EAC Agenda 05/04/2011
AGENDA
COLLIER COUNTY ENVIRONMENTAL ADVISORY COUNCIL
WILL MEET AT9:00 A.M., WEDNESDAY, MAY 4, 2011, IN THE BOARD OF COUNTY
COMMISSIONERS MEETING ROOM, ADMINISTRATION BUILDING, COUNTY
GOVERNMENT CENTER, 3299 T AMIAMI TRAIL EAST, NAPLES, FLORIDA
I. Call to Order
II. Roll Call
III. Approval of Agenda
IV. Approval of April 13, 2011 meeting minutes
V. Upcoming Environmental Advisory Council Absences
VI. Land Use Petitions
A. Gordon River Greenway Park Rezone (RZ - PL 2009-25)
and companion item Special Treatment Permit (ST - PL 2011-677)
Section 27 & 34, Township 39 S, Range 25 East
VII. New Business - none
VIII. Old Business
A. Watershed Management Plan Update
B. Update members on projects
IX Subcommittee Reports
X. Council Member Comments
XI. Staff Comments
XII. Public Comments
XIII. Adjournment
.****************************************.*************************
Council Members: Please notify Summer Araaue. Senior Environmental SDecialist no later than
5:00 D.m. on ADril 29. 2011 if vou cannot attend this meetina or if vou have a conflict and will
abstain from votina on a Detition /252-6290).
General Public: Any person who decides to appeal a decision of this Board will need a record of the
proceedings pertaining thereto; and therefore may need to ensure that a verbatim record of proceedings is
made, which record includes the testimony and evidence upon which the appeal is to be based.
Gordon River EAC Staff Report - May 4,20] 1
Item VLA.
ENVIRONMENTAL ADVISORY COUNCIL STAFF REPORT
MEETING OF MAY 4, 2011
I. NAME OF PETITIONERlPROJECT
Petition No.: PL 2009-25 Rezone and PI. 2011-677 ST Permit companion item
Petition Name: Gordon River Greenway Park Rezone and ST Permit companion item
ApplicantlDeveloper: Collier County Public Services Division,
Parks and Recrcation Dcpartment
Engineering Consultant: KimIey Horn and Assoc, J.P. Marchand
Environmental Consultant: Entrix, Inc., Raymond Loraine
II. LOCATION
The 123.6+/- acre subject property is located on the east side of GoodIette-Frank Road
(CR-851) and south of Golden Gate Parkway (CR-886), in Sections 27 and 34, Township
49 South, Range 25 East, Collier County, Florida.
III. DESCRIPTION OF SURROUNDING PROPERTIES
ZONING
DESCRIPTION
N-
A,C-3
Golden Gate Parkway
then Freedom Park,
Caribbean Gardens
Zoo, office park
S -
C-3, CON, City of Naples
Zoning District: PD
office buildings,
the Conservancy of
SW Florida
E-
A, PUD, City of Naplcs Zoning
District PD and C4
Bear's Paw Golf and
Country Club, singIe- family,
multi-family
development, airport
w-
A, CON, RSF-4, RMF-6, RMF-16,
City of Naples Zoning Districts:
vacant, undeveloped
land, offices, single-
Family, Conservancy
of SW Florida, Car-
ribean Gardens Zoo
Pagel of tI
Gordon River EAC Staff Report - May 4,2011
IV. PROJECT DESCRIPTION
The request is to Rezone several properties totaling 123.6:1: acres from Rural Agriculture
(A), Rural Agriculture (A) with a Special Treatment (ST) Overlay, Conservation (CON),
Conservation (CON) a with an ST Overlay, Commercial Intermediate (C-3), and
Residential Multi-family District 6 [RMF-6(3)] with an ST Overlay zoning districts to the
Public Usc (P) zoning district for a public park with an ST Overlay to be known as the
Gordon River Greenway Park (GRGP). A companion ST Permit request has been made
in conjunction with the rezoning request in order to impact areas within the ST overlay.
The main parcel is bordercd to the north by Golden Gate Parkway, to the south and west by the
Gordon River and to the east by Bear's Paw Golf Course. The Naples Airport borders the
southeastern most parcel and the two (2) westernmost pareels are bordered to the west by
GoodIette Frank Road and to the east by the Gordon River. The Gordon River is a Class III water
body that is listed as impaired by the Florida Department of Environmental Protection due to its
low dissolved oxygen concentration. Additionally, the Golden Gate Canal, a major drainage
canal that terminates at Naples Bay, enters the Gordon River along the eastern boundary of the
largest parcel.
The Collier County Gordon River Greenway Park (GRGP) site improvements and related
infrastructure for public use are proposed to create water quality systems and passive
recreation amenities within an ecological trail corridor. The proposed GRGP project is
designed to create a unique passive park along with a water quality system to mitigate and
reduce pollution levels in Gordon River and downstream surface waters that flow into
Naples Bay, within the Naples-Collier urban area. Primary components of the GRGP
project are depicted on the overall site concept plan (Exhibit 7 of EIS) are expected to
include:
. Storm water dry detention treatment areas and bio-retention swales
. Water control structures
. Passive park amenities such as recreational meandering pedestrian
. walkways, pavilions and boardwalks
. Fishing platform
. Parking, including shared parking facilities
. Designated environmental preserve areas
. Restroom facilities
. Pedestrian bridges
. Connection points to access roadways by others
. Park maintenance building
. Canoe/kayak launch facility at the Gordon River
. Gopher Tortoise Preserve
. Site landscaping
. Best management improvements to enhance water quality from stormwater runoff
along Golden Gate Parkway.
Page 2 of II
Gordon River EAC Staff Report - May 4, 2011
V. GROWTH MANAGEMENT PLAN CONSISTENCY
A. Future Land Use Element
The subject property is located within the Urban designated area (Urban - Mixed Use
District, Urban Residential Subdistrict) as identified on the Countywide Future Land Use
Map, and is within the Coastal High Hazard Area. This designation is intended to
accommodate a variety of residential and non-residential uses, including parks,
recreational facilities, and esscntiaI services as defined in the Land Development Code
(LDC). The Public Use District (P) is intended to accommodate government facilities that
provide essential services, including parks and recreational services facilities.
Furthermore, the proposed use is consistent with the Future Land Use Element (FLUE)
via Policy 5.5, which encourages the planning for expansion of County owned and
operated public facilities and services to existing lands that are designated for urban
intensity uses.
The P District is also intended for additional uses such as administrative services
facilities, not for profit child care facilities, collections and transfer sites for resource
recovery, communication towers, educational facilities, educational plants, essential
public service facilities, fairgrounds, libraries, museums, parking facilities, safcty services
facilities, and other comparable uses.
B. Conservation & Coastal Manal!ement Element
Objective 2.2
All canals, rivers, andjlow ways discharging into estuaries shall meet applicable Federal, State,
or local water quality standards.
Policy 2.2.2
In order to limit the specific and cumulative impacts of storm water run-off, storm water systems
should be designed in such a way that discharged water does not degrade receiving waters and
an attempt should be made to enhance the timing, quantity, and quality of fresh water to the
estuarine system. Non-structural methods such as discharge and storage in wetlands are
encouraged.
The Gordon River Greenway Park design will meet all federal, State, and local water quality
design standards; issuance of the ERP from the SFWMD will confirm this assertion. In addition,
as required by the Florida Communities Trust grant, water quality will be improved within the
currently impaired Gordon River by the onsite treatment of offsite runoff from Golden Gate
Parkway as discussed in Subsection f.i. (EIS, p. 15). The storm water runoff will be conveyed
through a storm water treatment unit to separate solids, grease and oils. The storm water will
then be conveyed through a pipe and released into a spreader swale enhancing the timing,
quantity and quality of the storm water to the estuarine system.
Objective 6.1
The County shall protect native vegetative communities through the application of minimum
preservation requirements. Thefollowingpolicies provide criteria to make this objective
measureable. These policies shall apply to all of Collier County except for the portion of the
Page 3 of II
Gordon River EAC Staff Report - May 4, 2011
County which is identified on the Countywide Future Land use Map (FLUM) as Rural Lands
Stewardship Overlay.
Policy 6.1.1
For the County's Urban Designated Area, Estates Designated Area, Conservation Designated
Area, and Agricultural/Rural Mixed Use District, Rural-Industrial District and Rural-Settlement
Area District as designated on the FLUM, native vegetation shall be preserved through the
appl iCa/ion of the following preservation and vegetation retention standards and criteria, unless
the development occurs within the Area of Critical State Concern (ACSC) where the ACSC
standards referenced in the Future Land Use Element shall apply Notwithstanding the ACSC
requirements, this policy shall apply to all non-agricultural development except for single-family
dwelling units situated on individual parcels that are not located within a watershed
management conservation area identified in a Watershed Management Plan developed pursuant
to policies supporting Objective 2.1 of this Element.
The Gordon River Greenway Park contains approximately 112.8 acres of native habitat of which
some 103.3 acres (approximately 91.6%) will not be impacted and 22.2 acres (19.7%) will be
placed in a Preserve. The preservation area exceeds the 15% native habitat requirement (16.92
acres) and includes most of the upland gopher tortoise habitat within the project.
Policy 6.1.4
Prohibited invasive exotic vegetation shall be removed from all new developments.
Nuisance and exotic species of plants, particularly Brazilian pepper, Melaleuca, Australian pine,
and Downy rose myrtle are required to be removed from the entire site during final site
inspections.
Policy 6.1. 7
The County shall require native vegetation to be incorporated into landscape designs in order to
promote the preservation of native plant communities and to encourage water conservation.
The Gordon River Greenway Park has been designed to showcase the native vegetation of Collier
County. Native vegetation will be incorporated into supplemental landscape designs.
Objective 6.2
The County shall protect and conserve wetlands and the natural functions of wetlands pursuant
to the appropriate policies under Goal 6. The following policies provide criteria to make this
objective measure able. The County's wetland protection policies and strategies shall be
coordinated with the Watershed Management Plans as required by Objective 2.1 of this Element.
The design of the Gordon River Greenway Park meets or exceeds all the applicable Policies
within this Objective. Approximately 91 .6% of the native wetland and upland habitats onsite will
not be developed. In addition, one of the major components of the project will include
environmental education.
Objective 7.1
The County shall direct incompatible land uses away from listed animal species and their
habitats. The County relies on the listing process of State and Federal agencies to identifY
species that require special protection because of their endangered, threatened, or species of
special concern status. Listed animal species are those species that the Florida Fish and Wildlife
Page 4 of Jl
Gordon River EAC Staff Report- May 4,2011
Conservation Commission has designated as endangered, threatened, or species of special
concern, in accordance with Rules 68A-27. 003. 68A-27.004, and 68A-27. 005, FAC and those
species designated by various federal agencies as Endangered and Threatened species published
in 50 CFR 17.
The only listed animal species observed onsite by the environmental consultant was the gopher
tortoise (Gopherus polyphemus). The consultant identified 316 burrows. County staff worked
with the applicant to develop a site plan to minimize impacts to the gopher tortoise and to
maximize preservation ofthe existing gopher tortoise habitat. Permitting for gopher tortoise
relocation adjacent to the zoo property is required and proposed to be done prior to any site
work. The removal and maintenance of nuisance and exotic plant species, specifically downy
rose myrtle, will improve the habitat of this species.
Objective 10.1
Priorities for shoreline land use shall be given to water dependent uses over water related land
uses and shall be based on type of water-dependent use, adjacent land use, and surrounding
marine and upland habitat considerations. The Collier County Manatee Protection Plan (NR-
SP-93-01) May 1995 restricts the location of marinas and may limit the number of wet slips, the
construction of dry storage facilities, and boat ramps, based upon the Plan's marina siting
criteria.
In accordance with Policies 10.0.0 and 10.1.4, the proposed canoe/kayak launch will be public,
prohibit motorized boats, and will impact only 0.2 I acres of disturbed mixed forested wetlands.
Objective 10.2
The County shall continue to insure that access to beaches, shores and waterways remain
available to the public and continue with its program to expand the availability of such
access and a method to fUnd its acquisition.
The proposed project is consistent with the aforementioned Objective, as well as Policies
10.2.3 and 10.2.4.
Objective 12.2
The County shall ensure that publicly funded buildings and publicly funded development
activities are carried out in a manner that demonstrates best practice to minimize the loss
of life, property, and re-building cost from the effects from hurricanes, flooding, natural
and technological disaster events. Best practice efforts may include, but are not limited
to:
a. Construction above the flood plain;
(Criterion met. The proposed project is consistent with the aforementioned Objective,
as well as Policies 10.2.3 and 10.2.4. Additionally, the applicant sustains that the
proposed habitable structures will be built at a minimum finished floor elevation of 7
feet, which is the minimum elevation required for the subject property by the current
FEMA Flood Zone Base Flood Elevation (AE7) map.)
b. maintaining a protective zone for wildfire mitigation;
(Criterion met. The proposed project site retains existing wetlands and proposes
opens space that will serve as a wildfire protective zone. In this regard, these
Page 5 of tl
Gordon River EAC Staff Report May 4, 2011
strategies are consistent with those included in the "Wildfire Mitigation In Florida
Land Use Planning Strategies and Best Management Practices" published by the
Florida Department of Community Affairs.)
c. installation of on-site permanent generators or temporary generator emergency
connection points;
(Criterion not applicable. The applicant sustains that emergency power generators are
not necessary for the proposed park structures. Staff is of the opinion that this
criterion is not applicable because the proposed structures will not serve as public
emergency shelters.)
d. beach and dune restoration, re-nourishment, or emergency protective actions to
minimize the loss of structures from future events;
(Criterion met. The applicant sustains that this criterion is not applicable. However,
staff is of the opinion that "protective actions to minimize the loss of structures from
future events" is a criterion that must be addressed. In this regard, the Florida
Building Code and the Florida Fire Prevention Code include requirements that
address this criterion.)
e. emergency road repairs;
(Criterion met. The applicant notes that the proposed project minimizes the amount of
road construction through the use of shared access points and parking areas.)
f. repair and/or replacement of publicly owned docking facilities, parking areas, and
sea walls, etc.
(Criterion met. The applicant states that publicly owned facilities will be designed to
industry and County standards to minimize maintenance and repair needs.)
VI. MAJOR ISSUES
A. Storm water Manal!ement
Storm water management for the Gordon River Greenway Park (GRGP) will consist of
two (2) separate systems. Both the Zoo Parking Node and the Northeast Parking Node
use typical catch basins and pipe to collect runoff from the parking areas and convey it to
dry detention pre-treatment areas before discharging through control structures with
bubble-up outfalls into wetlands. The receiving body for the outfalls is the Gordon River.
The Northeast Parking Node also proposes to provide storm water discharge conveyance
for a portion of Golden Gate Parkway after passing the road runoff through a
commercially distributed storm water treatment chamber. Storm water will not be
directed into the Upland Preserve. Storm water management concerns will be reviewed
at time of Site Development Plan submittal and will be required to meet the LDC. This
project will be permitted by South Florida Water Management District.
B. Environmental
1. Site Description and Proiect Description: Environmental Requirements
The main parcel contains wetlands along the Gordon River Greenway corridor and uplands with
Gopher Tortoise in the central eastern portion of the property. The western half Zoo Parking
node has been highly impacted as it has been part of the Zoo parking area. See the Listed
Page 6 of 11
Gordon River EAC Staff Report .- May 4, 2011
Species Map (Exhibit J 5 of EIS) for a comprehensive look at the wetlands, uplands, and listed
species on the property. The site will be enhanced through water quality improvements, wetland
enhancement, nuisance/exotic species removal, and proper land management activities. See
Exhibit 8 of the EIS for impacts to the entire site.
2. Wetlands
The wetland limits were verified by the SFWMD on February 6, 2009 (Exhibits I] and 12 of
EIS). The wetlands within the project boundaries total 80.1 acres. Permanent wetland impacts
totaling 2.36 acres inelude the following; 2.15 acres expected for the construction of the North
Park Node. The bioswale will receivc untreated storm water runoff from Golden Gate Parkway
and treat the runoff to improve watcr quality in the Gordon River. See Exhibit 13 ofEIS for
Wetland Impacts map.
The design of the project has been baIanccd between minimization of wetland impacts and the
simultaneous need to protcet listed species, e.g., gopher tortoise, habitat. The North Park Node
has been sited in wetlands of poor quality as close to Golden Gate Parkway as possible to
minimize access-assoeiated impacts and secondary impacts to Wetland 2. According to the ETS,
all boardwalk construction will minimize construction related impacts to the extent practicable
and shading impaets through construction of boardwalks 5 feet above surface elevations to allow
light penetration underneath.
3. Preservation Requirements
The Collier County Land Development Code Section 3.05.07.B requires designation of at least
15% of the native vegetation onsite as Preserve. For the subject project, the Preserve
requirement is ]6.92 acres (! 12.8 acres x 0.15). The Overall Project Site Concept Plan (Exhibit
7 of EIS) provides a designated Preserve of 22.2 acres. The onsite preserve prioritization
hierarchy in the LDC and OMP requircs that areas known to be utilized by listed species be a
high priority for preservation. Therefore, gopher tortoise habitat was a priority for preservation
in development of the site plan and nearly the entire occupied upland gopher tortoise habitat was
included in the designated Preserve (Exhibit 9 of EIS).
4. Listed Species
Approximately 3 I 6 gopher tortoise burrows were observed on site by the environmental
consultant. The project has minimized impacts to gopher tortoise habitat by locating the East
Node parking in Wetland 2 adjacent to Golden Gate Parkway. Permitting for the relocation of
gopher tortoises on the parcel adjacent to the zoo is required prior to site work. Potential effects
on gopher tortoises during nature trail construction will be evaluated through consultation with
the Florida Fish and Wildlife Conservation Commission and permitted as required. In addition,
the construction and visitor ioteraction will be addressed in the Preserve Management Plan
required with the Site Development Plan.
The bridges and canoe/kayak launch have been located as far away from the Yellow-crowned
Night Heron rookery as possible.
Page 7 of 11
Gordon River EAC Staff Report - May 4, 2011
VII. EXISTING ZONING AND OVERLAYS
A. Conservation (CON) Zonine
As stated in section 2.03.09.B. of the Land Development Code (LDC), the purpose and
intent of the Conservation District (CON) district is "to conserve, protect and maintain
vital natural resource lands within unincorporated Collier County that are owned
primarily by the public. All native habitats possess ecological and physical characteristics
that justifY attempts to maintain these important natural resources. Barrier islands, coastal
bays, wetlands, and habitat for listed species deserve particular attention because of their
ecological value and their sensitivity to perturbation. All proposals for development in the
CON district must be subject to rigorous review to ensure that the impacts of the
development do not destroy or unacceptably degrade the inherent functional values. The
CON District includes such public lands as Everglades National Park, Big Cypress
National Preserve, Florida Panther National Wildlife Refuge, portions ofthe Big Cypress
Area of Critical State Concern, Fakahatchee Strand State Preserve, Collier-Seminole
State Park, Rookery Bay National Estuarine Sanctuary Research Reserve, Delnor-
Wiggins State Park, and the National Audubon's Corkscrew Swamp Sanctuary (privately
owned), and C.R.E.W. It is the intent of the CON District to require review of all
development proposed within the CON District to ensure that the inherent value of the
County's natural resources is not destroyed or unacceptably altered. The CON District
corresponds to and implements the conservation land use designation on the future land
use map of the Collier County GMP.
To provide a brief history of the property, the site was previously zoned RO (Recreation
Open Space), C-3 (Commercial Intermediate), A-2, and RMF-6. When Collier County
created the Collier County Land Development Code in 1991, it created new zoning
districts and eliminated others with the adoption of the new code (Ord. 91-102). The RO
and A-2 designations of the subject property were changed to CON and A and the C-3
and RMF-6 district designations remained. RO is the closest zoning district in zoning
Ordinance 82-2 to the present CON district under the Land Development Regulations.
The previous RO designation allowed for more intensive recreational uses than the
requested P dcsignation.
The applicant has requested for the CON zoning to be rezoned to P (Public Use)
designation for use as a public park. The gopher tortoise in this area will be required to
be relocated prior to impacts in accordance with the FFWCC regulations.
B. Special Treatment (ST) Zonine Overlav - COMPANION ITEM
PL 2011-677
The project has a Special Treatment (ST) Overlay district designation on approximately
63.47 acres of the overall 123.6 acre project site. As a companion to the subject rezone
request, an ST permit application is being reviewed as part of the public hearing process.
Page 8 of 11
Gordon River EAC Staff Report - May 4, 2011
As stated in section 2.03.07.D. of the Land Development Code (LDC), the Special
Treatment (ST) overlay district classification will be used for those lands of
environmental sensitivity and historical and archaeological significance where the
essential ecological or cultural value of the land is not adequately protected under the
basic zoning district regulations established by Code or by ordinance. All land within the
ST overlay district shall be designated as environmentally sensitive.
Section 2.03.07.D. of the Land Development Code states the purpose and intent of the ST
overlay district, and reads as follows: "Within the County there are certain areas, which
because of their unique assemblages of flora and/or fauna, their aesthetic appeal,
historical or archaeological significance, rarity in the County, or their contribution to their
own and adjacent ecosystems, make them worthy of special regulations. Such regulations
are directed toward the conservation, protection, and preservation of ecological and
recreational values for the greatest benefit to the people of the County. Such areas
include, but are not necessarily limited to, mangrove and freshwater swamps, barrier
islands, hardwood hammocks, xeric scrubs, coastal beaches, estuaries, cypress domes,
natural drainage ways, aquifer recharge areas, and lands and structures of historical and
archaeological significance. The purpose of the "ST" district is to assure the preservation
and maintenance of these environmental and cultural resources and to encourage the
preservation of the intricate ecological relationships within the systems, and at the same
time, permit those types of development which will hold changes to levels determined
acceptable by the BCC after public hearing."
Including temporary impacts, the total proposed altered area within the ST overlay district
is 5.68 acres (9%), with 1.81 acres of that being proposed impervious area. Temporary
impacts include a two feet wide temporary construction impact area along both outside
edges ofthe boardwalk, a total 12 feet of temporary construction impact along the asphalt
trails, and potential cxcavation for utility piping/tic-in.
Within the ST overlay area, the following are proposed:
. The Northeast Development Node with its associated restroom, maintenance
storage building, pavilion, parking, stormwater treatment areas, landscaping, and
ancillary facilities.
. Passive park amenities such as recreational multipurpose pedestrian/bicycle trails,
boardwalks, associated shade structures, and lighting.
. Fishing platform.
. A water quality treatment facility to enhance water quality from stormwater runoff
along Golden Gate Parkway.
. Utility piping for water, sewer, and stormwater.
. Pedestrian bridge.
. Exotic plant removal.
The design of the project has minimized wetland impacts by locating the parking area
within wetlands of poor quality as close to Golden Gate Parkway as possible - discussion
Page 9 of It
Gordon River EAC Staff Report- May 4, 2011
above (B.2. Wetlands). The overall proposed GRGP project includes over 100 acres of
undeveloped upland and wetland habitats, including a 22.2 acre preservation area. As a
result of the proposed project, approximately 91% of the ST overlay area will remain
unaltered except for the removal of exotic plants. Therefore, staff is in agreement with
the applicant in stating that "the project will achieve the conservation goals envisioned
with the original designation of a general conservation ST Overlay in this area."
Final action on the site alteration plan requested with the Special Treatment Permit lies
with the Board of County Commissioners.
VII. COUNTY ATTORNEY OFFICE REVIEW:
The County Attorney Office has reviewed the staff report for 1) Gordon River Greenway
Park Rezone PL 2009-25 and 2) Special Treatment Permit PL 2011-677 revised on April
15,2011.
VIII. RECOMMENDATIONS
Staff recommends approval of I) Gordon River Greenway Park Rezone PL 2009-25
and2) Special Treatment Permit PL 201 1-677.
Page 10 of 11
Gordon River EAC Staff Repolt May 4, 2011
PREPARED BY:
~Ib!~
-su MERARA E
SENIOR ENVIRONMENTAL SPECIALIST
COLLIER COUNTY LAND DEVELOPMENT SERVICES DEPARTMENT
--
J CK MCKENNA, P.E.
. ENGINEERING REVIEW MANAGER
COLLIER COUNTY LAND DEVELOPMENT SERVICES DEPARTMENT
REVIEWED BY:
':"\
~"'....., i 1 J. kJ,v ii,
GERALD KURTZ, P.Ii.
MANAGER OF STORMW ATER AND ENVIRONMENT AL PLANNING
COLLIER COUNTY LAND DEVELOPMENT SERVICES DEPARTMENT
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~LOR Z,Jr.,P.l:.
DIRECTOR OF COLLIER COUNTY LAND DEVELOPMENT
SERVICES DEPARTMENT
APPROVED BY:
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NICK CAS ~~ L---/
GROWTH MANAGEMENT DIVISION DEPUTY ADMINISTRATOR
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Page 11 of II
colNer County
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Growth Management Division
Planning & Regulation
Memorandum
To:
Environmental Advisory Council
From:
Mac Hatcher, Senior Environmental Specialist
Date:
April 25, 2011
Subject:
Staff Summary - May 4, 2011 Watershed Management Plan Workshop Update
Objective: An update on the alternative analysis will be presented. Input we have received will be
discussed. In addition to the documents posted on our web pages the Low Impact Development
alternative will consider the standards in the Sarasota County Low Impact Development pro~ram, and
FDEP's proposed state wide stormwater rule draft Applicant's Handbook. The memo on Regulation
Review and AHernatives has been updated. The final draft Watershed plans will not be presented.
General information and support documents for the Watershed Management Plans are available at our
wcb pagc. The "Dischargc Watcr Quantitv" memo was updated and I anticipate having most of the
remaining technical memos posted prior to the meeting. I will update this memo with an email and list
any additional memos added to the web page prior to the meeting.
Considerations: Completion of the WMPs will support objective 2.1 of the Conservation and
Coastal Management Element of the County Growth Management Plan.
FISCAL IMPACT: There are no fiscal impacts at this time.
GROWTH MANAGEMENT IMPACT: Completion of the WMPs will support objective 2. I of the
Conservation and Coastal Management Element of the County Growth Management Plan.
PREPARED BY: Mac Hatcher, Senior Environmental Specialist, Growth management Division
/ Planning and Regulation
PBSJ
Technical Memorandum
To: Mac Hatcher, PM Collier County
From: Moris Cabezas, PBS&J
Peter deGolian, PBS&J
Preston Manning, DHI
Marcelo Lago, DHI
Date: April 11, 2011
Re: Watershed Model Update and Plan Development
Contract 08-5122, PO 4500106318
Element 1, Task 1.1: Surface Water Quantity
1.0 Objective
The purpose of this Technical Memorandum is to present the water quantity results of the Collier
County MIKE SHE/MIKEI I Existing Conditions Model (ECM). This Technical Memorandum
summarizes the predicted water budgets simulated by the ECM and discusses potential issues
identified through the water budgeting process. It addresses the following items:
.
Water Budget Components. This section describes the components used to define
the water budget in MIKE SHE.
.
Surface Water and Groundwater Budgets. This section describes the overall
surface water and groundwater budgets, and the water budgets developed for each
watershed (Figure 2-1).
.
Baseflow and Structure Operations. This section focuses on the distribution of
baseflow contributions within the Golden Gate - Naples Bay watershed. The section
will also evaluate the potential effect of changes in structure operations.
.
Canal Capacity. This section will identify locations water elevations in the canal are
predicted to exceed the top of bank elevation during storm events. This is another
factor that could help define potential changes in structure operations.
.
Conclusions. This section presents the conclusions of these analyses.
PBSJ
Collier County Watershed Model Update
and Plan Development
Figure 2-1. Collier County Watersheds and Coastal WBlDs
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f""oUnioo
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DCoUIiIIMlID$
DCollierWalllf5l1a(j$
DCoUnly8oundary
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o 2 4 Milll$
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2.0 Water Budget Components
A water budget analysis was conducted to understand the distribution of watershed inflows and
outflows. Figure 2.1 is a schematic of the water budget components. As shown, the primary
sources of inflow to a watershed are precipitation and applied irrigation. This water accumulates
on the ground surface as basin storage, runs off as overland flow or infiltrates into the ground.
Overland flow can be evaporated, discharged into the canal, or flow across watershed
boundaries. Water that infiltrates into the soils can be taken up by plants or percolate into the
water table (Surficial) aquifer. This water can then be removed from the Surficial Aquifer by
plant uptake, by moving laterally across the watershed boundary, by pumping to meet potable
water and irrigation needs, or by percolation to underlying aquifers. Any residual water is stored
in the aquifer. Similar processes occur in each of the deeper aquifers.
P8Sl
2
Collier County Watershed Model Update
and Plan Development
Figure 2.1. Schematic of MIKE SHE Water Budget
F'rJY.:lptntiOn
11T1i3ti"r.
T:)ti1 e..ilPOtfi"',Pfilt<in
.
1
+
<~E!~~
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< AaI.JJfer B04Jf'dJr" Flow )
Ptim, for 1m tY.1naroO P\1V5
l...tlSlltu~~Zortf
Intl1tr.ltlon
The components of the water budget are described in further detail below:
Inflows:
. Precipitation: This is water entering the watershed as rainfall. Some portion of
precipitation is intercepted by the vegetative canopy. The rest is applied to the ground
surface.
. Irrigation: This is the sum of all model predicted irrigation applied to the ground
surface in the watershed. This consists of water pumped from the Water Table (Surficial)
and Lower Tamiami aquifers and water applied from external sources such as reuse water
provided by Collier County or the City of Naples.
. Overland Boundary Inflow: This is water that enters a watershed as sheet flow from
adjacent watersheds. This typically occurs during large storm events in the wet season
when water ponded on the ground surface crosses a watershed boundary.
. Aquifer Boundary Inflow: This is groundwater that enters a watershed via subsurface
flow from adjacent watersheds. There are four aquifers in the model, so this component
can be broken in inflows per aquifer layer.
Outflows:
. Evapotranspiration (ET): The ET represents the combined total of direct evaporation
of water ponded on the ground surface or captured in the vegetative canopy and water
transpired from the soils and water table aquifer by plant uptake.
. Runoff: This represents the model predicted amount of overland flow that discharges
into the river and canal network. This component also includes stormwater runoff from
secondary and tertiary urban and agricultural drainage networks that are not explicitly
represented in the model.
. Baseflow: This component of the model represents groundwater inflows to the canal
network.
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3
Collier County Watershed Model Update
and Plan Development
. Pumping for irrigation and potable water supply: This item represents the total
volume of water pumped out of the aquifer system. Some portion of this water is applied
to the ground surface as irrigation. Water pumped for potable water supply is used as
reuse irrigation water or is injected into deep aquifers.
. Overland Boundary Outflow: This is water that leaves a watershed as overland flow
into adjacent watersheds or across the model boundary and typically occurs during large
storm events.
. Aquifer Boundary Inflow: This is groundwater that exits a watershed or the model via
subsurface flow. There are four aquifers in the model, so this component can be broken
in outflows per aquifer layer.
Storage Change:
. This component represents the total change in watershed storage. This includes overland
storage, storage in the unsaturated zone and storage in groundwater.
3.0 Surface Water and Groundwater Budgets
For the water budget analyses, data was extracted from the MIKE SHE/MIKEI I model results
files using a pre-defined Total Water Budget tool in the program. The model results were then
post processed to create water budgets for the entire model study area as well as for each of the
watersheds, Cocohatchee-Corkscrew (CC), Golden Gate Naples Bay (GGNB), Rookery Bay
(RB), and the combined Faka Union, Fakahatchee, and OkaIoacoochee-SR29 (FUFHOK)
watersheds. These watersheds are comprised of aggregated WBID areas.
Water budgets were generated for the model simulation period of January I, 2002 through
October 31, 2007. Budgets were developed for different time periods based on model simulation
data availability. The time periods include:
. Annual: The water budget represents average conditions during the water year. The
budget represents the period from November I - October 31. For example, the 2003
water year is the period from November 1,2002 - October 31, 2003. Water year budgets
were calculated for 2003 through 2007.
. Wet Season: The wet season is defined as July 1 - October 31. Wet season water
budgets were developed for the years 2002 - 2007. This period includes all the wet
seasons incorporated in the model simulation period.
. Dry Season: The dry season is defined as the period from November 1 - June 30. The
2003 dry season represents November 2002 - June 2003. Dry season water budgets were
developed for the years 2003 - 2007.
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4
Coliier County Watershed Model Update
and Plan Development
3.1. Water Budget Results
This section describes the results of the water budget analysis in terms of annual average, wet
season and dry season. In addition, water budgets were prepared for a wet year and a dry year
relative to the average annual conditions. Finally, seasonal water budgets were developed for
each watershed.
3.1.1 Water Budget Results for the Study Area
Table 3.1 shows the annual water year and seasonal water budget components for the study area.
Figure 3.1 shows the average water year budget for the entire study area. Figure 3.2 and
Figure 3.3 show the corresponding average wet season and dry season water budgets. The data
indicate that rainfall during the four (4) month wet season represents about 54 percent of the total
annual amount and that most is lost through ET.
Table 3.1. Annual Water Year and Seasonal Water Budgets for Study Area
~ Infl~... Evapo '..~
~eCIPjte~ rianSDlratttii\~
Drv Season Average
2003 31.10 1.57 24.45 1.65 1.93
2004 24.72 1.81 25.55 1.26 2.28
2005 35.79 1.81 25.08 3.31 2.24
2006 19.45 2.60 25.47 1.22 2.13
2007 17.17 3.50 24.69 0.16 1.06
Average 25.65 2.26 25.05 1.52 1.93
Wet Season Average
2002 21.14 0.31 16.22 1.38 1.85
2003 29.65 0.12 15.67 8.86 3.11
2004 34.72 0.08 16.26 8.70 2.87
2005 33.86 0.08 17.36 10.16 3.50
2006 30.59 0.43 17.17 5.31 2.80
2007 26.38 0.39 17.44 0.83 1.61
Average 29.39 0.24 16.69 5.87 2.62
Annual Averae:e
2003 60.75 1.69 40.12 10.51 5.04
2004 59.45 1.89 41.81 9.96 5.16
2005 69.65 1.89 42.44 13.46 5.75
2006 50.04 3.03 42.64 6.54 4.92
2007 43.54 3.90 42.13 0.98 2.68
Average 56.69 2.48 41.83 8.29 4.71
Cl1anse In
PumplllS StotaSe
2.17 3.15
2.44 .4.45
2.44 4.41
3.27 .9.57
4.21 .7.99
2.91 .2.89
0.63 1.14
0.39 .0.35
0.39 4.53
0.39 .0.51
0.71 3.62
0.71 6.26
0.54 2.45
2.56 2.80
2.83 0.08
2.83 3.90
3.98 .5.94
4.92 .1.73
3.43 .0.18
Runoff and baseflow are important components of the water budget as they represent about 15
and eight (8) percent of annual rainfall (8.3 and 4.7 inches, respectively). In other words, the
volume of groundwater that enters the canal network as baseflow is approximately 36 percent of
the total fresh water discharged into the canal network. It is important to point out that baseflow
PBSJ
5
Collier County Watershed Model Update
and Plan Development
discharges are the result of the construction of the drainage canals that cut into the water table
aquifer.
During the wet period, runoff is about 70 percent of the total contributions to the canal network.
However, in the dry season, the runoff volume decreases to about 44 percent of the total
contribution the canal network. Therefore, the majority of the dry season canal tlow is basetlow.
This is because runoff is highly sensitive to varying meteorological conditions, whereas basetlow
is relatively stable. The ratio of average runoff to average rainfall ranges from 20 percent in the
wet season to 6 percent in the dry season. On the other hand, basetlow (wet season = 2.62 inches
and dry season = 1.93 inches) remains at about 8 percent of rainfall.
Figures 3.2 and 3.3 also illustrate the seasonal variations in pumping and irrigation. As
expected, pumping and irrigation demand during the dry season represents about 85 percent of
the annual water budget for these two items.
Finally, the water budget also includes watershed storage. As shown in Figures 3.1, change in
storage as an annual average is negligible. Figures 3.2 and 3.3 show that about 2.5 inches of
storage is lost in the dry season, but that volume is recovered in the wet season. This indicates
that, at least during the simulation period 2002 - 2007, hydrologic characteristics of the study
area did not worsen, although no recovery is apparent.
PBSI
6
Collier County Watershed Model Update
and Plan Development
60
50
.. 40
.
~
v
& 30
~
~
a. 20
.
0
10
0
Figure 3.1. Average Water Year (2003 - 2007) Water Budget
.
-
8Mefl,;.,:..t.,
P:i"er
Outflows
-
Basdl,,'.\h.
Ri'.n
Outflows
-
PUPlping
I
I
i
!
i
>tN~ge (h"'l1g~ I
I
Storage
Figure 3.2. Average Wet Season (2002 - 2007) Water Budget
I
-
-
---1
!
i
I
!
I
,
,
I
~I
PI,If'lF'lng :,tQri:lge (h1>ng~ i
60
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.
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v 30
~ I I
~ 20
Q.
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0 10
0 - - - -
-10
60
50
..
. 40
'5
:f 30 I
~
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a. 20
.
0
10
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Pr~(ipit;,ti('n
Pre<iplt~i~m
Irrlg<rl:ior\
E'>'llIN
Tran~plr;,ti,'ri
Run.:,ff
Ba~~fk,,; tc'
Ri',er
I
St",rage J
Figure 3.3. Average Dry Season (2003 - 2007) Water Budget
Preclplt;.ort:lon
Irrh::i'ltiNI E',,~po
Tran~plratic,n
PUIi':,{f
Pumping teorl'lgeChlln\',e
Outflows Storage
Inflows
Irrig<rti':.n E,.;!ll"~
Tran~plrati.;.n
Rl.In,~ff
P8SJ
Inflows
Inflows
7 Collier County Watershed Model Update
and Plan Development
To assess the system characteristics during critical conditions, water budgets were developed for
both the driest dry season and the wettest wet season in the simulation period. Figure 3.4 shows
the results of the 2007 dry season (November 2006 through June 2007). Total precipitation
during this period amounted to about] 7 inches, which is about 33 percent less than the average
dry season rainfall for the entire simulation period. Figure 3.5 represents the extremely wet 2004
rainy season (July through October 2004) when Florida experienced three hurricanes in less than
45 days. Total rainfall accumulated during that season was almost 35 inches, which is about 20
percent more than the wet season average for the model simulation period.
Results of the analysis confirm that the change in runoff volume is much larger than the change
in precipitation. During the 2007 dry season, a 33 percent reduction in precipitation from the
period average resulted in an approximately 90 percent reduction in runoff volume. Similarly,
the 20 percent increase in precipitation during the 2004 wet season resulted in an about 50
percent increase in runoff volume. As stated previously, base flow is not affected as drastically as
runoff volume. The change in baseflow contribution is small during extremely wet conditions as
demonstrated by the 10 percent increase from average during the 2004 wet season. The impact is
more severe during dry weather conditions when it was reduced by about 50 percent from
average. It is important to point out that this also indicates that fresh water flows in the canal in
the 2007 dry conditions was almost exclusively baseflow.
The results of the annual and seasonal water budgets indicate that the management of both runoff
and baseflow are key to reducing the volume of water discharged to the estuaries. During the dry
season, the reduction of baseflow to the canal network appears to be the more critical issue. It
should be noted that structure operations are important to managing both discharge and baseflow
in the canal network.
During extreme dry weather, irrigation and pumping also increase substantially, accompanied by
a substantial reduction in watershed storage. Similarly to the annual average analysis, irrigation
and pumping are drastically reduced during extreme wet weather conditions and the watershed
storage is quickly recovered.
P8SJ
8
Collier County Watershed Model Update
and Plan Development
Figure 3.4. 2007 - Driest Dry Season Water Budget
60
\0
40
~ lO
~
~ lO
1>
. I
" 10
0
.'0
Pr.~iritlltic'n
I
-
-
Irri~!lti"n E"'lIP".TrM~lm1f:i"', Run.,ff
Ba::.flo,.-.\"RiiH
Punptni
~tur~i~ Ch,.,,~.
Outflows
Figure 3.5. 2004 - Wellest Wet Season Water Budget
60
\0
40
.
. I
-5 30
:i
~ '0
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.
" 10
0
-10
~rHlprti'tk."
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B,,~"fln".'t,' p",u
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~tor~ie (han~.
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3.1.2 Water Budget Results by Watershed
A verage water year and seasonal water budgets were also generated for each of the watersheds in
Collier County. As described for the entire study area, the majority of the precipitation is lost to
ET, which ranges between 50 and 60 percent in the wet season for all watersheds. During the dry
season, ET losses equal precipitation in all watersheds except Golden Gate - Naples Bay, where
ET is about 80 percent of precipitation. This is due to the high level of watershed urban
development, as water is quickly routed to the drainage network.
Cocohatchee-Corkscrew Watershed. The budgets for the Cocohatchee-Corkscrew watershed
are shown in Figures 3.6 - 3.8 and in Table 3.2. Model results indicate that the annual average
runoff volume is approximately 14 percent of rainfall. Most of the runoff comes from urban and
agricultural development. As an example, in the 2003 wet season results indicate that runoff was
more than nine (9) inches. Of that, 8.5 inches carne from urban and agricultural development.
PBSJ
9
Collier County Watershed Model Update
and Plan Development
Figure 3.6. Average Water Year Budget - Cocohatchee-Corkscrew Watershed
6S
"
-
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~"'''HI~fl
Infl,,,_,
Inflows
-
-
A'lUH'., [d'p" ~lJ~oh
8~"nJ.., T,..,,,,,,,,,o,,,,
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.
-
-
.
A~uii.,
6"un.j,,,,,
Q"tfl<.
-
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Ch,.,(e
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Figure 3.7. Average Wet Season Water Budget - Cocohatchee-Corkscrew Watershed
"
.
135
125
.
o
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Pr,,,pJtot,,,,, IITIIl;!!;"'"
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25.00
20.00
IS.00
10.00
5,00
0.00
P...,......
e.,......,Il,.., P","ping
Outflows
Figure 3.8. Average Dry Season Water Budget- Cocohatchee-Corkscrew Watershed
~':i.OO
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25.00
.
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Inflows
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PBSJ
20,00
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10
Collier County Watershed Model Update
and Plan Development
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Runoff flow contributions from natural areas are small because the majority is stored in the
Corkscrew Swamp. In addition, there is a large component of overland runoff flow that leaves
the Cocohatchee-Corkscrew watershed and enters the Golden Gate-Naples Bay, OkaIoacoochee-
SR 29, Fakahatchee, and Faka Union watersheds during large rainfall events due to the little
difference in elevation at the watershed ridges. In terms of baseflow, the amount relative to
runoff is only half of that computed for the entire study area. This can be attributed to the low
density of canals in the watershed.
Golden Gate-Naples Bay Watershed. The water budgets for the Golden Gate watershed are
shown in Figures 3.9 - 3.11 and in Table 3.3. The most important feature of this watershed is
that baseflow is the primary source of water to the canal network. It often exceeds 70 percent of
the canal flow during the dry season. This can be attributed to the density of canals throughout
the drainage area. Reducing baseflow to the canal network could have a significant effect on the
volume of water discharging to the Naples Bay Estuary.
Runoff exceeds 19 percent of rainfall and occurs primarily during the rainy season. As in the
Cocohatchee - Corkscrew watershed, most of the runoff is from urban development close to the
coast. The volume of water leaving the watershed via overland and aquifer flow is low and is
directly influenced by the presence of the canal network that drains the Surficial Aquifer and
directs water to the estuary systems.
Rookery Bay Watershed. The Rookery Bay watershed is diverse with urban development
located west of the Henderson Creek Canal. The central portion of the watershed is mostly
natural and consists of the Henderson Strand and portions of the Picayune Strand State Forest.
The southeast portion of the watershed is agricultural. In general, the percentage of runoff
relative to precipitation (I I percent) is low compared to the other watersheds. The low runoff
value is most likely associated to the lack of development in large parts of the watershed.
The seasonal water budget results shown in Figures 3.12 - 3.14 and Table 3.4 indicate that
surface runoff makes up 60 percent of canal flow during the wet season. However, during the
dry season, baseflow contributions often exceed 70 percent of canal flow. Wet season runoff
occurs primarily from the urbanized and agricultural areas; while dry season baseflow
contributions occur primarily in the Henderson Creek Canal.
P8Sl
13
Collier County Watershed Model Update
and Plan Development
Figure 3.9. Average Water Year Budget - Golden Gate - Naples Bay Watershed
ss
1---1
I
65
"
.
.
13s
t 25
.
o
15
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PrHlrrt>;l:l~n Irriilw~n O,."I""d
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Inflows
Outflows
Figure 3.10. Average Wet Season Water Budget - Golden Gate - Naples Bay Watershed
~'-i,OO
~o,oo
.
I
I I
-
.
I
I
-=:~
Store,.l
25..00
20.00
15.00
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Inflows
Outflows
Figure 3.11. Average Dry Season Water Budget - Golden Gate - Naples Bay Watershed
35.00
lO.DO
15.00
15.00
-
-
10.00
000
-
-
.
.
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10.00
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StQr. .
Inflows
Outflows
PBSI
14
Collier County Watershed Model Update
and Plan Development
Figure 3.12. Average Annual Water Budget - Rookery Bay Watershed
"5
"
45
.
~ 35
I
;; 15
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,
Pr"ipotllt""11 Irntal.';." O.".,I~nd
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35.00
Figure 3.13. Average Wet Season Water Budget - Rookery Bay Watershed
30_00
25.00
20.00
15,00
10.00
').00
0,00
P""ip_o
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-
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Figure 3.14. Average Dry Season Water Budget- Rookery Bay Watershed
n.ou
3000
15-00
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15.00
10_00
500
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-
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rrngotio" O"_~~""""f)' A~"IIo,S,"rdaIy ...o.r"""'rolI<I1 _t>R~or h_~1I>RI,tf ""~~ O"n"I'I(UO""*1 A_rS._...,
inI"", ..,"" ,,,.1'0., 0""""
Stor. .
Outflows
P8Sl
15
Collier County Watershed Model Update
and Plan Development
Faka Union, Fakahatchee, and Okaloacoochee-SR29 Watersheds. The water year and
seasonal water budgets for the Faka Union, Fakahatchee, and Okaloacoochee-SR29 watersheds
are shown in Figures 3.15 - 3.17 and in Table 3.5. There are a large percentage of agricultural
lands in the northern portion of the Fakahatchee and Okaloacoochee-SR29 watersheds; whereas,
the northern part of the Faka Union watershed includes rural residential areas. The remainder of
the watershed consists of wetlands or other natural areas; however, portions of the Golden Gate
Canal network drain large portions of the natural areas in the southern Faka Union watershed.
In the wet season, basefIow in these watersheds is equal to approximately 120 percent of runoff,
but during the dry season, the volume of basefIow is more than eight (8) times that of runoff.
The model results indicate that basefIow occurs primarily in the Faka Union watershed, although
there are basefIow contributions to the State Road 29 Canal in the Okaloacoochee - SR29
watershed. It is expected that the Picayune Strand Restoration Project will greatly reduce the
volume of basefIow in these combined watersheds.
The water budget results indicate a slight loss in stored water over the simulation period. This is
most likely attributed to the high basefIow contributions to the canal network in the Faka Union
watershed, although groundwater pumping for potable water supply and agricultural irrigation in
the northern parts of the watershed may contribute to loss of water.
PBSJ
16
Collier County Watershed Model Update
and Plan Development
Figure 3.15.
6'
55
4~
.
-5 3'
~
of lS
~
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0
1S
-
Average Water Year Budget - Faka Union, Fakahatchee
and Okaloacoochee-SR29 Watersheds
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Figure 3.16. Average Wet Season Water Budget - Faka Union, Fakahatchee
and Okaloacoochee-SR29 Watersheds
1\.00
10.00
15.00
10.00
r.. "'~""-"i
i
15,00
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1ritI... lr1ft.ow ~.."" ~O~
Inflows Outflows Stor_i_ J
. - I . I - -
10.00
5.00
000
Figure 3.17.
Average Dry Season Water Budget - Faka Union, Fakahatchee
and Okaloacoochee-SR29 Watersheds
15.00
1000
1500
1000
15.00
10,00
500
000
-5.00
.
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.
Prac",Won ~n 0........8_" A,!"ilor8o<<"'-r "".-1'""'1'_ R"""""'RilOf e._,,_ P__pio; ()u.t1.....~o..-.ltry ~..,.,g~.~ '""il'iI\SbIg'
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Inflows
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StOI"l II
P8SJ
17
Collier County Watershed Model Update
and Plan Development
4.0 Baseflow and Structure Operations
As discussed previously, the water budget discussion indicated the relative importance of
baseflow in the individual watersheds. Figures 4.1 and 4.2 show the average baseflow
contribution to the individual drainage features. The maps indicate that the wetland area in the
OkaIoacoochee Slough, Camp Keais Strand, and the Corkscrew Swamp provides groundwater
recharge (negative baseflow) on a year round basis. The maps also indicate that significant
baseflow contributions to the canal network occur especially in the Golden Gate and Faka Union
watersheds. These maps are consistent with the water budget results discussed in Section 3.0.
As also indicated previously, it is expected that completion of the Picayune Strand Restoration
Project will greatly reduce the baseflow contributions in the Faka Union watershed; therefore,
the remainder of this discussion will focus on baseflow and structure operations in the Golden
Gate - Naples Bay watershed.
A comparison of baseflow during the wet and dry seasons in the Golden Gate - Naples Bay
watershed indicates that substantially more baseflow occurs during the wet season than during
the dry. The water budget analysis showed that 8.5 I inches of basetlow occurs in the Golden
Gate ~ Naples Bay watershed during the wet season compared to 4.27 inches during the dry
season.
Figure 4.3 and Figure 4.4 show the average wet season and dry season baseflow contributions
in the Golden Gate - Naples Bay watershed. It is interesting to note that during the dry season,
recharge (negative baseflow) is predicted to occur in several locations immediately upstream of
operable gates, or near shallow potable water supply well fields. The greatest volume of dry
season recharge occurs immediately north of the CR951-1 structure which includes a pump to
divert water from the Golden Gate Main Canal into the CR95 I Canal. The results shown in
Figure 4.4 suggest that water pumped into the CR951 Canal is returning to the Golden Gate
Main Canal via baseflow. Groundwater recharge influenced by pumping for potable water
supply is also observed in the dry season near the GG-4 structure.
The maps also show that the highest predicted baseflow values occurs immediately downstream
of the operable structures and that baseflow decreases along the canal toward the next
downstream structure. This is most evident along the Cypress Canal segment between structures
CYP-I and GG-3. This pattern of baseflow along the length of a canal segment is the result of
staging water at different elevations upstream of each structure.
It should be noted that the ECM was setup to replicate the standard operating rules defined by
the SFWMD for each structure. These rules primarily rely upon the water levels upstream and
downstream of the individual structures and are designed to stage water at different elevations
for the wet and dry seasons and may contribute to the seasonal difference in baseflow. During
the wet season, the structures are operated to stage the canals at an elevation that is
approximately one foot (1 ft) lower than the dry season. The lower elevation, paired with higher
groundwater elevations due to rainfall, leads to an increase in basetlow.
P8SI
18
Collier County Watershed Model Update
and Plan Development
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Figure 4.5 shows the typical relationship between basetlow and the difference in groundwater
and canal water surface elevation in the Cypress Canal. The data clearly indicates that managing
canal stage to match groundwater elevations is important to reducing the volume of basetlow
entering the canal network. lt is our understanding that the existing structures are physically
limited in their ability to stage water at a higher elevation within the canal network. It is
recommended that the design of new and replacement structures consider seasonal groundwater
head elevation data. The ability to more closely match canal stage and the groundwater head
elevation will have long-term benefits to reduce basetlow to the canal network.
Figure 4-5. Relationship of Baseflow and (Head - Stage) Elevation Difference
Cypress Canal Upstream of GG-3 Structure
0.6
y = 0.1604x + 0.0033
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5.0 Analysis of Canal Conveyance Capacity
Model simulation results using the SFWMD design storm events were conducted to assess the
conveyance capacity of the existing canals. To evaluate canal capacity, the maximum predicted
water surface elevation at each cross-section in the canal was compared to the top of bank
elevation at those locations. The water level is defined as "Out of Bank" if the predicted
elevation is higher than that at one or both of the canal banks.
An important simulation parameter is the establishment of the model's initial conditions. For this
analysis it was assumed that the water elevations in the canals prior to the beginning of the storm
were those that occurred in September 4, 2004, after Hurricane Charley and prior to Hurricane
Francis. That assumption is consistent with numerous recent H&H& studies in Florida because it
is representative of a historical period when large back-to-back precipitation events occurred.
Figure 5.1 shows the locations where overtopping is predicted to occur during the 5-year, 72-
hour hour storm event. The results for the 10-, 25-, and 100-year storm events are very similar
indicating that canal overtopping would occur at the low lying areas. Most of the overtopping
PBSJ
21
Collier County Watershed Model Update
and Plan Development
occurs in wetland areas where inundation is expected to occur. However, the results also
indicate areas along the Cocohatchee Canal and within the Golden Gate -Naples Bay and
Rookery Bay watersheds that may be subject to flooding conditions due to limited canal
conveyance capacity.
The SFWMD has established emergency canal management protocols that require that the
structures be opened and the water levels in the canal network be lowered prior to large storm
events to provide additional canal conveyance to mitigate the risk of flooding. Therefore, the
conditions depicted herein may be conservative. However, overall results show that future
development would worsen an already difficult condition unless management strategies are
established to mitigate flooding risks.
Locations for the 5- r, 72-hr Storm Event
Legend
, .--1
, CJCollier\l\\3tersheds
--..'~alnageNet\Alork
5-yr/72-hr storm
In BanI<
PBSJ
22
Collier County Watershed Model Update
and Plan Development
6.0 Conclusions
Several conclusions are drawn from the water budget analysis.
. Critical water budget processes are storm water runoff and groundwater discharges to the
canal network through baseflow.
. Annual and seasonal average storm water runoff volumes are greatly influenced by the
amount of precipitation. Relatively small variations in precipitation results in large
changes in the volume of runoff.
. Baseflow contributions increase with canal density. Baseflow to the canal network in the
Golden Gate and Faka Union watersheds make up approximately 55 percent of canal
flow during the average year, and as much as 85 percent of canal flow during the dry
season. Reducing baseflow would have a significant effect on the volume and timing of
discharge to the estuary systems.
. The seasonal water budget analysis indicates a net balance in watershed storage over the
simulation period. Annual losses in storage occur during the dry season and are
associated with high baseflow contributions and with pumping from the Surficial and
Lower Tamiami Aquifers to meet potable and irrigation water supply needs.
. Collier County and the SFWMD should consider seasonal groundwater elevations to
establish updated seasonal controlled water levels in the canal network. Additional
flexibility to raise the stage in the canals and reduce baseflow contributions should be
considered when designing new or replacement control structures.
. Lowering the water surface in the canal network prior to large storm events is an
important management tool to provide storage within the canal network and to mitigate
flooding risks in Collier County.
. The existing conveyance capacity of the canal system is limited. Conditions would
worsen in the future unless management actions are implemented to control for the
impact of new development.
PBSJ
23
Collier County Watershed Model Update
and Plan Development