Evaluation of the Use of Reach Transmissivity to Quanity Leakage beneath Levee 31N, Miami-Dade County, Florida

Nemeth, Mark; Wilcox, Walter; Solo-Gabriele, Helena

To manage water levels in the conservation areas and freshwater deliveries to Everglades National Park, it is important to determine the volume of water seeping from the water conservation areas to the underlying aquifers. An accurate water budget to meet the competing natural and anthropogenic needs cannot be determined without this information. As part of the U.S. Geological Survey (USGS) place-based studies program, a study was conducted to evaluate methods for quantifying these seepage losses. The study site is located along Levee 31N and the adjacent canal in central Miami-Dade County (fig. 1). This levee is part of the eastern boundary of the Everglades wetlands. From the wetlands, water seeps into the Biscayne aquifer, which is about 70ft (feet) thick in the area directly beneath Levee 31N; the aquifer thickens to the east. Due to high permeability of the aquifer, water flows relatively fast toward urban and agricultural areas to the east. Seepage to the aquifer from the Everglades is critical for maintaining water levels in water-supply wells to the east and for preventing the inland movement of saltwater from the coast. However, lowering ground water levels to the east has resulted in increased ground-water flow eastward from Water Conservation areas 3A and 3B located northwest of Levee 31N, and reduced surface-water flows to the south. Levees 67 A and 67C were constructed in Water Conservation Areas 3A and 3B to direct water southward toward the central region of Everglades National Park. This water-management scheme has been effective in delivering water to the southwest; however, it has reduced flow to the southeast (the northeastern part of Everglades National Park). Altering historic flow directions and water-level durations has adversely affected parts of the Everglades ecosystem. Water managers are interested in restoring predevelopment flow conditions to the Everglades and are continually balancing the needs of maintaining (1) a healthy Everglades ecosystem, and (2) a sufficient municipal and agricultural water supply. Water in the northeastern part of Everglades National Park, located west of Levee 31N, as well as water in the Levee 31N Canal provide recharge for municipal well fields just east of Levee 31N. The canal also is used to deliver water to agricultural areas to the south. One of the needs of the restoration efforts is to account for all significant hydrologic inflows and outflows to the Everglades ecosystem. The seepage of ground water under Levee 31N constitutes a substantial outflow of water from this system. Restoration of the Everglades ecosystem will require a mosaic of accurate data to reveal a complete picture of this complex system.