Stormwater is runoff caused by rains or snowmelt that gets into stormwater drains and is carried away to disposal retention or detention ponds. From these ponds, the water is carried away to natural water sources like rivers or streams that then carry it to the ocean. Stormwater will carry with it dirt, dust, and other debris that lies on the surface and this can lead to a fair amount of pollution that can affect the quality of water in the natural water resources.
It is necessary to prevent this, and this can be done by using hydrodynamic separators, that are stormwater devices that use a process of cyclonic separation to separate out the pollutants from the water before it is disposed of. They are basically, flow through structures that have a unit for separation and settling that removes part of the solid pollutants and causes them to form sediments that can be collected and disposed of separately. These separators will not be effective in removing any dissolved pollutants.
Hydrodynamic separators use the physical action of flowing water by having internal structures that create a swirling vortex, that separate out the trash, debris, and oil that is part of the stormwater, and will have additional features that reduce the velocity of the flowing water that then causes the polluting materials to settle. They are less effective when the stormwater inflows are very great, as they have a tendency to scour out the sediments formed. These separators do not require any external power source, as the energy in the water flow itself serves to provide the necessary energy required for separating the pollutants that need removal.
These separators can be installed underground in parking lots, commercial sites, or large housing complexes. During storms, rainwaters tend to collect pollutants as it flows along surfaces that are impervious like roads, sidewalks or rooftops. The separators are designed to remove the oil, sediment, and trash from this water, before it makes it way again to the stormwater drainage system that can then carry it, relatively unpolluted, to a local stream or pond. There are many manufacturers of such separators and each of them has its own proprietary method of ensuring the required degree of separation that can clean the water. It helps to remove pollutants, improves the health of natural streams and rivers, and can improve the environment in general.
It is important that hydrodynamic separators are regularly maintained and cleared, as not removing these pollutants can lead to their being carried to streams and rivers and polluting them. They will get regularly filled with sediment that does need to be removed. They need to be of the proper size after judging the catchment and quantity of water that will pass through the separators. There needs to be a regular schedule of maintenance, which may have to be augmented during severe storms that increase the runoff.
Preventive maintenance by regularly cleaning the surfaces on the property can reduce the need for cleaning the separators, by preventing the buildup of the amount of material that needs separation.