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COASTAL HAZARDS OF PUERTO RICO is sponsored by the University of Puerto Rico Sea Grant Program. The content of this site is compiled by Professor Aurelio Mercado and the site design and administration work by Harry Justiniano. Located at the Physical Oceanography Laboratory, Department of Marine Sciences, University of Puerto Rico at Mayaguez, Puerto Rico.

          

 

INTRODUCTION

The island of Puerto Rico, located in the northeastern Caribbean Sea region, is vulnerable to many natural hazards. The purpose of this site is to present most of the hazard mitigation work done related to natural coastal hazards in Puerto Rico, specifically those brought about by hurricanes, beach erosion, and tsunamis. In this page we present the available coastal flood maps for Puerto Rico for both hurricane and tsunami-induced flooding. This compilation of coastal hazards information was funded by UPR/SG project R-123-1-00. It is hoped that in the future we will also be able to present coastal erosion rates. (Click Menu Bar for downloads) 

THE HURRICANE COASTAL HAZARD

The hurricane coastal hazard is basically due to the storm surge, and the accompanying surface gravity waves forced by the hurricane winds. Note that we do not consider the hurricane force winds since this is not related with the ocean. 

The National Oceanographic and Atmospheric Administration (NOAA) has been able to obtain hurricane data in the North Atlantic basin since 1851, obviously with better accuracy in the data the more recently it has been obtained. Figures 1 to 5 show the tracks stratified by storm category (in the Saffir/Simpson scale) for all hurricanes between 1851 and 2004, passing within the red box shown in the figure (this, and the other figures shown below, were made using the Hurrevac 2000 program, John Townsend, Sea Island Software). The approximate coordinates of the box are: northward boundary at 19.65N, southern boundary at 16.65N, western boundary at 67.75W, and eastern boundary at 64.75W. These figures are shown just to give an idea of what recent history shows as the hurricane threat to the island. Not all of the hurricanes shown did damage to the island. Table 1 show the number of hurricanes, by category, which passed through the box in the time span of 1851 to 2004, a total of 154 years. 

Table 1: Number of Hurricanes Passing Through Box


Category
Number of Storms
1
14
2
12
3
6
4
5
5
2
 
Figure 1:  Category 1 hurricanes, 1851 - 2004
 
In order for the storm surge to be a threat to the island the storm has to literally make a direct hit to the island, that is, the island has to be under hurricane force winds at some point in time. The storm surge has three components:  
 
    1. Pressure setup - due to the low atmospheric pressure accompanying the storm, causing the water level to rise (inverted barometer effect). This is noticeable even in deep water. 
    2. Wind setup when the storm makes landfall, or almost landfall, to the right of it (looking along the direction of motion) the winds blow from sea to land, inducing a piling up of water against the coastline, and consequently, raising the sea level. 
    3. Wave setup and ponding due to waves crashing against the coastline and the consequent piling up of water; also due to the piling up of water on the landward side of fringing reefs. 

Figure 2 - Category 2 hurricanes, 1851 - 2004.

Back in the 1980's the Federal Emergency Management Agency (FEMA) sponsored an update of the so-called Flood Insurance Rate Maps (FIRM), a project that was finalized in 1990. The project involved using NOAA's SLOSH storm surge model to come up with the 100-year return period stillwater elevation for Puerto Rico and the U.S. Virgin Islands. The maps were finally made available in 1999 by the National Flood Insurance Program (NFIP). 
 
Mercado (2005) reviews what was done in order to obtain the 100-year stillwater elevation, and a summary of the work was published by Mercado (1994). Related with this topic, the link Mercado (2004; Criterios para la construccion en la zona costanera) gives a review (in Spanish) of the main requirements for construction in the coastal zone (mostly taken from FEMA's Coastal Construction Manual). 
 
The hurricane coastal hazard due to wind-driven waves is being investigated right now under a research grant from Sea Grant. In this project we are assessing how exposed are to hurricane wind-forced surface gravity waves the coastal infrastructure located inside Puerto Rico's and the US Virgin Islands most important bays, ports, and harbors.  Figure 6 shows the locations to be studied. Basically, the project consists of using the SWAN wave model (see http://fluidmechanics.tudelft.nl/swan/default.htm) to propagate wind waves from offshore towards the sites of interest. There will be wind forcing according to the hurricane category. Once the waves reach the bay/port/harbor entrance we may be able to continue with the SWAN model inside the bay/port/harbor, or we may need to continue the propagation with a phase-resolving model. We are as of this moment exploring the possibility of using the Danish Hydraulic Institute's MIKE 21 Boussinesq wave module, BW. An important input for these models is the bathymetry grid. For this study we are using a combination of recently-acquired SHOALS bathymetry and older National Ocean Survey (NOS) depth soundings available from http://poseidon.uprm.edu. The NOS data was acquired, and some of locally digitized from smooth-sheets, as part of another Sea Grant sponsored project (Mercado, A., 1994),  Digitization of National Ocean Survey Hydrographic Smooth Sheets for Puerto Rico and the U.S. Virgin Islands,  Sea Grant College Program, University of Puerto Rico, 116 pp). As soon as the project is finished, the results will be posted in this same page.

Figure 3 - Category 3 hurricanes, 1851 - 2004.
 
Figure 4 - Category 4 hurricanes, 1851 - 2004
 
Figure 5 - Category 5 hurricanes, 1851 - 2004
 
 
Figure 6 - Locations for wave assessment

THE TSUNAMI COASTAL HAZARD

As Lander et al. (2003) show, tsunamis are also a hazard that has to be considered as a reality in the Caribbean Sea region. They are very well described by the phrase “the forgotten hazards because of obvious reasons. In the Caribbean Sea region we are exposed to tsunamis due to submarine earthquakes, landslides (subaerial and subaqueous), and submarine explosions. The submarine explosion threat is due to the active Kick'em Jenny submarine volcano, located just north of the island of Grenada, at the southeast corner of the Caribbean Sea. Though possibly locally dangerous, it is not a threat to Puerto Rico. The subaerial landslide tsunami threat is also of no concern to the Puerto Rico because it is associated with the active volcanoes at some of the eastern Caribbean islands. Again, any tsunami due to material falling from land to sea in these islands will be only of local concern. But just north of Puerto Rico we have the Puerto Rico Trench, which really presents a submarine landslide tsunami threat to the north coast of the island. 

Henceforth, in Puerto Rico we have to the possibility of tsunamis due to earthquakes and landslides. Recognizing this latent threat, and the consequences it will have on our densely populated coastal areas, UPR/SG took the lead back in 1997 and sponsored the first Caribbean Tsunami Workshop, followed by a series of applied research projects that culminated in the establishment in 2000 of the Puerto Rico Tsunami Warning and Mitigation Program (PRTWMP). This program was sponsored during its first three years by FEMA and the University of Puerto Rico, and it is right now sponsored on a yearly basis by the Puerto Rico Emergency Management Agency and the University of Puerto Rico. A WEB page is available where all of the final reports related with the Puerto Rico tsunami mitigation effort are posted, and its address is http://poseidon.uprm.edu. A summary of the PRTWMP is given in Mercado (2005). Also, Mercado and McCann (1998) present a numerical simulation of the 1918 Puerto Rico tsunami in which observations of the runups of the 1918 tsunami are compared with results of the Japanese Tsunami Inundation Mapping for Exchange (TIME) tsunami model. It is the good match of observations versus simulation results that gives confidence on the use of the TIME model to prepare the flood maps for hypothetical earthquakes. 

For information about the tectonic setting of Puerto Rico please see the reports, and links, at http://poseidon.uprm.edu and the recent article by Mann et al. (2004). Recent reviews of the submarine landslide tsunami hazard existing along the Puerto Rico Trench is given by ten Brink et al., (2004) and Grindlay et al. (2005). 

The link http://poseidon.uprm.edu shows the flood maps due to tsunamis. Please see this site for an explanation of the three kinds of maps posted on the page, and for additional reports. 

THE PUERTO RICO COASTAL FLOOD MAPS

The purpose of this page is to put together all of the available coastal flood maps for the island. For this purpose we use ARC View and ARC Map, together with the following shape files: 

a) Shape files describing the limits of the 100-year storm, which is the one used for regulatory purposes by the federal and state governments. These were obtained from the Puerto Rico Planning Board (PRPB), and the coastal values are the ones obtained by Mercado (1994), with the exception of the Base Flood Elevations inside the V zone (or zone 1M according to the PRPB. It is important to understand the nomenclature used by both PRPB and FEMA, which is described in the following table. 


Zone (FEMA)
Zone (Planning Board)
Characteristics
V
1M
High velocity water flow due to wind wave action of 3 ft, or more, in height, propagating over the 100-year stillwater flood. 

Floodway Area in Zone A
1
100-year high velocity water due to riverine flow. 
A
2
Floodable by 100-year storm surge, river, or rainfall ponding, but with low velocity. 

 

It should be mentioned that the only difference between an A (or, 2) zone flooded by the sea alone (i.e., no riverine flooding) and a V (or, 1M) zone is that wave action in the V (1M) zone is deemed to be capable of producing structural damage. It should also be mentioned that it is erroneous to assume that a Zone 2 is flooded only by riverine, or rainfall ponding, waters. There are Zone 2 areas in Puerto Rico where the flooding is just due to the storm surge.

b) Shape files showing the inland limits of the expected storm surge due to Category 1, 3, and 5 hurricanes. These are the electronic version of the Hurricane Storm Tide Atlas for Puerto Rico, prepared by the US Army Corps of Engineers (CoE) for hurricane evacuation purposes. Some of these shape files were obtained from the CoE in Jacksonville, FL, others were locally digitized, and a few were digitized by the USGS in San Juan, P.R. For an explanation about how these maps were prepared see Mercado (1994), and Mercado (2005). 

c) Shape files showing the inland penetration of storm-wave swash along the north coast of Puerto Rico (F. K. Fields and D. G. Jordan, “Storm-wave Swash Along the North Coast of Puerto Rico: Hydrologic Investigations. Atlas HA-430, USGS, 1972). In this report a series of maps show the areas flooded by large waves generated by distant extra-tropical storms that battered the north coast in three major events during the period 1962-1967 and in one lesser event in 1968. The data in these maps was digitized and converted to shape files. The relevance of this swash data lies in the fact that it clearly shows that wave damage and flooding can also be produced by distant storms, something which happens almost on a yearly basis along the north coast of the island. These are only available for the north coast. 

d) Shape files showing the inland limit of tsunami flooding, which were prepared as explained in the Puerto Rico Tsunami Warning and Mitigation Program Web page, http://poseidon.uprm.edu

All of these shape files were overlaid over georeferenced IKONOS photos, obtained from the Puerto Rico Office of Management and Budget, and better known by its Spanish name of Oficina de Gerencia y Presupuesto (OGP). Where cloud cover is a problem, use was made of air photos, also from OGP, obtained for the Municipal Revenue Collections Center (CRIM – Centro de Recaudaciones de Impuestos Municipales - by its Spanish acronym).  

ACKNOWLEDGMENT

The project of gathering all of the available coastal flood inundation data an putting it into a single set of maps was kindly supported by the University of Puerto Rico Sea Grant Program. Help in the digitization of some of the hurricane evacuation maps was kindly supplied by the Center for Applied Social Research of the Department of Social Sciences of the University of Puerto Rico, Mayaguez Campus, the US Geological Service in San Juan, P.R., and the International Institute of Tropical Forestry, USDA Forest Service, San Juan, P.R. 

REFERENCES

Grindlay, N., R., M. Hearne, and P. Mann, 2005.  High risk of tsunami in the northern Caribbean. Ameri. Geophys. Union, EOS,  86(12):121-132. 

Mann, P.,  E. Calais, and V. Huérfano, 2004. Earthquake shakes “Big bend” region of North America-Caribbean boundary zone. Amer. Geophys. Union EOS, 86(8):77-88. 

Mercado, A., 1994. On the use of NOAA’s storm surge model, SLOSH, in managing coastal hazards: the experience in Puerto Rico. Natural Hazards, 10:235-246. 

Mercado, A., 2003. Criterios para la construcción en la zona costanera. Bolet­n Manrino, Programa Sea Grant, Abril-Junio, 3-8. 

Mercado, A., 2003. El Sistema de Alerta 

Mercado, A., 2005.  AEMEAD-2005-Technology & coastal flood mapping. Presented at XV Conferencia Anual para el  Manejo de Emergencias, May 25-28. San Juan, P.R. 

Mercado, A., and W. McCann, 1998. Numerical simulation of the 1918 Puerto Rico tsunami. Natural Hazards, 18:57-76. 

ten Brink, U., W. Danforth, C. Polloni, B. Andrews, P. Llanes, S. Smith, E. Parker, and T. Uozumi,  Amer. Geophys. Union EOS, 85(37):349-360

 

 
 

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