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Puerto Rico Coastal Hazards Mapping

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Title: Puerto Rico Coastal Hazards Mapping


1
Puerto Rico Coastal Hazards Mapping
  • By David M. Bush
  • State University of West Georgia

2
The original source of much of this information
is
Bush, David M., Bruce R. Richmond, and William J.
Neal, 2001. Coastal Zone Hazard Maps Eastern
Puerto Rico. Environmental Geosciences, 8(1), p.
38-60.
3
Puerto Rico Coastal Hazards Maps
  • Goalto develop a tool for quick visualization of
    multiple coastal hazards
  • A basis for hazard mitigation and management
    recommendations
  • To be of use to
  • Coastal planners
  • Managers
  • Property owners
  • Potential property owners

4
PR Shoreline Setting
  • Compartmentalized
  • Geologic/oceanographic processes and hazards can
    be considered on a compartment-by-compartment
    basis
  • Highly developed in places

5
Six Types of Hazards Considered
  1. Shoreline-setting hazards (long-term problems)
  2. Marine hazards (short-term impacts of storms)
  3. Earthquake and slope hazards (ground shaking,
    landslides, liquefaction)
  4. Riverine hazards (historical floods)
  5. Development hazards (high-density or dangerous
    settings)
  6. Engineering hazards (stabilization, nourishment,
    sand mining)

6
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8
A side-looking airborne radar (SLAR) image
clearly shows the physiography of the 150 x 50-km
island of Puerto Rico. Several small rivers
drain to the north, and the northern coastal
lowlands are wide compared to the southern.
Courtesy of Simulation Systems, Inc.
9
Natural Hazards(after Bryant, 1991)
  • Of the top 25 natural hazards, those affecting
    coasts
  • 2. Tropical cyclones
  • 6. Extratropical storm
  • 7. Tsunami
  • 8. Sea-level rise
  • 10. Beach erosion
  • 13. Ocean waves
  • 14. Localized strong wind
  • 15. Subsidence

10
Examples of Natural Hazards Affecting Puerto Rico
  • Landslidesfrom rainfall and earthquakes
  • Waves and surge from winter storms
  • Hurricanes and tropical storms
  • Rainfall
  • Overwash
  • Erosion
  • Flooding
  • Wind
  • Rainfall from tropical waves

11
NOAA satellite image of Hugo nearing Puerto Rico
12
Hugo 1989
Major hurricanes affecting Puerto Rico seem to
follow one of two main paths. Hugo is 13.
13
USGS figure of path of the eye of Hurricane Hugo
as it crossed the Virgin Islands and Puerto Rico
14
St. Croix
San Juan National Weather Service radar positions
of Hugos eye. Note irregular path of storm
center when viewed in detail. Also note the
deflection (loop) in the path which resulted in
an extended battering of St. Croix.
15
Direct wave impact on first row of buildings,
Condado area of San Juan
16
Sand washover along the Pi?ones shoreline after
Hurricane Hugo. An estimated 500,000 cubic
meters of sand was washed ashore along this
stretch (Bush, 1991).
17
Overwash from Hugo extended several kilometers
along the Puerto Rico shoreline and extended 10s
of meters inland. From Bush (1991).
18
Post-Hugo field study estimated storm surge along
several coastal reaches. From Bush, 1991
19
Hugo was a relatively dry hurricane and caused
only local flooding as here at the R?o de la
Plata mouth.
20
Hugo caused hundreds of small landslides in the
mountains of Puerto Rico.
21
USGS map showing landslide susceptibility in the
municipality of Comer?o, Puerto Rico.
22
Swell from North Atlantic winter storms cause the
largest waves hitting the northern coast of
Puerto Rico. Here are tracks of several storms
studied by Fields and Jordan (1972).
23
The 1991 Halloween Noreaster caused storm-wave
swash flooding and overwash along the northern
coast of Puerto Rico as here in Isabela. Photo
taken January 1992
24
Three Kings Day storm, 1992, Puerto Rico, 24-hour
rainfall totals for selected areas. From El Nuevo
D?a newspaper.
25
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26
Coastal Erosion
  • Another major natural hazard in Puerto Rico
  • Many ways to measure
  • A simple way is a geoindicators assessment
    (Bush et al., 1999)

27
Geoindicators of Erosion
  • Dunes scarped or breached
  • Bluffs steep with no talus ramp
  • Peat, mud, or tree stumps exposed on beach
  • Beach narrow or no high-tide beach
  • Overwash passes or fans
  • Vegetation ephemeral or toppled along scarp line

28
Geoindicators of Severe Erosion
  • Dunes absent with overwash common
  • Active wave scarping of bluffs or dune remnants
  • Tidal channels exposed in surf zone
  • Vegetation absent
  • Engineering structures now on beach or offshore

29
Geoindicators of Accretion or Long-Term Stability
  • Dunes and beach ridges robust, unbreached,
    vegetated
  • Bluffs vegetated with stable (vegetated) ramp at
    toe
  • Overwash absent
  • Vegetation well-developed from interior maritime
    forest, to dune shrubs, and pioneer beach grass

30
Erosion rates for Puerto Rico were calculated in
detail from aerial photography by Thieler and
Danforth (1993).
31
Beach and dune sand mining may be the greatest
contributor to coastal erosion in the Caribbean.
32
1977 photo of impact of beach sand mining in
Puerto Rico
33
Tap roots of pine trees left stranded by erosion
(1991 photo). Beach sand mining along the
Pi?ones shoreline in Puerto Rico to build the
international airport contributed to a severe
erosion problem culminating in a massive seawall
built in 2000.
34
Aerial view of Pi?ones area taken after Hurricane
Hugo (1989). Sand mining created a severe
erosion problem.
35
Artificial dunes were built in the mid 1980s to
combat the Pi?ones erosion problem. Swell from a
January, 1988 winter storm removed most of the
dunes. The poles had been covered by over 10
feet of sand.
36
Another source of erosion information in Puerto
Rico is a qualitative discussion by Morelock
(1978). White bars show his critical erosion
areas. XXXs are seawalls.
37
Condado Lagoon
As in many places, a major contributor to coastal
hazard problems is overbuilding at the coast.
Here is the Condado sector of San Juan.
38
La Perla
The walled city of Old San Juan sits safely high
atop an eolianite ridge A squatter development
called La Perla built outside the walls on the
slopes of the ridge places many homes and people
in a hazardous location.
39
Seismic Hazards
  • Puerto Rico sits amid several active Caribbean
    and Atlantic tectonic zones
  • Hazards include ground shaking, liquefaction
    potential, and tsunamis

40
Generalized tectonic setting. From McCann (1984)
41
From McCann (1984)
42
October 1918 Mona Passage earthquake, Modified
Mercalli Scale. From McCann (1984). Mercalli
Scale of V can be enough to cause liquefaction in
which case all major metropolitan areas of Puerto
Rico are at risk.
43
Damage in Mayag?ez from the 1917 earthquake.
Photo courtesy of the Puerto Rico archives.
44
Damage in Mayag?ez from the 1917 earthquake.
Photo courtesy of the Puerto Rico archives.
45
Modified Mercalli Scale from November 1867 Virgin
Islands earthquake.
46
Much of the metropolitan San Juan development is
on artificial fill emplaced before or without
strict codes or enforcement. A disaster waiting
to happen.
47
Tropical weathering provides unstable material
easily destabilized by ground shaking during an
earthquake or by intense rains.
48
Notches cut into the weathered hillside for home
sites create oversteepened slopes with increased
potential for landslides.
49
Some slope stabilization efforts have been
undertaken such as in this example from the
Luquillo National Forest.
50
Hazard Categories considered in coastal hazard
map preparation
  1. Shoreline Setting Hazards
  2. Marine Hazards
  3. Slope and Seismic Hazards
  4. Riverine Hazards
  5. Development Hazards
  6. Engineering Hazards

51
Hazard Categories
  • Shoreline Setting Hazardslong-term severe
    shoreline problems (e.g., erosion).
  • Marine Hazardsshort-term storm impacts (e.g.,
    waves, storm surge)
  • Slope and Seismic Hazardsareas prone to
    landslides during earthquakes and heavy rains
    (e.g., steep slopes, weathered rock), or prone to
    liquefaction during earthquakes (artificial fill)

52
Hazard Categories
  • Riverine Hazardsareas with historical floods,
    dams upstream, etc.
  • Development Hazardshigh-density development or
    low-density development in dangerous location
  • Engineering Hazardsshoreline engineering
    negatively impacting shoreline (e.g., breakwater
    blocking longshore sand movement) or areas where
    natural protection has been removed (e.g., beach
    or dune sand mining)

53
Methodology
  • USGS topographic quadrangle maps are used as
    bases
  • Quads were numbered moving clockwise starting in
    San Juan
  • Within each quad, the shoreline is divided into
    natural geomorphic units representing "reaches"
    or "stretches" (coastal cells or coastal
    compartments).

54
Methodology, continued
  1. The individual shoreline stretches are numbered
    sequentially
  2. Published data evaluated to determine hazards
    that have been, are, or could be active within
    each shoreline stretch
  3. If a hazard is present within only part of a
    stretch it is counted as one-half of a hazard

55
Methodology, conclusion
  • Each coastal stretch is designated a relative
    hazard rating based on the following
  • E Extrememore than 4 identifiable hazards
  • H High3 to 4 identifiable hazards
  • M Moderateat least 2 hazards
  • L Low1 or no hazard

56
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57
List of Coastal Hazards Maps
  • Map 1. San Juan
  • Map 2. Carolina
  • Map 3. Río Grande
  • Map 4. Fajardo and Cayo Icacos (west)
  • Map 5. Fajardo and Cayo Icacos (east)
  • Map 8. Vieques
  • Map 7/9. Punta Puerca and Naguabo
  • Map 10. Humacao
  • Map 11. Punta Guayanés
  • Map 12/13. Punta Tuna and Yabucoa
  • Map 35. Vega Alta
  • Map 36. Bayamón

58
A portion of the Carolina, PR quadrangle.
Shoreline stretches delineation begins on these.
59
Carolina, PR, geologic quad. Shoreline stretches
easily identifiable between rocky headlands
(Quaternary eolianite, Qe).
60
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61
USGS Hydrologic Atlases provide data on
historical flooding such as this from Haire
(1975). Shades of blue represent different
floods.
62
Incursion of marine waters from storm surge and
storm-wave swash is a hazard especially on the
northern coast.
63
Historical storm-wave swash coastal flooding
caused by swell from North Atlantic winter
storms. Mapped by Fields and Jordan (1972).
64
Storm surge from Hurricane Hugo was minimal, but
enough to ground this ferry in Fajardo.
65
Their ship has come in!
66
Storm surge potential in Puerto Rico is
relatively low because of the narrow, steep
insular shelf. Surge from Hugo was typically
about 1.5 meters shown here to scale on two
typical shoreline types found in Puerto Rico.
Thus, storm surge flooding is not normally a
major problem.
67
A portion of the Carolina, PR, Coastal Hazard Map.
68
A portion of Coastal Hazard Map 36. Bayamón.
69
The portion of Coastal Hazard Map 1, San Juan.
70
Conclusions
  • Hazard maps compile already existing data
  • Maps allow at-a-glance visualization of important
    processes
  • Spreadsheet compiles existing or easily measured
    parameters
  • Can be expanded or altered to suit local needs
  • Low cost

71
El Morro Fort guards the entrance to San Juan
Harbor
72
References Cited
Bush, David M., 1991, Impact of Hurricane Hugo on
the Rocky Coast of Puerto Rico, (in) Finkl,
Charles W., and Pilkey, Orrin H., (eds.), Impacts
of hurricane Hugo September 10-22, 1989,
Journal of Coastal Research, Special Issue 8, p.
49-67. Bush, David M., William J. Neal, Robert S.
Young, and Orrin H. Pilkey, 1999. Utilization of
Geoindicators for Rapid Assessment of
Coastal-hazard Risk and Mitigation, Ocean and
Coastal Management, vol. 42, no. 8, p.
647-670. Bush, David M., Bruce R. Richmond, and
William J. Neal, 2001. Coastal Zone Hazard Maps
Eastern Puerto Rico. Environmental Geosciences,
8(1), p. 38-60. Bryant, E.A., 1991. Natural
Hazards. Cambridge University Press, 294
p. Fields, F.K., and Jordan, D.G., 1972,
Storm-wave swash along the north coast of Puerto
Rico U.S. Geological Survey Hydrologic
Investigations Atlas H.A. 432, in two sheets.
Haire, W. J., 1975. Floods in the Carolina-Rio
Grande area, northeastern Puerto Rico. U. S.
Geological Survey Hydrologic Atlas HA-533, 1
sheet. McCann, W.R., 1984, On the earthquake
hazard of Puerto Rico and the Virgin Islands In
Workshop on Geologic Hazards in PR, April 4-6,
1984, San Juan, PR U.S. Geological Survey
Open-File Report 84-761. Thieler, E.R. and
Danforth, W.W., 1993. Historical Shoreline
Changes in Puerto Rico, 1901-1987. Reston,
Virginia U.S. Geological Survey Open-File Report
No. 93-574, 267 p., 39 plates
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