Debris flow amplification in a moraine terrace and related engineering measures in the Zongzhai valley, southeastern Tibetan plateau

Abstract

Debris flows can quickly destroy basic facilities in mountainous areas, where suitable land resources are limited and towns are located on gentle slopes. To alleviate the threat of debris flows, two main approaches, based on debris storage or debris-flow excretion, have been proposed in recent decades in China. In August 2015, a debris flow occurred in the Zongzhai Valley for the first time in the last 100 years. Field surveys, section measurements and discharge calculations indicated that the bulking of the debris flow and the sediment entrainment were serious, resulting in the widening and deepening of the channel along the moraine terrace. Therefore, the two traditional mitigation methods appear to be inappropriate for the debris flows in Zongzhai Valley because this region lacks sufficient space for debris storage and economic support for a long drainage canal. This study analyzed the supply mechanism of the bed material and bank sediments along the moraine terrace and found that the bank collapse was mainly controlled by bed scour. Based on a literature review, we determined that the channel bed strength in the terrace should be increased and proposed that shallow dams be constructed to maintain the stability of the channel bed. The parameters of these shallow dams are provided in this article.