MEASUREMENTS OF BEDLOAD TRANSPORT IN THE NEARSHORE ZONE USING RADIOISOTOPIC SAND TRACERS

George Drapeau, Bernard Long

Abstract


A field study was conducted on the North Coast of the Gulf of St. Lawrence in Eastern Canada to evaluate sediment transport processes in a coastal area that would be affected by the modification of river regimes for hydropower production. Radioactive tracers were used to evaluate the mobility of coastal sediments. Three injections were carried out using Neodynium 147 (half-life 11.1 days), at 450, 550 and 2200 m. from the shoreline at depths from 3 to 10 m. The high sensitivity of the detection system allowed to monitor the study area for 44 days. The tagged sediments responded to waves and tidal currents and were sensitive to minor changes. Comparison of the patterns of evolution of the three injections permitted to evaluate the relative mobility of bottom sediments as a function of water depth and distance from shore. Bedload transport rates were calculated but they are related to specific events such as storms within the Gulf of St. Lawrence more than to steady state conditions.

Keywords


bedload; bedload transport; nearshore zone; radioisotopic tracer; transport measurement

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