SPATIAL AND SEASONAL VARIABILITY IN THE COMPONENTS OF THE RIVER HEAT-BUDGET

Detailed hydrometeorological measurements have been used to establish the components of the river heat budget for 495 days covering 18 study periods and 11 study reaches in the Exe Basin, Devon, UK. Averaging t he results across the whole data-set indicates that net radiation, fri ction, sensible heat transfer, condensation and bed conduction contrib uted 56.0, 22.2, 13.2, 5.8 and 2.8%, respectively, to the non-advectiv e energy gains, whereas net radiation, evaporation, sensible heat exch ange and bed conduction accounted for 48.6, 30.4, 10.6 and 10.4%, resp ectively, of the non-advective heat losses. Precipitation falling on t he river channel had little impact on the river heat budgets, but ener gy advected in groundwater accounted for an average 5% of the heat sto rage in the river. The magnitude and importance of the river heat budg et components were found to be variable in space and time. The influen ce of channel morphology, valley topography, riparian vegetation, subs tratum nature and hydrological conditions, especially the effects of r iver regulation, promoted inter-reach variability in the make up of th e heat budget and caused significant differences in energy fluxes at a local scale. Heat budget components also exhibited considerable diffe rences between seasons and varied from day to day for individual reach es. (C) 1997 by John Wiley & Sons.