|dc.description.abstract||Bedforms in nearshore environments are undulatory sedimentary structures
formed by wave-forced fluid-sediment interactions at the seabed. Signature
characteristics imprinted on the sediment fabric may be used to infer environmental
conditions in the past by comparison to bedforms in the geologic record. Lunate
megaripples and cross-ripples are bedforms with complex geometries that have been
observed in nearshore environments, however they are not well studied in the
literature and the conditions required for their formation are unclear. Previous
surveying methods have recorded observations using instruments installed in the
seafloor, which can disturb the sediment and obstruct fluid flow. The purpose of this
study is to refine methodology for observing lunate megaripples and cross-ripples noninvasively.
The study site, Crystal Crescent Beach, in Sambro, Nova Scotia, was selected
for its sandy bottom and clear water. A low cost, human-powered surface vehicle was
constructed using a surfboard as the platform for mounting (1) a video imaging device
to record bedform morphologies at varying depths, and (2) a sonar device connected to
GPS to detect and document ocean floor topography. Surveys were conducted prior to a
storm event, during the event, then after the event to observe bedform transformation.
Sand samples were obtained for analyzing grain size characteristics of the bedforms.
Weather, wind, and wave conditions were recorded before, during, and following
fieldwork to document potential physical conditions associated with bed geometries.
Still frames from videos of pre-storm seabed conditions compared to videos of poststorm
conditions showed recognizably different bedforms. In videos acquired during the
storm, suspended sediment in the water column made it difficult to observe the
seafloor. Analysis of weather data confirmed that large wave heights were associated
with high wind speed, and grain size analysis showed that more complex, threedimensional
bedforms occurred where there was variability in grain size. Figures created
using sonar data illustrated an overall change in beach geometry throughout the storm
event. Overall, observations were relatively high quality, allowing for identification
distinct ripple geometries and change in overall bed state associated with growth and
decay of storm wave conditions. This study demonstrated potential for examining
bedforms using low-cost, human-powered, instrumented surface vehicles. Therefore,
despite being an initial attempt, this study can be used as a basis for further studies of
bedform development in nearshore environments.
Keywords: Bedform, lunate megaripple, cross ripple, high||en_US