In this section
Clay-Putnam prevention/recovery strategy development process
A stakeholder process to develop long-term comprehensive strategies to achieve MFLs.
Waters in Florida lakes naturally rise and fall over time. Learn why.
Review the multi-year list of water bodies targeted by the District for development of MFLs.
Learn about the history and development of this special District MFLs rule.
An overview of minimum flows and levels
One way the St. Johns River Water Management District is working to protect and conserve Florida’s water resources is through the minimum flows and levels (MFLs) program. Establishing MFLs is an important step in the District’s work of planning for adequate water supplies for today and for future generations while also protecting water resources from significant harm. The District is setting MFLs for lakes, streams, rivers, wetlands, springs and aquifers.
What are MFLs?
MFLs are the minimum water flows and/or levels adopted by the District Governing Board as necessary to prevent significant harm to the water resources or ecology of an area resulting from permitted water withdrawals. MFLs define how often and for how long high, intermediate and low water flows and/or levels should occur to prevent significant harm. Two to five MFLs are typically defined for each system. The names of the MFLs are minimum infrequent high, minimum frequent high, minimum average, minimum frequent low and minimum infrequent low (see Figure 1).
Figure 2 represents two hydrographs depicting the fluctuation of high and low water levels or flow in a typical stream or lake over a long time period. The upper line represents the existing hydrologic conditions and the lower line represents the hydrologic conditions defined by the MFLs. The hydrologic conditions defined by the MFLs are similar to, but are usually lower than, the existing hydrologic conditions.
These two hydrographs can be summarized as the percentage of time each water level or flow is equaled or exceeded; this is called a water level or flow duration curve (Figure 3). The area below the MFLs curve (salmon-colored shaded area in Figure 3) represents the water reserved for protection of fish and wildlife or public health and safety. When use of water resources shifts the water levels below that defined by the MFLs, significant ecological harm is expected to occur.
The distance between the two curves (light blue shaded area in Figure 3) represents the water available for use that will not result in harm to the water resources.
Why set MFLs?
MFLs are established to define sustainable water use while protecting the water resources from significant harm caused by permitted water withdrawals. Establishing MFLs is a requirement of the state Legislature under Subsection 373.042(2), Florida Statutes (F.S.). In addition, establishing MFLs is required by the state Comprehensive Plan, the water resources implementation rule (formerly state water policy), and a 1996 governor’s executive order for priority water bodies.
Why are MFLs important?
The MFLs program provides technical support to the District’s regional water supply planning process (section 373.0361, F.S.), and permitting criteria for the consumptive use permitting program (Chapter 40C-2, Florida Administrative Code [F.A.C.]) and the environmental resource permitting program. MFLs identify a range of water flows and/or levels above which water might be permitted for consumptive use.
In addition, MFLs protect nonconsumptive uses of water, including recreation in and on the water, fish and wildlife habitats and the passage of fish, estuarine resources, transfer of detrital material, maintenance of freshwater storage and supply, aesthetic and scenic attributes, filtration and absorption of nutrients and other pollutants, sediment loads, water quality, and navigation.
How are MFLs determined?
Florida law states that the District’s Governing Board “shall use the best information and methods available to establish limits which prevent significant harm to the water resources or ecology.” District MFLs are typically determined based on evaluations of topography, soils and vegetation data collected within plant communities and other pertinent information associated with the water resource.
MFLs take into account the ability of wetlands and aquatic communities to adjust to changes in hydrologic conditions. MFLs allow for an acceptable level of hydrologic change to occur. When use of water resources shifts the hydrologic conditions below levels defined by MFLs, significant ecological harm can occur.
How are MFLs adopted?
MFLs are adopted as rules (Chapter 40C-8, F.A.C.) by the governing boards of the water management districts. Rule adoption involves public workshops, review by the Florida Department of Environmental Protection, and publication in the Florida Administrative Weekly. MFLs are to be reviewed periodically and revised as necessary under Florida law (Subsection 373.0421(3), F.S.).
How are MFLs applied?
MFLs apply to decisions affecting permit applications, declarations of water shortages and assessments of water supply sources. Computer water budget models for surface waters and groundwater are used to evaluate the effects of existing and/or proposed consumptive uses and the likelihood they might cause significant harm. The District’s Governing Board is required to develop recovery or prevention strategies in those cases where a water body or watercourse currently does not or is anticipated to not meet an established MFL. Water uses cannot be permitted that cause any MFL to be violated.
To learn more
If you would like additional information on MFLs, please contact Dr. G.B. (Sonny) Hall, Bureau of Water Supply, at (386) 329‑4368 or email@example.com.