Rainfall and Stormwater Runoff

Precipitation that falls on a natural landscape flows through a complex system of vegetation, soil, groundwater, surface waterways and other elements as it moves through the hydrologic cycle. Natural events have shaped these components over time to create a system that can efficiently handle stormwater through evaporation, infiltration and runoff.

Alterations to the natural landscape change the way the system responds to precipitation events. These changes often involve increasing impervious area, which results in decreased evaporation, infiltration and increased runoff. The increase in stormwater runoff results in runoff quantity or volume and runoff rate. These two factors cause the natural system to change such that negative environmental impacts such as accelerated erosion, greater or more frequent flooding, increased nonpoint source pollution, and degradation of surface waters occur.

Some level of stormwater runoff occurs as the infiltration capacity of the surface is exceeded. This occurs even in undisturbed, undeveloped watersheds. However, the volume and rate of peak runoff substantially increase as land developments occur. Stormwater management is a general term for practices used to reduce the impacts of this accelerated stormwater runoff. Stormwater management practices such as detention ponds and infiltration areas are designed to mitigate the negative impacts of increase runoff.

Stormwater Management Planning

Historically, the approach to stormwater management was to collect the runoff and convey it, via a system of inlets and pipes, as quickly as possible to the nearest stream. The increased volume of stormwater delivered quickly to receiving waters had a detrimental effect on the stream channel. Negative impacts such as server channel erosion and significant in-stream sediment deposits resulted. These impacts lead to unstable, deepened and widened channel, nuisance flooding, infrastructure damage, as well as increased culvert and bridge maintenance requirements.

The conveyance approach was later replaced with the stormwater management standards that largely exist today. This approach looks at lowering our development impact and managing the peak flows from sites.

Stormwater Planning and the Act 167 Process

Recognizing the increasing need for improved stormwater management, the Pennsylvania legislature enacted the Stormwater Management Act (Act 167 of 1978). Act 167 as it is commonly referred to enables the regulation of development and activities causing accelerated erosion.

The Act designates the Department of Environmental Protection as the public agency empowered to oversee implementation of the regulations. As described in Act 167, each county must prepare and adopt a stormwater management plan in consultation with the municipalities that is reviewed and updated at least every five years. Within six months of the county adoption and approval of the county stormwater management plan, each municipality must adopt and implement the county model or an amended plan as a municipal ordinance.
Crawford County’s Act 167 Status

In June of 2010, the Crawford County Commissioners adopted the Act 167 County Model Ordinance. Crawford County municipalities then followed suit, adopted or amending a version of the county model as a municipal ordinance. To date, all 51 Crawford County Municipalities have a stormwater Management Ordinance.

Municipal Ordinances

All municipal ordinances that have been filed at the Crawford County Planning Commission are provided below. If a copy of your municipality’s ordinance is not currently available, please contact your municipality directly.

Assistance with Stormwater Management Planning

The Crawford Conservation District is available for technical assistance to both municipalities and private individuals. Those planning a project which will increase impervious surface area should first contact their municipality where the project is proposed.

Stormwater Management Planning Resources

Individuals proposing a project which qualifies for the use of the Small Project Stormwater Management Application will need to determine the Hydrologic Soil Classification for their location. A sample copy of the Small Project Application is listed below. Check with your municipality first to determine if a revised copy of this form has been adopted.

A series of maps have been developed by the Crawford Conservation District and the County Planning Office indicating Hydrologic Soil Classification by color code. These maps were developed through funding provided by a Greenways Block Grant. Maps are organized by municipality.