On the relationship between bedload and suspended sand transport on the inner shelf, Long Island, New York

Abstract

Data obtained by a near‐bottom Profiling Concentration and Velocity system (PCV), deployed in 10 m water depth at a site 1 km from the Long Island coastline, are used to examine links between bedload and suspended sand concentrations. Calculations of bedload areal concentration C* are based on the empirical results of Vincent et al. (1981) and use the theoretical formulations of Grant and Madsen (1978, 1979) to describe the interaction between wave and current boundary layers. Suspended sand concentrations were obtained directly from an Acoustic Concentration Meter (ACM). Average suspended sand profiles Cz were found to fit closely to a log‐linear profile Cz = C1(1 ‐ A loge z/Z1), where C1 is the sand concentration at a height z1 = 1 cm from the bed and A is empirically determined as 0.22±0.005. A linear correlation is observed between the areal bedload concentration C* (the volume of bedload per unit area of the bed) and the suspended sand concentration 1 cm above the bed C1, with a correlation coefficient of 0.82 (significant at the 1% level), and supports the hypothesis of Einstein (1950) that bedload and suspended load are related through bedload concentration. It is also shown that the sedment threshold criterion of Komar and Miller (1973), when expressed as a ratio (here called the Komar ratio), can be used as a useful predictor for C1 under conditions where the wave orbital currents are much greater than the mean flow. These relationships offer the opportunity for the calculation of both bedload and suspended sand transport rates from measurements of the steady current velocity and wave parameters, combined with information defining the surficial sediments and local bottom topography.