Want Your Beach Scoured?

Bulkheads May Not Do It!

by Dr. Don Flora Ph.D., August 2010

Last month’s note spoke to the awfulness of bulkheads that prevent slides.  This time it’s scouring in front of bulkheads.

These comments are triggered by a Kitsap County Dept. of Community Development statement:  “Bulkheads don’t prevent the beach from eroding.  In fact, when waves hit the bulkhead, they scour out the beach’s natural sand, gravel and rock”.[1]

Well, yeah.  In fact, when high-tide waves hit just about anything, they suck back, pulling away some of whatever the waves’ energy can dislodge.

Beach scouring by passing container ships and fast passenger ferries has been notorious, leading even to lawsuits.  With and without bulkheads.

But are bulkheads especially vicious bouncers back?  At a May, 2009, conference on bulkheads a well-known researcher said:    “It has not been confirmed in the field or the laboratory whether currents and sediment transport rates will increase or decrease in front of a hardened shoreline, as compared to a non-armored section of beach, and whether the sedimentary environment will be significantly modified”.[2]

In some places backflowing wind and waves borrow sands and gravels from bulkheaded beaches.  Presumably the sediments join the trains of beach particles heading up or along or out from the beach.  After all, Puget Sound’s destiny is to be just a swale among low hills after Nature’s hydraulics have operated awhile.

Ah, but beaches without shore protection erode too, as they have done for those millennia just mentioned.  The land doth level into the sea.  Too, the whole dynamic of “drift cells” is based on erosion at the sending end.

Despite 150 years of shore protection there is no measure nor even mention of sandspits shrinking in a Bainbridge Island comparison of historic with present shore features.[3]  Even with half the island currently bulkheaded.

Nor can one find numbers for the “right” amount of bank failure to compensate for shore-drifted sediments; NEITHER FOR BAREHEADED NOR BULKHEADED BEACHES.  This despite adamant declarations that shore protection “can” change or displace shore profiles.[4]

In a Bainbridge Island shoreline assessment scouring is mentioned only in passing:  there is no enumeration of scoured places nor even a statement that it occurs locally.[5]

After two decades of field work, Kitsap County’s staff has drafted a shoreline inventory.[6]  In 500-plus pages scouring is not measured, mapped, nor mentioned.  Perhaps the scouring doctrine has drifted on, another bit of weathered, wayward dogmatic wrack.

————————

Notes:

[1] Kitsap County Department of Community Development. 2003. [Fact Sheet] 24-Bulkhead Alternative. Port Orchard, WA.

[2] Ruggier, Peter. 2009. Impacts of shoreline armoring o sediment dynamics. In:[Abstracts of] PugetSound Shorelines and the Impacts of Armoring: State of the Science. Alderbrook Inn,13 May 2009. US Geological Survey http://wa.water.usgs.gov/SAW/

[3] Coastal Geologic Service Inc. 2008 Bainbridge Island Current and Historic Coastal Geomorphic/Feeder Bluff Mapping [draft]. Bellingham

[4] Washington Department of Ecology. 2010. Focus on Shoreline Armoring-Healthy Shorelines Equal a Healthy Puget Sound. Pub. 10-06-04. 2010. Frequently Asked Questions-Marine Shoreline Armoring and Puget Sound. Pub. 10-06-003

[5] Williams, G.D.,et al. 2004. Bainbridge Island Nearshore Habitat Characterization & Assessment..Sequim: Battelle Memorial Institute

[6] Kitsap County Dept of Community Development, Environmental Programs. 2010.  Kitsap County Draft Shoreline Inventory and Characterization.  Port Orchard.

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