Minimum Flows and Levels:
Lower Santa Fe and Ichetucknee Rivers
Ecohydrology
Fall 2013
MFLs
• Florida law requires establishment of MFLs for streams,
springs, lakes, rivers (FS Sec. 373.042)
(a) Minimum flows for all surface watercourses in the area. The minimum
flow for a given watercourse shall be the limit at which further
withdrawals would be significantly harmful to the water resources or
ecology of the area.
(b) Minimum water level. The minimum water level shall be the level of
groundwater in an aquifer and the level of surface water at which further
withdrawals would be significantly harmful to the water resources of the
area.
• Use of historical conditions, best available information
• Protection of non-consumptive uses
Water Resource Values
…consideration shall be given natural seasonal fluctuations in water flows or
levels, non-consumptive uses, and environmental values associated with
coastal, estuarine, aquatic, and wetlands ecology…
1. Recreation in and on the
water,
2. Fish and wildlife habitats
and the passage of fish,
3. Estuarine resources,
4. Detrital material transfer
5. Maintenance of freshwater storage and supply,
6. Aesthetic and scenic
attributes,
7. Filtration & absorption
of nutrients and other
pollutants,
8. Sediment loads,
9. Water quality, and
10. Navigation.
After MFL Determination
• Prevention strategy
– What will we do to avert
future significant harm
given the trajectory of
flows and levels over
time?
– Permitting
• Recovery strategy
– What do we do given
that the water body is
already in violation of
the MFL
– Permitting
The Basins
• Lower Santa Fe
– River Rise to Suwannee
River
• Ichetucknee
– Springs to Santa Fe
• Priority Springs
– SFR: Hornsby, Poe,
Columbia, Rum Island,
July, Treehouse, Devils Ear
– IR: Blue Hole, Ichetucknee
Head Spring
Outstanding Florida Waters
• The entire Santa Fe River system is an OFW
– “Worthy of special protection because of their natural
attributes” (FS 403.061)
– Anti-degradation clause (no change in ambient water
quality AFTER the date a water body is designated as an
OFW)
– A higher bar for protection than ordinary water bodies
Geologic Setting
• Variable confinement
• Upper Floridan Aquifer
flowpaths are critical
– Springs, seepage create river
baseflow in SFR, all flow in IR
• Hawthorn Group is the
dominant confining unit
UFA Recharge
• Recharge to the aquifer (and thus
river and springs) is highly variable,
and governed by confinement
• Hence, SRWMD divided the MFL
process between Upper and Lower
Santa Fe River
Logic of MFL Development
• Historical Flow Analysis
– What would flow have
been had there been no
pumping?
– Model analysis of flowrainfall relationships
pre-pumping
– Model extrapolation
(given rainfall) to recent
conditions
– Residuals from model
predictions during postpumping period
establish the flow
decline
– When does flow decline
result in significant
harm?
• Water Resource Values
– Establish as a policy that
significant harm = a 15%
decline in any WRV
• Habitat area
• Duration of flooding
• Indicence of fish
passage
• Degradation of quality
– MFL as a misnomer –
protect a flow regime
– Consider impacts of
declining flow on ALL
WRVs
Step 1: Historical Flow Analysis
(what would have been)
• Obtain flow records
– Data for SFR since 1935
– Data for IR since 1932
• Extract baseflows
– Analysis done only on
flows not controlled by
storm runoff
– 120-moving average
analysis (there is NO
right answer)
• Assess trends
• Obtain rainfall records
– Lake City since 1927
– Gainesville since 1904
– Major disagreement
since 1970
• Extract trends
– Climate variation
• Model baseflow as a
function of rainfall
Flows, Baseflows and Trends
The 1970 Divide
Rainfall Analysis
Predicting Baseflow From Rainfall
• Multiple linear
regression model
– Q = b + a1*R1 + a2*R2 + …
– Where slopes (ai) are
effects of total rainfall
(RI) in 24 prior months
– Q is mean monthly
baseflow
• Made for 1941-1970
• No ET, no storage
Model Performance:
- Bias (no trend in residuals)
- Normality
Predicting Baseflow (post 1970)
• Take the MLR model and use recent rainfall
• Assess residuals (trends in the disagreement
measured flow and model predictions)
What Would Flow Have Been?
• Take inferred linear trend in residuals and add that flow
to observed flow to estimate what flow would have been
A Change in Flow Regime
(Flow Duration Curves)
Ok…so we can estimate flow
declines. Are they significant?
Impacts to Water Resource Values
Assessing Water Resource Values
• Surveys of floodplain vegetation and soils
– Hydric soils, extent of wetland habitats, frequency
of inundation
• In-stream habitat assessments
– Fish (and human) passage and habitat suitability
– Benthic animals, SAV, woody habitats
– Endangered species (oval pigtoe mussel, manatee,
Ichetucknee silt snail, Suwannee bass)
• Water Quality
Recent and Long-Term Positional
Hydrograph (RALPH)
• Assess frequency of critical depth or flow exceedance
• Assess increased (or decreased) frequency with
changing flow…what flow decline yield Δfreq > 15%?
Different WRVs…Different RALPHs
Notable Omissions
• No water quality trends of note
• No role for endangered organisms in MFL
setting
• SAV denudation was not a factor (e.g., in
Ichetucknee in response to recreation)
Setting the MFL
• At each critical flow, plot allowed flow reduction
• Average across WRVs to set MFL (137 cfs for SFR,
23 cfs for IR)
Current Status
(Flow Decline – Actual vs. Allowed)
• Santa Fe River
– Flow declines to date are
estimated to be 186 cfs
– Flow declines allowed are
137 cfs
– SFR is in “recovery” by 51
cfs
• Ichetucknee River
– Flow declines to date are 16
cfs
– Flow declines allowed are
23 cfs
– IR is in “prevention” with 7
cfs of allowable reduction