Geomorphological Processes and Human Impacts in River Basins (Proceedings of the International Conference held at Solsona, Catalonia, Spain, May 2004). IAHS Publ. 299, 2005., 124-130.

1 Department of Civil Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

2 Department of Hydraulic and Environmental Engineering, Federal University of Ceará, Campus do Pici, bl.713, 60.451-970, Fortaleza, Ceará, Brazil.

Abstract Reservoir survey is a reliable method for assessing sediment yield, which is a major environmental issue concerning impacts on water resources. The paper presents field surveys of one urban and six rural watersheds located in the Brazilian semiarid region, with a wide range of characteristics. Basin areas range from 3 to 1220 km²; reservoir capacity 0.5–126 Mm³; silting history 46–94 years; and hydrological regimes range from very dry "sertão" to mild mountain and coastal regions. Sediment yield assessment consisted of topo-bathymetric reservoir surveys; volume reduction computation; dry bulk density evaluation based on core samples; and trap efficiency estimation. Results showed per capita urban contribution to be 21 kg year^-1; average sediment yield to be 426 t km^-2 year^-1; and reservoir-volume reduction at a rate of 2% per decade. The Hidrosed model was applied and field data were used for its validation. Hidrosed showed good agreement with field data, with Nash and Sutcliffe efficiency coefficient 0.81 for Maner SDR formulation.

Key words Brazil; Ceará; Hidrosed; reservoir silting; sediment yield; semiarid