Weeki Wachee River System Recommended Minimum Flows and ...

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In a hydrodynamic model study, one generally makes runs on grids with varying resolution to determine the impact of the grid on the accuracy of the solution. Apparently, this was not done, or at least not reported, in the present study. While the longitudinal resolution of the horizontal dimension is probably sufficient in the computational grid (Figure 4-1, ATM 2007), the Panel believes that the number of sigma layers should have been varied to understand the impact of using more than 4 layers on the model’s solution. Another potential issue with the numerical grid relates to what is commonly called the “sigma problem.” When applying a model using a sigma stretched grid to represent the vertical dimension in an estuary with a channel having shallow areas on the sides, false motions of streamflow can occur along with false horizontal diffusion. If the water column is stratified in the channel by fresher water overriding more saline water, the important stratification and resulting density currents can be eroded away during long term simulations. It is widely recognized among modelers that a substantial amount of lateral resolution in the horizontal dimension of the model’s grid is required to minimize this problem. As noted above, the EFDC model application to the WWRS is only three cells wide. Since only the last few kilometers of the river are estuarine, and since vertical stratification of salinity in the water column doesn’t appear to be large in most of the river, the “sigma problem” may be small yet still play a role in the salinity simulations. The agreement between computed and recorded temperatures at Station No. 02310551, 2.3 km (1.4 miles) above the river’s mouth, is generally fair (Figures 4.14a and 4.14b, ATM 2007). However, matching temperature in a model that does not have the hydrodynamics well calibrated is easier than matching salinity since surface heat exchange plays a big role in the temperature of the water body. Perhaps the study’s focus on estimating the temperature refuge area for Manatees is why a greater effort was not made to improve the simulation of circulation and salinity patterns in the WWRS. 20
Determining the Impact of Flow Reductions on the Thermal Regime In the application of the numerical model to determine the impact of flow reductions on the thermal regime, an analysis of the air temperature record at Weeki Wachee Spring was performed to select a critical condition period. The winter of 2000 – 2001 was identified as a critical condition period when the mean daily air temperatures ranged as low as 1.7 ºC (35.1 ºF). Since temperatures at Bayport were not available to drive the boundary condition, a regression equation was developed (r 2 = 0.90) which relates water temperature at Bayport to three-day average air temperatures as the independent variable. It is possible that testing different averaging intervals and including the day of the year as an independent variable might have yielded even better results. Two baseline conditions of high and low flows were simulated over the representative period from October 2004 to March 2005 when temperatures might become critical for Manatee health and survival. With each baseline condition, Weeki Wachee flows were reduced to determine the impact on the river’s thermal regime in terms of the volume and area of water with a three-day average temperature ≥ 20 ºC (≥ 68 ºF). Only those cells with a minimum depth greater than 3.8 ft (1.2 m) were considered adequate for the Manatee. As can be seen in Figure 6.1 of the ATM report, only a few of the cells in the numerical model actually met the 3.8 ft criterion at minimum tide. It was found that a 10% reduction in the high flow scenario reduced the volume by more than 15%; however, only a 5% reduction in the low flow scenario reduced the volume of the thermal refuge by more than 15%. Nevertheless, even when the 15% loss limit is violated, it appears that the WWRS can support far more manatees than have ever been observed to utilize the river’s thermal refuge. This outcome tends to negate, at least in part, the uncertainties the Panel found in the presented EDFC model application. Water Quality The District merged and integrated some 23 disparate datasets spanning the 1984 through 2005 period of record into one comprehensive database. As such, the District is to be commended for its effort to use the best available data. On the other hand, the District’s water quality data 21
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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
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Postel, S. and B.Richter. 2003. Riv
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Stanford, J.A., J.V.Ward, W.J. Liss
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Culter, J.K. 1986. Water Chemistry.
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CHAPTER 10 - APPENDICES 10.1 Append
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The wavelet used is the symmlets wa
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explains, the energy plot shows the
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0 if no significant withdrawal Z =
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One advantage of using this regress
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Technical Memorandum January 22, 20
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Lecanto 1 & 2 #S Well Site Descript
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Figure 4. HSPF subbasins in the INT
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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
Page 198 and 199: 6.0 Discharge:Precipitation (cfs/in
Page 200 and 201: Nevertheless, a major concern with
Page 202 and 203: system grid is not totally orthogon
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Page 208 and 209: (taxa) richness in the WWRS. If the
Page 210 and 211: Freshwater Habitats Approximately 1
Page 212 and 213: ERRATA and EDITORIAL COMMENTS Page
Page 214 and 215: Page Paragraph Line Comment 14 Some
Page 216 and 217: Page Paragraph Line Comment 21 The
Page 218 and 219: Page Paragraph Line Comment 26 The
Page 220 and 221: REFERENCES Alber, M. 2002. A Concep
Page 222 and 223: Richter, B. D., J. V. Baumgartner,
Page 224 and 225: the regression equation used to pre
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Page 228 and 229: The Southwest Florida Water Managem
Page 230 and 231: the model in terms of tides, salini
Page 232 and 233: Attachment 1 - Comparison of salini
Page 234 and 235: Figure 1. Predicted drawdown (feet)
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