U.S. Department of the Interior a U.S. Geological Survey

U.S. Geological Survey

Programs in Puerto Rico

For more than 100 years, the U.S. Geological Survey (USGS) has been mapping, 

describing, and seeking to understand the 

Nation’s natural resources. The USGS is 

known for impartial data collection and 

interpretation that enables resource planners 

and others to make informed decisions. 

Today’s issues are more pressing than 

ever—understanding natural hazards to minimize their effects on life and property, the 

continuing need for mineral- and waterresource development, and understanding 

the effects of human activities on water and 

biological resources. 

As the Nation’s lead natural science 

agency, the USGS works with Commonwealth and other Federal agencies in 

addressing these issues in Puerto Rico. 

USGS maps, interpretive reports, and data 

are used by educators; municipalities; various local and Federal planning agencies; 

consulting firms; farmers; and other private 

citizens to manage Puerto Rico’s resources.

High-Energy Storms

Though frightening and economically 

damaging, hurricanes and other high-energy 

storms are vital to the long-term health of 

delicate marine and terrestrial ecologies in 

coastal areas (fig. 1). Marine geologists of 

the USGS working in the Commonwealth of 

Puerto Rico are confident that the long-term 

effects of Hurricane Hugo on the coastal 

environment are minimal, although the economic damage was significant. As part of the 

continuing research conducted in Puerto 

Rico, the shelf area offshore of the town of 

Luquillo was mapped using high-resolution 

sonar, seismic-reflection profiles, photographs, and bottom sampling following the 

passage of Hurricane Hugo. Sea-floor structure, local geology, and sediment characteristics indicate that a regional cross-shelf 

transport of sand occurs during storms, but 

that it is trapped by ridges to form sand 

deposits as much as 60 feet thick. Sand 

eroded from the beach front moves offshore, 

and the pathways for that movement can be 

documented by using remote imagery.

Assessing Landslide Hazards

High-energy storms also can bring large 

amounts of rainfall in very short periods of 

time to mountainous regions of Puerto Rico. 

These events can trigger hundreds of landslides, which are common in the mountainous areas of Puerto Rico where mean annual 

rainfall and the frequency of intense storms 

are high, and hillslopes are steep (fig. 2). 

Each year, landslides cause extensive damage to property and occasionally result in 

Index of Subjects

High-Energy Storms

Assessing Landslide Hazards

Beach Erosion and Coastal Development at 

Rincón, Puerto Rico

Hydrologic Data Collection

Floods and Droughts

Water, Energy, and Biogeochemical Budgets

Topographic Mapping

Geologic Mapping

Earth Observation Data

Figure 1. The entrance to the Caribbean National Forest (CNF) in northeastern Puerto Rico 

three days after the passage of Hurricane Hugo on September 18, 1989. Tree mortality was 

reported to be as high as 35 percent in the northeastern part of the CNF.

Figure 2. Two debris avalanche scars along 

Highway PR191 in the Sierra de Luquillo, 

Puerto Rico, measuring 600 meters from the 

ridge top to the two-lane highway visible in the 

foreground. The avalanches were triggered by 

intense precipitation in 1970 and 1989 with 

rainfall totals of 300 to 900 millimeters.

Earth Science in the Public Service
0 10

0 10 20 KILOMETERS

20 MILES

Mayagüez

Rincón

Isabela

Submerged

Sand Deposit

Cabo Rojo

Submerged

Sand Deposit

Escollo de Arenas

Submerged

Sand Deposit

Isla de Vieques

Isla de Culebra San Juan

Luquillo

Arecibo

Ponce

200 meter

depth contour

ATLANTIC OCEAN

CARIBBEAN SEA

Cabo Rojo

30′ 067° 30′ 066° 30′ 065°

18°

18°30′

17°30′

18°05′ Isla de Mona

18°10′

067°55′ 067°50′

Río

Coamo

Landslides

Río

Cibuco

Landslides

WEBB

Study Area

ATLANTIC OCEAN

CARIBBEAN SEA

GULF OF

MEXICO

Florida

PUERTO

RICO

Río

Blanco

Landslides

1 0 Kilometers 1

Punta Higuero

67 ̊16 ́W 67 ̊15 ́W

18 ̊21 ́N

18 ̊20 ́N

18 ̊19 ́N

18 ̊18 ́N

Punta Ensenada

Mona

Passage

Rincón

A

1

10

20

30

40

50

60

70

80

89

B

C

D

loss of life. Population density in Puerto 

Rico is high, 400 people per square kilometer, and is increasing. This increase is 

accompanied by the use of less desirable 

construction sites. As a result, human populations are becoming more vulnerable to 

landslide hazards.

 The principal objective of a 3-year USGS 

study in the Río Blanco, the Río Cibuco, and 

the Río Coamo Basins was to evaluate the 

geographic relations of landslide distribution 

across the range of topography, climate, 

soils, and bedrock geology that occur in 

Puerto Rico (fig. 3). An additional objective 

was to determine the rainfall accumulation 

and duration characteristics of storms likely 

to trigger landslides in the central mountains 

of the island and to develop a rainfall accumulation/duration threshold relation for 

Puerto Rico.

Study results indicate that landslides in 

the Sierra de Luquillo and the Sierra de 

Cayey consist mainly of shallow soil slips 

and debris flows with an average volume of 

120 cubic meters and can number as many 

as 20 per square kilometer. The mass of 

eroded material can be as high as 6,000 metric tonnes per square kilometer. Because 

most of the soil eroded by landsliding is 

delivered directly to river channels, fluvial 

sediment loads can remain high for many 

months following large storms. For example, 

a single landslide that occurred during Hurricane Hortense in the Río Icacos watershed 

in El Yunque introduced a mass of soil into 

the river that is equivalent to the average 

annual sediment yield for an entire year. The 

geomorphic effects of such storms will be 

visible on hillslopes and river channels for 

decades in the form of altered hillslope form 

and channel morphology. These results provide land-use managers and public-safety 

agencies with an inexpensive method that 

can be used to assess landslide hazards in 

Puerto Rico.

Beach Erosion and Coastal 

Development at Rincón,

Puerto Rico

A record of historical shoreline positions 

and erosion rates has been compiled for the 

area near Rincón, in western Puerto Rico, 

for 1950–94 (fig. 3). The study area includes 

approximately 8 kilometers of the northwestern coast, from Punta Higüero to Punta 

Cadena (fig. 4). Historical shoreline positions were obtained from aerial photographs. 

More recent shoreline position surveys were 

conducted using a portable, differential Global Positioning System.

Erosion rate data for Reach B indicate 

that there was a profound change in the historical trend between 1977 and 1987. 

Before 1977, the erosion rate in Reach B 

was about 0.5 ± 0.3 meters per year. From 

1987 to 1994, however, the erosion rate was 

more than 3.0 ± 1.0 meters per year. The 

increased erosion correlates with the 1983 

construction of a relatively small marina 

within Reach B. Emplacement of a breakwater/jetty system and the continued 

removal of dredged material at the marina 

entrance appear to be the major contributing 

factors to the recent increase in erosion 

rates. Human response to the increased rate 

of shoreline erosion has been a piecemeal 

seawalling of the shoreline. If left unmitigated, continuing shoreline stabilization 

with the piecemeal construction of seawalls 

and revetments may result in the rapid 

destruction of local beaches. Manmade stabilization structures also may reduce sediment supply to downdrift beaches, thus 

increasing the erosion of beaches that are 

used for recreation and tourism and that 

support a small, beach-based fishing fleet.

Hydrologic Data Collection

Since 1958, the USGS, in cooperation 

with 15 local and Federal agencies has been 

collecting a large amount of data pertaining 

to the water resources of Puerto Rico. These 

data constitute a valuable data base for 

developing an improved understanding of 

the water resources in Puerto Rico. These 

data include records on surface and ground 

water, water quality, and stream-sediment 

concentration and transport.

Surface water is a major source of drinking water, industrial supply, and irrigation in 

Puerto Rico. The surface-water data-collection program (fig. 5B) measures stream discharge and the amount of rain falling in 

specific river drainage basins. Water samples 

also are collected (fig. 5A) to determine the 

physical, chemical, and bacteriological characteristics of lakes, streams, and rivers.

 Long-term monitoring of ground-water 

levels gives insight into the withdrawal and 

recharge rates of aquifers, and provides 

essential information for managing these 

important water resources. The USGS maintains a computer data base that contains 

information on the physical and chemical 

characteristics of water in about 5,700 wells 

and springs in Puerto Rico. 

Figure 3. Location of Puerto Rico and various study sites.

Figure 4. The shoreline in the study area was 

divided into four distinct reaches based on 

erosion rates. The relative magnitude of 

shoreline movement between 1950-1994 is 

depicted by the transect line length.
Floods and Droughts

Floods can be extremely destructive in 

Puerto Rico because of the island’s topography and dense population. Nearly 70 nonnavigable rivers and streams—whose banks 

and drainage areas are dotted with communities—originate in the central mountain 

range. The stream valleys are narrow, relatively short, and steep—features that make 

the streams susceptible to flooding, particularly flash flooding.

Flash floods typically result from rainfall 

that is intense in the upper basins but that is 

sparse or nonexistent on the coast. Streams 

on the south coast are more susceptible to 

flash flooding than those on the north coast 

because of their shorter length and steeper 

gradient. Lag time from the occurrence of 

intense rainfall to the peak discharge is, therefore, least along the southern coastal plain.

Large areas of the coastal plain are subject to storm-surge flooding from hurricanes 

and other tropical storms. The coastal plain 

also is vulnerable to flooding by large 

coastal sea swells generated by winter 

storms over the Atlantic Ocean.

Although drought can be defined as a 

period of deficit in rainfall or water supply 

for an extended period of time, there is no 

single commonly accepted measure of 

drought in terms of water demand. In fact, 

there is no quantitative definition of drought 

that is universally acceptable. Most of the 

criteria used to identify drought have been 

arbitrary because a drought is something of 

a nonevent, as opposed to a distinct event 

such as a flood. Drought has no distinct 

onset and is recognizable only after a 

period of time. In addition, this period of 

time is variable because the time required 

for a drought to develop depends on many 

interacting variables.

Historically, droughts are rare in Puerto 

Rico (table 1). Significant droughts in recent 

years that affected large areas of Puerto Rico 

over an extended period of time occurred 

during 1966–68, 1971–74, 1976–77, and 

1993–94. The 1971–74 drought was the 

most severe drought on record in terms of 

streamflow deficits and duration, whereas 

the 1993–94 drought was most severe in 

terms of water-supply problems.

Water, Energy, and 

Biogeochemical Budgets

The humid tropics occupy 25 percent of 

the Earth’s land surface and by the year 

2000 will contain approximately 50 percent 

of the Earth’s population. Rapid deforestation in the humid tropics is recognized as a 

threat to both the economic development of 

the affected areas and to global climate. 

Development stresses include major adverse 

effects on soils, soil nutrients, surface-water 

quality, reservoirs, and increase the shortterm hazards of landslides and floods. To 

understand these processes and provide 

information useful for developing solutions 

to these problems as they may affect Puerto 

Rico, the USGS has developed a long-term 

Water, Energy, and Biogeochemical Budget 

program (WEBB) research site in the Sierra 

de Luquillo in eastern Puerto Rico. The site 

consists of the 11,300-hectare U.S. Forest 

Service-administered Luquillo Experimental Forest and the Río Grande de Loíza 

drainage basin, an agriculturally developed 

watershed.

The research work focuses on tropical 

geomorphic and biogeochemical processes 

that control the movement and transformation of water, energy, bedrock weathering 

products, and nutrients in the earth-surface 

environment (fig. 6). Detailed data are being 

obtained on hillslope and fluvial transport 

and erosion processes, soil-development, 

A

B

Figure 5. Water-quality (A) and surface-water 

(B) data-collection sites throughout Puerto Rico.

Table 1. Chronology of major and other memorable floods and droughts in Puerto Rico, 1899–1995 

[Recurrence interval: The average interval of time within which streamflow will be greater than a 

particular value for floods or less than a particular value for droughts; recurrence intervals calculated 

from U.S. Geological Survey data; —, not determined]

Flood 

or 

Drought

Date Area affected

Recurrence

 interval 

(years)

Flood Aug. 8, 1899 Islandwide Unknown

Flood Sept. 13, 1928 Islandwide 100

Flood Sept. 26, 1932 Islandwide Unknown

Flood Sept. 6, 1960 Eastern Puerto Rico 25 to 80

Flood Aug. 27, 1961 Northeastern Puerto Rico 2 to 25

Flood Dec. 9–11, 1965 Interior and north coast 2 to 25

Drought 1966–68 Islandwide 10 to 27

Flood Nov. 9, 1969 Eastern Puerto Rico 2 to 10

Flood Oct. 5–10, 1970 Eastern two-thirds of Puerto Rico 2 to 50

Drought 1971–74 Islandwide 15 to 26

Flood Sept. 16, 1975 Southwestern Puerto Rico 25 to 100

Drought 1976–77 Islandwide 5 to 28

Flood Oct. 7, 1977 Eastern Puerto Rico 2 to 10

Flood Oct. 26–27, 1978 Southern and eastern Puerto Rico 2 to 25

Flood Aug. 29–31, 1979 Eastern, southern, and northern Puerto Rico 2 to 25

Flood Sept. 4, 1979 Northern and eastern Puerto Rico 2 to 10

Flood Sept. 12–13, 1982 Southern Puerto Rico 2 to 25

Flood Nov. 3–5, 1984 Eastern Puerto Rico 2 to 10

Flood May 17–18, 1985 Northern and north-central Puerto Rico 20 to 100

Flood Oct. 6–7, 1985 Southern Puerto Rico >100

Flood Jan. 5–6, 1992 Northern and eastern Puerto Rico 10 to 100

Drought 1993–94 — —

Flood Sept. 9–10, 1996 Eastern Puerto Rico —
and nutrient cycling. These data are being 

used to develop sediment and water budgets 

and a geomorphic model of tropical landform development. This model can assist 

resource managers in identifying planning 

solutions to reservoir sedimentation, landslides, floods, and other development-related 

geomorphic problems that occur in densely 

populated tropical settings.

Topographic Mapping

Among the most popular and versatile 

products of the USGS in Puerto Rico are its 

1:20,000-scale topographic maps (1 inch on 

the map represents about 1,667 feet on the 

ground). These maps depict basic natural 

and cultural features of the landscape, such 

as mountains, lakes and streams, highways, 

boundaries, and geographic names. Contour 

lines are used to depict the elevation and 

shape of the terrain. Puerto Rico is covered 

by 67, which are useful for civil engineering, land-use planning, natural-resource 

monitoring, and other technical applications. These maps have long been favorites 

with the general public for outdoor uses, 

including hiking, camping, and exploring. 

Geologic Mapping

Geologic mapping of Puerto Rico is now 

largely complete at a scale of 1:20,000. 

Work on compiling a digitized geologic map 

of Puerto Rico at a scale of 1:200,000 as 

well as numerous other derivative maps that 

deal with natural geologic economic 

resources and various mineral resources also 

is underway.

Earth Observation Data

Through its Earth Resources Observation 

Systems Data Center near Sioux Falls, South 

Dakota, the USGS distributes a variety of 

aerial photographs and satellite image data 

products that cover the entire island of 

Puerto Rico. Mapping photographs of some 

sites go back about 40 years. Satellite 

images dating from 1972 can be used to 

study changes in regional landscapes.

The USGS and the U.S. Environmental 

Protection Agency are cooperating to create 

computerized (digital) images from aerial 

mapping photographs of Puerto Rico. These 

digital images will form a seamless data set 

for a geographic information system useful 

for assessing potential hazards, such as oil 

spills and non-point pollution sources, 

related to water resources.

USGS state representative

GSA Center

51 Federal Drive, Suite 400-15

Guaynabo, PR 00965

(787) 749-4346

Fax: (787) 749-4462

Email: dc_pr.usgs.gov

Additional earth science

information can be found by

accessing the USGS Home Page

on the World Wide Web at

http://www.usgs.gov/

For more information on

all USGS reports and products

(including maps, images,

and computerized data), call

1-800-USA-MAPS

The USGS provides maps,

reports, and information to help

others meet their needs to manage,

 develop, and protect America’s water,

energy, mineral, biological, and land

resources. We help find the natural

resources needed to build tomorrow,

and supply the scientific understanding needed to help minimize or mitigate the effects of natural hazards

and environmental damage caused

by natural and human activities. The

results of our efforts touch the daily

 life of almost every American.

U.S. Geological Survey

Fact Sheet FS-051-96

Figure 6. WEBB personnel mapping stream channels in 

the Luquillo Experimental Forest in northeastern Puerto 

Rico. Normal mapping techniques underrepresent stream 

networks in this tropical mountain setting due to the dense 

forest canopy, necessitating the use of Global Positioning 

System techniques to determine stream channel and 

headwater locations and extents.

For More

Information