182730

18°15'00"

Basin area

PUERTO RICO

CATAÑO

BAYAMÓN

GUAYNABO

CIDRA

50047550

EXPLANATION

LAKE-ELEVATION STATION 

AND NUMBER

DRAINAGE BASIN

BOUNDARY

TOWN OR CITY

Quebrada Prieta

Lago 

de Cidra

0

0 1

1

2

2

3

3

4

4 5 MILES

5 KILOMETERS

50047550

Río Sabána

Río de Bayamón

SEDIMENTATION SURVEY OF LAGO DE CIDRA, PUERTO RICO, AUGUST 2007

By Luis R. Soler-Lopez 

2010

STORAGE VOLUME, IN MILLION CUBIC METERS

POOL ELEVATION, IN METERS ABOVE MEAN SEA LEVEL

384.00

386.00

388.00

390.00

392.00

394.00

396.00

398.00

400.00

402.00

404.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00

Spillway elevation = 403.00 meters above mean sea level

2007

1997

Authority (PRASA), and was constructed in 1946 as a 6.54millioncubicmeter 

supplemental water supply for the San Juan metropolitan area. 

 The reservoir impounds the waters of Río de Bayamón, Río Sabana and 

Quebrada Prieta. The reservoir has a drainage area of 21.4 square kilometers. 

The dam is a concrete gravity and earthfill structure with a length of 

approximately 165 meters and a structural height of 24 meters. The spillway 

portion of the dam is an ungated ogee crest about 40 meters long with a crest 

elevation of 403.00 meters above mean sea level. Additional information and 

operational procedures are listed in Soler-López (1999).

 During August 14-15, 2007, the U.S. Geological Survey (USGS), 

Caribbean Water Science Center (CWSC), in cooperation with the PRASA, 

conducted a bathymetric survey of Lago de Cidra to update the reservoir storage 

capacity and actualize the reservoir sedimentation rate by comparing the 2007 

data with the previous 1997 bathymetric survey data. The purpose of this report 

is to describe and document the USGS sedimentation survey conducted at Lago 

de Cidra during August 2007, including the methods used to update the reservoir 

storage capacity, sedimentation rates, and areas of substantial sediment 

accumulation since 1997.

Method of Survey and Analysis

 The field techniques and bathymetric data reduction processes used for 

the 2007 survey were performed following procedures established by the USGS 

CWSC, and described in the previous bathymetric survey report of Lago de 

Cidra (Soler-López, 1999). The August 2007 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 November 1997 

(Soler-López, 1999). Survey navigation lines were established at a spacing of 

about 50 meters, beginning at the dam and continuing upstream along the 

different river branches of the reservoir. Geographic position and water depths 

Table 1. Comparison of the 1997 and 2007 sedimentation surveys of Lago de Cidra, 

Puerto Rico.

Data descriptor 1946

Year of survey

1997 2007

Total capacity, in million cubic meters

Years since construction

Sediment accumulation since construction, 

in million cubic meters

Sediment accumulation since previous survey, 

in million cubic meters

Storage loss since construction, in percent

Annual loss of capacity since 

construction in cubic meters

Annual loss of capacity since 

construction, in percent

Years since previous survey

Inter-survey loss of capacity, in 

cubic meters per year 

Estimated sediment trapping efficiency, 

1 in percent 

Inter-survey basin sediment yield, in 

cubic meters per year 

 

Long-term basin sediment yield, in cubic meters 

per square kilometer per year

Estimated year the reservoir would fill

with sediments

6.54

0

—

—

—

—

—

—

—

— 

—

— 

—

5.76

51

0.78

0.78

11.9

15,294

0.23

51

15,294

98

768

768

2374

5.63

61

0.91

0.13

13.9

14,918

0.23

10

13,000

96

666

765

2440

1Using the relation established by Brune (1953).

Table 2. Storage capacity table for Lago de Cidra, 

Puerto Rico, August 2007. 

Pool elevation, in 

above mean sea 

meters 

level

Storage capacity, in 

million cubic meters

403.00

402.00

401.00

400.00

399.00

398.00

397.00

396.00

395.00

394.00

393.00

392.00

391.00

390.00

389.00

388.00

387.00

386.00

385.00

 5.63

 4.70

 3.89

 3.18

 2.54

 1.97

 1.51

 1.15

 0.88

 0.66

 0.49

 0.36

 0.25

 0.17

 0.10

 0.06

 0.03

 0.01

 0.00

Figure 3. Aerial photograph of Lago de Cidra and its immediate surroundings showing 

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

 The 2007 data were stored and transferred into the USGS geographic informatio

system (GIS) where final analysis and volume calculations were made following simila

procedures used to develop the November 1997 bathymetric map of Lago de Cidr

(Soler-López, 1999). Field data from the August 2007 survey were used to generate 

bathymetric map representing the reservoir bottom in August 2007 (fig. 2). A triangulate

irregular network (TIN) surface model of Lago de Cidra was then generated from th

bathymetric map, and the reservoir volume was calculated using the GIS. The TIN 

surface model was used with the digital data for 1997 and 2007 to generate 

stage-storage curve and longitudinal profiles along the different river branches of Lago d

Cidra. A storage capacity table and curve were generated by calculating the TIN volum

at 1.00 meter elevation intervals.

Storage Capacity, Sedimentation Rates, and Useful Life

 Bathymetric data indicate the storage capacity of Lago de Cidra decrease

slightly from 5.76 million cubic meters in November 1997 (Soler-López, 1999) to 5.6

million cubic meters in August 2007 (table 1). The inter-survey (1997-2007) storag

capacity loss is about 2.3 percent, for a decrease of about 0.23 percent per year. Thi

decrease represents a reduction of 130,000 cubic meters between 1997 and 2007, for a

annual storage capacity loss rate of about 13,000 cubic meters. However, the long term 

Lago de Cidra capacity loss rate due to sedimentation has not changed measurably sinc

1997 (table 1), and may be a result of the relatively small drainage area (21.4 squar

kilometers, fig. 3) contributing to Lago de Cidra. An actualized storage capacity table an

curve are shown on table 2 and figure 4, respectively. 

 The comparison of longitudinal bottom profiles for 1997 and 2007 indicates tha

sediment accumulation in Lago de Cidra for this period was minimal (fig. 5). The greate

accumulation (averaging about 3 meters) occurred along the riverine zone of Lago d

Cidra in the Río Sabana approximately 3,200 to 4,000 meters upstream from the dam, an

in the Quebrada Prieta approximately 2,200 to 2,800 meters upstream from the dam 

Sediment deposition from 1997 to 2007 was minimal along the Río de Bayamón branc

and near the dam. The sediment deposition rate from 1997 to 2007 was about 3

centimeters per year along the Río Sabana and Quebrada Prieta branches. The mor

noticeable effect of sediment accumulation is that the reservoir surface area (floode

area) has been reduced on the Río Sabana and Quebrada Prieta riverine zones (fig. 5

Figure 6 shows an aerial photograph of the Lago de Cidra dam and the spillway section

 The long-term drainage area sediment yield rate of Lago de Cidra has remaine

nearly constant, decreasing from 768 cubic meters per square kilometer per year in 199

(Soler-López, 1999) to 765 cubic meters per square kilometer per year in 2007 (table 1

The inter-survey drainage area sediment yield, however, decreased by about 13 percen

from 768 to 666 cubic meters per square kilometer per year. According to the curren

storage capacity loss of about 13,000 cubic meters per year estimated for the 1997-200

period, the projected useful life of Lago de Cidra is about 433 years, to the year 2440. 

Summary and Conclusions

 During August 2007, the USGS Caribbean Water Science Center, in cooperatio

with the Puerto Rico Aqueduct and Sewer Authority, conducted a bathymetric survey o

Lago de Cidra to update the reservoir storage capacity and actualize the reservo

sedimentation rate by comparing 2007 bathymetric survey data with 1997 data.

 The Lago de Cidra storage capacity was 5.76 million cubic meters in Novembe

1997, which decreased to 5.63 million cubic meters by August 2007. The inter-surve

(1997-2007) storage capacity loss is about 2.3 percent, for a decrease of about 0.2

percent per year. This loss represents a reservoir sedimentation rate of about 13,000 cubi

meters per year between 1997 and 2007. On a long-term basis (1946–2007), however, th

sedimentation rate has remained constant at about 15,000 cubic meters per year.

 Most of the storage capacity loss of Lago de Cidra has occurred along the Rí

Sabana and Quebrada Prieta branches, where an average of about 3 meters of sedimen

has been accumulated between 1997 and 2007. Sediment accumulation has been minima

along the Río de Bayamón branch and in the vicinity of the dam. 

 The Lago de Cidra drainage area sediment yield has decreased about 13 percen

from 768 cubic meters per square kilometer per year between 1946 and 1997 to 666 cubi

meters per square kilometer per year between 1997 and 2007. On a long-term basi

however, the sediment yield has remained unchanged at about 765 cubic meters pe

square kilometer per year as a result of the relatively small sediment-contributing Lago d

Cidra drainage area of 21.4 square kilometers. 

 Although the life expectancy of about 433 years for Lago de Cidra is not 

pressing concern, sediment accumulation in the Río Sabana and Quebrada Priet

branches of the reservoir will continue forward towards the deepest parts of Lago d

Cidra, and will eventually start filling the reservoir near the dam. If the 1997-200

sedimentation rate remains constant, the useful life of Lago de Cidra may end by the yea

2440.

References Cited

Brune, G. M. 1953: Trap efficiency of reservoirs. Transactions of the American 

Geophysical Union 34, 407-418.

Soler-López, Luis R., 1999, Sedimentation survey of Lago de Cidra, Puerto Rico, 

November 1997: U.S. Geological Survey Water-Resources Investigations Report 

99-4144, 19 p., 1 pl.

18.0

15.0

2.0

9.0

6.0

6.0

5.0

4.0

13.0

13.0

13.0

1.0

8.0

12.0

2.0 8.0

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8.0

9.0

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12.0

2.0

1.0

9.0

DAM Quebrada Prieta bra

Quebrada Prieta bra

Río de Bayamón branch Río de Bayamón branch

Río Sabana branch

Río Sabana branch

Figure 4. Relation between water-storage capacity and pool elevation of Lago de 

Cidra, for 1997 and 2007.

18°12'00"

18°11'30"

18°11'00"

18°10'30"

Spillway section Spillway section

Figure 6. Aerial photograph of the Lago de Cidra concrete dam and spillway section. Photograph courtesy of the Puerto R

Electric Power Authority, May 2006.

0 250 500 750 1,000 METERS

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

8.0

7.0

6.0

4.0

2.0

1.0

4.0

2.0

2.0

4.0

3.0

12.0

5.0

10.0

11.0

9.0

2.0

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9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

5.0

5.0

2.0

Figure 1. Location of Lago de Cidra in the Río de Bayamón basin, Puerto Rico.

Shoreline modified from the U. S. Geological Survey quadrangles Caguas and Comerío, Puerto Rico, 

1941, Lambert Conic Conformal Projection.

Puerto Rico State Plane coordinate system (Puerto Rico Datum, 1940 adjustment)

Figure 2. Bathymetric map of Lago de Cidra, Puerto Rico, for August 2007.

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

DISTANCE FROM THE DAM, IN METERS

Vertical scale greatly exaggerated

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

2007

1997

DEPTH, IN METERS BELOW SPILLWAY ELEVATION OF 403.00 METERS 

ABOVE MEAN SEA LEVEL

Río Sabana branch

Río de Bayamón branch

Quebrada Prieta branch

~ 3 m

~ 3 m

Figure 5. Longitudinal bottom profiles along the thalweg of the Río de Bayamón, Río Sabana, and Quebrada Prieta branches of Lago de Cidra, 

Puerto Rico, for 1997 and 2007.

EXPLANATION

1.0 RESERVOIR BOTTOM CONTOUR- Depth of the reservoir bottom, 

in 2007, in meters below spillway elevation of 403.00 meters above 

mean sea level. Contour interval variable. 

Shoreline shown as red line equal to zero depth or

spillway elevation of 403.00 meters above mean sea level.

nch

Río Sabana branch

66°09'00" 66°08'30" 66°08'00" 66°07'30" 66°07'00"

8°12'30"

8°12'00"

8°11'30"

8°11'00"

8°10'30"

8°10'00"

8°09'30"

0 0.5 1 0.25 Kilometers

0 0.25 0.5 1 Miles

1

1

1

1

1

1

1

Río Sabana branch