Stability of giant sand waves in eastern Long Island Sound, U.S.A.

A combination of a highly accurate bathymetric surveying technique and in-situ submersible observations and measurements were used to assess the migrational trends and morphological changes of large sand waves (Ht ??? 17 m) in eastern Long Island Sound. Although residing in a high-energy tidal environment characterized by a net westward sediment flux, the large bedforms are relatively stable over the short term. Over a 7 month period, 55.1% of a total 2942 m of sand wave crestline lengths migrated less than the horizontal accuracy limits of navigation (2 m). Approximately 35% of the remaining sand wave crests migrated less than 4 m. Net migration of the sand wave crests in the study area was 0.2 m. In addition, the bulk form (center of area in profile view) or the base of the sand waves showed little, if any, movement. These data, in conjunction with flow data within the sand wave field, suggest that net migration rates are greater than the time span of this study and/or the sand waves move in response to large residual flows created by high-energy, aperiodic storm events. The latter scenerio suggests that day to day processes only serve to rework and modify the sand waves. ?? 1990.