Stormwater Management in Pennsylvania

Stormwater has traditionally been treated as a nuisance, and past stormwater “management” techniques aimed to get rid of stormwater as quickly as possible. Today, we consider the opposite to be true: stormwater is seen as a valuable resource because it is the ultimate source of the water we use in our everyday lives and which feeds our rivers and streams.

For all practical purposes, stormwater management in Pennsylvania occurs at the local level: individual municipalities are ultimately responsible for adopting zoning ordinances and subdivision and land development regulations that incorporate stormwater management programs. Pennsylvania’s communities vary tremendously: there are great differences geographically, socioeconomically, and culturally, just as there are vast differences between conditions in and challenges facing pristine watersheds and those in highly urbanized areas. The goal of the Commonwealth’s stormwater management program is to enable municipalities enough flexibility to adapt to local conditions, while still encouraging rigorous local programs that integrate with the larger watershed(s) of which they are a part.

The average annual precipitation in Pennsylvania ranges from less than 34 inches to more than 50 inches per year, with most of the annual volume of rainfall coming from 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, with more than 95% coming from storms of 3 inches or less. Even though Pennsylvania is impacted by the occasional tropical hurricane, large 50-year and 100-year storms occur so rarely that despite dumping huge amounts of water when they do take place, they actually account for an insignificant amount of total rainfall volume when they are averaged out year after year.

Managing rainfall from the many small storm events, while also accounting for the volume spikes that will occur during major storms, is key to stormwater management success.