Weeki Wachee River System Recommended Minimum Flows and ...

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October 8,2008 Florida Fish and Wildlife Conservation Commission Commissioners Rodney Barreto Chair Miami Brian S. Yablonski Vice-Chair Tallahassee Kathy Barco lacksonville Ronald M. Bergeron Fort Lauderdale Richard A. Corbett Tampa Dwight Stephenson Delray Beach Kenneth W. Wright Winter Park Executive Staff Kenneth D. Haddad Executive Director Nick Wiley Assistant Executive Director Karen Ventimiglia Deputy Chief of Staff Office of Policy and Stakeholder Coordination Mary Ann Poole Director (850) 41S5272 (850) 922-5679 FAX Managing fish and wildlife resources for their longterm well-being and the benefit of people. 620 South Meridian Street Tallahassee. Florida 32399-1600 Voice: (850) 488-4676 Hearinuspeech impaired: (800) 955-8771 (T) (800) 955-8770 (V) MyFWC.com Martin Kelly, Ph.D. Southwest Florida Water Management District 2379 Broad Street Brooksville, FL 34604-6899 Re: Weeki Wachee River System recommended Minimum Flow and Level, Hernando County Dear Dr. Kelly: The MarineIEstuarine Subsection of the Florida Fish and Wildlife Conservation Commission's (FWC) Division of Habitat and Species Conservation has coordinated the agency review of the recornrnended Minimum Flows and Levels (MFL) for the Weeki Wachee River System. Provided below are FWC's comments and recommendations regarding this MFL. Project Description To protect Florida's water resources fiom "significant harm" the Florida Legislature directed the Florida Water Management Districts to establish MFLs for lakes, streams, and rivers (Chapter 373.042, Florida Statutes.). In compliance with this legislative directive the Southwest Florida Water Management District (SWFWMD) has drafted a recornrnended MFL for the Weeki Wachee River System. The Weeki Wachee River flows over 7 miles fiom its starting point at Weeki Wachee Spring. This river system has a 38-square-mile watershed and an approximate 260-square-mile springshed. The SWFWMD used the time frame of 1984 to 2004 to establish a baseline flow that averaged 162 cubic feet per second (cfs) for the Weeki Wachee River. Potentially Affected Resources Anthropogenic effects mainly in the form of groundwater withdrawals have resulted in an estimated 17 cfs decline in spring flow since 1961. The reduction of flow within both the watershed and springshed could affect spring, riverine, and estuarine habitats along with their associated diverse assemblage of fish and wildlife. The SWFWMD examined a variety of environmental indicators for their sensitivity to a reduction of flow levels. The resources considered included fish, invertebrates, mollusks, manatee warm-water habitat, benthic communities, submerged aquatic vegetation, and salinity regimes. Modeling evaluations of these resources did not indicate a break-point or resource collapse for any of these factors before reaching a 15% change in habitat availability, which is the SWFWMD's measure for significant harm that was based on Gore et al. (2002). The most restrictive outcome was found in the changes for the salinity regime of the lower river, which would have resulted in the MFL being based on a predicted shift in the 15 parts per thousand (ppt) isohaline; however, these results were deemed unreliable due to the influence of the Mud River and its highly saline flow. The flow from the Mud River
Martin Kelly, Ph.D. Page 2 October 8, 2008 has been sporadically measured and these measurements have indicated a highly variable flow of -5 1 to +I28 C~S. Due to these variable conditions, the 15-ppt isohaline was not selected as the determining factor for the MFL; rather the MFL is based on a mean percent flow reduction of all composite criteria used during a high-flow period and a low-flow period. The mean flow reduction of all the criteria used is recommended as being 10.1 % during low-flow scenarios and 10.7% during high-flow scenarios. The SWFWMD has noted that these reductions would take into account current flow reductions (about 9.5% reduction when compared to baseline period average to date) due to groundwater withdrawals, so remaining reduction capacity would be between 0.6 and 1.2% in flow. Comments and Recommendations Due to the proposed MFL, we expect a small reduction of existing manatee warm-water habitat in the Weeki Wachee River. Warm-water habitat is considered the limiting factor for the manatee population in Florida. This becomes considerably more relevant when projections into the future suggest that warm-water habitat created by the thermal discharges of coastal power plants will diminish, which could affect over half of the estimated manatee population that currently uses them. Warm-water habitat for manatees provided by natural spring systems is therefore critical to the recovery of this species into the future. Although a relatively small number of manatees currently use the Weeki Wachee River as a warm-water refuge, this can change rather quickly as history has shown at Volusia Blue Spring. Over the course of 38 years manatee use of Volusia Blue Spring increased over 1700% (n = 11 in 1970 to n = 202 in 2008). The FWC believes the SWFWMD's use of an average of 10 manatees using Weeki Wachee River as a warm-water site is an underestimate. The Weeki Wachee River has had few winter aerial surveys, which have been conducted under less than optimal visibility conditions due to the abundant vegetation overhanging the river along its margins. The all-time high count number of 34 manatees observed on February 13,2006, is an indication that many more manatees are familiar with, and use, this warm-water rehge; and manatees are documented as exhibiting a great degree of site fidelity in the use of warm-water rehges. Conclusion The SWFWMD's proposed minimum flow level set at a 10% reduction in historic flow would reduce manatee warm-water habitat fi-om the area and volume that was available within the Weeki Wachee River system historically. The FWC does not advocate a loss of warm-water habitat; however, the proposed 10% reduction in the baseline flow of the Weeki Wachee River system has already largely occurred and represents the current system. Summary The FWC compliments the SWFWMD on its thorough review of the data and potential impacts to the natural resources of this river system. After reviewing the information
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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
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animals can survive chronic exposur
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Figure 5-3 Number of Aerial Manatee
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Figure 5-5(a) Molluscan Presence /
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Table 5-11 Rank Order of Mollusc Ab
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Figure 5-5 Polymesoda caroliniana A
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Figure 6-1 Plankton Tow Flows Compa
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In application, a baseline area and
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6.1.4 Benthos Protection for benthi
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Figure 6-3. Location of the Three P
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7.2 Manatee Approach Establishing a
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Figure 7-2 Joint Probability of Occ
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Figure 7-3 Maximum Day Manatee Usag
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Figure 7- 6 Example Calculations fo
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Figure 7- 7 Estimation of Flow Redu
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Figure 7-8. Summary Results for the
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The reductions in flow that meet th
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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
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Page 180 and 181: United States Department of the Int
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
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Page 200 and 201: Nevertheless, a major concern with
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Page 220 and 221: REFERENCES Alber, M. 2002. A Concep
Page 222 and 223: Richter, B. D., J. V. Baumgartner,
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Attachment 1 - Comparison of salini
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Figure 1. Predicted drawdown (feet)
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