RESPONSE OF A MICROTIDAL WAVE-DOMINATED BARRIER TO CLOSELY TIMED EXTRA-TROPICAL CYCLONES

On 16 October 2002, the first of three extra-tropical cyclones impacted the microtidal, wave-dominated south facing coast of Rhode Island within a three week time span. We measure beach profiles at five localities along the south shore of Rhode Island, including site CHA-EZ. CHA-EZ is located on the Charlestown Barrier, Charlestown, R.I., and has a weekly profile record dating back to October 1977. Seven profiles measured at site CHA-EZ over the three-week time frame, provide a record of short-term changes along the shoreline. The first storm, a strong class two extra-tropical cyclone (nor’easter in the Dolan and Davis 1991, classification scheme), occurred on 15-16 October 2002, three days after neap tide, with a storm surge elevation only 1.7m above mean lower low water. Even under neap tide conditions, storm waves and swash eroded most of the berm and left an erosional dune scarp up to 1.5m high along most of the barrier. Measurements taken on 17 October showed a severely erosional storm-beach profile with a flat beach A profile recorded at low tide on 18 October, showed onshore migration and welding of a small (0.6m high) swash bar. Quick recovery to a depositional profile is a common aspect of these microtidal beaches. A second storm, (class one) occurred on 26 October and returned the beach to a post-storm profile, displaying a small runnel and 0.3m high swash bar. Welding of a large swash bar was almost complete by 2 November and only a small portion of the runnel was still evident. A profile recording the effect of the third nor’easter, a small class one storm on 6 November 2002, was obtained on 8 November. The 8 November profile showed no net change in volume since the 2 November profile, however the morphology had changed; a narrow, convex berm, typical of a recovering beach had formed. Recovery of the beach continued, and by 15 November, a narrow (10m) storm berm had developed landward of a 12m wide neap berm. The storm berm continued to develop through the spring-tidal cycle into a more mature recovered profile with a wide (25m) berm, effectively translating foredune material back to the berm. This documentation of short-term cycling on a microtidal shoreline indicates that small, Class 1 and 2 storms can affect beach configuration if they occur over a short time span as first reported by Hayes and Boothroyd (1969) for mesotidal beaches.