Allegheny River Headwaters Watershed Conservation Plan

Allegheny River Headwaters Conservation Plan
Chapter 3. Water Resources
moderate stream flow, reduce flooding, and filter pollution. Vernal pools—seasonal depressions covered
by shallow water for variable periods of the year and sometimes completely dry during others—are a type
of marsh wetland (U.S. EPA 2 ).
Bogs are wetlands with spongy peat deposits and acidic waters. A thick layer of sphagnum moss
blankets the bog wetland. Precipitation is the only source of water and nutrients. Bogs are beneficial,
because they absorb precipitation and prevent or reduce flooding (U.S. EPA 2 ).
Peat-forming wetlands that receive nutrients from runoff and groundwater are fens. Although similar
to bogs, fens are less acidic and can have higher nutrient values. Functionally, fens help improve water
quality, reduce the risk of flooding, and provide habitats for unique plant and animal communities (U.S.
EPA 2 ).
Swamps are wetlands dominated by woody plants and characterized by saturated soils during the
growing season and standing water during certain times of the year. There are two types of swamps—
forested and shrub swamps. Swamps are beneficial in removing nutrients and preventing flooding (U.S.
EPA 2 ).
Floodplains
Lands adjacent to a waterway that allow floodwaters to dissipate are termed floodplains. These
scenic and valuable habitats are extremely beneficial in reducing streambank erosion, sedimentation,
flooding, loss of property, and degradation of water quality. Some even consider floodplains to be natural
sponges due to their ability to absorb and slowly release floodwaters, decreasing velocity and volume, and
recharging groundwater. Floodplains also improve water quality by trapping sediment and capturing
pollutants, similar to wetlands.
Floods and floodplains are typically defined by the likeliness of a flood event. A 100-year flood is a
flood that has a one percent chance of occurring in a given year.
Beginning in 1968, Federal Emergency Management Agency (FEMA), through the National Flood
Insurance Act, administered the National Flood Insurance Program (NFIP). This program was established
to allow property owners to purchase flood insurance protection at a reduced rate in communities where
floodplain ordinances were adopted. The floodplain ordinances must meet regulatory standards of the
NFIP and Pennsylvania Floodplain Management Act. All communities within the project area have
ordinances and are eligible to purchase flood insurance protection (FEMA, 2008; FEMA, 2010).
The threat of flooding and the degree of damage fluctuates depending upon the impacts of human
activity. Activities, such as development in the floodplain, dredging, and channelization, alter and deepen
the stream channel to accommodate and increase volume of water. When the channel is straightened, the
water has fewer obstacles to maneuver around and quickly gains speed. With a deeper, straighter channel,
the velocity of flow increases. When the force of water hits the streambank, the soil erodes, adding
sedimentation to the waterway and decreasing the size of the floodplain. With less area available to
absorb the water in the floodplain, flooding occurs when streams breach their banks.
Floodplains provide critical habitat for common, rare, threatened, and endangered species that
flourish in floodplains and have adapted to these unique conditions. Plant species are limited based on soil
types and water tables, while animal species are limited based upon the habitat provided by the plant
species. Floodplain flora and fauna are discussed in more detail in the Biological Resources chapter.
3-8