Review the Topographic Map of Hazard City Where Is the Steepest Land of the Town Located?

SUMMARY

This chapter presents the concept of multiple hazard mapping, describes the benefits of using multiple hazard maps relative to individual hazard maps, and explains the preparation and utilize of such maps.

When an area is exposed to more than than 1 hazard, a multiple take chances map (MHM) helps the planning team to analyze all of them for vulnerability and risk. By facilitating the interpretation of hazard information, it increases the likelihood that the information will be used in the controlling process. In either the planning of new development projects or the incorporation of hazard reduction techniques into existing developments, the MHM can play a role of great value.

In this chapter, the MHM discussed is primarily for utilize in an integrated development planning study.

The master purpose of MHM is to gather together in one map the different hazard-related data for a study surface area to convey a composite moving picture of the natural hazards of varying magnitude, frequency, and area of effect. A MHM may also be referred to equally a "composite," "synthesized," and "overlay" take a chance map. One area may suffer the presence of a number of natural hazards. (Figure six-1 is a tabulation of natural phenomena that can be considered for presentation on such maps). Using individual maps to convey information on each hazard can be cumbersome and confusing for planners and decision-makers considering of their number and their possible differences in area covered, scales, and detail.

Many natural hazards can be acquired by the same natural event. The inducing or triggering mechanism which can interconnect several hazards can more easily be seen through the use of a MHM. Characteristics of the natural phenomenon and its trigger mechanisms are synthesized from dissimilar sources and placed on a single map.

Additionally, the effects and touch on of a single take a chance result, as in the example of volcanoes and earthquakes, include different types of impacts, each having unlike severities and each affecting different locations.

The MHM is an excellent tool to create an sensation in mitigating multiple hazards. It becomes a comprehensive belittling tool for assessing vulnerability and chance, peculiarly when combined with the mapping of disquisitional facilities as discussed in Chapter 7.

The adoption of a multiple hazard mitigation strategy too has several implications in emergency preparedness planning. For example, it provides a more equitable basis for allocating disaster planning funds; stimulates the use of more than efficient, integrated emergency preparedness response and recovery procedures; and promotes the creation of cooperative agreements to involve all relevant agencies and interested groups: It must exist emphasized that the MHM will not run across the site-specific and hazard-specific needs of project engineering design activities.

The effective use of natural hazard information to avoid impairment or to reduce loss requires a considerable try on the role of both the producers and the users of the information. Unless the scientific and engineering information is translated for the layman, the effective user community is limited to other scientists and engineers. If the users do non become adept in interpreting and applying technical information, the information is likely to be misused or even neglected in the development planning process. Studies past Kockelman (1975, 1976, 1979) on the use of globe-science data by urban center, county, and regional planners and conclusion-makers in the San Francisco Bay region of the Usa testify that the most effective utilize of hazard information is achieved when maps clearly depict the likelihood of occurrence, location, and severity. Furthermore, risk reduction was more likely when agencies had scientists or engineers on their staffs. Their skills permitted a broader utilise of the technical data, and the agencies were able to make interpretations of the information for their own purposes.

Effigy 6-i EXAMPLES OF NATURAL PHENOMENA WHICH MAY BE Hazardous

Atmospheric

Hailstorms
Hurricanes
Lightning
Thunderstorms
Tornadoes
Tropical storms

Volcanic

Ashfalls
Gases
Lava flows
Projectiles and
lateral blasts
Pyroclastic flows
Tephra (ashes, cinders, lapilli)

Hydrologic

Littoral flooding
Desertification
Drought
Erosion
River floods
Storm surges

Other Geologic

Droppings avalanches
Expansive soils
Rockfalls
Submarine slides
Subsidence

Seismic

Mistake ruptures
Ground shaking
Lateral spreading
Liquefaction
Seiches
Tsunamis

Wildfire

Brush
Forest
Savannah
Urban conflagration

B. PREPARING MULTIPLE HAZARD MAPS

1. Translated Information
two. Sources and Compiling Information
3. Timing

A prerequisite to compiling private hazards information onto one map is obtaining or creating a base of operations map upon which to identify this information. Characteristics and examples of such base maps are discussed in the side by side section, on map format. The base map is usually selected during the preliminary mission; the squad needs only to select a calibration appropriate to the written report area. This initial map also may serve as an alphabetize to more detailed hazard maps. Several base maps at different scales may be used, depending upon the final written report area or areas and the predominating calibration of the individual adventure maps. The most detailed individual hazard map may be selected every bit the base of operations if information technology provides adequate geographic orientation. The base of operations map used for an MHM can exist the same as that used for the critical facilities map described in Chapter 7.

one. Translated Data

Much hazard information will exist in the form of scientific investigations into the process and prediction of a potentially hazardous event and observations of the impact of past events (Du Bois, 1985), such as volcano inventories and records of flood crest elevations. It is frequently in forms other than maps. This information, although a prerequisite to an MHM, is non readily understood by the layman. It must exist "translated" for planners and conclusion-makers and placed on maps.

Successful translation must exist in a format that a planning team tin can understand. Only fifty-fifty more important, the information must be perceived every bit explaining a chance that may adversely impact life, property, or socioeconomic activities. This can be accomplished by providing iii elements-location, likelihood of occurrence (frequency or return period), and severity. A planner or decision-maker evaluating a specific land use, construction, or socioeconomic activity is not ordinarily interested in a potential event whose (i) occurrence is not expected for a very long time, (2) location is not known, or (3) size or upshot is not bully. These elements vary with the phenomenon, for example:

- Coastal areas annually exposed to winds of specific velocity and storm surges of specific runups.
- Floodplains and floodways which volition be impacted past specific velocities and water heights from rainfall duration and intensity having a fifty-year recurrence interval.

- Fault rupture zones, liquefiable geologic materials, and landslide-susceptible areas having significant vertical or horizontal displacement by a postulated earthquake of a specific magnitude with a likelihood of occurring within the next one- or two-hundred-year menstruum.

BENEFITS OF MULTIPLE HAZARD MAPPING

- A more than concise focus on the effects and impacts of natural phenomena on a particular area is possible during early on planning stages.

- Many hazards and the trigger mechanism of each tin can exist viewed at the aforementioned fourth dimension. Common reduction or mitigation techniques can be recommended for the same portion of the study expanse. Inadequate or missing take a chance information (location, severity, or frequency) can be more easily identified.

- A study area or a sub-surface area tin can be expanded, reduced, or deleted. Study areas can be divided into sub-areas requiring more information, additional assessments, or specific reduction techniques.

- More than realistic evaluation of risks to new development are possible.

- Appropriate gamble reduction techniques tin can be more easily built into the investment project formulation.

- Selection of appropriate land uses can become more rational.

Figure half-dozen-2 illustrates the types of information needed. All three elements may not be available for all hazards. In compiling an MHM it is just equally important to know what is missing. More information can be sought or prepared, just at least those evolution and investment decisions existence based on less than adequate information should be noted.

It is too important to distinguish between a hazard that can be defined as not present versus one whose presence cannot be properly evaluated because of limited information. For instance, a conservative arroyo to development because of "inadequate" take chances information can be counterproductive over time. If the planner's or decision-maker'due south response to an "exaggerated" potential hazard is to avoid the area or recommend expensive resistive design, a brownie trouble will occur when a "realistic" potential gamble is discovered.

There is a vast array of sources of hazard data, including various public and private libraries, offices and reference centers at international, national, regional, and customs levels. These entities may exist concerned with infrastructure, community facilities, economical evolution, resource exploration, land use planning, emergency preparedness, geotechnical studies, disaster response, and many other activities. Sometimes these sources coordinate their compiling of chance information, but information technology cannot always be expected. Many of the users of development planning information are as well compilers of natural run a risk information. Tinsley and Hollander (1984) have compiled a list of governmental earth-science agencies and selected major international organizations whose functions are similar to those of the U.S. Geological Survey.

Some adventure information tin can be extracted or inferred from photographic, topographic, geologic, hydrologic, climatologic, and soils information already prepared for settled regions. Chapter 10 of this primer, on landslide run a risk mapping, suggests local authorities responsible for public works, forestry, and agricultural activities equally being valuable sources of information because of their familiarity with past issues.

The System of American States (1969) in its casebook on physical resource investigation for environmental development cites suggestions for obtaining information on hazards. These include existing resource surveys; aerial photography; personal reconnaissance; exploratory, reconnaissance, semi-detailed, and detailed surveys; aeriform photography, orthophotos, and photogrammetric mapping; geologic surveys; alluvion studies; and soil erosion surveys.

Gamble information may also be obtained from remote sensing information (run across Chapter 4). Various sources of data on floods, desertification, earthquakes, landslides, and other natural hazards are given in Appendix A and Capacity 8 through 12.

CHARACTERISTICS OF INFORMATION NEEDED TO ASSESS NATURAL PHENOMENA

- Location
- Likelihood of occurrence
- Severity

Figure vi-2 - EXAMPLES OF THE TYPES OF Data NEEDED TO Appraise THE Take a chance POTENTIAL OF NATURAL PHENOMENA

	EARTHQUAKE	LANDSLIDE	HURRICANES	RIVER FLOODS
LOCATION	Epicenters	Inventories	Landfall	Aqueduct
	Geologic formations	Geologic formations	Path	Floodway
		Slope		Floodplain
				Elevation
SEVERITY	Intensity	Velocity	Current of air velocity	Volume
	Magnitude	Deportation	Rainfall	Velocity
	Acceleration			Rate of ascent
	Displacement
LIKELIHOOD OF OCCURRENCE	Recurrence interval	Earthquake recurrence	Historical occurrence	Historical return periods
	Sideslip rates			Flood of record
	Historical seismicity	Rainfall patterns		Blueprint result
		Bank cutting rates

Compiling information from these diverse sources includes four steps: collecting, evaluating, selecting, and combining, as described in the box beneath.

The overview of natural hazards by Bender (1986) for the St. Kitts and Nevis project provides an case of a preliminary evaluation of available take a chance information based on readily available information. The Santiago-Mira study (OAS, 1984a) demonstrates the importance of getting a "quick picture of the region's development bug. This involved sending an 'advance human' to the study surface area to make up one's mind the primary problems and identify experienced local technicians."

Chapter x includes recommendations which are applicable to all hazards, not only to landslides: initial consultation with technical specialists, identification of hazards early on in the planning process, and an initial review of the type and content of bachelor information. Because of the toll and time in compiling information to brand an MHM, consideration should be given to collaborating with other users.

The drove of general chance information began years agone as function of development assistance agency programs. Within electric current OAS project procedures, the collection of specific take chances information begins when a member land makes a formal request for technical assistance and continues through the integrated development planning process (run into Affiliate 1). Sending a ii-person team to the field for 2 weeks for a quick data drove attempt represents a relatively depression-cost method for initiating collection of specific natural hazard information (OAS, 1984a).

COMPILING Information ON MULTIPLE HAZARDS

- Collecting base maps and appropriate risk information from the various sources identified in this book

- Evaluating the uniformity, accurateness, and completeness of such information-areal coverage, detail, content, elements (likelihood, location, and severity), format, and symbols.

- Selecting the most appropriate base of operations map and scale to be used, hazards to exist shown, and symbols to portray those hazards.

- Combining the selected individual take a chance information onto the MHM in an accurate, clear, and convenient fashion.

During the preliminary mission, hazard information collection can exist accomplished by:

During subsequent study stages, the general criteria for data collection should emphasize:

- Striving for the same level of detail.
- Answering specific questions nearly development problems.
- Using national institutions as sources.
- Drawing on local do experience.-
- Identifying projection ideas (or mitigation techniques).
- Using local research institutions and universities.
- Keeping descriptions to a minimum and emphasizing analysis.

C. MAP FORMAT

1. Base Map
2. Calibration and Coverage
3. Hazards to be Shown
4. Types of Symbols

Maps are the almost effective way to convey actual and relative location. Maps can be simply defined as apartment geographic portrayals of information through the use of symbols. A good introduction to types and content of maps, data overlays and extractions, and country utilise and land cover mapping may be seen in the Coastal Mapping Handbook (Ellis, 1978). Such approaches assist the MHM not only convey that natural hazards be, but besides to annotation their location, severity, and likelihood of occurrence in an accurate, clear, and convenient manner.

The area covered, scale, detail, hazards shown, and format of a MHM can range widely:

- Globe: i:thirty,000,000
- Continent: 1:5,000,000, 1:ii,000,000
- Region: 1:500,000, 1:200,000, one:96,000, one:fifty,000
- Community or settlement: 1:24,000, i:12,000
- Building sites: 1:10,000, 1:2,500

It has been said that the usefulness of a map is in its omissions. Except for its orientation information (roads, rivers, coastlines, place names) the map should exist as uncluttered and stripped down as possible. Natural hazards are the information to be emphasized.

Discussion of the of import aspects of MHM follows: base map, scale and coverage, hazards to exist shown, and types of symbols to be used. References are fabricated to nine examples (Figures half dozen-iii through 6-11) which may appear deceptively elementary. Two are in color, one is computer-generated, one shows merely two hazards while others testify many, some stand solitary while others are accompanied by extensive explanations.

1. Base Map

Creating a base map from scratch is a hard and fourth dimension-consuming task; therefore, it is desirable to utilize an existing map or controlled photograph as a base. An adequate base map must be planimetric, that is, a representation of information on a aeroplane in true geographic relationship and with measurable horizontal distances; and must have sufficient geographic reference information to orient the user to the location of the hazard. The top of a map is usually oriented to the north, but non always. Hence, a "north arrow" on each map canvass is mandatory.

Discussion of geographic referencing systems such every bit longitude and latitude, state airplane coordinate systems, or Universal Transverse Mercator (UTM) grid systems is beyond the telescopic of this chapter. Many different projections are suitable and an indication of the map projection used as well as an insert map showing the location of the study area is very helpful.

Figures vi-3 through 6-11 are all planimetric maps, and each has sufficient reference information for the scale and area covered. For example, the map of the world (Figure half dozen-3) shows national boundaries and major cities; other maps show highways and rivers; some fifty-fifty show local street names and building site boundaries (Figure 6-11).

Sometimes a base map is available that shows hypsography, that is, elevations of country higher up bounding main level (Figure half-dozen-nine). These maps are sometimes chosen "topographic" or "contour line" maps. The elevation and profile data tin be interpreted to help present the location and severity of flood, landslide, fault rupture, hurricane, and other potential hazards. Cadastral (belongings ownership boundary) maps can be fantabulous base maps, although they often have a scale larger than is needed for regional evolution planning. Controlled aerial photographs, photograph maps, radar images, and satellite photography tin also exist used for base maps.

2. Scale and Coverage

Map scale is the mensurate of reduction in size from the actual environs to that portrayed on the map. The scale tin be expressed as a ratio between the map distance and the actual altitude. For instance, the calibration on Figure 6-5 is one:500,000 which means that 1 centimeter on the map equals 500,000 centimeters (or 5,000 meters or v kilometers) on the ground. Large-scale maps show less detail for a large area.

Larger scales are more than common for regional development planning (1:500,000 through 1:50,000; Figures half dozen-five through 6-nine), and customs evolution plans (i:24,000 through i:12,000; Figures half-dozen-10 and six-11). The scale selected will depend upon the map'southward purpose. There are no best scales, but more appropriate ones to coincide with planning requirements.

The calibration used for an MHM is dependent upon not simply the gamble information to be shown but as well upon the calibration of the base of operations map. If a choice of scales is bachelor, then the following factors become important in making the option:

- Number of hazards to be shown.
- Hazard elements to be shown.
- Range of relative severity of hazards to be shown.
- Area to be covered.
- Use of the map in conjunction with other planning documents.
- Role of the map; for example, whether it is to be an index or detail map.

Often the individual adventure maps to be used are at unlike scales. This may crave an enlargement or reduction to the scale of the base map selected. Utilise of controlled photographic or computer mapping methods makes this procedure easy and accurate.

iii. Hazards to be Shown

Any number of hazards tin can exist shown, depending upon scale, symbols, and coverage chosen. On a i-sheet topographic base map (Effigy vi-ix), simply flood and landslide hazards are shown. On the 5-sheet map (Figure 6-10), several hazards and thirteen zones of geologic materials are shown. This dense gamble information is then supplemented by ii sheets of explanations. To avoid overcrowding, hazards tin can be combined manually (Effigy 6-viii), or by computer (Figure vi-7), and into regulatory zones (see Chapter 7).

four. Types of Symbols

Everything shown on an MHM besides as the base map is a symbol representing reality. Symbols are selected for their legibility and clarity and/or map production characteristics; for example, creative (Figure 6-iii), numerical (Figures 6-iv and 6-x), convention (Figures 6-five and 6-vi), computer printout (Figure six-7) innovation (Effigy six-8), resemblance to flooding (Figure 6-9), or ease of regulations (Figure 6-11).

Some symbols may convey a sense of the chance (Figure vi-v); others are totally abstract (coastal hazards in Figure 6-8). Some symbols represent derived combinations of hazards (geologic trouble index in Figure 6-vii) or hazards combined for ease of reading (see Affiliate 7).

Likelihood of occurrence or frequency can be shown by isolines to represent the number of thunderstorm days per year (Figure 6-3) or to split up areas of landslide frequency (Effigy 6-9). Areas take been used to show maximum seismic intensity in 50 years and the number of tropical storms and cyclones per year (Figure half-dozen-three), and flooding in 100 years (Figure 6-9).

Location can exist shown through the employ of basic geometric symbols-a indicate, a line, or an area. For example, points take been used to show tornadoes and volcanoes (Figure half-dozen-iii); lines have been used to show preferred tracks of tropical storms (Effigy 6-3), fault rupture (Figures six-10 and 6-11), or tsunamis (Figure 6-3); and areas take been used to testify flooding, landslides, or erosion zones (Figures 6-5 and vi-vi).

Figure half-dozen-3 - World map of natural hazards

Source: Munchener Ruckversicherungs-Gesellschaft. Earth Map of Natural Hazards, scale 1:30,000,000. (Munich, Federal Republic of Germany, 1978). Permission to publish.

Figure 6-4 - Maximum Earthquake map of South America

Source: Adapted from Regional Seismological Centre for Southward America (CERESIS). Maximum Intensity Map of Southward America. (Santiago, Chile: CERESIS, 1985).

Figure 6-5 - Natural Hazards map of the Paraguyan Chaco

Source: Adapted from OEA. Proyecto de Desarrollo Urbano Paraguayo, Mapa de Riesgos Naturales del Chaco Paraguayo, Area de Programa iv-C (Washington, D.C.: Organization of American States, 1985).

Severity can be shown equally points, although lines are more often used, for example, to bear witness equal numbers of winter gales (Figure half-dozen-3), relative severity of coastal hazards (Figure 6-xi) or coastal erosion (Figure 6-10). Areas have been used to betoken severity, such as maximum seismic intensity (Figure 6-4), or a combination of hazards (Effigy half dozen-7). In addition, areas tin can be used to prove requirements or recommendations for further study, for example, site investigations to determine fault rupture location (Figure half-dozen-11) or geotechnical investigations prior to development (see Affiliate vii).

Innumerable variations of points, lines, and areas are available to the maker of an MHM. Lines tin can be solid, long-dashed, brusque-dashed, or composed of points and question marks equally conventionally used past geologists in mapping inferred faults (see Figure vi-10 and Affiliate 7). Areas can exist shaded (Figures 6-4 and half-dozen-11), patterned (Figures 6-5,6-6, and 6-seven) colored (Figure 6-3 and 6-four) or patterned and colored (see Affiliate 7). Examples of the diverse representations of points, lines, and areas may be seen in Effigy 6-xi. A thorough discussion of graphic pattern is found in Robinson, Sale, and Morrison (1978).

D. OTHER FORMS OF MULTIPLE HAZARDS Information

1. Cross section of Effects
2. Photographs of Damage
three. Atlas of Hazards
4. Plan for Reducing Hazards
5. Analyses of Land Capability
half dozen. Unmarried Event with Multiple Hazards
7. Series of Strip Maps
8. Photo Maps
nine. Geographic Information Systems
10. Data Processed by Figurer

The foregoing discussions and examples have addressed ane class of the MHM, mainly the single-sheet planimetric map combining several hazards with relatively simple explanations. This form of MHM may not always exist the nearly suitable. Other forms of the multiple hazards information may provide increased coverage, greater detail, or more hazards. Sometimes information helpful to making a development or investment decision is already available, for example, cost estimates, graphic evidence of damage, or take chances reduction suggestions. Information in a form processed or capable of being processed past calculator may be available. Examples of some of these other forms follow.

one. Cross section of Furnishings

1 form for showing severity is by means of a cross section through an affected surface area. Yet, to be useful to planners and conclusion-makers, it must be accompanied past a planimetric map showing the area! extent of the hazard. For case, the geologic effects of fault rupture, basis shaking, seismic sea wave flooding, liquefaction, and landsliding were predicted for a recurrence of a magnitude six.v convulsion. The hazards are shown on regional scale map sheets (1:125,000) and the severity is indicated by a cross department (Figure six-12) at a horizontal calibration of 1:150,000 in Borcherdt (1975).

ii. Photographs of Damage

The use of photographs of actual damage is an excellent technique for communicating a general awareness of the effects of hazards. They can besides be used to illustrate the specific furnishings of hazardous phenomena. For example, Hays (1981) uses photographs of buildings seriously damaged by flooding, hurricanes, landslides, and subsidence that occurred throughout the United States. Ziony (1985) uses photographs of structures such as hospitals, highway overpasses, electric power stations, and dams that failed or were seriously damaged by diverse earthquake furnishings-ground shaking, fault rupture, liquefaction, landslides, and tsunamis. Steinbrugge (1982) uses numerous photographs of damaged buildings, failed structures, and disrupted building use caused by earthquakes, landslides, tsunamis, and volcanoes. Photographs of bodily damage acquired by a specific type of outcome can be keyed to an MHM to show where similar damage has occurred.

iii. Atlas of Hazards

A presentation of several hazards in an atlas class provides greater opportunity for discussions, diagrams, photographs, recommendations, and references. For example, geologic and hydrologic hazards caused past seismic, atmospheric, or volcanic phenomena are mapped at scales of approximately ane:twenty,000,000 or larger. The maps are accompanied by diagrams of the processes, discussions of loss trends, photographs of damage, and suggested reduction techniques in the report past Hays (1981).

4. Program for Reducing Hazards

Sometimes multiple take a chance information is in the grade of a hazard reduction programme which includes information on individual hazards. For case, the nature, magnitude, and costs of basis shaking, landslides, flooding, erosion, expansive soils, mistake rupture, volcano, tsunami, and subsidence hazards are discussed in a report past Alfors and others (1973) for an entire country. Maps of each gamble at a calibration of one:5,000,000 are accompanied past loss-reduction recommendations which include mapping of the hazards and enquiry into their processes.

Figure 6-vi - Landslide and overflowing risk map for Jubones, Commonwealth of Ecuador

Source: Adapted from OEA. Plan Hidráulico del Jubones, República del Republic of ecuador, Vol. Sick, Mapa three-A12. (Washington, D.C.: Organization of American States, 1984).

Figure 6-seven - Computer-Generated map summarizing several hydrologic, seismic, and other geological hazards - Geologic problems alphabetize (GPI)

Source: Adjusted from Santa Barbara County Planning Department. Seismic Condom and Safety Element. (Santa Barbara, California: Santa Barbara County Planning Department, 1979).

Figure 6-8 Coastal risk map for Saint Lucia

Source: Adapted from OAS. Saint Lucia Littoral Hazard Map. (Washington, D.C.: Organisation of American States, 1984).

Figure half dozen-9 Natural Hazards map for the Republic of Honduras

FLOOD Risk Information

The expanse prone to floods represents approximately 100-year issue, that is, in a given year at that place is a ane percent probability that this effect will occur. The information was based on Landsat data (MSS), orthophotomaps (scale 1:x,000) and field observations. Certain zones inside the surface area which are not prone to floods are not delimited because the 20m contour interval does non allow the identification of the high zones in the coastal apparently.

LANDSLIDE RISK INFORMATION

The areas of frequent versus exceptional landslide occurrence are delimited by isolines of points where the landslides cover one percent of the surface. Areas with less than one pct of coverage are designated "infrequent," and areas with more than one percent of coverage are designated "frecuente."

Source: Adapted from OEA. Proyecto de Desarrollo, Islas de Bahía-Atlántida, República de Republic of honduras, Mapa de Riesgos Naturales. (Washington, D.C.: Organization of American States, 1985)

Figure six-x - Geotechnical chance synthesis map

Legend: The explanation for this map is complex, combining data on geologic processes, such as faulting, landsliding, coastal erosion, and liquefaction, with information on geologic materials, shown past numbers on the map. The material units are farther subdivided by both seismic and engineering characteristics. For example, areas designated "2b" are underlain by alluvial fan deposits ranging in coarseness from silt to gravel, have poor to fair slope stability, moderate liquefaction potential, skilful to fair stability in terms of the intensity of ground shaking during a 7.v-viii.3 in earthquake, and have good foundation properties.

Source: Adapted from San Mateo County Planning Department and Leighton and Associates. Geotechnical Hazards Synthesis Map (San Mateo County, California: San Mateo Planning Department and Leighton and Associates, 1974).

NATURAL HAZARD INFORMATION AND Display SYMBOLS
SYMBOL	Convulsion	Hurricane	Rood	Landslide	Volcano
Bespeak	Epicenter site	Landfall mensurate	Row site	Landslide site	Volcano
LINE	Mistake	Path	Rood elevation	Direction of slide	Direction of lava flow, ash, or gas
Expanse	Seismic intensity	Storm surge	Rood-prone expanse	Landslide-decumbent area	Coverage of ash, gas or lava flow

The additional costs required to reduce a hazard (and thus overcome a constraint to development) tin can be crucial information for a lender or donor. For instance, a method of evaluating country-use proposals by estimating the "social" costs that are attributed to hydrologic, seismic, and other geologic characteristics is described past Lard et al (1979) and is accompanied by composite maps for a sit-in area (1:125,000). Costs are computed from a consideration of reduction techniques, probability of future impairment, or lost opportunities. Toll is expressed in current dollars, and therefore provides a mutual basis for evaluating and comparing different state uses and different constraints and resource. Constraints to development include ground shaking, fault rupture, tsunamis, seiches, landslides, fault pitter-patter, avalanches, stream flooding, subsidence, liquefaction, expansive soils, erosion, and volcanic activity. Resources include minerals, construction materials, energy, water, soil, and scientific and educational sites.

6. Single Issue with Multiple Hazards

Information technology should be remembered that the effects of a single event, as in the case of volcanoes and earthquakes, tin can include diverse hazards, each having unlike severities and each affecting different locations. The consideration of i event, then, should result in the assessment and mapping of several hazards. Hazard zones for lava flows, ash clouds, lateral blasts, and mudflows are mapped at 1:62,5000 for a potential volcanic eruption by Miller (1980).

vii. Series of Strip Maps

Sometimes a physiographic province-uplands, lowlands, or coastlands-is used every bit the footing for mapping, and various hazards within that province are assessed. For instance, xi hundred miles of Pacific Ocean coastline are mapped (1:l,000 to 1:100,000) and divided into three run a risk zones reflecting diverse combinations of littoral erosion-cliff retreats, slumps, bluff collapses, landslides, rockfalls, seawall breaches, moving ridge-thrown debris, world flows, tsunamis, and storm surges - by Griggs and Savoy (1985). (Run into Chapter 7.)

8. Photo Maps

Orthophotos, stereoscopic photographs, and photographs with some topographic data are invaluable to an experienced interpreter. These maps can be used not only as base maps but to accurately locate potential hazards. For case, floodplain boundaries during high water, contempo storm damage paths, fault rupture zones, or past landslides can be seen on photographs. This data sometimes can exist interpreted to obtain location and severity.

9. Geographic Information Systems

The nature and capability of geographic information systems (GIS) provides an excellent basis for processing and presenting information in a map form (Bender et al., 1989). Natural hazards can be the data that is processed and presented. For example, liquefaction potential, relative state surface stability during earthquakes, 100-and 500-year inundation zones, and potential surface rupture were entered into a GIS from original data at a scale of 1:24,000 past Alexander et al. (1987) to demonstrate the utilize of digital mapping technology for reducing natural hazards. (Run into Affiliate 7)

Figure vi-xi - CADASTRAL MAP SHOWING GEOLOGIC AND SEISMIC HAZARDS

Legend: Shaded expanse indicates a zone where site investigations are required considering of an active or potentially active mistake. Letters indicate specific hazards that demand to be investigated and evaluated: Dr, surface area of high potential for ground displacement; Ds, area of high potential for earthquake-induced landslide; Due east/F, areas of depression to moderate potential for whatsoever geologic hazard.

Source: Adapted from Santa Clara County Department of Land Development Engineering and Surveying. (San Jose, California: Santa Clara County Section of Land Evolution Engineering and Surveying, 1977).

Effigy vi-12 - CROSS-Section SHOWING PREDICTED GEOLOGIC Effects OF A POSTULATED EARTHQUAKE MAGNITUDE half dozen.5 ON THE SAN ANDRES Mistake

Legend: The severity of each earthquake effect is indicated qualitatively by thickness of underlining and quantified to the extent permitted by the current state of the fine art for seismic zonation on a regional scale (non shown). The severity of the predicted convulsion effects generally depend on the type of underlying geologic material.

Source: Borcherdt, R.D. (ed.). Studies for Seismic Zonation of the San Francisco Bay Region, U.S. Geological Survey. Professional Newspaper 941-A. (Reston, Virginia: U.S. Geological Survey, 1975).

Figure 6-thirteen - COMPUTER-GENERATED MAP SHOWING SUSCEPTIBILITY TO LIQUEFACTION Run a risk

Legend: The white areas and lighter patterns within the computer-assay area boundary bespeak low problem ratings. The darker areas indicate moderate problem ratings. No high trouble areas are included in the surface area shown.

Source: Adapted from Santa Barbara Canton Planning Section. Seismic Safety and Condom Elements. (Santa Barbara, California: Santa Barbara County Planning Department, 1979).

x. Data Processed by Figurer

Computer mapping techniques are discussed in Chapters, if accurate information on hazards (location, severity, and likelihood of occurrence) at an appropriate scale is available, its processing by computers can be some other invaluable tool. For case, ten hydrologic, seismic, and other geologic hazards were evaluated and rated according to their relative severity. The areal extent and severity of the hazards were transferred to 2-hectare (five-acre) filigree base maps, and the ratings for individual hazards were encoded to produce computerized maps (1:96,000). Each gamble evaluated was given ane of three ratings-high, moderate, or none to low (Figure 6-13). The Santa Barbara County (California) Planning Section (1979) devised a arrangement for rating the hazards for a given area on both an individual and a collective basis-information that so could be candy by estimator.

The resulting geologic problem alphabetize (GPI) values were obtained by multiplying each risk past a weighting cistron that took into account the seriousness of the adventure, the difficulty of alleviating it, and the frequency of its occurrence. The GPI was calculated for each 2-hectare cell in the estimator-analysis areas and then assigned to the appropriate severity category and displayed on a computer-produced map (Figure 6-7). These calculator GPI maps thus reflect a summation of the ratings delineated on the individual hazard maps.

E. LIMITATIONS

1. Credibility
ii. Likelihood, Location, and Severity
3. Accuracy versus Precision
4. Scale
5. Abuse
half-dozen. Synthesis versus Detail
7. Use of Caveats

This affiliate extends only to examples of MHM; it does not address the limitations of the private run a risk maps or other gamble information transferred onto the MHM. The following discussions are directed not only to MHM users just to MHM makers for three reasons: (one) makers are users of the individual hazard maps or other data and must be just as aware of their limitations, (2) makers must exist aware of the numerous opportunities for misinterpretation or misuse that users volition make of their production, and (3) makers must attempt to provide caveats on the face up of the MHM.

Information technology must be emphasized that all the hazard data shown on the MHM, and also the base map data, are but symbols-some conventional, others abstract, and some innovative. Users must advisedly read the explanations (sometimes called legends), all caveats, and any supplemental text accompanying a map. The MHM maker is a central person and should go out a runway (or record) for the MHM user, for example, sources of information used, scales enlarged or reduced, and limitations of the private hazard information.

1. Brownie

It must be emphasized that the information shown on an MHM is but 1 cistron that the planner or decision-maker will exist considering. The information must exist clear, user-friendly, and non simply authentic merely perceived equally authentic. For example, Affiliate 10 includes a note that "reliability may be questioned" when a landslide adventure map at a calibration of 1:50,000 was based on a slope steepness map at a calibration of 1:250,000. The location, severity, and likelihood of occurrence of each take a chance must be given or, if unknown, clearly stated equally such.

It should be remembered that the location, design, and operation of future critical facilities and the strengthening, abandonment, and operation of existing critical facilities will be afflicted past a consideration of the information shown on the MHM.

two. Likelihood, Location, and Severity

Because of the geographic nature of maps, the location requirement is met, simply this is not necessarily so with regard to severity and likelihood of occurrence. The user must non assume that because severity and likelihood are given (in Figure 6-three) for seismic and windstorm events they are as well given for tsunamis and volcanoes; they are not.

The likelihood, location, and severity elements of certain natural hazards tin be easily affected past human being activities. For example, DeGraff (1985) notes that it "is entirely possible to... crusade a major failure to occur in a moderate hazard zone. Likewise, it is possible to significantly disturb a site inside a high or farthermost zone without causing a landslide."

Zones with different levels of hazard severity-low, moderate, or high-represent relative, not absolute, hazards. In add-on, such levels are not predictive, but rather bespeak a relative susceptibility to the hazard occurring. Chapter 10 notes that landslide "susceptibility" just identifies hazardous areas, not "when" the landslide might occur.

3. Accuracy versus Precision

A prerequisite for the locational accuracy of adventure information is the accuracy of the base map selected. The gamble data available and transferred to an MHM may be authentic, but the level of precision varies greatly. This is not necessarily because of calibration or resolution, but considering of the number of the field investigations, lack of information, blazon of experiments, and knowledge of the processes involved. For instance, the three littoral zone severity levels shown in Figure 6-8 for earthquakes, volcanoes, floods, stiff winds, and landslides vary considerably when the historical basis is examined.

Another example is the location of the seismic intensity zone boundaries shown on Figure 6-four. According to Steinbrugge (1982), some observers assign the intensity equally the maximum at the location, while others assign an average. Apparently, this leads to variations in location of the boundaries.

A tertiary example is the apply of an isoline or an isopleth to indicate likelihood or frequency. Affiliate x points out that such a map is not a substitute for indicating potential risk. Sometimes a high frequency of past landslides indicates a greater probability of future landslides; at other times it may signal a lower probability of future landslides because an area has stabilized.

4. Scale

Obviously, the calibration selected controls the size of the surface area and the amount of information that can exist shown. However, resolution (or accuracy of location) is besides affected. For instance, if a small calibration map (1:1,000,000) using a 1/millimeter-broad line symbol (for fault rupture, storm path, or boundary betwixt gamble zones) is enlarged ten times (i:100,000), the line symbol becomes one centimeter wide. Similarly, reduction of indicate and line symbols may upshot in their de-emphasis or even disappearance.

The MHM maker should assume that at some time the map volition exist enlarged or reduced. Map titles and explanations are usually unaffected by enlargements or reductions, but not the literal and numerical scales. Literal scales (i millimeter equals one hundred m meters) and numerical scales (one:100,000) remain accurate merely for the original map. Therefore, a graphic scale must be placed on each map.

Spherical surfaces when portrayed on a planimetric map are only accurate at the contact of the plane with the actual sphere surface; diverse cartographic projection techniques are used to reduce the baloney. The projection technique used can exist given or variable graphic scales can be used to alert users (Figure 6-3). Depending upon the scale and accuracy of the hazard data, this distortion may not be crucial, especially if the base map has sufficient geographic information to locate the hazards.

5. Abuse

Reality is usually difficult to perceive; this difficulty is increased when maps are used. If a map is treated equally reality, information technology becomes easy to view the hazards in impersonal terms. The magnitude of the hazards is dwarfed, people are invisible, disquisitional facilities and other information may expect like a board game.

When planners and determination-makers care for a map equally mere symbols and condone the physical reality information technology represents, the results can exist disastrous. Development planners or investors, for example, may be tempted to locate infrastructures needed for economic development along a line that looks the straightest and most convenient on the map. Such a route may lie inside a fault-rupture zone. A dot symbol representing a town or a specific number of people conveys nada about the town's economic base or the peoples' characteristics-age, schooling, skills, gender, or income sources. The map manner is non ever the best style; its limitations must be appreciated.

Examples of the misuse of maps by vertical and horizontal distortion, density of symbols, contrasting colors, scales, or the use of symbols and colors which have suggestive, connotative powers across their denotative function are discussed by Muehrcke (1978).

6. Synthesis versus Particular

Filling an MHM with the symbols from several private risk maps may requite the impression of a more thorough study, but, of course, this is not true. Simplified multiple hazard maps just create an awareness of what information exists, and (even more important) what data is missing. An MHM cannot substitute for detailed studies and site-specific investigations. For instance, the landslide and flood hazards map (one:200,000) for the Jubones River Bowl in Ecuador draws attention to the hazards that volition touch on the irrigation arrangement. It cannot be considered sufficient detail for project planning, but rather it indicates where large-calibration (1:25,000 to 1:2,500) technical studies are needed.

vii. Use of Caveats

Caveats concerning the limitations of MHM should preferably exist placed on the map but as well tin exist included in the text accompanying the map. Methods used, assumptions made, or other factors concerning the individual hazard maps used to prepare the MHM can also be shown. Examples of caveats that might be institute on a map follow:

- The relative swelling-pressure potential of geologic materials is intended for employ as a guide; it cannot and should not supercede detailed field study and laboratory investigations of swelling pressures at specific sites.
- The relevance of the hazard information varies according to date, quality, and calibration of the aerial photographs used for photo interpretation and the blazon and amount of field investigations.

- Landslide deposits smaller than 500 anxiety (150 m) in the longest dimension are not shown because they are as well pocket-size to be clearly identified on the photographs or clearly portrayed on the topographic base map.

- The age of a relatively well known volcanic consequence is based on a range of radiocarbon dates, stratigraphic position, soil-profile development, ring counts on copse, or other methods of approximation. Relatively poorly known events can be approximated by comparing their stratigraphic position with the stratigraphic position of well dated events.

- Some landslide hazard zones are suitable only for regional planning purposes. They serve equally a guide to whether landslides will pose a problem for a evolution projection and identify locations needing remedial measures. The zones depicted are non intended, nor suitable, for evaluating landslide risk for a specific site.

- Inundation boundaries drawn on the maps by interpolating between the mudflow lateral limits at next cantankerous-sections using the topographic contours written report are not a prediction that the droppings dam will neglect or that a mudflow inundation will result if the blockage fails.

- The scale of the map may prohibit the analogy of sufficient item to allow use of the map for individual site studies. Evaluation of the potential for subsidence of geologic materials at individual sites should be performed by an engineering specialist.

- Full general studies of liquefaction potential are not a substitute for site-specific evaluations. The maps are small calibration and signal full general areas where susceptible materials are likely to be present.

- These maps are approximations; they do, still, provide a regional guide to those areas where liquefaction should be considered a potential take chances and where special investigations may be needed.

- The earthquake magnitude used is considered to be the maximum effect that tin can be generated in an area, however no speculation is fabricated apropos the likelihood of the consequences should the evaluated event occur.

- Non all active faults can exist identified; those faults active at depth because of known seismic activity may be and so poorly defined at the surface that including them in a surface-rupture gamble zone is impractical.

Decision

Multiple hazard maps are an important tool in the integrated development planning process. When combined with the critical facilities map discussed in Affiliate 7, they get a primal determinant in locating and funding new evolution. Failure to consider all of the natural hazards in the development planning process and to provide for their reduction volition event somewhen in the loss of lives, bodily injuries, property damage, critical facility failures, and disruption of of import economic activities. Depending upon the size of the event, its location, and its effects, the bodily impact of the chance can be catastrophic and disastrous.

A recent guidebook by the OAS Department of Regional Evolution and Environment (1987b) clearly restates the issue:

Conflicts between natural hazards and evolution activities. result from a confrontation between hazardous natural events and human being activeness. So-called "natural disasters" occur considering we take not paid sufficient attention to natural chancy phenomena. Indeed, the term "natural disaster" is misleading for this reason: information technology places the blame on nature when, in fact, the arraign belongs to those who decided that projects be implemented under circumstances that jeopardize the very objectives that the development activities were designed to meet.

The emphasis of the integrated evolution planning procedure is on the development of natural resource, energy, infrastructure, agriculture, manufacture, human settlements, and social services (OAS, 1984a). Information technology emphasizes the drove and assessment of data on natural hazards to reduce their adverse touch on that development. It is believed that if the hazards are assessed and appropriate reduction techniques are incorporated into each stage of the integrated development planning process, social and economical disasters caused past natural hazards tin exist avoided or substantially reduced.

Equally of import is the mental attitude of those national, regional, and community scientists, planners, engineers, and conclusion-makers involved in the collection and cess of hazard information for new development. Many of them are fundamental people with responsibilities for existing development. Their use of hazard information for new development volition exist enhanced by their interest in using the data to encounter their responsibilities in sustaining existing development.

I last reiteration: the credibility, accuracy, and content of an MHM is no greater than the private adventure information from which the MHM was compiled. Any limitations are merely transferred from the individual hazard data to the MHM.

REFERENCES

** Alexander, R.H., et al. Applying Digital Cartographic and Geographic Information Systems Technology and Products to the National Earthquake Hazards Reduction Program: Proceedings of a Workshop on "Earthquake Hazards along the Wasatch Front, Utah," Open-File Report 87-154 (Reston, Virginia: U.S. Geological Survey, 1987), pp. 100-146.

Alfors, J.T., Burnett, J.L, and Gay, T.E., Jr. "Urban Geology, Master Plan for California, the Nature, Magnitude, and Costs of Geologic Hazards in California and Recommendations for Their Mitigation" in California Partition of Mines and Geology Message 198 (Sacramento, California, 1973).

** Bender, Due south.O. St. Kitts and Nevis Forestry Development and Resource Management Planning Projection: Report on Natural Hazards Assessment and Settlement Evolution Planning in Saint Kitts and Nevis (Washington, D.C.: Organization of American States, 1986).

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Blair, M.L. "Planning for Flood-loss Reduction in the Napa Valley" in A.O. Waananen, J.T. Limerinos, W.J. Kockelman, W.E. Spangle, and Chiliad.L. Blair, Inundation-prone Areas and Land-use Planning-Selected Examples from the San Francisco Bay Region, California, Professional Paper 942 (Reston, Virginia: U.S. Geological Survey, 1977), pp. 46-65.

Blair, Grand.50, and Spangle, W.Due east. Seismic Prophylactic and State-use Planning-Selected Examples from California, Professional Paper 941-B (Reston, Virginia: U.S. Geological Survey, 1979).

** Borcherdt, R.D. (ed.). Studies for Seismic Zonation of the San Francisco Bay Region, Professional person Paper 941-A (Reston, Virginia: U.South. Geological Survey, 1975).

* Brown, R.D., Jr., and Kockelman, West.J. Geologic Principles for Prudent Land-utilise: A Decisionmaker'due south Guide for the San Francisco Bay Region, California, Professional Paper 946 (Reston, Virginia: U.S. Geological Survey, 1983).

De Graff, J.Five. Landslide Hazard on St. Lucia, West Indies (Washington, D.C.: Arrangement of American States, 1985).

** Du Bois, R. A Natural Hazards Assessment of the Coastal Area of Saint Lucia, West Indies (Washington, D.C.: Organization of American States, 1985).

* Ellis, M.Y. (ed.). Coastal Mapping Handbook (Washington, D.C.: U.S. Geological Survey and Office of Coastal Zone Direction, 1978).

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* Kockelman, Westward.J. "Some Techniques for Reducing Landslide Hazards" in Bulletin of the Association of Applied science Geologists, vol. 23, no. 1 (1986).

* - "Using World-science Information for Convulsion-hazard Reduction" in J.I. Ziony (ed.), Evaluating Earthquake Hazards in the Los Angeles Region-An Earth-science Perspective, Professional Paper 1360 (Reston, Virginia: U.Southward. Geological Survey, 1985).

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- "Flood-loss Prevention and Reduction Measures" in A.O. Waananen, et al Inundation-decumbent Areas and State-use Planning-Selected Examples from the San Francisco Bay Region, California, Professional person Paper 942 (Reston, Virginia: U.Due south. Geological Survey, 1977), pp. 23-30.

- Use of U.Due south. Geological Survey Earth-scientific discipline Products by Canton Planning Agencies in the San Francisco Bay Region, California, Open-File Written report 76-547 (Menlo Park, California: U.Southward. Geological Survey, 1976).

- Employ of U.S. Geological Survey Earth-science Products by City Planning Agencies in the San Francisco Bay Region, California, Open-File Report 75-276 (Menlo Park, California: U.S. Geological Survey, 1975).

** Kockelman, Westward.J., and Brabb, E.East. "Examples of Seismic Zonation in the San Francisco Bay Region" in E.Eastward. Brabb (ed.), Progress on Seismic Zonation in the San Francisco Bay Region, Round 807 (Reston, Virginia: U.S. Geological Survey, 1979).

** Laird, R.T., et al Quantitative Land-capability Analysis, Professional person Paper 945 (Reston, Virginia: U.South. Geological Survey, 1979).

Miller, C.D. Potential Hazards from Future Eruptions in the Vicinity of Mount Shasta Volcano, Northern California, 3 plates, Bulletin 1503 (Reston, Virginia: U.S. Geological Survey, 1980).

** Muehrcke, P.C. Map Utilize: Reading, Analysis, and Estimation (Madison, Wisconsin: J.P. Publications, 1978).

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* - Multiple Chance Mitigation: Report of Workshop on Mitigation Strategies for Communities Prone to Multiple Natural Hazards (Washington, D.C.: National Academy Press, 1983).

* Organisation of American States, Section of Regional Evolution. Form on the Use of Natural Hazards Information in the Preparation of Investment Projects, vol. 1, xv annexes (Washington, D.C.: Organization of American States, 1987a).

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** - Natural Hazards Map of the Paraguayan Chaco, Plan Area iv-C calibration ane:500,00 (Washington, D.C.: Organization of American States, 1985).

** - Proyecto de Desarrollo, República de Honduras, Riesgos Naturales, Map calibration i:50,000 (Washington, D.C.: Organización de los Estados Americanos, 1985).

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** - Saint Lucia Coastal Hazard Map, Prepared with the Collaboration of the Ministry of Agronomics, Lands, Fisheries, Cooperatives and Labour of the Government of Saint Lucia, scale 1:50,000 (Washington, D.C.: Organization of American States, 1984b).

** - Plan Hidráulico del Jubones, República del Republic of ecuador, vol. 3 (Washington, D.C.: Organización de los Estados Americanos, 1984c).

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** Regional Seismological Eye for S America (CERESIS). Maximum Intensity Map of Due south America, calibration 1:5,000,000 (Lima: Regional Seismological Heart for South America, 1985).

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* Key reference.
** Key reference specifically for multiple run a risk mapping.

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