Flow past a sand mining pit

Abstract

In the present thesis, evolution of bed due to sand mining is studied by one dimensional flow and sediment modeling using HEC-RAS 5 (Hydrologic Engineering Centre - River Analysis) Software. HEC-RAS uses continuity and momentum equations for water flow and sediment continuity equation for sediment flow. The governing partial differential equations are solved using an implicit finite difference scheme. A numerical model is constructed in HEC RAS. The numerical model is validated using experimental data available in literature. In addition, the numerical model is also validated simulating by reproducing the experimental results obtained at Hydraulics Laboratory at IIT Gandhinagar. The numerical model is used to study the evolution of a hypothetical channel bed. Effects of flow characteristics, pit characteristics and sediment characteristics on bed evolution due to sand mining are studied. It is found that the sediment carrying capacity of water increases with discharge but this relationship is not linear. Also if the discharge is made fluctuating, rather than constant during the simulation time, the head cutting and pit migration increases. The pit migration and pit filling rate is found to be greatly affected by the shape of pit. The depth of the pit does not affect the upstream and downstream erosion but sediment deposition in the pit increases with the increase in pit depth up to a certain limit. Whereas, on doubling the pit width, the deposition in the pit is also doubled. The location of pit and number of mining pits is also found to be affecting the bed morphology.