Bottom Sediment Suspension due to Wave-Current Effects at the Mouth of the Columbia River, USA

This paper investigates seabed sediment suspension due to the presence of waves and currents at the Mouth of the Columbia River (MCR). Relevant data were measured at a location 6 km offshore the MCR in a water depth of 19 meters with seabed sediment composed of fine to medium sand. The analyses described in this paper address the following question: When waves and currents interact along the seabed of an ebb tidal shoal, what is the effect on bottom sediment (sand) suspension? Special considerations included: assessing the modification of waves by current, describing the spectral relationship between bottom current and peak sediment suspension, and investigating wave group effects. Results indicate that: Currents influence the pressure signal for PUV measurements which can result in erroneous results for calculated wave height and period; The coherence between waves and response of suspended sediment is high yet complex due to multiple spectral peaks from waves, wave grouping, higher order effects; The RMS value of wave-induced bottom current can be used to identify grouping frequency which impacts suspended sediment response.