Examining the concept of baseflow using end-member mixing analysis (Invited)
Abstract
Baseflow represents the condition a catchment returns to after storm events and is often used as a reference point in mixing models of an unforced state. Frequently baseflow samples are considered indicative of an 'old water' or ground water end member. To test the assumptions, 28 storms at the Panola Mountain Research Watershed, near Atlanta, GA, were examined using a three-component chemical mixing model to determine the relative contributions of end members at baseflow and during storms. A discriminant analysis indicated that a 6-month humidity index, precipitation volume, and storm duration were significant in determining the pattern of end-member contributions during these storms. The results indicate that baseflow varies markedly across seasons and is a mixture of varying proportions of two 'groundwater' (i.e., saturated zone) end members. The only consistent finding is that vadose water did not contribute to baseflow. More broadly, the change in concentration between baseflow and stormflow was far more predictable for those solutes whose vadose zone concentration was outside the range of concentration defined by the two groundwater endmembers because there was a consistent direction of change during a storm; if the end member concentration of the vadose water lay between the groundwater end members, the chemical response of the stream depends on the baseflow composition at the start of the storm. This finding explains why it is difficult to define a simple concentration-discharge function to explain both baseflow and storm samples across many storms. Therefore, the concept of baseflow is valid as a reference point for a given storm, but should not be considered a single reference state across seasons.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.H23N..08H
- Keywords:
-
- 1879 HYDROLOGY Watershed;
- 1806 HYDROLOGY Chemistry of fresh water