The effects of drainage on high flows hav~ been studied by means of a conceptual runoff
model (HBV/PULSE). To find parameters, typical for drained wetlands, the model was
calibrated 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 had
different 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 specific
period, 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 simulate
the drainage of a 1000 km
2 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 were
used. 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.
SMHI , 1993. , p. 36