Learning lessons as we build green solutions

How does the Department of Environmental Protection (DEP) protect our drinking water, properties, streams and the Chesapeake Bay from the harmful effects of stormwater pollution?

By using the combined resources and talents of engineers, landscape architects, ecologists, planners and local community members to think of innovative solutions to solving the problem of stormwater pollution. DEP learns a lot of lessons from trying out new restoration designs, even if a design does not go completely as planned.

Taking the First “Step”

A new solution DEP is utilizing to reduce stormwater pollution and restore streambanks is called regenerative step pools.  In an eroded channel where stormwater frequently flows, a regenerative step pool allows water to be absorbed into the ground, while the pollutants are taken out of the water by sand and mulch.

Dennis Avenue median before the stormwater restoration project.

A regenerative step pool stormwater conveyance system is built to stabilize and restore an eroded drainage area. By creating a series of pools that drop in elevation (like big stairs), with cobble riffles between, the water is slowed down, and water collected by the pools seeps back into the ground. DEP engineers thought that by doing this the streambanks would be protected from erosion, and road sediment would be trapped behind the pools.

A Test Run of the Regenerative Step Pools

A regenerative step pool was recently build in the Dennis Avenue Green Streets in Silver Spring. Through the Dennis Avenue project, DEP has found that this approach has its pros and cons.

Dennis Avenue step pools before the plantings.

What works:

• During a rainstorm, water is slowed before reaching Sligo Creek.
• Road grit loaded with pollutants is dropped into the channel instead of going to Sligo Creek.
• The channel looks much better and complements the ongoing stormwater treatment work along the road.

Neighbors have been pleased by the transformation of the weedy channel, with its nicks and tears of erosion, into a stormwater feature showcasing native plants.

What doesn’t work:

• Between rainstorms, water stays too deep in the pools for plant survival, and raises a possible concern about mosquitoes.
• High loads of road sediment are dropped into the pools during storms, impacting plant survival in the pools.
• Too much surrounding clay prevents water from draining out of the pools.

So while the pools are providing water quality and erosion reduction benefits, they are holding water between rainstorms and not infiltrating as much as hoped.

Early problems with the step pools included the occasional standing water.

Lessoned Learned

First, DEP had to find the source of the problems listed above. They discovered that water does not drain into the ground because of the hard clay soils in the stream valley.

To correct the problem of too much standing water, DEP put slotted well pipes in the ground to see if they could improve drainage through the surface layer.  They also added more plants to reduce erosion on the slopes, absorb extra water and  create a habitat for other wildlife, like birds and insects. DEP will look for more solutions to improve drainage, which might include raising the level of the pools and adding plants to the pools to suck up the water.

Mosquito predators, such as dragonfly larvae, were added to the regenerative step pool, to prevent mosquitoes taking over the area. If mosquitoes happen to develop over the summer, DEP will then add a bacteria called Bacillus, or Bti, that kills mosquitoes (but leaves other wildlife unharmed).

Dennis Avenue regenerative step pools after the plantings and redesigns.

Community Involvement

A key part of the success of new stormwater techniques is the involvement of the local community. Neighbors near the pools alert DEP to any problems and volunteer their time to remove trash from the channel so that the stormwater can properly be filtered.

Many neighbors are also finding solutions on their own properties to control and clean stormwater from their roofs and driveways.

If you want to know how to reduce the amount of water that comes off of your property, you can visit the DEP RainScapes website for information on techniques and some of the cash incentives that the county offers.

The next time you enjoy a walk along Sligo Creek and Dennis Avenue, stroll on over and enjoy the improved natural habitat at this area and in the nearby park—and maybe you have a solution DEP has not thought of!

By Mary Travaglini, Planning Specialist, Watershed Management Division, DEP