After the first systematic hydrological measurements in small first-order catchments in the Swiss Emmental (starting 1903) the forest hydrologists were looking for similar measurements in a region with Flysch geology. This was motivated by extensive afforestation in these areas since the 19th century and the related question of the vegetation effect on the water balance. After a first experiment in the canton Fribourg (Rotenbach und Schwändibach) that was not really successful, the young researcher Hans M. Keller was mandated in the early 1960s to establish a new long-term forest hydrological monitoring in the Alptal valley (canton Schwyz). His team set up eleven runoff stations between 1967 to 1973 in the main tributaries of the Alp river. All of them were destroyed on 23 June 1974 in one single flood event. Subsequently, it was decided to rebuild only three of them, but in a much more robust way. The corresponding catchments differed considerably in the forest coverage and allowed to draw conclusions about the impact of the forest on runoff.