IWRA Proceedings

AbstractINTRODUCTION In large reservoirs, one of the most important variables of the water balance is the volume of water stored. In many situations, the volume of water in the reservoir is obtained by means of the elevation-area- volume curve and it is used the elevation of a single point (generally, close to the dam). In this situation, when reservoir presents a steep water surface slope, the volume estimation can present error, which causes damage for reservoir operation and water resources management. OBJECTIVE The objective of this work is to evaluate the potential of the hydrodynamic modeling to supply information related to storage volume and to determine the time variation of the flooded area in large reservoirs. In addition, the results obtained can help to improve the understanding of the influence of the water surface slope in the estimation of the water balance in large reservoirs. METHODS The study was accomplished at Sobradinho reservoir located at São Francisco River in Northeast of Brazil. The reservoir has an area of 4,214 km2 and 350 km long. Sobradinho is the major reservoir of the hydroelectric power plants system located at São Francisco River and it is responsible for generating energy and regularizing the discharge. The drainage area at the Sobradinho dam is 498,425 km2. We have applied the hydrodynamic model Mike 11 HD developed by Danish Hydraulic Institute (DHI). This model uses Saint Venant equations to predict the space and time variation of stage and discharge in rivers and reservoirs. For geometric definition of the reservoir, it was used aerophotogrammetric and bathymetric survey and also data obtained from Digital Elevation Model SRTM-90 (Shuttle Radar Topographic Mission). The floodplain was defined by means of Landsat images. RESULTS AND CONCLUSION The results showed that the volume calculated with the hydrodynamic model is quite higher than to the volume estimated by the elevation-volume curve. On the other hand, the model results are similar to the values obtained with water balance. The deviation of the values estimated with the elevation-volume curve occurs because the water surface in reservoir is not horizontal. In such kind of reservoir, the hydrodynamic model is able to represent this characteristic of the flow. The dynamic of the flooded area was also simulated by the model. This information can be used, for instance, for the definition of the reservoir operation impact over the users located around it. A Decision Support System (DSS) will be soon built with the tools presented in this work, helping the decisions about the multiple water uses in Sobradinho reservoir. The DSS will reduce the forecast errors, which are usual in operation of complex systems as Sobradinho.