Navigational safety at risk: The impact of sand Mining in a key waterway in China

Abstract

AbstractThe Caowei River is an important part of the planned high‐grade waterway network in China. Since 2016, the deterioration in the navigation flow conditions of the Xiangshuikan reach has made traveling upstream through the waterway more difficult for ships and raised emerging navigation safety concerns. To better understand the causes of the deterioration in the waterway navigation conditions after 2016, we examined the topographic and hydrological changes of the Caowei River and investigated the navigable flow conditions of the Xiangshuikan reach. The results showed that the Caowei River has generally been scoured since 2006 due to sediment depletion and that the dramatic riverbed downcutting (15.47 m in the deepest cut of thalweg elevation) in the Xiangshuikan reach was likely caused by illegal sand mining which extracted the fine sand underlying the clay overburden in this segment and led to the formation of two extremely large steep headcuts. It was found that a large water surface gradient, rapid flow velocity, and disordered flow pattern occurred near the larger upstream headcut during the low‐water‐level period, which made ship navigation more challenging. In 2019, the measured maximum local water surface gradient and maximum flow velocity reached 3.97‰ and 3.28 m/s, respectively. Additionally, the increase in the low flow at Caowei station and the decrease in the low water level at Lujiao station further aggravated the navigation conditions of the Xiangshuikan reach. These findings reveal the considerable complexity of the response of the channel navigation flow conditions to the topographic and hydrological changes in the lake area, providing valuable information for channel regulation and river management in the Dongting Lake area and other rivers.