Projects & Studies
Willow Waterhole Prairie Management Area
The Harris County Flood Control District is required to establish a 15-acre native coastal prairie conservation area in the Willow Waterhole Stormwater Detention Basin’s Compartment 3, which is located on a 74-acre property northeast of the South Post Oak Road/South Main Street intersection in southwest Houston.
The 279-acre Willow Waterhole basin complex, in 6 planned compartments, is part of the Brays Bayou Federal Flood Damage Reduction Project (Project Brays), a multi-year, $550 million project that will substantially reduce flooding risks in the Brays Bayou watershed. The project is a cooperative effort between the Harris County Flood Control District and the U.S. Army Corps of Engineers.
The Flood Control District purchased the Willow Waterhole property for flood damage reduction and the original plan called for excavating the entire Compartment 3 site for stormwater detention. Per National Environmental Policy Act (NEPA) compliance, the discovery of an endangered species triggered the requirement for the establishment of a 15-acre native coastal prairie conservation area in Compartment 3.
NEPA requires that federally-funded projects, such as Project Brays, undergo an extensive environmental assessment and that projects avoid or compensate for impacts to natural resources.
During the NEPA compliance process, biologists surveyed the Willow Waterhole basin properties and discovered an endangered plant species, Hymenoxys texana or Texas prairie dawn, in Compartment 3. This plant is associated with coastal prairie habitat, a critically impaired habitat of the Gulf Coast.
Remnants of coastal prairie were also found on the property close to the rare plant.
As a result of the findings, the Flood Control District prepared the Willow Waterhole Prairie Management Plan, in coordination with U.S. Fish and Wildlife Service (USFWS), which details how the endangered species would be preserved in the 15-acre conservation area, named the Willow Waterhole Prairie Management Area. Multiple organizations provided input during the plan’s development, including the Texas Parks & Wildlife Department, Coastal Prairie Partnership, Houston Audubon Society, Texas Gulf Coast Master Naturalists and Texas A&M University.
The Flood Control District is required by law to implement the plan.
WILLOW WATERHOLE PRAIRIE MANAGEMENT AREA
The first step in the Willow Waterhole Prairie Management Plan was to map the full extent of the coastal prairie remnants and the Texas prairie dawn colonies, which were found in two locations in the Willow Waterhole Prairie Management Area (marked North Sector and South Sector on the site map below). The Flood Control District then launched a three-phased effort to protect this species by conserving and restoring its coastal prairie ecosystem.
Phase 1, in 2010, involved the partial removal of trees and undesirable vegetation in the North Sector (refer to site map), which is located south of the Willowbrook and Post Oak Manor neighborhoods. Next, the Flood Control District started inventorying and monitoring the ecosystem, which has shown a remarkable ability to return to its original, natural state as a coastal prairie. To date, over 300 species of native plants have been found within this area, including many colorful wildflowers.
Phase 2, in November 2013, and included the partial removal of trees and undesirable vegetation in the South Sector, which is located near the eastern end of Gasmer Drive, north of South Main Street; and the partial removal of trees and undesirable vegetation in the North Sector. A forested buffer (shown in light green on the site map) will remain between the neighborhoods and the North Sector. District experts and community leaders agreed upon allowing individual trees to remain within the prairie as mottes: groups of trees interspersed within a prairie. Refer to site map for location of current mottes in the North Sector.
Phase 3, in late 2015, and included removal of trees, undesirable vegetation, and debris within the South Sector. Final motte locations can be seen in the site map below. A forested buffer (shown in light green on the site map) will remain between the prairie area and railroad tracks.
The following procedures were followed during each Phase of prairie restoration:
- Tree Removal: While the effort will require the removal of some larger trees, the Flood Control District plans to avoid where possible the removal of healthy, desirable large trees in the two sectors. Tree removal is a necessary step to establishing a coastal prairie habitat because fast-growing trees can overwhelm and displace the grasses and wildflowers that give prairies their valuable characteristics. The Harris County Flood Control District’s contractor will remove shrubs, saplings and small trees in the North and South sectors. Hardwood trees larger than approximately 10 inches in diameter cannot be removed due to equipment limitations. Trees larger than 10 inches in diameter will be evaluated for removal or to remain as a motte.
- Tree Evaluation: Flood Control District biologists will evaluate the condition, location, number and species of the remaining trees within the Prairie Management Area to determine which trees to include as mottes, which are groupings of trees. These selected trees will be flagged, cataloged and mapped.
- Motte Creation: Based on the site-wide tree evaluation, the Flood Control District’s contractor will remove trees that were not selected to be included within the mottes.
- Prairie Establishment: Mulch created from tree removal will be raked into the motte areas. This will reveal the buried prairie seedbank and soil, allowing the native grasses and wildflowers to germinate and flourish.
- Undesirable Vegetation Removal: The Flood Control District’s contractor will remove all exotic, or non-native, vegetation in the North and South sectors, including Chinese Tallow, Crepe Myrtle, Pampas grass, Oleander and others. This is done to prevent encroachment by species with the ability to displace the Texas Prairie Dawn and other native species.
- Management, Monitoring and Maintenance: The Flood Control District will manage the Willow Waterhole Prairie Management Area according to the Willow Waterhole Prairie Management Plan. Management activities include cyclic or semi-annual high-deck mowing, woody plant removal, and select herbicide application. The Flood Control District will adjust the management plan as needed.
As this site becomes established, it will be a great community asset by conserving one of the last urban coastal prairie sites in Harris County, and will offer educational opportunities for children and adults to learn about these endangered coastal prairie habitats.
PRAIRIE ACCESS PLAN DEVELOPMENT
The Flood Control District worked with a landscape architect to develop a public access plan for the Willow Waterhole Prairie Management Area, which includes:
- Secured access for pedestrians
- Interpretive signage and educational opportunities
- Public amenities, such as trails, if funding becomes available
The District reached out to the community and interested stakeholder groups to provide input into this planning process. Three public meetings were held to discuss and develop the Willow Waterhole Public Access Plan.