir impoundment remains unclear. To address this issue, field geotechnical property surveys, laboratory tests, and numerical simulations were employed to evaluate bank collapse susceptibility. The results showed that (i) bank collapse mainly occurs in slopes with a small cohesion and internal friction angle of less than 30°; (ii) the main effects of wave action on bank collapse are scour, erosion, and cyclic impact on the bank slope: wave erosion occurs in the bank slope with a wave height of less than 1.0 m, cohesion of less than 90 kPa, and slope angle of less than 30°, and wave impaction mainly occurs at the area with a wave height of more than 2.0 m and a slope angle of more than 30°; (iii) for valley reservoirs, softening of water on the slope rock and soil mainly reduces cohesion, which commonly occurs within 30 days; the cyclic action of wave impact load mainly damages the structure and reduces the internal friction angle. The influence of waves on bank collapse is mainly related to the wave height and wave velocity. The antiwave impact broken energy of rock and soil is an important index to evaluate whether bank collapse occurs in the long term, which is related to the strength, structure, and impact resistance. The present research is helpful to better understand the mechanism and evolution process of reservoir bank collapse.

Highlights

Reservoir bank collapse is one of the most important geological disasters, affecting the security of immigration engineering in the reservoir areas and reservoir capacity [1,2,3,4]
The effect of waves on bank collapse is mainly reflected in the impact of periodic wave loads and erosion on the bank slope
In the reservoir area of the Miaowei hydropower station, 90% of the bank collapses occurred in the range of 10–20 km from the dam (15% of the total length of the reservoir), and 90% were distributed in the residual soil; strong toppling was observed where strong wave action of the total 33 collapses occurred

Summary

Introduction

Reservoir bank collapse is one of the most important geological disasters, affecting the security of immigration engineering in the reservoir areas and reservoir capacity [1,2,3,4]. On 3 October 2001, a reservoir collapse in Sichuan Province in southwest China caused deaths, with people missing and injured. The wave induced by the “720” bank collapse of Xiaowan reservoir in the Lancang River led to people missing. On 11 August 2012, a 180,000 m3 reservoir collapsed in Zhoushan, Zhejiang province, killing at least 10 people and injuring 27 others. Accurately predicting reservoir bank collapse is a key issue in the construction of water conservation projects. Intensive investigation or modelling of bank collapse predictions has not been performed. The mechanism of bank collapse must be studied to analyse the sections in which bank collapse may occur, and it is necessary to use the corresponding analysis results to predict the scope of collapse

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