Low-flow hydrology in low-order basins in Canada

Bhamjee, Rashaad
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University of Guelph

There is insufficient information about streamflow conditions in low-order, headwater streams in Canada despite being important hydrological and eco- logical features. A defining characteristic of many of these streams is that they experience intermittent flow during drier periods. As such, these streams are especially sensitive to change. There are numerous challenges with monitoring ephemeral streamflow activity, and the connectivity of these streams to both their hillslopes, and to downstream areas. The aim of this thesis was to quantify and describe the dynamics of low-flow conditions in temperate headwater streams. Coupling an electrical resistance sensor with a new flow-detection sensor, a paired-sensor monitoring approach was used to monitor ephemeral activity in two small headwater catchments in southern Ontario. The timing of the transition between a continuously flowing stream to an intermittent stream differed between sites, with one site transitioning at the end of May, and the other at the end of August. These transition times were attributed to differences in precipitation during the field season, and compared to 40-year climate averages for each month. Predictors of flow were determined using monthly binary logistic regression models and found to vary monthly over the study period. Predictors such as maximum rainfall intensity were found to be more seasonal, while others such as total rainfall, were more consistently identified. An analysis of 40-year trends in discharge and low-flow indicators was conducted for unregulated streams in Canada. Annual discharge decreased widely across Canada with the timing of significant decreases occurring mainly during the summer months, and increases in the winter months. Significant decreases to the number of low-flow days were observed, however, regions with significant increases to both the number and length of low-flow events were also observed. Changes to the frequency and timing of low-flow conditions in headwater streams can impact the hydrology and ecology of downstream waterways and the connectivity of hillslopes with fluvial systems. Long-term relationships between climate variables and low-flow conditions cannot be fully understood without adequate monitoring in headwater streams. Understanding the forms, processes, and functions of these critical, but vulnerable, temporary waterways has a long way to go in Canadian hydrology.

Canada, Headwater streams, Low-order basins, Ephemeral activity, Climate variables