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

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periods of high flow (Block 3) and may also be inundated by flows occurring during Block 1 in some years. The percent-of-flow reductions derived for Block 2 flows at the gage site were considered to be limiting factors and evaluated for development of prescribed flow reductions for Block 2 for the Braden River near Lorraine gage site when flows exceed the low-flow threshold. 4.8 Prescribed Flow Reduction for Block 3 Junk et al. (1989) note that the “driving force responsible for the existence, productivity, and interactions of the major river-floodplain systems is the flood pulse”. Floodplain vegetation development and persistence does not, however, necessarily depend wholly on inundation from the river channel. Groundwater seepage, hyporheic inputs, discharge from local tributaries, and precipitation can also lead to floodplain inundation (Mertes 1997). However, because river channel-floodplain connections are important, can be influenced by water use, and may be a function of out-of-bank flows, it is valuable to characterize this connectivity for development of minimum flows and levels. Highest flows, including out-of-bank flows, are most likely to occur during Block 3, which for the Braden River extends from June 20 to October 24. Minimum flows developed for this period are intended to protect ecological resources and values associated with the floodplain by maintaining hydrologic connections between the river channel and the floodplain and maintaining the natural variability of the flow regime. This goal is accomplished through HEC-RAS modeling and use of long-term inundation analyses to evaluate floodplain feature inundation patterns associated with channel-floodplain connectivity. Based on these analyses, a prescribed flow reduction for Block 3 can be developed. 4.8.1 Floodplain Connection Analyses – Application for Block 3 HEC-RAS model output and long-term inundation analyses were used to evaluate floodplain inundation patterns associated with river flows at the 15 floodplain vegetation cross-sections and associated flows at the Braden River near Lorraine gage site. Inundation of elevations associated with floodplain features, including vegetation classes and soils, was evaluated to establish percent-of-flow reductions that would result in no more than a 15% reduction in the number of days of inundation during Block 3, based on flows during two benchmark periods (1989 through 1993 and from 1994 through 2005). The percent-of-flow reductions were considered to be limiting factors and used for development of prescribed flow reductions for the Braden River near Lorraine gage site during Block 3. 4-21
Chapter 5 Results and Recommended Minimum Flows 5.1 Overview Results from modeling and field investigations on the Braden River were assessed to develop minimum flow criteria/standards for ensuring that ecological functions associated with various flows and levels are protected from significant harm. A low-flow threshold based on historic flows is recommended for the USGS Braden River near Lorraine FL gage site, along with prescribed flow reductions for Blocks 1, 2, and 3. Based on the low-flow threshold and prescribed flow reductions, short-term and long-term compliance standards are identified for establishing minimum flows and levels for the upper Braden River. 5.2 Low-Flow Threshold The low-flow threshold defines flows that are to be protected throughout the year. The low-flow threshold is established at the higher of two flow criteria, which are based on maintaining fish passage and maximizing wetted perimeter for the least amount of flow in the river channel. The low flow must also be historically appropriate. For the upper Braden River, the low-flow threshold was developed for the USGS Braden River near Lorraine gage site. 5.2.1 Fish Passage Criteria Flows necessary to reach a maximum water depth of 0.6 foot to allow for fish passage at each cross-section in the HEC-RAS model of the Braden River between the USGS Braden River at Linger Lodge and Braden River at Lorraine gage sites are shown in Figure 5-1. At most cross-sections, the minimum water surface elevation that would allow for fish passage was lower than the elevation associated with the lowest modeled flow. These cross-sections were located in pool or run areas, where fish passage would be possible during low-flow periods. Inspection of the data indicated that flows equal to or greater than 7.4 cfs at the Braden River near Lorraine gage would be sufficient for fish passage at all sampled sites. The fish passage criterion for the Braden River was, therefore, established at 7.4 cfs. 5-1
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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
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Figure 2-4. 1999 land use/cover map
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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
Page 81 and 82: 4.4 Seasonal Flow and Development o
Page 83 and 84: Wetted Perimeter - Sta. 44.9 25 20
Page 85: factors, the most conservative of w
Page 89 and 90: Wetted Perimeter Requirements Flow
Page 91 and 92: 40 35 30 25 20 15 10 5 0 May June M
Page 93 and 94: Floodplain profiles and vegetation
Page 95 and 96: mean elevation of the Oak/popash ve
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
Page 111 and 112: The second standard was developed t
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
Page 131 and 132: steps to reduce the uncertainty and
Page 133 and 134: 2007). In addition, the approach us
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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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