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Stormwater Management

What Goes In Here..............................................................................Comes Out Here.


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. Click Here For More on Watersheds. 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.

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. 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.  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.  These pollutants include sediment, phosphorous, nitrogen, automotive fluids, deicing chemicals, cleaners, heavy metals and other substances.  Pollutants washed into the stream can negatively affect the stream's aquatic habitat and the quality of the stream water.  Decreased groundwater levels can result in decreased dry weather flows. During dry parts of the year, stream flow is sustained by groundwater.  More rain lost to runoff means less groundwater available to supply streams during dry weather.  In some cases, streams can dry up completely during these periods.  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.


At some point in the past, Dauphin County’s watersheds would have been covered with forest.  Forest land is an excellent stormwater manager.  Uneven terrain, an absorbent layer of organic material covering the forest floor, forested wetlands and permeable soil cover all contribute to the forests ability to retain rainwater.

As the land was settled, forests were cleared for farmland and settlements.  Farmland and settlements gave way to towns.  Towns expanded and today, development continues to expand into previously undeveloped areas.  This continued development has diminished the ability of watersheds to retain rainwater.   The excess rainwater becomes stormwater runoff.

Early efforts to manage stormwater were to collect stormwater and remove it as quickly as possible from an area through a system of inlets and pipes which dumped the runoff into the nearest stream.  As discussed above, the increased volumes of runoff being delivered to streams more often caused degradation of the stream.

Since then we have learned a lot about stormwater runoff.  Today, sound 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.

To accomplish this, new development uses stormwater Best Management Practices, also known as BMPs Click Here For More on BMP's.  BMPs are methods and structures used in new development to infiltrate stormwater and treat stormwater before it reaches streams.  These practices can be grouped into two categories; structural practices and non structural practices.


Structural practices include various BMPs that are actually constructed to treat stormwater.  Examples of these practices include infiltration devices, inlet treatment devices, rain gardens, swales and pervious concrete and asphalt.  The goal of these structures is to infiltrate or filter stormwater before it leaves a site to reduce the negative impacts of runoff on water resources.

Structural practices, such as this rain garden, treat stormwater before it reaches a stream. (Photo courtesy of City of Lincoln Nebraska, watershed Management Division)


Examples of these practices include rules, regulations and planning instruments such as Subdivision and Land Development Ordinances (SALDOs), Stormwater Management Ordinances Zoning Ordinances, and Floodplain Ordinances.  The goal of the non structural practices is to incorporate requirements and planning into the development process before construction begins.  A well thought out development plan will work with the characteristics of a development site to minimize the amount of stormwater runoff generated and plan ahead for managing stormwater. 

Sound planning and working with site characteristics can minimize the adverse impacts of stormwater runoff on water resources.


DCCD provides 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, develops educational materials and has installed a demonstration tour of stormwater Best Management Practices (BMPs) Click Here For More on the BMP Tour at the Dauphin County Agriculture and Natural Resources Center in Middle Paxton Township.

In addition to the educational efforts, the Conservation District also coordinates Dauphin County Act 167 Stormwater Management planning and the Municipal Separate Storm Sewer System (MS4) compliance efforts.  Click on the links below for more on these programs.

Click Here For More on Act 167 Stormwater Management

Click Here for More on Municipal Separate Storm Sewer System (MS4) Regulations

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1451 Peters Mountain Road Dauphin PA 17018 phone: 717-921-8100