When rain falls to the land surface in quantities that exceed the land surface's ability to absorb, or infiltrate, stormwater runoff is produced. The amount of runoff is dependent on the intensity of rainfall, the length of the rainfall event and the characteristics of the surface upon which the rain falls. These characteristics include the slope of the land, the land cover and soil types. The amount of runoff can range from none to tremendous amounts. For example, a short, light rain falling on very permeable soils may produce no runoff while a heavier rain falling on a parking lot will produce larger amounts of runoff.
A watershed is an area of land that drains to a common point. For example, the Paxton Creek watershed is the area of land that, when runoff is produced in this area, the runoff will drain to the Paxton Creek and discharge to the Susquehanna River. In this example, the common point to which the watershed drains is the mouth of Paxton Creek at the Susquehanna River.
As the land surface in a watershed is altered (through activities such as clearing forests, grading and development) runoff characteristics change in response to the activity. For example, if a forested area is cleared and replaced with a parking lot, the amount of runoff produced in any given rainfall event will increase. Generally, the result of these alterations is that more runoff is produced and delivered to the receiving stream in greater quantities and more quickly. This results in less water being retained in the watershed for groundwater recharge and larger stream flows occurring more often. Further, runoff often carries with it a wide variety of pollutants that are washed from the land surface into receiving streams either directly or through storm sewer systems.
The end results of this are negative impacts to the stream. Stream banks and beds can erode in response to the increased flows. The eroded material, sediment, washes downstream and can clog culverts and bridges, produce in-stream sediment deposits and harm the stream's ability to support aquatic life. Decreased groundwater levels can result in decreased dry weather flows. Pollutants washed into the stream can also negatively affect the stream's aquatic habitat and the quality of the stream water. Thus, improperly managed stormwater can have a negative impact on a stream's aquatic habitat, water quality, aesthetics and value as a recreational resource for swimming, boating and fishing.
The eroding channels and sediment may also cause increased maintenance costs for nearby infrastructure such as sewer lines, culverts and roads. Increased frequency of higher flows may also cause increased frequency of nuisance flooding and property damage.
MANAGING STORMWATER
Proper stormwater management efforts attempt to minimize the above problems by addressing not only the quantity of stormwater produced, but also the quality of the stormwater and the amount of water that is lost from the watershed. The underlying philosophy of current programs is to manage stormwater as the resource that stormwater really is - not as a nuisance problem to be eliminated as quickly as possible. Stormwater is, after all, rain water and rain water is the ultimate source of the water we use in our daily activities and the source of the water which supplies our streams.
Part of DCCD's mission is to provide education on the problems associated with stormwater runoff and solutions to these problems. The District conducts workshops and participates in workshops hosted by related agencies. Additionally, the District has installed a demonstration tour of stormwater Best Management Practices (BMPs) at the Dauphin County Agriculture and Natural Resources Center in Middle Paxton Township.
Click here to read about DCCD's on-site Stormwater BMP demonstration tour.
DCCD is also involved with two programs that seek to address the issues of stormwater quantity and quality: Act 167 stormwater management planning and Municipal Separate Storm Sewer System (MS4) regulations.
