Sedimentation Study of Dos Bocas Reservoir, Puerto Rico

Client: Puerto Rico Electric and Power Authorithy (PREPA)

Contract Period: 2016-2017 (Project Duration: 8 months)

Dos Bocas reservoir, in service since 1942, has been losing capacity to sedimentation and now has less than 40% of its original capacity remaining. Together with Caonillas reservoir, these two reservoirs supply 100 mgd of potable water to north coast communities of Puerto Rico. This makes it the largest source of water supply in Puerto Rico. It is also important for electrical power generation; the 18 MW power plant at Dos Bocas produces about 33.2 GWh/yr of electricity.

The principal sedimentation problems at Dos Bocas are: (1) encroachment of sediment onto the intake structure supplying the turbines, and (2) loss of storage capacity. Also, the Dos Bocas low level power intake currently represents the only means to control the release of water downstream to the Superaqueduct project’s intake. If this power intake is obstructed or removed from service for any type of maintenance, water can be released downstream only by spillway overflow. Therefore, it was also desired to make an underwater inspection of the intake, clear trash and logs away from the intake, and to develop an alternative for the controlled delivery of water downstream in the event that the power intake is out of service. Components of this project components included:

  • 1. Bathymetric survey. Performed bathymetric survey of Dos Bocas reservoir and prepared updated stage-storage curve.
  • 2. Sediment sampling. Sampled reservoir sediments using vibracore equipment, and prepared granulometric analysis of the recovered samples.
  • 3. Yield analysis. Prepared a firm yield analysis at Dos Bocas reservoir, including the effect of all upstream reservoirs and diversion tunnels, and recommended an operating rule to maximize firm yield, without compromising power production.
  • 4. Auxiliary outlet. Identified feasible alternatives to release water downstream to PRASA in case that PREPA's power intake is out of service. Prepared schematic design and cost estimate.
  • 5. Sediment management. Determined the benefits of sediment removal from operational and financial points of view. Analyzed different sediment management alternatives for immediate and long-term solutions.