Longshore sediment transport rate measured by short-term impoundment

The total longshore sediment transport rate in the surf zone was measured a t a temporary groin installed at Indian Rocks Beach, west central Florida. Approximate mass balance between updrift accumulation and downdrift erosion , which served as an indicator of reliability, was obtained in four of the six runs, which were subjected to further analysis. Magnitudes of three of the four transport rates were considerably lower than predictions by the Co astal Engineering Research Center formula calculated based on contemporaneo us measurements of the breaking waves. Error analysis indicated that the de termination of the longshore wave-energy flux factor carried a 22-48% maxim um uncertainty, and the measured volume-change rate carried a 22-43% uncert ainty. The combined uncertainties produce a 40-90% maximum uncertainty in d etermination of the empirical transport coefficient K appearing in the Coas tal Engineering Research Center formula. Comparable or greater uncertainty in K-values probably exists in the total database available for calibrating predictive formulas. The range in values of K in these measurements cannot be explained by measurement error or uncertainty. Therefore, it is conclud ed that K is not a constant and that other factors may enter, such as break er type, turbulence intensity, and threshold for sediment transport.