Lago Caonillas, a reservoir owned by the Puerto Rico Electric Power Authority and located in the central part of Puerto Rico, is one of the two reservoirs (the other being Lago Dos Bocas) proposed to supply water for the Puerto Rico Aqueduct and Sewer Authority project called the Superaqueduct. The reservoir was impounded in 1948 and originally provided about 55 .66 million cubic meters of water for hydroelectric power generation. Sediment derived from the reservoir basin has been transported and deposited in the reservoir bottom, substantially decreasing the water storage capacity over time. Successive bathymetric surveys indicated that in 1990 the storage capacity was 49.25 million cubic meters, decreasing to 48.80 million cubic meters in 1995 and to 42.27 million cubic meters in 2000. This represents an overall storage loss of about 11.5 percent by 1990, 12.3 percent by 1995 and 24.1 percent by 2000. The long-term sedimentation rate of the reservoir was about 153,000 cubic meters per year in 1990, remaining almost constant at about 146,000 cubic meters per year in 1995, but nearly doubling to 258,000 cubic meters per year in 2000. The two-fold increase in sedimentation rate, and consequently, the reservoir storage capacity loss, can be attributed to Hurricane Hortense in September 1996 and Hurricane Georges in September 1998. Twenty-four percent of the original storage capacity of Lago Caonillas has been lost to sediment accumulation. About 49 percent of the reservoir sediment was deposited in the last five years, demonstrating the impact of these major storms on the reservoir.
Based on the ratio of storage capacity to inflow rate, the estimated trapping efficiency of Lago Caonillas is about 93 percent for 2000. The sediment yield of the Lago Caonillas net sediment-contributing drainage area (total drainage area minus the reservoir surface area) of 218.74 square kilometers, is about 1 ,266 megagrams per square kilometer per year. This represents an increase of about 69 percent in the material transport and deposition process of the Lago Caonillas basin between 1990 and 2000. The life expectancy of Lago Caonillas was more than 300 years in 1995; however, at the storm-accelerated sedimentation rate, the life expectancy has decreased to about 164 years. This implies that the reservoir could be filled with sediments by the year 2164 if major hurricanes continue to pass through Puerto Rico regularly (every 2 to 4 years).