Ash on snow a tool - A tool to prevent flooding? - Paper presented at the Nordic Hydrological Conference (Uppsala, Sweden June, 2000)

Years with late spring in combination with thick snow-pack constitute risk for flooding. To decrease that risk, the possibility of spreading albedo-lo wering material (wood ash) on parts of a basin snow has been examined. By b lackening the snow more solar radiation is absorbed and the snowmelt is enh anced. If sun-exposed parts of the basin are ash-treated (before normal run off starts) the runoff will be distributed over a longer period of time and the risk of flooding will be reduced. Wood ash in different concentrations was spread on small snow plots and melt rates and albedo were measured. Fo r snow covered with 0.03 kg ash m(-2), the albedo was decreased from approx imate to 0.60 for natural snow to approximate to 0.25, resulting in approxi mate to 90% more absorbed short-wave radiation. Melt on the ash treated sur face, (daily average snow water equivalent), was 70% larger than melt on na tural snow (12 and 7 mm d(-1) respectively). A five times larger concentrat ion (0.15 kg m(-2)) only increased the melt rate to 14 mm d(-1). The temper ature-index method was shown to be inadequate for modelling the melt rate f or the ash treated snow. A radiation-index model, based on absorbed incomin g short wave radiation, was shown to model the melt rate better than the te mperature-index method.