ABSTRACT: Watertable response characteristics in hillslopes dominated by preferential flow.

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Abstract

Characterizing areas in a watershed based on the water table behaviour should help us to better understand and predict internal watershed processes. Areas with a similar response pattern could also be used to apply semi- distributed models, especially in watersheds with limited data. If lateral preferential flow is a dominating runoff process, the water table response typically shows a distinct hydraulically-limited pattern. This response is characterised by a capping of the rising water table when the lateral preferential flow features are activated and subsurface flow still increases. At our forested study site on the west coast of British Columbia, Canada, we expected that this response would be related to the contributing area since nearby hillslope excavations showed that the development of preferential flow network was positively correlated to the contributing area. We mapped the watershed into three predetermined zones and installed 25 piezometers to sample the water table dynamics. The objectives were 1) to characterize the water table – runoff relationship, 2) to prove preferential flow by observable characteristics, and 3) to test the feasibility of identifying areas within a watershed that are dominated by lateral preferential flow. We could identify the extreme water table responses; however, the watershed areas were not well defined. In addition, there was no strong relationship between the hydraulically-limited response and observable watershed characteristics. Although areas might still be useful for grouping the hillslope processes, the water table response measured with piezometers may not be an appropriate indicator for mapping the watershed into areas with runoff dominated by lateral preferential flow.

Bibliography of Canadian Geomorphology