Storm-Water Quality Control Basin with Micropool

Abstract

Since the early 1990s, a water quality capture volume (WQCV) has been recommended for stormwater quality enhancement designs. However, lacking further guidance on how to shape the basin for this recommended volume, the current practice is to assume that the WQCV would lead to a satisfactory sediment trap efficiency provided that the drain time can be as long as 40 hours. In this study, the sediment trap efficiency method is modified to take basin dimension, drain time, and micropool into consideration. A water quality control basin (WQCB) should be designed with a preselected drain time and water surface area and then evaluated by its sediment trap efficiency. For a typical urban residential development with sediment particles consisting of clay, silt, and sand, a drain time for WQCB can be between 12 and 40 hours with its sediment trap efficiency varied from 60 to 80%. A drain time longer than 12 hours may result in a diminishing return on sediment trap efficiency. The performance of WQCB can be improved with a micropool. The case study indicates that a micropool can only increase the sediment trap efficiency from 80 to 89% when its storage volume increases from zero to WQCV. It implies that the major function of micropool is to control resuspended solids and buoyant debris.