title: Delineating baseflow contribution areas for streams - A model and methods comparison.
abstract: This study addresses the delineation of areas that contribute baseflow to a stream reach, also known as stream capture zones. Such areas can be delineated using standard well capture zone delineation methods, with three important differences: (1) natural gradients are smaller compared to those produced by supply wells and are therefore subject to greater numerical errors, (2) stream discharge varies seasonally, and (3) stream discharge varies spatially. This study focuses on model-related uncertainties due to model characteristics, discretization schemes, delineation methods, and particle tracking algorithms. The methodology is applied to the Alder Creek watershed in southwestern Ontario. Four different model codes are compared: HydroGeoSphere, WATFLOW, MODFLOW, and FEFLOW. In addition, two delineation methods are compared: reverse particle tracking and reverse transport, where the latter considers local-scale parameter uncertainty by using a macrodispersion term to produce a capture probability plume. The results from this study indicate that different models can calibrate acceptably well to the same data and produce very similar distributions of hydraulic head, but can produce different capture zones. The stream capture zone is found to be highly sensitive to the particle tracking algorithm. It was also found that particle tracking by itself, if applied to complex systems such as the Alder Creek watershed, would require considerable subjective judgement in the delineation of stream capture zones. Reverse transport is an alternative and more reliable approach that provides probability intervals for the baseflow contribution areas, taking uncertainty into account. The two approaches can be used together to enhance the confidence in the final outcome.
authors.affiliation: Center for Applied Geoscience, Hölderlinstr. 12, 72074 Tübingen, University of Tübingen, Germany; Institute for Modelling Hydraulic and Environmental Systems (LS(3))/SimTech, Pfaffenwaldring 5a, D-70569 Stuttgart, University of Stuttgart, Germany; Department of Earth and Environmental Sciences, EIT 2051B, 200 University Avenue West, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. Electronic address: reynoldtor@hotmail.com.
authors.forename: Reynold
authors.initials: R
authors.lastname: Chow
authors.affiliation: Department of Earth and Environmental Sciences, EIT 2051B, 200 University Avenue West, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. Electronic address: michael.e.frind@gmail.com.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Frind
authors.affiliation: Department of Earth and Environmental Sciences, EIT 2051B, 200 University Avenue West, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. Electronic address: frind@uwaterloo.ca.
authors.forename: Emil O
authors.initials: EO
authors.lastname: Frind
authors.affiliation: Department of Earth and Environmental Sciences, EIT 2051B, 200 University Avenue West, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. Electronic address: jpjones1856@gmail.com.
authors.forename: Jon P
authors.initials: JP
authors.lastname: Jones
authors.affiliation: Department of Earth and Environmental Sciences, EIT 2051B, 200 University Avenue West, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. Electronic address: marcelosousa1@gmail.com.
authors.forename: Marcelo R
authors.initials: MR
authors.lastname: Sousa
authors.affiliation: Department of Earth and Environmental Sciences, EIT 2051B, 200 University Avenue West, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. Electronic address: drudolph@uwaterloo.ca.
authors.forename: David L
authors.initials: DL
authors.lastname: Rudolph
authors.affiliation: Department of Geology and Geological Engineering, Université Laval, Pavillon Adrien-Pouliot (Room PLT-4709), Québec, QC G1V 0A6, Canada. Electronic address: john.molson@ggl.ulaval.ca.
authors.forename: John W
authors.initials: JW
authors.lastname: Molson
authors.affiliation: Institute for Modelling Hydraulic and Environmental Systems (LS(3))/SimTech, Pfaffenwaldring 5a, D-70569 Stuttgart, University of Stuttgart, Germany. Electronic address: wolfgang.nowak@iws.uni-stuttgart.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Nowak
mesh_terms: D000465:Algorithms; D060587:Groundwater / Q000737:chemistry*; D062070:Hydrology; D008962:Models, Theoretical; D009864:Ontario; D045483:Rivers / Q000737:chemistry*; D035501:Uncertainty; D014872:Water Movements