Field Observations and Stochasticity of Sediment Transport Rates

Sediment transport rates are presented on a wave-resolved basis using field data from experiments conducted in Duck, NC, and Arch Cape, OR in 2022. The two field sites represent an intermediate and dissipative beach, respectively. Measurements of sediment concentration were made using acoustic profiling instruments in the wave bottom boundary layer. The concentration data were paired with Doppler velocity data to determine a transport rate for each wave in the dataset. Probability distributions of per-wave sediment transport rates are compared against numerically calculated probability distributions using the model of van der A et al, which parameterizes many wave bottom boundary layer processes. Statistics derived from the probability distributions are used to quantify the intrinsic uncertainty in morphodynamic prediction due to the random wave field. Intrinsic uncertainty is found to be greater in instances of onshore transport when the transport is wave-dominated, and is weaker during offshore undertow-dominated transport. The magnitude of the intrinsic uncertainty is found to be comparable to the epistemic error that would result from uncertainty of model input data and model free parameters of +/- 10%, hence represents a non-trivial source of uncertainty for morphodynamic models.