Denton Creek Park: A Deep Exploration into Natural Systems and Effects of Urbanization
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 TBG Partners, Verdunity, and Biohabitats, the project team initiated the endeavor by walking the full site with municipal staff from the City of Grapevine and collecting base data to study the full site systems. As the team dug into the site context, it became evident that a full regional analysis was needed. This analysis focused on connections to proximate destinations, such as schools and community centers that could utilize the park system, future connections to a planned regional trail system and an inventory of other Grapevine parks and their existing amenities. 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 existing infrastructure.
The project team then took a deep dive into the watershed analysis to understand the various water sources feeding the creek and overall effects on the larger system. Through our analysis, 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. Because it is susceptible to long durations of high-volume flows, the creek’s main channel has been incised vertically as far as possible and exists in a stage 3 creek condition of the 5 stage Channel Evolution Model.
Moreover, lower volume discharges from adjacent detention and retention ponds provide additional erosion impacts, resulting in severe overall creek 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 locals who run, walk, bike and would 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 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. As the team transitioned from Discovery to Development, it became apparent they would need to adopt different options, at different price points to help tell the story ecologically as well as present the options as a potential phasing of elements. The first option was the preferred natural terrace solution. It gives the highest impact to stabilize the creek channel, provides educational benefits to the users with engagement into the terraces and collects water running off from the slopes prior to entering the creek system. This option gives the highest value ecologically, environmentally and recreationally, affecting the triple bottom line at every level.
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 including 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, the team modeled what the creek would look like with no pedestrian improvements, and how even 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 is currently using the data gathered during the Discovery Phase and the graphics created during the Development phase to meet individually with council members and educate them on the issues and potential solutions.