Groundwater Gradients, Soil Moisture and Stream Mapping in a Boreal Landscape

• Main Author: Erdbrügger, Jana
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2024
• Subjects: Institute of Geography; UZH Dissertations; 910 Geography & travel; Northern Sweden
• Online Access: https://www.zora.uzh.ch/id/eprint/259331/; https://www.zora.uzh.ch/id/eprint/259331/1/jerdbr-thesis.pdf; https://doi.org/10.5167/uzh-259331

Small headwater catchments are highly dynamic systems, but we often lack data and understanding of the hydrological processes taking place there. This study focused on the Krycklan catchment (67.8 km2) in Northern Sweden and the dynamics of the shallow groundwater tables, stream emergence and soil moisture over time and in space. It is generally assumed that, in humid climates, the groundwater table is a subdued copy of the surface topography but there is currently no guidance on what resolution DEM to use in hydrological analyses. Nevertheless, detailed microtopography, as can be retrieved from high-resolution Digital Elevation Models (DEMs), is unlikely to affect groundwater topography. A first step, therefore, was to look at the effects of DEM- smoothing and -aggregation on the calculated flow directions and derived catchment boundaries. For more than 40 % of the Krycklan catchment area the calculated flow directions depend strongly on the degree of smoothing or aggregation of the DEM. These are areas with local slopes in the opposite direction of the general slope, flat areas, ridges, and incised streams. We calculated the drainage area for 40 locations, outlets of catchments of different sizes, and found that the processing of the DEMs affected small catchments (i.e., first-order streams) the most. This highlights the need to carefully consider the effects of DEM smoothing or -aggregation on the calculated flow directions and drainage areas as the shifts in catchment boundaries and drainage areas can have a significant effect on the calculated water balance. To compare the results from the theoretical DEM analyses with real observations, a network of groundwater wells was installed in two areas in the Krycklan catchment. One is a small headwater catchment (3.5 ha; 54 wells) and the other a hillslope (1 ha; 21 wells). The wells were 274 cm deep on average (range of 70–581 cm). The positions of the wells were determined using a Light Detection and Ranging (LiDAR) scanner. The groundwater-level variations were ...