Three-Dimensional Modeling of Turbid Density Currents in Imha Reservoir, South Korea

The propagation dynamics of the turbid density currents of the Imha Reservoir is investigated using the FLOW-3D computational fluid dynamics code. The renormalization group (RNG) $\kappa \text{-}\epsilon$ turbulence scheme in a Reynolds-averaged Navier–Stokes (RANS) framework was applied for the field investigation. A new particle dynamics algorithm was developed and coupled with the FLOW-3D model to simulate the settling of sediment particles, and the model was tested with field measurements during Typhoon Ewiniar. The coupled model correctly predicted the spatial and temporal evolution of intrusive density currents with plunging flows at a depth of 20 m and interflows propagating downstream at about $0.2\mathrm{m}/\mathrm{s}$. The simulation results with sediment settling demonstrated that the ratio of transported to initial sediment concentration ($C_0/C_i$) varies as a function of particle size $d_s$ and sediment concentration. Density currents can be classified into three regimes: (1) a suspended regime ($d_s<10\mathrm{\mu m}$), where interflows will transport most of the sediment inflows from the reservoir inlet to Imha Dam; (2) a transition regime ($10\mathrm{\mu m}<d_s<40\mathrm{\mu m}$), where deposition rates alter the flow dynamics; and (3) a deposition regime ($d_s>40\mathrm{\mu m}$), where sediment particles rapidly settle out without forming a density current. For the suspended regime, river inflows will define three different types of density currents in the reservoir: (1) interflows when $C_i<\mathrm{2,000}\mathrm{mg}/\mathrm{L}$; (2) multiple intrusions when $\mathrm{2,000}<C_i<\mathrm{3,000}\mathrm{mg}/\mathrm{L}$; and (3) plunging underflows when $C_i>\mathrm{3,000}\mathrm{mg}/\mathrm{L}$.