Weeki Wachee River System Recommended Minimum Flows and ...

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Technical Memorandum January 22, 2008 Appendix 2-2 TO: THROUGH: FROM: Mike Heyl, Chief Environmental Scientist, Ecological Evaluation Section Marty Kelly, Ph. D., Manager, Ecological Evaluation Section Mark Barcelo, P.E., Manager, Hydrologic Evaluation Section Ron Basso, P.G., Senior Professional Geologist, Hydrologic Evaluation Section Subject: Predicted groundwater withdrawal impacts to Weeki Wachee Spring based on numerical model results 1.0 Introduction Weeki Wachee Spring, located at the headwaters of the Weeki Wachee River, lies just southwest of the junction of U.S. Highway 19 and State Highway 50 (Figure 1). The river extends westward 7.5 miles from the main spring vent through predominantly lowlands (coastal swamps and marshes) to the Gulf of Mexico. There are nine springs associated with or in proximity to the Weeki Wachee system (SWFWMD, 2001). With the exception of first magnitude Weeki Wachee Spring main vent, most of the springs in the Weeki Wachee area have very limited flow and water quality data. Mean annual discharge for the Weeki Wachee main spring averaged 173 cubic feet per second (cfs) or 112 million gallons per day (mgd) for the period 1931-2006. Weeki Wachee Spring discharges from the bottom of a conical depression with gentle side slopes. The spring pool measures 165 ft (50.3 m) east to west and 210 ft (64 m) north to south. Spring depth is 45 ft (13.7 m) over the vent in the center of the pool (Florida Geological Survey, 2001). Bare limestone is located near the vent, but none is exposed around the pool edges. The water is clear and light greenish blue, and a boil is visible in the center of the pool. Thick, filamentous algae cover the majority of the spring bottom, and there are some native aquatic grasses in the spring pool. The spring is rich with fresh and salt water fishes and aquatic turtles. Prior to establishment of a Minimum Flow (MF), an evaluation of hydrologic changes in the vicinity of the spring is necessary to determine if the water body has been significantly impacted by existing groundwater withdrawals. The establishment of the MF for Weeki Wachee Spring is not part of this report. This memorandum describes the hydrogeologic setting near the spring and provides the results of several numerical model simulations of predicted spring flow change due to existing groundwater withdrawals. 2.0 Hydrogeologic Conditions In most of Tampa Bay Water's central system wellfield area, a distinct, surficial sand aquifer overlies the semi-confined Upper Floridan aquifer. However, a rather sharp transition to a regionally unconfined Upper Floridan aquifer occurs along a line from northwest Pasco County through the northern part of Cross Bar wellfield to the Brooksville Ridge physiographic region ____________________________________________________________________________________________ Proposed Minimum Flows and Levels for Weeki Wachee River Page 133 of 164 Appendices
Figure 1. Location of Weeki Wachee Spring. (Figure 2). North of this boundary, the Upper Floridan Aquifer (UFA) is primarily unconfined except beneath the clay-rich, low infiltration soils of the Brooksville Ridge. Where the UFA is unconfined is a highly karst-dominated region. Dissolution of limestone is an active process via infiltration of rainwater because the limestone units of the UFA are close to land surface and poorly confined. Numerous sinkholes, internal drainage, and undulating topography that are typical of karst geology dominate the landscape. These active karst processes lead to enhanced permeabilities within the Floridan aquifer. Reported transmissivity values of the Upper Floridan aquifer based on three aquifer performance tests in western Hernando County range from 200,000 to 1,200,000 ft 2 /day (SWFWMD 1999). Three first-magnitude springs (> 100 cfs discharge), the Crystal River group, Homosassa, and Weeki Wachee are found within this region. In addition, the highest recharge rates to the UFA occur in west-central Hernando and Citrus Counties with values ranging between 15 and 22 inches per year (Ross and others, 2001). 3.0 Numerical Model Results A number of regional groundwater flow models have included the Weeki Wachee Spring area. Ryder (1982) simulated the entire extent of the Southwest Florida Water Management District. In 1993, the District completed the Northern Tampa Bay groundwater flow model that covered a 2,000 square mile area of Hillsborough, Pinellas, Pasco, and Hernando Counties. In 2002, the USGS simulated the entire Florida peninsula in their Mega Model of regional groundwater flow (Sepulveda, 2002). The most advanced simulation of the Weeki Wachee Spring region and ____________________________________________________________________________________________ Proposed Minimum Flows and Levels for Weeki Wachee River Page 134 of 164 Appendices
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Weeki Wachee River System Recommend
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Conversion Table Metric to U.S. Cus
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5.2 FISH ..........................
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Figure 3-2 Location of Bathymetric
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LIST OF TABLES Table 1-1 Rule-of-Th
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Table 8-1 Summary of Weeki Wachee M
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Executive Summary Minimum Flows and
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CHAPTER 1 - PURPOSE & BACKGROUND OF
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1) flood flows that determine the b
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the area." What constitutes "signif
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Table 1-1 Rule-of-Thumb Estimates f
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this report identifies specific res
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1.6 Content of Remaining Chapters I
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CHAPTER 2 - WATERSHED CHARACTERISTI
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# # # circular vent 1.8 meters in d
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Figure 2-5 1970s Aerial with 1999 U
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is a variation of the Seminole word
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Figure 2-6 Hurricane Tracks near Ba
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varied by period. The variation was
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2.3.2 Baseline Period Figure 2-10 i
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found (ktau p=0.06) between total g
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similarly across the springsheds ex
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Figure 2-15 Wavelet Filtered Discha
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Figure 2-16 INTB Groundwater Model
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2.6 Seasonal Blocks As described in
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Table 2-6 Median (cfs) Flow by Bloc
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# # # Surface waters in this stretc
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3.1.3 Segmentation Segmentation was
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Figure 3-5 Dominant SAV and Median
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Figure 3-6 Sediment Characteristics
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Figure 3-7 Shoreline / Buffer Veget
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CHAPTER 4 - TIDE, SALINITY & WATER
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Two additional harmonic pairs were
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Figure 4-5. Median Bottom Salinity
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Figure 4-7 Salinity Range (1984-200
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uncovering in response to strong wi
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E) Salinity = β o + β 1 *Flow 2 +
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Additional exploratory attempts usi
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86 = 186 cfs, SWFWMD 1994-96 = 167
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A regression of the form below was
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Table 4-8 Median Water Quality of W
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Figure 4-10 Nitrate Concentration a
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CHAPTER 5 - BIOLOGICAL CHARACTERIST
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Figure 5-1 Principal Component Anal
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measured volume sampled which was t
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5.2.2 Relation to inflow Response t
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Table 5-7 Location Response (km u )
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Table 5-9 Abundance Response to Inf
Page 98 and 99: animals can survive chronic exposur
Page 100 and 101: Figure 5-3 Number of Aerial Manatee
Page 102 and 103: Figure 5-5(a) Molluscan Presence /
Page 104 and 105: Table 5-11 Rank Order of Mollusc Ab
Page 106 and 107: Figure 5-5 Polymesoda caroliniana A
Page 108 and 109: Figure 6-1 Plankton Tow Flows Compa
Page 110 and 111: In application, a baseline area and
Page 112 and 113: 6.1.4 Benthos Protection for benthi
Page 114 and 115: Figure 6-3. Location of the Three P
Page 116 and 117: 7.2 Manatee Approach Establishing a
Page 118 and 119: Figure 7-2 Joint Probability of Occ
Page 120 and 121: Figure 7-3 Maximum Day Manatee Usag
Page 122 and 123: Figure 7- 6 Example Calculations fo
Page 124 and 125: Figure 7- 7 Estimation of Flow Redu
Page 126 and 127: Figure 7-8. Summary Results for the
Page 128 and 129: The reductions in flow that meet th
Page 130 and 131: probably accounts in part for the d
Page 132 and 133: Postel, S. and B.Richter. 2003. Riv
Page 134 and 135: Stanford, J.A., J.V.Ward, W.J. Liss
Page 136 and 137: Culter, J.K. 1986. Water Chemistry.
Page 138 and 139: CHAPTER 10 - APPENDICES 10.1 Append
Page 140 and 141: The wavelet used is the symmlets wa
Page 142 and 143: explains, the energy plot shows the
Page 144 and 145: 0 if no significant withdrawal Z =
Page 146 and 147: One advantage of using this regress
Page 150 and 151: Lecanto 1 & 2 #S Well Site Descript
Page 152 and 153: Figure 4. HSPF subbasins in the INT
Page 154 and 155: Most of the limestone mines located
Page 156 and 157: 3.1.3 Septic Tank Recharge in the S
Page 158 and 159: Figure 10. Groundwater grid in the
Page 160 and 161: Basso, R.J., 2004, Hydrogeologic Se
Page 162 and 163: 10.2 Appendices - Chapter 3 Appendi
Page 164 and 165: 10.3 Appendices - Chapter 4 Appendi
Page 166 and 167: Appendix 4-2 Data Sources Water qua
Page 168 and 169: Appendix 4-3 Water Quality Trend Gr
Page 170 and 171: Water Quality Trend Graphics, conti
Page 180 and 181: United States Department of the Int
Page 182 and 183: October 8,2008 Florida Fish and Wil
Page 184 and 185: Martin Kelly, Ph.D. Page 3 October
Page 186 and 187: Scientific Peer Review of the Propo
Page 188 and 189: Determining a low flow need during
Page 190 and 191: Current state water policy, as expr
Page 192 and 193: Spring, Twin Dees Spring and possib
Page 194 and 195: under varying flow regimes. The fir
Page 196 and 197: Weeki Wachee Rainfall, Springflow a
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6.0 Discharge:Precipitation (cfs/in
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Nevertheless, a major concern with
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system grid is not totally orthogon
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In a hydrodynamic model study, one
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analysis was rather cursory. The Di
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(taxa) richness in the WWRS. If the
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Freshwater Habitats Approximately 1
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ERRATA and EDITORIAL COMMENTS Page
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Page Paragraph Line Comment 14 Some
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Page Paragraph Line Comment 21 The
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Page Paragraph Line Comment 26 The
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REFERENCES Alber, M. 2002. A Concep
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Richter, B. D., J. V. Baumgartner,
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the regression equation used to pre
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and the three independent approache
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The Southwest Florida Water Managem
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the model in terms of tides, salini
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Attachment 1 - Comparison of salini
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Figure 1. Predicted drawdown (feet)
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