Piezometric response in zones of a watershed with lateral preferential flow as a first-order control on subsurface flow

Characterizing zones of a watershed based on the water table is used to understand and predict internal watershed processes. In watersheds dominated by lateral preferential flow, the water table response typically shows a distinct hydraulically limited pattern. This response is characterized by a capping of the rising water table when the lateral preferential flow features are activated and subsurface flow still increases. 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 with the contributing area. The watershed was stratified into three predetermined zones and installed 25 piezometers to measure 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. Watershed zones were not well defined and there was no strong relationship between the hydraulically limited response and observable watershed characteristics. Although zones might still be useful for grouping the hillslope processes, the piezometric response may not be an appropriate indicator for mapping the watershed into areas with runoff dominated by lateral preferential flow. Copyright (C) 2010 John Wiley & Sons, Ltd.