Field measurements of longshore sediment transport during storms

This paper presents an analysis of longshore sediment transport (LST) rates based on an accumulation of data obtained during five storms. Direct measurements of velocities and suspended sediment concentration were conducted at a minimum of nine positions across a barred profile in waves up to H m0=3.5 m to provide a measure of the cross-shore distribution and total suspended-load sediment transport rates. The study was conducted at the US Army Engineer Waterways Experiment Station's Field Research Facility, located in Duck, NC. Measurements were made using the Sensor Insertion System (SIS) which provides an economical means to collect the required information. The largest LST rate computed from the measurements was 1780 m 3 h −1. Although the cross-shore distribution of the LST varied, it most often had two peaks associated with wave shoaling and breaking at the bar and near the beach. Comparisons of measurement results with predictions using the `CERC' LST formula show the predicted rates were sometimes higher and other times lower; suggesting that additional terms may be required for short term predictions during storms. Comparisons to a `Bagnold' type formulation, which included a velocity term that could account for wind and other effects on LST, show better agreement for at least one of the storms. These results are intended to help fill a void of information documenting the cross-shore distribution and LST rates, particularly during storms.