ASSESSMENT OF THE GEOMORPHOLOGICAL IMPACT OF MILL DAMS IN SCOTLAND: THE CASE OF BALDERNOCK

A range of adaptations have been made historically to river channels to accommodate water mills, including mill dams, sluices, and mill races (‘lades’ in Scotland, ‘leats’ in England). These modifications imply a series of geomorphological and biological impacts on rivers that are regionally related to the density of mills and mill dams. Thus, mill dam location generates impacts at their construction, but after hundred of years of mill dams controlling river flows, their removal may also generate geomorphological and biological impacts on channels. This study analyses mill dam location in Scotland and then examines the specific case of the impacts of the Baldernock Mill, north of Glasgow. The history of the Baldernock Mill dam was reconstructed from a sediment core in the the mill dam (using core logging, standard sedimentological analyses, Pb and Cs isotopes analyses, and optically stimulated luminescence), along with analysis of historical maps and aerial photograph interpretation. The data show that this mill dam was probably constructed in c.1815 and breached in c.1890. The sediment record shows a change in grain sizes of sediment trapped before and after dam breaching but there appear to be no post-breaching changes in planform character of the channel downstream of the dam. This finding, which can be related to the geological and geomorphological characteristics of most of the rivers in Scotland (largely bedrock channels dominated by glaciation-derived knickpoints that reflect either sub-glacial processes or glacio-isostatic rebound), explains why the impacts of mill dam failure in settings such as northern Britain are not as dramatic as has been found in the rivers of England and mid-Atlantic USA.