Stop-gap dune construction post-Sandy

In the post-Sandy world, dunes have become a hot-topic, and rightfully so. Ignoring the property-rights and easements issues, there is a bit of debate regarding how high, how wide, etc. Again, this is a good thing as not all dunes are created (either naturally or engineered) equal, and it is best to think the whole thing through instead of just piling sand up and declaring it done.

The issue of the Army Corps of Engineers’ (ACOE) designs and plans for beach replenishment and engineering will likely be addressed at a later date, but I do want to express my concerns with the stop-gap measures being put into play by individual townships.

Many towns were left with significantly narrowed beaches and no dunes, having been washed away by the storm surge and swell generated by Sandy. Recognizing that, all things considered equal (and I will address the things not equal among some areas in a later article), the more robust dunes did indeed appear to shield communities better than those lacking them or having, for lack of a better term, poor-excuses for them. This lit a fire under the officials’ office chairs and they started piling sand to buffer against any future storms if they came (and came, they did, notably the Dec 7th, 20th, and 27th Nor’easters, as well as a number of additional storms in early 2013).

The problem with this approach is there was not much material on-hand; the beaches were significantly reduced, and much of the sand from the beach was in the roadways and even in the bays behind the barrier islands. At first, the old rules applied, and it was contrary to DEP regulations to re-use the sand in the streets on the beaches as it was filled with potentially hazardous debris (glass, nails, timber, macadam, concrete, pipe, etc.), contaminated by household, automotive, and industrial chemicals and sewage from backed-up town service lines, and considered debris, itself. Soon post-event, this moratorium was lifted with the instructions that the sand was to be sieved (which removes most, not all, of the debris, but in the time-of-need this was a calculated risk that officials were willing to assume), and some of this washed-over sediment was returned to be used for dune fortification/replenishment, but it was not enough to pile a sufficient wall of sand.

Not able to recover enough dune-building material from the West-side of the beaches, officials, armed with loaders and dozers , then looked to the East and started pushing sand. The problem with this approach is that it stole from Peter to pay Paul, further weakening an already-weakened beach system (and it is important to look at it as a system rather than just a volume of sand).

See, what happens under normal circumstances, even a post-Sandy beach, is that the beach is not a flat-topped plateau of sediment; there is a natural slope to the sand before it reaches the dunes that helps to dissipate wave energy using distance, friction, and gravity. Gravity is key here; water is heavy (64 pounds per cubic foot, or almost 8.5 pounds per gallon), so it has to fight its own weight as it is pushed up an incline, the steeper the incline, the shorter the distance it will go before it is halted by its own mass).

Natural or well-engineered beach profile

Unfortunately, this phenomenon was not accounted for, and the dozers wound up creating flattened beach profiles when stealing sand for the “dunes” (and I use quotation marks here as an unvegetated pile sand does not rival, nor qualify, as a natural or well-engineered dune). This removes the biggest ally in the equation (gravity) and essentially provides a straight-shot for waves to have their way with the well-intended piles of sand.

Sand bulldozed from beach to pile sand as rudimentary dune

Eventually, if not corrected, this will allow for erosion of the bases of the dunes, toppling forward (Eastward) of the sediment, and eventually result in dune failure.

Dune failure cause by erosion of base

While one could easily argue that establishing a rudimentary artificial dune-line as a shield for what lies behind it (homes, roads, personal property, township infrastructure, etc.) was absolutely necessary and worth the risk, and I can neither honestly dismiss this claim nor do I have a better recommendation besides “go get that sand for the dune from a nebulous alternate inland location”, people in the know regarding this predicament are keeping an eye on the beaches and dunes during every coastal storm, new/spring tide, and swell event until sand is deposited back on the beaches, either through natural or well-engineered anthropogenic means, and build that incline back up to a more comfortable angle.  It is also a principle that should be kept in mind when designing and executing a beach replenishment project.