The Evolution of Type E Sediment Basins
High Efficiency Sediment (HES) basins have become standard practice on many construction and development sites as a practical means to manage runoff during the construction phase and meet water quality criteria, design objectives and project conditions. The IECA Best Practice Erosion and Sediment Control (BPESC) provides design guidance for 2 types of HES basins: Type A and Type B basins.
Both Type A and B basins incorporate a forebay, level spreader, main basin cell and emergency spillway, and are setup to operate in a flow through manner, with a automated dosing unit located at the inlet to the forebay. A Type A basin will also include a floating decant which is designed to skim the clean water from the surface as the basin fills, and also dewater the basin to the bottom of the settling zone following the rainfall event. Implementation of Type A and B basins have provided significant improvements to managing the quality and quantity of water discharged from a wide range of sites, however like anything they have limitations… This has resulted in the evolution of Type E basins.
A Type E basin is effectively a HES basin with a regulating dam directly upslope of the basin. The Type E arrangement overcomes the key constraint of a HES basin in that a single inlet point is not critical, as all runoff from the upslope catchment is directed into the regulating dam (allowing multiple inflow points). From a design perspective this allows greater flexibility in locating the basin onsite and achieving the required levels (i.e. fall through the basin), and in many instances a smaller overall footprint.
Benefits of a Type E basin from an operational perspective include:
Reduced water treatment (i.e. less flocculating agent required if construction water is drawn from the regulating dam);
More accurate & efficient dosing;
Reduced maintenance time & cost with desilting typically limited to the regulating dam during operational life.
As sediment control practices continue to evolve, Type E basins are proving to be a highly practical and effective solution for complex sites and challenging catchments.
