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Title: Final Environmental Impact Statement : Lake Tohopekaliga Extreme Drawdown and Habitat Enhancement Project, Osceola County, Florida, Volume II : Integrated Surface and Groundwater Model for Lake Tohopekaliga Drawdown Project
Authors: United States. Army. Corps of Engineers. Jacksonville District.
Keywords: Environmental protection
Tohopekaliga, Lake (Fla.)
Publisher: United States. Army. Corps of Engineers. Jacksonville District.
Abstract: This report documents the building, calibration and application of an integrated surface water-groundwater model (ISGM) developed for South Florida Water Management District (SFWMD) by DHI and GeoModel, Inc. The ISGM is based on the MIKE SHE/MIKE11 code developed by DHI. The code has previously been applied to a number of SFWMD projects including the Alligator Lake drawdown study conducted jointly by SFWMD and DHI in 1998/1999. The MIKE SHE/MIKEl 1 code has the capability of simulating the major flow components of the hydrologic cycle, which makes the model very well suited for lake drawdown studies and, in particular, refill scenarios. The lake refill process is a complex interrelationship between climate and surface and sub-surface runoff processes combined with the operation of hydraulic control structures. A correct simulation of the lake water level and the aquifer recovery process requires and integrated modeling approach and a detailed description of the storage and hydraulics of lakes, canals and hydraulic control structures. Lake Tohopekaliga (Lake Toho) is one of the larger lakes in the Kissimmee Chain of Lakes. The Kissimmee Chain of Lakes is located in the upper Kissimmee Basin that extends from Orlando southward through Lake Kissimmee covering portions of Osce-ola, Orange, Polk and Lake Counties. These lakes feed the Kissimmee River, forming the headwaters of the greater Kissimmee-Okeechobee-Everglades ecosystem. Major lakes in the chain include Kissimmee, Toho, East Lake Toho, Hatchineha, Cypress, Gentry and Alligator. Historically the lakes fluctuated between two and ten feet seasonally, providing natural cleansing and drying out which sustained the natural flora and fauna. The natural water level fluctuations supported the fishery and wildlife habitat, but made residential and agricultural developments difficult if not impossible due to flooding. After severe floods in the 1940's the lake water level fluctuations were controlled by improving canal conveyance and by introducing a number of hydraulic control structures (gates) and today the lake water level regime is largely controlled by the operation of these gates. Lake water level drawdown help to reestablish and sustain fish and wildlife habitats. Controlled extreme drawdown is the management technique currently used to mimic the natural cleansing and drying process. During a drawdown lake levels are lowered up to six feet below their normal low pool stage and while the lake levels are low, organic matter and shoreline vegetation are physically removed. Lake water levels will be kept low for as much as 60-90 days in order to allow exposed sediments to dry out promoting die-off of undesired vegetation and the development of native vegetation regimes. Subsequently the downstream regulation gates are closed and the lake recovers back to its normal regulation scheme. Depending on the climatic conditions this recovery process may go on for several months or longer. The Florida Fish & Wildlife Conservation Commission has planned and extreme drawdown for Lake Toho starting in November 2001. Traditionally the Commission sponsors the drawdown projects while federal and local government organizations support the projects, for instance, with technical expertise. The present project is funded by SFWMD in support of the drawdown study. The proposed Lake Toho drawdown study would temporarily modify the normal lake water level regulation schedule to 48.5 feet. The normal regulation schedule varies between 52-55 feet. The objectives of the present study is to develop an integrated surface water-groundwater model (ISGM) with the ability to predict potential impacts of the lake drawdown on groundwater levels in the surrounding region.
Description: Environmental Impact Statement
Rights: Approved for Public Release; Distribution is Unlimited
Size: 238 pages/135.52 Mb
Appears in Collections:Environmental Documents

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