Sustainable Hydropower Study, Urrá Reservoir, Colombia

Client: EMEC, SAS, Montería, Colombia

Contract Period: 2013-2014

The 1822 Mm3 Urrá Reservoir, the largest hydropower reservoir in Colombia, is located on the Sinú River which drains into the Caribbean Sea. The project, which began operating in 1999, has 340 MW of installed capacity with a design discharge of 700 m3/s. Bathymetric studies indicated that the reservoir is experiencing accelerated sedimentation, with an annual storage loss of 1.14%. This poses a problem of storage loss, and delta sedimentation also presents navigational problems which affects protected indigenous communities. One feature of this site is the security risk in the upstream area of the reservoir which precludes field work and sediment monitoring in that area.

We were initially contracted to review bathymetric studies, performed by others, which contained unexplained problems. Our review of the data uncovered several types of errors, and portions of the survey were re-done following guidelines we provided. We were subsequently contracted to perform a partial bathymetric survey and sampling of submerged sediments (by vibracore) to monitor the advance of sandy delta sediments, which were advancing toward the dam at the rate of approximately 1 kilometer per year.

Sediment transport modeling was the performed to better understand the rate and pattern of sediment deposition along the reservoir over the next 100 years using the Bureau of Reclamation’s SRH-1D software. This analysis was used to evaluate alternative operational scenarios and to develop a strategy to maximize the period that the reservoir can be operated without structural modification of the intake to exclude coarse sediment from the turbines. Recommendations for future sediment monitoring were also given.

A hydrologic operational model with a 1-day time step was constructed to analyze the long-term energy production and its relationship to storage loss from sedimentation. This was coupled to daily spot prices (which in Colombia vary seasonally because hydropower is the dominant electricity generator), and an operating rule was developed allowing the project to continue generating the current level of power income, despite storage loss, under the current seasonal pricing structure in Colombia.