Sand mining impact on Poyang Lake: a case study based on high-resolution bathymetry and sub-bottom data

Poyang Lake in the Changjiang (Yangtze) River catchment has undergone frequent spring drought since 2003, and some researchers attributed this phenomenon to sand mining and the lakebed deformation in the outlet channel linking the lake with Changjiang River main channel. However, there is still a lack of high-resolution subaqueous geomorphological evidence of how sand mining led to lakebed deformation in the outlet channel. We examined the bed morphology and sub-bottom sedimentary structure of the outlet channel, using a multibeam echo sounder and sub-bottom profiler in Poyang Lake. We found that: (1) the subaqueous micro-topography types of the outlet channel are characterized by sand mining disturbance, natural erosional topography, and flat bed and dunes, accounting for 44.9%, 21.4%, 28.6%, and 5.1% of the channel area, respectively; and (2) sand mining activity affects the local bed topography extensively and significantly. The depth of sandpits caused by sand mining varied from 1.4 m to 12 m deeper than the surrounding bed surface, with 4.41 m of depth increase on average. Hence, the large-scale high-intensity sand mining activities and their significant geomorphic effects demand for an improved assessment for future management and longer-term sustainability. Because of the large-scale and ongoing high-intensity sand mining activities in the Poyang Lake outlet channel, these effects should raise caution in the future and contribute to monitoring efforts that are essential to implement sustainable management solutions. The present study and techniques implemented can serve as a scientific reference for dam construction and sand mining within the Poyang Lake basin.