Erodibility of cohesive glacial till bed sediments in urban stream channel systems

摘要

A major challenge in urbanizing watersheds in southern Ontario is the development of a broader understanding of semi-alluvial stream channels with streambeds and lower banks consisting of consolidated glacial till bed sediment. This investigation focuses on the erosive resistance of two distinct glacial till bed sediments within the Greater Toronto region, the Sunnybrook till and the Halton till. The study reviews the distinct nature and properties of till sediment and compressional and shear strength which can be significant controls on the erosion of the till sediment in stream channels. Critical shear stress and an erodibility coefficient were measured with an in situ jet-tester, and sediment strength using a penetrometer and a shear vane tester. Bulk properties were investigated through sediment cores. From over 50 jet-tests, power-law functions were used to determine erodibility coefficients as a function of critical stress for each till sediment. Empirical relations were developed to estimate critical stress from best-correlated sediment strength and bulk properties. The study offers insight into the considerable complexity of the factors controlling the erosion of glacial till sediments and identifies implications for management of semi-alluvial streams.