The Southwest Florida Water Management District’s Governing Board recently adopted minimum flows for portions of the Alafia and Myakka rivers, along with minimum and guidance levels for five lakes.
The 5 lakes include: Lakes Allen, Harvey and Virginia in Hillsborough County; Lake June-In-Winter in Highlands County; and Lake Parker in Polk County.
A minimum flow or level is the limit at which further water withdrawals will cause significant harm to the water resources and/or environment. The District Governing Board sets these limits as part of achieving a balance between meeting human water needs and those of Florida’s natural systems.
Highlands, Hillsborough and Polk County lakes
The District adopted two types of levels for lakes: minimum and guidance. Minimum levels are set to prevent significant harm to the water resources. Guidance levels are used to describe expected water level fluctuations.
The minimum levels were developed to protect lake-fringing wetlands, connectivity among lake sub-basins, dock-use, species diversity, aesthetics, recreational use and natural patterns of water circulation within the lakes. The District sets a low minimum level and a high minimum level to protect these lake attributes and promote ecosystem integrity by ensuring fluctuation in lake water levels. The low minimum level defines water surface elevations that must be equaled or exceeded 50 percent of the time. The high minimum level must be equaled or exceeded 10 percent of the time.
The guidance levels describe expected lake fluctuations and were developed as advisory information for lakeshore residents and local governments.
There are three guidance levels. They include a flood elevation that may be expected about every 10 years, and a high water level and a low water level.
The low level may be exceeded 90 percent of the time and the high level may be exceeded 10 percent of the time.
For more information about the minimum and guidance lake levels, please contact Doug Leeper at (352) 796-7211, ext. 4272, or 1-800-423-1476, ext 4272.
Freshwater Segment of the Alafia River and the upper Myakka River
The District established minimum flows for different sites along the two rivers for the dry and wet seasons.
The freshwater segment of the Alafia River is mainly located in Hillsborough County, with a small portion located in Polk County. The upper Myakka River is the portion of the river from Myakka City to S.R. 72 in Manatee and Sarasota Counties.
The minimum flows are based on preserving natural, seasonal flow patterns, protecting habitat availability for fish and other aquatic organisms, and ensuring river floodplain inundation.
The minimum flows include a short-term minimum flow threshold, short-term seasonal flows and long-term compliance standards. The short-term minimum flow threshold is used to determine if water may be withdrawn from the river. The short-term seasonal flows identify how much water can be withdrawn from the river based on the previous day’s flow.
For example, if flow in the Alafia River is greater than 59 cubic feet per second, water would be available for withdrawal. How much could be withdrawn would be determined by a chart that includes different ranges for different times of the year based on seasonal flow.
The long-term minimum compliance standards identify the lowest average flows that may be expected for five- and ten-year periods, when the short-term minimum flows are being met. These standards are developed using the short-term minimum flows and long-term flow records.
For more information about the minimum flows established for the freshwater segment of the Alafia River and the Upper Myakka River, please contact Marty Kelly at (352) 796-7211, ext. 4235, or 1-800-423-1476, ext 4235.