East Fork Lewis River Habitat Enhancement
Clark County Public Works

Vigil-Agrimis, Inc. (VAI) is providing assessment, feasibility and design services to Clark County Public Works for a series of aquatic habitat enhancement sites along a 1½-mile reach of the East Fork Lewis River (EFLR).  Sites are located on the main stem and along existing off-channel habitat features.  Several of the sites are located upstream of the SR503 bridge over the EFLR in popular Lewisville Park.  The remaining sites are located downstream of the bridge in the vicinity of Daybreak Park. The projects proposed at the sites benefit federally listed threatened steelhead, Chinook, coho and chum salmon by increasing and enhancing off-channel rearing habitat and  main stem rearing and spawning habitat.

VAI began by reviewing five conceptual projects at Lewisville Park identified in the Lower East Fork Lewis River Habitat Restoration Plan.  Staff used existing data including 2-foot LiDAR contours, an hydraulic model of the mainstem in HEC-RAS and targeted field investigations of channel cross sections, profiles, habitat features, vegetation, and general geomorphic conditions to determine typical low and high flows in the East Fork Lewis River and relate those water surface elevations to existing off-channels habitat features.  Features include alcoves and side channels. The primary design goal was to increase access to these features by fish during low flows and to enhance habitat quality by adding in-channel wood while protecting park infrastructure. 

Lewisville Park Sites: Five concept-level (30%) designs were developed and presented to County staff from public works, parks and legacy lands, the Lower Columbia Fish Recovery Board (LCFRB) and the LCFRB Technical Advisory Committee (TAC).  Each design discussion touched on habitat benefits, affect on park infrastructure, cost and potential maintenance requirements.  The committee selected two projects to take forward to preliminary (75%) design. One expanded an existing alcove downstream of the Lewisville Park boat launch and the other improved access to the outlet of the existing side channel just upstream of the SR503 bridge. 

Upper Daybreak Park Sites: In addition to the Lewisville Park sites, VAI was asked to develop preliminary designs for two additional sites near Daybreak Park.  Design criteria focused on habitat benefits, cost, and potential maintenance requirements.  One improved access and enhanced habitat at the inlet to a long side channel.  The other expanded the area of high quality habitat accessible to fish by selectively removing barriers.  

VAI staff installed groundwater monitoring wells with level loggers at these locations to better understand the effect of hyporheic flow and groundwater on off-channel features.  The data was used to determine the amount of excavation that would be required to provide access to off-channel habitat at low flow.  Designs use excavation combined with the placement of engineered large wood jambs to create self-maintaining rearing and spawning habitat that is accessible during low summer flows.  The project relies on mechanical construction at three of the sites.  The fourth site is difficult to access with heavy equipment.  Construction in this area will be accomplished by selectively felling trees and hand excavation.