DOWNVALLEY GRADIENTS IN FLOW PATTERNS, SEDIMENT TRANSPORT AND CHANNEL MORPHOLOGY IN A SMALL MACROTIDAL ESTUARY: DIPPER HARBOUR CREEK, NEW BRUNSWICK, CANADA

Dipper Harbour Creek's lower reaches run through a narrow salt marsh on the Bay of Fundy, New Brunswick, Canada. This 2 km long section of the creek constitutes an extreme example of a tide‐dominated estuary exhibiting strong downvalley morphology and sedimentology gradients. Dipper Harbour Creek drains a basin of roughly 8.8 km2, but except during the spring snowmelt freshet, tidal flow so overshadows freshwater flow within the salt marsh reach that the system essentially functions as a tidal creek. To identify and explain the main geomorphic processes controlling the creek system, records were collected in summer 1993 of tidal stage and velocity fluctuations, sand dune migration rates, bed material composition, channel cross‐sectional geometry and channel sinuosity. Bed materials become progressively finer upvalley, with deposits of medium to coarse sands concentrated in the highly sinuous central reach of the creek during the summer. Current velocities within the creek are strongly flood‐dominant, featuring a consistent low‐stage peak in flood velocity, a secondary high‐stage flood surge, and a weaker ebb peak occurring around bankfull stage. Under summer low freshwater discharge conditions, the predominant direction of bed sand transport is upvalley. The spring freshet, however, causes a major downvalley shift of sand deposits, suggesting a seasonal cycling of medium to coarse sands within Dipper Harbour Creek.