Proposed Minimum Flows and Levels for the Upper Segment of the Myakka River, from Myakka City to SR 72 Proposed Minimum Flows and Levels for the Upper Segment of the Myakka River, from Myakka City to SR 72 November 2005 Ecologic Evaluation Section Resource Conservation and Development Department Southwest Florida Water Management District Brooksville, Florida 34604-6899 Marty Kelly Adam Munson Jonathan Morales Doug Leeper The Southwest Florida Water Management District (District) does not discriminate upon the basis of any individual’s disability status. This non- discriminatory policy involves every aspect of the District’s functions, including one’s access to, participation, employment, or treatment in its programs or activities. Anyone requiring accommodation as provided for in the American with Disabilities Act should contact (352) 796-7211 or 1-800-423-1476, extension 4215; TDD ONLY 1-800-231-6103; FAX (352) 754-6749. 2 Table of Contents TABLE OF CONTENTS.................................................................................................................................I TABLE OF FIGURES.................................................................................................................................. IV LIST OF TABLES...................................................................................................................................... VIII EXECUTIVE SUMMARY.............................................................................................................................. X ACKNOWLEDGEMENT ........................................................................................................................... XIII CHAPTER 1 MINIMUM FLOWS AND LEVELS ....................................................................................... 1-1 1.1 OVERVIEW AND LEGISLATIVE DIRECTION ......................................................1-1 1.2 HISTORICAL PERSPECTIVE...........................................................................1-2 1.3 THE FLOW REGIME .....................................................................................1-2 1.4 ECOSYSTEM INTEGRITY AND SIGNIFICANT HARM ...........................................1-4 1.5 SUMMARY OF THE SWFWMD APPROACH FOR DEVELOPING MINIMUM FLOWS 1-4 1.5.1 A Building Block Approach.................................................................1-6 1.6 FLOWS AND LEVELS ....................................................................................1-8 1.7 CONTENT OF REMAINING CHAPTERS ............................................................1-9 CHAPTER 2 BASIN DESCRIPTION WITH EMPHASIS ON LAND USE, HYDROLOGY AND WATER QUALITY..................................................................................................................................... 2-1 2.1 OVERVIEW .................................................................................................2-1 2.2 WATERSHED DESCRIPTION (MATERIAL IN THIS SECTION WAS TAKEN LARGELY FROM MYAKKA RIVER COMPREHENSIVE WATERSHED MANAGEMENT PLAN, SWFWMD 2004) ............................................................................................2-1 2.2.1 Geographic Location..........................................................................2-1 2.2.2 Climate...............................................................................................2-3 2.2.3 Physiography .....................................................................................2-3 2.2.4 Hydrogeology.....................................................................................2-4 2.3 LAND USE CHANGES IN THE MYAKKA RIVER WATERSHED ..............................2-5 2.3.1 Myakka River Watershed...................................................................2-5 2.3.2 Flatford Swamp Sub-Basin ..............................................................2-11 2.3.3 Owen Creek Sub-Basin ...................................................................2-15 2.3.4 Tatum Sawgrass Sub-Basin ............................................................2-18 2.3.5 Upper Myakka Lake Sub-Basin .......................................................2-21 2.3.6 Upper Myakka River Sub-Basin.......................................................2-24 2.3.7 Myakka River between the Lakes Sub-Basin...................................2-27 2.4 HYDROLOGY.............................................................................................2-30 2.4.1 Overview..........................................................................................2-30 2.4.2 Florida River Flow Patterns and the Atlantic Multidecadal Oscillation .2- 30 2.4.3 Myakka River Flow Trends ..............................................................2-34 2.4.4 Benchmark Periods .........................................................................2-46 2.4.5 Seasonal Flow Patterns and the Building Block Approach ..............2-47 2.5 WATER CHEMISTRY ..................................................................................2-50 i 2.5.1 Water Quality Data ..........................................................................2-50 2.5.2 Macronutrients: Phosphorus and Nitrogen.......................................2-50 2.5.3 Potassium and Trend Analysis of Selected Chemical Constituents.2-51 CHAPTER 3 GOALS, ECOLOGICAL RESOURCES OF CONCERN AND KEY HABITAT INDICATORS ............................................................................................................................................ 3-1 3.1 GOAL – PREVENTING SIGNIFICANT HARM .....................................................3-1 3.2 RESOURCES AND AREA OF CONCERN...........................................................3-2 3.3 RESOURCE MANAGEMENT GOALS AND KEY HABITAT INDICATORS ..................3-2 3.3.1 Fish Passage and Recreational Use..................................................3-3 3.3.2 Wetted Perimeter Inflection Point ......................................................3-4 3.3.3 In-Channel Habitats for Fish and Macroinvertebrates........................3-4 3.3.4 Woody Habitats .................................................................................3-5 3.3.5 Hydrologic Connections Between the River Channel and Floodplain 3-6 CHAPTER 4 TECHNICAL APPROACH FOR ESTABLISHING MINIMUM FLOWS AND LEVELS FOR THE MYAKKA RIVER ...................................................................................................................... 4-1 4.1 OVERVIEW .................................................................................................4-1 4.2 TRANSECT LOCATIONS AND FIELD SAMPLING OF INSTREAM AND FLOODPLAIN HABITATS.........................................................................................................4-1 4.2.1 HEC-RAS Cross-Sections .................................................................4-2 4.2.2 PHABSIM Cross-Sections .................................................................4-2 4.2.3 Instream Habitat Cross-Sections .......................................................4-3 4.2.4 Floodplain Vegetation Cross Sections ...............................................4-3 4.3 MODELING APPROACHES.............................................................................4-6 4.3.1 HEC-RAS Modeling ...........................................................................4-6 4.3.2 Physical Habitat Simulation (PHABSIM) Modeling ............................4-9 4.3.3 Recent and Long-term Positional Hydrograph/Analyses..................4-13 4.4 SEASONAL FLOW AND DEVELOPMENT OF BLOCKS 1, 2, AND 3......................4-14 4.5 LOW FLOW THRESHOLD ............................................................................4-15 4.5.1 Wetted Perimeter Standard .............................................................4-15 4.5.2 Fish Passage ...................................................................................4-16 4.6 PRESCRIBED FLOW REDUCTION FOR BLOCK 1 ............................................4-17 4.6.1 PHABSIM – Application for Block 1 .................................................4-18 4.7 PRESCRIBED FLOW REDUCTION FOR BLOCK 2 ............................................4-18 4.7.1 PHABSIM – Application for Block 2 .................................................4-18 4.7.2 Snag and Exposed Root Habitat Analyses – Application for Block 2...4- 19 4.8 PRESCRIBED FLOW REDUCTION FOR BLOCK 3 ............................................4-19 4.8.1 Floodplain Connection Analyses – Application for Block 3 ..............4-20 CHAPTER 5 RESULTS AND RECOMMENDED MINIMUM FLOWS ...................................................... 5-1 5.1 OVERVIEW .................................................................................................5-1 5.2 LOW FLOW THRESHOLDS ............................................................................5-1 5.2.1 Fish Passage Standards....................................................................5-1 5.2.2 Wetted Perimeter Standards..............................................................5-2 5.2.3 Low Flow Threshold...........................................................................5-3 5.3 PRESCRIBED FLOW REDUCTION FOR BLOCK 1 ..............................................5-4 ii 5.4 SHORT-TERM COMPLIANCE STANDARDS FOR BLOCK 1 ..................................5-6 5.5 PRESCRIBED FLOW REDUCTIONS FOR BLOCK 3.............................................5-6 5.5.1 Inundation of Floodplain Features .....................................................5-7 5.6 SHORT-TERM COMPLIANCE STANDARDS FOR BLOCK 3 ................................5-15