Lithology’s Watermark in the Geometry of Scottish Stream Networks
2018
Guy, Robin | Mudd, Simon
River geometry has been hypothesised to reflect climate. Recent studies have presented a clear link between river junction angle and local climate, in that the more humid the landscape, the wider the angle between joining tributaries. This dissertation focuses specifically on the controls upon junction angles of streams in Scotland, an area which has received limited focus. It was hypothesised that Scotland’s diverse underlying geology would disrupt the expected disruption of junction angles, and this disruption has indeed been confirmed. The entire Scottish river network, compromising more than 20,000 unique junction angles, was analysed digitally and remotely following the extraction of hydrological information from high-resolution DEMs. A mean junction angle value of 67.367o was established across Scotland and it was recognised that across 9 bedrock groups there are contrasting degrees of divergence from this mean value. Five groups (of igneous and metamorphic rock) present <1.3o of divergence from the mean figure, while four groups (all of sedimentary rock type) instead present ~4o of deviance. Additionally, one group, Cambrian geology, exceeded this value by 17.12o, although due to a small sample size, it is likely that figure acts as an outlier. Despite these differences, it was found that underlying bedrock does not have a statistically significant control upon the formation of stream junction angles following a chi-squared test for significance at p = 0.230. Due to an apparent stability close to a mean value of 67.367o, it is proposed that Scotland’s stable climate instead acts as the primary controlling force and thereby the conclusions of past research are confirmed.
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