Hydropower Influences on River Ice Dynamics and Channel Morphology: A Matter of Thermal and Flow Scales

English Abstract:

Hydropower development of a river raises questions regarding the influences of the development on ice dynamics and channel morphology in the river downstream: Will the development change ice dynamics in the river; if so, how? If the changes are substantial, how will the modify channel morphology of the river; if so, how? My paper addresses these questions and shows how these questions revolve around the relative scales of thermal and flow processes at the development site. In simple terms, the scales define the volume of ice formed in the river relative to the volume of water flow passing through the channel during winter. Hydropower may alter the relative magnitude of the two scales, typically doing so by changing the quantities of water and water-borne heat entering the channel during winter. At the extremes of a hypothetical gauge formed by the relative magnitudes of the two scales, hydropower exerts little influence on river ice processes and channel morphology, because the volume of water flow dwarfs the volume of ice formed (large river, lower latitude), or conversely the volume of ice dwarfs the volume of water flow (small river, higher latitude). However, hydropower shifts the relative scales of ice and water, moving river conditions to a more dynamic, middle region of the gauge. When such a shift occurs ice potentially becomes a more active agent in shaping channel morphology, as it affects the distribution of an erosive flow, and the flow in turn has sufficient force to drive ice against channel boundaries. The nature of the material forming channel boundaries plays a substantial role limiting the extent to which the river ice and water flow influence channel morphology. More resistant boundary material will withstand higher levels of abrasion by water flow and ice, while boundaries formed in alluvium and weak soils are less able to do so. My paper discusses the hypothetical gauge concept and suggests topics for research.