Revegetation of a Detention Basin in Harris County, Texas: Lessons Learned

摘要

Post-construction establishment of native vegetative cover on side slopes of a multi-use stormwater multi-pool detention basin in Harris County, Texas proved to be a challenge for the Harris County Flood Control District (HCFCD). Harris County lies on the humid, sub-tropical, gulf coastal plain and receives 1.22 m (48 inches) of annual rainfall. Created for flood damage reduction and water quality enhancement, the 108 hectare-m (880 acre-foot) capacity detention basin in the Sims Bayou watershed was excavated to a depth of approximately 10.4 m (34 feet) below existing ground elevation. The basin side slopes and central "hill" were created from the excavated basin clay soils. Insufficient quality topsoil from the site's grassland/fallow farmland was available for application to slopes as specified in the contract documents. The basin slopes were, therefore, formed from subsurface clays and silty clays. Dry application seeding of native grasses and forbs, performed over an 8-month period from fall 2005 to spring 2006, was unsuccessful in stabilizing slopes. Tree planting and installation of a subsurface irrigation system produced further unchecked soil disturbances. Sediment filled the backslope drain system concentrating overland flows and causing gullies to form in the basin side slopes. Attempts to repair erosion prior to re-seeding activities were impeded in the areas where native trees were planted. After approximately 2 years of repeated site stabilization attempts, actions to stabilize the site and to repair gullies over 3.05 m (10 feet) deep will begin in 2008. The site will become a demonstration site for products and techniques not commonly used on HCFCD projects. First, the hill slopes and upland slopes will be stabilized, then the swales' drainage function will be restored and the site will be stabilized to further prevent erosion. As enhancements - trees, irrigation systems, native grasses and forbs, etc. are added. Timing of activities and communication between HCFCD divisions and careful oversight of the re-vegetation activities at the site are critical to successful establishment of the long-term goal of native vegetative cover on HCFCD detention basins.