Quantification of Ground-Water Seepage Beneath Levee 31N, Miami-Dade County, Florida

The primary objective of this investigation was to quantify seepage below Levee L31N. The amount of water lost to the L-31N Canal versus the fraction that flows below the canal was estimated. A conceptual model was developed for the site based upon results from an on-going stable isotope (oxygen -18 and deuterium) study. Quantification of seepage rates were based upon a computer model, MODBRANCH, which couples both groundwater and surface water flows. Particular attention was 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 was incorporated into MODBRANCH; this relationship was believed to be more suitable for transient conditions. The reach transmissivity relationship was 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 were used to develop an algorithm for real time estimation of seepage beneath Levee L31N. It was expected that this algorithm would estimate seepage using head differences at monitoring stations in the vicinity of the levee.