“Stream restoration” is a very broad term that can be as little as removing blockages within systems (a destructive log jam or human generated trash) to redesigning and restructuring a stream within its floodplain. Stream degradation from increased imperviousness in the watershed is often a byproduct of urbanization that negatively impacts water quality. The channel size and flow of a stream is directly related to the watershed that drains into the stream. The size of the watershed, the landuse, and soils are some of the determining factors. Increased volume and velocities of stormwater runoff due to increased imperviousness may lead to channel erosion, channel incision, and streambank undercutting. Obstructions such as downed trees and dumped materials (trash, concrete, etc) may also impede stream flow. Stream Restoration is one way that developed areas can increase their water quality and improve natural habitat for wildlife and residents.
The basic goal of almost all stream restorations is to improve the health of the system. The benefits are many, and which benefits result is largely dependent upon the methods or activities that lead to restoration. Among the benefits are increased dissolved oxygen within the water (better for fish and other critters), increased habitat for aquatic organisms, decreased erosion and thus reduced sediment transport, increased water quality, decreased maintenance activities and more efficient flow through the system. The City of Alexandria is fortunate in that stream restoration is one of the tools available through the Chesapeake Bay Program to meet state and federal mandates to clean up the Chesapeake Bay.
City streams suffer increased flows with elevated velocities when urbanization occurs. These increased velocities result in erosion of the banks and beds of the stream and negatively impact water quality and stream aesthetics.
The City previously completed Phases I and II of the Stream Assessment Program. Phase I of the program was completed in 2004 and involved the identification and mapping of perennial and intermittent streams, defining the intermittent/ephemeral stream interface and approximate limits of ephemeral streams. Phase II of the program was completed in 2008 and involved the assessment of fifty-seven stream reaches within the City’s eight local watersheds. Information related to stream conditions was collected relating to habitat, infrastructure impacts, problem areas, stream characteristics, and geomorphic classification. The information from these studies will continue to be used to prioritize streams for restoration.
Phase III of the stream assessment studies is currently in the final stages and developed a prioritized list of stream restoration projects. The scope of work included assessing, evaluating, and ranking five potential project sites using a decision matrix with a comprehensive list of criteria to prioritize the projects. The two top ranking projects were segments along Strawberry Run and Taylor Run. Conceptual designs are being developed for these two highest-ranking potential project sites. It is anticipated that after this study is complete and has received stakeholder input, the Strawberry Run and Taylor Run Stream Restoration projects may be considered for final design and construction within the next several years. In preparation, the City has applied for Stormwater Local Assistance Fund (SLAF) Grants to help offset funding for the selected projects.
- Community Meeting - December 5, 2018
Phase III Stream Assessment Study: Potential Stream Restoration Projects
7:00 pm at Douglas MacArthur Elementary School Library
The Strawberry Run project completed in 2010 is located just north of Duke Street for approximately 600 linear feet upstream towards Fort Williams Parkway. Strawberry Run suffered from high velocities as evidenced by the down-cutting creating the vertical side banks and depressed stream bed. There was also a considerable amount of concrete and other debris in the stream creating erosive forces that was removed. The potential new Strawberry Run restoration project discussed above would be situated just north of the previous Strawberry Run Stream Restoration that was completed in 2010.
The philosophy of this particular stream restoration was to reconnect the stream with the floodplain and attempt to maintain the sinuosity (the amount of curve in the stream) so as create as great of variety of habitat within the stream and riparian area as possible. This involved adding cross vanes to roll the water away from the banks centering the flow, control the change in hydraulic grade line, and prevent down-cutting of the channel. J-hooks were added to direct erosive flows away from the streambank, center the flow, and provide scour pools for fish habitat. Other components of natural channel employed were using jute matting to stabilize toe and bank slopes – anchored with a variety of pins and willow stakes at the toe. Willow stakes serve to anchor the matting but moreover to provide a network of natural root systems to anchor the banks in place against erosive flows.
Before Picture After Picture
Download the Strawberry Run Restoration presentation.
The Chambliss Crossing project along Holmes Run near the Dora Kelly Nature Park incorporated stream restoration and a multi-use stream crossing across Holmes Run. The engineering and design analysis explored alternatives for a crossing and stream bank restoration for the banks between North Chambliss Street and the city limits.
The Design was exceedingly sensitive to community desires and the process engaged the local community.
- No rise in water surface elevation
- Maintained as much of the meadow as possible
- Updated the findings of an existing 2002 site/feasibility study for the Holmes Run Multi-Use Crossing with particular consideration paid to recent flood events
- Included hydrology and hydraulic analysis at a preliminary crossing location to identify and propose stream bank stabilization and restoration options which should also be incorporated into design and construction plans
- Included all environmental assessments and environmental impact statements
- Completed design for a crossing and shared-use path connections to existing trails
- Incorporated streambank stabilization/restoration for the banks between North Chambliss and the city line