Minimum Flows and Levels
What the Law Says About Minimum Flows and Levels (MFLs)
Florida law requires the water management districts to establish MFLs for surface waters and
aquifers within their jurisdiction (section 373.042(1), F.S.) The minimum flow for a surface
watercourse is defined as the "...limit at which further withdrawals would be significantly
harmful to the water resources or ecology of the area". The minimum water level of groundwater
in an aquifer and level of surface water in a watercourse is defined as the "limit at which
further withdrawals would be significantly harmful to the water resources of the area" (section
373.042(1), F.S.). The statute further directs water management districts to use the best available
information in establishing the MFL level. Each water management district must also consider, and at
its discretion may provide for, the protection of non-consumptive uses in the establishment of MFLs
(section 373.042, F.S.) In addition, a baseline condition for the protected resource functions must
be identified through consideration of changes and structural alterations in the hydrologic system (section
These MFLs are being developed pursuant to the requirements contained within the "Florida
Water Resources Act", and specifically, Sections 373.042 and 373.0421, F.S., as part of a
comprehensive water resources management approach geared towards assuring the sustainability of the
The proposed MFL's are not a "stand alone" resource protection tool, but should be
considered in conjunction with all other resource protection responsibilities granted to the water
management districts by law. This includes consumptive use permitting, water shortage management,
and water reservations. A model framework identifying the relationship between these tools is
discussed in this document and was used in developing the MFLs. In addition, the District has
completed Regional Water Supply Plans pursuant to Chapter 373.0361 F.S., which also include
recommendations for establishment of minimum flows and recovery and prevention strategies.
In Practicable Terms ...
However, establishing minimum flows and levels alone will not be sufficient to maintain a
sustainable resource or protect it from significant harm during the broad range of water conditions
occurring in the managed system. Setting a minimum flow is to be viewed as a starting point to
define water needs for sustainability. The necessary hydrologic regime for restoration of defined
priority water bodies includes the use of water reservations and other water resource protection
tools. Achieving the required water levels throughout these systems is an overall, long-term
Before MFLs are calculated, scientific determination of how changes to flows and levels influence
the preservation of water quality in a water body should be made to guard against having
catastrophic effects upon a local economy.
Difficult issues attend use of MFLs as a tool for water management.
Local Uses First. An additional Rule of Law is "local uses first",
meaning, that a region must first apply its naturally occurring water resource before it calls upon
resources from another district, or another district may apply to use that naturally occurring water
However, a danger is that MFLs for a given resource in times of plenty may lead to a proposition
to extract water "surplus" to the MFL, and move it into a man made facility, such as a
reservoir or pipework, for use to replenish supplies in times of shortage. This may appear to be a
good thing until another district applies to use the water from the reservoir as it is no longer
considered a "natural" resource.
In recent years this has become a serious issue in the region mainly due to propositions from the
Withlacoochee Regional Water Supply Authority (WRWSA) inspired by a consultant to the effect that
when watercourse or aquifer levels happen to be be above the set MFLs then pumping should be used to
allow water to be moved away from its native region to supply needs elsewhere. Moreover, this has
led to water management district staff engaged upon the task of setting MFLs to refer to such
surplus margin in terms of a proportion above a given MFL.
Furthermore, taking water from underground into a reservoir usually diminishes the resource by
allowing volumes to evaporate back into the atmosphere at high rates instead of conserving the
Stream Flow and Algae. Algae formations occur more readily in slower moving and
stagnant waters than in faster flowing streams.
To determine the stream velocity at which algae of any chosen pernicious species would likely be
inhibited, according to presence of given limiting nutrients, is not easy. Nevertheless, algae
formations degrade water quality and their inhibition should be reflected in MFL calculations.
Combination of Flows into a Watercourse. When a water body, such as a river
system, has many feed sources, any one or more of the feeds can have adverse impact upon that
Consider Crystal River/Kings Bay, for example. Thirty named springs and very many more unnamed
vents supply water to that system. A balance of clean fresh and salt water is required in suitable
quantities in estuarine areas for promotion of healthy sea grass meadows, which provide summer
habitat for the protected manatee population, and, in addition, support the nurture and diversity of
both recreational and commercial fish stocks. The sea grasses have become established in biomass
there over many decades according to the water mix. Adverse effects promoted by changes to the
balance of that mix degrade quality of the sea grass meadows. Such degradation remains in effect for
long periods of time. The dependent fishing and eco-tourism industries are vital to the region's
economic health. "Lose the grasses and the manatees go".
Moreover, the health of those meadows depend upon levels of nutrients conveyed to the river in
watershed and springshed (surface and underground) flows. The levels which actually reach the
estuary are governed by the mix of submersed aquatic and exotic plants which consume them on their
way to the estuary. These issues also should be reflected on the calculation of MFLs.
Salt/Fresh water interfaces. This is discussed on the page addressing
Saltwater Intrusion, under
the Education Section - Aquifers and Springs.
From the altruism, " Water is life; without water, we have nothing. Without water, we die.",
attributed to Parker, and the risk to which the freshwater lens system is exposed reported by Klein,
Causseaux and Fretwell, and the emphasis lent by Rick Copeland , et al, in FGS Bulletin 69, to the
correlation between progressive degradation of spring water quality over time with flow rate
reductions, it follows that the freshwater lens systems of the region should be a prime candidate
for conservation and protection under F.S. 373.042 (1)(b), and (2).
Since the resulting variation in saltiness has such profound effects upon local ecology provision
should be made for such measurements to be allowed for in calculating MFLs.
Effects of distant water sources. Waters emerging from the aquifer as spring
discharges often travel long distances over extended periods of time, through underground conduits
before emerging at the surface. Quality and stream velocity of the emerging waters may well be
influenced by events several miles away.
An example of this most probably affects the principal source of fresh water entering the Crystal
River/Kings Bay today. Moreover, discharges from several spring outlets may have their feed from the
same remote source. The collection of springs comprising Hunter, Catfish, Magnolia, Idiots Delight
and Three Sisters Springs, which have maintained fresh water characteristics while others have not,
is a case in point. These fresh water feeds are thought to come from supplies from Levy County by
way of the Rainbow River and Lake Rousseau.
Such phenomena of high potential impact need to be reflected in MFL calculations.
Click here to also see news item by Sam Lyons.