Fields, Fred K.

FLOODS IN THE GUAYANILLA-YAUCO AREA, PUERTO RICO. 1969.

GEOLOG;C/41. •

OF-5

UNITED STATES

DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

FLOODS IN THE GUAYANILLA-YAUCO AREA,

PUERTO RICO

by Fred K. Fields

Prepared in cooperation with

COMMONWEALTH OF PUERTO RICO

Department of Public Works

Open-file Report

November 1969

(Prior to publication as

Hydrologic Investigations Atlas)

CONTENTS

Page

Rio Guayanilla basin 4

Flood history 6

Flood frequency 9

Flood profiles 13

13Inundated area

Rio Yauco basin 16

Flood history 18

Flood frequency 19

Flood profiles 21

23Inundated area

24High-water mark information

24Water-surface elevations

24Depth of flooding

24Cooperation and acknowledgment

25Additional information

2

ILLUSTRATIONS

Page

Figure 1. Location of Rio Guayanilla and

Rio Yauco drainage basins 5

2. Profile of abandoned railroad

embankment 7

3. Upstream Highway PR-2 bridge spanning

Rio Guayanilla 8

4. Stage-discharge relation of Rio

Guayanilla at upstream Highway PR-2

bridge 10

5. Flood-frequency relation of Rio

Guayanilla at upstream Highway PR-2

bridge 11

6. Flood profiles, Rio Guayanilla 14

7. Area inundated at Guayanilla, 1932 and

1954 floods 15

8. Diagram of flow diversions into and

out of Rio Yauco basin 17

9. Flood stage-discharge relation of Rio

Yauco at Escuela Arturo Lluberas.. 20

10. Flood profiles, Rio Yauco 22

3

FLOODS IN THE GUAYANILLA-YAUCO AREA, PUERTO RICO

by Fred K. Fields

This report is a compilation of data pertaining to

floods in Rios Guayanilla and Yauco, based principally

upon information obtained from residents in the study area.

This information is a useful tool in making land-use and

development decisions.

The Guayanilla and Yauco basins lie in the south-

western part of Puerto Rico. The streams flow southward

from the rugged Cordillera Central and empty into Bahia

de Guayanilla. The lower basins are devoted principally

to the production of sugarcane and are subject to destruc-

tive floods. Details pertaining to basin features, flood

frequency, flood profiles, and inundated areas are discussed

by individual basins. All elevations given are in meters

above mean sea level.

Rio Guayanilla basin

The Rio Guayanilla basin is the easterly basin of

the study area shown in the location sketch, figure 1.

It has a drainage area of 18.5 square miles at the

U.S. Geological Survey gaging station 2.4 kilometers

north of Guayanilla, and 20.8 square miles at the upstream

Highway PR-2 bridge (of three Highway PR-2 bridges across

Rio Guayanilla). The total drainage area of the basin is

about 31 square miles.

OCEANO ATLANTICO

67°15' 67°00' 66°45'

18°301--

Ca

CD

'CI 18°151 4)

cd U)cd 04

Rio Yauco basin

. ,

\ . Rio Guayanilla

basin

Cabo Rojo Yauco• Lajas (

• CrUayanilla

18°00'

MAR CARI•BE

0 5 10 miles 1 t ,tArea of this report

0 10 kilaneters

Portion of Rio Grande de Atiasco basin from which flow.is diverted to Rio Yauco basin

Boundary of drainage basin

Figure 1. Location of Rio Guayanilla and Rio Yauco drainage v4.3ins.

5 6

The lower floodplain is an alluvial fan and most of

the city of Guayanilla is on the floodplain. Four high-

way bridges span Rio Guayanilla in the study area. The

abandoned railroad embankment that crosses the flood plain

downstream from Guayanilla is an important feature that

affects floodwater movement. The embankment profile is

shown in figure 2. Rio Guayanilla is diverted at three

places for irrigation. However, no dams exist that would

reduce the magnitude of floodflow.

Flood history

The earliest floods documented in this basin occurred

in 1876 and 1886. Stages of these floods, cited in highway

damage reports, could not be recovered. The flood of

August 8, 1899, is the greatest known flood. Since the

1899 events, major floods occurred in 1926, 1928, 1932,

and 1954. Small floods, being less destructive and less

spectacular, usually are soon forgotten. However, flood

elevations were recovered for the lesser floods that

occurred in 1955, 1958, 1960, 1963, and 1966. A tabulation

of flood stages and estimated discharges at the upstream

Highway PR-2 bridge is given below. The bridge is shown

in figure 3.

14

cr) •-4 12 Railroad embankment

10 Water surface, flood of l>a / September 13, 19288 d coi.c• cn Guayanilla cqct,

6 bo boi c4

Ground surface-1 2

0 2 4 6 8 12 16 20 24 STATIONING, IN HUNDREDS OF METERS

Figure 2.--Profile of abandoned railroad embankment between Highways PR-335 and PR-336.

7

Figure 3.--Upstream HighwAy 2a-2 spanning Rio Guayanilla. The 1(.:S=1 L..600d reached the low bean of this bridge. The top of the bridge railing is about the same elevation as the crest of the 1899 flood.

8

Elevation above Peak discharge, mean sea level, in cubic feet

Date in meters per second

August 8, 1899 22.0 39,000

September 13, 1928 20.9 23,000

September 21, 1932 21.3 28,000

October 13, 1954 20.5 18,000

May 6, 1958 19.4 6,400

September 14, 1961 18.5 2,800

The 1926 flood stage was not established at the

upstream Highway PR-2 bridge. Flood elevations. farther

downstream indicate the magnitude of the flood was

slightly less than that of the 1928 flood. Stage and

corresponding discharge at this site permit the develop-

ment of the stage-discharge relation shown in figure 4.

Flood frequency

Historical floodmark elevations were used in

conjunction with discharge records collected at the Rio

Guayanilla near Guayanilla gaging station, unadjusted for

the intervening 2.3 square miles of drainage area, to

establish a flood-frequency relation at the upstream

Highway PR-2 bridge. The general relation of recurrence

interval to river stage and discharge is shown in figure 5.

Stage and discharge for selected recurrence intervals are

tabulated below.

9

22 August 18, 1899

'September 21, 1932

September 13, 1928 October 13, 1954

20 -

May 6, 1958-4w 19n8

September 14, 1961

L_ L-118 4 7 10 20 40

DISCHARGE, IN THOUSANDS OF CUBIC FEE PER 32COND

Figure 4.--Flood stage-discharge relation of Rio Guayanilla at upstream Highway PR-2 bridge.

10

50 r .1 1 I 1

F;3

f% 40 a, August 8, 1899 E-4

C.)

VI 30

September 21, 1932

0

cf) September 13, 19282 .444 October 13, 19540 20 B September 14,1961* E-4 November 12, 1965* H

May 6, 1958 z

August 3, 1963*

* Fran gaging station records- ] 0 1 1 1 1 1 1 1 1 1 1 1 2 4 7 10 20 40 70 100

RECURRENCE INTERVAL, IN YEARS

Figure 5.--Flood -frequency relation of Rio Guayani] at upstream Highway PR-2 bridge.

11

Recurrence Elevation above Peak discharge,

interval, mean sea level, in cubic feet in years in meters per second

5 19.0 4,500

10 20.0 13,000

20 20.7 21,000

30 21.2 27,000

50 21.7 34,000

There is no means of predicting the date a flood of

a given magnitude will occur. If a long-enough record

of floods is available, however, the average recurrence

interval of such a flood and the probability of its

occurrence in any year can be computed. The recurrence

interval, or frequency, of a flood of specific magnitude

is the average length of time during which that flood has

been equaled or exceeded. For floods greater than the

10-year flood, the reciprocal of the recurrence interval

is virtually the probability of occurrence in a year;

thus a 20-year flood will have a 5-percent chance of

occurring in a year, and a 50-year flood will have a

2-percent chance.

At the upstream bridge on Highway PR-2, a flood

elevation of 20.0 meters has an indicated 10-year recur-

rence interval. However, the 20.0 meter elevation was

exceeded 3 times during the 7-year period 1926-32. It

12

thus is emphasized that recurrence intervals are average

figures--the average number of years in which floods of

a specific magnitude have been equaled or exceeded.

Flood profiles

Flood elevations referenced to the arbitrary base

line shown on the topographic map are shown in figure 6.

The 1932 and 1954 flood profiles are well defined above

an elevation of 8 meters. The 1928 flood profile is

poorly defined and has been drawn on the basis of the

shape of the other flood profiles. The 1928 and 1954

profiles are estimated in the reach from 0.4 to 1.8 kilo-

meters above the stream mouth.

Inundated area

The area inundated by the 1928 flood has been

delineated on the large topographic map. The area

inundated by the 1932 and 1954 floods at Guayanilla

is shown in figure 7. The 1928 flood was selected to

be shown on the large map because it is known to have

intermingled with Rio Yauco and to have been consistent

with the Rio Yauco inundation area of 1928. The inundated

area in the vicinity of El Faro and along Rio Macana is

undefined and has been estimated. The effect of the

abandoned railroad embankment upon the height of the

water could not be defined from the available floodmarks.

13

24 T

22

T Deck elevation 20- Bridge-

Low bean elevation 1-1 18 _

/.••• •

z 16 }), . • 0.•

14 .

September 27,1932 •• •-• •

12 U) ?=-ti 10 Central Rufinal Highway PR-2 bridges

/A 8 September 13, 1928

H " Ab: ' 12d railroad crossing „ • • •••60

E-4 g 4 October 13, 1)54

---,--- - I 2- o Q.

LRailroad bridge I _I L I__ :_l_ J _1 _1 __I__ L i 1 f _ 1 - L___ -4._ ____ o 1 ____1 __I_ _1

0 1 2 3 4 DISTANCE UPSTREAM FRai MOUTH, IN KILOMETERS

Figure 6.--Flood profiles, Rio Guayanilla.

, .

Septembtrz7193Z" Otob-er 13;1954'' 0 B AN. D 0

0N

%CI-171r( \\

c)

11

Figure 7.-- Area inundated in the vicinity of Guayanilla by the floods of September 27, 1932, and October 13, 1954.

15

The flood boundaries delineated on the topographic

maps provide a record of historic facts that reflect

channel and flood-plain conditions existing at the time

of each flood. No attempt was made to appraise the effect

of later changes in the channel or flood plain. The Rio

Guayanilla channel was dredged in 1948, 1952, and 1965,

and increasing urbanization may have changed runoff

characteristics.

Highway PR-2 will be relocated upstream from the

present (1968) upstream bridge. The inundation pattern

of future flood may be affected by this relocation, by

the possible relocation and improvement of the stream

channel, by the removal of the railroad embankment, and

by other cultural changes.

Rio Yauco basin

The Rio Yauco basin is the westerly basin shown in

the location sketch, figure 1. The drainage area of the

basin at Escuela Arturo Lluberas, 1.3 kilometers northwest

of Central San Francisco, is 45.5 square miles. The total

drainage area of the basin is about 48 square miles. These

areas include that part of the basin upstream from Antonio

Lucchetti Dam.

Reservoirs partly regulate streamfiow within this

basin. A schematic diagram of the interconnected reservoir

system is shown in figure 8. Lagos Yahuecas, Guayo, Toro,

6C0 Dam spillway crest _

Tam. - - _ Connecting tunnel 1

Diversion from Rio I IN 400,_ Grande de Afiasco\ Yahuecas Dambasin to Rio Yauco\

4 c, Guayo Dam1_ :e 303, basin Prieto Dam

o Power plants H 2 -E-4 _„-Antonio Lucchetti Dam

Lx1

100 N-- Diversion to Rio Loco basin w ''---Loco Dam

Figure 8.--Schematic diagram of streamflow diverted into and out of Rio Yauco basin.

17

and Prieto, the four reservoirs in the headwaters of

Rio Grande de Afiasco, have a combined storage capacity

of about 20,000 acre-feet. These reservoirs, constructed

during 1955 and 1956, divert flow from 39 square miles of

the Rio Grande de Afiasco basin to Lago Yauco (above

Antonio Lucchetti Dam) on Rio Yauco. Lago Yauco also

collects flow from 17.3 square miles of the Rio Yauco

basin, and it has a storage capacity of 16,500 acre-feet.

Water from Lago Yauco then is conveyed to Lago Loco for

power generation and for distribution to Valle de Lajas

for irrigation.

One major flood, in 1960, has been experienced at

Yauco since the construction of Antonio Lucchetti Dam in

1953. The numerous irrigation diversions on Rio Yauco

from Yauco to Escuela Arturo Lluberas have minor influence

on flood discharge. Six highway bridges and one foot

bridge span Rio Yauco in the study area.

Flood history

The earliest flood known on Rio Yauco was in 1867

during Hurricane San Narciso, when the highway bridge at

Yauco was destroyed. No data were recovered to indicate

the magnitude of this flood. The greatest known flood

to occur in the basin was on August 1899. Other major

floods occurred in 1926, 1928, and 1960. A tabulation

of stage and approximate discharge of historical floods

at Escuela Arturo Lluberas is shown below.

18

Elevation above Peak discharge, mean sea level, in cubic feet

Date in meters per second

August 8, 1899 10.9 42,000

September 13, 1928 9.9 18,000

September 18, 1960 9.5 10,000

November 11, 1961 8.8 2,900

April 28, 1962 8.4 1,800

September 27, 1963 8.9 3,300

July 21, 1968 8.6 2,200

Flood stages after 1926 were collected at the Highway

PR-335 bridge about 50 meters east of the school. These

elevations have been transferred upstream to the school

as a common point on the basis of the indicated water-

surface slope,

Flood stage and discharge define the relation shown

in figure 9.

Flood frequency

Sufficient data are not available to define a flood-

frequency relation for Rio Yauco. The 1899 flood is

estimated to have a recurrence interval of about 70 years

and the 1928 flood a recurrence interval of about 35 years.

The scattered flood discharge information relating to

floods after the construction of Antonio Lucehetti Dam is

19

E-4

T-T-1 I12.0 J cr, 11.0 August 8, 1899

10.0r- September 13, 1928 J September 18, 1960

cs) 9.0 September 27, 1963* November 11, 1961*

0 fill 8 • 7 July 21, 1968*

8.4 1- c,-April 28, 1962k

*Elev. transferred to Escuela A. Llub_ras J- I .Al L-8.2--

1 2 4. 7 10 20 40 70 100 DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND

Figure 9 .--Flood stage-discharge relation of Rio Yauco at Escuela Arturo Lluberas.

20

not sufficient to define the present (1967) flood-

frequency relation.

Flood profiles

The 1928 and 1968 flood elevations, referenced

to the arbitrary base line on the topographic map, are

shown in figure 10. The 1928 water-surface profile

between the elevation range of 13 to 26 meters is not

defined by floodmarks, but it has been estimated. An

average value of high-water marks was used near the

elevation of 28 meters. Although several residents

along the reach from 5 to 9 kilometers upstream from

the mouth recalled the 1928 flood, the west edge of the

valley has been changed, mainly by road construction,

and old landmarks have been erased. One resident

recalled that the flood reached Escuela Segunda Unidad

de Barinas, but could point out no definite elevation of

the flood. The profile has a probable accuracy of +0.5

meter at elevations above 12 meters.

The flood of July 21, 1968, was not a major event,

but its profile provides a basis for estimating the

1928 flood profile. Rio Yauco is confined at low

discharge by small levees downstream from about kilometer

2.5. The 1968 profile below this point is not applicable

for comparison with the 1928 flood and is not shown.

_1

I N M

E TE

RS

AB

OV

EM

EAN

SEA

LEV

EL

'RT, R

VA

TIO

N,

Highway PR-23o

28

0c, 26 .0_

September 13, 1928

24

22

20 -

18 z

16 Escuela Arturo Lluberasi

14 Highway PR-335 July 21, 1968 12

10

Service road 8

6 I

4 Deck elevation - Low beam elevation 2

1 1 L _I 1 t i 1 0 1 2 3 4 5 6 . 7 8 9 10

DISTANCE UPSTRELn FR MOUTH, IN KILOMETERS

Figure 10.--Flood profiles, Rio 1:11,x

Inundated area

The area inundated by Rio Yauco during the 1928

flood is shown on the topographic map. The delineated

boundary reflects the channel and flood-plain con-

ditions at the time of the 1928 flood. No attempt was

made to ascertain the effect of later changes in the

channel and flood plain, or in runoff characteristics.

Apparently only the buildings along Rio Yauco in

the vicinity of Highway PR-2 and at the southeastern

tip of the city were affected by the flood. Water may

have backed up some distance in Quebrada Berrenchin

along the west and south edge of Yauco, but the extent

could not be determined.

Housing has been expanding onto the flood plain of

Rio Yauco on the basis of unproven confidence that Lago

Yauco has eliminated major floods. Lago Yauco may

reduce the frequency of flooding, but it will not

eliminate floods, particularly at times when it may be

at full capacity. A service road recently has been

constructed across the lower flood plain of Rio Yauco,

which crosses Rio Yauco at baseline station 2.05 and

extends to Punta Verraco. This and other changes along

the channel and in the flood plain may well affect the

inundation pattern of future floods.

23

High-water mark information

The inundated areas have been delineated on the

basis of flood-stage information furnished by residents.

Field surveys were conducted to determine the elevation

of the flood stages.

Water-surface elevations

The estimated water-surface contours of the

September 13, 1928, flood for both basins and of the

1932 and 1954 floods at Guayanilla are shown on the

topographic maps.

Depth of flooding

Depth of flooding at any point may be estimated by

subtracting the ground elevation from the water-surface

elevation. Each is shown by contours on the map. In-

termediate estimates of depth may be determined by

interpolation.

Cooperation and acknowledgment

This report was prepared as part of the floods

investigation authorized by a cooperative agreement

between the Department of Public Works, Commonwealth

of Puerto Rico, and the United States Geological Survey.

Many of the flood data were provided by the Department

of Public Works. Historical flood information was made

available by the general archives of the Instituto de

Cultura Puertorriqueha and by many residents of the

study area.

Additional information

Additional information relating to floods on Rio

Guayanilla and Rio Yauco can be obtained from the

U.S. Geological Survey, San Juan, Puerto Rico, or from

the Area of Flood Control and Maintenance of Beaches

and Rivers, Departamento de Obras P5blicas, Santurce,

Puerto Rico.

25

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