Sandwave mobility in Start Bay, Devon.

Abstract

The work presented in this thesis concerns the investigation of the movement and stability of the sandwaves on the Skerries Bank in Start Bay, Devon. Initially, side scan sonar records of the sea bed of Start Bay were examined and an area on the Skerries Bank was selected for detailed study. The positions of the sandwaves in this area were accurately found by echo sounder, using sextants for navigation. By repeatedly surveying the same areas, the progressive displacement of the sandwaves was found over a period of two years. The magnitude and direction of the sandwaves' displacement was predicted from tidal current measurements and there was good agreement with the measured displacement. One particular sandwave was subjected to a very detailed investigation of its reciprocative displacement, for a period of several months. A diver-operated acoustic rangemeter system was used for this work. It was found that the reciprocative displacement, predicted from tidal current measurements, was an order of magnitude smaller than the measured displacement. Reasons for this are discussed. The reciprocative motion of the dunes has also been measured. The effect of sediment grain size on sandwaves has been investigated. It has been found that sandwaves only occur when the sediment grain size lies between 0 and 2 phi. Also, the relationship between water depth and sandwave wavelength has been examined. Measurements have been made of the sediment characteristics at a number of points over a sandwave profile. The effect of storms on sandwave shape has been observed. It has also been found that the 'catback' sandwave cross-section occurs when sandwaves bifurcate. From these results a better understanding has been obtained the way in which sandwaves move and of the stability of sandwaves on a tide-swept Bank, such as the Skerries.

Date of Award	1979
Original language	English
Awarding Institution	University of Bath