by Susan Kenzle, ASLA
The plan to restore lower Waller Creek in Austin, Texas has been decades in the making, beginning with the City of Austin’s U.S. Bicentennial project in the 1970s. Waller Creek—named after Judge Edwin Waller, who chose this location for the new capital of Texas—is one of two natural waterways that ran through the town of Waterloo, the precursor to the current city of Austin. Waller Creek is the most heavily developed tributary watershed of the Colorado River within the city limits, with over 60% impervious cover surrounding it. Waller Creek’s six-square-mile watershed includes over 3,700 acres of residential, university, commercial, civic, and other land uses. The creek’s location in the heart of the city accounts for its low water quality and highly eroded nature. It’s a prime example of the “urban stream syndrome” characterized by “flashier hydrograph, elevated concentrations of nutrients and contaminants, altered channel morphology, and reduced biotic richness, with increased dominance of tolerant species.”
Austin is in the “Flash Flood Alley” of Central Texas due to its steep terrain, rocky and clay-rich soils, and high rainfall rates. The lower reach of Waller Creek traverses the City’s downtown corridor, where several damaging floods in the past decade inundated large areas along the creek banks. Significant flooding occurred here in 1915, 1938, 1981, and 2015 until the completion of the Waller Creek tunnel, a mile long flood diversion structure, removed 28 acres of downtown from the 100-year floodplain, allowing for various development projects, as well as for the development of a world-class chain of parks and trail system called the Waterloo Greenway.
The rejuvenation of Waterloo Park and the restoration of Waller Creek running through it was the first phase in a multi-year public-private partnership between the Waterloo Greenway Conservancy (WGC) and the City of Austin to create a trail system and chain of parks from UT Austin to Lady Bird Lake.
The design team, along with the Conservancy and the City’s Technical Advisory Group developed a Creek Corridor Framework Plan, the result of over a year of in-depth analysis and data collection as a high-level planning document to guide the more detailed planning. The interdisciplinary team of experts came from diverse disciplines: landscape architecture, engineering, biology, park operations, lighting design, and more. The document’s 10 design principles and priorities were founded on functional criteria that characterize a healthy stream as defined by the City of Austin’s Watershed Protection Department’s regulatory tool called the Functional Assessment of Floodplain Health. The intent of this assessment was to provide a simple, accurate, and locally derived tool that could be used to record a pre-project baseline and, later, to assess post-restoration success. The goal of this tool is to raise the pre-construction functional assessment score of a project area from low to higher, from say poor to good or better, thereby achieving ecological functional lift. The design team took the parameters from the tool and developed a “toolkit” of design solutions that provide a common language of stream restoration techniques across disciplines based on elements of natural channel design.
The plan for the creek restoration in Waterloo Park incorporated many elements shown in the diagram above: deep pools, rock lunkers, cross vane, and emergent logs, plus revegetation with Central Texas native and adapted plants.
Creek restoration projects are inherently destructive, ripping apart the cross section to reshape and rebuild. In this case, it involved removing an old creekside trail and rubble eroding out of the slope below a building upon which it was built, and elimination of invasive plants such as pervasive Arundo donax or giant reed. Work occurred between July 2019 and April 2021, most of it during COVID lockdown.
The first step was to clear the vegetation and start herbicide treatment of the Arundo donax, a process that was repeated throughout the project as new shoots appeared. Next was the demolition of the existing trail and retaining walls and clearing the creek of rubble eroding from the slope. The trail was removed as it constituted an obstruction to creek flows during storm events and was in the 100-year floodplain.
Although the preference in Austin’s creek restorations is for softer, green solutions this is not always possible. Due to the velocity of creek flows during rain events in this segment of Waller Creek and the proximity of an existing structure next to the creek, the designers included “kickback walls” of caliche limestone blocks, a sedimentary rock formed through a process of precipitation of calcite and other minerals, that is a waste product from local quarries. These bank-armoring walls are modeled after iconic limestone bluffs commonly seen in the Central Texas Hill Country to provide a more natural aesthetic.
One cross vane and associated pool boulders were included. Cross vanes are stones placed in streams in the shape of a “C” or “V” to direct the water away from the banks and towards the center of a waterway, to decrease shear stress on the banks to prevent erosion. They also dissipate the stream’s energy during high flows.
Trees removed for the project were salvaged and used on the slopes as woody debris. Woody debris, (aka logs-on-slope and stumpery) on the floodplain helps dissipate energy during high flow events, creates a nursery area for plant seedlings, a refuge and habitat for smaller wildlife and insects. As the wood decomposes, it’s a source of fungi, and adds organic matter (carbon) and nutrients into the soil.
Fish lunkers are a way to provide toe stability and edge cover, shade, and hiding spots for aquatic habitat where it is challenging to add habitat by other, more natural means such as wooden structures or undercut areas of banks.
Lastly, a diversity of vegetation installed during the project provides roots to stabilize the banks to prevent erosion and to filter pollutants from getting into the water, as well as shade, habitat, and beauty. In this project, the contractor planted 147 trees, 532 shrubs, almost 15,000 plugs, and seeds. Other plants came in naturally via wind, birds, and washed in with creek flow.
The results from two years after construction are striking. No longer a neglected section of creek, the restored portion of Waller Creek in Waterloo Park is a healthier, verdant creek and riparian area where one can find fish, turtles, hawks, raccoons, and great blue heron catching a meal, among other wildlife.
The next phase of the Waterloo Greenway, The Confluence, will be in the bottom of the watershed and will connect 4th Street to Lady Bird Lake. It started construction this year, building the lessons learned and techniques used during Phase One in Waterloo Park.
Susan Kenzle, ASLA, PLA, ISA, is a project manager in the City of Austin’s Watershed Protection Department focused on projects in the Waller Creek District. She started in the department as a Landscape Architect working on stream restoration and green stormwater infrastructure projects with a team of engineers. Before coming to the City, Susan spent a decade in Austin’s private sector working on various commercial development projects. She holds a Master of Landscape Architecture degree from Utah State University with a focus on restoration and landscape water conservation.