Volume IV, Number 6
eMDE is a quarterly publication of the Maryland Department of the Environment. It covers articles on current environmental issues and events in the state.
Plants in a variety of sizes, shapes, and colors cover the parking garage roof -- and capture rainfall that would otherwise carry pollutants into a nearby creek and, eventually, the Chesapeake Bay. A few blocks away, a newly planted “modular wetland” catches trash and filters runoff before it can reach the waterway.
In Takoma Park, American Recovery and Reinvestment Act (ARRA) grants are helping to improve Maryland waterways. The Montgomery County city received a portion of the $119.2 million in ARRA grants that Maryland invested in the improvement of the State’s water quality and drinking water infrastructure.
The tremendous demand for water infrastructure projects was illustrated by the more than $3.7 billion in requests for ARRA grants that MDE received from various counties, cities, and towns across the state. After carefully reviewing nearly 600 applications, MDE chose “shovel-ready projects” from every county in the state to receive a portion of the funding. The difference that these projects have made can be seen in downtown Takoma Park.
Takoma Park received a $69,500 ARRA grant to help pay for the installation of a $76,700 green roof. It received $195,400 to help pay for more than $215,000 in stormwater control improvements at the end of Linden Avenue where it meets Sligo Creek.
Stormwater runoff is the fastest-growing source of pollution to the Chesapeake Bay. Urban and suburban runoff contribute 20 percent of Maryland’s nitrogen load to the Bay. Nitrogen is the most serious pollutant to the Bay. It promotes the growth of algae, leading to lower dissolved oxygen levels in the water.
Takoma Park recently showed off its projects when nearby Silver Spring was named Maryland’s “Capital for a Day.” Accompanied by Takoma Park Mayor Bruce Williams and City Manager Barb Matthews, MDE Secretary Shari T. Wilson visited the new stormwater controls on Linden Avenue and toured the parking garage’s green roof.
The garage is below street level, and its roof serves as a patio. Still, it shares the properties of other green roofs.
A green roof is a roof that is partially or entirely covered by a growing medium or soil substrate that allows for the growth of vegetation. Most green roofs include additional layers such as a filter membrane and a drainage system that allow the plants to absorb and filter rainwater. Aside from their aesthetic appeal, green roofs are environmentally preferable because they are capable of reducing potentially harmful stormwater runoff by up to 60 percent. In addition, they have been proven to combat the “urban heat island” effect, a phenomenon in which urban areas with little or no vegetation form an “island” of temperatures much higher than those of their rural surroundings.
The green roof on top of the parking garage covers about 2,800 square feet. The garden is composed of a variety of sedum plants -- leaf succulents that are ideal for retaining large amounts of water at any given time. The sedum plants and growing medium act as a sponge, absorbing more than half of the fallen rainwater. The rest of the water is filtered through a permeable membrane before draining from the roof.
On Linden Avenue right above Sligo Creek, a stormwater inlet and pipe were removed and replaced with a modular wetland system. Similar to a green roof, a modular wetland is made up of soil substrate that allows for the growth of plants. After the stormwater is filtered through the wetland, the runoff is then directed through an “innovative perimeter filter” that removes a variety of pollutants before allowing the water to safely discharge into the creek.
A retaining wall, designed to slow the flow of stormwater was removed and replaced by a more durable structure. The Linden Avenue project was built in six months. In both cases, these projects show us that increasing rainwater filtration can also provide terrific aesthetic benefits – a green outdoor sitting space and a spot to pause and view the Creek.
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