CHEEL, R.J., Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada L2S 3A1, rcheel@craton.geol.brocku.ca; UDRI, A., Department of Geologie, Freiburg Universitat, 7800 Freiburg, i. br., Germany.

Experiments were conducted in a 0.305 by 9m flume on a bed of quartz sand with a mean diameter of 0.18mm. The experiments included eight runs over the following range of conditions: flow depths from 0.0605 to 0.0680m, flow velocities from 0.51 to 0.90m /s and Froude Numbers (F) from 0.63 to 1.1.

For F < 0.83 dunes developed and became longer and lower as F increased. At F=0.83 the bed was nominally plane but locally and temporarily developed low in-phase waves or dunes. Bed profiles showed symmetrical bedwaves with average length (L) of 0.26m and average height (H) of 0.005m. At F=0.88 stationary in-phase waves (L=0.29m; H=0.0045m) dominated but were periodically replaced by plane bed due to a reduction in wave amplitude concurrent with downstream migration. For F=0.91 in-phase waves were antidunes (L=0.35m; H=0.013m) that repeatedly underwent cycles of vertical growth followed by breaking or decay. A complete cycle was characterized by: increased height of bed and water surface waves --> upstream migration --> breaking or decay --> planing of bed surface --> growth of new in-phase waves (initially migrating downstream and then remaining stationary during continued vertical growth). Each wave normally behaved independently of other waves although less commonly a breaking wave would trigg er breaking of the next downstream wave. For F>1.0 in-phase waves behaved as above but a breaking wave would more commonly cause breaking of other waves. With increasing F it became more common for waves to break and rebuild quickly without complete pla ning of the bed surface. However, complete cycles were frequent with the following significant differences: (1) the upstream-migrating antidune developed upstream slopes that approached 25 degrees; (2) planing was accomplished by the rapid migration of a low, asymmetrical bedform through the antidune trough.

With increasing F, internal stratification varied from horizontal to gently undulating, form-concordant laminae -->low-angle (<7degrees) upstream-dipping laminae with minor, low-angle downstream-dipping laminae -->increasingly steeper backset and foreset laminae with strongly curved lower bounding surfaces. Internal fabric is characterized by a-axis parallel to and imbricate into the flow. Imbrication is steepest within backset laminae compared to low-angle foreset and horizontal laminae. In general, mean imbrication angle and dip-angle of backset laminae both increase with F.