Sediment Suspension in the “Starving” Jingjiang Reach, Downstream from the Three Gorges Dam, China

The Jingjiang Reach of Yangtze River has significantly changed its sediment regime since the beginning of this century, i.e., the once equilibrium reach has become starved of sediment due to the impoundment of the Three Gorges Dam. Recent measurements in the Jingjiang Reach have revealed anomalous vertical profiles of suspended sediment. Without appropriate modification, traditional suspension formulae, e.g. Rouse Equation may cause up to 40% errors when applied to estimate the sediment flux in those unsaturated flows. Compared to Rouse Equation, Han’s Equation for nonequilibrium sediment-laden flow performs better in the upper part of a vertical, but still underestimates the concentration near riverbed, i.e. within 10% of water depth, where the observed value is much higher than its theoretical expectation. To solve the problem, this study develops a fractional advection-diffusion equation to characterize the dynamics of nonequilibrium sediment suspension. After validating the equation against field measurements in the Jingjiang Reach, we find that the proposed physical model can describe the real-world sediment profiles in “starving” river reaches. The promising stochastic approach shows good application future since more large dams are to be built in West China.