摘要
IntroductionThe alteration of watercourses has been extensive in Sweden as well as in other industrialised countries. Since the end of the last century the water table of about 2500 lakes have been lowered in order to reclaim farmland. More than 600 of these have been completely drained. This particular activity came to a halt at the end of the 1950s whereas the ditching of wetlands and dredging and channelisation of watercourses for the benefit of forestry are still ongoing activities. The regulation of rivers for the purpose of meeting differential needs of hydroelectric power commenced in the beginning of this century, At that time, the floating of timber constituted the economically most important profit from exploitation of northern Swedish rivers.
