The Application of One-Dimensional NonThe Application of One-Dimensional Non-Equilibrium Sediment Transport Model in Desilting Basin-Equilibrium Sediment Transport Model in Desilting Basin

Desilting basins are often used as the heads of diversion projects in which coarse sediment particles in the water flow are deposited. Based on a one-dimensional non-equilibrium sediment transport theory, a mathematical model of the sediment depositions in a desilting basin was established in this study. The proposed model could not only calculate the sediment deposition rates in the desilting basin, but also profile the sedimentation distributions along the desilting basin, as well as the deposition rates of each particle size group, and the changes of suspended sediment concentrations and gradations. The model was used to calculate the sediment deposition in a desilting basin in the Central Yunnan Water Diversion Project. The years 1966, 1996, 1977 and 1973 were selected as the representative years which had corresponded to the diversion guarantee rates of 25%, 50%, 75% and 95%, respectively. The calculation results showed the following: (1) The silting thicknesses along the desilting basin in all of the guarantee-rate years displayed the same distribution regularity. That was, the silting thicknesses near the inlet sections were observed to be larger (between 2.84 and 5.32m), which was followed by gradual decreases until the silting thicknesses near the outlet sections were between 0.33 and 0.68 m; (2) The sediment deposition rates during the years with different guarantee rates were approximately 34%; (3) The deposition rates of the sediment with coarse particles (greater than 0.05 mm) were between 87.08% and 90.91%; (4) The percentages of the sediment particles with diameters greater than 0.05 mm near the outlet sections ranged between 4.50% and 6.29%. In order to figure out the effects of the desilting basin scales on the deposition rates, three design schemes were put forward, including lower or raising the bottom level of the desilting basin by 2 m and extending the desilting basin by 50%. The results showed that the scale changes of the desilting basin had no significant effects on the overall sediment deposition rates, except the particle sizes greater than 0.05 mm. The main reason of slight effects being analyzed was the finer sediment applied, with a median particle size of 0.0153mm.