Sedimentation survey of Lago de Matrullas, Puerto Rico, December 2001

Lago de Matrullas reservoir, constructed in 1934, is located at an altitude of approximately 730 meters above mean sea level in the municipality of Orocovis in central Puerto Rico, and has a drainage area of 11.45 square kilometers. The reservoir is part of the Puerto Rico Electric Power Authority Toro Negro Hydroelectric Project, which also includes the Lago El Guineo reservoir and a hydroelectric plant to the south of the insular hydrographic divide. Historically, the drainage area had been protected from soil erosion by dense vegetation and the lack of basin development. However, transportation, potable water, and electric power infrastructure construction has facilitated development in rural areas resulting in the clearing of land. This trend in land-use changes is impacting the useful life of Lago de Matrullas.

The reservoir storage capacity has been reduced from 3.71 million cubic meters in 1934 to 3.08 million cubic meters in 2001. This represents a total storage-capacity loss of 0.63 million cubic meters by 2001 (17 percent), or a long-term annual storage loss of 0.25 percent per year. The sediment trapping efficiency of Lago de Matrullas has been estimated at approximately 90 percent. If the current long-term sedimentation rate continues, Lago de Matrullas would fill by the year 2328. However, this life expectancy could be reduced at a faster than predicted rate as a result of rural development in the Lago de Matrullas basin and the high sediment trapping efficiency of the reservoir.