Minimum Flows and Levels: Lower Santa Fe and Ichetucknee Rivers

1. Minimum Flows and Levels:Lower Santa Fe and Ichetucknee Rivers Ecohydrology Fall 2013

2. 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

3. 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 fresh-water 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.

4. 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

5. 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

6. 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

7. 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

8. 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

9. Logic of MFL Development • Historical Flow Analysis • What would flow have been had there been no pumping? • Model analysis of flow-rainfall relationships pre-pumping • Model extrapolation (given rainfall) to recent conditions • Residuals from model predictions during post-pumping 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% declinein 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

10. 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

11. Flows, Baseflows and Trends

12. The 1970 Divide

13. Rainfall Analysis

14. 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

15. Predicting Baseflow (post 1970) • Take the MLR model and use recent rainfall • Assess residuals (trends in the disagreement measured flow and model predictions)

16. 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

17. A Change in Flow Regime(Flow Duration Curves)

18. Ok…so we can estimate flow declines. Are they significant? Impacts to Water Resource Values

19. 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

20. 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%?

21. Different WRVs…Different RALPHs

22. 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)

23. 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)

24. 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