Environmental Impact of Midnight Pass Reopening Project

Sarasota County, Florida is undertaking the work necessary to plan, design and permit a project to reopen Midnight Pass. In support of the design studies for the project, a hydrodynamic model study was conducted that served two main purposes: (1) provide a tool to aid the engineering design by evaluation of design alternatives and optimization of the inlet dimensions, and (2) provide a framework for evaluation of potential project induced environmental changes (e.g., salinity, temperature, estuary water residence time, etc.) and identify alternatives with the least adverse impacts and greatest potential benefits. This paper presents the setup, calibration and application of a two-dimensional hydrodynamic model (EFDC) to determine the environmental and scientific merits of this project. The model study area includes an interconnected bay system that includes Little Sarasota Bay, several other bays and four existing inlets (Longboat Pass, New Pass, Big Sarasota Pass, and Venice Inlet). Model calibration and verification comparisons to observed data demonstrate that the model is capable of representing the hydrodynamics and salinity transport of the bay system. Several project alternatives were simulated to evaluate the current velocities in the newly opened inlet, the impacts to the circulation and flushing characteristics of Little Sarasota Bay, and impacts to the stability of nearby inlets also connected to the bay system. Based on an evaluation of each alternative, a preferred alternative with the least adverse impacts and greatest potential benefits was recommended.