The City of Austin retained Geosyntec to stabilize approximately 450 linear feet of eroding stream bank along lower Buttermilk Creek to protect a threatened multi-family structure and to rehabilitate and restore riparian habitat along adjacent portions of the stream channel.
Urbanization and increased impervious cover in the contributing watershed of the stream has resulted in increased volume and frequency of storm runoff and stream flow, which in turn led to stream erosion. The eroding stream bank undermined an existing storm drain and fence, and was threatening other infrastructure. The project objective was to design and implement engineering solutions to stabilize the existing stream bank, protect threatened infrastructure, restore native vegetation along the creek corridor, and preserve existing aquatic habitat.
Geosyntec’s scope of services included a field survey of the existing channel conditions; a geotechnical investigation; hydraulic analyses of existing and proposed conditions; bank stabilization system analysis and design; riparian restoration design; preparation of detailed plans, specifications, and a construction cost estimate; construction permitting; bid phase assistance services; and construction phase assistance
services. The project team used a variety of analysis methods to optimize the stabilization system design, which needed to be completed in an expedited time frame, within a limited drainage easement and without adversely affecting the 100-year floodplain. Geosyntec designed a drilled soldier pile and concrete lagging retaining wall for creek bank stabilization, which was combined with native limestone block facing and reinforced vegetated soil slopes to resist erosion and retain a natural aesthetic. Geosyntec developed detailed plans, specifications, and a construction cost estimate for the bank stabilization design. The plans and specifications included provisions for protecting the bedrock stream bed during construction to preserve the existing pool/riffle sequence and aquatic habitat. Geosyntec led the hydraulic evaluation, demonstrated no impact to the floodplain, and developed the design to meet U.S. Army Corps of Engineers Nationwide Permit 13 requirements. Geosyntec also coordinated the project with the Texas Historical Commission, U.S. Fish and Wildlife Service, Texas Parks and Wildlife Department, and City’s General Permit office. During the bid phase, Geosyntec reviewed contractor submittals and recommended the selected contractor. Geosyntec also provided construction phase services.
Geosyntec’s design provided an innovative and constructible bank stabilization measure that restored stream functionality and protected residential properties. The project was designed and constructed within the City’s allotted budget and accelerated schedule.