Human impacts on riverbed morphology and hydrology in the lower reaches of the West River, China

Abstract

AbstractNatural and anthropogenic factors have led to a series of fluvial sedimentation and hydrological changes in the lower West River, China. To evaluate the influence of human activities on the channel's morphology and examine the hydrological responses, we analyzed channel adjustments and changes of low water levels in the main river channel between Wuzhou and Zhaoqing that occurred over the recent decades. Due to a remarkable decrease in the suspended sediment concentration, the suspended sediment outputs during this period were larger than the sediment inputs for 27 consecutive years from 1987 to 2013. Therefore, the riverbed became a sediment source, with a high scouring of riverbed material. Between 2004 and 2014, the channel capacity of the lower reaches increased by 302.02 × 106 m3, and the average riverbed elevation decreased by 2.21 m, approximately 11.8% of which was caused by bed sediment loss induced by natural scour through sediment depletion; the remainder was caused by waterway engineering and sand mining, accounting for 0.8 and 87.4%, respectively. Approximately 91.3% of 1,312 river cross‐sections exhibited downcutting, indicating significant adjustment of the riverbed. This resulted in a substantial decline in the low water level in the 44‐km upstream section above Ducheng, which is located at the end of the tidal limit during dry seasons. However, this change was not noticeable in the section below Ducheng owing to the small water surface gradient and tidal influence. These findings reveal that human activities are a major driving force in the evolution of large rivers and the complexity of the hydrological responses to riverbed downcutting in a tidal reach, providing useful information for future river sand mining management and navigable engineering design of the lower West River and other rivers.