Bedform Migration and Bedload Sediment Transport in Combined Wave-Current Flows

Bedload transport is an important mechanism for sediment flux in the nearshore. Yet few studies examine the relationship between bedform evolution and net sediment transport. Our work contributes concurrent observations of bedform mobility and bedload transport in response to current dominant, wave dominant, and combined wave-current flows in the nearshore. Findings show that bedload sediment flux from migrating bedforms during combined wave-current conditions account for more transport than wave dominant flows or current dominant flows alone. Bedforms were observed to transport the most sediment during periods with strong currents and waves or with high energy skewed waves. Additionally, when bedform orientation and transport direction were aligned there were elevated transport levels. Eleven bedload transport models formulated to be used in combined flows (both shear and energetics based), were compared with sediment flux estimated from measured bedform migration. Results show that regardless of flow type, bedform migration rates are directly proportional to the total kinetic energy contained in the flow field and that a shear based approach to estimate transport is non-trivial due to the complexities associated with estimating the flow friction factors. Results show that an energetics type sediment transport model may be most representative of observations and easiest to estimate without robust boundary layer measurements.