SARASOTA COUNTY LIDO KEY HURRICANE & STORM DAMAGE REDUCTION PROJECT

Transcription

1 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 US ARMY CORPS US ARMY OF CORPS ENGINEERS OF ENGINEERS JACKSONVILLE Jacksonville DISTRICT District

2 2 OVERVIEW PROJECT SCOPE 1971 Authorized WRDA 1999 Authority was contingent on a feasibility assessment of the project Feasibility Study with Environmental Assessment (amended April 2004) determined that project was technically sound, environmentally acceptable and economically justified

3 3 OVERVIEW PROJECT FEATURES Project Scope Project Length (ft) = 8,280 (R-35 to R43) 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) Three groins along the southern portion 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

4 4 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

5 5 PLACEMENT LIDO KEY 2013 MHW Line 80 Design 5 MHW Line - Design Berm Advanced Berm MHW Line - Advanced Berm FDEP Monument R-39 (Lime Tree Resort/Condos)

6 6 SOURCE BSP BORROW AREAS D2 C B

7 7 RETAIN SOUTHERN GROINS

8 PROJECT PLAN BORROW AREA QUESTIONS?

9 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?

10 BORROW AREA FOOTPRINTS D2 C B

11 In the long term: Updrift Shoal These areas will be deeper Existing Conditions

12 HOW WILL THIS AFFECT SIESTA KEY? % Increase in wave energy here and here % Decrease in wave energy here and here Results from the CMS morphologic model yields No indication of increased erosion over the Existing Condition at Siesta Key

13 EFFECT ON CURRENT NAVIGATION? Navigable water greater than 6m depth without project Navigable water greater than 6m depth with project No significant difference in navigable water depths without and with project

14 PROJECT PLAN SOUTHERN GROINS GENERAL QUESTIONS?

15 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?

16 HOW LONG? HOW MUCH SPACE IN BETWEEN? Present Day

17 HOW BIG ARE THEY?

18 CAN I WALK ALONG THE BEACH?

19 CAN I SWIM IN THE SURF ZONE? CAN I NAVIGATE PAST THEM?

20 PROJECT PLAN SOUTHERN GROINS HYPOTHETICAL QUESTIONS?

21 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?

22 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!

23 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

24 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

25 Groins Anchor the Nourishment

26 LIDO KEY SPP Questions/Discussions Milan A. Mora, P.E. Project Manager Jacksonville District Water Resources Branch 701 San Marco Boulevard Jacksonville, FL