line in the sand

coastal adaptation in response to sea level rise 

During a year-long investigation led by Professor Kristina Hill, the dredge cycle and coastal processes of Tidewater, Va were researched to understand the habitat, recreational, and storm defense benefits of a sand engine compared to linear nourishment and how this strategy might be deployed.

Because of their extensive investment in a hybrid system of sea wall, pump station and beach nourishment during “Operation Big Beach,” the hotel strip of Virginia Beach now supplies a significant quantity of sand to the region through longshore drift.  As this “line in the sand” must now be continually maintained, the site was seen as appropriate for an even larger nourishment.

zandmotor + aerial perspective

In the dutch zandmotor’s hybrid construction process, hopper dredges first connect to offshore pumping stations which pipe their dredge slurry to the beach where it is graded into a type of scaffold for the sand engine (this is the conventional process for Virginia Beach’s linear nourishment as well).  Economy of operation is achieved when the sand engine reaches out enough for hoppers to “rainbow” the dredge directly adjacent to the sand engine.  Both techniques can be used simultaneously, where hoppers’ pipe a portion of their slurry in order to reach a suitable depth to rainbow the remaining amount.  In the above rendering, the sand engine has been placed in Virginia Beach for scale, this option was not seen as feasible due to the proximity of stormwater outfalls and the pier.  Instead, a distributed system was explored with the goal of realizing the cost savings of  rainbowing dredge from hoppers, the habitat benefits of uncompacted sand migration, and the recreational value of a new surf break.

exploded axon

The sand engine is viewed as a landscape of infrastructure, designed based on the logistics of construction and continual replenishment.  Four linear berms are spaced according to dredger hopper draft and the fetch required to perpetuate dune formation.  Directly perpendicular to prevailing wave direction, dredge quickly fills behind each ridge creating a series of salt marshes, aided through hydroseeded Spartina species, while also encouraging a new wave break for surfing.

section perspective

tsand engine section2

animation stillxs

This work was presented to Virginia Beach coastal engineers, beach managers, planners, hotel owners and the chamber of commerce during the summer of 2012.  While the concept was received favorably, the site continues to be problematic due to the infrastructural conflicts mentioned earlier, perceived aesthetic expectations of visiting tourists, and an observed conflict with surfers outside of the designated surf zone.  Instead, Sandbridge, VA, (20 minutes to the south) has emerged as a more feasible location for this strategy.  With a reputation of being a more “natural” beach experience thanks to its proximity to a Back Bay National Wildlife Refuge and False Cape State Park, the community has a dedicated fund for beach nourishment, would benefit from the addition of a surf break and is also subject to similar long-shore currents which would continue to disperse sand to the north.

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