DOWNVALLEY GRADIENTS IN FLOW PATTERNS, SEDIMENT TRANSPORT AND CHANNELMORPHOLOGY IN A SMALL MACROTIDAL ESTUARY - DIPPER HARBOR CREEK, NEW-BRUNSWICK, CANADA

Dipper Harbour Creek's lower reaches run through a narrow salt marsh o n the Bay of Fundy, New Brunswick, Canada. This 2 km long section of t he creek constitutes an extreme example of a tide-dominated estuary ex hibiting strong down-valley morphology and sedimentology gradients. Di pper Harbour Creek drains a basin of roughly 8.8 km(2); but except dur ing 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 process es 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 de posits of medium to coarse sands concentrated in the highly sinuous ce ntral reach of the creek during the summer. Current velocities within the creek are strongly flood-dominant, featuring a consistent low-stag e peak in flood velocity, a secondary high-stage flood surge, and a we aker ebb peak occurring around bankfull stage. Under summer low freshw ater discharge conditions, the predominant direction of bed sand trans port is upvalley. The spring freshet, however, causes a major downvall ey shift of sand deposits, suggesting a seasonal cycling of medium to coarse sands within Dipper Harbour Creek.