Sand Waves in the Tidal Entrance to Chesapeake Bay: Preliminary Observations

Abstract

Sand waves are present on the bottom in the tidal entrance to Chesapeake Bay. As far as known they are confined largely to the northern part of the entrance in an area of sand shoals and tidal channels. The waves found are 5 to 10 feet in height, and 200 to 800 feet in crest-to-crest length. They occur in water 15 to 35 feet deep and are found both atop shoals and in channels. Symmetrical and asymmetrical profile types were observed. Near the tidal current thalweg in North Channel, sand waves are largely asymmetrical and face seaward with the ebb. At greater lateral distances away from the thalweg, symmetrical forms are more common, a situation suggestive of equal ebb and flood currents. With even greater distance, sand waves are not developed, a situation suggestive of current incompetence. In a closed-end flood channel, asymmetrical sand waves face landward toward the closed end of the channel with the flood current. On one sand shoal, marginally-located sand waves face convergently toward the higher center of the shoal where symmetrical waves are found. Sand wave migration is believed to be a factor in the maintenance and evolution of some tidal shoals.