Evaluation of Methods to Determine Ground-water Seepage Below Levee 31N, Dade County Florida

The primary objective of this investigation is to quantify seepage below Levee L31N. The amount of water lost to the L-31N Canal versus the fraction that flows below the canal will be estimated. A conceptual model is currently being developed for the site based upon results from an on-going stable isotope (oxygen -18 and deuterium) study. Quantification of seepage rates will be based upon a computer model, MODBRANCH, which couples both groundwater and surface water flows. Particular attention will be devoted to model performance under transient conditions caused by fluctuations in the stage of the L-31N Canal and pumping operations of the West Wellfield. In addition, an alternative leakage relationship based on reach transmissivity will be incorporated into MODBRANCH; this relationship is believed to be more suitable for transient conditions. The reach transmissivity relationship will be evaluated in comparison to MODBRANCH's existing leakage relationship, which is based on Darcian flow through the bed of the surface water channel. Modeling results will be used to develop an algorithm for real time estimation of seepage beneath Levee L31N. It is expected that this algorithm will estimate seepage using head differences at monitoring stations in the vicinity of the levee.

Plans to restore historical hydrologic conditions in the northeast section of Everglades National Park (ENP) include the raising of water levels in ENP and water conservation area 3B, which overlie the Biscayne aquifer, an extremely permeable aquifer. The increase in water levels is likely to cause an increase in seepage losses to the east. Quantifying this seepage loss is necessary for water management purposes as well as for models of the Everglades and coastal systems. Levee L-31N has been identified as a critical area for potential water losses. The L-31N study site includes a wetland area within ENP on the west; the L-31N Canal flows from north to south through the longitudinal center of the site, and the eastern portion of the region is a suburban area of Miami which includes a major municipal wellfield, the West Wellfield, and rock mining activities.

This project was completed in 1999.