José Nilson Beserra Campos

Risks and uncertainties in reservoir yield in highly variable intermittent rivers: case of the Castanhão Reservoir in semi-arid Brazil

Abstract We analyse the risks and uncertainties in the assessment of reservoir yields in Northeast Brazil using Monte Carlo simulation. The case study considers the Castanhão Reservoir, which is located in the Jaguaribe River in the State of Ceará. The hydrologic regime of the reservoir inflow was obtained from a 37-year historical series. From the data, 600 series of annual inflows for 30 years were generated. The operation of the reservoir was simulated to estimate the uncertainties and risks regarding the water supply by the reservoir. The variability of regulated streamflows with 30-year horizons, measured by their coefficients of variation, is 27%. It was also found that the mean probability of failure for the 600 traces, with a mean release equal to the mean yield and an assumed 10% risk of failure, was 12.5%, which is 25% greater than the value of 10% used to estimate the yield. Editor D. Koutsoyiannis; Associate editor S. Blazkova Citation Campos, J.N.B., Souza Filho, F.A., and Lima, H.V.C., 2014. Risks and uncertainties in reservoir yield in highly variable intermittent rivers: case of the Castanhão Reservoir in semi-arid Brazil. Hydrological Sciences Journal, 59 (6), 1184–1195. http://dx.doi.org/10.1080/02626667.2013.836277

Reservoir Yield Vulnerability Under Global Change

There is no scientific consensus on how climate changes will modify the hydrological cycle. Climate models still need to be improved in order to better evaluate accurately these changes. Predictions of regional effects on the hydrological cycle vary significantly among different models. Nevertheless, there is a consensus on global precipitation and evaporation increase.

Flood damping by reservoirs: proposition of a graphical parametric method

Flood reduction constitutes an important characteristic of surface reservoir design. Thus, to ensure that minimum safety standards are met, the Safety Dams Act was approved in 2010. Many multipurpose surface reservoirs are aging and getting out of the current technical standards. In Ceará State, Brazil, there are several dams built for many decades, with spillways sized by empirical formulae which are currently outdated. This article contributes to improve the understanding of the morphological and hydrological factors involved in the process of damping floods in reservoirs and the development of a simple application method that estimates the damping, from such factors. To do so, hydrological simulations of several scenarios representative of reservoir and hydrographic basins configurations were performed. As a result, the impact of each parameter on flood damping was determined. A graphical method was proposed in which all the morphological parameters of the basin and the reservoir were aggregated into a single dimensionless parameter the Reservoir Damping Index (Φ). With the value of Φ calculated, it is possible to estimate the damping capacity of the reservoir. This method can be used for the design of new reservoirs or for the verification of reservoir spillways already constructed with other methodologies.