BUILDING STRONG - Siesta Key Association

Report
SARASOTA COUNTY – LIDO KEY
HURRICANE & STORM DAMAGE
REDUCTION PROJECT
Information Presentation
BOCC Joint Meeting
City of Sarasota
Sarasota County
US Army Corps of Engineers
22 October 2013
Sarasota, Florida
Presented by:
Milan A. Mora, P.E.
Jason Engle, P.E.
James LaGrone
Kathleen McConnell
BUILDING
BUILDINGSTRONG
STRONG®®
US ARMY
OF ENGINEERS
| Jacksonville
District
US ARMY CORPS
OFCORPS
ENGINEERS
| JACKSONVILLE
DISTRICT
2
OVERVIEW – PROJECT SCOPE
 Authorized WRDA 1999
• Authority was contingent on a feasibility
assessment of the project.
1971
• 2002 Feasibility Study with Environmental
Assessment (amended April 2004)
determined that project was technically
sound, environmentally acceptable and
economically justified.
1986
2006
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3
OVERVIEW – PROJECT FEATURES
Project Scope



Project Length (ft) = 8,280 (R-35 to R43)




Three groins along the southern portion
Design berm elevation (ft) = +5 NGVD
Approximately 460,000 cy of design and 615,000 cy
of advance material (1,075,000 cy for Initial Const)
Borrow Areas: Big Sarasota Pass (BSP) & New Pass
5-year nourishment interval over 50-year life
615,000 cy required for each re-nourishment
D2
C
B
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PROJECT PLAN
 1) Placement:
• Place approximately 1.1M CY of sand on Lido
Key
 2) Source:
• Obtain Sediment for Nourishment of Lido Key
• Egmont Key (Tampa Bay)
• Offshore of Longboat Key
• Ebb Shoal at Big Sarasota Pass (BSP)
• New Pass – Future
 3) Retain:
• Construct Three (3) groins at the south end of
Lido Key
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5
PLACEMENT – LIDO KEY
2013 MHW
Line
80’ Design
Berm @ 5’
MHW Line Design Berm
Advanced
Berm
MHW Line Advanced Berm
150’
150’
FDEP Monument R-39
(Lime Tree Resort/Condos)
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SOURCE – BSP BORROW AREAS
D2
C
B
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7
RETAIN – SOUTHERN GROINS
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PROJECT PLAN –
BORROW AREA QUESTIONS?
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BORROW AREAS?
 What are the proposed borrow area
footprints?
 How will this affect Big Sarasota
Pass morphology?
 How will this affect Siesta Key?
 What are the effects on the
navigation channel?
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BORROW AREA FOOTPRINTS
D2
C
B
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In the
long
term:
Updrift
Shoal
These
areas
will be
deeper
Existing Conditions
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HOW WILL THIS AFFECT SIESTA KEY?
% Increase
in wave
energy here
and here
%
Decrease
in wave
energy
here
and here
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Results from
the CMS
morphologic
model yields
No
indication of
increased
erosion over
the Existing
Condition at
Siesta Key
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EFFECT ON CURRENT NAVIGATION?
Navigable water
greater than 6m depth
without project
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Navigable water
greater than 6m
depth with project
No significant
difference in navigable
water depths without
and with project
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PROJECT PLAN –
SOUTHERN GROINS
GENERAL QUESTIONS?
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SOUTH LIDO KEY GROINS
 What are the plans for the groins?
• How long are they?
• How much space is between
them?
• How big are they?
• Can I walk along the beach?
• Can I swim in the surf zone?
• Can I navigate past them?
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HOW LONG? HOW MUCH SPACE IN BETWEEN ?
460’
800’
600’
350’
2004
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500’
Present Day
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HOW BIG ARE THEY?
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CAN I WALK ALONG THE BEACH?
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CAN I SWIM IN THE SURF ZONE?
CAN I NAVIGATE PAST THEM?
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PROJECT PLAN –
SOUTHERN GROINS
HYPOTHETICAL QUESTIONS?
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What if the groins do not work?
 What is the effect on Lido Beach?
 What is the effect on Siesta Key?
 How will the groins affect the ebb
shoal in BSP?
 Why nourish the beach if we are
installing structures?
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WHAT IS THE EFFECT ON LIDO KEY?
WHAT IS THE EFFECT ON SIESTA KEY?
Sediment
Bypassing to
BSP Ebb Shoal
Downdrift
Effects
Groins are constructed to anchor the nourishment template – not to intercept
Sediment at the expense of downdrift beaches or ebb shoal morphology!
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How will the groins affect the ebb shoal in BSP?
Sediment
Bypassing to
BSP Ebb Shoal
Downdrift
Effects
Adequate sediment bypassing at the seaward end of the groin structures will
deter the growth of a crescentic shoreline . Adequate bypassing to the Ebb Shoal
ensures that BSP will maintain its morphology – seen by lack of erosion in the
shoal itself
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Why nourish the beach if we are
installing structures?
Groins are constructed to anchor the
nourishment template – not to
intercept sediment at the expense of
downdrift beaches or ebb shoal
morphology!
Groin construction without an
associated nourishment project can
lead to downdrift erosion and a lack
of sediment supply to downdrift
systems
The groins are designed to work with the nourishment design template – should the
beach erode shoreward of the design template, Emergency measures are implemented
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Groins – Anchor the Nourishment
1986
1983
1981
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LIDO KEY SPP
Questions/Discussions
Milan A. Mora, P.E.
Project Manager
Jacksonville District
Water Resources Branch
701 San Marco Boulevard
Jacksonville, FL 32207
904-232-1454
[email protected]
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