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Contribution of alluvial groundwater to the outflow of mountainous catchments

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Käser Daniel, Hunkeler Daniel,
Project Groundwater resources under changing climatic conditions
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Original article (peer-reviewed)

Journal Water Resources Research
Volume (Issue) 52(2)
Page(s) 680 - 697
Title of proceedings Water Resources Research
DOI 10.1002/2014wr016730

Abstract

Alluvial aquifers in mountainous regions cover typically a limited area. Their contribution to catchment storage and outflow is rarely isolated; alluvial groundwater discharge under gauging stations is generally assumed negligible; and hydrological models tend to lump alluvial storage with other units. The role of alluvial aquifers remains therefore unclear: can they contribute significantly to outflow when they cover a few percent of catchment area? Should they be considered a dynamic storage unit or merely a transmission zone? We address these issues based on the continuous monitoring of groundwater discharge, river discharge (one year), and aquifer storage (6 months) in the 6 km(2) alluvial system of a 194 km(2) catchment. River and groundwater outflow were measured jointly through coupled gauging stations. The contribution of alluvial groundwater to outflow was highest at the outlet of a subcatchment (52 km(2)), where subsurface discharge amounted to 15% of mean annual outflow, and 85% of outflow during the last week of a drought. In this period, alluvial-aquifer depletion supported 75% of the subcatchment outflow and 35% of catchment outflow. Thus 3% of the entire catchment supported a third of the outflow. Storage fluctuations occurred predominantly in the aquifer's upstream part, where heads varied over 6 m. Not only does this section act as a significant water source, but storage recovers also rapidly at the onset of precipitation. Storage dynamics were best conceptualized along the valley axis, rather than across the more conventional riparian-channel transect. Overall the contribution of alluvial aquifers to catchment outflow deserves more attention.
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