Rotational Impoundment Management
The District manages 4,000 acres of coastal mangrove swamps and salt marshes to abate saltmarsh mosquitoes and sandflies by minimizing available exposed mud for breeding during the summer. The District's Impoundment Program uses an ecosystem management approach for salt marsh mosquito control, following adaptive strategies based on biological and chemical research. This is an example of insect control by a resource management method that does not require pesticides.
The impoundments are open to natural tides most of the year but are kept flooded (partly closed, with constant water exchange) during the summer breeding season to minimize the amount of exposed mud available for mosquito egglaying, a procedure known as rotational impoundment management (RIM). The ecosystem management protocols result in multi-species benefits, especially for fish and wading birds. These areas also provide recreational value to the visitors and residents of the County, by providing opportunities for hiking, biking, fishing, crabbing and wildlife observation.
Land Acquisition Efforts
The District's land acquisition/mitigation/donation program is a critical component of its impoundment management effort. This program has been successful in helping to acquire: Bear Point Sanctuary, Vitolo Family Park, Blind Creek Park (ocean to river), Ocean Bay, Queens Island, Kings Island, Indrio Blueway, Harbor Branch Preserve, and Wildcat Cove.
Public ownership of the impoundments and adjacent natural coastal communities is necessary to achieve maximum public benefits and ecological improvements. This leads to better mosquito control through non-chemical methods and enhanced public access and recreational opportunities along the Atlantic beachfront and Indian River Lagoon.
Acquisition and restoration has been accomplished through various Preservation 2000 and federal grant programs, including: Florida Communities Trust, Conservation and Recreation Lands, Save Our Rivers, Save Our Coast, and State of Florida Recreation and Parks (Additions & In-Holdings). Special thanks go to the National Coastal Wetlands Restoration Act Grant Programs for their unwaivering support of coastal wetlands preservation and restoration in St. Lucie County.
Bear Point Mitigation Bank
The Bear Point Impoundment is an approved 317-acre mitigation bank that is located on County-owned wetlands adjacent to the Indian River Lagoon. It is located within Mosquito Control District Impoundment 1, about 1.3 miles south of Ft. Pierce Inlet, in Sections 12 and 13, Township 35 South, Range 40 East (Class III Waters). Click here for location map.
The bank was permitted by both the Florida Department of Environmental Protection (FDEP) and the U.S. Army Corps of Engineers (ACOE) and can be utilized as mitigation for impacts at other locations within the service area, from Sebastian Inlet to St. Lucie Inlet along the Indian River Lagoon,. The bank was permitted for a total of 49.8 estuarine mangrove credits from the FDEP and 43.3 credits from the ACOE.
The District has conducted mitigation activities that include enhancing water quality and wildlife habitat by increasing water exchange, removing exotic plants, and continuing to improve management practices. The main basis of the mitigation plan is the enhancement of water quality and hydrology by adding twenty-four 36-inch culverts through the impoundment levee and increasing the volume of pumped water (using an additional pump station, previously permitted). The additional gated culverts allow significantly increased water, nutrient, and faunal exchange during the open culvert months (generally mid-September to mid-April), simulating natural conditions with no levee.
During the flooded, pumping period (May-September), about 49,000 gallons per minute are continuously pumped into the impoundment. After an initial “pump-up,” with culvert gates closed, the volume of pumped water is maintained, and several of the culvert gates are partly or completely opened, to mimic the natural tidal volume exchanged, while maintaining desired water levels
During the pumping period, the target water exchange volume is 80% of what would naturally be exchanged if the levee were not present. Although this volume will not always move freely in and out of all the culverts, several different types of culvert gate allow various discharge types: bottom water, surface water, outflow only, two-way exchange. The setting and adjustment of these control structures regulate circulation and water quality in the impoundment, and are changed weekly, based on water level and water quality data. The mitigation plan also calls for at least one draw-down in the summer for a 2-week period to allow for more complete flushing of water and to enhance feeding opportunities for wading birds.
In addition to enhancing the hydrology, flooding the impoundment with salt water helps reduce exotic infestation. Invasive exotic plants on the levee include Australian pines, Brazilian peppers, and grasses, which are controlled as needed by regular cutting and herbiciding. Those sites are revisited on a regular basis for follow-up treatment and to confirm the re-establishment of native vegetation.
Student Research Paper Supports St. Lucie County Impoundments
During 2015, a Satellite High School student wrote a 38-page research paper on St. Lucie County’s Rotational Impoundment Management system. He ultimately determined that the water quality in the two impoundments he tested – Bear Point Preserve and Harbor Branch Preserve – mimic for the most part the water quality adjacent to the impoundments in the Indian River Lagoon. This conclusion further demonstrates the quality and effectiveness of the County’s impoundment system in improving coastal habitat for fish and marine life. The impoundments also help to boost the County’s tourism and educational opportunities through their limited public access.
Click here for a link to Kendall Karcher’s research paper, which won first place and best of show in the Brevard Intracoastal Science and Engineering Fair in February 2016.