ASSESSING FLOODPLAIN RECHARGE AND INFILTRATION BELOW A CONSTRUCTED WETLAND, NORTH CENTRAL TEXAS

The constructed wetlands of the East Fork Wetlands (EFW) project were designed for the North Texas Municipal Water District (NTMWD) to provide partially treated water for a municipal water supply. The water budget of any constructed wetland system consists of a well-controlled inflow and a less-controlled outflow. The uncontrolled outflows of evaporation, transpiration, and infiltration combined can be a significant quantity of the outflow total. Currently at EFW evaporation and transpiration are assumed to be the two primary components of the uncontrolled outflow. Infiltration is considered to be nonexistent or negligible. However, borings during the construction planning stages detected sandy lenses and saturated zones in the Trinity River alluvium indicating potential recharge within the floodplain. The goals and objectives of this study are to characterize the alluvial groundwater below the East Fork Wetlands and to quantify infiltration to better understand the overall water budget at the wetlands.

Field assessments include vegetation surveys; flow calculations; evaporation measurements; installation of piezometers and seepage meters to measure water levels and infiltration; installation of weather station equipment; and measurement of transpiration with an infrared gas analyzer. Information and measurements will be organized in a database and used for statistical and modeling analysis. Characterization of the subsurface was constructed using descriptions of cuttings from driller logs, well completion diagrams, and mapping.

Characterizing the infiltration will improve understanding of the EFW water budget and provide a baseline for groundwater studies in this wetland that will allow for further assessments of ecologic impacts in the future. The increasing reliance on constructed wetlands as a source and process in providing municipal water supply suggests that there is a need to understand the water budgets and groundwater processes in constructed wetlands more completely.