Sedimentation Survey of Lago Guerrero,

Puerto Rico, May 2001

Water-Resources Investigations

Report 02-4169

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

PUERTO RICO ELECTRIC POWER AUTHORITY
U.S. Department of the Interior 

U.S. Geological Survey 

Sedimentation Survey of Lago Guerrero, Puerto Rico, 

May 2001 

By Luis R. Soler-López 

Water-Resources Investigations Report 02-4169 

In cooperation with the 

PUERTO RICO ELECTRIC POWER AUTHORITY 

San Juan, Puerto Rico: 2002 
U.S. DEPARTMENT OF THE INTERIOR 

GALE A. NORTON, Secretary 

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director 

Use of trade names in this report is for identification purposes only and does not imply endorsement by the 

U.S. Government. 

For additional information write to: Copies of this report can be purchased from: 

District Chief 

U.S. Geological Survey U.S. Geological Survey 

GSA Center, Suite 400-15 Branch of Information Services 

651 Federal Drive Box 25286 

Guaynabo, Puerto Rico 00965 Denver, CO 80225 
CONTENTS


Abstract ................................................................................................................................................................ 1


Introduction .......................................................................................................................................................... 1


Dam and Reservoir Characteristics ...................................................................................................................... 1


Method of Survey................................................................................................................................................. 3


Field Techniques ............................................................................................................................................ 5


Data Processing ............................................................................................................................................. 5


Storage Capacity and Reservoir Bathymetry ....................................................................................................... 7


Reference.............................................................................................................................................................. 7


PLATE 

[Plate is in pocket] 

1. Lago Guerrero, Puerto Rico, Bathymetry, May 2001 

FIGURES 

1. Map showing location of Lago Guerrero in northern Puerto Rico ................................................................. 2


2. Diagram showing spillway structure representation of Lago Guerrero dam, Puerto Rico ............................. 3


3.-5. Map showing


3.	 Planned cross-section locations for the May 2001 bathymetric survey of Lago Guerrero, 


Puerto Rico.............................................................................................................................................. 4


4. Actual track lines for the May 2001 bathymetric survey of Lago Guerrero, Puerto Rico......................... 6


5. Longitudinal distances along the central portion of Lago Guerrero, Puerto Rico ..................................... 8


6.-8. Graphs showing


6.	 Selected cross-sections generated from the TIN surface model of Lago Guerrero, Puerto Rico, 

for May 2001........................................................................................................................................... 9 

7. Longitudinal profiles along the central portion of Lago Guerrero, Puerto Rico for May 2001 ................ 11


8.	 Relation between water-storage capacity and pool elevation for Lago Guerrero, Puerto Rico, 

for May 2001........................................................................................................................................... 12 

TABLES 

1. Storage capacity of Lago Guerrero, Puerto Rico, for May 2001 .................................................................... 5


Contents IV 
CONVERSION FACTORS, DATUMS, ACRONYMS, and TRANSLATIONS 

Multiply By To obtain

 Length 

centimeter 0.03281 foot 

millimeter 0.03937 inch 

meter 3.281 foot 

kilometer 0.6214 mile

 Area 

square meter 10.76 square foot 

square kilometer 0.3861 square mile 

square kilometer 247.1 acre

 Volume 

cubic meter 35.31 cubic foot 

cubic meter 0.0008107 acre-foot 

million cubic meters 810.7 acre-foot

 Volume per unit time (includes flow) 

cubic meter per second 35.31 cubic feet per second 

cubic meter per second 15,850 gallon per minute 

cubic meter per second 22.83 million gallons per day

 Mass per area (includes sediment yield) 

megagram per square kilometer 2.855 ton per square mile 

Datums 

Horizontal Datum - Puerto Rico Datum, 1940 Adjustment 

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)--a 

geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, 

formerly called “Seal Level Datum of 1929”. 

Acronyms used in this report 

BLASS Bathymetric/Land Survey System 

DGPS Differential Global Positioning System 

GIS Geographic Information System 

PREPA Puerto Rico Energy Power Authority 

TIN Triangulated Irregular Network 

USGS U.S. Geological Survey 

Translations 

Spanish English 

Lago Lake (in Puerto Rico, also reservoir) 

Río River 

V Contents 
Sedimentation Survey of Lago Guerrero, Puerto Rico,


May 2000 

By Luis R. Soler-López 

Abstract 

Lago Guerrero, a small reservoir owned by 

the Puerto Rico Electric Power Authority, is part 

of the Isabela Hydroelectric System and is located 

in Aguadilla, in northwestern Puerto Rico. The 

reservoir had a storage capacity of about 127,376 

cubic meters in May 2001 and a maximum depth 

of about 5.8 meters. 

Records on dam construction and original 

topography and storage capacity were not 

available; therefore, sedimentation rates could not 

be determined. However, Lago Guerrero 

presumably was constructed during the 1930’s 

because it receives water from lago Guajataca, 

which was constructed in 1928. The May 2001 

bathymetric survey of Lago Guerrero established 

baseline data that are essential to calculate 

sedimentation rates, sediment yields, storage loss, 

and sediment deposition sites within the reservoir. 

INTRODUCTION 

The U.S. Geological Survey (USGS) in 

cooperation with the Puerto Rico Electric Power 

Authority (PREPA) has conducted numerous 

hydrographic and sedimentation surveys in reservoirs 

used for public water supply, hydroelectric power 

generation, and irrigation of croplands. On May 30, 

2001, the USGS conducted a bathymetric survey of 

Lago Guerrero to determine the storage capacity of the 

reservoir and establish baseline data that will be the 

basis for future reservoir capacity comparisons and 

sedimentation rate and sediment yield estimates. 

Data on geographic location and water depth 

were collected simultaneously using a differential 

global positioning system (DGPS) coupled to a digital 

depth sounder. These data were then stored and 

transferred into the USGS geographic information 

system where final analysis and volume calculations 

took place. A contour map, cross sections representing 

the reservoir bottom, and a longitudinal section 

representing the central portion of the reservoir bottom 

were generated, from the digital data. 

DAM AND RESERVOIR CHARACTERISTICS 

Lago Guerrero is an excavation structure 

constructed in the limestone karst region of 

northwestern Puerto Rico (fig. 1). The reservoir was 

constructed by digging a hole in the ground and 

cutting the limestone to form a dam wall. It is part of 

the Isabela Hydroelectric System and receives water 

released from Lago Guajataca through a 26-kilometer 

concrete channel (Pablo Roman, PREPA, written 

commun., 2001). Additional inflow may come from 

runoff from the surface water drainage basin of the 

reservoir; however, it is presumed to be negligible 

compared to the almost constant inflow from Lago 

Guajataca. 

Records on dam construction, reservoir 

structures, and original capacity are not available, 

therefore, reservoir capacity comparisons, 

sedimentation rate estimates and sediment distribution 

characterization are not possible. However, the 

reservoir was probably built in the 1930’s since it 

receives water from Lago Guajataca, which was 

constructed in 1928, and the logical order of 

construction for the reservoir system would be from 

up to downstream. 

Dam, Reservoir, and Drainage Basin Characteristics 1 
Figure 1. Location of Lago Guerrero in northwestern Puerto Rico. 

2 Sedimentation Survey of Lago Guerrero, Puerto Rico, May 2001 
The reservoir is used for hydroelectric power 

generation at power plant no. 2, located about 0.5 

kilometer downstream from the dam. Recently, the 

reservoir has also been used for water supply by the 

residents of the Aguadilla area through a pump house 

located about 20 meters upstream from the dam. An 

uncontrolled cast-iron pipe spillway with a diameter of 

1.22 meters is located on the downstream face of the 

dam at an elevation of 125.73 meters above mean sea 

level (Pablo Roman, PREPA, written commun., 2001) 

(fig. 2). Flow over the spillway is probably infrequent 

since water inflow is regulated and most of the 

outflow is through the pump house structure. 

METHOD OF SURVEY 

The bathymetric survey of Lago Guerrero 

involved planning, data collection, data processing, 

and analysis of the results. A geographic information 

system (GIS), was used to plan the survey lines and to 

analyze the bathymetric data. Cross-section locations 

were established at spacings of 15 meters, starting 

at the dam and continuing upstream to the reservoir 

(fig. 3). Geographic position and water depths were 

acquired simultaneously, using a differential global 

positioning system interfaced to a depth sounder. The 

soundings were subsequently adjusted to represent 

water depths below spillway elevation. The pool 

elevation of the reservoir was measured at the PREPA 

measuring staff before and after the data collection 

process. The water level slightly changed during the 

data-collection process. To account for this change, a 

time-elevation correction factor was applied to adjust 

the measured depths to represent depths below 

spillway elevation. A bathymetric map representing 

the reservoir bottom in May 2001 was then generated 

(plate 1). 

Figure 2. Spillway structure representation of the Lago Guerrero dam, Puerto Rico. 

Method of Survey 3 
Figure 3. Planned cross-section locations for May 2001 bathymetric survey of Lago Guerrero, 

Puerto Rico. 

4 Sedimentation Survey of Lago Guerrero, Puerto Rico, May 2001 
Field Techniques 

The data collection process took place on May 

30, 2001. Data were collected using the bathymetric/ 

land survey system (BLASS), developed by Specialty 

Devices Inc. The system uses two Novatel OEM 

global position system (GPS) receivers. The GPS units 

were first used in a static mode to establish reference 

marks at several sites overlooking the reservoir. These 

sites were later used as master stations for geographic 

positioning control. Satellite information was 

simultaneously recorded for one hour at a control 

station located at the USGS office, (latitude 

18°25’58.9269”N., longitude 66°06’51.7128”W.) 

established by the USGS and at a benchmark (latitude 

18°03’52.0489”N., longitude 67°40’03.7365”W.), at 

the dam, overlooking the reservoir. Once established, 

one GPS unit was installed at the dam benchmark 

station, and the other GPS unit was installed in the 

survey boat. The GPS on board the survey boat 

independently calculated a position every second 

while receiving a set of pseudo-range correction 

factors from the master station in order to maintain a 

positional accuracy within 2 meters. Water depths 

were measured using a SDI-IDS depth sounder. The 

depth recorder shows depth to the nearest 0.01 meter, 

and was calibrated at a water depth of 5.5 meters. The 

bathymetric survey software HYPACK (Coastal 

Oceanographics, Inc.) received and recorded the 

geographic position and depth once every second 

while in survey mode. A total of 1,710 data points 

were collected over the entire reservoir. HYPACK 

runs on a portable personal computer, and is used to 

record data and to navigate. The helmsman of the 

survey boat is provided with a graphical display 

showing the lakeshore, the location of the planned 

cross sections, the real-time position of the survey boat 

while underway, and indicators of speed and the 

amount of deviation from the planned lines. A total of 

14 cross sections at a 15-meter spacing were planned 

in the office. The actual track lines of the May 2001 

bathymetric survey of Lago Guerrero are shown in 

figure 4. No electronic or multipath errors, which 

could affect the satellite signals, occurred during the 

data collection process. 

Data Processing 

Initial editing and verification of the position 

and depth data were performed using the HYPACK 

program. The edited data were then transferred into 

the GIS for processing and analysis. The data points 

were color coded according to the different depths, 

and contour lines were drawn to match the 

corresponding color and depth ranges. The 

bathymetric contour lines were then converted into 

a surface model by creating a triangulated irregular 

network (TIN). The TIN surface model of the 

reservoir bottom consists of thousands of adjoining 

triangles with x, y and z coordinates assigned to all 

vertices (Environmental Systems Research Institute, 

Inc., 1992). The volume of the reservoir was then 

calculated at incremental pool elevations of 0.3048 

meter to develop an elevation-capacity relation curve 

and table (table 1). 

Table 1. Storage capacity of Lago Guerrero, 


Puerto Rico, May 2001


[All elevations are in meters above mean sea level; all 


capacities are in cubic meters]


Pool elevation Storage capacity 

125.73 127,376 

125.58 122,768 

125.28 113,642 

124.97 104,635 

124.67 95,747 

124.36 86,999 

124.06 78,501 

123.75 70,261 

123.45 62,271 

123.14 54,606 

122.84 47,289 

122.53 40,309 

122.23 33,685 

121.92 27,364 

121.62 21,328 

121.31 15,731 

121.01 10,727 

120.70 6,238 

120.40 2,552 

120.09 551 

119.79 0 

Method of Survey 5 
Figure 4. Actual track lines for the May 2001 bathymetric survey of Lago Guerrero, Puerto Rico. 

6 Sedimentation Survey of Lago Guerrero, Puerto Rico, May 2001 
STORAGE CAPACITY AND RESERVOIR 

BATHYMETRY 

In May 2001, the storage capacity of Lago 

Guerrero was 127,376 cubic meters at spillway 

elevation of 125.73 meters above mean sea level, and 

a maximum depth of 5.8 meters. The longitudinal 

distance of Lago Guerrero along the central portion of 

the reservoir is shown on figure 5. Cross sections 

depicting the reservoir bottom from shore to shore, 

and a longitudinal bottom profile of Lago Guerrero are 

shown on figures 6 and 7, respectively. The reservoir 

bottom in the vicinity of the spillway pipe is at an 

elevation of about 121 meters above mean sea level. 

The relation between pool elevation and storage 

capacity of Lago Guerrero is shown on figure 8. 

The original storage capacity of the reservoir 

and construction data are not available, therefore, 

sedimentation rates, sediment yield, and storage 

capacity loss cannot be calculated. However, all these 

parameters are expected to be low compared to a 

reservoir constructed on a natural river channel. The 

water inflow to Lago Guerrero comes from releases at 

Lago Guajataca through a concrete channel and 

erosion is considered to be minimal. Only sedimentrich releases from Lago Guajataca, as well as sheet 

erosion from the adjacent Lago Guerrero basin, likely 

discharge sediments into Lago Guerrero. Water 

releases from Lago Guajataca are probably the most 

important source of sediment influx to the reservoir. 

Future bathymetric surveys as well as measurement of 

suspended sediment concentrations of the water 

entering the reservoir through the irrigation channel 

are probably the best tools for monitoring the storagecapacity loss of Lago Guerrero. 

REFERENCE 

Environmental Systems Research Institute, Inc., 1992, 

Surface modeling with TIN, Surface analysis and 

display: Redlands, Cal., 8 chapters. 

References 7 
Figure 5. Longitudinal distance along the central portion of Lago Guerrero, Puerto Rico. 

8 Sedimentation Survey of Lago Guerrero, Puerto Rico, May 2001 
Figure 6. Selected cross-sections generated from the TIN surface model of Lago Guerrero, Puerto Rico, 

for May 2001. Refer to figure 3 for cross-section locations. 

References 9 
Figure 6. Selected cross-sections generated from the TIN surface model of Lago Guerrero, Puerto Rico, 

for May 2001. Refer to figure 3 for cross-section locations–Continued. 

10 Sedimentation Survey of Lago Guerrero, Puerto Rico, May 2001 
References 11


Figure 7. Longitudinal profile along the central portion of Lago Guerrero, Puerto Rico, for May 2001. 
Figure 8. Relation between water-storage capacity and pool 

elevation for Lago Guerrero, Puerto Rico, for May 2001. 

12 Sedimentation Survey of Lago Guerrero, Puerto Rico, May 2001 
District Chief

Caribbean District

U.S. Geological Survey

Water Resources Division

GSA Center, Suite 400-15

651 Federal Drive

Guaynabo, Puerto Rico 00965-5703

Soler-López—SEDIMENTATION SURVEY OF LAGO GUERRERO, PUERTO RICO, MAY 2001—WRIR 02–4169