Allegheny River Headwaters Watershed Conservation Plan

Allegheny River Headwaters Conservation Plan
Chapter 3. Water Resources
and surfaces, transforming it into water vapor in the atmosphere. When water vapor cools, it condenses to
form clouds, and precipitation falls to the earth’s surface once enough vapors condense. Some water seeps
into the ground, becoming groundwater. The remaining water runs off the land contributing to stream
flow. It is used by vegetation, or evaporates back into the atmosphere, continuing the cycle.
Groundwater and Surface Water
When water is stored below the surface it is called groundwater. Water that is stored on the surface
in ponds, lakes, or wetlands is surface water. Groundwater and surface water are often considered
separate resources, but they are the same; water is constantly moving back and forth from surface level to
below ground.
Base flow is the flow of a waterway supplied solely by groundwater, with no surface water or runoff
joining it. When a waterway is dry, the water table has dropped below the land surface. During dry
seasons, the entire flow of many waterways is provided explicitly by groundwater. This causes the water
table to drop slowly due to diminished recharge of the groundwater supply as a result of a lack of
precipitation and the use of precipitation by growing plants.
Groundwater
Groundwater is stored in empty spaces and cracks between soil, sand particles, gravel and rock. As
previously mentioned, rain causes some water to permeate the ground and replenish the supply. When all
the empty spaces and cracks have been filled, the water table has reached the upper surface of the zone of
saturation.
The depth of the water table is influenced by topography. In valleys, it is closer to the surface than in
hilly and mountainous regions. Where the water table intersects the surfaces, it forms streams, lakes, and
wetlands; the water is then classified as surface water.
In Pennsylvania, 100 inches of water—equivalent to 80 trillion gallons—is stored underground.
While underground, water flows through the cracks and layers of rock. Gravity supplies the pressure
needed to force the water’s flow from higher elevations—such as the hills and mountains—to the valleys
and lower elevations where the water table is exposed. However, unlike surface water, groundwater
receives additional pressure from the weight of the water above it. This can cause water in the discharge
area to flow upward; if enough pressure is achieved, gravity can be overcome. Slope and permeability
impact the rate at which groundwater flows. Groundwater moves slowly at an average rate of 35–1,100
feet per year (Fleeger, 1999; A brief explanation on groundwater flow systems and groundwater
hydrogeology in Pennsylvania).
In Pennsylvania, 37 percent of the population obtains
water from wells and springs for drinking and domestic
uses, while in rural areas the dependency of groundwater is
higher (League of Women Voters). Springs are formed
when groundwater flow is blocked by non-permeable rocks
and is forced to flow laterally in permeable layers until it is
discharged at the surface. Therefore, it is important that the
quality of groundwater is protected. It is a well owner’s
responsibility to ensure their drinking water is safe for
consumption by conducting frequent water quality analysis.
Groundwater, if not protected, can become
contaminated. The methods in which we utilize land
resources may impact the quality of our water. Waste
Agricultural practices, such as allowing
livestock access to waterways, increases
erosion, sedimentation, and nutrient
pollution; streambank fencing and
alternative watering systems are
examples of best management practices
to decrease impacts to water quality and
improve livestock health
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