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HOME OF PELICAN ISLAND
SPECIAL CITY COUNCIL MEETING
COLLIER CREEK IMPROVEMENT PROJECT
Called by Council Member Wolff
AGENDA
WEDNESDAY, OCTOBER 3, 2007 - 6:00 PM
CITY COUNCIL CHAMBERS
1225 MAIN STREET, SEBASTIAN, FLORIDA
AGENDA ITEMS MAY REINSPECTED /N THE OFFICE OF THE CITY CLERK
1225 MAIN STREET, SEBASTIAN, FLORIDA
Individuals will address the City Council with respect to agenda items immediately before deliberation
of the item by the City Council -time limit five minutes where public input allowed
CALL TO ORDER
2. PLEDGE OF ALLEGIANCE
3. ROLL CALL
4. SPECIAL MEETING ITEM
A. Collier Creek Project Staff Update (City Engineer Information from 8/22/07 Meeting)
B. Council Discussion and Direction
5. ADJOURN (All meetings shall adjourn at 10:30 pm unless extended for up to one half hour by a majority
vote of City Council)
HEARING ASSISTANCE HEADPHONES ARE AVAILABLE /N THE COUNCIL CHAMBERS FOR ALL
GOVERNMENT MEETINGS.
City Council tvleetir~gs ire Scheduled for Live Bro~dc~st on Cc~cast Ch~anne125
ANY PERSON WHO DECIDES TO APPEAL ANY DECISION MADE WITH RESPECT TO ANY MATTER
CONSIDERED AT THIS MEETING WILL NEED A RECORD OF THE PROCEEDINGS AND MAY NEED TO
ENSURE THAT A VERBATIM RECORD OF THE PROCEEDINGS IS MADE, WHICH RECORD INCLUDES THE
TESTIMONY AND EVIDENCE UPON WHICH THE APPEAL IS TO BE HEARD. (286.0105 F.S.)
IN COMPLIANCE WITH THE AMERICANS WITH DISABILITIES ACT (ADA), ANYONE WHO NEEDS A SPECIAL
ACCOMMODATION FOR THIS MEETING SHOULD CONTACT THE CITY'S ADA COORDINATOR AT 589-5330 AT
LEAST 48 HOURS IN ADVANCE OF THIS MEETING.
TO: Members of the Sebasti y Council
FROM: AI Minner, City Mana r /
RE: SPECIAL MEETIN - LIER'CREEK
DATE: Friday, Septemb 8, 2 7
Attached with this correspondence is an update memo from Dave Fisher on the Collier Creek
Project and the Special Meeting packet prepared by the Clerk's Officer.
The packet contains the same information provided to Council when I had this item placed under
my matters at the August 22, 2007 Regular Meeting. In short, these materials summarized that
the selected option of construction of the canal with rip-rap is still considered the best alternative.
In addition to these materials, Dave Fisher has provided an update. In a-mail from, dated
September 28, 2007, Dave has provided information to Council on Canal activities. Basically, the
project is now ready to be let for bid by October 23`d. In addition, we have also received
notification that the City will receive the EPA/FDEP 319 Grant in the amount of $500,000 to help
finance this project.
At the Special meeting, I anticipate of short report presented by Dave Fisher. This report will
again update Council on the project and visit the work we did over the summer to demonstraight
that the rip-rap alternative is still the best construction processes. Also, at the meeting will be
CDM. In closing the Special Meeting, I have placed under item 4.6 "Council Discussion and
Direction". Here I anticipate any questions, discussion and consideration of changing the course
of the project that Council may want to entertain.
As always, should you have any questions on this or any other matters, please feel free to
contact me at your earliest convenience.
Jeanette Williams
From: David Fisher
Sent: Friday, September 28, 2007 10:37 AM
To: Alfred Minner
Cc: Sally Maio; Jeanette Williams
Subject: Collier Canal Dredging Project Update
AI --
As discussed, following is a summary update of recent items regarding the Collier Canal Dredging Project.
Water Quality Sampling
City has recently taken samples in and adjacent to the canal for water quality testing. Testing and analysis of those
samples corroborate the estimated loadings in the Watershed Management Model water quality estimates previously
submitted to FDEP. City will continue to monitor the water quality in the Collier Canal and Twin Ditches on an ongoing
basis.
Value Engineering -Design of Rip-Rap Slope Cross-Sections
Value engineering discussions and analysis have determined the cross-section of the rip-rap side slope can be
revised to eliminate the intermediate layer of gravel between the fabric lining and the rip-rap rock thereby avoiding the
need to draw down the water level during construction. This measure will enable faster, more inexpensive
construction and avoid potentially bothersome drawdown pumping operations.
Asbestos
An ongoing review of the asbestos issues indicates "the chances that asbestos is present in the sediment in amounts
that could possibly be harmful are extremely low, if not impossible. The asbestos report indicated that the [bulkhead
material -chrysolite] contained 10% asbestos. The report also indicated that 1 % is the EPA threshold for asbestos-
containing material. Therefore, the [total amount ot] sediment that is excavated must contain 10% asbestos [bulkhead
material -chrysolite] to contain 1 % asbestos overall. [But] the volume or mass of [bulkhead material] ... is [relatively]
insigniifcant compared to the volume or mass of [total] sediment that will be removed. ... Although there is little, if any,
chance that the sediment could contain harmful amounts of asbestos, it is prudent to recommend testing to prevent
potential issues.... {The expectation is] that nothing will be found. The analytical results coupled with a calculation of
the amount of asbestos [bulkhead material] it would take to comprise 10% of the sediment should easily satisfy even
the most cautious mother whose child might play in that pile of dirt" [even if allowed, which it won't be].
• EPA /FDEP 319 Grant for $500,000
City has received confirmation it is being awarded a $500,000 matching funds grant for the project. The grant contract
agreement can be in place within 6 weeks following confirmation of the project scope (say by early December) and
allow the City to be immediately reimbursed for anything spent on the project since 1 October 2006 (about $60,000)
with ongoing reimbursement going forward for any further project expenditures up to an overall total of $500,000. A
significant condition of the grant is an ongoing water qulaity testing program - onging for the next 3 to 4 years at least.
• Out to Bid Schedule
Project is currently on track to go out to bid by 23 October 2007.
• Pedestrian Bridge over Collier Canal at Hardee Park
Detailed plans are now going forward to for the design and construction of a long-span steel frame pedestrian bridge
adjacent (but not connected) to the Barber Street road bridge at Hardee Park. This bridge can be in place within the
next 9 months and would pose no conflict with canal navigation or impending project construction operations.
-- Dave Fisher
Collier Canal Stormwater Retrofit Project
Review of Status
16 August `07
Introduction
The Collier Canal Stormwater Retrofit Project, aka the Collier Canal Dredging Project, is now
ready for final evaluation prior to soliciting bids for construction. This purpose of this report is to
update and summarize the status prior to the construction bid process.
Background
Since construction of the City's canal system in the 1960s, no continual maintenance dredging
program has been pertormed. This has resulted in severe deposition and erosion problems that
have led to a degradation of water quality both in-canal and of discharge to downstream areas,
particularly in the approximately one-mile stretch of Collier Creek canal from CR-512 running in a
northwesterly direction to the control structure near Hardee Park. Further, there is extensive
bulkhead failure occurring along much of the perimeter of that particular stretch of the Collier
Creek canal
To remedy the problems of the canal and to restore the area to a system that functions as it was
originally intended, the City proposes to do the following.
• Dredge the canal to lower the bottom elevation approximately 8.5 feet to increase the
permanent pool storage volume and improve water quality of the stormwater runoff
discharged to the St. Sebastian River.
• Stabilize the existing vertical side slopes to prevent erosion of the adjacent land into the.
detention facility by retrofitting the existing canal bulkheads with fabric and stone rip-rap
on 3:1 side slopes extending down to two feet below normal water level.
• Adjust the water control structure at the downstream end of the canal near Hardee Park
to effectively control the discharge of runoff subsequent to storm events.
Current Status
In the course of planning, designing, and permitting the project over the past several years, the
following items and guidelines have been established.
• The current budgeted amount for the project within the City's Stormwater Capital
Improvement Bond Funding is $3,513,000 of which approximately $466,000 has been
spent to date in the planning, design, and permitting for the project. There is a $500,000
grant now in process and expected to be awarded for this project within the next few
weeks from FDEP through the EPA.
The proposed perimeter /side slope stabilization measures have been discussed and
reviewed extensively. The current design calls for rip-rap cladding on the perimeter side
slopes as opposed to sod or new vertical bulkheads. A further recent engineering
investigation into the viability of two specific alternatives, (1) a sodded side slope
scenario and (2) a new vertical bulkhead combined with a 20-foot natural horizontal
"ledge" along the interior perimeter on each side of the canal, produced findings that
generally indicate: (1) the sodded side slope alternative is feasible from a construction
and maintenance point of view but the intended improvement to water quality is
significantly diminished; and (2) the scenario involving a new vertical bulkhead combined
with a 20-foot ledge on each side provides significantly enhanced water treatment and
16 August `07
Pg 1 of 5
DWF
Collier Canal Stormwater Retrofit Project
Review of Status
16 August `07
quality but cannot be recommended as a responsible alternative because of a very low
factor of safety in the resulting slope stability from the ledge downward into the dredged
area. [See the attached memo /report from CDM regarding this further investigation
and comparison of perimeter /cross-section options.] These findings support going
forward with the current design calling for rip-rap on the side slopes.
• Permits now in hand from St. Johns River Water Management District (SJRWMD) and
the Army Corps of Engineers (ACOE) reflect approval for the rip-rap side slopes and
also call for:
• The proposed dewatering area for dredged material to be located on a portion of
Hardee Park;
• Wetland mitigation measures in the area of Hardee Park; and
• A detailed and pre-approved dewatering program to maintain water quality and
flow in the canal and to protect perimeter /slope stability during construction.
• City policy established and/or stated during project planning and discussion includes the
following items:
• There is to be no special assessment to property owners adjacent to the
retrofitted canal for this project.
• The City accepts the responsibility of maintaining the canal, including its
perimeter within the City right-of-way.
• The original planning criteria for the project of supporting and further establishing
a future curb and gutter program in the area of the canal is now abandoned.
There is no longer any plan for such a curb and gutter program.
• The project may go forward in phases as available funding permits.
• Construction of the project will be contracted out through a controlled bid process
to determine the best responsible, responsive contractor with the lowest
proposed construction cost. The construction contract will include major
insurance requirements, payment and performance bonds, and provisions for
liquidated damages.
• The construction program will call for close monitoring and inspection and will
include an important component for ongoing information, communications, and
relations dealing with concerns of property owners adjacent to and impacted by
the retrofitted area(s). Such concerns will likely include existing pools and docks,
clearing of trees and vegetation, irrigation lines drawing water from the canal,
handling of existing bulkhead material, construction access and traffic, noise
levels and temporary disruptions due to construction operations, and restoration
of top of slopes to an acceptable condition at the end of construction.
The construction bid process will call for alternative bids for doing the project in
phases or combined phases. The extent of the work to be done under the initial
construction contract will be determined at least in part by the lowest acceptable
bid package. A first phase of construction, at a minimum, will include mitigation
and the retrofitting of Collier Creek canal from CR-512 to the Fleming Street
bridge.
16 August b7
/~V~ Pg2of5
DWF
Collier Canal Stormwater Retrofit Project
Review of Status
16 August `07
The construction bid package and construction management program will call for
detailed specific programs and methodology for: dewatering operations in the
canal work areas; handling, containment, and dewatering of dredged material;
required mitigation; handling of asbestos and other problematic materials; noise
and traffic control; and addressing property owner concerns in a proactive, timely
manner.
• Criteria in determining approval of a construction contract package will include
the possibility of applying savings in construction costs on this project to other
projects in the City's Stormwater Capital Improvement Program that may be
underfunded.
• There are a number of privately owned vacant-lots along the Collier Creek canal
that might be utilized for construction access and operations. Such tots may be
acquired or leased by the City under agreement(s) with the owners.
• The City is now going forward with the construction of a new pedestrian bridge
that will span the Collier Creek canal on the north side of the Barber /Lake Street
bridge at Hardee Park. Planning, design, and construction of this bridge will be
done simultaneously with going forward with the Collier Creek Canal Retrofit
Project.
Conclusion /Recommendation
Staff now recommends that going forward with the Collier Canal Stormwater Retrofit Project as
designed, permitted arid previously authorized by Council is now possible and timely. To that
end, arrangements are being made to have the project out to bid by October 2, 2007.
Construction bids can be ready for initial review by the City on November 13, 2007. Should
Council decided not to move forward with this project or modify its scope; it is recommended that
the items detailed in this report be discussed in a Special Meeting. Also note that any change in
the project's scope will delay the project by approximately 6 months.
16 August ~7
Pg3of5
DWF
Collier Canal Stormwater Retrofit Project
Review of Status
16 August `07
Outline of Options for Perimeter /Cross-Sections
Option Estimated Some Some
Range of Cost Advantages Disadvantages
Going Forward
(A) Rip-Rap cladding on side
slo es. Now designed and permitted and Access to /from canal waters
... Scenario 1: From CR-512 to ready to out to bid for construction becomes problematic.
Flemin Street Bride $1,300,000 by early October with completion
... Scenario 2: From CR-512 to in more than 18 months. This alternative is a "compromise"
a rox.1/2 wa betty. brid es $2,500,000 solution and may not be happily
... Scenario 3: From CR-512 to Likely affordable to do entire canal embraced by all adjacent property
Barber /Lake Street bride $3,800,000 as originally proposed. owners.
... Scenario 4: From CR-512 to
be and Barber St. bride $4,400,000
(B) Sodded side slopes.
Provides better, more gentle Significant reduction in water
... Scenario 1: From CR-512 to $1,500,000 access to canal waters. treatment and resulting quality.
Flemin Street Brid e
... Scenario 2: From CR-512 to $2,400,000 Likely to be more inexpensive Will take additional design and
a rox.1/2 wa betty. brid es overall than rip-rap alternative if permitting but is not likely to save
... Scenario 3: From CR-512 to $3,300,000 entire canal project is done. significantly more entire canal'is
Barber /Lake Street bride not done.
... Scenario 4: From CR-512 to $3,700,000
be and Barber St. bride High level of maintenance req'd.
(C) New vertical bulkheads
with 20' wide ledge on each
side inside canal ROW. Provides vertical bulkheads Cannot be recommended because
... Scenario 1: From CR-512 to $2,100,000 combined with "ledges" suitable for of too low factor of safety for slope
Flemin Street Bride flora and fauna. stability downward from the ledges
... Scenario 2: From CR-512 to $3,300,000 into the dredged area.
a rox.1/2 wa betty. brid es Is likely to be preferred by adjacent
... Scenario 3: From CR-512 to $6,200,000 property owners to alternatives Probably not enough funding
Barber /Lake Street bride involving side slopes (either rip-rap available to do the entire canal
... Scenario 4: From CR-512 to $7,200,000 or sod). area initially proposed.
be and Barber St. brid e
(D) New vertical bulkheads
without any ledge inside canal
ROW. Provides good water quality and is Relatively expensive and will
... Scenario 1: From CR-512 to $2,900,000 likely the preferred scenario by require additional design and
Flemin Street Bride adjacent property owners. permitting.
... Scenario 2: From CR-512 to $5,500,000
a rox.1/2 wa betty. brid es Probably not enough funding
... Scenario 3: From CR-512 to $8,700,000 + available to do the entire canal
Barber /Lake Street bride area initially proposed.
... Scenario 4: From CR-512 to $10,000,000 +
be and Barber St. brid e
16 August 07
Pg4of5
DWF
Collier Canal Stormwater Retrofit Project
Review of Status
16 August `07
RECAP -RANGE OF ESTIMATED FURTHER COST FOR VARIOUS ALTERNATIVES
Scenario 1: Scenario 2: Scenario 3: Scenario 4:
From CR-512 to From CR-512 to From CR-512 to From CR-512 to
Plan Fleming Street approx. half-way Barber /Lake beyond Barber / Comment
Bridge between bridges Street bridge Lake bridge
1250 LF 3000 LF 5000 LF 5900 LF
Now permitted
f
(A) Rip-Rap
cladding on
$3,800,000
$4,400,000 bidding by
early
October (with
side slopes. construction
completion within
18 months).
Additional design
(B) Sodded
side slopes.
$3,300,000
$3,700,000 and permitting
required.
(C) New vertical
bulkheads Cannot be
combined with
20' wide (edge
$2,100,000
$3,300,000
$6,200,000
$7,200,000 recommended
due to low factor
on each side of safety for slope
inside canal stability.
ROW.
(D) New vertical
bulkheads Most expensive
without any
ledge Inside
$5,500,000
$$,700,000
$10,000,000 solution.
canal ROW. (+) (+)
Scenarios 1 and 2 Vertical bulkhead alternatives (Plans
Comment under all Plans (A-D) C and D) likely not affordable for
are likely affordable. Scenarios 3 and 4.
\\
16 August b7
Pg5of5
DWF
CDNI
Memorandum
To: City of Sebastian
From: Doug Moulton, P.E.
Date; August 13, 2007
Subject: Collier Canal Stormwater Improvement Project - Amendment No. 2
The water quality modeling provided previously for the City of Sebastian's EPA 319 grant for
Collier Canal was revised based upon two alternative cross sections. The results of this water
quality. modeling are compared with the original results.
The alternative cross sections are defined as follows:
^ Sodded sideslopes from top of existing walls at 4 foot horizontal to 1 foot vertical to canal
center ("sod"), and
^ Replacement of failing bulkheads with 12 foot wall; maintaining existing canal bottom for
20 feet into channel; dredging 10 feet deep in center of canal only ("hybrid").
These two configurations are shown on Figures 1 and 2, respectively.
The effectiveness of water quality treatment is largely a function of the permanent pool
volume (PPV) (i.e. volume of water below the normal water level (NWL)). Due to the varying
width and depth of Collier Canal along its length, in the original analysis the PPV in both
existing and proposed conditions was calculated using the functionality of AutoCAD. In the
current analysis, as the alternative cross sections have not yet been incorporated into the
design drawings, a simpler method was used- to calculate the volume. The cross sectional area
was calculated based upon Figures 1 and 2 and this was multiplied by the length of the canal
(6,000 feet). Table 1 presents the cross sectional areas, and the residence time in days.
The residence time was calculated by applying the ratio of the alternative PPV to the 14 Day
of PPV as shown on Table 2-5 in the EPA 319 Grant Application. The 14 Day PPV was
calculated to be 66.3 ac-ft.
~3
t)ocumenteode
City of Sebasti,
July 5, 2007
Page 2
Table 1- Cros:
Scenario
Original Propo;
Altemative (rip-
s
Altemative 1 s
Altemative 2
h brid 594 81.8 17.3
Based upon the calculated residence times and the equations presented in Evaluation of
Alternative Stormwater Regulations for Southwest Florida Draf 1 Report (ERD, 2003) the pollutant
removal efficiencies are presented in Table 2.
I~
Table 2 -Removal Efficiencies for Conventional Pollutants
O-fg/nal
Proposed
Altemative
N -a
Alternative
1 so
AftemaBve
2 N
N 46.2% .44.0% 51.3%
Phos horns 62.8% 60.7% 67.6%
TSS 72.0% 69.4% 78.0%
BOD 61.4% 51.8% 82.4%
Malting use of the original Watershed Management Model (WIVIlVI) two additional scenarios
were developed malting use of the removal efficiencies presented in Table 2. The results of
this analysis are presented in Table 3.
As shown. Table 3, Alternative 1(sod) provides a lower level of treatment than the original
configuration (rip-rap). Based upon the calculated residence time, which is 2.2 day less than
the original (rip-rap), this is a reasonable reduction. It is noted; however that there still
remains a significant reduction in the pollutant loading which ultimately will discharge into
Indian River Lagoon.
]n contrast, Alternative 2 (hybrid) provides a greater level of treatment. In this case the
residence time increases from 9.5 to 17.3 days, this provides a significantly more treatment
than either of the other two alternatives.
Doamentcode
City of Sebastian
July 5, 2007
Page 3
Table 3 -Pollutant Load Reduction
BMP's Installed TSS TP TN BOD
Wet Detention I r I r I r 1 r
m
Pre-Pro ect
45,189
518
5,832
19,472
EQ
~ Post-Pro ect 37 214 458 5 327 12 632
Q ~, .
~ .'
. Load Reduction 7 975 60 505. 6840
~
t
~ % Reduction 17.6% 11.6% 8.7% 35.1%
c Pre-Pro ect 45189 518. 5 832 19 472
Post-Pro ect 40,670 484. 5545 15 774
is
Load Reduction 4 518 34 287 3 698
m
a % Reduction 10.0% 8.6% 4.8% 19.0%
~.
Pre-Pro ect 45189 518 5,832 19 472
s
a Post-Pro ect 29 240 399 4 822 5 760
m
~ Load Reduction 15 849 119 1 010 13 712
m
a % Reduction 35.3% 23.0°~6 17.3% 70.4%
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IVlemorandum
To: Jennifer ebster
~,~.'
From: Tom Nichols and Honghua Zhao
Date: 27 June 2007 (revised 13 August 2007)
Subject: Slope Stability Analyses
Two Alternative Designs
Canal Stormwater Retrofit
City of Sebastian, Florida
As requested, we have completed the slope stability analyses for two alternative canal cross
sections proposed by the Owner. These alternatives include slopes that are both steeper and,
shallower than the permitted slope. The proposed alternatives include:
(a) Sodded side slopes from top of existing walls to canal center.
(b) Replacement of bulkheads with 12 foot sheet pile wall; maintaining existing canal
bottom for 20 feet into the channel;-dredging 10 feet deep in center of canal only.
Design Soil Profile
Information from two previous geotechnical reports conducted by Universal Engineering
Sciences was used to develop the design soil profile:
^ Subsurface Exploration & Testing, Proposed Canal Dxedging, January 21, 2005
^ Subsurface Exploration, Proposed Seawall Replacement, July 26, 2004.
The design soil profile and slope stability analysis of the current permitted design was
summarized in the CDM Memo to Jeiuzifer Webster, dated 13 December 2006.
Stability Analysis
The current permitted design includes a 3H: 1V slope starting at EL 8.5 and rising to the top
of the existing pile cap elevation which is approximately EL 19 with a geosynthetic wrapped
riprap protection starting at EL 13.5.
The proposed alternative (a) slopes are 4H: 1V beginning at the canal bottom at EL 8.5 and
rising to the top of the existing pile cap elevation which is approximately EL 19. The proposed
2~
C:\Documenls and Se111ngslnichdstwlDesktoplTlNN-JlW-07-o1.doc
' Jennifer Webster
27 June 2007
Page 2
alternative (b) slopes are 1.5H:1V beginning at the canal bottom at EL 5.5 and rising to EL
13.5 and then connecting to the 20-foot riprap protected slope portion. The sheet pile wall will.
remain with the pile cap at EL 19. For both alternatives, the existing canal bottom is much
shallower and will need to be excavated/dredged to the final shape.
Slope stability modeling was conducted using SLOPE/W, a two dimensional simulation
software package, released by GEO-SLOPE/W International Ltd. (2004). The stability
analyses were first run on the proposed alternative (a) and (b) models assuming the canal
water level and groundwater behind the slope were equal. Additional analyses were made
assuming the canal water Level was lower than the groundwater behind the slope by 1 foot
and 2 feet to simulate potential rapid drawdown conditions. The results of the analyses are
summarized in Table 1.
Table 1
Slope Stability Analyses Results
____ _
Water Table
Factor of Safe
Condition Alternative (a) -Sod Alternative (b) - Hybr7d
15.5 ft 2.08 1.03
;:.NGVD 1929 ;
__ _ _ _
13.5 ft 2.04 0.96
,NGVD 1929.
_-
1 foot ,
1.92
1.Q2
Drawdown
2-foot 1.77 0.$9
Drawdown
Conclusions
A minimum factor of safety of at least 1.5 is generally considered acceptable for global slope
stability. Based on our analyses, the factor of safety of 1.5 was not met by proposed
Alternative (b) -Hybrid for any of the four scenarios presented above. Therefore, this
alternative is not recommended, However, the factors of safety for slope stability analyses for
Alternative (a) -Sod were satisfactory and exceeded the factor of safety of 1.5.
During construction, temporary lowering of the water ul the canal c1n temporarily reduce the
factor of safety. If the proposed Alternative (a) -Sod is selected, it is still recommended that
drawdown occurs gradually and does not exceed 2 feet. Water levels behind the slope will
need to be monitored during conshuction using piezometers and restrictions will be required
on how far the canal water level can be lowered during construction.
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CaDocumanls and SetlingstriicholslwlDesktoplTWN,1LW-0T-01 doc
Jennifer Webster
27 June 2007
Page 3
firosion protection is required for the 4H to 1V slope in Alternative (a) -Sod within the zone
where water level fluchxations will occur.
Closure
These recommendations have been prepared for design of the proposed Collier Canal
Stormwater Retrofit located in the City of Sebastian as understood at this time and described
in this report. The alternative design cross sections provided by Jennifer Webster were used
as a basis for our analysis. This report has been prepared in accordance with generally
accepted engineering practices. No other warranty, express or implied, is made.
C:1Documenls end Selt(ngsVitcholshvl0asktopClWN~.1lW-0T-Ot.doc
23
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{ 1901 HighwayA-f-A, Suite 301
Yero'Beach;"Florida 32963
Celt 772 23:1-4301
fax: 772 231 •.4332
August 16, 200.7
~l'x., David Fisher, P,E,
City Engineer
City of Sebastian
1225 IVI'an.StlAeet
Sebastian, !Florida 32958
Subjeetr Collier Canal Stormwater Reh oft.Project
Slope Stability Analyses ariel Water Quality Modeling
Deax 1klr. Fisher:
CD1~!1 performed slope stability arlaiyses anel evaluated: the water. quality benefits for -two
alternative crass sections, The alternative cross sections are defined as folio°ws:
^ Alternative 1. Sodded sdeslopes from top: of existing walls at 4 foot 11o~~izontai to 1 foot
vertical.to canal center
^ Alternative 2: Replacement of fayling bulkheads with a;12 foot wall; rnaisitairiing existing
canal boftom for 20 feet info channel (and: protecting with xip/rap) and dredging 10 feet
deep rn center of canal :only at a 1.5 to 1 sicleslope
The sIape stability analysis determined that Alternative 1 meets. the acceptable factor of safety
ciite>.~ia; as long as the water level: in fine -canal is moxutored and the drawdown does not
exceed 2 feet.. The .analysis cletex.mincci, that Alternative 2 does not meet the factor of safety
criteria and is not:recoxnrrl:ended. Please see the attached slope stability analysis
rnemorandurn. ,
The water quality modeling shows that the largest pollutant reduction comes fi om
Alternative 2, therefore the slope stability analysis shows this alternative is not feasible.
Altei~iative 1,-shows a reduction aver the existing conditions, however not as large a
reduction as the pe>.znitted cross section (rip/rap). Please see the attached water quality
memorandum.
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consultln .•en ineerin jb1368.doc
9 .9 g • consfruetion • operations
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'Mr. David Fisher, P.E.
August 1f, 2U07
Page 2
T'fte reduction m water quality associated with Alternative 1 may jeopardize grant funding
and: increase x~utigation costs. Further investigation with both St. John's River Water
Management District and The Florida Department of Environmental Protection to deterxr-ine
the potential extent of i~€pact this may have on the project.
'V"ery!trtt~~ ynu~rs;
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~~enrti~cr L. tNe'bster
Camp Dresser & 1VIcKee Ine.
Files 2582=430:56-0~3
ec: Ana I3eMelo, CDI~!I/WPB
Epic Grotlce, CT~1+I/URB
Tom Nielols, ~DIVI/QRL
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