The Waller Creek Conservancy, City of Austin (Watershed Protection Department)
Michael Van Valkenburgh Associates, Inc (MVVA)
Waller Creek is a highly urbanized stream in downtown Austin, Texas. The creek has experienced severe flooding, channel erosion, and degraded water quality. The intense wet-weather flows in the creek will be controlled by the construction of a large tunnel that will route stormwater beneath downtown Austin and deliver excess flow to Lady Bird Lake. Upon completion, the Waller Creek Tunnel will remove approximately 28 acres of downtown land from the 100-year floodplain, creating a new hydrologic condition for the creek and a unique opportunity for urban revitalization and ecological restoration of the Waller Creek Corridor.
In 2011, The Waller Creek Conservancy launched an international competition to redesign Waller Creek. LimnoTech was part of the winning design team led by MVVA. The design considerations outlined by the City’s Watershed Protect Department included hydrological and ecological connectivity from Waterloo Park to Lady Bird Lake; a stable stream system design that provides sustainable form and function given a controlled flow regime; native riparian landscape that restores the natural and traditional character of a local stream; stormwater treatment opportunities; community outreach and educational opportunities; and flood safety and infrastructure protection.
The design concept had to address severe flooding, channel erosion, slope failures, invasive species, and degraded water quality that has been historically experienced in Waller Creek. Design concepts for the creek also needed to account for an existing plan to construct a large stormwater diversion tunnel (i.e., the Waller Creek Tunnel) that would convey most of the creek’s flows underground to the downstream Lady Bird Lake.
LimnoTech’s primary role in this multi-phase project has been to evaluate the effects of a highly modified hydrology on the creek hydraulics, channel form, and ecology. This has included developing an in-depth understanding of the creek under a range of flow conditions through field observations and modeling, and managing the effect of stormwater flows on creek hydraulics and water quality.
We are using hydrologic and hydraulic models (HEC-HMS and HEC-RAS) of the creek system to evaluate the effects of varying flow regimes on water surface levels and stresses under the full range of flow conditions to inform channel design and habitat creation. An adapted creek geomorphology that responds to these new hydrologic conditions requires alterations of individual channel sections and design plans that vary by reach. The reach-scale design plans use a combination of hard and soft channel modifications that will facilitate the planned human use of the restored waterway.
As the Waller Creek design has advanced, an important part of the project has been working with City, Conservancy, and regional planners to develop a common understanding of the project objectives. Careful phasing of the project has allowed for different sections of the creek design to be sequenced and funded independently to allow the project to progress. Ultimately, we are working towards creating an urban ecology that provides a healthy and functional urban waterway, environmental benefits, and recreational opportunities for the people of Austin, Texas.