Walnut Creek Outfall Erosion Bank Phase II (Sites 3 & 4)
Austin, TX
Walnut Creek Outfall Erosion Bank Phase II (Sites 3 & 4) | Austin, TX
Following construction of the 96-inch effluent outfall line from the Walnut Creek Wastewater Treatment Plant to the Colorado River (~1997), the Austin Water Utility constructed two bank stabilization projects (Sites 1 & 2) on Walnut Creek to prevent stream migration into the line that runs parallel to the creek corridor. Additionally, two unprotected sites upstream of the past projects have created some concern for future erosion into the line. The Austin Water Utility initiated this project to install protective measures for the two unprotected sites (Sites 3 & 4).
As the prime consultant for this project, CAS staff performed all drainage engineering and design; managed subconsultant engineering efforts for land surveys, permitting, landscape architecture, geotechnical, cost opinions, archeology and CADD support. CAS prepared Preliminary Engineering (PER) and Final Engineering Reports, HEC-RAS models, scour and riprap calculations, stream bank stabilization designs, engineering plans, specifications, cost opinions, and bid documents to stabilize the stream bank slopes at the two unprotected sites. The existing top of the bank on the eastern side of the creek was preserved and new embankment material, 24-inch class rock armoring, and grade control structures were used to relocate 1,085 feet of creek channel away from the 96-inch effluent line.
The stream bed was actually moved approximately 40 feet to the west. CAS assisted/managed US Army Corps of Engineers, Texas Historical Commission (Archeology investigation), and City Site Plan permits for the project. Submittals included the PER, 30%, 60%, and 90%, and 100% plans and documents. Bid and construction phase services were also provided for this project including: bid analysis, submittal reviews, responses to RFIs, analysis of Change Orders/Claims, and site observations for Contractor compliance with intent of the design. Awarded at $1.26 million, the project was successfully completed within City expectations for budget and schedule duration.
