The Rio Beni a tributary of the Madera River, drains a basin some 6800km2 on the eastern slopes of the Andes. The relief, reaching altitudes over 6000m, is the cause of uneven precipitation and differential input to the various basin zones. Sediment tansport, and hence erosion, is also affected by this spatial variation. Over several years the recorded variation was smaller for large basins, whereas over a one year period input distributions reveal the influence of glaciers. -M.Dean