Floods of

September 6, 1 960, 

in Eastern Puerto Rico

GEOLOGICAL SURVEY 

CIRCULAR 451

PREPARED IN COOPERATION WITH THE PUERTO RICO WATER RESOURCES AUTHORITY, THE PUERTO
Floods of September 6, I960, in 

Eastern Puerto Rico

By Harry H. Barnes, Jr., and Dean B. Bogart

Prepared in cooperation with the Puerto Rico Water Rescources 

Authority, the Puerto Rico Aqueduct and Sewer Authority, 

and the Puerto Rico Industrial Development Co.

GEOLOGICAL SURVEY CIRCULAR 451

Washington 

7961
United States Department of the Interior

STEW ART L. UDALL, SECRETARY

Geological Survey

THOMAS B. NOLAN, DIRECTOR

Free on application to the U.S. Geological Survey, Washington 25, 0. C.
CONTENTS

Page. Page 

Abstract............................ 1 The floods..........--..---.-.-.-.-- 2

Introduction...-._................-_- 1 Flood damage.-....---..-.--.------- 7

Acknowledgments-..--...--....-..... 1 Summary of flood discharges --------- 7

The storm_...--_..._._._.__-._---_- 2

ILLUSTRATIONS

Page

Figure 1, Rainfall map for September 5 7-..--.............--.__..._...........--_-.- 3

2. Flood debris in a street in Humacao .........-.-......-.------.------------- 4

3. High-water mark in Humacao --.--._.._..............-.._....__.....------- 4

4* Bridge opening clogged by bamboo .._...__.......--....-__._--__--_--------- 4

3» Rock-filled channel above bridge on Rio Turabo-.---..-----.----. .... -- 4

6j> Location of flood-measurement sites............................. ......... 5

7* Damage to floodwall in Juncos._._..............................__...._..... 6

8i, Heavily eroded and redeposited bank of Rio Grande de Loiza at San Lorenzo..... 6

9^ Damaged bridge on Rio Limones near Limones..........._........._.._...--- 6

10* Relation of unit discharge to drainage area ...._.__._....._..........._...... 8

11. Discharge hydrographs for selected gaging stations _.___......_............. 10

12. Discharge hydrograph, Rio Grande de Loiza at Loiza Dam..................... 12

TABLES

Page 

Table 1. Summary of flood damage, September 6 ._._._.__._.._......-.-..--.........«- 7

2. Summary of flood stages and discharges in eastern Puerto Rico for floods of

September 6. ..-...._......_............._..._....._............_... 9

3. Record of stage and discharge, Rio de La Plata at Toa Alta.................... 11

4. Record of stage and discharge, Rio Grande de Loiza at Caguas--.-.-.-.----.--- 11

5. Record of stage and discharge, Rio Hicaco near Naguabo---------------------- 13

III
Floods of September 6, I960, in Eastern Puerto Rico

By Harry H. Barnes, Jr., and Dean B. Bogart

ABSTRACT

The floods of September 6, 1960, were the greatest known 

on many streams in eastern Puerto Rico. There were 117 

lives lost, 30 persons missing, and 136 injured. Total 

damage was estimated in excess of $7 million. Several 

thousand persons were forced from their homes by the floods 

as 484 houses were destroyed and more than 3,600 others 

were damaged. All main highways and most secondary 

roads were impassable for a short period during the floods 

and damage to them was heavy.

Following the passage of Hurricane Donna off the northeast coast, rains of very high intensity fell over parts of 

the eastern half of the island, beginning about 9 p.m. 

September 5. By dawn September 6, xains totaling more 

than 10 inches over a large area produced floods in every 

river basin from the Rio Grande de Man at i eastward. Flood 

discharges on the Rio Humacao, Rio Turabo, and Rio 

Valenciano were the greatest known and rank high among 

the notable floods on streams that drain from 6 to 15 square 

miles.

An outstanding feature of the floods was the unusually 

high magnitude of peak discharges 9 of the 24 peak dis - 

charges determined had Myers ratings greater than 80 per - 

cent.

INTRODUCTION

The floods of September 6, 1960, in the 

eastern half of Puerto Rico rank among the 

most disastrous floods ever experienced on 

the island.

The passage of Hurricane Donna off the 

north coast of Puerto Rico caused torrential 

rains over eastern Puerto Rico during the 

night of September 5 6, and produced destructive floods in all river systems from 

the Rio Grande de Manati eastward. Before 

dawn on September 6, more than 100 persons 

were dead and many others were injured as a 

result of the floods. Damage to highways and 

bridges, railroads, utilities, farmlands, livestock, and other public and private properties 

was in excess of $7 million. Emergency 

housing, food, and water had to be provided 

for hundreds of the homeless in Humacao and 

San Lorenzo by the American Red Cross and 

Commonwealth authorities.

Rains of 10 inches or more fell over a 

large area of the eastern interior section of 

the island during a 6-to 8-hour period beginning about 9 p.m. on September 5. Maximum 

rainfall of record occurred at several stations. Residents of the area indicated the 

floods on many streams were the highest that 

could be recalled. Floods on the Rio Humacao, 

Rio Turabo, and Rio Valenciano were particularly outstanding.

The prompt dispatch of survey crews 

proved to be valuable as the pertinent floodmarks were deteriorating rapidly through the 

action of rains that fell almost daily for the 

remainder of September.

General descriptions of the storm and 

floods, peak stage and discharge for the September 1960 floods and for previous maximum floods at selected gaging stations, peak 

stage and discharge at miscellaneous sites, a 

discharge hydrograph and a table of discharge at selected times at three gaging stations, and a summary of flood damage are 

included in this report.

ACKNOWLEDGEMENTS

The documentation of basic streamflow 

records in Puerto Rico is a part of a continuous cooperative program with agencies of 

the Commonwealth of Puerto Rico. The preparation of this report is part of a supplemental investigation program financed through a 

special cooperative agreement between the 

U.S. Geological Survey and the Puerto Rico 

Water Resources Authority, Raf ael V. Urrutia, 

executive director; the Puerto Rico Aqueduct 

and Sewer Authority, Juan Labadie Eiirite, 

executive director; and the Puerto Rico Industrial Development Co., Carlos M. Passalacqua, president.
FLOODS OF SEPTEMBER 6, 1960, IN EASTERN PUERTO RICO

Because of the need to perform the fieldwork and office computations pertaining to 

flood-peak discharge as promptly as possible, 5 hydraulic engineers from the United 

States, and 5 engineers and engineering aids' 

from the Puerto Rico Water Resources Authority were assigned to the San Juan district 

for a 30-day period after the floods. The 

fieldwork and office work of determining 

peak discharges by indirect methods were 

directed by Harry H. Barnes, Jr., flood specialist, Atlanta, Ga., under the general supervision of Tate Dalrymple, chief of the 

Floods Section, Water Resources Division.

The collection and compilation of the basic 

stage and discharge record as well as the 

associated analyses for the special flood investigations were under the direction of Dean 

B. Bogart, project hydrologist.

The U.S. Weather Bureau, the Office of 

Civil Defense, and other agencies provided 

information for the report.

THE STORM

On September 2, 1960, Hurricane Donna 

was located about 1,200 miles east-southeast 

of Puerto Rico. By the evening of September 5, Donna had moved through the northern 

Leeward Islands to a position about 100 miles 

north of San Juan. Beginning about 9 p.m. on 

September 5, and continuing until 3 or 4 a.m. 

September 6, rains of very high intensity fell 

over parts of eastern Puerto Rico. Light 

rains continued until daybreak.

Precipitation intensities were outstanding 

at many of the weather stations during the 

period of heavy rain. At Carite Dam, 25 

miles south of San Juan, 6.10 inches was 

measured in 2 hours between 9 and 11 p.m. 

Gages in the eastern section of the island at 

El Yungue, Rio Blanco, and Fajardo recorded 

3 inches in 1 hour during the night.

The largest rainfall total reported was 

18.76 inches on the northeast slope of the 

Luqillo Mountains near Sabana. Naguabo and 

Cayey reported 24-hour totals of 14.60 and 

14.07 inches, respectively. High-intensity 

rain amounting to 10 inches or more fell over 

an area about 15 by 40 miles extending from 

Barranquitas, in the central interior, to the 

east coast of the island.

An isohyetal map of the storm rainfall for 

September 5 7 is shown on figure 1. The 

isohyets are drawn through points of approximately equal values and caution is advised 

in interpolation of the lines. This is particularly true in the mountainous area between 

Cayey and Humacao where inconclusive reports suggest that the total rainfall during 

the storm period may have been considerably 

higher than that indicated by the map.

No hurricane-force winds were observed 

in Puerto Rico during the passage of Hurricane Donna, except for a brief flurry at 

Roosevelt Roads which may have been tornadic in character. Tides of 4 to 6 feet above 

normal were reported along the east and 

north coasts of the island.

THE FLOODS

Damaging floods were widespread on both 

large and small streams throughout the eastern half of Puerto Rico. At Humacao, near 

the southeast coast, 90 persons were drowned 

as floodwaters of the Rio Humacao swept 

through the low-lying areas of the city (figs. 

2, 3) during the predawn hours of September 

6. The rate at which the level of this unprecedented flood rose was so rapid that victims 

were unable to reach safety even after being 

warned of the danger. Residents at Ciales 

reported a bore on the Rio Grande de Manati, 

one of the largest rivers on the island.

Many landslides occurred on the cultivated 

slopes of the island's mountainous interior. 

Highways along the mountainsides were 

blocked in many places and dangerously undermined or destroyed in others. Large 

amounts of soil, rock, and bamboo were 

dumped into the streams by the landslides 

and channel erosion.

Bamboo is used rather extensively throughout the island to check roadside erosion and 

protect streambanks. The dislodged bamboo 

that was swept away by streams proved to be 

a menace to bridges and culverts. In many 

places bridge and culvert openings were 

completely blocked by the debris (fig. 4), 

forcing floodwaters over or around the 

structures, and resulting in large washouts.

In the upper reaches of the Rio Turabo, 

deposition of rock and gravel raised the
Figure 1. Isohyetal map of eastern Puerto Rico showing storm rainfall, September 5 7.
FLOODS Of SEPTEMBER 6. 1960. IN EASTERN PUERTO RICO

Figure 2. -Flood debris in a street in Humacao.

Figure 3. After the recession of the floodwaters at the northwest 

edge of Humacao. Note the man pointing to the high-water 

mark above his Head.

riverbed above the highway and bridge 

(fig. 5) at points between Gaguas and La 

Plaza. Sharply angled fresh rock, in addition 

to the usual rounded and bleached-out boulders, was particularly noticeable in the channels. Several of the older citizens living 

along the Rio Turabo north of La Plaza indicated that the flood on September 6 was the 

greatest known.

Floods along the small tributaries in upper 

reaches of the Rio Grande de Manati were 

high, but were not particularly outstanding. 

However, downstream at Giales the peak 

Stage exceeded the previous maximum of 

record by 3 feet and destroyed the gaging 

.Station.

At Comerio Dam, the Rio de la Plata produced a peak discharge of 101,000 cfs (cubic 

feet per second) from its 140-square-mile 

drainage basin. The design head for the dam 

was exceeded by more than 3 feet and water 

poured over the abutments of the spillway. 

The generation of hydroelectric power was 

interrupted when the powerhouse was flooded 

prior to the peak. Farther downstream at the 

Toa Alta gaging station, the river rose 29.1 

feet, of which 15 feet was in 1 hour.

Peak discharges or stages were determined 

at 25 sites on streams in eastern Puerto 

Rico (fig. 6).

Figure 4. Bridge opening completely clogged, mostly by 

bamboo.

Figure 5. View from downstream tide of bridge on Rio Turabo 

near La Plaza. Note the rock-filled channel above the bridge.
Flood-measurement sites

Numbers correspond to those in table 2.

Figure 6. Map of eastern Puerto Rico showing location of flood-measurement pointsj floods of September 6.
FLOODS OF SEPTEMBER 6, 1960, IN EASTERN PUERTO RICO

Peak discharges in the middle reaches of 

the Rio Valenciano rank among the highest 

known for streams that drain from 6 to 15 

square miles. At Juncos, the floodwall protecting the city along the left bank of the 

river was overtopped and extensively damaged (fig. 7). Downstream from the mouth of 

Rio Valenciano, floodwaters of Rio Gurabo 

overtopped the bridge handrails at Highways 

185 and 181, and washed out the bridge approaches. The gaging station at Gurabo was 

damaged and put out of action. The railroad 

bridge 1 mile downstream was destroyed.

At San Lorenzo the floodwaters of Rio 

Grande de Loiza destroyed practically all 

houses and buildings in its path (fig. 8). The 

only evidence left of previous habitation was 

partly exposed foundations along the boulderand debris-littered banks.

The gaging station on the Rio Grande de 

Loiza at Highway 30 recorded a rise of 12 

feet in 1 hour. Shortly after 5 a.m. September 6, the river crested at a stage of 31.2 

feet on the gage. It was reported by local 

residents that the floodwaters rose 42 feet 

just below Loiza Dam at Trujillo Alto. At 

Carolina the peak discharge through the 

bridge on Highway 3 was 197,000 cfs from a 

contributing area of 239 square miles. Below 

this point floodwaters, in their rush to the 

sea, broke out of the Loiza's canalized main 

channel and found outlet through Laguna La 

Torrecilla about 8 miles to the west. Practically the entire coastal plain between Highway 3 and the low ridge at the Atlantic beach

Figure 8. Heavily eroded and redeposited bank of RioGrande de 

Loiza at San Loreazo. Several houses formerly occupied this area.

Figure 7. View showing damage to floodwall along left bank at 

Rio Valenciano in Juncos.

Figure 9,> Bridge on Rio Limones near Limones. Wingwall from 

left side was found intact about 50 feet downstream; the remains of the wingwall from the right side can be seen in the 

foreground.

became a large lake about 10 miles long. 

Highway 3 was under water at several places.

The Rio Sabana and the Rio Fajardo, draining the northern and eastern slopes of the 

Sierra de Luquillo, produced notable floods.

Along the coastal highway from Naguabo, 

at the eastern end of Puerto Rico, to Santa 

Isabel, on the south-central coast, practically 

every principal stream overtopped the highway (fig. 9). Floods on the Rio Blanco and 

Rio Guayanes were particularly destructive. 

According to interviews with residents along 

the coast northeast of Yabucoa, the magnitude
SUMMARY OF FLOOD DISCHARGES

of flooding on streams of this area was less 

than that for the floods of 1928.

FLOOD DAMAGE

The damage caused by the floods of September 6 exceeded $7 million. A summary 

of estimated damages is given in table 1.

Table 1. Summary of Hood damage, September 6 

. [Adapted from Civil Defense Corps data]

Public property:

Department of Public Works (roads and bridges). $3,201,000 

Aqueduct and Sewer Authority.............................* 247,000

Land Authority......................................................... 600,000

Water Resources Authority (power)....................... 104,000

Communication Authority........................................ 20,000

Total................................................................ 4,172,000

Private property:

Houses.................................................................... 1,496,000

Agriculture:

Crops.................................................................... 924,000

Livestock and poultry........................................ 91,000

Facilities............................................................ 298,000

Other.................................................................... 74,000

Utilities................................................................. 26,000

Total....................................................__.... 2.909.000

Total damage................................................. $7,081,000

Human suffering was great there were 

117 deaths, 30 persons missing, and 136 injured. Emergency hdusing, medical attention, 

food, and clothing were provided for- thousands as 484 houses were destroyed and about 

3,600 others damaged. The Civil Defense 

Corps "and the American Red Cross assisted 

more than 30,000 persons in 33 towns.

Damage to agriculture was high as 8,300 

acres of sugar cane, coffee, bananas, and 

other crops were damaged. Over 800 head of 

livestock were killed.

Total damage to roads and bridges exceeded $3 million. During the floods, all main 

highways and most secondary roads were 

impassable for a short period. At Humacao, 

the highway bridge over Rio Humacao was 

destroyed and traffic was not restored for 

more than 3 weeks. It was reported that the 

temporary bridge over Rio Humacao was destroyed on December 1, 1960, by a somewhat 

lesser flood.

SUMMARY OF FLOOD DISCHARGES

Records of past floods in Puerto Rico are 

very scanty. Michael A. Quinones, former 

chief engineer, Puerto Rico Water Resources 

Authority, suggests in a study of major floods 

in Puerto Rico 1 that "the absence of record 

may be partly due to the fact that most of the 

major floods have occurred during hurricanes 

when most of the people are too busy looking 

for protection of their own lives, and partly to 

lack of curiosity in determining afterwards 

the magnitude of the floods."

Hydrologic information indicates that the 

floods of September 6, 1960, were the greatest known over much of eastern Puerto Rico. 

The only previous flood in the area with which 

they may be compared occurred September 

13 14,1928, during the San Felipe hurricane. 

Quinones' study of the 1928 flood at Comerio 

Falls Dam indicates that the peak discharge 

was slightly higher than thatof the 1960 flood.

The peak discharges for the floods of September 6, 1960, were determined at 24 sites. 

Peak discharges, expressed in- cubic feet per 

second per square mile, are plotted against 

drainage area on figure 10. Comparison of 

these floods with outstanding floods that have 

occurred in other places indicates that the 

floods on the Rio Humacao, Rio Valenciano, 

and Rio Turabo (drainage areas of from 6 to 

15 square miles) rank among the highest 

known.

The peak discharge at 9 sites had a Myers 

rating in excess of 80 percent; the discharge 

at 4 of these sites exceeded 100 percent. 

Compilations of record peak discharges on 

streams in the United States and some foreign 

streams 2' 3 reveal only 14 known events 

(from drainage areas of less than 250 square 

miles) in which the Myers rating exceeded 80 

percent.

1Quinones, M. A., 1953, High intensity rainfall and major 

floods in Puerto Rico: Am. Soc. Civil Engineering Proc., v. 79, 

Separate 364.

2 Iindsey, R. K., Kohler, M. A., and Paulhus, J. C. H., 1949, 

Applied hydrology: New York, McGraw-Hill Book Co., Inc., 

689 p.

SCreager, W. P., Justin, J. D., and Hinds, J., 1954, Engineering for dams: New York, John Wiley and Sons, Inc., v. 1, 

245 p.
FLOODS OF SEPTEMBER 6, 1960, IN EASTERN PUERTO RICO

£!O

aim ativnos QNoaas uad iaaj oiano NI
SUMMARY OF FLOOD DISCHARGES

It is significant that each of the high-yield 

streams mentioned above head on the northern slope of the Sierra de Cayey between 

Cayey and Humacao. During the storm, 

Weather Bureau radar units tracked the 

northeastward movement of the most intense 

rainstorm over this area. The orographic 

influence of the mountain range that rises abruptly from the south coastal plain is shown 

by the rainfall pattern (fig. 1).

Peak discharges at stream-gaging stations 

and at other points in eastern Puerto Rico 

are summarized in table 2. The reference 

numbers in the table apply to figures 6 and 

10.

Table 2. Summary of flood stages and discharges in eastern Puerto Rico for flood of September 6

[Each station in this table has 1 or 2 entries listed under maximum floods; the first pertains 

to the flood being reported on, and the second pertains to the maximum flood previously known 

during the period of record]

No,

1

2 

3

4 

5

6 

7

8

9

10

11 

12 

13

14 

15

16 

17 

18 

19 

20

21 

22 

23 

24 

25

Stream and place of determination

Rio Grande de Manati at Ciales____ 

Rio de la Plata near Cayey »/ «/ ________

Rio de la Plata at Proyecto La 

Plata. 

Rio de la Plata at Comerio Dam ___

Rio de la Plata at Toa Alta __ _____

Rio Bayamon near Aguas Buenas __ 

Rio Bayamon Dam near Aguas 

Buenas. 

Rio Turabo near La Plaza ________

Quebrada de las Quebradillas near 

Caguas. 

Rio Grande de Loiza at Caguas ____

Rio Gurabo near Juncos __________

Rio Valenciano near Las Piedras «, 

Rio Valenciano tributary near Las 

Piedras. 

Rio Valenciano at Juncos _________

Rio Gurabo at Gurabo _________ _ _

Rio Grande de Loiza at Loiza Dam. 

Rio Grande de Loiza at Carolina. __ 

Rio Sabana at Luquillo___________.

Rio Fajardo near Fajardo__ _____

Rio Hicaco near Na^abo __ ___

Rio Humacao at Las Piedras ______

Rio Humacao at Humacao __ _ _ _ _.

Rio Guamani near Guayama __ _ __.

Rio Majada near Salinas __________

Rio Coamo at Coamo _____________

Drainage 

area 

(sq mi)

128

42.2 

63.1

140 

204

hs.s

6.82 

6.25

89.7

23.6 

6.86 

.76

15.3 

59.6

207 

239 

7.01 

14.9 

1.24

6.54 

10.0 

5.65 

22.0 

48.4

Period 

of 

record

1946-60

1959-6C 

1914-60 

1960

1960

1960 

1960 

1960

1960 

1960

1960 

1960 

1960 

1960 

1945-54, 

1958-6C 

1960 

1960 

1960 

1960 

1960

Maximum floods

Date

Sept. 6, 1960 

Aug. 12, 1956 

Sept. 6, 1960

_ _ _ - do ______

Aug. 14, 1960 

Sept. 6, 1960 

Sept. 14, 1928 

Sept. 6, 1960 

Aug. 14, 1960 

Sept. 6, 1960 

__ do _____

__ do__ __ __

do

kug. 14, 1960 

Sept. 6, 1960 

__ do _______

do _

__ do _______

Aug. 21, 1960 

Sept. 6, 1960 

do

do

__ do _____

__ do__ __ __ 

Oct. 25, 1953 

Sept. 6, 1960

__ do__ _____ 

do

do

Gage 

height 

(feet)

22.7

19.7

30.5 

10.0

35.8 

22.4

31.2 

20.0

27.7

13.75

6. 513 

8.1

Discharge

Gfs

77,300

51,000 

54,500

101,0*00 

116,000 

95,500 

9,800 

2 8,000 

12,800

224,000 

8,150

71,500

28,000 

28,800 

1,770

37,100

6,600 

170,000 

197,000 

8,500 

14,500 

1,660 

2,560 

20,800 

31,600 

2,580 

11,000 

14,300

Gfs per 

sq mi

604

1,210 

864

721 

829 

468 

481 

808 

692

3,520 

1,300

769

1,190 

4,200 

2,330

2,420

111 

822 

824 

1,210 

974 

1,340 

2, -060 

3,180 

3,160 

457 

500 

295

1Drainage area above Cidra Dam not included. 2Estimated on basis of field survey.
10 FLOODS OF SEPTEMBER 6, 1960, IN EASTERN PUERTO RICO

Rio Hicoco ntor Noguobo 

Drotnog* or*a 1.24 sq mi

u 40

Rio 6rande dc Loiza at Caguat 

Drainage area 89.7 sq mi

Rio de La Plata at Too Alto 

Drainoge area 204 tq mi

12 6 12 6

6

12 6 12 6 12 6 12 6 

HOURS

SEPTEMBER I960

Figure 11. Discharge hydrographs for selected gaging stations September 5 8.
SUMMARY OF FLOOD DISCHARGES 11

Five gaging stations are operated by the 

Geological Survey in the flood area 4 recording gages and 1 nonrecording. During 

the flood the gaging station on Rio Grande de 

Manati at Ciales was completely destroyed. 

The station on Rio Gurabo at Gurabo was extensively damaged. The other two recording 

gages, both bubble type, had some damage to 

the intake system. The discharge hydroTable 3. Record of stage and discharge, Rio de La Plate at 

ToaAlta

Date and time

Sept. 5 

12 p. m -*, . .,

Sept. 6 

5 a. m _.».__.^_^MMM.J»H__1M6 __ _ ______ . » 

6:30. __ __

7___ ______________

8. ....................

9_ ....................

10 ....................

11 ___ ._ .............

11:30 ... __ ..........

12 m _______ .......

1 p. m, __ ____

2>_ _____________ __

3_ ....................

4 .....................

5 .....................

7 _______________

9. ....................

lip* m_-______________

Sept. 7 

2 a, m____ _

4.__ ________ .......

8 .....................

12 m __ .... __ ....

4 p. m __ _

8 .....................

12 p. m __

Sept. 8 8 a.m. _ ____ __ __ _ __

2 p, to. .»______________

4 .....................

6 .....................

12 p. m .-___. ..... 

Gage 

height 

(feet)

6.65 

6.65

7 ^n

16.20

22.00

24.20 

26.10

29.60

33.00

35.40

35.80

35.10

31.80

29.40

27.50

26.00

24.80

22.75

21.30

20.80

19.20

18.00

16.90

15.10

14.00

13.15

12.65

1 9 1 5

11.70

12 20

12.50

12.30

Discharge 

(cfs)

230 

230

4.R9

4 flQfl

10,900

16,800 

23,900

41,700*

67,000

92,500

95,500

88,900

57,300

40,400

30,300

23,400

18,700

12,600

9 4. on

8 ^4n

6,240

5,200

4,450

3,600

3,100

2,720

2,490

2,270

2,080

2,290

2,420

2,340

graphs for selected gaging stations are shown 

in figure 11; stages and discharges for selected time intervals are listed in tables 3, 

4, and 5.

The discharge hydrograph for Loiza Dam 

is shown as figure 12. Discharge over the 

spillway was slightly regulated by the operation of taintor gates.

Table 4. Record of stage and discharge, Rio Grande de 

Loiza at Caguas

Date and time

Sept. 5 

12 p. m _ ...............

Sept. 6

1 a. m.. _-_-____--__----

2 ___________ . ......

3 ___ _. - ..........

4 _________ - _____ .

5 -

5:15 -

6 _______________ .

6:55 __ ...............

7 _____ __ ________ -

8 ......................

8:10 __ .... _ ....

9_.__ __ -

10__-_.- -

11...... ...............

12 m ___»_____________-

Ip, m _..._.__.. .._.

2 ________________

4 ......................

6 _______ - -___._-

9 _____ ...............

12 p. m _ ^__.

Sept. 7 

6 a^ m _..-.--_-_-___-_-

12 m . _- ...

6 p. m _________________

12 p. m -

Sept. 8 

6 a. m __ _______ __

12 m .

ft p-zn*.__--- . _________ _

12 fW a.m. ^ » 

Gage 

height 

(feet)

7.31

13.9

20.6

24.2

25.1

30.8

31.2

30.2

28.2

28.6

30.0

30.4

29.0

24.8

19.3

18.5

17.6

16.8

15.1

12.3

11.3

11.0

10.6

10.3

10.0

9.80

9.60

9.40

9.20

9.10

Discharge 

(efs)

200

5,260

20,100

33,400

37,400

69,000

71,500

65,200

52,900

55,200

63,900

66,600

57,600

36,100

16,300

14,100

12,000

10,200

7,100

3,240

2,240

1,970

1,620

1,370

1,230

1,110

994

886

786

73&
DISCHARGE , IN THOUSANDS OF CUBIC FEET PER SECOND

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SUMMARY OF FLOOD DISCHARGES 13

Table 5. Record of stage and discharge, Rio Hicaco near Naguabo

Date and time

Sept. 4

12 p. m- ...... ------ .........

Sept. 5

5 a.m«...... ..........

6 ........................

8..... ____ .... ____ ...

9 ___ ...................

10 .......................

11. ----_--.-_-----_.. __

12 m._ __ .- ___ . ___ ...

2 p. m_ ___________________

6_ ___ ___ ____ ____ ___

9 __ __ __ __ __ __ _____ __

10 __ ___ _ ___ _ _______

11 __ _ __ _____ ___ __ __ _

12 p. m_ __________________

Sept. 6

12:30 a,. m________________

1 _________ _ ___..__.__

2 _______ ____ _ ___ __

2:30 __ ______ _ ____ _

Gage 

height 

(feet)

0.23

.20

.23

.60

.60

1.40

2.20

1.30

.65

.32

.26

9Q

2.90

3.86

3.20

4.00

5.80

6.50

Discharge 

(cfs)

7

6

7

29

29

102

206

01

*39

12

q

10

320

572

375

618

1,320

1,660

Date and time

Sept. 6 Continued 

3 p.m...................

4 .......................

5.... __ ...... __ ..

6 __ . ..........

6:30 ______ _ . .......

7 ____________ ......

7:30 ____ ....... ...

8_______________. ___..__

9_ __ ___ ____________

9:30 _ ___ ___ ________

10____ ___ __ ___ __ ...

11 ___ _ __ ___________

12 m_ __ __ __ __ __ __ ...

3____ __ __ __ _____ __ __

6_. _____________________

12 p.m__-__--___________

Sept. 7

6 a. m_____ ______________

12 m ______ _ __ ._ __ __

12 p. m_-___--_--__-.-___

Gage 

height 

(feet)

5.80

5.20

4.35

3.60

4.95

4.50

5.40

5.00

3.00

4.52

4.20

2.00

1.20

.82

.55

.40

.34

.30

.27

.23

Discharge 

(cfs)

1,320

1,050

743

490

981

799

1,140

1,000

337

806

687

177

81

46

26

16

13

10

9

7

IHT.DUP,,D.C.61- 93 ?o2