SEDIMENTATION IN STORAGE TANK STRUCTURES

Although storage tanks provide an effective means of reducing the magn itude and frequency of combined sewer overflow discharges, and thereby of alleviating urban watercourse pollution, poorly designed storage s tructures frequently suffer from maintenance problems arising from sed imentation. The development of design guidelines that optimise the sel f-cleansing operation of storage structures is clearly a priority for urban drainage research. This paper describes a system that has been d eveloped to study sediment deposition in laboratory model-scale storag e structures. The patterns of deposition resulting from a selection of flow regimes are described, and the need for time-varying and time se ries storm tests is highlighted. Sedimentation patterns are shown to p redominantly depend on the flow field, and the critical bed shear stre sses for deposition and erosion in the model situation are identified. Hence, the potential application of numerical models to the design pr oblem is discussed.