Chapter 1 Minimum Flows and Levels - Southwest Florida Water ...

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4.5 Low-Flow Threshold Protection of aquatic resources associated with low flows is an important component of minimum flows and levels implementation. To accomplish this goal, it is necessary to develop a low-flow threshold, which identifies flows that are to be protected in their entirety (i.e., flows that are not available for consumptive-use). To determine this threshold, two low-flow criteria are developed. One is based on the lowest wetted perimeter inflection point; the other is based on maintaining fish passage along the river corridor. The low-flow threshold is established at the higher of the two low-flow criteria, provided that comparison of that criterion with historic flow records indicates that the criterion is reasonable. Although flows less than the low-flow threshold may be expected to occur throughout the year, they are most likely to occur during Block 1. 4.5.1 Wetted Perimeter Output from multiple runs of the HEC-RAS model was used to generate a wetted perimeter versus flow plot for each HEC-RAS cross-section of the Braden River corridor (see Figure 4-7 for an example and Appendix WP for all plots). Plots were visually examined for inflection points, which identify flow ranges that are associated with relatively large changes in wetted perimeter. The lowest wetted perimeter inflection point for flows up to 25 cfs was identified for each crosssection. Inflection points for flows higher than 25 cfs were disregarded since the goal was to identify the lowest wetted perimeter infection point for flows contained within the stream channel. Many cross-section plots displayed no apparent inflection points between the lowest modeled flow and 25 cfs. These cross-sections were located in pool areas, where the water surface elevation may exceed the lowest wetted perimeter inflection point even during low flow periods. For these cross-sections, the lowest wetted perimeter inflection point was established at the lowest modeled flow. The lowest wetted perimeter inflection point flows at each HEC-RAS cross-section were used to develop a wetted perimeter criterion for the Braden River near Lorraine gage site. 4-17
Wetted Perimeter - Sta. 44.9 25 20 Flow (cfs) 15 10 5 0 4.1 cfs 0 20 40 60 80 100 Wetted Perimeter (feet) Figure 4-7. Wetted perimeter versus discharge at HEC-RAS transect number 44.9 in the Braden River. Wetted perimeter values for modeled flows up to 25 cfs are shown and the lowest wetted perimeter inflection point for this cross-section is identified. 4.5.2 Fish Passage For development of minimum flows, it is desirable to maintain longitudinal connectivity along a river corridor, to the extent that this connectivity has historically occurred. To secure the benefits associated with connectivity and sustained low flows, a 0.6-ft fish-passage criterion was used to develop a low flow standard for the Braden River. The fish-passage criterion has been used by the District for development of proposed minimum flows and levels for the upper Peace (SWFWMD 2002), Alafia (Kelly et al. 2005a), middle Peace (Kelly et al. 2005b) and Myakka (Kelly et. al. 2005c) rivers and was found to be acceptable by the panel that reviewed the proposed upper Peace River flows (Gore et al. 2002). Further, Shaw et al. (2005) also found that “the 0.6-ft standard represents best available information and is reasonable”. Flows necessary for fish-passage at each HEC-RAS cross-section were identified using output from multiple runs of the HEC-RAS model. The flows were determined by adding the 0.6-ft depth fish-passage criterion to the elevation of the lowest spot in the channel cross-section and determining the flow necessary to achieve the resultant elevations. At many cross-sections, the minimum channel elevation plus 0.6-ft resulted in a water surface elevation lower than the elevation associated with the lowest modeled flow. These crosssections were located in pool or run areas, where fish passage could occur during periods of little or no flow. For these sites, the flow requirement for fish passage was established at the lowest modeled flow. 4-18
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Proposed Minimum Flows and Levels f
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Table of Contents TABLE OF CONTENTS
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5.5 PRESCRIBED FLOW REDUCTION FOR B
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Figure 2-19. Potassium concentratio
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Figure 5-13. Median daily flow at t
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mean feature elevations are listed
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For the high flow season of the yea
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Acknowledgements The authors would
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fluctuations in water flows or leve
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Common to this list and the flow re
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Fundamental to the approach used fo
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300 250 Block 1 Block 3 Block 2 Flo
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are outlined in Chapter 4. In Chapt
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as the freshwater segment upstream
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attributed to analytic precision di
Page 31 and 32: Figure 2-4. 1999 land use/cover map
Page 33 and 34: Table 2-2. Land use/cover and land
Page 35 and 36: Figure 2-8. 1999 Land use/cover map
Page 37 and 38: Figure 2-10. 1972 Land use/cover ma
Page 39 and 40: Smith and Stopp (1978) note that "i
Page 41 and 42: 2.4.2.1 Multidecadal Periods of Hig
Page 43 and 44: 2.4.3.2 Step Trend in River Flows K
Page 45 and 46: Table 2-4. Results of Kendall's tau
Page 47 and 48: 2.4.4 Benchmark Periods Climate-bas
Page 49 and 50: Oscillation were examined. On a sea
Page 51 and 52: Water Chemistry 2.4.6 Water Quality
Page 53 and 54: Braden River near Lorraine, FL 0.6
Page 55 and 56: Peace River at Arcadia, FL 10 Potas
Page 57 and 58: Table 2-8. Summary statistics for B
Page 59 and 60: 3.2 Resources and Area of Concern T
Page 61 and 62: habitat, the greater area of stream
Page 63 and 64: levels such as fish have been shown
Page 65 and 66: Figure 3-1. Example of low flow in
Page 67 and 68: USGS Braden River near Lorraine gag
Page 69 and 70: instream cross-sections were sample
Page 71 and 72: Figure 4-2. Upstream vegetation cro
Page 73 and 74: supports water surface profile calc
Page 75 and 76: The HEC-RAS model was run using 21
Page 77 and 78: Adult Spotted Sunfish Adults - Brad
Page 79 and 80: species of interest. For example cu
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Page 87 and 88: Chapter 5 Results and Recommended M
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Page 93 and 94: Floodplain profiles and vegetation
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Page 97 and 98: Table 5-3. Mean (±SD) flows at the
Page 99 and 100: Elevaton (NGVD) 27.0 22.0 17.0 12.0
Page 101 and 102: Table 5-7. Median elevations, in fe
Page 103 and 104: 80 70 60 Flow reduction (%) 50 40 3
Page 105 and 106: Table 5-8. Recommended percent flow
Page 107 and 108: 100 90 80 % DOMINANCE 70 60 50 40 3
Page 109 and 110: Table 5-9. Mean elevation of instre
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Page 113 and 114: Table 5-10. Proposed Minimum Flows
Page 115 and 116: Division Information and Technology
Page 117 and 118: Hupalo, R., C. Neubauer, L. Keenan,
Page 119 and 120: communities in the corridors of the
Page 121 and 122: Wharton, C.H., W.M. Kitchens, E.C.
Page 123 and 124: Confined Aquifer - A term used to d
Page 125 and 126: Instream Habitats - A specific type
Page 127 and 128: Riffle - A relatively shallow reach
Page 129 and 130: Chapter 8 Appendix A A Review of
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2007). In addition, the approach us
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with limited biological knowledge o
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the other factors listed above or w
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have now been developed and adopted
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An example of the primary output fr
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prevent negative effects associated
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methods, such as LiDAR, to improve
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habitat reduction criterion and the
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Summary, Special Publication SJ2002
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Errata / comments by page number in
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4-20 Section 4.7.1, 1 st paragraph,
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Chapter 9 Appendix B - Staff Respon
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2) The panel notes that the period
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4) One aspect of Chapter 2 should b
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Preventing Significant Harm - 15% C
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they aren't getting enough particul
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Habitat Criteria and Characterizati
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Compliance Standards and Proposed M
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Glossary of Terms 13) When an inter
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