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A Stream Runs Under It: Restoring the Broad Branch Tributary

This used to be a stream bed. (photos courtesy of the District Department of the Environment)

by Steve Saari
Watershed Protection Specialist
District Department of the Environment

If all goes according to plan, Forest Hills will have a new neighbor by next spring – a new stream! Though really, the stream is an old neighbor that will be returning to its old home.

How is that possible? How can the city bring a stream back where there is currently nothing? Through a process called “daylighting” – that’s how. Daylighting is the process of returning a stream that has been piped in back to the surface.

In this case, the stream originates from a spring on National Park Service land behind Politics and Prose and flows to a bridge near the intersection of 36th Street, NW and Nevada Avenue, NW. At this point, the stream enters a pipe which flows beneath Broad Branch Road until the water comes again to the surface as Broad Branch, a tributary to Rock Creek. The NPS and the District Department of the Environment are working together to bring the stream back to life.

Left: One of the few places where the stream sees daylight. Right: A bridge where the stream is piped.

It is not clear why the stream was piped out of its historic channel, but the District of Columbia will be happy to have it back at the surface because, unlike piped streams, streams at the surface make good neighbors.

Surface streams improve water quality by exposing water flowing through it to sunlight, air, soil, and vegetation, all of which help process and remove pollutants. Furthermore, the restoration will reduce nutrient and sediment pollution from erosion caused by fast-flowing stormwater, by creating meanders and floodplain wetlands which will have wider cross-section and a greater channel depth than the pipe it will replace.

DDOE photo of stormwater erosion.

In addition to bringing the stream to the surface, the project will also slow down and clean stormwater coming from adjacent streets, alleys and rooftops by directing it into rain gardens which are landscaped areas that slow, cool, and filter dirty storm water from our streets. This clean stormwater will add to the base flow of the newly daylighted stream – ensuring that it has flow during hot, dry summer months.

So where exactly will this new stream located? It will start on the east side of the 36th Street bridge, meander through National Park Service land to Linnean Avenue, cross under Linnean in a culvert, then continue through Department of Transportation, National Park Service, and Peruvian Embassy lands along Broad Branch Road. The stream will again go underground for a short distance before coming above ground for good where Broad Branch currently emerges. The entire project length is about 1,600 feet.

The stream daylighting effort has a few “firsts” for the city:

• It is the first piped stream to be returned to the surface;
• It is the first stream restoration project that will be in part on embassy lands – making it an international stream restoration project; and
• It is the first stream restoration project in the District to include “sand seepage wetlands” – a technique that uses sand berms to create shallow wetland areas to create habitat and feed the main stream channel.

As with all new neighbors, the new stream has created some anxiety among adjacent homeowners, who ask: Will the new neighbor bring trouble to Forest Hills in terms of flooding and mosquitoes? The answer in both cases is no. The stream has been carefully designed to ensure that it can handle its flows – even the strong, flashy storms we seem to be having more of lately. Furthermore, because the new stream will create habitat for frogs, salamanders, dragonflies and bats and because the water will be moving rather than stagnant, there should be fewer mosquitoes rather than more.

Here is what the DDOE hopes Broad Branch will look like once the stream is brought back to the surface. Left: A downhill-flowing “conveyance” that guides the water and fights erosion. Right: A recently-restored stream.

The new stream will also make a few upgrades to its new digs. Among them are:

• New rain gardens treating about 1.8 acres of impervious area;
• 5,418 square feet of new wetlands;
• 1,600 linear feet of new stream;
• Hundreds of new trees to shade the stream;
• New habitat for fish and wildlife; and
• An amenity for the Forest Hills neighborhood.

So this spring, once the stream has moved in, please drop by and say “hi,” and enjoy the new wildlife it will bring to the neighborhood.

 

Author Description

Tracy Johnke

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Comments (3)

  1. Andrea Stone Wednesday - 19 / 09 / 2012 Reply
    This all sounds great but what impact will this have on the deer population? Doesn't this give them more places to drink and feed? If so, we could see even more on the roads near sundown, increasing the danger to motorists and the costs to homeowners whose landscaping they eat. I'd like to hear NPS on that subject. Thanks.
  2. Anthony Tuesday - 09 / 09 / 2014 Reply
    This is awesome. We really need to do more to preserve/restore whats left of a wonderful and diverse ecosystem. The parts of DC that intrigue me personally are the ones that man has not made.
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