St. Johns River Water Management District. Al Canepa, MFL Development and Prevention and Recovery Strategies Initiative Leader

Transcription

1 Al Canepa, MFL Development and Prevention and Recovery Strategies Initiative Leader

2 Today s Discussion Points 1. Extreme water level changes are normal in some sandhill lakes 2. Changes primarily due to rainfall variability, not surface water or groundwater withdrawals 3. Minimum flows and levels (MFLs) protect from withdrawal impacts, not climate variation 4. MFLs protect throughout natural range of fluctuation

3 Today s Discussion Points 1. Extreme water level changes are normal in some sandhill lakes

4 What are Sandhill Lakes? Figure From U.S. Geological Survey Circular 1137

5 Sandhill Lakes Along Trail Ridge Camp Blanding Kingsley Lake Lowry Lake Keystone Heights Lake Brooklyn Lake Geneva

6 News Headline: North Florida Lakes Still Dry The level of Lake Brooklyn near Keystone Heights has dropped 17 feet in three years, stranding all boat docks and making the lake virtually unsafe for boaters. Sentinel, Sept. 30, 1957

7 Sentinel Photo, Sept. 1957

8 News Headline: Lot of Water Under Lake Brooklyn Bridge Now Florida Times-Union, Oct. 16, 1960

9

10 Water Levels Change Through Time What is recorded and how it is displayed

11 Water Levels Change Through Time

12 Water Levels Change Through Time

13 Water Levels Change Through Time

14 Water Levels Change Through Time

15 Water Levels Change Through Time This graph of changes in water level through time is called a HYDROGRAPH

16 Elev. In Feet Recorded Water Levels in Lake Brooklyn Lake Level Varies 30+ feet Year 80 Average Lowest Lake Bottom Elevation

17 Lake Level Fluctuations 30 feet vs. 5 feet

18 Why are these two lakes, within just a few miles of each other, so different?

19 How They Likely Formed Figure from U.S. Geological Survey Circular 1137

20 Lake Brooklyn Site A Sinkhole Collapse Feature Showing Breached Confining Unit Modified From SDII (1992)

21 Lake Brooklyn Site B Major Vertical Displacement of Confining Unit Modified From SDII (1992)

22 Kingsley Lake Schematic Modified from U.S. Geological Survey Circular 1137

23 Today s Discussion Points 2. Changes primarily due to rainfall variability, not withdrawals

24 Yearly Rainfall Difference From Average

25 inches Yearly Rainfall Surplus/Deficit (5-year moving average)

26 Compare 5-Year Average Rainfall Deficit with Brooklyn Lake Levels Brooklyn Hydrograph Rainfall 5-year Moving Average

27 U.S. Geological Survey Report Hydrology of Brooklyn Lake Near Keystone Heights, Florida (Clark, et.al., 1963) This unusually large recession was a result of deficient rainfall during more than a 3-year period, January 1954 to May 1957.

28 Pumping Versus Climate SJRWMD has examined: Double mass balance Pumps off model scenarios Early water level maps What does this mean on-the-ground?

29 Elev. In Feet Lake Brooklyn Hydrograph: Pumps On Versus Pumps Off Year Average Lowest Lake Bottom Elevation

30 Lake Brooklyn Water Level at 90 Feet Elevation

31 Today s Discussion Points 3. MFLs protect from withdrawal impacts, not climate variation 4. MFLs protect throughout natural range of fluctuation

32 What Are MFLs? Limit beyond which further withdrawals would be significantly harmful to the water resources or the ecology of the area Section (1), Florida Statues (F.S.)

33 Elevation (ft) St. Johns River Water Management District MFLs Protect Through Range of Fluctuation High Natural hydrologic regime Low Time (years)

34 Elevation (ft) St. Johns River Water Management District MFLs Protect Through Range of Fluctuation High Natural hydrologic regime Existing hydrologic regime Low Time (years)

35 Elevation (ft) St. Johns River Water Management District Time (years) MFLs Protect Through Range of Fluctuation High Low MFLs hydrologic regime (recovery needed)

36 Elevation (ft) St. Johns River Water Management District MFLs Protect Through Range of Fluctuation High Low Time (years) MFLs hydrologic regime (consumptive use available)

37 Water Resource Values Section , Florida Administrative Code Consider seasonal fluctuations, nonconsumptive uses and environmental values, 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 pollutants Sediment loads Water quality Navigation

38 In Summary 1. Extreme water level changes are normal in some sandhill lakes 2. Changes primarily due to rainfall variability, not withdrawals 3. Minimum flows and levels (MFLs) protect from withdrawal impacts, not climate variation 4. MFLs protect throughout natural range of fluctuation

39 Questions?

40 MFLs Method Point 2 Multiple MFLs required to protect aquatic and wetland systems. Maintaining essential characteristics of natural flooding and drying regime protects water resource structure and functions.

41 MFLs Method Point 3 MFLs represented as hydrologic statistics Magnitude (flow or water level) Duration (how long, days) Event Return Interval (how often event recurs, years)

42 MFLs Method Point 3 MFLs represented as hydrologic statistics Event MFLs Water Level (feet) Duration (days) Return Interval (years) Minimum frequent high Minimum average Minimum frequent low

43 MFLs Method Point 4 SJRWMD MFLs method primarily ecologically based Field data collection identifies important water resource features to be protected.