Development of sand-bedded rivers in glaciated, Southern Ontario

English Abstract:

Many studies of river and floodplain sedimentology demonstrate their complexity and the need to simplify observations in the form of standard models. A standardized description, classification, and interpretation of fluvial deposits or facies models were revised by Miall (2010) to represent the behavior of meandering rivers. A field investigation was undertaken to test the applicability of the accepted meandering sand-bedded river facies model to sand-bed rivers in Southern Ontario. A challenge in this environment is the influence of non-alluvial channel boundary materials such as glacial outwash sands, till, and glaciolacustirne clay. The presence of these materials in some channel beds and banks, and entrenchment as these rivers approach the Lake Erie base level, suggest that these rivers are not in equilibrium and that recognized “models” may not be appropriate at predicting channel behaviour. A multi-faceted approach (sedimentology, channel surveys, geophysics, etc.) is used to characterize the mechanisms and formation of fluvial sedimentary structures and the processes controlling the lateral and vertical mobility of these active channels. It appears these sand-bedded rivers are resistant to change, and that laterally accreting surfaces may represent middle-late Holocene migration patterns. This is demonstrated by limited bank migration rates, anonymously tall (5 m+) meander bends with low width to depth ratios, and sediment profiles characterized by basal hardpan clays occasionally overlain by coarse gravel lag deposits. A C14 age of 8670 ± 30 years BP at river bed level also suggests that these channels, and associated floodplains, may be less dynamic over the long term when compared to the standard model of meandering, sand-bedded rivers.