Stormwater—water from rain or melting snow that does not soak into the ground immediately. Stormwater flows from rooftops, over impervious areas and bare soil, and through sloped lawns and fields.
Stormwater management—the process in managing and/or capturing the runoff. It is important because it can lead to pollution, erosion, flooding and many other environmental and health issues if not properly understood and maintained.
As it flows, runoff collects and transports soil, pet waste, pesticides, fertilizer, oil and grease, leaves, litter, and other potential pollutants that ultimately wind up in local bodies of water. A single garden hose can supply enough water to wash left behind contaminants from the landscape into our local water bodies, so you can only imagine what an entire rain event can do.
Modern approaches have been designed to rebuild the water cycle and eliminate direct contamination.
Infiltration pits are common for projects such as homes, garages, outbuildings, etc. Runoff is directed into the pit or in voids between the stones and slowly infiltrate into the soil. The soil acts as a filter and removes pollutants. Infiltration devices and associated practices can achieve up to 70 to 98 percent contaminant removal.
Retention ponds, also known as wet ponds, have a permanent pool of water that fluctuates in response to precipitation and runoff from the contributing areas. Maintaining a pool discourages resuspension and keeps deposited sediments at the bottom of the holding area. Some contaminants are removed through biochemical processes. Wet ponds can achieve 40 to 60 percent phosphorus removal and 30 to 40 percent total nitrogen removal.
Detention ponds are typically dry except during or after rain and snow melts. They are common in the developments within West Manheim to collect the impervious runoff. The pond is used to slow down water flow and hold it for a short period of time, usually 24 hours. Detention basins reduce peak runoff rates associated with storms, decreasing flood damage and settle stormwater particles. Although detention ponds can vary in size and shape, all of the ponds are designed to be separate from local groundwater supplies to prevent movement of dissolved pollutants from surface water to groundwater sources.