HR: 17:10h
AN: H24A-05    [Abstracts]
TI: Testing the Variable Source Area Hypothesis Using Tracers and GIS in an Nested Mesoscale Catchment
AU: * Tetzlaff, D
EM: d.tetzlaff@abdn.ac.uk
AF: University of Aberdeen, Department of Geography and Environment, University of Aberdeen, Aberdeen, AB24 3UF United Kingdom
AU: Soulsby, C
EM: c.soulsby@abdn.ac.uk
AF: University of Aberdeen, Department of Geography and Environment, University of Aberdeen, Aberdeen, AB24 3UF United Kingdom
AU: Waldron, S
EM: s.waldron@geog.gla.ac.uk
AF: Department of Geography and Geomatics, University of Glasgow, Glasgow, G12 8QQ United Kingdom
AU: Malcolm, I
EM: I.A.Malcolm@marlab.ac.uk
AF: FRS Freshwater Laboratory, FRS Freshwater Laboratory, Faskally, Pitlochry, PH16 5LB United Kingdom
AU: Dunn, S
EM: S.Dunn@macaulay.ac.uk
AF: The Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH United Kingdom
AU: Lilly, A
EM: A.Lilly@macaulay.ac.uk
AF: The Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH United Kingdom
AB: Hydrometric and natural tracer investigations were combined with a GIS analysis of the 31km2 Girnock catchment (Cairngorm National Park, Scotland), to assess the significance of the variable source areas model in explaining dominant runoff process and mean residence times within the catchment. The catchment has a complex geology, soil cover and topographic organisation. Gran alkalinity was used to demonstrate that catchment geology has a dominant influence on baseflow chemistry, but low storm flow alkalinity indicated that flow paths originating in the acidic horizons in the upper profile of catchment soils dominated storm runoff generation. Chemically-based hydrograph separations at the catchment scale indicated that around 70% of annual runoff was derived from surface and near surface hydrological sources. Similar contributions (64-77%) were estimated for virtually all major sub-basins. delta18O ratios in precipitation (mean: -9.36, range: -16.10 to -5.02) and streamwaters (mean: -9.11, range: -11.65 to -7.42) were used to assess mean catchment and sub-basin residence times which were consistently in the order of 4-6 months. GIS analysis showed that these tracer-based diagnostic features of catchment functioning were consistent with the landscape organisation of the catchment. Soil maps derived from the UK HOST (Hydrology of Soil Type) data base indicated that the catchment as a whole, and individual sub-basins, were dominated by responsive soils such as Histosols and gleysols in valley bottom areas. Spatial analysis of soil cover - in combination with a catchment topographic index - predicted extensive areas of saturation in valley bottom areas that expand during hydrological events from return flow of hillslope groundwaters and direct precipitation generating saturation overland flow. Thus during storm events, a variable source area model agrees well with the high degree of hydrological connectivity between catchment hillslopes and the stream channel network. However, groundwater re-charge in the catchment is complex and characterised by much more marked heterogeneity than implied by the variable source area concept.
DE: 1860 Streamflow
SC: Hydrology [H]
MN: Fall Meeting 2005