October 9-13 2005 Flood Event Report

 

During the period from October 9th through October 13th 2005, Puerto Rico and the U.S. Virgin Islands were affected by a heavy rainfall event and the associated flooding. This type of weather pattern is observed occasionally during October and results in significant rainfall and flooding across the area. This inclement weather pattern was largely due to the combination of a vigorous upper level low pressure over the Atlantic that moved southwest and was expected to affect the local area during the weekend, in combination with a surge of moisture that was to move northward from the Caribbean Sea into Puerto Rico and the U.S. Virgin Islands. This complex weather system provided all the ingredients necessary to maintain a very unstable atmosphere across the entire area. The results were widespread heavy rainfall…flash flooding and mudslides over many sections of Puerto Rico.

 As early as Wednesday October 6th, the Hazardous Weather Outlook issued by the National Weather Service Weather highlighted the potential for showers and thunderstorms over the weekend with heavy rainfall leading to flash flooding and persisting through the middle of the following week. As the scenario became more certain, NWS forecasts, summaries and discussions early on Friday October 7th indicated that weather conditions were forecast to undergo deterioration beginning Saturday night and by Sunday, widespread heavy rainfall was expected with copious amounts of rainfall. This scenario was forecast to persist through Monday night or Tuesday. By the morning of Saturday October 8th due to the imminence of the event, a hydrologic statement was issued discussing the potential accumulation of 5 to 10 inches of rainfall across the area Sunday October 9th through Monday October 10th.  The antecedent conditions for flash flooding were in place since the previous weeks had been generally wet and the local soils were nearly saturated and river and stream levels above normal. The forecast even indicated that rainfall chances were to remain high for Tuesday October 11th and Wednesday October 12th as the upper level low was to begin exiting the region and the additional rainfall was to aggravate the flooding conditions.
 

Images from Flood Event

 

 

Hydrologic Summary

 

 As aforementioned, the month of October started out to be a very wet month for the island of Puerto Rico (PR).  Rainfall totals for the first two weeks of the month were way above average for many locations, with some municipalities reporting over 20 inches.

 

Highest Rainfall Accumulations from October 4th – 14th , 2005

ADSP4

Adjuntas

24.92

PRTP4

Ponce

23.58

VINP4

Villalba

19.66

 

While the most widespread flooding occurred during the second week of the month, the first week set the stage for what would be a significant event for the island of Puerto Rico.   The rainfall during the first week caused some flooding around the region and also was instrumental since this resulted in the area soils being saturated and reservoirs and lakes with decreased capacity.  The computed Flash Flood Guidance for 9pm on October 10th indicated very little rainfall would be needed to cause flooding and flash flooding across the islands.  The chart below shows the threshold of rainfall (approximately) needed in a defined time period in a particular zone to begin flooding.  The following chart shows that throughout Puerto Rico and the Virgin Islands 4.1 inches (*max) or less of rainfall in 1 hour, 3 hour or 6 hour period will result in flooding anywhere in the forecast area (all zones).

 

911 PM EDT MON OCT 10 2005

 

Puerto              Rainfall needed

Rico &             to cause flooding

VI Zones          within time frames

 

:IDENT    1HR   3HR   6HR  ZONE NAME

====================

PRZ001    0.5/  0.9/  1.4 :PR FFG ZONE 1

PRZ002    0.8/  1.7/  2.6 :PR FFG ZONE 2

PRZ003    0.6/  1.1/  1.6 :PR FFG ZONE 3

PRZ004    0.5/  0.9/  1.4 :PR FFG ZONE 4

PRZ005    1.0/  1.9/  2.9 :PR FFG ZONE 5

PRZ006    0.4/  0.8/  1.3 :PR FFG ZONE 6

PRZ007    1.2/  2.1/  3.0 :PR FFG ZONE 7

PRZ008    1.9/  3.0/  4.1* (*max) :PR FFG ZONE 8

PRZ009    0.6/  1.1/  1.6 :PR FFG ZONE 9

PRZ010    0.9/  1.6/  2.3 :PR FFG ZONE 10

PRZ011    1.6/  2.7/  4.0 :PR FFG ZONE 11

PRZ012    0.9/  1.8/  2.7 :PR FFG ZONE 12

PRZ013    0.9/  1.8/  2.7 :PR FFG ZONE 13

VIZ001    0.9/  1.8/  2.7 :VI FFG ZONE 1

VIZ002    0.9/  1.8/  2.8 :VI FFG ZONE 2

.END

 

 

Figure 1 – 1 day total

 

To add to the complexity was the fact that the system remained almost stationary and continued to pump rain across the region for a few days.  The heaviest 24 hour rainfall amounts were for the period 8am October 10th through 8am October 11th was on the average of 5 inches with maximum values of over 11 inches.  These values definitely exceeded the computed Flash Flood Guidance values.  This rainfall would prove too much for most river systems but was especially devastating for the Puerto Rico river systems which had already been saturated from the rains of the previous week.

 

 

Figure 2 - 5 day total

 

 

Corresponding Rainfall totals > 10 ins for … Oct. 9th – Oct. 13th (reports at 8am)

 

DESCRIPTION

9-Oct

10-Oct

11-Oct

12-Oct

13-Oct

SUM

 

B SLTILLO NR ADJNTS

1.84

0.68

8.64

5.45

2.67

19.28

PONCE 7N/R PORT TIBS

1.13

1.7

11.57

4.03

0.21

18.64

VILLALBA 3NE/BAR APE

1.99

1.99

7.35

4.35

0.17

15.86

LAGO GARZAS/ADJUNTAS

0.64

1.22

7.26

4.55

1.84

15.52

RIO INABON NR PONCE

1.1

2.59

7.76

3.82

0.19

15.46

ICACOS NR NAGUABO

1.19

1.67

7.7

3.02

1.8

15.39

PORTUGUES BLO DAM

3.06

1.39

7.41

2.95

0.25

15.06

QUEB GUABA/NAGUABO

1.47

1.68

7.26

2.67

1.47

14.56

RIO COAMO @ COAMO

1.03

2.54

6.65

3.56

0.35

14.13

MET STN AT RIO ICACO

1.45

1.72

6.68

2.59

1.66

14.1

BRIO SALIENTE/JYUYA

1.27

1.63

6.91

3.49

0.2

13.5

RIO CUYON-COAMO-ALRT

0

1.18

8.23

2.99

0.79

13.19

VIVI/ADJUNTAS 4E

1.57

0.39

4.64

4.39

1.92

12.91

LAGO LUCCHETTI

1.11

1.04

5.62

4.6

0.52

12.89

PORTUGUES-PONCE

2.54

1.58

5.07

2.53

0.31

12.03

BRIO CONSEJO/ADJNTS

1.48

0.38

4.31

3.88

1.97

12.03

ADJUNTAS 5WNW/AG STN

1.96

 

5.17

4.23

0.19

11.56

TOA VACA ABV L T V

0.67

2

5.74

2.98

0.16

11.55

BLANCO NR FLORIDA

2.14

1.36

4.33

1.82

1.52

11.18

YAUCO 1NNE, PR

1.53

1.04

3.5

3.96

1.14

11.18

GURABO BL EL MANGO

0.31

2.57

4.87

1.87

1.41

11.03

BRIO COLLORES/JYUYA

1.2

0.41

5.38

3.85

0.06

10.91

RIO SALIENTE@COABEY

1.41

0.99

5.04

3.42

0.04

10.9

LAGO TOA VACA,

0.47

2.54

5.65

2.1

0.07

10.84

L ANA MARIA/COTO LRL

0.97

2.06

4.99

2.57

0.17

10.76

L PRIETO/ADJNTAS 10W

2.04

0.28

3.49

4.35

0.47

10.64

YAUCO 1NNE/RIO YAUCO

1.14

1.27

4.04

3

1.01

10.47

LAGO ICACOS DAMSITE

0

 

5.51

3.14

1.72

10.38

CMP SANTIAGO/SALINAS

0.61

2.41

5.14

1.77

0.38

10.32

BOCA GRNDE NR JAYUYA

1.06

0.45

4.83

3.89

0.05

10.28

R JACAGUAS@JUAN DIAZ

1.67

2.33

4.31

1.74

0.21

10.26

LAGO CARITE@GATE TWR

0.27

1.46

5.96

1.8

0.63

10.13

JAUCA @ PASO PALMA

0.96

0.28

4.03

4

0.85

10.13

RIO LA PLATA-BARRANQ

0.75

0.94

2.95

5.04

0.35

10.04

 

 

 

 

 

 

 

 

 

 

 

As a result, flooding was widespread across Puerto Rico with some municipalities also reporting mud slides.  All varieties of flooding were common … from urban and poor drainage to flash flooding and river flooding at many of the NWS forecast locations.  Flooding was reported at nine (9) of Puerto Rico’s thirteen (13) NWS forecast locations.   A total of 31 locations across Puerto Rico (over 60 locations with defined Flood Stages) exceeded Flood Stage. Most of the flooding was minor to moderate (27 points) with 4 locations indicating major flooding. 

 

The Ponce and Adjuntas (southern PR) area recorded the highest 24 hour rainfall amounts of over 11 inches which was determined to be on the order of a 10 year rainfall return rate. 

 

While many of the smaller, “flashy” basins in the Ponce area (area with highest rainfall totals) including … but not limited to … the Rio Cerrillos (major flooding …10.62ft), Rio Inabon (major flooding) and Rio Jacaguas experienced moderate to major flooding, minor to major was also reported along the larger basins of  the  Rio de la Plata, Rio Grande de Manati , Rio Guanajibo and Rio de Anasco .  Of these larger basins, the Rio de la Plata at Toa Alta (major flooding influenced by dam operations) and the Rio Grande de Manati at Manati along the north coast of the island rose into the moderate / major flood categories. 

 

Gaged sites that exceeded 15 feet crests were; Rio de La Plata at Comerio …17.59 ft, at Proyecto La Plata … 17.25 ft, at Toa Alta … 21.33 ft, Rio de Anasco at Guacio … 18.13 ft,  Rio Caonillas at Paso Palma … 19.07 ft, Rio Grande de Loiza at HWY 183 … 16.53 ft, blw Dam … 23.04 ft,  Rio Gurabo at Gurabo … 19.04 ft, Rio Grande de Manati at Manati … 33.17 ft, Rio Guayanilla at Guayanilla … 15.50 ft, Rio Inabon at Real Abajo … 19.05 ft, Rio Jacaguas at Juana Diaz … 19.24 ft and Rio Cibuco at Vega Baja … 15.00 ft.

 

*** see Table 1 at bottom for Crest Details.

 

 

Preliminary Effects

 

The Governor of Puerto Rico declared seventeen municipalities under State of Emergency. The initial declaration was for Lares and Juana Diaz, but was later expanded to include Salinas, Santa Isabel, Ponce, Yauco, Peñuelas, Utuado, Jayuya, and Toa Baja. A later update included the municipalities of Humacao, Maricao, Aibonito, Moca, Yabucoa, Villalba, and the Street number 9 of the Santa Catalina sector in Bayamon.

 

Flood effects on the population of southern and interior Puerto Rico were significant. Four homes in the La Atomica area of Juana Diaz were washed away by River Rio Guayo. About 102 persons and 38 families in the southern municipalities of Puerto Rico were evacuated to shelters. Numerous landslides occurred in the interior sectors, especially in the municipality of Lares, which was the worst affected.  Several homes were declared unsafe for living due to terrain failures induced by rainfall and other considerations.  There was one indirect death as a 21 year old male attempted to swim across a swollen river in Coamo while playing a game with friends.

 

Heavy damage was sustained by the Agricultural sectors of the island. The Puerto Rico Farm Bureau estimated losses at 20 million. Vegetables farmers lost 7 million in crops and infrastructure; coffee crops and paths 5 million; plantains, bananas, and watering systems 3 million; milk and loss of production 2 million, cattle and respective infrastructure 2 million, feed and chicken farms and citrus product losses 1.5 million.

Although the main damages were flooding related, there were also damages caused by winds gusts associated with thunderstorms.

 

Department of Transportation and Public Works estimated damages to roads in Lares due to landslides at 1.5 to 2.0 million.

 

* Damages reports were based on local daily newspapers reports.

 

Table 1 … Summary of River Crests for Flood Event

 

 

 

 

RIVER AND STATION

FLOOD

STAGE

 

(FEET)

ABOVE

FLOOD STAGE

CREST*

From … To

*Flood Category

STAGE                 (FEET)

DATE

TIME

(UTC)

    

                                                                                                                                        

           

RIO QUEBRADA GUABA        10.0                  10/11                      *minor                    10.31         10/11     02:45

      NR NAGUABO (NGHP4)

 

RIO CERRILLOS                        6.0                    10/11 – 10/13          *major                    10.62         10/11     06:50

       ABV LAGO CERRILLOS (PCEP4)

 

RIO CULEBRINAS AT              14.0                  10/09                      *minor                    14.25         10/09     03:00

     MARGARITA DAM                14.0                  10/11                      *minor                    14.01         10/11     16:00

       (MODP4)                         

 

**RIO DE LA PLATA                  11.0                  10/11 – 10/12          *moderate              17.59         10/11     06:30

AT COMERIO (COMP4)

      

 

RIO DE LA PLATA                        14.0               10/11                      *minor                    17.25         10/11     06:10

    AT PROYECTO LA PLATA (AIBP4)

 

 

RIO DE LA PLATA                     16.0                  10/11 – 10/12          *minor                     21.04        10/11     07:25

       BLW LA PLATA DAM (NASP4)

     

**RIO DE LA PLATA AT            16.0                  10/11 – 10/12          *moderate/major  21.33         10/11     11:00

        AT COMERIO (COMP4)

 

RIO DESCALABRADO             10.0                  10/13                      *minor                    10.55         10/13     11:45

      nr LOS LLANOS (DESP4)

 

RIO GRANDE DE ANASCO     14.0                  10/11 – 10/12           *minor/moderate 18.13          10/11    05:45

      at BO. GUACIO (ANBP4)

 

**RIO GRANDE DE ANASCO 11.0                  10/11 – 10/12           *moderate             14.79         10/11     06:55 

         at SAN SEBASTIAN (SEBP4)

 

**RIO GRANDE DE ARECIBO                        11.0                        10/14                       *minor                   11.62                                                           10/14                04:15

       NR SAN PEDRO (AREP4)

 

RIO GRANDE DE ARECIBO   10.0                  10/11 – 10/13          *minor                     10.94        10/11     15:00

       ABV UTUADO, (UTUP4)  

 

RIO GRANDE DE ARECIBO   12.0                  10/11 – 10/13          *minor                    13.71          10/11    01:30

     … ADJUNTAS at HWY 135(ADKP4)

 

RIO GRANDE DE ARECIBO   14.0                  10/11                      *minor                    14.73         10/11     03:20

      BLW UTUADO (UTXP4)

 

RIO CAONILLAS                        16.0                   10/11                      *minor/moderate 19.07         10/11     07:45

     at PASO PALMA (JAXP4)

 

RIO SALIENTE                               11.0              10/11                       *minor                   11.17         10/11     07:00

     at COABEY nr JAYUYA (JAYP4)

 

 

RIO GRANDE DE LOIZA            14.0                10/11                       *minor                   16.53         10/11     17:15

     AT HWY 183(SLNP4)

 

 

RIO GRANDE DE LOIZA           22.0                 10/11                        *minor                  23.04         10/11     19:30

     BLW DAM(TRUP4)              

 

RIO CANOVANAS                     10.0                  10/10                       *minor                   10.50         10/10     14:05

     nr CAMPO RICO (CNAP4)

 

 

**RIO GURABO                          18.0                  10/10                        *minor                  19.04         10/10     16:45

        at GURABO (GURP4)

 

 

**RIO GRANDE DE MANATI    25.0                  10/11 – 10/13           *moderate/major  33.17         10/11     12:00

        at MANATI (MANP4)

 

 

**RIO GRANDE DE MANATI    10.0                 10/11                      *moderate              12.47         10/11     05:50

        AT CIALES (CIAP4)

 

 

**RIO GUANAJIBO                    20.0                  10/11 – 10/15          *moderate              22.77         10/12     11:50

        at HORMIGUEROS (HORP4)

 

RIO GUAYANILLA                     12.0                  10/11 – 10/13           *moderate             15.50         10/11     04:45

    at GUAYANILLA (GYAP4)

 

      

RIO INABON                               10.0                  10/11                       *moderate/major 19.05         10/11     02:45

       AT REAL ABAJO (IANP4)       

 

RIO JACAGUAS                         14.0                  10/11                      *minor/moderate   19.24         10/11     16:00

     AT JUANA DIAZ (JUAP4)

 

RIO LOCO …  LAJAS IRRIGATION CANAL

 

    YAUCO BLW DAM(LOEP4)  7.0                  10/10                      *minor                    8.69           10/10     07:15

 

 

RIO MAMEYES                             11.0                10/12                       *minor                   12.07         10/12     13:30

    AT MAMEYES(MSEP4)

 

 

  **RIO CIBUCO                             15.0               10/11                       *minor                   15.00         10/11     10:55

           AT VEGA BAJA (VGBP4)

 

 

RIO TOA VACA                             8.0                 10/11                      *minor                     9.40          10/11     03:15

       

 

RIO MAJADA                              10.0                  10/11                      *minor                    11.46         10/11     04:55      

 

 

**  - NWS Forecast Point