LAND-USE, SOIL-EROSION, AND RESERVOIR SEDIMENTATION IN AN ANDEAN DRAINAGE-BASIN IN ECUADOR

Rapid sedimentation is a major problem at the reservoir of the Amaluza dam on the Paute river where more than half of Ecuador's electric pow er is produced. With this in mind extensive small-plot experiments wer e conducted with portable rainfall simulators to investigate the runof f dynamics and erosional responses of different soils and land uses in the 5,186 km2 Paute drainage basin. The results, combined with field observations and morphometric data, indicate that patterns of contempo rary land use largely control the production and movement of runoff an d sediment from slopes. Abandoned farmlands play an important role due to their great extent and to their runoff and erosional characteristi cs, while recently plowed crop lands absorb rain of the more frequent intensities. The integrated behavior of surfaces with different land u ses on the same slope requires the study of erosion to extend beyond i ndividual agricultural plots. Topography, proximity to the reservoir, presence of delivery networks, and in-stream material extraction are k ey non-agricultural factors affecting sediment movement into the reser voir.