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Water supply

Minimum flows and levels (MFLs)

Frequently asked questions

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.

The St. Johns River Water Management District updates its MFLs priority list annually. The priority list is based on the importance of the waters to the state or region and the existence of or potential for significant harm caused by withdrawals to water resources or ecology. It includes waters that are experiencing or may be expected to experience adverse impacts because of existing or future water withdrawals.

Why are MFLs important?

The MFLs program provides technical support to the district’s regional water supply planning process (section 373.709, 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.

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.

MFLs do not “drought-proof” a system or mitigate the impacts of climate change.

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 Register. 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. In order for an applicant to obtain a consumptive use permit, the consumptive use must be in accordance with the MFL and any approved prevention and recovery strategies.

What triggers a reevaluation?

MFLs reevaluation is an ongoing process. The district intends to reevaluate most MFLs at some point in order to apply new data and techniques that have been developed since the original MFL was set. The criteria used for setting MFLs for different types of lakes has evolved as the district’s understanding of the hydrologic characteristics of different types of lakes has improved. Current models are more sophisticated, and analytical tools and data continue to improve.

If methodologies have changed or if the adopted MFLs are based on outdated criteria and indicators, staff will determine when a reevaluation is necessary and prioritize as needed.

What are prevention and recovery strategies?

Prevention and recovery strategies are developed and implemented to ensure that MFLs will not be violated by future water withdrawals (prevention), or will be recovered to meet their MFLs (recovery) if a violation caused by withdrawals has already occurred.

Prevention and recovery strategies call for water withdrawals to be maintained at or below sustainable limits, or for impacts from water withdrawals to be mitigated through water supply development projects — such as reclaimed water, aquifer recharge and water supply projects — and conservation and regulatory measures. These strategies are designed to ensure that fundamental characteristics of a water body are maintained over time, to achieve equity among water users, to provide users with greater certainty regarding allocations, and to ensure that MFLs are met.

When a water body’s water levels fall below the MFLs, is it a violation of MFLs?

Not necessarily. It is expected that water stages will vary above, among and below the elevation components of MFLs. Importantly, MFLs have a water level component, a duration component at that level, and a return interval component for the defined event (i.e., defined by the stage and duration components). An MFL is in violation if it is too low, for too long, too often, or does not get high enough for long enough, often enough. That is, MFLs compliance is a factor of long-term hydrologic statistics, not a point-in-time water level.


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St. Johns River Water Management District
4049 Reid Street, Palatka, FL 32177
(800) 725-5922