LARGE-SCALE VOLUME CHANGE AND PROGRADATION OF POWER SQUADRON SPIT DURING A TRANSGRESSION AT CAPE LOOKOUT, NORTH CAROLINA

Eustatic sea level is rising, yet many regions of the world still experience local progradation and accretion. Welding of swash bars onto the beach face can significantly increase the volume and surficial area of coastal landforms that are not traditionally associated with sea level transgression. Nearshore bars are significant reservoirs of sediment, and documenting volume changes due to welding of bars can have implications for regional sediment budgets and beach nourishment needs. The study area is an example of a system where welding of swash bars results in large-scale volume change and progradation. Because of its particular location in the complicated Cape Lookout region, this spit plays an integral role in the regional sediment budget. Although the spit has been rapidly prograding since the early part of the 1900s, the actual rates of linear, areal, and volumetric growth have never been accurately documented.

The volume of sediment incorporated into Power Squadron Spit was documented by calculating the subaerial and subaqueous volume separately. Subaerial volume was determined by conducting a ground survey of the spit north of a rock jetty using real-time-kinematic GPS technology. The subaqueous volume was ascertained by comparing bathymetric data from 1940 and 1998.

The total volume of sediment incorporated into Power Squadron Spit is estimated to be 19 million m³. This represents a deposition rate of approximately 317,000 m³/yr. The generally accepted rate of longshore sediment transport from the Core Banks limb (to the east) of the Cape Lookout system is 400,000 m³/yr. Although the values for longshore sediment transport rate and spit accumulation rate are of the same order of magnitude, Core Banks and Power Squadron Spit are separated subaqueously by the extensive Cape Lookout Shoals, and many processes that may link the two are poorly understood. Further survey work is underway to determine the frequency and magnitude of welding of intertidal swash bars, the connection between spit growth and storm activity, and possible linkages between the two limbs of the Cape Lookout system.