douglas w. mann, p.e., d

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Update on the Town of Longboat Key’s Permeable Adjustable Groins Performance

Douglas W. Mann, P.E., D.CE

Florida Shore & Beach Preservation AssociationFebruary 14, 2013

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2010 Construction

TOWN OF LONGBOAT KEY’S PERMEABLE ADJUSTABLE GROINS

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2010 Early Response


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Comparison of the Islander Hot Spot


2004 (3 years post 2001 nourishment) 2010 (4 years post 2005/2006 nourishment)

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2011 Conclusions from the Initial Monitoring

5TOWN OF LONGBOAT KEY’S PERMEABLE ADJUSTABLE GROINS

► Permeable adjustable groins show promise as a viable erosion control structure.

► From a beach management perspective, the groins in addition to the nourishment are better at managing the sand resources than nourishment alone.

► If the north beach trends continue, the groins may need to be adjusted to increase the permeability to enhance bypassing.

► Future monitoring will continue, enabling the Town, CPE, and FDEP to determine any future actions in this area, which may include increasing the permeability of the seaward ends of one or both groins.

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Overview


► 2011 shoreline trends► 2012 adjustment process► Effects of Tropical Storm Debby on the coastal processes ► Future Town actions► Future PAG applications

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Location Map


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Aerial Location Map


Net Transport =50,000 to 90,000 cy/yr.Net Transport =50,000 to 90,000 cy/yr.

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Historical Shoreline Changes


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Jul 06 to Oct 09 North groin south groin

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Initial 2010 Shoreline Response


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Oct 09- Oct 10 Jul 06 to Oct 09 North groin south groin

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November 2011

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18 Months Ground View


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Shoreline Changes

Shoreline Change Rate from 07/06 to 10/09 Shoreline Change Rate from 10/09 to 10/10

Groin South Groin

Shoreline change 10/10 to 10/11

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2010-2011 Shoreline Response


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Photo courtesy of the town of Longboat Key, November 2011

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18 Months Oblique


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Overview


► 2011 shoreline trends► 2012 adjustment process► Effects of Tropical Storm Debby on the coastal processes ► Future Town actions► Future PAG applications

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Adjustable Elements


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April 2012 Adjustment


► Adjustment consisted of removal of:– 120 concrete elements from the north groin– 90 concrete elements from the south groin

► Cost was around $28k. This is about 3 percent of the initial cost of the groins.

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Photo courtesy of James Linkogle, TLBK

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Adjustment Operation


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Adjustment Operation (cont’d)


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June 12, 2012

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Post Adjustment Response


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Photo courtesy of NOAA

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Tropical Storm Debby Forcing


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Storm Surge


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Photo courtesy of David Bullock, TLBK

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Tropical Storm Debby Passage – June 23-28, 2012


01M042012D25TOWN OF LONGBOAT KEY’S PERMEABLE ADJUSTABLE GROINS

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Tropical Storm Debby Induced Changes


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Shoreline Change Rate from 07/06 to 10/09 Shoreline Change Rate from 10/11 to 07/12North Groin South Groin

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Time frame 2.75 years.

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Net Post Groin Changes (thru TS Debby)


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Shoreline Change Rate from 07/06 to 10/09 Shoreline Change Rate from 10/09 to 07/12North Groin South Groin

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November 2012


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Seasonal Sediment Transport November 2012


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Future Town Actions


► 2013 Interim Beach Re-nourishment Project will place approximately 100,000 cubic yards of sand on the southern shoreline to offset impacts from the groins.

► Ongoing permit required monitoring to evaluate the adjustment.

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Town of Longboat Key, near Longboat Pass. Photo courtesy of LBK

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Future PAG Applications


TSGI4

TSGI4 What are PAGs?The Shaw Group Inc., 2/6/2013

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Future PAG Applications


Manatee County – Replacement of the 1960s vintage permeable groins at Cortez Beach.

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Summary


► PAGs at the Islander Club Condominium are continuing to meet the goals of the project.

► PAGs are a useful tool for hotspot management when used in conjunction with beach nourishment.

► An economical adjustment of the groins was achieved.► Post Debby shoreline response reflected a south to north transport.

Recent observations reflect a return to a north to south transport pattern.► Future applications of PAGs are in permitting.

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Acknowledgements


► Juan Florensa, LBK, Public Works Director► James Linkogle, LBK► Julien Devisse, E.I.

Douglas W. Mann, P.E., D.CESenior Coastal Engineer

[email protected]

CONTACT

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douglas w. mann, p.e., d

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