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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 the soil type(s). The magnitude of runoff ranges depending on the characteristics of the site. 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 encompasses the area of land that drains to Paxton Creek, which in turn discharges to the Susquehanna River. In this example, the common point to which the watershed drains would be 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 (an impervious surface that does not allow for infiltration), the amount of runoff produced in any given rainfall event will be greater. Generally, the result of these land alterations is increased runoff, which reaches the receiving body of water more quickly.  This results in less water being retained in the watershed for groundwater recharge and higher stream flows, and potentially flooding, occurring more frequently.

Increased stormwater runoff results in negative impacts to the stream. Erosion of stream beds and banks may occur in response to the increased flows. The eroded material, known as sediment, washes downstream and can clog culverts and bridges, produce in-stream sediment deposits, and harm the stream's ability to support aquatic life. Eroding channels and sediment may also lead to 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 in addition to 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 that are washed into the stream can negatively affect the stream's aquatic habitat, as well as the quality of the stream water.  Poor water quality can negatively affect the recreational value of the stream, which includes fishing, swimming, and boating.

Increased runoff can lead to decreased groundwater recharge, in turn leading to decreased dry weather flows. Stream flow is sustained by groundwater during dry parts of the year, and precipitation 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 were covered with forest.  Under forested conditions, stormwater is managed naturally.  Uneven terrain, an absorbent layer of organic material covering the forest floor, forested wetlands, and permeable soil cover all contribute to the forest’s ability to retain rainwater.

As the land was settled, forests were cleared for farmland and settlements, which then gave way to towns. Towns expanded and today, development continues to expand into previously undeveloped areas.  This continued development has led to increased impervious surfaces, and thus has diminished the ability of rainwater to infiltrate.  This excess rainwater runs along the surface of the land, and is known as stormwater runoff.

Early stormwater management efforts consisted of collecting stormwater and removing it from the site as quickly as possible, typically through the use of inlets and pipes, which conveyed stormwater to the nearest stream.  As discussed above, the increased volumes of runoff being delivered to streams often caused degradation of the stream.

Since the early days of stormwater management, we have learned a great deal about stormwater runoff.  Today, sound stormwater management efforts attempt to minimize the aforementioned problems by managing stormwater as a resource, and not as a nuisance.  After all, stormwater is rain water, supplying not only our streams, but also our communities, with water.

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 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 in order 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 non-structural 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.


Low Impact Development (LID) strategies are another form of stormwater management and encompass both structural and non-structural practices.  LID is a relatively recent concept, and refers to systems and practices that use or mimic natural processes that result in the infiltration, evapotranspiration or use of stormwater in order to protect water quality and associated aquatic habitat.  LID strategies aim to manage runoff as close to its source as possible.  Some examples of Low Impact Development strategies include rain gardens, infiltration basins, green rooves, permeable paving, rain barrels, and bioretention basins, among others.  For more information on LID strategies visit the EPA LID page.


DCCD provides education regarding the problems associated with stormwater runoff as well as the solutions to these problems. The District both conducts its own workshops, 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.  For additional resources visit our Additional Links/Publications page.

Click Here For More on Act 167 Stormwater Management

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

About Stormwater

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