Figure 5. Aerial photograph of the Guayabal Dam and Lago Guayabal looking in the upstream 

direction. Photograph courtesy of the Puerto Rico Electric Power Authority, taken on May 9, 

2006, during a dam-safety inspection helicopter flight.

COMPARISON OF STORAGE CAPACITY AND SEDIMENTATION TRENDS OF

LAGO GUAYABAL, PUERTO RICO-DECEMBER 2001 AND OCTOBER 2006

By Luis R. Soler-López

2008

Prepared in cooperation with the

PUERTO RICO AQUEDUCT AND SEWER AUTHORITY

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

SCIENTIFIC INVESTIGATIONS MAP 2008-3016

 Comparison of storage capacity and sedimentation trends 

of Lago Guayabal, Puerto Rico-December 2001 and October 2006

By Luis R. Soler-López, 2008

Figure 6. Aerial photograph of Lago Guayabal and part of Lago Toa Vaca, and surroundings 

showing development. Photograph from the U.S. Army Corps of Engineers, 2007 Puerto Rico.

66°30'30" 66°30'00" 66°29'30"

18°05'30"

18°06'00"

18°06'30"

0 0.25 0.5 1 Mile

0 0.25 0.5 1 Kilometer

Lago

Toa 

Vaca 

Lago

Guayabal

Vaca branch

branch

Río Toa

Río Jacaguas

Figure 2. Bathymetric map of Lago Guayabal, Puerto Rico, October 2006.

66°30’30” 66°30’00” 66°29’30”

18°06’00”

18°05’30”

18°06’30”

Shoreline modified from the U.S. Geological Survey, Ponce, and Río Descalabrado 

Puerto Rico, Quadrangles 1970, and 1972, respectively. 

Photorevised in 1982. Lambert conformal conic projection. 

Puerto Rico state plane coordinate system. (Puerto Rico datum, 1940 adjustment)

Reservoir bottom contour – Depth of the reservoir 

bottom, October 2006, in meters below top of gates 

elevation of 103.94 meters above mean sea level. 

Contour interval 1.0 meter. 

Additional 0.3 meter contour added and specified in 

the map. Shoreline shown as thicker, red line equal 

to zero depth or top of gates elevation. 

EXPLANATION. 

Río Jacaguas branch

Selected cross section and identification number

Río Toa Vaca branch

0

0 500 1,000 Feet

200 400 Meters

13.0

1

9

6

7

9

10

8

11

12

13

14

15

4

3

2

Dam

1.0

12.0

6.0

11.0

10.0

9.0

8.0

7.0

6.0

5.0

4.0

5

3.0

2.0

1.0

1.0

0.3

Introduction 

 Lago Guayabal dam is located on the Río Jacaguas in the municipality of 

Villalba in southern Puerto Rico, about 4 kilometers north of the town of Juana Díaz and 

about 5 kilometers south of Villalba (fig. 1). The dam is owned and operated by the 

Puerto Rico Electric Power Authority (PREPA) and was constructed in 1913 for the 

irrigation of croplands in the southern coastal plains of Puerto Rico. The reservoir 

impounds the waters of the Río Jacaguas and those of the Río Toa Vaca, when the Toa 

Vaca dam overflows or releases water. The reservoir has a drainage area of 53.8 square 

kilometers. The dam is a concrete gravity structure with a normal pool (at top of flashboards) elevation of 103.94 meters above mean sea level (Puerto Rico Electric Power 

Authority, 1988). 

 During October 2006, the U.S. Geological Survey (USGS), Caribbean Water 

Science Center, in cooperation with the Puerto Rico Aqueduct and Sewer Authority 

(PRASA) conducted a bathymetric survey of Lago Guayabal to update the reservoir 

storage capacity and actualize the reservoir sedimentation rate by comparing the 2006 

data with the previous 2001 bathymetric survey results. The purpose of this report is to 

describe and document the USGS sedimentation survey conducted at Lago Guayabal 

during October 2006, including the methods used to update the reservoir storage capacity, sedimentation rates, and areas of substantial sediment accumulation since December 

2001. The Lago Guayabal sedimentation history up to 2001 was published by the USGS 

in 2003 (Soler-López, 2003); therefore, this report focuses on the comparison between 

the 2001 and current bathymetric surveys of Lago Guayabal.

Storage Capacities, Sedimentation Rates, and Reservoir Life Expectancy

 The December 2001 storage capacity of the reservoir was 6.12 million cubic 

meters (Soler-López, 2003), and by October 2006, the reservoir storage capacity was 

reduced to 5.82 million cubic meters (table 1). This represents a reduction between 2001 

and 2006 of 300,000 cubic meters (or 5 percent in 5 years) for an annual storage capacity 

loss rate of about 60,000 cubic meters. An actualized storage capacity table and curve 

were generated by calculating the TIN volume at 1-meter elevation intervals (table 2,

fig. 3).

 Sediment accumulation in Lago Guayabal between 2001 and 2006 has been minimal. Figure 4, which shows selected cross sections of the Lago Guayabal bottom from 

shore to shore, indicates that the reservoir bottom has changed little, particularly near the 

dam (fig. 5), where accumulation is negligible. The greatest changes, though minimal, 

have occurred in the reach extending from cross section 5 (fig. 2) up to the Río Jacaguas 

branch of Lago Guayabal (fig. 6). In this area, an average of about 1 meter of sediment 

has accumulated since 2001, for an average deposition rate of about 20 centimeters per 

year.

 The Lago Guayabal drainage area sediment yield rate decreased slightly from 

1,235 cubic meters per square kilometer per year to 1,184 cubic meters per square kilo-

 Method of Survey and Analysis

 The field techniques and bathymetric data reduction processes used for the 

2006 survey were performed following procedures established by the USGS Caribbean Water Science Center and described in the previous bathymetric survey report of 

Lago Guayabal (Soler-López, 2003). The October 2006 bathymetric survey was 

conducted using a differential global positioning system (DGPS) coupled to a digital 

depth sounder similar to the setup used for the survey conducted in December 2001 

(Soler-López, 2003). The survey navigation lines were established at a spacing of 

about 50 meters parallel to the dam face of the reservoir and continuing upstream 

along the Río Jacaguas branch and the Río Toa Vaca branch (fig. 2). Geographic position and water depths were acquired simultaneously using a DGPS interfaced to a 

depth sounder. The pool elevation of the reservoir was measured at the USGS lakelevel station 50111300 (Lago Guayabal at damsite near Juana Díaz). The soundings 

were subsequently adjusted to represent water depths below normal pool elevation. 

 The 2006 data were stored and transferred into the USGS geographic information system (GIS) where final analysis and volume calculations were made following 

similar procedures used to develop the 2001 bathymetric map of Lago Guayabal reservoir (Soler-López, 2003). From the field data a bathymetric map representing the 

reservoir bottom in October 2006 was generated (fig. 2). A triangulated irregular 

network (TIN) surface model of Lago Guayabal was then created from the bathymetric 

map, and the reservoir volume was calculated using the GIS. From the TIN surface 

model, a stage-storage curve (fig. 3) and longitudinal profiles along the different tributary branches of Lago Guayabal were in turn generated from the digital data for 2001 

and 2006.

meter per year between 2001 and 2006 (table 1). This change, however, represents a 

difference of only 4 percent, which is statistically negligible. According to the current 

storage capacity loss of about 60,000 cubic meters per year estimated for 2001-2006, the 

Lago Guayabal life expectancy is about 97 more years or to year 2103; this result is 

essentially equal to the life expectancy determined for 2001, which was to year 2101.

Summary and Conclusions 

 During October 2006, the U.S. Geological Survey, Caribbean Water Science 

Center, in cooperation with the Puerto Rico Aqueduct and Sewer Authority, conducted 

a bathymetric survey of Lago Guayabal to update the reservoir storage capacity and 

actualize the reservoir sedimentation rate by comparing the 2006 data with the previous 

2001 bathymetric survey results.

 The Lago Guayabal storage capacity was 6.12 million cubic meters in December 

2001, which was reduced to 5.82 in million cubic meters by October 2006. The intersurvey (2001-2006) storage capacity loss is about 5 percent for a decrease of about 1 

percent per year. This loss represents a reservoir sedimentation rate of about 60,000 

cubic meters per year. 

 Most of the storage capacity loss of Lago Guayabal has occurred along the Río 

Jacaguas tributary branch, where an average of about 1 meter of sediment has accumulated between 2001 and 2006. Along the Río Toa Vaca branch, accumulation has been 

negligible because the Toa Vaca Dam acts as an effective sediment trap. The Lago 

Guayabal drainage area sediment yield is essentially unchanged compared to the previous survey. The drainage area sediment yields are estimated at about 1,235 and 1,184 

cubic meters per square kilometer per year for the 2001 and 2006 surveys, respectively. 

 Although the life expectancy of about 97 years for Lago Guayabal may not be a 

pressing concern (assuming a long-term storage loss rate of about 60,000 cubic meters 

per year), sediment accumulation in the Río Jacaguas branch of the reservoir has continued forward towards the deepest parts of Lago Guayabal, which could eventually start 

filling the reservoir near the dam. If the sedimentation rate of 60,000 cubic meters 

estimated between 2001 and 2006 continues, the useful life of Lago Guayabal may end 

by the year 2103.

References Cited

Puerto Rico Electric Power Authority, 1988, Guayabal Dam, Villalba, Puerto Rico, 

Phase 1 Inspection Report: National Dam Safety Program, 1986.

Soler-López, L.R., 2003, Sedimentation History of Lago Guayabal, Puerto Rico, 1913-

2001: U.S. Geological Survey Water-Resources Investigations Report 03-4198, 28 

p., 2 pls.

2001

2006

105.00

100.00

95.00

90.00

0.0 5.0 10.0

VOLUME, IN MILLION CUBIC METERS

Normal pool elevation = 103.94 meters

Figure 3. Relation between pool elevation and storage capacity of Lago Guayabal, Puerto 

Rico, for 2001 and 2006.

ATION, IN METERS ABOVE MEAN SEA LEVEL ELEV

Table 2. Storage capacity table for Lago Guayabal, Puerto 

Rico, for October 2006.

Pool elevation, in meters Storage capacity,

above mean sea level in million cubic meters

103.94 5.82 

102.94 4.65 

101.94 3.76 

100.94 3.07 

99.94 2.51 

98.94 2.02 

97.94 1.59 

96.94 1.22 

95.94 0.88 

94.94 0.60 

93.94 0.35 

92.94 0.16 

91.94 0.03 

90.94 0.00

Table 1. Compari

Puerto Rico.

son between the 2001 and 2006 sedimentation survey results of Lago Guayabal, 

Data descriptor Year of survey

1

2001 2006

Drainage area at damsite, in square kilometers 53.8 53.8

Reservoir surface area, in square kilometers 1.44 1.36

Pool elevation, in meters above mean sea level

Capacity, in million cubic meters

Live storage, in million cubic meters

103.94

6.12

6.12

103.94

5.82

5.82

Dead storage, in million cubic meters 0.0 0.0

Years since construction 88 93

Inter-survey storage loss, in million cubic meters

Inter-survey annual loss of capacity, in million cubic meters

Long-term storage loss, in percent

Inter-survey annual loss of capacity, in percent

0.64

42,667

107

0.30

0.30

60,000

110

0.60

Estimated drainage area annual runoff, in million cubic meters 24.22 24.22

Trapping efficiency, in percent 93 93

Sediment yield, in cubic meters per square kilometer per year 1,235 1,184

Year the reservoir would fill with sediments 2,101 2,103

1

All 2001 data are derived from Soler-López (2003).

SECTION 1

SECTION 2

SECTION 3

SECTION 4

SECTION 5

DEPTH, IN METERS BELOW NORMAL POOL ELEVATION OF 103.94 METERS ABOVE MEAN SEA LEVEL

SECTION 6

SECTION 7

SECTION 8

ELEVATION, IN METERS ABOVE MEAN SEA LEVEL

DISTANCE FROM THE LEFT BANK, IN METERS Vertical scale greatly exaggerated

SECTION 11

103.94

98.94

93.94

88.94

SECTION 12

103.94

98.94

93.94

88.94

Figure 4. Selected cross sections generated from the triangulated irregular network (TIN) surface model of Lago Guayabal, Puerto Rico, for 2001 and 2006.

Enlarged view

SECTION 10 0 80

0

2

Enlarged view

SECTION 9

0

0 100

2

200

Enlarged view

SECTION 13

103.94

98.94

93.94

88.94

0

2

0 100 200

0 100 200 300 400 500 600 700 800 900 1,000 0 100 200 300 400 500 600 700 800 900 1,000 0 100 200 300 400 500 600 700 800 900 1,000

2001

2006

Enlarged view

SECTION 15

103.94

98.94

93.94

88.94

0

2

0 100

Enlarged view

SECTION 14

103.94

98.94

93.94

88.94

0

5

10

15

0

5

10

15

0

5

10

15

0

5

10

15

0

5

10

15

0

2

0 100 200

EXPLANATION

2001

2006

EXPLANATION

2001

2006

EXPLANATION

Figure 1. Location of Lago Guayabal in the Río Jacaguas basin and areas served by the Juana Díaz Irrigation District in 

southern Puerto Rico.

CARIBBEAN SEA

SANTA SALINAS

ISABEL

JUANA

DÍAZ

VILLALBA

COAMO

AIBONITO

BARRANQUITAS

CAYEY

PUERTO RICO

Part of the south coastal plain

in the Juana Díaz Irrigation District

Drainage basin boundary

Lake-elevation station

and number

EXPLANATION

Town or city

Map Location

50111300

50111300

Lago

Guayabal

66°30'00" 66°15'00"

17°57'30"

18°10'00"