title: A Study of the Correlation of Sub-Aqueous Beach Profile Change and the Coastal Storm Impulse (COSI) Parameter
Creators: name: Conner, Kevin Bryan
Publisher: name: Old Dominion University Libraries
Year: 2011

description: The Coastal Storm Impulse (COSI) parameter is a recently developed storm-strength parameter that was first introduced at the San Diego, California International Conference of Coastal Engineering in 2006 (ICCE) and further examined in 2008 at the ICCE in Hamburg, Germany. This new parameter used the principles of conservation of horizontal momentum to combine storm characteristics such as surge, wave dynamics, currents, and duration into a relative scale used to classify and measure storm response and impacts. The resultant classification system was intended to evaluate potential coastal erosion and the associated loss of coastal infrastructure, as well as provide a storm strength parameter that is linked with the physical parameters of incoming storms other than wind speed alone.

Recent research conducted exploring the application of the COSI parameter to predict coastal erosion has shown there is no correlation between the currently computed COSI parameter and coastal erosion of the sub-aerial beach profile (Walker, 2010). This thesis work correlated COSI parameters computed from wave data measurements collected at Duck, North Carolina between 1994 and 2003 to observed volumetric changes within the sub-aerial beach profile. Prior to this research it was thought that all storms measured at the study site should produce some measurable erosion and that the degree of this erosion would increase with increasing storm intensity, measured by the COSI parameter. These inconclusive results have prompted further investigation of the COSI parameter calculation as well as examination of corresponding beach morphology.

This research expanded on previous research by covering six additional topics related to the observed volumetric change at Profile 188 and its relationship to the COSI parameter. First, the volumetric change of the sub-aqueous portions of the beach at Profile 188 and 190 were computed. These measured changes were compared to COSI parameters for corresponding storm events and it was found that there was no apparent correlation. Secondly, the sub-aqueous volumetric changes at Profile 188 to the sub-aerial changes computed by Walker (2010). This section attempted to determine any potential sediment exchange between the two sections of the profile and how these exchanges may impact the COSI parameter correlation. It was found that the volumetric changes between the two sections did not respond uniformly and that there was not a mass balance of the sediment exchange between the two sections of the profile. Third, the morphology of the profile was examined to measure the impact of the bar positions and magnitudes on the volumetric changes previously measured. It was found that the magnitude and position of the bars could not be directly linked to the profile changes observed at these two locations. The fourth item investigated was the influence of the timing of beach surveys. This included the temporal relationship between the pre- and post-storm surveys and between the timing of the storm event peak and the post-storm survey. This section attempted to determine if longer durations between these two metrics negatively influences the correlation to the COSI parameter. The comparisons of these durations to the measured profile responses did not correlate. This is most likely as a result of beach recovery following a storm event beginning much sooner than the timing of the post-storm surveys. The fifth area investigated was the variability of the Dean Number throughout the storm duration to attempt to explain previous findings of similar storms producing varying volumetric responses. It was found that the Dean Number variations throughout the storms were profound and no pattern could be identified to explain the variations in profile response to the storm events of this thesis. Finally, the influence of the wave angle of approach was measured and compared to the volumetric responses. It was determined that the measured wave angle has a significant impact on the observed volumetric changes. This is significant due to the fact that the wave angle of approach is assumed to be parallel to the beach within the calculation of the COSI parameter and may explain the lack of any correlation between the COSI and measured volumetric change.

Future research into the COSI parameter should include investigations into modification of the COSI parameter calculation. Currently the computation assumes that approaching waves are shore parallel, which may be influencing the correlation between volumetric losses and the COSI. Additionally, the survey database that is being used for the correlation comparisons is not capturing the storm profile at sufficient time intervals to adequately measure storm response. Inclusion storm profile data collected during storm events through systems such as the Coastal Lidar and Radar Imaging System (CLARIS) would enable accurate measurement of peak profile erosion and recovery rates. Analysis of this level of survey data should improve correlation to the COSI and allow for more accurate adjustments to the parameter.