FORESHORE MORPHODYNAMICS AT DUCK

19 June 2001

Source: http://postoffice.nrlssc.navy.mil/abstract%2028.htm

FORESHORE MORPHODYNAMICS AT DUCK, NC

K. T. Holland
Naval Research Laboratory
Stennis Space Center, MS 39529-5004
A. Sallenger
US Geological Survey

Abstract

Most prior attempts at modeling the evolution of swash zone morphology has lacked simultaneous measurements of the interaction between hydrodynamic and morphodynamic forces over relatively large temporal and spatial scales (hours to days and 10s to 100s of meters, respectively). Recent advances in technology show promise for providing such measurements in this dynamic region through the use of a stereometric video technique capable of measuring three-dimensional foreshore morphology to roughly centimeter accuracy [Holland and Holman, 1997]. This method monitors the progression of the swash edge over a single wave cycle and typically samples several thousand estimates of the foreshore surface in addition to measurement of the 3-D swash edge time series.

Measurements of foreshore surfaces and swash motions sampled during the Duck94 and SANDYDUCK experiments at Duck, NC showed distinctive patterns of net sediment transport and morphologic change in response to hydrodynamic forcing. Estimates were made over study regions of up to 50 m in the cross-shore and 100 m in the along shore. Analysis of these observations showed erosion rates of up to 0.25 m³/hr. These rates were partially correlated with spatial gradients in swash flow velocity, however, the magnitudes predicted by a simple sediment transport model were dissimilar to observations suggesting that other factors, including groundwater and tidal influences could be equally important. Of particular interest were instances where forcing conditions were approximately equivalent, yet morphologic response was dramatically dissimilar. Also monitored was an almost complete cycle of cusp development and destruction.