Permeable Parking Lot Considerations for Karst-Clay Soils On Military Lands.

Vegetated Permeable Pavement Trial – Fort Hood, TX Stormwater mitigation becomes an increasing problem as natural flow paths are changed to result in increased flow rates, less infiltration, and higher pollutant concentrations. Concrete ditch linings, inadequate earth grading, and extended periods of dry season are all common occurrences at Fort Hood, Texas which add to stormwater management problems. The site chosen for this study is a parking lot serving multiple office buildings and training facilities. The design must concentrate runoff, hold the water to allow infiltration, remove Petroleum Oil Lubricants (POLs), allow for treatment of overflow, and create an eye appealing green space. Ideally stormwater treatment would be incorporated into the existing landscape and serve a vital need for each area as well. The chosen solution is a vegetated, permeable, parking lot with a bioswale overflow. The new parking lot will be installed at the base of an existing asphalt lot to catch and mitigate all runoff. Any overflow will be directed to a bioswale over flow ditch to have a further chance to be treated. This idea fits the design requirements because it serves a vital need for additional parking in a growing area and adds a much needed stormwater mitigation technique that fits the site. Rainfall, contributing runoff, infiltration rate, holding capacity, evapotranspiration, and outflow were calculated starting with a 2 year 24 hour rainfall event as the basis of size requirements. The greatest problem with this area of Texas is high rainfall rates and slow infiltration rates. A 10 year event would not be feasible to hold all runoff at one time so the bioswale option must be implemented to receive overflow from parking lot area. This area will be monitored with sampling units and data loggers at each outflow point throughout the process to monitor amount of water mitigated by the parking lot, holding basin, and drainage bioswale. At the conclusion of this project, more information will be gained into the effectiveness of vegetation to treat runoff, the costs and maintenance associated with such a project, and the feasibility of increasing infiltration in poor soils.