Effect of axis orientation on the stability of a coastal promontory

Coastal promontories are found commonly along the coast protruding their axes to the coastal ocean. In this study stability of a coastal promontory under tidal flow is examined using a numerical model analyzing vorticity generation and bedload divergence. Idealized promontories with axes normal and inclined to the tidal flow are examined for their stabilities. The coastal promontory with axis normal to the tidal stream induces deposition at left hand tip off the promontory and erosion along the left hand flank of the promontory. As a result the axis of the promontory tends to incline cyclonically from the axis normal to the tidal stream. On the other hand, deposition is expected along the axes of the promontories inclined 15° and 30° from the axis normal to the tidal stream and erosion along the left hand side of the promontories. These promontories with the inclined axes appear to be more stable than the one whose axis is normal to the tidal stream. The results correspond well with the fact that Portland Bill, England and Gay Head, Massachusetts, U.S. have their axes inclined cyclonically from the axis normal to the tidal stream.