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Sedimentation History of Lago Dos Bocas, Puerto Rico, 1942-2005

By Luis R. Soler-López

 

In cooperation with the
PUERTO RICO AQUEDUCT AND SEWER AUTHORITY

 

Scientific Investigations Report 2007-5053

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ABSTRACT

The Lago Dos Bocas Dam, located in the municipality of Utuado in north central Puerto Rico, was constructed in 1942 for hydroelectric power generation. The reservoir had an original storage capacity of 37.50 million cubic meters and a drainage area of 440 square kilometers. In 1948, the construction of the Lago Caonillas Dam on the Río Caonillas branch of Lago Dos Bocas reduced the natural sediment-contributing drainage area to 310 square kilometers; therefore, the Lago Caonillas Dam is considered an effective sediment trap.

Sedimentation in Lago Dos Bocas reservoir has reduced the storage capacity from 37.50 million cubic meters in 1942 to 17.26 million cubic meters in 2005, which represents a storage loss of about 54 percent. The long-term annual water-storage capacity loss rate remained nearly constant at about 320,000 cubic meters per year to about 1997. The inter-survey sedimentation rate between 1997 and 1999, however, is higher than the long-term rate at about 1.09 million cubic meters per year. Between 1999 and 2005 the rate is lower than the long-term rate at about 0.13 million cubic meters per year.

The Lago Dos Bocas effective sediment-contributing drainage area had an average sediment yield of about 1,400 cubic meters per square kilometer per year between 1942 and 1997. This rate increased substantially by 1999 to about 4,600 cubic meters per square kilometer per year, probably resulting from the historical magnitude floods caused by Hurricane Georges in 1998. Recent data indicate that the Lago Dos Bocas drainage area sediment yield decreased substantially to about 570 cubic meters per square kilometer per year, which is much lower than the 1942-1997 area normalized sedimentation rate of 1,235 cubic meters per square kilometer per year.

The impact of Hurricane Georges on the basin sediment yield could have been the cause of this change, since the magnitude of the floods could have nearly depleted the Lago Dos Bocas drainage area of easily erodible and transportable bed sediment. This report summarizes the historical change in water-storage capacity of Lago Dos Bocas between 1942 and 2005.

TABLE OF CONTENTS

Abstract

Introduction

Purpose and Scope

Dam, Reservoir, and Basin Characteristics
Method of Survey

Field Techniques

Data Processing
Historical Sediment Accumulation and Effect on Reservoir Storage
Lago Dos Bocas Sediment Trapping Efficiency
Lago Dos Bocas Drainage Area Sediment Yield and Reservoir Life Expectancy
Summary and Conclusions
References Cited
Appendix 1. Explanation of Mathematical Calculations and Examples Used to Attain the Results Given on Table 2

 

PLATE

1. Lago Dos Bocas, Puerto Rico, Bathymetry, August 2005 (450 KB)

 


The citation for this report, in USGS format, is as follows:

 

Soler-López, L.R., 2007, Sedimentation history of Lago Dos Bocas, Puerto Rico, 1942-2005: U.S. Geological Survey Scientific Investigations Report 2007-5053, 36 p., 1 pl.


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Please visit http://pr.water.usgs.gov/ for more information about USGS activities in the Caribbean (Puerto Rico and the U.S. Virgin Islands).



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