Influence of stream bank seepage during low‐flow conditions on riparian zone hydrology

Abstract

We examined the effect of sustained stream bank seepage during base flow conditions on the hydrology of two riparian zones in lowland agricultural areas in southern Ontario, Canada. Hydrometric data and subsurface chloride patterns over a 2‐year period indicated that stream inflow to the riparian zone sustained a reversed water table gradient inland for periods of up to 4 months in summer and autumn at one of the riparian sites. Stream bank seepage occurred throughout the year at the second riparian site where hillslope inflow was restricted by an upslope spur. Despite high evapotranspiration rates in summer, stream inflow maintained a zone of saturated riparian sediments that extended up to 25 m inland. A bromide tracer injection at the stream bank interface indicated that bank seepage occurred along preferential flow paths in a poorly sorted gravel layer at the two riparian sites. Conceptual models of humid temperate riparian zones have focused on hillslope to stream hydrologic flow paths. However, our results suggest that sustained stream bank inflow during low‐flow conditions can exert a dominant control on riparian hydrology in lowland landscapes where level riparian zones bounded by perennial streams receive limited subsurface inflows from adjacent slopes.