Sligo Creek Fish Passage Improvements

From 2003-2004, the Maryland National Capital Park and Planning Commission (M-NCPPC), through consultants listed under Maryland State Highway Administration Contract No. PG3445173, carried out improvements on four sites along the lower Sligo stream corridor between Riggs Road and the Sligo confluence with Northwest Branch. This was done as part of the Wilson Bridge Project Environmental Initiatives. These improvements removed barriers to migratory fish entering Sligo Creek to spawn at each of the four sites. With these improvements, along with others carried out on the Northwest Branch, lower Sligo Creek may become accessible to migratory fish. The Friends of Sligo Creek Natural History Committee page describes the progress towards Bringing Migratory Fish Back to Sligo.

Map numbers refer to sites of photos below.

Photo Site #1

Photo Site #2

Photo Site #3

Photo Site #4

Northwest Branch and Sligo Creek Stream Restoration Goal

Restore upstream fish migration in Northwest Branch and Sligo Creek by modifying twelve existing “in-stream” fish barriers. Barriers are in the form of exposed utility lines and dams that were installed in the past to protect utility lines and control water elevations. Because most of these utilities are still in use, removal of the utilities is not practical. Therefore, each of the blockages will be modified by constructing natural rock structures known as riffle-grade control structures (RGC) and boulder-step pools (BSP). The RGC and BSP structures serve to raise upstream water surface elevations through flow constriction and water elevation control. Within the RGC, a low flow channel will be designed to provide the appropriate velocities and depths of flow during spring fish spawning season. In addition to ensuring appropriate velocity and flow characteristics, the structures provide fish resting areas in the form of large boulders where fish can rest and make use of the flow eddies to propel them upstream.

Location

Twelve locations along Northwest Branch and Sligo Creek. The graphic below shows the individual locations, labeled NW 1-8 and SC 1-4. All of the construction projects will be completed “in-stream” using a combination of heavy equipment and manual labor.

Background

This enhancement activity is a portion of the environmental mitigation plan for the Woodrow Wilson Bridge Project. This and other projects in Maryland and Virginia are intended to offset environmental impacts to natural resources associated with construction of the new Woodrow Wilson Bridge and its contributing interchanges. This Project is a result of the cooperative efforts of the Maryland-National Capital Park and Planning Commission (M-NCPPC), the Maryland State Highway Administration, the Federal Highway Administration, and the Virginia Department of Transportation.