Observations on some geotechnical issues relating to hazard and disaster mitigation.
At least one type of natural hazard exists nearly everywhere on our planet. No one is immune to these hazards, and entire historical civilizations have been destroyed by various natural disasters. The great many life forms on this planet adapt, adjust, or conform to their natural surroundings, or exploit them in some basically passive manner. Only humans approach their environment consistently in an active, aggressive manner, adapting and modifying the environment to suit them. Nearly always, these modifications are for immediate or short-term purposes, without considering the intermediate to long-term implications. In so doing, fundamental natural processes often are thwarted, and solutions are proposed that modify or attempt to contradict these processes. Humans still do not realize that the natural processes will prevail eventually. In this paper, some natural hazards and disasters are discussed, along with the geotechnical issues involved and how they relate to the broader issue of disaster mitigation. Some basic suggestions are made for future implementations.
SOME BASIC DEFINITIONS
Hazards to humans are of many types, and they can be classified as: (a) natural, from atmospheric and/or geologic processes, (b) medical/social, such as epidemics and famine, and (c) technological, such as biological and chemical agents, hazardous materials, transportation accidents, utility disruption, etc. The focus herein is on natural hazards.
A natural hazard can be defined as "a naturally occurring event that poses danger to humans and/or their assets". More quantitatively, a natural hazard can be defined as "the probability of occurrence, within a period of time and locale, of a potentially dangerous natural phenomenon". In 2001 alone, natural hazards killed over 25,000 people and caused some USD 36 billion in damage worldwide (Natural Hazards 2005).
Table 1 shows a generalized summary of natural hazards. For convenience, they are grouped first into the relatively common geologic and atmospheric hazards, which need to be addressed in normal hazard planning. Then the extreme natural hazards are listed, more for general interest than any other reason, because these approach "doomsday" scenarios that can not be addressed in normal hazard planning.
All but one or two of the geologic hazards are known well within the geotechnical engineering community. They are studied at our universities, and they are known well in practice. We may not have good solutions for all of the related design problems, but the fundamentals are understood, at least conceptually. Drought is a specialized case that can lead to extreme changes in effective stress state and subsequently all geotechnical properties, and to desertification in the extreme. Geomagnetic storms do not affect the geotechnical conditions directly, but they disrupt the geomagnetic field which, in turn, disturbs communications, power, computers, instrumentation, etc. In other words, most support systems are influenced negatively.
The atmospheric hazards also are studied and are known well. They often have a symbiotic relationship with the geologic hazards, in many cases triggering the geologic hazard. Climate change and the el nino/la nina phenomena are longer-term issues that influence the frequency and intensity of the other atmospheric hazards.
The extreme natural hazards are exactly that--extreme! They are of interest and are important, but their frequency and intensity are so far into the extreme tails of any design distributions that they can not be considered in plausible design scenarios. For the International Decade for Natural Disaster Reduction, which was a United Nations program for the 1990s, the focus was on earthquakes, windstorms, tsunamis, floods, landslides, volcanic eruptions, wildfires, grasshopper and locust infestations, and drought and desertification.
Within the United States, all of the hazards listed in Table 1 are plausible and do occur, and the great majority are common, unfortunately.
Figure 1 is an interesting 1978 graphic. Unfortunately, I have not seen any update. However, the relative values should still be approximately valid. As shown, the mean annual economic impact of "expansive soil" is the largest, by far, followed by floods and then slides. Mean annual loss of life is dominated by floods, with "earthquakes" a distant second. This figure shows an unfortunate reality in perception and in research financing. Although "expansive soil" is by far the largest mean annual loss in the aggregate, it is something that occurs in small increments and therefore is not perceived as more than a local nuisance. Significant earthquakes, on the other hand, are few and far between, but their effects are large and visible, and they receive a great deal of high visibility press coverage. So where does the majority of the research funding go? To earthquakes, of course! Perhaps our priorities need some re-direction.
A natural disaster can be described as a natural event with catastrophic consequences. Or "a disaster is a social disruption that can occur at the level of the individual, the community, or the state" (Kreps 1986). Or "disasters occur when hazards meet vulnerability" (Blaikie et al. 1994). Within the last year, three incredible natural disasters occurred--the December 2004 tsunami in Southeast Asia, the August and September 2005 hurricanes in the south-central U.S., and the October 2005 earthquake in northeast Pakistan. In these cases, either extreme loss of life occurred, numbering in the tens of thousands, and/or extreme loss of assets occurred, in excess of USD 100 billion. Can these disasters be prevented? At this time, the answer is no. Can the impact of these disasters be minimized? The answer is yes. Traditionally, two approaches have been used: (a) mitigation, which includes actions taken before, during, and after to minimize the impact, and (b) response, which includes short-term emergency efforts by first-responders and longer-term efforts to provide human needs (food, shelter, etc.) and to re-establish the infrastructure. In the past, response efforts have predominated. However, considering these recent disasters, it is clear that much is yet to be done in this area. For the future, there will be increasing use of sound hazard mitigation strategies that include risk management and engineering.
Hazard mitigation is the process of minimizing, or possibly eliminating, the risk to people and/or their assets from natural hazards, usually through careful planning. Solutions can range from engineering design, such as earthquake-resistant design, to limiting or eliminating human activities in potentially hazardous areas, such as hurricane-prone coastal areas and floodplains. Hazard mitigation ideally is dedicated to breaking the cycle of repeated damage and reconstruction.
As described by the Board on Natural Disasters (1999), "comprehensive mitigation planning includes: (a) determining the location and nature of the potential hazards, (b) characterizing the population and structures (present and future) that are vulnerable to specific hazards, (c) establishing standards for acceptable levels of risk, and (d) adopting mitigation strategies based on an analysis of realistic costs and benefits. In practice, mitigation may be difficult to implement, both politically and economically."
The Board on Natural Disasters (1999) also noted that there are five high-priority tasks to be pursued. First, improve risk assessments. Much has been done in modeling risk within the engineering community. Realistic models exist, but calibrations are somewhat limited. Second, implement mitigation strategies. Implementation can be tricky because it involves comprehensive land-use planning. These measures are rarely adopted locally without mandates from higher levels of government, and the local people must be convinced that the hazard is a real threat. However, relatively straightforward matters, such as implementing sound building codes and ensuring that they are followed, can do much in minimizing losses. Third, improve technologies that support warnings and the dissemination of, and response to, warnings. Forecasts and warnings are vital for mitigation, and they must be as good as possible. Implementation, maintenance, and monitoring are potentially weak links in this important issue. Fourth, improve the basis for natural disaster insurance. This enormous financial issue needs to be addressed better by linking disaster policy, risk-reduction strategies, and incentives to minimize risk. And fifth, assist disaster-prone developing nations. This humanitarian and technological effort is necessary to ensure that these nations actually can develop into productive members of the worldwide community. After all, the interests of all countries extend worldwide at this time.
Figure 2 presents many of these issues graphically. As shown, there are many issues, from many sectors, that all play key roles in reducing hazard loss. Moving in clockwise fashion, the first two issues relate to society, individuals, and education. People, collectively and individually, need to make informed decisions about risks and hazards. The third and fourth issues relate to insurance and economics and how they play a role in setting reduction and reconstruction strategies. The fifth and sixth issues are largely technological, such as quantifying uncertainty and risk and developing mitigation measures.
[FIGURE 2 OMITTED]
SOME GEOTECHNICAL ISSUES
Geotechnical issues pervade many aspects of hazards, disasters, and mitigation. As noted previously, most of the geologic and atmospheric hazards are known and studied. We can calculate the ideal behavior of these hazards, but we can not assess the risks well. Considering the three recent disasters noted previously, it is clear that our concepts of "acceptable risk" need re-evaluation. It is also clear that infrastructure maintenance is sorely lacking on a global basis, which means that the risk of a disaster clearly is greater than it was at the time of design and construction. Is this increased risk acceptable?
Let us think about some natural geotechnical systems. Most natural systems evolve gradually, and in nature there is a "geo-redundancy" that provides some protection for these systems. For example, natural slopes normally are broken or benched, vegetation grows most everywhere, and the types of vegetation vary in height, lateral expanse, and root structure. These all represent natural "energy dissipators" that will minimize the atmospheric loading functions and provide additional geotechnical stability. Consider now the effects of urbanization in this terrain. Slopes are re-shaped, and their grades are made uniform. Vegetation is removed, and paving is done for streets and parking. Well-trimmed lawns and localized decorative vegetation are installed. Suddenly the loading functions become more severe because the runoff increases dramatically and the infiltration into the natural vegetation decreases. In addition, the new vegetation systems (i.e., lawns) provide very little assistance in slope stability. The result is that loading is increased, resistance is decreased, and therefore the risk increases.
Many other examples can be cited, such as: (a) housing within littoral drift zones, (b) modification of barrier islands, (c) construction within actively-creeping fault zones, (d) construction on creeping slopes, (e) river channelization and/or levee construction that virtually eliminates beneficial flooding that replenishes soil nutrients and maintains vegetation, (f) channelization that results in increased storm surge, etc. The list continues almost indefinitely. The point to be made is that we need to work with natural processes, adapt them to our needs, and maintain or enhance the geo-redundancy. Most policies to date are the opposite and are directly confrontational to the natural processes. Sooner or later, nature will win the battle. Instead, we need to follow the adage quoted below.
"Nature to be commanded must be obeyed" Francis Bacon, Novum Organum, 1620
Hazards exist everywhere. This paper reviewed the types of natural hazards, subsequent disasters, and issues of mitigation, which go well beyond the technological. Geotechnical matters are prominent within all of these. As discussed, for the future, we really must work more with and within natural processes.
Blaikie, P, Cannon, T, Davis, I & Wisner, B (1994). "At Risk: Natural Hazards, People's Vulnerability, & Disasters", New York: Routledge.
Board on Natural Disasters (1999). "Mitigation Emerges as Major Strategy for Reducing Losses Caused by Natural Disasters", Science, 284, 18 Jun 99, 1943-47.
Kreps, GA, Ed. (1986). "Social Structure & Disaster", Newark: Univ. Delaware Press.
Meade, C & Abbott, M (2003). "Assessing Federal Research & Development for Hazard Loss Reduction", Santa Monica: RAND.
NaturalHazards.org website (2005).
Robinson, GD & Spieker, AM, Eds. (1978). "Nature to be Commanded", Prof. Paper 950, U.S. Geological Survey, Washington.
FRED H. KULHAWY, Honorary Member, ASCE School of Civil and Environmental Engineering Cornell University, Hollister Hall Ithaca, New York 14853-3501, USA
Table 1. Geologic, atmospheric, and extreme hazards. Geologic Hazards drought earthquake erosion (coastal, river/stream bank) expansive soil flood geomagnetic storm sinkhole slide (natural slope, constructed slope, snow/ice avalanche, volcanic lahar) subsidence (local, regional) tsunami volcano Atmospheric Hazards climate change el nino and la nina fog heat wave summer storm/thunderstorm (lightning, wind, rain, hail) tornado tropical cyclone (hurricane/ typhoon, storm surge) wildland fire winter storm/blizzard (wind, snow, ice) Extreme Natural Hazards ice age extraterrestrial impact solar flare supervolcano megatsunami Figure 1. Mean annual losses in U.S. from geologic hazards (Robinson & Spieker 1978). HAZARD LIVES DOLLARS FLOODS >85 $1,200 MILLION EARTHQUAKES >8 $100 MILLION LANDSLIDES Unknown $1,000 MILLION COASTAL EROSION Unknown $300 MILLION EXPANSIVE SOIL Unknown $2,200 MILLION OTHERS Unknown $100 MILLION Others: subsidence, creep, fault displacement, liquefaction of sand and clay, dust, waves caused by earthquakes, volcanoes Note: Table made from bar graph.