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TBG wins Texas ASLA Honor Award for Work on Denton Creek

Jodi House

We’re excited to share that our work on Denton Creek has been awarded a Texas ASLA Honor Award in the Planning & Analysis Category! Continue reading for more on the project.

Located in Grapevine, Texas, a city in the Dallas/Fort Worth Metroplex northwest of downtown Dallas, Denton Creek Park is a forthcoming recreational environment that began with a master-planning effort in 2016 and has blossomed into a more holistic analysis of the watershed and ecological systems. Comprised of the TBG Partners, Verdunity, and Biohabitats, the project team initiated the endeavor by walking the full site with municipal staff from the City of Grapevine. Analysis then focused on regional context — including connections to proximate destinations, such as schools and community centers that could utilize the park system, as well as future connections to a planned regional trail system — and included an inventory of other Grapevine parks and their existing amenities. Next, the team analyzed the watershed to understand the various water sources feeding the creek and effects on the larger system. It was determined that a golf course upstream was introducing large amounts of pollutants and a nearby spillway of the Grapevine Lake dam was the source of high volumes of water during storm events. These efforts clarified that the creek would flood for multiple reasons, including not only stormwater run-off to the creek itself, but also from the lake overflowing and inundating the creek system.

The analysis further revealed that the property was being utilized not only for the 4,500-foot-long creek system and floodway, but as the home of multiple utilities. Major water and sewer infrastructure were already being impacted by erosion to the point that the creek bank is within 5 feet of impacting existing infrastructure. Because it is especially susceptible to long durations of high-volume flows, due to its downstream proximity to the Grapevine Lake dam, the creek’s main channel has been incised vertically as far as possible and exists in a stage 3 creek condition. Moreover, lower volume discharges from adjacent detention and retention ponds provide additional erosion impacts, resulting in severe overall erosion and multiple issues warranting system stabilization. Impacts include loss of bank material, compromising the natural floodplain and riparian edge biota, and the presence of pollutants such as bacteria in high concentrations bound to soil material in banks adjacent to the creek. In addition, impacts include degradation of downstream water quality, impacts to habitat and loss of recreational use value from bank erosion and sedimentation, impacts to major water and sewer infrastructure, and significant financial, environmental and quality of life impacts from unstable and erosive streams.

Bank erosion to a portion of the creek upstream had already required interventions, which encompassed the use of hard armoring for erosion control — essentially concrete stabilization at a cost exceeding $1 million. The project team recognized that the site would eventually receive that same armored detail — unless the city and key decision-makers were educated and enlightened to a more naturalistic and beneficial solution. The creek’s erosion had reached a low point; it hit bedrock and couldn’t go any deeper and thus would only keep widening — but because of the utilities, it physically can’t widen. In a naturalistic condition, the creek would have natural terraces and multiple points to spread out the water volume during large rain events, which is the direction sought by the project team.

A user analysis exercise unfolded concurrently that gauged potential park users and their various needs, establishing three broad user groups. The first group includes patrons who stay for 30 minutes to one hour, primarily encompassing locals who run, walk, bike and use the space to pass through or for brief recreation. The second group falls into the one- to two-hour duration of stay, who primarily will drive to the site and come from throughout the region. These patrons will want parking and elements like a pavilion and seating areas, playgrounds, bridge connections spanning the creek to residential areas, etc. A forthcoming restaurant and entertainment venue adjacent to the park will provide additional patrons to the site. The final group includes larger groups who stay for multiple hours, such as visiting school children, senior citizens, church groups, camps, etc., which would desire restroom facilities, amphitheaters and other larger-scale gathering spaces.

The creation of an environmental sensitivity map overlaid multiple diagrams onto the site and showed prudent locations for structures and high-intensity program uses versus areas to leave untouched. At this point the project team made several presentations to the city, showing three options and associated costs for each. The first option was the preferred natural terrace solution, while the second was a simplified version and the third was the least impactful. Given the large array of data and the need to present an all-encompassing visual package, the project team prepared a more streamlined package that lucidly explains the local context, user analysis, current conditions, the critical conditions for erosion and utilities, as well as the monetary and environmental impacts of the three options.

In order to accommodate financial parameters, the second and third options essentially leave the creek bank in its current condition and provide pedestrian improvements and park amenities outside of the bank edge. The second option still utilizes environmental approaches like bioswales, bioretention areas and ecosystem regeneration, just outside the creek zone. The simplest, third option is more minimalistic and primarily encompasses connecting to a regional trail. In addition, because the project team knew it would arise in discussions, they showed what it would look like to add the creek armor with no pedestrian improvements, and how even just armoring a portion of the creek would affect the other side and additional areas, while a natural terrace solution, in turn, would benefit adjacent areas. The city’s parks and recreation department then used the analysis package to meet individually with council members and educate them on the issues and potential solutions.

What started as a park planning project evolved into a much larger analysis of watershed and environmental impacts, and the project team developed a master plan that considers multiple alternatives for the creation of the new park, each considering different levels of stream restoration. The recommended plan for the project includes full natural creek stabilization, the creation of a connected network of constructed wetlands, bioswales and bioretention systems, recreational and educational amenities throughout, and limited structural stabilization where critical utilities cannot be relocated.