Differential Damage Assessment due to Dam Failure

Angel Menendez, Leandro Kazimierski, Martin Sabarots Gerbec

Tuesday 30 june 2015

12:48 - 12:51h at South America (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Flood risk assessment, Poster pitches

Parallel session: Poster pitches: 5J. FloodRisk - Assessment

A failure Risk Assessment process is presently being undertaken for Yacyreta dam, built on the Parana River (South America). Many particular features make this problem singular: (i) the large dimensions of the Parana River, the second largest plain river in South America (mean discharge of about 12,500 m3/s); (ii) the huge volume of Yacyreta reservoir (21 hm3); (iii) the long total embankment length (66 km), partitioned into 7 different sectors; (iv) the interception of a lateral creek. A 1D model, based on HEC-RAS, has been implemented in order to calculate wave propagation along a 300 km extension downstream from the dam, plus 400 km upstream Paraguay River, the main tributary of the Parana River. The model domain includes the whole reservoir, and a 30 km stretch upstream from its tail. A Digital Elevation Model (DEM) of the impacted zone was built, based on a combination of SRTM data, cross sections surveys, and some local topographic studies. Operation policies for the two spillways and the power plant were implemented. The breach evolution was represented through an empirical model. The model was carefully calibrated based on long term water level time series at several gaging stations. A verification of the model, and the associated DEM, was performed by comparing flooded areas from properly processed satellite images with those obtained from the model results, obtaining a very satisfactory agreement. Failure scenarios were established by defining breach locations for every embankment sector, and different statistically significant initial conditions. The model was used to delimit the zones downstream the dam where flood levels would be higher than the ones associated to natural floods. Additionally, the model indicated the increase in the rate of rise of the water level relative to natural floods. These results are being used to adjust the flood warning system.