EFFECT OF TIDE ON THE COASTAL GEOMORPHOLOGY OF PROMONTORIES

Effect of the tide on the geomorphology of coastal promontories is examined with tidal vorticity and sediment transport using a numerical model. Promontories whose axis is normal to the coastline show residual deposition in an area off their northwestern tips and erosion their upstream sides. The positive and negative vorticities also develop on both sides of the promonty. Promontories with the axis 30 degree cyclonic from the normal axis show reduced magnitudes of tidal vorticity and deposition/erosion compared with those whose axis is normal to the coastline. The deposition also occur along the axis not off the northwestern tip suggesting they are more stable compared with those whose axis is normal. An asymmetric promontory with the cyclonic axis orientation shows minimal vorticity generation and deposition/erosion suggesting it is most stable among promontories considered in this study. Gay Head, a promontory in Vinyard Sound, MA, U.S. and Portland Bill, a promontory in English Channel appear to support the results of this study.