Stream Restoration

• Introduction
• Restoration Goals
• Strawberry Run Restoration
• Holmes Run / Chambliss Crossing Project

Introduction

“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. 

Restoration Goals

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 Environmental Management Ordinance (Article XIII of the Zoning Ordinance) to comply with the water quality performance criteria set by Section 13-109(E)(5). 

City streams suffer increased flows with elevated velocities when urbanization occurs.  Erosion of the banks and beds are a result that negatively impact water quality and aesthetics as well.

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Strawberry Run Restoration

Strawberry Run is an urban stream that runs north to south through Ft.Williams Park, south past Duke Street, into Lake Cook and eventually into Cameron Run.  Ft. Williams Park is located north of Duke Street between Fort Williams Parkway and Donelson Street.  Strawberry Run suffers from high velocities as evidenced by the down-cutting creating the vertical side banks and depressed stream bed.  There is also a considerable amount of concrete and other debris in the stream that serves to negatively deflect flows creating erosive forces.

Restoration Goals

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. 

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Holmes Run / Chambliss Crossing Project

The City of Alexandria has completed its study of Holmes Run near the Dora Kelly Nature Park.  Based on input from technical experts and the community, the City is proceeding with preparation of construction documents for the stream restoration and a crossing.  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.

Project Schedule
The project is now in the 90 percent design phase with construction planned for 2011-2012.

Considerations
The Design was exceedingly sensitive to community desires and the process engaged the local community.

Goals:
No rise in water surface elevation
Maintain as much of the meadow as possible

• Updates the findings of an existing 2002 site/feasibility study for the Holmes Run Multi-use Crossing with particular consideration paid to recent flood events
• Includes 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
• Includes all environmental assessments and environmental impact statements
• Completes design for a crossing and shared-use path connections to existing trails
• Incorporates streambank stabilization/restoration for the banks between North Chambliss and the city line