|Castro Filho, C|
Submitted to: International Commission on Large Dams
Publication Type: Proceedings
Publication Acceptance Date: 9/20/2002
Publication Date: 9/20/2002
Citation: COCHRANE, T.A., CASTRO FILHO, C., CAVIGLIONE, J.H., NORTON, L.D., JOHANSSON, L.P. REDUCTION OF SEDIMENT DELIVERY TO THE ITAIPU RESERVOIR: A NEW VISION THROUGH THE IMPLEMENTATION OF MONITORING TECHNIQUES AND WATERSHED MANAGEMENT. INTERNATIONAL COMMISSION ON LARGE DAMS. 2002. p. 808-821. Interpretive Summary:
Technical Abstract: An increase in agricultural land use in the lower Paraná river basin in southern southeast and center western Brazil has contributed to an increase in soil losses in the region. The effects of increasing soil losses through water erosion and the eventual deposition of these sediments in the reservoirs downstream have potential adverse impacts. Sediment transported by rivers and siltation of the downstream Itaipu hydroelectric reservoir can lead to loss of energy production, reduction in navigability of the rivers and reservoirs, and disruption of the aquatic ecosystem. Evaluation of the sediment transport and sediment loading of the Reservoir formed by the Itaipu Dam is difficult because of the magnitude of the watershed and river system feeding the lake and the many complicating factors influencing the system. In order to evaluate the problem at Itaipu, a methodology was developed to measure the sediment transport in the rivers of the watershed and determine high erosion risk areas within the watershed using the Revised Universal Soil Loss Equation (RUSLE). This methodology includes the organization and collection of existing digital data such as digital elevation information, erosivity data on rainfall, soil data for erodibility information and land-use information from remote sensing to be used in a GIS for the variables needed to drive the RUSLE model. The rivers draining into the Reservoir were instrumented with monitoring equipment that would automatically measure stage height and turbidity. The stage height was automatically measured with pressure transducers and data loggers. Turbidity was measured with custom built equipment that used an optical sensing chip and a data logger that sensed the clarity of the water. Each monitoring station was calibrated for the sensor output versus the actual sediment concentration of the water. The major rivers draining into the Reservoir and the reach below the Itaipu Dam were equipped with monitoring equipment to obtain an estimate of the amount of sediment entering and leaving the Reservoir. Preliminary modeling results identify high erosion risk areas within the Itaipu watershed. River monitoring results, consequently, show that a majority of the sediment comes from the major tributaries of the Paraná River that drain these areas of high erosion risk. The impact of this research clearly shows that recommended watershed management programs need to be implemented by local, state, and federal authorities that will stimulate adoption of soil conservation strategies to reduce sediment yields within the watershed.