The effects of drainage on high flows hav~ been studied by means of a conceptual runoffmodel (HBV/PULSE). To find parameters, typical for drained wetlands, the model wascalibrated for two small catchments, one in central Sweden and one in south eastem Finland,where runoff data were available for drained and undrained conditions. The catchments haddifferent characteristics, and the calibration procedure yielded two different parameter sets.
The drainage effects in these small basins were studied by simulating the runoff, for a specificperiod, using model parameters for drained and undrained conditions. In the Swedish catchment,the effects on the runoff were almost negligible. In the Finnish catchment, the peak and low flows, as well as the total runoff volume increased considerably during the first 10 years after drainage.
The drainage parameters found for the small experimental basins, were also used to simulatethe drainage of a 1000 km2 catchment in central Sweden, with a 20 % coverage of swamps.Hard.ly any effects could be seen when the parameters from the small Swedish basin wereused. With the Finnish parameters there was a slight increase in peak and low flows, and the total runoff volume increased by 3.5 %. When extreme flows were simulated, by entering a design area rainf all sequence into the model, the diff erences between peak flows for drained and undrained conditions were fully negligible.