The Influence of the Reservoir Geometry Input Approach on the Dam Breach Outflow Hydrograph La Plata Dam Breach Analysis, Toa Alta, PR

Abstract Only - The reservoir volume plays one of the most important roles while determining the dam breach outflow hydrographs. Further than the reservoir volume itself, the volume shape, or stage-volume relationship, is of great relevance while routing inflow hydrographs through the reservoir or while modeling the reservoir drawdown. The approach used to define the stage-volume relationship on our hydraulic model will also influence the final results of the outflow hydrographs.
The results of the 2017 dam breach analysis for La Plata Dam, located in Toa Alta Puerto Rico and owned by the Puerto Rico Aqueducts and Sewers Authority, are the basis for our paper. La Plata reservoir has a particular, long and narrow, horizontal geometry. The lake extends upstream for 6.3 miles whereas the average width of the impoundment volume is around 250 meters along the downstream 2-miles reach and less than 100 meters along the upstream 4.3-miles reach.
To determine the breach hydrograph the reservoir volume was defined using two different input approaches. As the first approach, the common stage-volume curve of the reservoir was used to define the reservoir volume in a single node of the model. A second approach was followed with cross sections, channels and stage-volume nodes. The model for that second approach was built to match the stage-volume curve of the first approach. The results of the analysis revealed the importance of considering the reservoir geometry while determining the approach to be used to define the reservoir stage-volume relationship on the hydraulic model. This paper will present the approach used to build a cross sections-channels-nodes model that is consistent with the reservoir stage-volume curve and will also present and discuss the comparison of the resulting breach hydrographs and the implications on the dam breach analysis.