5th UF Water Institute Symposium Abstract

Submitter's Name Max Wallace
Session Name Poster Session - Watershed & Wetland Management
Poster Number 67
Author(s) Max Wallace,  University of Florida (Presenting Author)
  Sanjay Shukla,  University of Florida
  Where is your watershed? Lessons from a watershed delineation in Florida with low topographic gradients and complex drainage network
  Lake Trafford is a ~1600 acre freshwater lake in Collier County, Florida. The lake is an important recreational resource and the headwaters for Big Cypress Preserve. Hydrologic, biologic, and chemical changes to the watershed have deteriorated the health of the lake. In an effort to restore the lake, the Florida Department of Environmental Protection (FDEP) established Total Maximum Daily Loads (TMDLs) for total nitrogen and total phosphorus entering the lake using the watershed model Hydrologic Simulation Program-Fortran (HSPF). Field visits and discussions with stakeholders indicate potential uncertainties in the watershed boundary used by the FDEP. Errors in watershed boundary delineation will result in invalid determination of watershed area, nutrient sources, and allocation of nutrient loads to different land use types. Accurate delineation of watershed boundary is the first step in development of the Basin Management Action Plan (BMAP). The goal of this study is to delineate the watershed using field measurements and topographic modeling. Inundation area maps were created for median and extreme lake levels using a high resolution LiDAR derived digital elevation model to identify potential seasonal surface water connectivity. A network of pressure transducers was installed around the floodplain to compare surface water gradients and establish preferential flow directions between the lake and adjacent ecosystems. Flow direction through hydraulic structures and natural sloughs crossing the current watershed boundary were verified after rainfall and pumping events using a handheld Acoustic Doppler Velocimeter. Initial field surveys have found areas on the order of 10% current watershed area to be removed or added to the current watershed and it is clear that the TMDL analyses for the lake must be revised using an updated watershed boundary. This study suggests that watershed boundaries should not be accepted without some level of skepticism especially in flat topographic regions like the Everglades.