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Six Mile Cypress
INTRODUCTION
Lee County's attention is focused on the Six Mile Cypress Watershed. Environmental concerns and development pressures have greatly intensified since 1976 when the citizens of Lee County voted to approve a County wide tax to acquire the Cypress Slough. The opening of I-75 in 1979 and the Southwest Florida Regional Airport in 1983 further stimulated growth. The resultant development pressures have significantly affected surface water flows within the watershed.
The December 1982 satellite photograph on the cover demonstrates the concentration of growth along the east side of the Cypress Slough. From a water management standpoint, the primary problems in the Six Mile Watershed are:
1. SPACE
2. CONTINUITY (of systems)
3. FUNDING
Lee County, with funding assistance from the South Florida Water Management District (SFWMD), recognized and began to address these problems. In 1989, Lee County directed its Surface Water Consulting Team to prepare, as the first priority, a Six Mile Cypress Watershed Plan. Because the plan is a lengthy four volume technical document, this Executive Summary is offered as a guide to focus on existing problems, goals, funding and implementation.
The plan is presented in four volumes:
I EXECUTIVE SUMMARY
II PLANNING AND IMPLEMENTATION
III TECHNICAL APPENDICES
IV WORKING PLAN
Volume II includes a discussion and analysis of key issues, recommended goals, strategies and implementation. Volume III, through its appendices, forms the scientific and technical background used to develop the plan. Volume IV is the working plan and will be a loose leaf collection of plan details including the latest revisions.
BACKGROUND
The initial pressure on the Six Mile Watershed (SMW) resulted from construction of I-75 and the Southwest Florida Regional Airport (RSW). Stimulus for further development pressures came with the construction of Colonial Boulevard, Daniels Road and Alico Road, all connectors to I-75. The construction of the Colonial Blvd. extension to SR-82, the six-laning of Daniels Road and the beginning of the Minnesota Twins baseball complex are under way. RSW has far exceeded its growth projections and a major expansion to the south is now being planned. The 5,500 acre Gateway Community is under construction and Alico, Inc. is presently planning a major new development in the southeast area of the SMW. Obviously, the development pressures are rapidly intensifying.
Acquisition of the environmentally sensitive Six Mile Cypress Slough was initiated with passage of the County wide referendum in 1976. Although initially scheduled for acquisition only between SR-82 and Daniels Road, this purchase has been extended south of Daniels Road to Ten Mile Canal, with many of the parcels already under County ownership or control. Six Mile Parkway has generally formed an impenetrable boundary along the west side of the slough. However, major developments such as Cross Creek, Eagle Ridge and Briarcrest are pressing in on the edges of the Slough from the east. An aerial flight along the easterly boundary of the Slough makes it quite apparent that the potential to create surface water flow-way corridors to the east is rapidly vanishing. These corridors are essential to environmental and surface water system continuity. Although now impressive on the satellite image, it can easily be visualized that the Six Mile Cypress Slough is becoming to this area of Lee County what Central Park appears to be as one flies into New York City. Six Mile Slough will be the only green emerald visible in a mosaic of urban development.
There is little topographic relief in the Six Mile Watershed, which makes flood control difficult and expensive. Historically, sheetflow was to the west and southwest. This sheetflow has been interrupted by developments, dikes, interstate fill and local road fills. This interruption of sheet flow is especially obvious along the easterly edge of the Six Mile Cypress Slough. The key element in the plan to reestablish corridors through these rapidly developing areas is space. This "space" can cost up to $100,000 per acre for still vacant uplands.
The basic assumptions for preparing a Six Mile Watershed Plan follow:
o The intensity of development pressures will increase.
o Environmental protection of the Six Mile Cypress Slough is paramount.
o Serious flooding now occurs throughout the watershed, primarily because east to west flow-way corridors were not perpetuated through developing areas.
o The very flat topography combined with space constraints dictate that hydraulic gradients be held nearly level and rights-of-way be limited.
o Water quality monitoring, and protection of future water quality are of particular concern in this watershed.
o A critical need exists for an organized system of environmental/surface water management corridors.
o The combining of wetlands and waterways into a continuous, integrated corridor plan brings organization to the surface water management system.
o Core wetlands considered for the greenway corridors were carefully reviewed and estimated to be jurisdictional and therefore will not be easily removed from the system.
o Identifiable corridors protected by conservation easements provide the best means of assuring their perpetuation.
o If the remaining vacant lands in the watershed develop without a corridor plan, funding requirements for corridor reestablishment will become almost insurmountable.
o A "no action" approach will prove to be very unsatisfactory with the arrival of the next major storm event.
GOALS
The following goals are grouped as they relate to the previously stated problems of Space, Continuity, and Funding.
SPACE
o Protect and buffer the Six Mile Cypress Slough.
o Create an organized Surface Water Management Plan for the Six Mile Basin.
o Develop the potential to better regulate the Slough hydroperiods for environmental and water conservation purposes.
o Monitor water quality trends and make recommendations for improvement.
CONTINUITY (of corridor systems)
o Establish a system of continuous environmental/surface water management corridors.
o Prepare a workable flood control plan using the corridor concept.
o Develop the corridor plan to upgrade existing systems and convey required flood flows through developed areas.
o Establish corridors which can be perpetuated and economically maintained.
o Provide a method for altering the plan while retaining specified goals.
FUNDING
o Prepare cost estimates, for land acquisition and for improvements through developed areas, to upgrade existing systems.
o Develop alternative funding sources.
o Prepare an implementation plan.
PLAN APPROACH
The following discussion of Plan Approach, Goals, and their accomplishment directly relates to the Lee County/Consultant Contract numerical outline. Contract section titles listed below are followed by numbers which coincide with tasks designated in the contract for ease of reference. Volume II of the Six Mile Plan presents "Planning and Implementation" in technical detail and follows contract numbering designations also. The discussion below integrates goals listed on the previous page with the contract elements discussed in Volume II. Previously stated goals are shown in bold type for emphasis.
WATERSHED BOUNDARY MAP (46-A - 8.01)
The first step in preparing a Master Plan for SMW was to establish the overall basin boundary and related sub-watershed boundaries. The SMW boundary used in this plan is defined by ordinance and is delineated on the map in Figure 1 in the back of this volume. The Six Mile Cypress Slough boundary follows the acquisition line as approved by Lee County. The initial step required to protect and buffer the Six Mile Slough was to establish watershed and sub-watershed boundaries. These boundaries are shown in Figure 1. Once the boundaries are defined, surface water runoff figures required for downstream conveyance design can be determined. These runoff figures, together with an evaluation of existing systems, provide information required to create an organized surface water management plan for the Six Mile Watershed.
SENSITIVE LANDS (.02)
Sensitive lands information was primarily developed from the Lee County Resource Protection Area/Transition Zone (RPA/TZ) map, National Wetlands Inventory, and the Lee County Soil Survey. Potential areas for integration into flow-way corridors were based on known wetland conditions and their locations relative to the main slough and tributary corridors. The consulting team believed that obtaining the largest of the contiguous wetland and transitional forest lands, without regard to vegetation or current hydrological condition, would best serve to preserve natural flow-ways. A "Sensitive Lands Overlay Map" was prepared from aerial photograph interpretation delineating potential acquisition areas as well as other wetlands associated with limb tributary corridors. Aerial reconnaissance revealed slight adjustments to the previously mapped "sensitive lands" and the overlay map was corrected accordingly. This verification of sensitive lands initiated a goal to establish a system of continuous environmental/surface water management corridors. These corridor tributaries to the Six Mile Cypress Slough are shown schematically in Figure 2. "Corridor core wetlands" were selected and shown in Volume II Corridor Maps to indicate their integral importance to selected Environmental/Surface Water Corridors. They are in no way intended to represent all County designated sensitive lands.
CONVEYANCE ELEMENTS AND RIGHTS-OF-WAY (.03 & .04)
Many of the existing conveyances generally have less capacity than the peak runoff rate from the 1-year - 1-day storm event. To improve upon existing facilities, the major needs are space to provide wide lakes and the incorporation of existing wetlands into a continuous system. The lakes create a low headloss conveyance to provide good flood control and also a settling of particulates to improve water quality. Other water quality benefits can be obtained from integration of the existing wetlands and/or creation of wetland fringes along portions of the lake bank. Many existing culverts are undersized and will need replacement. Very few of the existing conveyances have rights-of-way that will allow Lee County to perform maintenance and make improvements. The acquisition of rights-of-way is very important to establish corridors which can be perpetuated and economically maintained. A Flow-way Corridor Map for the South Daniels Area is shown as an example in Figure 3.
GROUNDWATER TABLES (.05)
A network of groundwater table wellpoints was installed and systematic readings taken at intervals of two weeks during the 1989 wet season. This information, together with data from existing SFWMD and USGS surface water recorder and water table readings, respectively, were used to assist in establishing water control structure crest elevations. This information was important in assisting to develop the potential to better regulate the hydroperiods for environmental and water conservation purposes. Additional data should be gathered from this network to provide for a more statistically accurate determination of the average wet season water table.
HYDROLOGY (.06)
Extensive field information such as continuous stage, periodic crest level, and rainfall data is available in this watershed. It is discussed in more detail in Volume II with the actual recorded data located or referenced in Volume III. The U.S. Corps of Engineers HEC-1 model was used to simulate the existing hydrologic conditions for the Six Mile Cypress Slough and runoff from contributing sub-watersheds. HEC-2 was used to model the Six Mile Cypress Slough and sub-watershed limb tributaries. Evaluation of existing and future contributing flows is relatively simple in this watershed. A peak flow rate was established in 1978 based on the capacity of the downstream receiving water. The HEC-1 modeling generally confirmed this as an existing condition.
QUANTITY MODEL (.07)
The quantity modeling for SMW was performed using the HEC-1 and HEC-2 models developed by the U.S. Army Corps of Engineers. The HEC-1 model was used to simulate the existing runoff conditions as stated above. Flood profiles for the main slough and the sub-watersheds were calculated using the HEC-2 model. An example is Figure 4 which shows the Plan and Flood Profiles for the North Eagle Ridge Corridor. The design flow used in the modeling was basically the 37 cubic feet per second per square mile (csm) for the 25-year - 3-day event. Water levels and flow measurements within the basin were used to provide calibration for the modeling. The main objective of the quantity model was to show that with system improvements the goal of flood control for a 25-year - 3-day event could be obtained.
QUALITY MODEL (.08)
The modeling of water quality for SMW was accomplished using a non-point source spreadsheet type model developed by Camp Dresser & McKee and tailored to the Six Mile Cypress Basin. Calibration was performed using the past year's water quality monitoring data provided by Lee County. The model showed a need for use of best management practices and improved treatment of sewage effluent from the package treatment plants and septic tanks now prevalent within the basin. Another important benefit of the model was that it showed that the use of RPA's within the surface water management system will act as a polishing mechanism for water received from projects using best management practices and as a safety net should some of these on-site treatment facilities not function properly.
WATER BUDGET (.09)
A water budget analysis was prepared for the SMW. The primary input components in the analysis were precipitation, surface water inflows and groundwater inflows. Primary losses were surface water runoff, groundwater outflows, evaporation and transpiration (ET), vertical leakage and consumptive water withdrawals. Surface water inflows from adjacent watersheds are minimal and groundwater inflows tend to balance outflows, therefore the major source of gain is precipitation with the major losses being surface water runoff and ET. Details on evaluation of these gains and losses are found in Volumes II and III. The water budget analysis focuses on gains and losses to the Six Mile Cypress Slough itself. The slough is primarily affected by surface water inflow from the tributaries, surface water outflow to Ten Mile Canal and ET. Therefore, it is apparent that to increase the slough hydroperiod, flow into the strand must be increased with outflow being decreased. The primary means of accomplishing this are as follows: 1) decrease outflow by raising pool levels and reducing discharge, where possible, 2) resist diversions of water away from the slough and into other systems, 3) seek additional inputs of waters from adjacent systems, where beneficial and practical. Pursuing these approaches creates situations which tend to develop the potential to better regulate the hydroperiods for environmental and water conservation purposes.
SYSTEM CAPACITY AND PROPOSED IMPROVEMENTS (.10 and .11)
Each of the sub-watersheds was analyzed for improvements needed to provide flood control for the 25-year - 3-day storm event. Corridor systems were surveyed and conceptually designed in order to prepare cost estimates for land acquisition and for improvements through developed areas, to upgrade existing systems. The improvements needed to bring the existing facilities up to this level were estimated to cost in the range of ten million dollars. These improvements are needed with or without additional development within the basin. Additional improvements will be required across undeveloped property, as that property is developed and incorporated into the overall system. The basic premise of the proposed improvements is that the rate of runoff for the 25-year - 3-day event will not change with development of the watershed. The level of service provided by the proposed system would be the 25-year - 3-day event. This is in comparison to the existing system that, in many places, will not adequately pass a 1-year - 1-day event. The proposed improvements have taken into account the need for low maintenance facilities that provide not only flood control but a continuous system that links isolated wetlands and provides continuous corridors for wildlife as well as the conveyance of excess surface water. The proposed facilities may also provide some detention needed for the proposed developments and may provide a source of irrigation water. These potential uses should be evaluated as each development is reviewed by the SFWMD and the Lee County Division of Water Resources (DWR).
FUNDING AND IMPLEMENTATION (.12 and .13)
Funding and implementation are discussed in detail on pages 11 and 12. One of the key goals of this process is to develop alternate funding sources that are equitable and fair. Although extreme development pressures create discomfort, they also provide impetus to prepare an implementation plan and stimulate action. Implementation is only a matter of time, for the first flooding crises will certainly bring action. Pressures to find funding sources will definitely mount with time because rapidly increasing land values will not likely allow serious flooding conditions to go unresolved.
FUNDING
The entire watershed has been evaluated and improvements are proposed to facilitate both water quantity and quality enhancements. Since the watershed is sparsely developed, the majority of the lakes, weirs, culverts, and interconnected wetlands will be provided as development occurs in accordance with the conceptual watershed plan. The funding needs discussed below are for those areas that require immediate upgrade of existing facilities. These facilities serve both existing developments and outlying areas. The proposed facilities are an integral part of the conceptual watershed plan.
The estimated construction cost to upgrade existing facilities to desired levels is approximately twelve million dollars. This money is to pay for specified land acquisition, conveyance systems, and water control structures. A portion of the money will also be used for aesthetic and environmental enhancements.
Several approaches to funding are available with the primary ones being SFWMD joint participation, a water conservation utility, Municipal Service Benefit Unit (MSBU) assessments and ad valorem taxes. SFWMD joint participation is through several programs such as Save Our Rivers, Surface Water Improvement Management Plan, and the Infrastructure Improvement Fund. Funding for O&M and administration is most practical through a utility. MSBU assessments for the Capital Improvements Plan (CIP) could be applied on a per acre basis and perpetuate the equity established by the allowable runoff of 37 csm.
The establishment of a water conservation utility will provide an equitable means of funding annual O&M needs. An average monthly user fee between three dollars and five dollars per Equivalent Residential Unit (ERU) is anticipated initially in order to create a dedicated funding source to promote O&M activities related solely to the stormwater system. Funding for CIP projects can be available immediately with assessments and joint participation with SFWMD programs.
IMPLEMENTATION
Implementation of the corridor plan, once endorsed, should greatly facilitate coordination throughout the watershed. The corridor plan will provide a framework from which existing and proposed connecting systems can be integrated. It will establish a practical approach for creating continuous greenway corridors of wetlands and lakes. Most important, through a systematic approach to land acquisitions and conservation easements, the SMW Plan will insure maintenance and perpetuation of these greenway systems.
Upgrading of Existing System - The primary problem throughout the SMW is the need for conveyance systems to penetrate through existing developments to Six Mile Cypress. Although the corridor plan was prepared for the entire watershed, it is proposed that capital improvements will only be scheduled for areas of existing constrictions.
Extension of Corridors - It is anticipated that the extension of corridors will normally be incorporated into future development plans. Encouragement for creation of these corridors could be in the form of allocation of detention storage, use of acreage to determine density allotments, etc.
Flexibility - The corridor plan should remain flexible. Waterway widths and depths need to remain consistent and core wetland areas should be retained in the corridor plan. However, waterway location should remain flexible to provide the landowner with a maximum of plan alternatives.
Funding - CIP funding from a flood control standpoint can easily be related to a per acre cost. This is illustrated by the existing allowable runoff rate of 37 csm. This uniform allowable outflow rate (watershed policy since 1978) basically insures that all acreages are treated equitably from a water quantity standpoint. From a maintenance and water quality perspective, an impervious area approach is more equitable and thus lends itself to a user fee technique.
Phasing of Action Plan - To facilitate immediate action, land acquisitions and system improvements will be broken into two phases. The first phase construction costs are estimated at four million dollars. They will involve key facilities which will be concentrated on the downstream (westerly) ends of the proposed corridors.
Recommendations:
o Present SMW plan to County Commission for approval.
o Review plan with Six Mile Cypress Basin Development Review Board and request their endorsement.
o Make plan available through County staff to general public for use as a guide.
o Present plan to SFWMD staff and Board for endorsement.
o Encourage new developments to fit the SMW Plan or prepare an equivalent alternative plan for submission to DWR for approval.
o Authorize initial steps toward land acquisitions.
o Prepare construction plans for key corridor upgrade improvements.
- Pursue joint funding from County and SFWMD sources.
- Initiate Phase I of the corridor upgrade plan.
Action - Progress - The need for the SMW Plan is apparent. Permit applications by Cross Creek Estates and Woodland Walk are under review and are being coordinated with the proposed SMW Plan. An Eagle Ridge easement along the proposed south corridor has been acquired from their Property Owners Association and is being submitted to the County Commission for approval. The "Cypress Arm," north of Penzance Road, was approved for inclusion into SFWMD's Save Our Rivers acquisition program through the efforts of Commissioner Ray Judah and Six Mile Preserve Manager, Roger Clark. The SMW Plan has "before its completion" already accrued benefits in right-of-way reservations, potential land purchases and scheduled improvements far beyond its costs.
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