The Well-Kept Secret About Bulkheads

by Dr. Don Flora PhD

Bulkheads don’t stop slides. 

That’s a headline in a Kitsap County handout, authored a while back by the Department of Community Development.  Here’s the text:

Bulkheads do little to prevent sliding of the upper bank.  They simply can’t withstand the sheer force of a saturated, sliding hillside.[1] 

If true, that’s great news for the environment.  Bulkheads aren’t preventing ‘feeder bluffs’ from doing their thing, plopping sediments to bulk up the beach and migrate along ‘drift cells’.  Some other scourge of the nearshore must be found lest some doctrinaire critics of shore protection will be out of work.  Perhaps the depredations of starfish will now get the full recognition they deserve. 

But is it true?  Is shore protection pointless?  Yes and no. 

Yes—prolonged rain, on the order of weeks, often triggers bluff failures.  A study of slides in Seattle showed that, of 1300 slides recorded over a century, most happened in concert with sogginess.[2]

 These ecologic events can be helped along by trees at the tops of bluffs.  Often leaning, such trees usually have their largest rations of biggest limbs on the seaward sides.  In any case trees’ overall weight, roots and all, encourages slides. 

Obviously bulkheads have nothing to do with rainstorms nor precarious trees.  But wait…

No—Bluffs occupy 60 percent of Puget Sound shores.  They don’t owe that sheared condition just to rain.  5000 years ago, long after the rains began, Puget Sound’s nearshore was curvaceous and softly rounded, “…like the present upland areas of the central Puget Sound lowlands”.[3]  Currents and waves carved out the undercut scarps that became prey to sogginess and the weight of bluff-top trees.

The Department of Ecology says,  “Bulkheads can reduce the natural delivery of sand and gravel to our shorelines.”[4]  This because “Bluffs are subjected to wave attack at the toe of the slope, which contributes to intermittent bluff retreat…”[5] 

And undercutting accounts for the landward migration of beaches over centuries, which wouldn’t happen if wave action were constantly blocked by beach plops from above.[6]  Or bulkheads.

In fact, bulkheads are good enough at stopping slides that they are blamed for all manner of things.  The key complaint is that upper-beach spawning gravels disappear.  Across from Bremerton on Sinclair Inlet, Ross Point has for decades been one of the most productive surf smelt sites in the central Sound.  Yet it has a partial bulkhead.

Spawning-gravel migration is apparently unmeasured, and I understand there are no plans to do so.  After a recent shoreline protection conference one of its co-chairs remarked:

One wonders why the workshop was focused on managing shoreline armoring given the limited Scientific research that has been done on the effects of armoring. One can wonder, but that’s exactly what local planners and the state Dept. of Ecology are doing throughout the Puget Sound region.  They are focused on eliminating bulkheads that protect people’s homes without  scientifically valid proof  of harm.[7]

And as mentioned in an earlier “Sentry”, an analysis of Bainbridge shore data has revealed that there is no correlation – none – between bulkhead prevalence and habitats, the latter referring to eelgrass extent and forage-fish spawning space.  At least around the island, and probably the County, bulkheads are neither good nor bad for habitats.[8]                                   


[1] Kitsap County Department of Community Development.  2003. (Fact Sheet) 24-Bulkhead Alternatives. Port Orchard

[2] Schulz, William H. 2007. Landslide susceptibility revealed by LIDAR imagery and historical records, Seattle, Washington.  Engineering Geology 89:67-87.

[3] Downing, John. 198 “The Coast of Puget Sound, Its Processes and Development”.  Seattle: Washington Sea Grant Program.

[4] Washington Department of Ecology. 2010. Frequently Asked Questions-Marine Shoreline Armoring and Puget Sound. Publication No. 10-06-003. Dated 02/05/10(Rev 2/11/10). Olympia: DOE Shorelands and Environmental Assistance Program.

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

[6]  Geologist Leland Jones has estimated that the exposed eastern side of Bainbridge Island has retreated about six inches per year, on average. Seemingly not much, but losing 5 feet in ten years can obviously be a big problem. On the apparently benign west side of the island, a single storm plus high tides washed out ten feet over two days. This is in a low-bank setting where bluff collapse was not a factor. Riprap now repels the rape of that resource.

[7]  Shipman, Hugh. 2009. E-mail to Puget Sound Shoreline Planners.

[8]  Flora, D. F.  209. Evidence of Near-Zero Habitat Harm from Nearshore Development. On various Puget Sound Web sites including KAPO.org and  Bainbridge Shoreline Homeowners

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