BUBBAs History Spotlight: Broad Branch and Linnean Park Tributary (2015)

BUBBAs History Spotlight: Broad Branch and Linnean Park Tributary (2015)

One of the goals of the BUBBAs contest is to shed light on the best and most innovative restoration projects across the Chesapeake Bay Watershed. So, it seems only natural that the 2015 BUBBAs Grand Prize went to a project that shed new light, literally, on a previously buried urban stream in the District of Columbia.

Broad Branch and Linnean Tributary project, post-restoration

The restoration of the Linnean Park tributary and daylighting and restoration of Broad Branch were two linked projects located in Northwest, Washington DC.  The goal of this effort was to restore in-stream habitat and improve the urban hydrology of these two tributaries that flow to Rock Creek through a combination of bioretention, regenerative stream channel (RSC) design, and stream daylighting.

One portion of the project involved daylighting a part of a stream that was put into a pipe in the mid-1930’s.  Daylighting this section of the Rock Creek watershed recreated riparian habitat in an area that had not had surface stream for eighty years and created at least a half-acre of new wetlands.

To ensure that the newly-created stream had surface flow throughout the year and that the stream was clean and healthy, the project also involved directing stormwater from adjacent streets, alleys, and rooftops into bioretention cells by creating curb cuts and redirecting storm sewers.  These bioretention cells slow, cool, and filter that stormwater which then recharge the groundwater table thereby providing an additional source of clean baseflow to the new stream.

Bioretention cell during construction

In addition to the stream daylighting, the project entailed constructing three RSCs.  RSCs are a type of stream restoration technique that slows down, treats, and infiltrates stormwater flows through the creation of pools and riffle-weir grade controls that greatly reduce erosive forces and positively impact the ecology of a drainage area. 

Among the early successes for the project were improvements to riparian habitat. The effort connected existing habitats and produced several new vernal pools for a previously isolated spring that supports a spotted salamander population. In addition to the in-stream habitat created, the project removed invasive plants including bamboo, English ivy, Japanese knotweed and tear thumb, replacing them with a mix of natives.

Monitoring was conducted both before and after restoration to evaluate the efficacy of the RSC technique and may help resource managers to better understand the role stream restoration can play in restoring our urban waterways.  The monitoring effort included monitoring habitat, flows, stability, and pollutant removal efficiency for the eight pollutants required to be monitored through the District’s Municipal Separate Storm Sewer permit.

Overall, the last five years have seen both challenges and improvements to the initial project. While it required a few repairs, the project has held up well against a series of high intensity storm events in the District. The most difficult issue has been keeping down invasive species and getting plants established.  The initial plan was for maintenance to be performed by the local neighborhood group. While that worked for a while, the magnitude of work has since exceeded the abilities of their volunteers.  DOEE is now moving to contract for a more consistent maintenance regime on this and all of their projects.

The Linnean Creek and Broad Branch Project still functions today as a learning opportunity for District residents. The site is now a teaching tool used for field visits with students (pre-COVID-19).  Project partners also installed photo monitoring points at key locations throughout the project area.  Visitors can take photos with their phones and upload them to a photo sharing site where they will aid the District in monitoring the site over time. 

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