Spatial heterogeneity of lake sediment hydraulic conductivity, hydrological connectivity and causes analysis under the influence of sand mining activities: In-situ tests in a typical large sand mining lake (Poyang lake)

Sand mining engineering will change the saturated hydraulic conductivity (K) of sediments, which is an important parameter determining the connectivity of surface water-sediment-aquifer system and the stability of shoreline. However, the research about K and hydrological connectivity of lake sediment under the influence of sand mining activities is still limited. In this study, 90 standpipe tests were conducted in the global largest sand mining lake (Poyang Lake) to measure K of lakebed sediment in different directions. Geostatistics, connectivity index and remote sensing were used to analysis the spatial heterogeneity of K, hydrological connectivity and sand mining effect on K. Results showed that the spatial variability of K was strong in Poyang Lake. K_v, K_s, K_h varied from 1.85 × 10⁻⁶ to 9.43 × 10⁻² cm/s, 3.63 × 10⁻⁶ to 9.95 × 10⁻² cm/s, 1.29 × 10⁻⁶ to 5.16 × 10⁻² cm/s. Gaussian model of K_v, K_s and K_h fitted the experimental variogram best. Poyang Lake sediments were composed of silt, silty loam, sandy loam and loamy sand. Hydrological connectivity index varied from −29 to 35 among the test points. d₂₀ and d₅₀ had the strongest correlation with K. Power function model was the best fitting model of K and characteristic grain size. Large-scale sand mining engineering affected the heterogeneity of K and hydrological connectivity by changing sediment grain composition, geomorphic type, groundwater depth and hydrodynamic conditions. The results provide important references for lake sediment permeability researching, sand mining engineering management and slope instability prevention in similar large sand mining lakes.