U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3368

Sheet 1 of 1

Prepared in cooperation with the

Puerto Rico Aqueduct and Sewer Authority

Sedimentation Survey of Lago Caonillas, Utuado, Puerto Rico, September–November 2012

By

Luis R. Soler-López

2016

Introduction

Construction of the Lago Caonillas reservoir was completed in 1948 to provide water for hydroelectric 

power generation along the northern coast of Puerto Rico. The reservoir had an original storage capacity of 

55.66 million cubic meters (Mm3) (Soler-López, 2001). The dam is located about 4 kilometers (km) east of the 

town of Utuado and 6 km northwest of the town of Jayuya (fig. 1). 

The Puerto Rico Electric Power Authority (PREPA) owns and operates the Lago Caonillas reservoir, 

and since 1996, the reservoir has become an essential part of the Puerto Rico Aqueduct and Sewer Authority 

(PRASA) North Coast Superaqueduct Project. Water releases for hydroelectric power generation from 

Lago Caonillas are captured in Lago Dos Bocas downstream of the Caonillas Dam where hydroelectric power 

is generated again. Releases from Lago Dos Bocas flow into the Río Grande de Arecibo, which replenishes 

the public-supply raw-water intake pool of the North Coast Superaqueduct about 10 km downstream from 

the Lago Dos Bocas Dam. As of 2010, the Superaqueduct supplied about 4.44 cubic meters per second (m3/s) 

(348,616 cubic meters per day [m3/d]) of potable water to communities along the northern coast, from Arecibo 

to the San Juan metropolitan area (Molina-Rivera, 2010).

Because of the importance of Lago Caonillas to the North Coast Superaqueduct, the U.S. Geological Survey 

(USGS), in cooperation with PRASA, conducted a sedimentation survey of Lago Caonillas between September 

and November 2012. The results of this survey were compared to the results of a similar survey (Soler-López, 

2001) conducted in February 2000 to infer the loss of reservoir storage caused by sedimentation. Data collection 

began in September 2012; however, low water levels restricted the survey extent to about half of the reservoir, 

leaving the river deltas unaccounted for in the survey. Intense rainfall during October 2012 raised the water level 

to spillway elevation, and the remaining part of the reservoir was then surveyed. The results of this survey were 

used to update estimates of the reservoir’s storage capacity and its useful life. 

Methods of Survey and Analysis 

The field techniques and bathymetric data reduction processes used for the 2012 survey were performed 

following procedures established by the USGS and described in a previously published survey report of 

Lago Caonillas (Soler-López, 2001). The September–November 2012 bathymetric survey was conducted using 

a bathymetric/land survey system, consisting of a global positioning system (GPS) coupled to a digital depth 

sounder. A total of 155 survey navigation lines were established at 50-meter (m) intervals, beginning at the 

dam and continuing upstream along the river branches of the reservoir. Geographic position (accuracy of less 

than 2 m) and water depths (accuracy of 2 centimeters [cm] ±1 percent of the measured depth) were acquired 

simultaneously using the GPS interfaced to the depth sounder. The reservoir pool elevation was monitored at the 

continuous recording USGS lake-level monitoring station Lago Caonillas at damsite near Utuado, Puerto Rico, 

USGS station number 50026140 (fig. 1). The fathometer was calibrated prior to each day of survey by using a 

bar check.

The September 2012 pool elevation data for Lago Caonillas were adjusted to represent the depth relative 

to the spillway elevation. For November 2012, however, the reservoir was at the crest of the spillway structure, 

and therefore, depth data did not require adjustment. A total of 21,513 data points were collected over the entire 

reservoir. Volumetric calculations of reservoir capacity were made using a geographic information system 

(GIS) following procedures similar to those described in Soler-López (2001). Field data from the September–

November 2012 survey were used to generate a bathymetric map representing the reservoir bottom (fig. 2). 

Data points were color-coded according to their specific depths, and same-color points were connected with a 

Basin area

Study area

PUERTO RICO Surface-water noncontributing area

EXPLANATION

Drainage basin boundary

Caño Tiburones flow direction

Tunnel flow direction 

Town or city

ATLANTIC OCEAN

0

0 1

1

2

2

3

3

4

4 5 MILES

5 KILOMETERS

66°47'30" 66°32'30"

18°27'30"

18°15'00"

Base from U.S. Geological Survey digital data

Río

Río

Río

Río

Río

Río Caonillas

Caonillas

Río Río

Jauca

Río

Río

Río

Cidra

Río

Río

Grande

Río Grande

Río

Río

Caricaboa

Saliente

Grande

de

de

de

Jayuya

obicerA

obicerA

Río

Río

Lago

Dam

Lago

Pellejas

Lago

Adjuntas

Lago Viví

Lago

Garzas

Lago

Caño Tiburones

Tanamá

Limón

Limón

La

Venta

Yunes

Viví

Tunnel

Tunnel

Tunnel

Tunnel

Tunnel

Viví

Vacas

Pellejas

San Juan

Hatillo

Barceloneta

Jayuya

Arecibo

Adjuntas

Utuado

Florida

Super

aqueduct

Dos Bocas

Caonillas

Lago

Jordan

Figure 1. Location of Lago Caonillas within the Río Grande de Arecibo Basin, Puerto Rico.

0 750 1,500 2,250 3,000 FEET

0 250 500 750 1,000 METERS

Southern Branch

Rio Caonillas Branch

Eastern Branch

DAM

66°39'30" 66°39'00" 66°38'30"

18°16'30"

18°16'00"

18°15'30"

18°15'00"

18°14'30"

39 

26 

36 

33 

32 

38 

37 

36 

32 

26 

26 

18 

14 

4 

12 

4 

30

10 

12 

20 12 

18 

12 

16 

12 

22 

2 

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22

18 

14 

32 

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30 29 

29 

28 

26 24 

10 

22 

10 

2 

20 

18 

18 

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12 

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8 

6 

4 

2 

16 

14 

12 

10 

8 

2 

4 

6 

4 

2 

6 

4 

2 

4 

4 

2 

12 

EXPLANATION

Reservoir bottom contour—Depth of reservoir bottom, 

 November 2012. Contour interval 1 meter (m) from 39 m

 to 28 m, and 2 m from 26 m to 2 m. Datum is spillway

 elevation of 251.76 meters above mean sea level

Shoreline—Equal to zero depth or spillway elevation

30

Figure 2. Bathymetric map of Lago Caonillas, Utuado, Puerto Rico, for September–November 2012.

line to draw depth contours. A triangulated irregular network (TIN) surface model of Lago Caonillas was then 

generated from the bathymetric map, and the reservoir volume was calculated using GIS. The 2000 and 2012 

TIN surface models were used to compare the 2000 and 2012 sedimentation surveys (table 1), and to generate a 

stage-storage curve and longitudinal profiles along the different branches of Lago Caonillas for 2000 and 2012. 

A storage capacity table and curve were generated by calculating the TIN volume at 1.00-m elevation intervals 

and are shown on table 2 and figure 3, respectively. Bathymetry data used for this analysis are available in 

Soler-López (2016).

Storage Capacity, Sedimentation Rate, and Useful Life 

The storage capacity of Lago Caonillas decreased slightly from 42.27 Mm3 in February 2000 (Soler-López, 

2001) to 39.55 Mm3 in September–November 2012 (table 1). This decrease represents a reduction of 2.72 Mm3, 

for an annual storage capacity loss rate of about 226,670 m3/yr. The intersurvey (2000–2012) storage capacity 

loss was about 6 percent, representing a decrease of about 0.5 percent per year. 

The Lago Caonillas long-term capacity loss rate attributed to sedimentation has not changed substantially 

relative to its capacity in 1948 when the reservoir was completed. The capacity decreased from 257,500 cubic 

meters per year (m3/yr) during 1948–2000 to 251,720 m3/yr during 1948–2012, for a reduction of 2.2 percent 

(table 1). Although the long-term sedimentation rate has remained nearly unchanged (257,500 in 2000 

compared to 251,720 m3/yr in 2012), the annual loss rate of Lago Caonillas has shown a gradual decrease 

from 257,500 m3/yr during 1948–2000 to 226,670 m3/yr during 2000–2012. This trend may be due to sediment 

depletion in the Lago Caonillas hydrographic basin following Hurricane Georges (1998). The hurricane flushed 

sediment stored upstream of the Lago Caonillas Basin and not only deposited it within the reservoir, but also 

reduced readily available sediments for transport. Similar trends were observed at the following four reservoirs 

in Puerto Rico following Hurricane Georges: Lago Patillas, Lago de Cidra, Lago Loíza, and Lago Dos Bocas 

(Soler-López, 2010a, b; 2012a, b). 

Most of the sediment accumulation and associated storage capacity loss of Lago Caonillas has occurred 

within the eastern and Río Caonillas branches of the reservoir. Within the eastern branch, sediment accumulation 

is noticeable from about 1,500 m upstream from the dam, where about 2 to 7 m of sediment was deposited 

between 2000 and 2012 (fig. 4A). Within the Río Caonillas branch, sediment accumulation is evident from 

about 3,500 m upstream from the dam, where about 2 to 4 m of sediment was deposited between 2000 and 2012 

(fig. 4B). Within the southern branch, sediment accumulation is noticeable from about 3,200 m upstream from 

the dam, where about 2 to 5 m of sediment was deposited between 2000 and 2012. fig. 4C). In the vicinity of the 

Caonillas Dam, minor sediment deposition and scour occurred. 

The sediment trapping efficiency of Lago Caonillas for 2012 was estimated by using the capacity-to-inflow 

ratio established by Brune (1953). On the basis of the long-term annual sediment inflow of 248.01 Mm3 and the 

2012 water storage capacity of 39.55 Mm3, the trapping efficiency was estimated to be 93 percent.

The long-term drainage area sediment yield rate of Lago Caonillas has remained nearly constant since 

2000. Based on a long-term sediment trapping efficiency of 93 percent (Soler-López, 2001), the sediment yield 

of the reservoir basin decreased from 1,266 cubic meters per square kilometer, per year ([m3/km2]/yr) in 2001 to 

1,237 [m3/km2]/yr in 2012 (table 1, Soler-López, 2001). 

Based on the long-term (1948–2012) storage-capacity loss of about 251,720 m3/yr and assuming a constant 

sedimentation rate, the projected useful life of Lago Caonillas is about 157 years, ending in about 2169. This 

predicted useful life of Lago Caonillas is nearly equal to the previously estimated useful life of 164 years 

(Soler-López, 2001). 

Table 1. Comparison of results of historical reservoir sedimentation surveys.

[km2, square kilometer; Mm3, million cubic meters; m3, cubic meter; m3/km2-yr, cubic meter per square kilometer per year; N/A, not applicable]

Data descriptor Year of survey

2000 2012

Reservoir surface area, in km2 2.69 2.39

Change in full reservoir surface area (relative to year 2000), in km2 N/A 0.30

Change in full reservoir surface area (relative to year 2000), in percent N/A 11

Capacity, in Mm3 42.27 39.55

Years since construction 52 64

Sediment accumulated since construction, in Mm3 13.39 16.11

Long-term (from reservoir construction) storage loss, in percent 24.1 28.9

Long-term (from reservoir construction) annual loss of capacity, m3 257,500 251,720

Long-term (from reservoir construction) annual loss of capacity, in percent 0.46 0.45

Sediment trapping efficiency, in percent 93 93

Drainage area sediment yield, in m3

/km2-yr 1,266 1,237

Table 2. Storage capacity for Lago Caonillas, Puerto Rico, 2012, at 1-meter elevation intervals.

Pool elevation,

in meters above

mean sea level

Storage capacity,

in million

cubic meters

251.76 39.55

250.76 37.22

249.76 34.98

248.76 32.90

247.76 30.90

246.76 29.03

245.76 27.25

244.76 25.63

243.76 24.06

242.76 22.56

241.76 21.12

240.76 19.72

239.76 18.37

238.76 17.12

237.76 15.91

236.76 14.78

235.76 13.68

234.76 12.63

233.76 11.62

232.76 10.68

Pool elevation,

in meters above

mean sea level

Storage capacity,

in million

cubic meters

231.76 9.78

230.76 8.95

229.76 8.16

228.76 7.43

227.76 6.72

226.76 6.03

225.76 5.37

224.76 4.73

223.76 4.11

222.76 3.51

221.76 2.94

220.76 2.41

219.76 1.92

218.76 1.48

217.76 1.11

216.76 0.79

215.76 0.50

214.76 0.27

213.76 0.10

212.76 0.00

205

210

215

220

225

230

235

240

245

250

0 10 20 30 40 50

2012

EXPLANATION

2000

Pool elevation, in meters above mean sea level

Storage volume, in million cubic meters

Figure 3. Relation between water-storage capacity and pool elevation 

of Lago Caonillas, Puerto Rico, for 2000 and 2012.

Summary and Conclusions 

During September–November 2012, the U.S. Geological Survey, in cooperation with the Puerto Rico Aqueduct 

and Sewer Authority, conducted a sedimentation survey of Lago Caonillas to estimate current (2012) reservoir 

storage capacity and the recent (2000–2012) reservoir sedimentation rate by comparing the 2012 bathymetric survey 

data with the February 2000 data. 

The Lago Caonillas storage capacity, which was 42.27 million cubic meters in February 2000, decreased to 

39.55 million cubic meters by September–November 2012. The intersurvey (2000–2012) storage capacity loss 

was about 6 percent, corresponding to a decrease of about 0.5 percent per year; this loss represents a reservoir 

sedimentation rate of about 226,670 cubic meters per year between 2000 and 2012. On a long-term basis, however, 

the sedimentation rate has remained nearly constant, decreasing from about 257,500 to 251,720 cubic meters per 

year during 1948–2000 and 1948–2012, respectively.

Most of the sediment accumulation and associated storage capacity loss of Lago Caonillas has occurred within 

the eastern and Río Caonillas branches of the reservoir. In the vicinity of the Caonillas Dam, minor sediment 

deposition and scour have occurred.

The Lago Caonillas drainage area sediment yield has decreased by about 2 percent since the previous survey, 

from 1,266 cubic meters per square kilometer per year in 2000 to 1,237 cubic meters per square kilometer per year 

in 2012. If the long-term sedimentation rate of 251,720 cubic meters per year remains constant, the useful life of 

Lago Caonillas may end in about 2169.

Selected References 

Brune, G.M., 1953, Trapping efficiency of reservoirs: Transactions of the American Geophysical Union, v. 34, 

no. 3, p. 407– 418.

Molina-Rivera, W.L., Estimated water use in Puerto Rico, 2010: U.S. Geological Survey Open-File Report 2014–1117,

35 p., accessed June 2014 at http://dx.doi.org/10.3133/ofr20141117.

Soler-López, L.R., 2001, Sedimentation survey of Lago Caonillas, Puerto Rico, February 2000: U.S. Geological 

Survey Water-Resources Investigations Report 01–4043, 25 p., 1 plate.

Soler-López, L.R., 2010a, Sedimentation survey of Lago Patillas, Puerto Rico, March 2007: U.S. Geological Survey 

Scientific Investigations Map 3128, 1 plate. [Also available at http://pubs.usgs.gov/sim/3128/.]

Soler-López, L.R., 2010b, Sedimentation survey of Lago de Cidra, Puerto Rico, August 2007: U.S. Geological 

Survey Scientific Investigations Map 3118, 1 plate. [Also available at http://pubs.usgs.gov/sim/3118/.]

Soler-López, L.R., 2012, Sedimentation survey of Lago Dos Bocas, Utuado, Puerto Rico, January 2010: U.S. 

Geological Survey Scientific Investigations Map 3217, 1 sheet. [Also available at http://pubs.usgs.gov/sim/3217/.]

Soler-López, L.R., 2016, Spatial data for the sedimentation survey of Lago Caonillas, Utuado, Puerto Rico, 

September–November 2012: U.S. Geological Survey data release, accessed July 2016 at https://dx.doi.org/

10.5066/F74M92NT.

Soler-López, L.R., and Licha-Soler, N.A., 2012, Sedimentation survey of Lago Loíza, Puerto Rico, July 2009: 

U.S. Geological Survey Scientific Investigations Map 3219, 1 plate. [Also available at http://pubs.usgs.gov/

sim/3219/.]

0

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0 500 1,000 1,500 2,000 2,500 3,000

A. Eastern branch

2012

EXPLANATION

2000

0

5

10

15

20

25

30

35

40

45

0 1,000 2,000 3,000 4,000 5,000 6,000

Depth, in meters below spillway elevation of 251.76 meters above mean sea level

B. Río Caonillas branch

0

5

10

15

20

25.

30

35

40

45

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

Distance from dam, in meters

C. Southern branch

Figure 4. Longitudinal bottom profiles along the thalweg of the, A, eastern, B, Río Caonillas, and C, southern 

branches of Lago Caonillas, Puerto Rico, for 2000 and 2012.

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government.

For sale by U.S. Geological Survey, Information Services, Box 25286, 

Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://dx.doi.org/10.3133/sim3368.

Suggested citation: Soler-López, L.R., 2016, Sedimentation survey of 

Lago Caonillas, Utuado, Puerto Rico, September–November 2012: 

U.S. Geological Survey Scientific Investigations Map 3368, 1 sheet, 

http://dx.doi.org/10.3133/sim3368.

ISSN 2329-132X (online)