Author(s): Robert Ettema; Edward W. Kempema
Keywords: Rivers; Heat; Altitude; Latitude; Ice
Abstract: Heat-flux sensitivity can have important effects on the morphology, ecology, and human uses of river channels draining mountains. The spatial scale of a channel reach influences the channel's energy budget, typically causing a channel's heat-flux sensitivity (or heat sensitivity) to decrease along watersheds draining mountains or hills to a sea or large lake. Consequently, a smaller channel (or lower-order stream) conveying less water at the upper end (say, mountainous part) of a watershed is thermally more sensitive than is a larger channel (or higher-order stream) conveying water through a plain headed towards the watershed's downstream end. River channels receive most of their solar energy as land areas do, by absorbing solar and longwave radiation. But river channels, generally, are unique in being able to move and store part of this energy. As spatial scale of a channel's cross-section increases, so does this ability, though the channel's heat sensitivity concurrently decreases. The ability to move and store energy, together with water's physical behavior, dampens the intermittent nature of solar radiation and diminishes a channel's heat sensitivity. Heat sensitivity is defined herein as the temporal rate at which a channel's water temperature changes in response to input of heat. Local conditions of terrain, groundwater, and anthropomorphic inputs of heat also more readily affect smaller channels. To understand the behavior (morphology, ecology, and the design of effective hydraulic structures) of rivers draining mountains, the heat fluxes entering or exiting specific river channels must be considered.