Reevaluation of Minimum Flows for the Chassahowitzka River System Final Draft October 2019 Reevaluation of Minimum Flows for the Chassahowitzka River System Final Draft October 2019 Southwest Florida Water Management District Brooksville, Florida 34604-6899 Gabe Herrick, XinJian Chen, Chris Anastasiou, Ron Basso, Natasha Mendez-Ferrer, Nicole Ortega, Danielle Rogers, and Doug Leeper The Southwest Florida Water Management District (District) does not discriminate on the basis of disability. This nondiscrimination policy involves every aspect of the District’s functions, including access to and participation in the District’s programs and activities. Anyone requiring reasonable accommodation as provided for in the Americans with Disabilities Act should contact the District’s Human Resources Office Chief, 2379 Broad St., Brooksville, FL 34604- 6899; telephone (352) 796-7211 or 1-800-423-1476 (FL only), ext. 4703; or email [email protected]. If you are hearing or speech impaired, please contact the agency using the Florida Relay Service, 1(800) 955-8771 (TDD) or 1(800) 955-8770 (Voice). Page i Reevaluation of Minimum Flows for the Chassahowitzka River System October 2019 The geological evaluation and interpretation contained in the report entitled Reevaluation of Minimum Flows for the Chassahowitzka River System has been prepared by or approved by a Certified Professional Geologist in the State of Florida, in accordance with Chapter 492, Florida Statutes. Ronald J. Basso, Jr. Professional Geologist License No. PG 0001325 Page ii TABLE OF CONTENTS TABLE OF CONTENTS ............................................................................................................. III EXECUTIVE SUMMARY ........................................................................................................ VIII CHAPTER 1 - INTRODUCTION ................................................................................................. 1 1.1 2013 MINIMUM FLOWS EVALUATION AND RULE .................................................................... 1 1.2 LEGAL DIRECTIVES AND USE OF MINIMUM FLOWS AND LEVELS ............................................. 2 1.2.1 Relevant Statues and Rules ...................................................................................... 2 1.2.2 Environmental Values ................................................................................................ 3 1.3 VERTICAL DATUM ............................................................................................................... 4 1.4 DEVELOPMENT OF MINIMUM FLOWS AND LEVELS IN THE SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT ........................................................................................................... 4 1.4.1 Significant Harm ........................................................................................................ 5 1.4.2 Flow Definitions ......................................................................................................... 8 1.4.3 Adaptive Management ............................................................................................... 9 1.5 DIFFERENCES BETWEEN THE ORIGINAL MINIMUM FLOW EVALUATION AND THIS 2019 REEVALUATION ........................................................................................................................ 9 CHAPTER 2 - PHYSICAL SETTING AND DESCRIPTION OF THE CHASSAHOWITZKA RIVER SYSTEM ...................................................................................................................................13 2.1 LOCATION AND DESCRIPTION OF RIVER SEGMENTS AND SPRINGS .......................................17 2.2 WATERSHED LAND USE AND COVER ..................................................................................20 2.3 GAGE DATA ......................................................................................................................21 2.3.1 Chassahowitzka River near Homosassa, FL (Gage No. 02310650) .........................24 2.3.2 Chassahowitzka River near Chassahowitzka, FL (gage No. 02310663) ...................31 2.3.3 Chassahowitzka River at Dog Island near Chassahowitzka, FL (gage No. 02310673) ..........................................................................................................................................37 2.3.4 Chassahowitzka River at Mouth near Chassahowitzka, FL (gage No. 02310674) ....43 2.4 BOTTOM SUBSTRATES .......................................................................................................47 2.5 FLOW RECORDS ...............................................................................................................47 Page iii 2.5.1 Differences in Flow Records .....................................................................................47 2.5.2 The General Flow Record .........................................................................................48 CHAPTER 3 - WATER QUALITY CHARACTERISTICS AND RELATIONSHIPS WITH FLOW . 50 3.1 INTRODUCTION ..................................................................................................................50 3.1.1 Water Quality Classification ......................................................................................50 3.1.2 Impaired Waters Rule ...............................................................................................51 3.1.3 Numeric Nutrient Criteria ..........................................................................................53 3.1.4 Total Maximum Daily Loads (TMDL) ........................................................................54 3.1.5 Water Clarity .............................................................................................................55 3.2 OVERVIEW OF WATER QUALITY DATA SOURCES .................................................................55 3.2.1 Active Water Quality Data Collection ........................................................................55 3.2.2 Inactive Water Quality Data Collection ......................................................................62 3.3 SPATIAL VARIATIONS IN WATER QUALITY CONSTITUENTS ....................................................64 3.3.1 Total Nitrogen ...........................................................................................................64 3.3.2 Nitrate + Nitrite .........................................................................................................66 3.3.3 Total Phosphorous ...................................................................................................68 3.3.4 Soluble Reactive Phosphorous and Orthophosphate ................................................71 3.3.5 Chlorophyll ...............................................................................................................74 3.3.6 Water Clarity .............................................................................................................77 3.4 TEMPORAL VARIATION IN WATER QUALITY CONSTITUENTS ..................................................80 3.4.1 Total Nitrogen ...........................................................................................................80 3.4.2 Nitrate + Nitrite .........................................................................................................83 3.4.3 Total Phosphorous ...................................................................................................85 3.4.4 Soluble Reactive Phosphorous and Orthophosphate ................................................86 3.4.5 Chlorophyll ...............................................................................................................88 3.4.6 Water Clarity .............................................................................................................90 Page iv 3.5 RELATIONSHIP BETWEEN FLOW AND WATER QUALITY CONSTITUENTS ..................................91 3.5.1 Flow Record for Water Quality Analysis ....................................................................91 3.5.2 Spring Vents .............................................................................................................92 3.5.3 River Mainstem ........................................................................................................95 3.5.4 Estuary .....................................................................................................................99 CHAPTER 4 - BIOLOGICAL STATUS AND TRENDS FOR THE CHASSAHOWITZKA RIVER SYSTEM ................................................................................................................................. 101 4.1 VEGETATION ...................................................................................................................101 4.1.1 Land Cover .............................................................................................................101 4.1.2 Shoreline vegetation surveys ..................................................................................101 4.1.3 Submerged Aquatic Vegetation ..............................................................................109 4.1.4 Effects of Salinity and Sea Level on Vegetation ......................................................119 4.1.5 Vegetation Summary ..............................................................................................120 4.2 BENTHIC MACROINVERTEBRATES .....................................................................................120 4.2.1 Oysters ...................................................................................................................120