Measurement of Bedload Transport in a Coastal Sea Using Serial Multibeam Surveying: Assessing bedload formulae using sand dune migration
Abstract
Processing of six serial multibeam surveys of a headland‐associated sand bank off the coast of New Brunswick resulted in an estimation of the spring‐neap averaged rate of sediment transported in its migrating sand dunes. Bedload was estimated in two separate ways, one technique using measurements of migration rate and bedform height (bedform celerity method) and another that was based on direct volumetric measurements of sediment transport at the crest by measuring displaced lee‐slope and stoss‐slope volumes between time‐lapsed surveys and dividing by the time interval (volumetric method). The two methods returned comparable estimates of net sediment transport rate, but the volumetric method allowed separate inspection of stoss and lee‐slope transport rates and was simpler in its application. Comparison of the observed bedload with five predictors based on hydrodynamics revealed that most of the formulations did a poor job of predicting the bedload transport in this area probably because of the enhancing effect of the presence of the bedforms in increasing the total shear stress and therefore suspension transport while the excess skin friction remained low, implying low rates of bedload transport.
The morphology of the sand dunes changes noticeably across the sand bank. The sequence is as follows: low, two‐dimensional dunes, increasing in wavelength, height, sinuosity and asymmetry to form three‐dimensional dunes on the thickest and shallowest part of the bank are replaced by dunes with lee‐side scours becoming more prevalent and the formation of lunate megaripples along the landward edge and off the tip of the sand bank. These visual changes, together with measurements of lee‐slope volume deficits, suggest that the bedforms change in response to decreasing cohesion, increasing peak bottom stress and eventually decreasing volume of available bedload as the effect of dune crest localized suspension increases.
Department
Center for Coastal and Ocean Mapping
Publication Date
1-26-2012
Journal Title
Sediments, Morphology and Sedimentary Processes on Continental Shelves: Advances in Technologies, Research, and Applications
Publisher
Wiley
Digital Object Identifier (DOI)
Document Type
Book Chapter
Recommended Citation
Duffy, G. and Hughes Clarke, J.E., 2012, Measurement of Bedload Transport in a Coastal Sea Using Serial Multibeam Surveying: Assessing bedload formulae using sand dune migration: IAS Special Publication # 44, Sediments, Morphology and Sedimentary Processes on Continental Shelves, p. 249-272.