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|Title:||Barrier island migration over a consolidating substrate|
|Authors:||Rosati, Julie Dean.|
|Publisher:||Coastal and Hydraulics Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||ERDC/CHL TR ; 09-8.|
Barrier islands that overlie a compressible substrate load and consolidate the underlying subsurface. Through time, the elevation and aerial extent of these islands are reduced, making them more susceptible to inundation and overwash. Sand washed over the island and onto back-barrier marsh or into the bay or estuary begins the consolidation process on a previously non-loaded substrate, with time- dependent consolidation a function of the magnitude of the load, duration of load, and characteristics of the substrate. The result is an increase in the overwash, migration, breaching, and segmentation of these islands. This research determined the degree to which consolidation affects the evolution of barrier island systems overlying a poorly- consolidated substrate, both for natural islands and those that have been restored with an infusion of sand from an external source. A two-dimensional (cross-shore) mathematical model was developed, tested with field data, and then applied to evaluate how a compressible substrate modifies long-term barrier island evolution. The model spans time durations of years to decades and represents cross-shore evolution of a sandy barrier island due to erosion, runup, overwash, migration, and time-dependent consolidation of the underlying substrate due to loading by the island. The implications of two strategies for restoring these islands (a one-time “Initial” large-scale infusion of sand from an external source versus traditional “Incremental” beach nourishment and subsequent smaller maintenance volumes) were tested. Barrier islands overlying a compressible substrate are more likely to have reduced dune elevations due to consolidation, incur overall volumetric adjustment of the profile to fill in compressed regions outside the immediate footprint of the island, and experience increased overwash and migration when the dune reaches a critical elevation with respect to the prevalent storm conditions. Initial large-scale infusion of sand from an external source decreased the cross-shore migration rate, consolidation rate, and rate of dune lowering for barrier islands overlying compressible substrate as compared to the Incremental restoration. The reduction in the migration and consolidation processes for the Initial Method resulted in more stability of the island as compared to the Incremental Method.
|Appears in Collections:||Technical Report|