Caribbean Water Science Center Science Plan 1999<

Hydrologic Hazards

According to Water Resources Division Memorandum No. 99.30 entitled “Priority Issues for the Federal-State Cooperative Program, Fiscal Year 2000”:

HYDROLOGIC HAZARDS--Economic losses from hydrologic hazards amount to several billions of dollars annually.  Monitoring the occurrence and magnitude of these extreme events and studying the basic processes underlying these hazards will lead to improving the ability to forecast probability of occurrence and likely magnitudes, and help prepare for and prevent disasters.  Increasing real-time access to streamflow data through telemetry at gaging stations and through improved presentation on the Internet remains particularly important for disaster preparedness.

The major hydrologic hazards in Puerto Rico and the U.S. Virgin Islands are floods, droughts, and landslides.  In the last ten years four hurricanes have struck the islands: Hurricanes Hugo, Marilyn, Hortense, and Georges.   The total damage in Puerto Rico from Hurricane Georges was estimated to be 1.9 billion dollars.  There have been three major droughts in Puerto Rico in this decade. In terms of loss of life, the worst landslide disaster in the history of the United States took place in Ponce, Puerto Rico.  In 1985, a tropical depression which later became Tropical Storm Isabel, dropped a total of 625 millimeters of rain in 24 hours.  A hillslope in Barrio Mameyes, saturated by this rainfall, failed and more than 120 people died as an entire hillside covered with homes slid downslope.

In response to these hydrologic hazards, the Caribbean District in cooperation with local government agencies has established a real-time hazard alert network.  The network consists of 129 hydrologic data-collection sites equipped with satellite telemetry instrumentation.  It includes streamflow, lake-stage, rainfall, and meteorological stations in Puerto Rico, the U.S. Virgin Islands, and, after Hurricane Mitch, three stations in Central America.

Most of the flood maps prepared in Puerto Rico by the USGS documented floods that occurred prior to the 1980’s.  Since almost all the flood plains inundated by these past floods have experienced topographic changes caused mainly by stream channelization and the construction of highways and levees the effect of these structures in the flood levels is unknown.  Consequently, new flood maps need to be prepared.

Information Needs and Deficiencies

1. The real-time hazard alert network needs to be expanded to cover other areas.   Most of the USGS rain gage network is located in valley bottoms at surface-water gaging stations.  New rain gages at ridge and hill top locations are needed.
   
   
2. Although good, the user interface of the real-time hazard alert network, could be improved to make it easily understood by the cooperators and the general public.
   
   
3. In Puerto Rico the correlation between flood levels and flood hazard zones is not well established.
   
   
4. Instrumentation is needed to monitor soil moisture during extreme hydrologic events and a methodology needs to be developed to determine landslide hazards.
   
   
5. Flood maps need to be prepared for future floods in flood plains where numerous changes to the topography have occurred.
   
   
6. Only limited assessment of landslide susceptibility has been completed in Puerto Rico and none has been completed in the U.S. Virgin Islands.

Program Opportunities

1. Expand the real-time hazard alert network to cover other areas in the Caribbean Region and Central America, as well as improve the topographic distribution of rain gages in Puerto Rico and U.S. Virgin Islands.
   
   
2. Continue to improve the user interface of the real-time hazard alert network for our cooperators and the general public through the internet.
   
   
3. Provide information to decision making agencies on the relationship of flood levels to hazard zones.
   
   
4. Install soil tensiometers at strategic telemetered locations throughout Puerto Rico and the U.S. Virgin Islands to measure soil moisture during hydrologic events and develop a methodology to determine landslide hazards.
   
   
5. Prepare flood maps after major floods.
   
   
6. Develop landslide susceptibility maps for Puerto Rico and the U.S. Virgin Islands at the municipality or quadrangle scale.

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