Water temperatures and heat budgets in Dorset chalk water courses

Field measurements have established the heat budgets for stations on two wa ter courses which drain catchment areas dominated by the upper chalk in Dor set, UK. Information on the main advective and non-advective heat fluxes we re collected during winter and summer periods in 1994 at a site near to a s pring source on a tributary of the River Piddle, and at a station situated downstream on the River Bere. Inputs of heat energy were dominated by radia tive fluxes, with net radiation receipt accounting on average for around 90 % of the non-advective total in both summer and winter. Sensible heat (conv ective/conductive) transfer from the atmosphere was enhanced in the summer by the lower water temperature of these spring-fed streams, while relativel y warm water temperatures during winter enhanced heat losses by evaporation , which was the dominant non-advective heat loss component in this season. Significant heat losses also occurred by sensible transfer and by back radi ation. Summer measurements revealed that conduction of heat into the non-ve getated gravel bed of the River Piddle tributary was the dominant form of l oss, but this output was strongly reduced in summer by weed cover on the be d of the River Bere, Considerable daily and diel variability was evident in non-advective heat flux components. Heat advected into the study reaches v ia precipitation was negligible, but groundwater inflows added to the heat storage of the water courses in both winter and summer. This effect was mos t marked at the headwater site and in the summer season because of lower st reamflow discharge. Copyright 1999 John Wiley & Sons, Ltd.