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Riverbend Environmental
Education Center, a non-profit organization, is a valuable
community resource since it serves to educate the public, especially
children, about environmental processes. The Center is found in an
environmentally precarious location since the Center's building and its
protected acreage are found at the bottom of a steep valley many miles
below disturbed riparian acreage. The velocity and volume of runoff
worsens each year and causes damage in Lower Merion Township and to the
Center’s property, where a flood took out a bridge in 2004.
In 2004, the Center underwent
a master planning process in order to outline areas of program
growth and habitat restoration initiatives. The planning process
identified Best Management Practices (BMPs) to reduce water volumes and
erosion and
improve the quality of outflow into Saw Mill Run, including: 1)
Porous asphalt parking lot; and 2) Bioswale. These BMPs were installed
during October 2006.
1) Porous Asphalt
Parking Lot
The replacement of the Center’s parking lot was a top priority because
oils, road salts, and other nutrients were unloading into adjacent Saw
Mill Run during storm events. The old asphalt parking
area was also due to be replaced, so the timing corresponded well.
The recharge
bed underlying the porous asphalt stores water and allows it to percolate
into the ground. During construction, soil
below the storage bed was loosened at the natural substrate level to
allow for greater infiltration and aquifer recharge. This has improved
water table levels and calmed water velocity in the vicinity.
This stormwater BMP has
had a positive effect on Saw Mill Run. Erosion has subdued and aquatic
diversity is improving. Pollution (e.g. nutrients and heavy metals),
trash and sediments are filtered by the porous asphalt, and thus are
prevented from entering Saw Mill Run. Spring Mill Road was re-contoured
on one side to capture runoff as well.
2) Bioswale
Additional water running off the porous asphalt is discharged into a bioswale, which
acts as a second line of defense before pollutants and nutrients can
reach Saw Mill Run. This vegetated swale uses soil and native plants to
infiltrate stormwater, trap pollutants, calm water velocity, regulate
water temperature, facilitate evapotranspiration, and recharge the water
table.
The bioswale plant list
(including shrubs, trees, and seed mixes) and planting sequence are
available
here.
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