BY: Michelle Hopkins, PE, CFM; Mark Schwartz, PE, CFM; and Nirjhar Shah, PhD, CFM, EI
AMEC-BCI in conjunction with TKW Consulting Engineers, Inc. has been working with the South Florida Water Management District (SFWMD) on a hydrologic restoration project in southwestern Florida. Located in Lee County, the project site is in the City of Bonita Springs and forms a part of the Imperial River Watershed (Figure 1). The project was initiated in response to the recommendations of the South Lee County Watershed Study (SLCWS) that was conducted following severe flooding that occurred in 1992 and 1995 in the City of Bonita Springs.
Formally known as the Southern Corkscrew Regional Ecosystem Watershed (Southern CREW) Critical Project, the project encompasses an area of 4,150 acres and extends westward from the Lee-Collier county line (Figure 1). Based on the proposed restoration objectives outlined by the U.S. Army Corps of Engineers’ (USACE) environmental assessment (EA) of the Southern CREW project area in 1999, SFWMD made the Southern CREW project a part of its Comprehensive Everglades Restoration Program (CERP).
The main objective of this project is to hydrologically restore, without offsite impacts, this environmentally sensitive area that has been altered by the residential development, roads, and agricultural ditches. AMEC-BCI’s role in this high profile restoration project was to modify and use numerical modeling of the area as a means to provide rationale for measurements and comparisons of the proposed restoration actions. The model developed for this project was also used to identify potential off-site impacts by providing quantitative estimates of water depth, groundwater response and hydroperiod. For this project, AMEC-BCI selected DHI’s MIKE SHE (DHI 2008a and 2008b) as a modeling program of-choice to represent the integrated surface and ground water system.
The surface water quality standards of Florida establish a dissolved oxygen (DO) standard of 5.0 mg/L for Class III waters (FL Statutes Chapter 62-302, F.A.C.) Concentrations below this for extended periods of time can lead to fish kills and other negative ecological impacts if the aquatic system has structured itself around higher oxygen concentrations. Any deviations from this minimum level are typically assumed to be of anthropogenic origin related to excess organic material or nutrient loading from the watershed. While this is often true, and usually related to point and nonpoint source pollution loads, some water bodies receive high loads of organic materials from natural sources such as forests and wetlands. The effect of these natural organic loads is accentuated in warm, slow moving, low gradient rivers and lakes with long hydraulic residence times. There is interest in revising the standard to better reflect these types of systems to avoid dedicating resources to fix a perceived impairment that actually reflects a healthy system.
Former muck farming practices on St. Johns River Water Management District’s (SJRWMD) Area 7 in Emeralda Marsh Conservation Area left elevated soil organochlorine pesticides (OCPs) that posed a potential threat to piscivorous birds. In 2004, SJRWMD worked in conjunction with AMEC-BCI and Lake County Water Authority (LCWA) to design a spoil disposal project that would result in reduced fish exposure to OCPs in Area 7. The design involved overlaying the contaminated sediments with spoil material from Lake Griffin canals, which were being dredged by LCWA for maintenance.