Runoff from rain and snowmelt (stormwater) is the second largest contributor to water quality impairment in Pennsylvania today.
Rain in PA
There was a time when "point source pollution" flowing into waterways from industry and sewage treatment facilities was the biggest threat to water quality. Today, non point source pollution (such as abandoned mine drainage, atmospheric deposition, earth moving activities, on-lot septic systems, timber harvesting, and runoff from urban areas and agricultural lands) is the cause of most water quality problems across the country, including here in Pennsylvania.
In many parts of the state, stormwater overwhelms aging sewage infrastructure, causes flood damage, and puts people's health at serious risk. Unfortunately, these problems aren‘t limited to major storms; they often result from the average rainfall event. Human activities have altered the landscape so dramatically that the natural system of “stormwater management” no longer works.
The average annual precipitation in Pennsylvania ranges from less than 34 inches to more than 50 inches per year, with most coming during small, frequent storms. Some 65% of the state’s average annual rainfall occurs in storms that drop less than 1 inch in a 24 hour period; more than 95% comes from storms of 3 inches or less. Even though Pennsylvania has been hit by several tropical storms and hurricanes over the past century—with devastating results—the large 50-year and 100-year storms occur so rarely that they actually account for an insignificant amount of total rainfall volume when averaged out year after year.
Dealing with rainfall from the many small storm events, while planning for the massive volume spikes that do occur during major storms, is the key to stormwater management success.
Runoff: Waste or Resource?
Traditionally, we have treated stormwater as a nuisance, and past management techniques focused primarily on flood prevention. Stormwater detention basins were built in the belief that capturing water from large storms was the only concern. The Commonwealth is rife with thousands of these "giant bathtubs" that were built for volume control.
The thinking has shifted in recent years, with the realization that basins were largely ineffective. Today, the focus of stormwater management is upon preserving the integrity and quality of water in our rivers and streams—and throughout a watershed as a whole. Stormwater is seen as the limited resource it is and is considered a valuable natural asset to be used, not abused.