Calculating Buffer Zones Widths for Protection of Wetlands and Other Environmentally Sensitive Lands in St. Johns
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CALCULATING BUFFER ZONE WIDTHS FOR PROTECTION OF WETLANDS AND OTHER ENVIRONMENTALLY SENSITIVE LANDS IN ST. JOHNS COUNTY JEA PROJECT NO.: 19270-485-01 Submitted to: ST. JOHNS COUNTY PLANNING DEPARTMENT 4020 Lewis Speedway Road St. Augustine, Florida 32095 Submitted by: JONES, EDMUNDS & ASSOCIATES, INC. 730 N.E. Waldo Road, Building A Gainesville, Florida 32641 In collaboration with: MARK T. BROWN, Ph.D. UNIVERSITY OF FLORIDA CENTER FOR WETLANDS AND WATER RESOURCES Post Office Box 116350 Gainesville, Florida 32611-6350 and RICHARD HAMANN, ESQ. UNIVERSITY OF FLORIDA COLLEGE OF LAW Post Office Box 117629 Gainesville, Florida 32611-7629 January 2000 TABLE OF CONTENTS 1.0 INTRODUCTION . .... .............. .. ............... ... .. .. " I-I 1.1 PROJECT GOALS .... ..... .. ... ...... ....... ... ... ......... I-I 1.2 ECOLOGICAL VALUE OF BUFFER ZONES ............. .. ......... 1-2 2.0 PROTECTING WETLAND-DEPENDENT WILDLIFE HABITAT ..... ... .. 2-1 2.1 SPATIAL REQUIREMENTS .................. .. ................. 2-1 3.0 PROTECTING WETLANDS FROM TURBIDITY AND SEDIMENTATION ..... 3-1 3. 1 SEDIMENTATION AND TURBIDITY LOOK-UP TABLE ........... .. 3-2 3.1.1 Look-up Table ............. ... .. .. ......... ...... .... 3-2 3.1.2 Calculation Procedure .. .. ... .... .. .. ............... ..... 3-2 4.0 PROTECTING WETLANDS FROM GROUNDWATER DRAWDOWN . .... 4-1 4.1 MODELING REQUIREMENTS AND LIMITATIONS .................. 4-1 4.2 DRAWDOWN IMP ACT CALCULATIONS FOR ST. JOHNS COUNTY . .. 4-2 4.3 WETLAND DRAWDOwN LOOK-UP TABLES ... ...... ...... .. 4-3 5.0 DETERMINATION OF A BUFFER WIDTH ...... ... ..................... 5- 1 5.1 ALTERNATIVE BUFFER WIDTHS . ....... .... ..... .. .. .. .. .. 5-1 5.2 BUFFER ESTABLISHMENT ....... .... ..... .. .................. 5-1 5.3 BUFFER HABITAT ... ............ .............. ............. 5-1 6.0 REFERENCES . ...... ................... ....... .. .. .. .. 6-1 APPENDICES Appendix A Species List of Wetland-Dependent Native Wildlife Species of St. Johns County Appendix B Spatial Requirements by Species Listed in Ascending Order by Habitat Appendix C Soils Information in St. Johns County (Source: st. Johns County Soil Survey) Appendix D Hydrologic Methodologies for Predicting Peak Stormwater Discharge Appendix E List of Threatened and Endangered Species in St. Johns County Appendix F Stormwater Guidelines "'." ... .,'/'\\ AQ"n 1n,omRl1ffe:r Reoort.wpd TABLE OF CONTENTS LIST OF FIGURES 2.1 Spatial Requirement eft) A and B Cypress Wetlands ............ .. .... ..... 2-4 2.2 Spatial Requirement eft) A and B Hardwood Swamp' ............... ... ... ... 2-5 2.3 Spatial Requirement eft) A and B Freshwater Marsh .... .............. ... .. ... 2-6 2.4 Spatial Requirement eft) A and B Saltwater Marsh ..... ...................... 2-7 2.5 Spatial Requirement eft) A and B Flatwoods ............................... .. 2-8 2.6 Spatial Requirement eft) A and B Hammock .. .............................. 2-9 2.7 Spatial Requirement eft) A and B Sandhill .. .. ... ........ : .......... .. .. 2-10 4.1 Simulated Drawdowns A & B ...... .. ............. ... , .................. 4-6 4.2 Simulated Drawdowns A& B ... .... , .. ........ .. ...... ... .. ....... 4-7 4.3 Simulated Drawdowns A & B .............. .. ............. ... ... ...... 4-8 4.4 Simulated Drawdowns A & B ......... ................. ....... .. ....... 4-10 5.1 Environmentally Significant Lands .......... .. ..... '. ... ... .. .. ... ... ..... 5-5 W:\192.70\48501 0700\Buffer Report.wpd LIST OF FIGURES LIST OF TABLES 2.1 Summary of Published Data Describing Recommended Buffer Zones for Protection of Wildlife Species. 2-3 2.2 Spatial Requirement (ft) to Protect Various Percentages of Species for Each Habitat Type (Data from Figures 2.1 - 2.7) ................................. .. ... 2-11 3.1 Recommended Wetland Buffers to Minimize Sedimentation in Wetlands and to Control Turbidity in Adjacent Open Waters ..... .. .. .. .......... ..... 3-3 3.2 Mannings Roughness Coefficients (n) .... ................. ...... .. .. .... 3-4 4.1 Buffer Distances When Surficial Aquifer Drawdown of 0.5 Feet is Acceptable .... 4-4 4.2 Buffer Distances When Surficial Aquifer Drawdown of 1.0 Feet is Acceptable ..... 4-5 5.1 Buffer Widths for St. Johns County as Proposed by County Planning Staff ... ...... 5-2 5.2 Appropriate Plantings for Buffer Zones ............. ........ .. ... .. ........ 5-3 W·\l CI170\4R;<;n 1n7nn\R!ln~r Reoort.wod LIST OF TABLES l.0 INTRODUCTION St. Johns County's adopted 1990 Comprehensive Plan PoHcy p.l.3.7 requires vegetative buffers of at least 25 feet to be maintained between natural drainage courses and developed areas to protect the water quality of the drainage course. This buffer requirement has been expanded through Article N of the Land Development Code to require a 50-foot minimum natural upland buffer between development lands and the St. Johns River, Matanzas River, Guana River, Tolomata River, and their associated wetlands and water bodies, regardless of any other regulatory agency requirement of a lesser distance. However, in recent years the county has determined a minimum of 25 or 50 feet around wetlands in the county may not be sufficient to protect water quality given the variety of wetlands and other environmentally sensitive lands. Further, the Comprehensive Plan requires that the county protect environmentally sensitive lands (wetlands adj acent to Outstanding Florida Waters [OFWsJ, Class IT waters, Class ill waters, Aquatic Preserves, estuaries, wetlands adjacent to shellfish harvesting areas, all major rivers, and headwaters to major creeks and estuaries) through the establishment of buffers. Jones, Edmunds & Associates, Inc. (JEA), is working in collaboration with Dr. Mark T. Brown (University of Florida Center for Wetlands and Water Resources) and Dr. Richard Hamarm and Jeff Wade (University of Florida Center for Governmental Responsibility) to develop a buffer zone ordinance that will further protect environmentally sensitive land from development activities. This report presents the methodology necessary for calculating buffer zone widths as determined through scientific studies for protecting wetland habitat. Additionally, it presents reduced buffer distances as suggested by county staff as alterative buffer widths and will subsequently be used to develop a buffer ordinance for St. Johns County. 1.1 PROJECT GOALS Upland vegetative buffers are widely regarded as necessary to protect wetlands, streams, and other aquatic resources. However, buffer size requirements have typically been established by political acceptability, not scientific merit. This often leads to insufficiently buffered aquatic resources and the false perception that the resources are being properly buffered from potential impacts. Numerous scientific studies have shown that relatively wide buffers (1.50 to more than 300 feet) are necessary to protect wetland (JEA et al. 1999). The dilemma exists that undersized buffers may place aquatic resources at risk; however, buffers that are too large may unnecessarily deny landowners the use of a portion of their land. Therefore, it is important to determine the minimum buffer width necessary for protection of sensitive environmental resources. Three goals have been identified that are used to determine buffer sizes: protection of wildlife habitat; minimization of sediment transport into wetlands; and minimization of groundwater drawdown in wetlands. This buffer report provides the methodology for calculating buffer sizes necessary to achieve these three goals in St. Johns County. A single buffer width is then recommended that is appropriate for protecting all three wetland resources. Alternatives to one large buffer distance, as suggested by county staff, is also presented. A previous report summarizes the information that was reviewed and assessed for developing buffer zone widths for the county, including identification and classification of ecological habitats, review of other county ordinances, review of other wetland regulations, review of related reports and studies, and review of legal implications (JEA et al. 1999). HI.\ 1 O"}7(l\1I 0<;(\1 n7nmR"ff"r R" nnrt 'I.vnrl INTROOUCTION 1.2 ECOLOGICAL VALUE OF BUFFER ZONES The differences between developed hinds and natural ecological areas are significant, and the more intensely developed, the greater the differences. Frequently on developed lands, native vegetation is removed and replaced with exotic ornamentals, soil drainage is altered, soils become compacted and covered with impervious materials, and wildlife species are displaced by human activities. The gradient in intensity of noise, waste, temperature, light, structure, and activity from undeveloped to developed lands is intense. In this edge between development and natural areas, water runoff carries sediments, nutrients, and pollutants. Noise and activities from development intrudes into the edge and interferes with wildlife activities. Wildlife popUlations also suffer greatly from predation from domesticated cats and dogs that are allowed to roam unconstrained and from predation from animals such as the brown-headed cowbird that flourishes in disturbed habitats and preys on smaller and more vulnerable birds such as the painted bunting, a prized resident of St. Johns County and a species of great concern by the Audubon Society and wildlife biologists. The area immediately adjacent to wetlands is often a transition zone between wetlands and uplands and exhibits vegetation, soils, and hydrologic characteristics that are similar