Hydrologic model for design and constructed wetlands

The Trinity River Mitigation Bank was proposed to develop and use a mature, contiguous, diverse riparian corridor along the West Fork of the Trinity R iver near Dallas, Texas, USA. In the proposed wetland design, water would b e diverted from Walker Creek as necessary to maintain wetland function. The refore, assessment of the magnitude and continuity of the flow from Walker Creek was paramount to successful wetland operation. The Soil and Water Ass essment (SWAT) model was used to assess whether the sustained flow (storm f low and base flow) from the Walker Creek Basin could maintain the proposed bottomland wetland ecosystem. For this study, SWAT was modified to allow po nded water within the prescribed wetland to interact with the soil profile and the shallow aquifer. The water budget was prepared for the wetland base d on a three-step process. First, data required to run the model on Walker Creek, including soils, topographic, land-use, and daily weather data were assembled. Next, data required to validate the model were obtained. Since s tream flow was not available at the proposed site, flow from a nearby water shed with similar soils, land use and topography were used. In the final st ep, the model was run for 14 years and compared to the measured water balan ce at the nearby watershed. The model results indicate that the wetland sho uld be at or above 85 percent capacity over 60 percent of the time. The wet land did not dry up during the entire simulated time period (14 years) and reached 40 percent capacity less than one percent of the time during the si mulation period. The advantages of the continuous simulation approach used in this study include (1) validation of wetland function (hydroperiod, soil water storage, plant water uptake) over a range of climatic conditions and (2) the ability to assess the long-term. impact of land-use and management changes.