Sedimentation History of Lago Guayab

Puerto Rico, 1913-2001

Water-Resources Investigations

Report 03-4198

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 History of Lago Guayabal, 


Puerto Rico, 1913-2001


By Luis R. Soler-López 

Water-Resources Investigations Report 03-4198


In cooperation with the 

PUERTO RICO ELECTRIC POWER AUTHORITY 

San Juan, Puerto Rico: 2003

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 .......................................................................................................................................................... 2


Dam, Reservoir, Basin Characteristics, and General Land-Use History.............................................................. 4


Method of Survey................................................................................................................................................. 9


Field Techniques ............................................................................................................................................ 21


Data Processing ............................................................................................................................................. 22


Previous Bathymetric Surveys, Storage Capacities, and Sediment Accumulation .............................................. 22


Trapping Efficiency.............................................................................................................................................. 25


Sediment Yield ..................................................................................................................................................... 26


Summary .............................................................................................................................................................. 27


References Cited .................................................................................................................................................. 28


PLATES 

[Plates are in pocket] 

1. Lago Guayabal, Puerto Rico, Bathymetry, December 2001 

2. Lago Guayabal, Puerto Rico, Pre-impoundment Topography from 1908 Land Survey Prepared in 1913


Contents III 
FIGURES 

1.-3. Map showing 

1.	 Location of Lago Guayabal in the Río Jacaguas Basin and areas served by the 


Juana Díaz Irrigation District in southern Puerto Rico........................................................................... 2


2. Isohyet map of the mean-annual rainfall distribution in Puerto Rico ....................................................... 3


3.	 Predominant agricultural land use in the west-central mountainous areas of 


Puerto Rico during the mid-20th century ............................................................................................... 6


4. Graph showing Puerto Rico coffee production from 1897 to 1963................................................................ 7


5.-9. Map showing


5.	 Current Lago Guayabal drainage area showing basin disruption, reservoir 


shoreline, and tributaries to the Río Jacaguas......................................................................................... 8


6.	 Planned cross-section locations for the December 2001 bathymetric survey of


 Lago Guayabal, Puerto Rico.................................................................................................................. 11


7.	 Actual track lines of the December 2001 bathymetric survey of Lago Guayabal, 


Puerto Rico ............................................................................................................................................. 12


8.	 Triangulated irregular network (TIN) surface model of Lago Guayabal, 


Puerto Rico, for December 2001 ............................................................................................................ 13


9. Reference longitudinal distance along the central portion of Lago Guayabal, 


Puerto Rico ............................................................................................................................................. 14


10.-14. Graph showing 

10.	 Selected cross sections generated from the TIN surface model of Lago Guayabal, 


Puerto Rico, for 1913, 1950, 1986, and December 2001 ....................................................................... 15


11.	 Longitudinal profiles generated from the TIN surface models along the thalweg 


of Lago Guayabal, Puerto Rico, for 1913, 1950, 1986, and December 2001 ........................................ 20


12.	 Relation between water storage capacity and pool elevation of Lago Guayabal, 


Puerto Rico, for 1913, 1950, 1986, and 2001......................................................................................... 21


13.	 Lago Guayabal volume variations from 1913 to 2001 ............................................................................. 24


14.	 Reservoir trapping efficiency as a function of the ratio between storage capacity 


and annual water inflow volume............................................................................................................. 26


TABLES 

1. Principal characteristics of Lago Guayabal and Guayabal dam, Puerto Rico ................................................ 5


2. Storage capacity table for Lago Guayabal, Puerto Rico, for December 2001................................................ 9


3. Historical sedimentation trends of Lago Guayabal, Puerto Rico, 1913-2001 ........................................... 10


IV Contents 
CONVERSION FACTORS, DATUMS, ACRONYMS, and TRANSLATIONS 

Multiply By To obtain

millimeter 

centimeter 

meter 

kilometer 

square meter 

square kilometer 

square kilometer 

cubic meter 

cubic meter 

million cubic meters 

cubic meter per second 

cubic meter per second 

cubic meter per second 

megagram per square kilometer 

 Length 

0.03937 

0.03281 

3.281 

0.6214 

 Area 

10.76 

0.3861 

247.1 

 Volume 

35.31 

0.0008107 

810.7 

 Volume per unit time (includes flow) 

35.31 

15,850 

22.83 

inch 

foot 

foot 

mile

square foot 

square mile 

acre

cubic foot 

acre-foot 

acre-foot

cubic feet per second 

gallon per minute 

million gallons per day

 Mass per area (includes sediment yield) 

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 

DOQ Digital Orthophoto Quadrangle 

GIS Geographic Information System 

GPS Global Positioning System 

PREPA Puerto Rico Electric Power Authority 

TIN Triangulated Irregular Network 

USGS U.S. Geological Survey 

Translations 

Lago Lake (in Puerto Rico, also reservoir) 

Río River 

Contents V 
Sedimentation History of Lago Guayabal, 


Puerto Rico, 1913-2001 

By Luis R. Soler-López 

Abstract 

The Lago Guayabal dam, located in the 

municipality of Villalba in southern Puerto Rico, 

was constructed in 1913 for irrigation of 

croplands in the southern coastal plains and is 

owned and operated by the Puerto Rico Electric 

Power Authority. The reservoir had an original 

storage capacity of 11.82 million cubic meters 

and a drainage area upstream of the dam of 112 

square kilometers. Sedimentation has reduced the 

storage capacity to 6.12 million cubic meters in 

2001, which represents a storage loss of about 48 

percent. However, the actual sediment 

accumulation in the reservoir during the 88 years 

is greater, because some sediment removal was 

conducted between 1940 and 1948 by dredging 

and sluicing. This report summarizes the 

historical data from a 1913 land survey and eight 

bathymetric surveys conducted between 1914 and 

2001, and the relation of high sedimentation to 

agricultural land practices within the Lago 

Guayabal basin and six major hurricanes which 

made landfall on the island. 

The reservoir had an area-normalized 

sedimentation rate of about 1,863 cubic meters 

per square kilometer per year between 1913 and 

1936 from a 112 square kilometer basin. In 1972, 

a new dam upstream along the Río Toa Vaca 

impounded runoff from 57.5 square kilometers, 

and sediment transport to Lago Guayabal was 

reduced. A comparison of bathymetric survey 

results between 1972 and 2001 indicates an areanormalized sedimentation rate of 1,120 cubic 

meters per square kilometer per year or about 60 

percent of the rate between 1913 and 1936. The 

significant reduction (almost half) of the 

sedimentation rate after the Toa Vaca dam was 

built may indicate that erosion susceptibility of 

the Río Toa Vaca watershed is about twice that of 

the Río Jacaguas watershed impounded by Lago 

Guayabal. 

INTRODUCTION 

The Puerto Rico Power Electric Authority 

(PREPA) owns and operates the Lago Guayabal 

reservoir, located in southern Puerto Rico on the Río 

Jacaguas, about 5 kilometers north of the town of 

Juana Díaz and about 5 kilometers south of the town of 

Villalba (fig. 1). Because the south coast of Puerto 

Rico receives as little as 900 millimeters per year 

annual rainfall (Calvesbert, 1970), the reservoir was 

constructed as part of a major irrigation infrastructure 

project completed in 1914 to convey water for the 

cultivation of sugarcane along the southern coastal 

plains of the island. 

Mean annual rainfall in the Lago Guayabal 

basin is about 1,800 millimeters, but can vary from 

less than 900 to more than 3,800 millimeters per year 

(Calvesbert, 1970) (fig. 2). These rainfall amounts, 

combined with the moderate erosion hazard of the 

Caguabo and Humatas soils that have slopes between 

20 to 60 percent (Gierbolini, 1979) and the poor landuse management practices that have prevailed in the 

basin, have substantially impaired the reservoir storage 

capacity. Bathymetric surveys at Lago Guayabal have 

been conducted on a frequent basis given its 

importance as an irrigation source to the coastal plain 

which receives on average less than 1,150 millimeters 

of rainfall per year, with average pan evaporation rate 

of about 2,000 millimeters per year. 

Introduction 1 
2 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 

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

southern Puerto Rico. 
Introduction 3

Figure 2. Isohyet map of the mean-annual rainfall distribution in Puerto Rico (modified from Calvesbert, 1970).
The U.S. Geological Survey (USGS), in 

cooperation with PREPA, conducted a bathymetric 

survey of Lago Guayabal during December 2001 using 

a differential global positioning system (DGPS) 

interfaced to a depth sounder. The field-collected data 

were then transferred into a geographic information 

system (GIS), which was used to determine the 

existing storage capacity, sedimentation rates, and 

sediment distribution, and to predict the useful life of 

the reservoir. This report provides the PREPA with the 

necessary information to more effectively manage the 

water resources in the Lago Guayabal Basin. Data 

from the December 2001 bathymetric survey were also 

compared with previous studies performed in 1914, 

1936, 1950, 1951, and 1986 to define the historical 

long-term and inter-survey sedimentation rates, and 

the storage capacity loss, and to provide a current and 

accurate bathymetric contour map. 

DAM, RESERVOIR, BASIN 

CHARACTERISTICS, AND GENERAL 

LAND-USE HISTORY 

The Lago Guayabal dam structure was 

completed in 1913. It is located on the Río Jacaguas, 

in the municipality of Villalba in southern Puerto Rico, 

about 5 kilometers north of Juana Díaz and about 

5 kilometers south of Villalba (fig. 1). The dam was 

designed to provide about 11.82 million cubic meters 

of storage for irrigation of sugarcane crops in southern 

Puerto Rico. When built, the spillway elevation was at 

99.06 meters above mean sea level. However, the 

spillway was raised to 100.89 meters above mean sea 

level to allow the installation of flashboards during 

1950-51 to compensate for the storage capacity loss as 

a result of high sediment influx to the reservoir. After 

the flashboards were installed, the normal pool 

elevation of Lago Guayabal was 103.94 meters above 

mean sea level. The reservoir drainage area was 112.0 

square kilometers in 1913, however, the drainage area 

was artificially reduced when the Lago Toa Vaca dam 

was constructed on the eastern tributary of the 

reservoir (Río Toa Vaca) in 1972. 

The dam is an Ambursen structure of slab and 

buttress construction with a structural height of 39.62 

meters, and a length of 602.89 meters with buttresses 

at 5.49-meter centers (table 1). An earthfill structure 

with a concrete core extends from the left end of the 

non-overflow portion of the dam to the left abutment. 

The original 1913 spillway structure is located on the 

right abutment and had an elevation of 99.06 meters 

above mean sea level. Twenty intermediate piers, each 

0.91 meter wide, separate the crest into 21 bays which 

are controlled by automatic flashboards 10.06 meters 

wide by 3.05 high in the fully raised position. 

Irrigation releases from the reservoir are 

provided by an intake structure located on the 

upstream face of the non-overflow section of the dam 

between buttresses 20 and 21, and has an invert 

elevation (lower structure portion) of 87.17 meters 

above mean sea level. This information and other 

characteristics of Lago Guayabal dam are presented in 

table 1. 

The Lago Guayabal basin is within the Caguabo 

and Humatas soil series in south central Puerto Rico 

(Gierbolini, 1979). These series generally consist of 

well drained, moderately steep to very steep, and 

moderately permeable soils, with a moderate erosion 

hazard. Hill slopes range from 20 to 60 percent. The 

solum of the Caguabo series is 36 to 61 centimeters 

thick, and the Humatas series solum is 76 to 132 

centimeters thick. Surface runoff in these soils is rapid; 

thus, the moderate susceptibility to erosion. 

The Caguabo soils for the most part have 

remained in pasture, brush, with some shallow-rooted 

crops, such as pigeon peas that can be cultivated 

without the need of irrigation and adapt well to local 

soils. For many years, the Humatas soils have been 

planted with a wide variety of crops, which include 

coffee, yams, plantains, and tanniers. In addition, 

some areas are covered with native pasture 

(Gierbolini, 1979). 

Aerial photographs or topographic maps of the 

Lago Guayabal drainage area were not available at the 

time of construction or used over time as a tool for the 

comparison of the vegetation coverage and land use 

changes. However, by the early and mid-20th century, 

the Lago Guayabal drainage area was affected by an 

intensive use for agricultural purposes. During the first 

half of the 20th century, agriculture was primarily 

limited to the cultivation of export crops (coffee, 

tobacco and sugarcane) within large farmlands under 

private ownership. In 1941, the Puerto Rico 

Legislative Assembly created the Lands Authority 

with the purpose of re-distributing parcels of land 

among the predominantly rural population living as 

4 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
“agregados” or land-attached workers. This newly 

created authority had the power of expropriating lands 

in excess of 2 square kilometers from non-resident 

corporations, and selling the land to people who 

wished to cultivate it. The Lands Authority also played 

a major role in upgrading cultivation and harvest 

techniques to improve crops production. Figure 3 

shows a 1959 map with the principal crops cultivated 

within the south-central portion of Puerto Rico, 

including the Lago Guayabal drainage area 

(Gaztambide-Vega and Arán, 1959). Coffee was the 

predominant crop cultivated in the basin, with sugar 

cane as the secondary crop principally within the Río 

Toa Vaca basin portion of the Lago Guayabal basin. 

It is important to point out some facts about the 

cultivation of coffee, which enhances soil erosion. 

Coffee seedlings were planted in loose, unstable soil 

free of leaf litter below the forest canopy, during the 

rainy season, which is a sensitive period in terms of 

erosion susceptibility. Throughout most of the first 

half of the 20th century, the coffee variety planted 

required shade, thus a forest canopy was maintained. 

This coffee variety produced larger, healthier coffee 

plants, but the fruit production was smaller compared 

with a plant variety that thrived best exposed to direct 

sunlight. In general, the coffee production was about 

10 times higher per unit of surface area when exposed 

to sunlight, as compared to plants requiring shade of a 

forest canopy (Picó, 1964). This finding encouraged 

clearing of large forested areas to plant coffee under 

sunlight. However, the coffee plants died sooner than 

those requiring shade. Therefore, additional land 

clearing was required for the planting of new seedlings 

to maintain coffee production. Figure 4 puts in 

perspective the importance of coffee planting 

throughout the upland eastern half of Puerto Rico. 

During the period 1913-1920, coffee production was 

high (fig. 4), thus erosion potential from the upper 

parts of the drainage area could have been at its 

maximum, and later it may have decreased 

considerably after mid-1920’s. 

Table 1. Principal characteristics of Lago Guayabal and Guayabal dam, Puerto Rico 

(modified from PREPA, 1988) 

Total length of dam, in meters 602.89 

Maximum height of dam, in meters 39.62 

Invert elevation of intake structure, in meters above mean sea level 87.17 

Original crest elevation of spillway structure, in meters above mean sea level 99.06 

New crest elevation of spillway structure, in meters above mean sea level 100.89 

Normal pool elevation after the installation of flashboards, in meters above mean sea level 103.94 

Maximum discharge capacity, in cubic meters per second1 2,060.0 

Original drainage area at damsite, in square kilometers1 112.0 

New drainage area at damsite after the Toa Vaca dam construction, in square kilometers2 54.5 

Original reservoir surface area at elevation of 99.06 meters above mean sea level, in square 1.19 

kilometers 

Reservoir surface area after the installation of flashboards, in square kilometers3 1.44 

Maximum depth during the December 2001 bathymetric survey, in meters 13.0 

1

 From PREPA, 1988.


2 Calculated using GIS and 1:20,000 scale topographic map.


3 Calculated using GIS at normal pool elevation.


Dam, Reservoir, and Basin Characteristics, and General Land-Use History 5 
6 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001

Figure 3. Predominant agricultural land use in the west-central mountainous areas of Puerto Rico during the mid-20th century 

(modified from Gaztambide-Vega and Arán, 1959).
Figure 4. Puerto Rico coffee production from 1897 to 1963 (modified from the Puerto Rico 

Department of Agriculture, in Picó 1964). 

Sugarcane, though a secondary crop cultivated 

in the past, also required land clearing and tilling. 

Although coffee and sugarcane were the principal 

crops within the basin, their cultivation has declined 

since, but have not completely disappeared. At 

present, the cultivation of pigeon peas is locally 

significant and this type of crop also requires land 

clearing and tilling. 

In addition to the effect of agricultural land use, 

the Lago Guayabal drainage basin has been affected 

by six major hurricanes since construction of the 

Guayabal dam: Hurricane San Felipe in 1928, 

Hurricane San Nicolás in 1931, Hurricane San Ciprián 

in 1932, Hurricane Betsy in 1956, Hurricane Hortense 

in 1996, and Hurricane Georges in 1998. These 

historical climate events and crop cultivation methods 

presented an unfavorable scenario, which may have 

contributed in reducing the storage capacity of Lago 

Guayabal and thus, its safe yield for irrigation 

purposes. 

Although agricultural practices, in general, 

enhance land erosion, the transport component from 

cultivated lands to streams is the most critical for the 

rapid mobilization of sediment. Figure 5 shows parts 

of digital orthophoto quadrangles (DOQ’s) from aerial 

photographs taken between October 31, 1993, and 

November 13, 1995, showing the Lago Guayabal 

drainage area to the Río Jacaguas. From the photo 

mosaic, it is evident that within the Río Jacaguas basin 

above Lago Guayabal, the distance between any 

location to a perennial stream channel (as shown in the 

USGS, 1:20,000 scale topographic quadrangles) is 

generally on the order of hundreds of meters but not 

exceeding two kilometers. The high drainage density 

of tributaries plays a major role, particularly during 

major storms and rainfall events, which will be 

explained later in this report. 

Dam, Reservoir, and Basin Characteristics, and General Land-Use History 7 
Figure 5. Current Lago Guayabal drainage area showing basin disruption, reservoir shoreline, 

and tributaries to the Río Jacaguas. 

8 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
METHOD OF SURVEY 

The 2001 bathymetric survey of Lago Guayabal 

involved planning, data collection, data processing and 

analysis. An Arc/Info GIS was used to establish the 

survey lines and to analyze the collected data. Survey 

lines were planned at a spacing of 50 meters, 

beginning at the dam and continuing upstream along 

the two branches of Lago Guayabal (fig. 6). 

Bathymetric data were collected during December 

2001 using a depth sounder coupled to a DGPS to 

control the horizontal position of the survey boat. 

A geo-referenced digital map of the reservoir shoreline 

and the planned survey lines were loaded into a 

portable personal computer and served as the guide for 

bathymetric data collection. The reservoir pool 

elevation was monitored at the continuous-recording 

USGS lake-level station Lago Guayabal at damsite, 

near Juana Díaz Puerto Rico (station number 

50111300 in fig. 1). The pool elevation of Lago 

Guayabal, although close to, was not at the crest of the 

top of the gates; therefore, the sounding data were 

adjusted using a time-elevation correction factor to 

represent depths at normal pool elevation of 103.94 

meters above mean sea level. 

A total of 10,456 data points (depth soundings) 

were collected over the entire reservoir (fig. 7) while 

navigating along the planned survey lines (fig. 6). The 

depths along the cross sections were plotted, and 

1-meter interval contour lines of equal depth were 

drawn from the shoreline to the deepest parts of the 

reservoir (plate 1). The procedure used to contour the 

reservoir bottom is explained in a later section of this 

report. These contour lines were then converted into a 

triangulated irregular network (TIN) describing the 

surface model of the reservoir bottom (fig. 8). The TIN 

represents the reservoir bottom surface model as 

thousands of adjoining triangles with x, y, and z 

coordinates assigned to all vertices (Environmental 

Systems Research Institute, Inc. 1992). The 

longitudinal distance of the reservoir along the 

thalweg is shown on figure 9, and the original 1908 

topography prior to the impoundment of the Lago 

Guayabal reservoir is shown on plate 2. 

The GIS utilized the TIN to calculate the storage 

capacity (table 2) and thickness of sediment 

accumulation. The 1913 reservoir storage was 

compared with the 1914, 1936, 1950, 1951, 1964, 

1972, 1986, and 2001 calculated storage capacities as 

reported by previous bathymetric surveys to obtain 

estimates of historical sediment accumulation rates, 

and to estimate the useful life of the reservoir based on 

historical data (table 3). Bathymetric or topographic 

maps were available only for 1913, 1950, and 1986. 

Therefore, selected cross sections depicting the 

reservoir bottom from shore to shore, as well as 

longitudinal profiles of the reservoir bottom along the 

thalweg of Lago Guayabal were generated for 1913, 

1950, 1986, and 2001 from their TIN surface models 

(figs. 10 and 11). The relation between pool elevation 

and reservoir storage capacity for 1934 and for 

December 2001 was generated by calculating the 

reservoir volume at 1-meter elevation intervals 

(table 2) and is shown in graphical form on figure 12. 

Table 2. Storage capacity table for Lago 

Guayabal, Puerto Rico, for December 2001 

[all elevations in meters above mean sea level; all capacities 

in million cubic meters] 

Pool elevation Storage capacity 

103.94 6.12 

102.94 4.93 

101.94 3.96 

100.94 3.22 

99.94 2.63 

98.94 2.13

 97.94 1.69

 96.94 1.31

 95.94 0.97

 94.94 0.68 

93.94 0.42 

92.94 0.22 

91.94 0.07 

90.94 0.00 

Method of Survey 9 
---

---

---

---

---

Table 3. Historical sedimentation trends of Lago Guayabal, Puerto Rico, 1913-2001

 [--- undetermined] 

Year 1913 1914 1936 1950 1951 1964 1972 1986 2001 

Storage capacity, in million cubic 11.82 11.77 7.02 5.27 12.09 9.37 7.89 6.76 6.12 

meters 

Live storage, in million cubic meters 11.32 4.61 11.93 9.37 7.89 6.76 6.12 

Dead storage, in million cubic 0.50 10.66 0.16 0 0 0 0 

meters 

Years since construction 0 1 23 37 38 51 59 73 88 

Sediment accumulated, in million 0 0.05 4.80 6.55 2

6.73 9.45 10.93 12.06 12.70 

cubic meters 

Long-term storage loss, in percent 0 0.4 41 55 57 80 93 102 107 

Long-term annual loss of capacity, 0 50,000 208,696 177,027 177,105 185,294 185,254 165,205 144,318 

in cubic meters 

Long-term annual loss of capacity, 0 0.4 1.78 1.49 1.50 1.57 1.58 1.40 1.22 

in percent 

Inter-survey storage loss, in million 0 0.05 4.75 1.75 0.18 2.72 1.48 1.13 0.64 

cubic meters 

Inter-survey annual loss of capacity, 0 50,000 215,909 125,000 180,000 209,231 185,000 80,714 42,667 

in cubic meters 

Inter-survey annual loss of capacity, 0 0.4 1.84 1.0 2.0 1.77 1.62 0.6 0.3 

in percent 

Sediment trapping efficiency, in 93 93 91 87 93 92 93 94 93 

percent 

Drainage area sediment yield, in 0 485 2,070 1,836 1,719 1,818 1,795 31,618 31,235 

megagrams per square kilometers 

per year 

Year that the reservoir would fill 2149 1970 1980 2019 2015 2015 4

2070 52101 

with sediment 

1 The increase in dead storage from 1913 to 1950 represents the sediment removal activities between 1940 to 1948.


2

 Sediment accumulation includes the sediment dredged and sluiced, plus the long-term sedimentation rate for the period 1950 to 1951


 (PREPA, 1988). This accumulation is carried on after the flashboards installation. 

3 Sediment yield adjusted by the drainage area reduction in 1972. 

4 Using the 1972-86 inter-survey sedimentation rate because the sediment contributing drainage area was reduced in 1972. 

5

 Using the sedimentation rate of 61,034 cubic meters per year from 1972 to 2001 because the sediment contributing drainage area was 

reduced in 1972. 

10 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
Figure 6. Planned cross-section locations for the December 2001 bathymetric survey of 

Lago Guayabal, Puerto Rico. 

Method of Survey 11 
Figure 7. Actual track lines of the December 2001 bathymetric survey of Lago Guayabal, 

Puerto Rico. 

12 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
Figure 8. Triangulated irregular network (TIN) surface model of Lago Guayabal, 

Puerto Rico, for December 2001. 

Method of Survey 13 
Figure 9. Reference longitudinal distance along the central portion of Lago Guayabal, 

Puerto Rico. 

14 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
Figure 10. Selected cross sections generated from the TIN surface model of Lago Guayabal, 

Puerto Rico, for 1913, 1950, 1986, and December 2001. Refer to figure 6 for cross-section 

locations. 

Method of Survey 15 
Figure 10. Selected cross sections generated from the TIN surface model of Lago Guayabal, 

Puerto Rico, for 1913, 1950, 1986, and December 2001—Continued. Refer to figure 6 for

 cross-section locations. 

16 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
Figure 10. Selected cross sections generated from the TIN surface model of Lago Guayabal, 

Puerto Rico, for 1913, 1950, 1986, and December 2001—Continued. Refer to figure 6 for 

cross-section locations. 

Method of Survey 17 
Figure 10. Selected cross sections generated from the TIN surface model of Lago Guayabal, 

Puerto Rico, for 1913, 1950, 1986, and December 2001—Continued. Refer to figure 6 for 

cross-section locations. 

18 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
Figure 10. Selected cross sections generated from the TIN surface model of Lago Guayabal, 

Puerto Rico, for 1913, 1950, 1986, and December 2001—Continued. Refer to figure 6 for 

cross-section locations. 

Method of Survey 19 
Figure 11. Longitudinal profiles generated from the TIN surface models along the thalweg of Lago Guayabal, Puerto 

Rico, for 1913, 1950, 1986, and December 2001. 

20 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
Figure 12. Relation between water storage capacity and pool elevation 

of Lago Guayabal, Puerto Rico, for 1913, 1950, 1986, and 2001. 

Field Techniques 

The bathymetric survey of Lago Guayabal was 

conducted on December 5, 2001. Data were collected 

using the bathymetric/land survey system (BLASS) 

developed by Specialty Devices, Inc. The system 

consists of two Novatel global positioning system 

(GPS) receivers interfaced with a depth sounder model 

SDI-IDS Intelligent. The GPS receivers monitor the 

horizontal position of the survey boat, while the depth 

sounder collects data on water depths. The GPS 

receivers were first used in static mode to establish a 

benchmark overlooking the reservoir. Satellite 

information was recorded simultaneously at the USGS 

District Office benchmark (referred as “USGS roof”) 

(latitude 18°25’N., longitude 66°06’W.) and at a site 

overlooking the reservoir. Then, the benchmark 

coordinates for “Guayabal dam” (latitude 18°05’N., 

longitude 66°30’W.), were calculated using the postprocessing software CENTIPOINT. The new 

benchmark indicated a horizontal error of less than 10 

Method of Survey 21 
centimeters. Once established, the “Guayabal dam” 

benchmark was established as the reference station. 

One GPS receiver was installed at the reference station 

and the other GPS unit was installed in the survey boat 

as the mobile station. The GPS on board the survey 

boat independently calculates a position every second 

while receiving a set of correction signals from the 

reference station and converting the system into a 

DGPS. This combination maintained the survey boat 

horizontal position accuracy within two meters. The 

bathymetric survey software HYPACK was used to 

navigate and collect data by integrating the depth and 

position data and storing the x, y, (geographic 

location) and z (depth) coordinates in a portable 

personal computer. A total of 71 survey sounding lines 

were planned in the office using the GIS (fig. 6); 

however, sediment accumulation and vegetation 

growth in riverine areas limited the data collection to 

only 45 cross sections (fig. 7). 

Data Processing 

Initial editing of the December 2001 data was 

performed using the HYPACK software. Positions 

were corrected to eliminate anomalies that occurred 

when the correction signal from the reference station 

was lost because of local topographic features or 

electromagnetic interference. Position errors were 

corrected by interpolating back to the mid-point 

between the correct antecedent and preceding position. 

The depth data were also corrected to eliminate 

incorrect depth readings. Incorrect depth readings can 

result from insufficient signal gain or because floating 

debris interferes with the transducer face. The 

incorrect depth readings were also interpolated 

between the correct antecedent or precedent depth 

readings. Once corrected, the edited data were 

transferred into the GIS database for further 

processing. The Arc/Info GIS software was 

customized to color-code the depth data according to 

different depth intervals. Data points of the same color 

code were connected by adding a line between them, 

and a contour map of the reservoir bottom depth was 

generated (plate 1). The bathymetric contour map 

(plate 1) was used to create the TIN surface model of 

the reservoir bottom for 2001 (fig. 8). In addition, the 

1908 pre-impoundment topography of Lago Guayabal, 

the 1950, and 1986 bathymetric maps were converted 

into TINs to generate cross sections and longitudinal 

profiles. 

Sampling the TIN every 5 meters along selected 

cross sections generated profiles representing the 

reservoir bottom from shore to shore for 1913, 1950, 

1986, and 2001 (fig. 10). The same procedure used in 

generating the selected cross-section profiles was 

employed to generate the longitudinal profile along the 

thalweg of Lago Guayabal for the same years (fig. 11). 

The selected cross sections were located to represent 

flooded areas of reservoir, whereas the longitudinal 

profiles were located at the deepest part of the 

reservoir bottom from the dam to tributary river deltas. 

The 1913, 1950, and 1986 bathymetric survey 

maps were scanned, geo-referenced (assign real-world 

coordinates and map projection), and converted into a 

TIN using the GIS. From these TINs, volumes were 

calculated; however, they yielded volumes that varied 

from 3 to 12 percent of the officially reported values. 

Since these differences could be attributed to different 

survey resolutions and methodologies, the reported 

storage capacities of each bathymetric survey were 

used for all calculations in this report. In addition, the 

1951 and 1972 reservoir storage capacities were 

estimated using long-term sedimentation rates to 

standardize the analysis in order to account for the 

installation of flashboards during 1950-51, and the 

impoundment of the Río Toa Vaca branch to the east of 

Lago Guayabal drainage area in 1972 (refer to fig. 1). 

PREVIOUS BATHYMETRIC SURVEYS, 

STORAGE CAPACITIES, AND SEDIMENT 

ACCUMULATION 

The Lago Guayabal reservoir has been affected 

by a high sediment load and the consequent storage 

loss since its construction in 1913. A bathymetric 

survey conducted in 1914 indicated a storage capacity 

of 11.77 million cubic meters, which is essentially 

equivalent to the original storage capacity calculated 

from the topographic survey map prepared prior to 

reservoir impoundment in 1913. A second survey 

conducted in 1936 showed a reservoir storage of 7.02 

million cubic meters, a decrease of 41 percent in the 

23 years following impoundment. As a result of the 

rapid storage capacity loss due to sediment 

accumulation, corrective actions were taken to 

22 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
compensate for the storage loss. Between 1940 and 

1948, dredging and sediment flushing through the 

sluice gates were conducted. However, these efforts 

this analysis does not take into consideration that the 

sediment load from the Río Toa Vaca basin is being 

trapped in Lago Toa Vaca reservoir. 

were abandoned because they increased storage 

capacity by about 10 percent, making the effort 

unsuccessful because the reservoir was losing about 

1.8 percent storage capacity per year as can be inferred 

by the previous 1936 survey. Another bathymetric 

survey conducted during 1950 showed a reservoir 

storage capacity of 5.27 million cubic meters, or a 

storage loss of about 55 percent. This storage loss and 

the resulting decrease of the reservoir yield for 

irrigation purposes prompted the decision to raise the 

pool elevation. After the installation of flashboards 

(identified in this report as 1951 for practical 

differentiation purposes), the reservoir storage 

capacity was increased from 5.27 million cubic meters 

to 12.09 million cubic meters, or about 2 percent 

increase above the original storage capacity of 11.82 

million cubic meters. Although this corrective measure 

was effective in re-establishing storage capacity, the 

storage capacity loss problem continued. During 1964, 

a bathymetric survey indicated further sediment 

accumulation, reducing the storage capacity to 9.37 

million cubic meters. 

When the Toa Vaca dam was completed on the 

Río Toa Vaca tributary in 1972, this resulted in two 

benefits for Lago Guayabal: (1) the net effect of 

reducing the drainage area of Lago Guayabal, thus, 

reducing the sediment load; and (2) water that would 

have been impossible to store in Lago Guayabal and 

eventually lost to the river downstream was then stored 

in an upstream reservoir. 

An estimate of the storage capacity of Lago 

Guayabal in 1972 was derived by using the 1964 longterm storage loss (sedimentation rate) and multiplying 

it by the number of years between 1964 and 1972, and 

subtracting the result from the 1964 reported volume. 

This yielded an estimated volume of about 7.89 

million cubic meters. 

In 1986, the USGS in cooperation with PREPA, 

conducted another bathymetric survey of the reservoir. 

This survey indicated a reservoir storage capacity of 

about 6.76 million cubic meters. Although the storage 

capacity loss continued, the annual rate of storage loss 

apparently decreased considerably, corroborating the 

effectiveness of the Toa Vaca dam construction project 

in terms of the useful life of Lago Guayabal. However, 

The current USGS survey during December 

2001 used GIS and DGPS technology and showed a 

water storage volume of about 6.12 million cubic 

meters. The historical trend of reservoir storage 

capacity is presented in graphical form on figure 13 

and in table 3. 

 Note in figure 13 that the rate of change in 

reservoir storage loss for the period 1913 to 1936 and 

1951 to 1972 are essentially equal. If the storage loss 

rate is normalized by dividing the storage loss rate 

(cubic meters per square kilometer) by drainage area 

(square kilometers) to obtain an area-time storage loss 

rate in cubic meters per square kilometer per year, the 

1913-1936 and 1951-1972 sedimentation rates were 

1,863 and 1,787 cubic meters per square kilometer per 

year, respectively, and averaged 1,825 cubic meters 

per square kilometer per year. After the Río Toa Vaca 

was impounded by the Toa Vaca dam in 1972, the 

Lago Guayabal storage loss rate decreased to about 

1,120 after adjusting the drainage area to 54.5 square 

kilometers. The sedimentation rate of the Río Toa 

Vaca portion of the original Lago Guayabal basin can 

be estimated by using the following relation: 

(Fraction of Río Jacaguas basin) x (Rate of Río 

Jacaguas basin) + (Fraction of Río Toa Vaca 

basin) x (Rate of Río Toa Vaca basin) = 1,825 

cubic meter per square kilometer per year 

Thus, (0.49) x (1,120) + (0.51) x (Rate of Río Toa 

Vaca basin) = 1,825 cubic meter per square 

kilometer per year 

Therefore, the sedimentation rate of the Río Toa 

Vaca basin portion of the original Lago Guayabal 

drainage area could have been in the order of 3,000 

cubic meters per square kilometer per year. This 

estimated sedimentation rate from the Río Toa Vaca 

basin portion is in close agreement with the calculated 

area-normalized storage loss rate of Lago Toa Vaca of 

about 3,086 cubic meters per square kilometer per year 

(Soler-López, USGS, unpublished data, written 

commun., 2001). The Lago Guayabal 2001 storage 

capacity at 1-meter elevation intervals is presented on 

table 2 and the graphical relation between pool 

elevation and storage capacity is shown in figure 12. 

Previous Bathymetric Surveys, Storage Capacities, and Sediment Accumulation 23 
Figure 13. Lago Guayabal volume var

 The Lago Guayabal water-intake structure used 

for irrigation releases is located at the upstream face of 

the non-overflow section of the dam, between 

buttresses 20 and 21, at an invert elevation of 87.17 

meters above mean sea level. The volume of water 

contained above the elevation of the intake structure is 

referred to as the live (useful) storage and the volume 

below it is referred to as the dead storage (in the 

original design the dead storage is used to 

accommodate sediment without disabling reservoir 

structures). According to the 2001 bathymetric data, 

the reservoir bottom in the vicinity of the water intake 

tower had reached an approximate elevation of 90.94 

meters above mean sea level. This suggests that the 

sediment accumulation around the structure is 3 

meters thick, and that all the water contained in Lago 

iations from 1913 to 2001. 

Guayabal volume is within the live storage. Therefore, 

the water intake which feeds the Canal de Juana Díaz 

could be silted under 3 meters of sediment if not 

operated regularly. 

The long-term sediment accumulation in the 

reservoir is not uniform. Along the Río Jacaguas 

branch, the profile presented on figure 11 indicates 

that a 21-meter thick layer of sediment has deposited 

near the dam. A uniform thickness of about 21 meters 

of sedimentation extends to a distance of about 1,250 

meters upstream from the dam. A sediment layer about 

12 meters thick, between a distance of 1,250 and 2,250 

meters has been deposited, and a layer about 4 meters 

thick has been deposited in the riverine portion of the 

Río Jacaguas tributary. The long-term sediment 

deposition rates in these same segments are 24, 24, 14, 

24 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001
and 4 centimeters per year, respectively, averaging 

about 17 centimeters per year. On the Río Toa Vaca 

branch, sediment deposition patterns are the same as in 

the Río Jacaguas branch up to about 1,150 meters 

upstream from the dam (fig. 9), where the total 

thickness of sediment deposition is about 13 meters. 

The total thickness of sediment deposition is about 11 

meters at about 3,000 meters upstream from the dam. 

The deposition rates in the Toa Vaca branch averages 

about 14 centimeters per year. 

The morphology of the reservoir bottom 

immediately after impoundment was wedge-shaped, 

very similar to the topographic relief of the 

surrounding hill slopes. Thus, it provided little 

submerged surface area for sediment deposition. After 

years of sediment accumulation, the topographic relief 

of the impounded area changed from a wedge to a 

trapezoidal-shaped surface. Therefore, sediment 

accumulation was dispersed over a larger area and the 

decrease in water depth due to sediment deposition is 

at a lesser rate. As an example of this process, the 

deposition rate near the dam from 1913 to 1950 was 

34 centimeters per year; for the period of 1950 to 1986 

it decreased considerably to about 6 centimeters per 

year; and, from 1986 to 2001 it increased slightly to 

about 13 centimeters per year. This apparent nonuniform long-term deposition rate process is more 

evident in reservoirs that have been surveyed on a 

more frequent basis (Webb and Soler-López, 1997). 

TRAPPING EFFICIENCY 

Heinemann (1981) considered trapping 

efficiency to be the most informative descriptor of a 

reservoir. Trapping efficiency is the proportion of the 

incoming sediment that is deposited or trapped in a 

pond, reservoir or lake and is dependent on several 

parameters, including sediment particle size, 

distribution, the time and rate of water inflow to the 

reservoir, the reservoir size and shape, the location of 

the outlet structure, and location and discharge 

schedules (Verstraeten and Poesen, 2000). 

Many empirical studies showing the relation 

between reservoir storage capacity, water inflow, and 

trapping efficiency have been conducted in the past, of 

which the work of Brune (1953) is the most widely 

used and accepted. Brune developed a curve (fig. 14) 

that estimates the trapping efficiency of a reservoir 

based on the ratio of storage capacity to annual water 

inflow volume. The trapping efficiency of Lago 

Guayabal was estimated using the relation established 

by Brune (1953) and was standardized by the drainage 

area reduction during 1972. For the period of 1913 to 

1972, the drainage area was 112.0 square kilometers 

and since then (after the Toa Vaca dam construction), 

it is 54.5 square kilometers (table 1). 

The Lago Guayabal drainage basin contains no 

streamgaging station to measure annual inflow to the 

reservoir. To estimate how much rainfall becomes 

runoff into the Lago Guayabal drainage area, the 

average ratio of runoff to rainfall (runoff/rainfall) of 

0.25 was used (Giusti and López, 1967). The longterm average rainfall in the Lago Guayabal basin is 

1,778 millimeters per year (Calvesbert, 1970). Thus, 

multiplying the mean-annual rainfall of 1,778 

millimeters in the Lago Guayabal basin by the runoff/ 

rainfall ratio of 0.25, the estimated runoff for the Lago 

Guayabal basin is 444 millimeters per year. This 

number multiplied by the current 54.5 square 

kilometers drainage area of Lago Guayabal, yields an 

estimated inflow to the reservoir of 24.22 million 

cubic meters per year. With a present storage capacity 

of 6.12 million cubic meters, the ratio of storage 

capacity to inflow is 0.25. The reservoir drainage area 

supplies enough runoff to renew the total storage an 

average of about four times per year, based on this 

estimate of mean-annual inflow. 

Using the median curve of Brune’s (1953) 

relation (fig. 14), and the corresponding annual inflow 

for each year, the ratio of storage capacity to inflow 

may have varied from 0.10 in 1950 to a maximum of 

0.32 in 1972 (fig. 14). This gives an estimated change 

of the sediment trapping efficiency from 87 percent in 

1950 to 93 percent in 1972; and, a long-term average 

trapping efficiency of Lago Guayabal of 92 percent for 

the period 1913 to 2001. However, the trapping 

efficiency of a reservoir decreases as sediment fills the 

reservoir and lowers the storage capacity, according to 

Brune’s (1953) empirical relation. 

Trapping Efficiency 25 
Figure 14. Reservoir trapping efficiency as a function of the ratio between storage capacity 

and annual water inflow volume. 

SEDIMENT YIELD 

Sediment yield has been defined by the 

American Society of Civil Engineers as the total 

sediment outflow measurable at a point of reference 

for a specified period of time per unit of surface area 

(McManus and Duck, 1993). Based on this definition, 

several factors need to be normalized to take into 

consideration the drainage area upstream of the Toa 

Vaca dam and the change in trapping efficiency of 

Lago Guayabal. Therefore, for the bathymetric 

surveys previous to and including 1972, a net sediment 

contributing basin area of 110.81-square kilometers 

(the basin area minus the 1.19 square kilometer 

reservoir surface area) was used in the estimate, and 

for the surveys after 1972, the reduced drainage area 

of 54.5 square-kilometers was used. Although table 3 

summarizes the historical sediment yields of the Lago 

Guayabal drainage area, only the 2001 sediment yield 

calculation is discussed herein. 

For the period of 1972 to 2001 the total 

estimated volume of sediment contributed to Lago 

Guayabal from a reduced drainage area of 54.5 square 

kilometers was estimated by dividing 1.77 million 

cubic meters of sediment accumulation (the volume 

loss between 1972 and 2001) by the estimated 2001 

trapping efficiency of 0.93, which is 1.90 million cubic 

meters. This estimated rate of sediment influx (1.90 

million cubic meters) divided by the years between 

1972 and 2001 (29 years), results in an average of 

65,517 cubic meters per year. The estimated rate of 

sediment influx of the Lago Guayabal basin (65,517 

cubic meters per year) divided by the net sediment 

contributing area of 53.06 square kilometers, (the total 

drainage area of 54.5 square kilometers minus the 1.44 

26 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
square kilometer surface area of the reservoir) results 

in an average basin sediment yield and reservoir 

storage loss 1,235 cubic meters per square kilometer 

per year. An estimate of the sediment yield from the 

drainage area of Lago Guayabal on a mass basis can 

be obtained by using the sediment dry-bulk density of 

one gram per cubic centimeter reported for Lago 

Yahuecas, a reservoir located about 25 kilometers 

northwest of Lago Guayabal (Soler-López and others, 

1998). Therefore, the Lago Guayabal sediment yield 

on a mass basis is 1,235 megagrams per square 

kilometer per year. 

The life expectancy of Lago Guayabal, or any 

other reservoir, can be estimated by dividing the 

remaining storage capacity by the annual storage 

capacity loss. However, in this case, the average 

storage capacity loss of Lago Guayabal since 1972 

was used because it is a reliable indicator of the true 

volume loss after the construction of the Lago Toa 

Vaca dam. Based on the average reservoir storage loss 

between 1972 and 2001, the reservoir would be 

completely silted in about 100 years, or by about 2100. 

SUMMARY 

The December 2001 bathymetric survey of Lago 

Guayabal was conducted by the USGS, in cooperation 

with PREPA, using state-of-the-art GIS and DGPS 

technology. A series of anthropogenic and 

climatological events, including agricultural land-use 

practices and six major hurricanes, that could have 

adversely affected the storage capacity of Lago 

Guayabal were analyzed. The reservoir was losing 

storage capacity at a faster rate than at present (2001); 

however, when Lago Toa Vaca was constructed in 

1972 in the Río Toa Vaca tributary to Lago Guayabal, 

the rate decreased about 40 percent. The December 

2001 bathymetric survey of Lago Guayabal indicates 

that the reservoir had lost about 12.70 million cubic 

meters of water storage capacity. This represents a 

long-term storage loss of about 1.22 percent per year. 

With a current reservoir trapping efficiency of about 

95 percent, any increase in rural development and land 

disruption within the Lago Guayabal drainage area 

could result in an increased sediment yield, which is 

currently about 1,235 cubic meters per square 

kilometer per year. At the current long-term 

sedimentation rate and estimated sediment trapping 

efficiency, Lago Guayabal would be completely silted 

by the year 2100. Although the life expectancy of 

Lago Guayabal was a pressing concern in the early 

years after impoundment, the life expectancy of the 

reservoir has increased, according to recent data. 

However, sediment accumulation in the reservoir can 

impair the use of essential reservoir structures such as 

the outlet to the Canal de Juana Díaz. 

Summary 27 
REFERENCES CITED 

Brune, G.M., 1953, Trap efficiency of reservoirs: 

Transactions of the American Geophysical Union, 

v. 34, no. 3, p. 407-418. 

Calvesbert, R.J., 1970, Climate of Puerto Rico and the 

U.S. Virgin Islands: U.S. Department of 

Commerce, Environmental Science Services 

Administration, 29 p. 

Environmental Systems Research Institute, Inc., 1992, 

Surface modeling with TIN, Surface analysis and 

display: Environmental Systems Research 

Institute, Inc., Redlands, California, p. 4-1, 6-1. 

Gaztambide-Vega, F., and Arán, P.P., 1959, La Isla de 

Puerto Rico, Rand McNally & Co., p. 38-87. 

Gierbolini, R. E., 1979, Soil survey of Ponce area of 

southern Puerto Rico, U.S. Department of 

Agriculture, Soil Conservation Service, p. 12-23, 

1 pl. 

Giusti, E.V., and López, M.A., 1967, Climate and 

streamflow of Puerto Rico: Caribbean Journal of 

Science, v. 7, no. 3-4, September-December, 

1967, p. 87-93. 

Heinemann, H.G., 1981, New sediment trap efficiency 

curve for small reservoirs: Water Resources 

Bulletin, v. 7, p. 825-830. 

McManus, J., and Duck, R.W., eds., 1993, 

Geomorphology and sedimentology of lakes and 

reservoirs; Chapter 6 of Reservoir sedimentation 

rates in the Southern Pennine Region, UK: 

London John Wiley & Sons, p. 73-92. 

Picó R., 1964, Geografía de Puerto Rico, Parte II, 

Editorial Universitaria, Universidad de Puerto 

Rico, Río Piedras, p. 85-99. 

Puerto Rico Electric Power Authority, 1988, Guayabal 

Dam, Villalba, Puerto Rico, Phase 1 Inspection 

Report: National Dam Safety Program, 1986. 

Soler-López, L.R., Webb, R.M.T., and Pérez-Blair, 

Francisco, 1998, Sedimentation survey of Lago 

Yahuecas, Puerto Rico, March 1997: U. S. 

Geological Survey Water-Resources 

Investigations Report 98-4259, 15 p., 2 pls. 

Verstraeten, G., and Poesen, J., 2000, Estimated trap 

efficiency of small reservoirs and ponds: methods 

and implications for the assessment of sediment 

yield: Progress in Physical Geography, v. 24, 

no. 2, p. 219-251. 

Webb, R.M.T., and Soler-López, L.R., 1997, 

Sedimentation History of Lago Loíza, Puerto 

Rico, 1953-1994: U. S. Geological Survey WaterResources Investigations Report 97-4108, 18 p., 9 

pls. 

28 Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001 
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 HISTORY OF LAGO GUAYABAL, PUERTO RICO, 1913-2001—WRIR 03–4198