Calculation of Side-Separated Contributions to Stream Networks – A New Tool to Characterize Riparian Zones

T. Grabs1, Jan Seibert2, Kelsey Jencso3, Brian McGlynn3
1 Department of Physical Geography and Quaternary Geology, Stockholm University, SE-106 91 Stockholm, Sweden
Telephone: +46 (0) 768024224
2 Department of Geography, University of Zurich, CH-8057 Zurich, Switzerland
Telephone: +41 (0) 44 6355200
3 Watershed Hydrology Lab, Montana State University, 334 Leon Johnson Hall, Bozeman, Montana 59717
Telephone: +1 406 994 7690

Streams play a key role in many environmental studies and research areas. From a hydrological perspective, streams and other flow pathways carry the spatio-temporally convoluted signal of all upstream, hydrologically-connected processes. Modern tools for GIS-based hydrological landscape analysis (HLA) embrace this concept for calculating values of upslope area or for aggregating upslope terrain indices. Recent studies, however, suggest that not all upslope processes contribute equally to the observed stream signal and that particularly riparian zones hold the key for a better understanding of stream responses. Riparian zones are, by nature, elongated strips of land directly adjacent to a stream network and located on both of its sides. Being the last stage before a drop of water enters a stream network, the potential imprint left by riparian zones is likely to be considerably larger than indicated by their actual extend. However, traditional HLA methods used to characterize these zones are mostly inapplicable because most methods fail to account for small extend of riparian zones and for the fact that they are located on opposite sides in a stream network. To overcome limitations of traditional HLA methods, we developed a novel method to calculate side-separated contributions from adjacent hillslopes. Water table and elevation data from the 22 km2 Tenderfoot Creek catchment, Montana, demonstrated clearly the importance of the new method. Separating contributions from the two sides produced significantly different results than produced by standard HLA methods. More importantly, only upslope area calculated by the new method was able to predict the hydrological connection between hillslope and riparian water tables as observed in 24 transects along the stream network.

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