Partial river canalisation has modified flow from a small high-altitude river basin, located near La Paz in the Andes. Summer precipitation generates flow which occurs mainly during two months of the year. Because of the steep slopes and small size of the basin, discharge rates vary considerably and are subject to abrupt change. Above a certain water depth in the channelized section, waves are observed at the surface. These waves may surge down the river at about 10 m/s, in the form of liquid and solid flow. Upstream, in the non-channelized section, flow remains continuous. -from English summary