Flood Risk and Hazard Assessment on Lulu Island by Paul Arthur
Flood Risk and Hazard Assessment on Lulu Island
By
Paul Arthur Jacobs
B. Sc. Honours, Simon Fraser University, 1975
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE
in
THE FACULTY OF GRADUATE STUDIES
(Department of Civil Engineering)
We accept this thesis as conforming
to the required standard
THE UNIVERSITY OF BRITISH COLUMBIA
November 1986
©Paul Arthur Jacobs, 1986 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.
Department of
The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3
Date acnwee-K t, i i
ABSTRACT
Lulu Island contains most of the Municipality of Richmond.
Richmond is a growing community with 100,000 population located south of the city of Vancouver in the Fraser River estuary. The flood hazard from both the sea and the Fraser River are well known and to protect against it, an extensive diking system has been built. Despite this diking system a significant residual flood hazard has been created by the extensive development on the island. In addition, concerns have been raised about potential flooding from earthquake damage and a predicted rise in sea level due to global warming.
This thesis analyses the extent of the flood hazard from various sources. New techniques of risk analysis and findings on risk perception are used to examine the flood risk. The role of contingency planning for flood control in conjunction with dikes is examined. Finally, the role of flood insurance is discussed as a method of providing information about flood risk levels to floodplain users.. Conclusions are drawn about the adequacy of current flood control measures and recommendations are made to improve them. ACKNOWLEDGEMENTS
In the course of this study assistance was received from many sources. I am particularly indebted to the people involved in providing flood protection at all levels of government for their time, access to their documentation, and, most of all, for sharing their expertise with me.
From the federal government, I would like to thank Dr.
Sandy D'Aquino, Jim Leung, Neill Lyons, and Jim Oakey of the
Water Planning and Management Branch of Inland Waters.
From the British Columbia government, I would like to thank
Eric Bonham, Ron Henry, Robin Round, Sandra Smith, and Jake
Wester of the Ministry of Environment and Parks.
From the Municipality of Richmond, I would like to thank
Alex Jamieson, Don Mclver, and Henry Pelzer.
In addition, I would like to thank my thesis advisor S. 0.
Russell for his guidance, cooperation, and most of all for his careful listening.
Finally, I would like to thank my wife, Maruta Jacobs, for her careful editing and general support. iv
TABLE OF CONTENTS Abstract ii Acknowledgements iii List of Tables v List of Figures vi Glossary vii Introduction 1 Literature Review 6 The Flood Hazard 34 Risk Analysis and Perception 48 Contingency Planning and Other Measures to Reduce Damage 59 Flood.Insurance 65 Conclusions 69 Recommendations 71 Bibliography 73 Appendices 78 - Appendix A - Tables 79 - Appendix B - Figures 85 - Appendix C - Expected Flood Damage Calculation for Lulu Island .... 90 V
LIST OF TABLES I. Terms for Classifying Hazard Potentials 79 II. U. S. Army Corps Engineers Hydraulic Evaluation Guidelines: Recommended Spillway Design Floods .. 79 III. Value of Commercial Building Permits Issued 80 IV. Annual Probabilities of Combined Flood Hazards .. 80 V. Predicted Changes to Tidal Levels 81 VI. Flood Damage Estimate for Lulu Island 81 VII. Federal-Provincial Flood Damage Cost Sharing Formula 82 VIII. Example Rule of Thumb Flood Protection Level Chart 83 vi
LIST OF FIGURES
1 . Map of the Western End of the Lower Fraser Valley 86 2. Risk-Hazard Perception Rating Chart 87 3. Map of Full Tidal Relief Zone 88 4. Raised Road Alignment 89 vi i
GLOSSARY Capitation - A method of payment for medical services in which the physician receives a fixed amount annually per patient for all health care services used. Climatological Change - A long term, world-wide, warming trend that has been postulated based on increased levels of carbon dioxide in the atmosphere. The most significant aspect of this change from the point of view of this study is the melting of polar ice sheets and a subsequent 1m rise in sea level. Highway 99 - The freeway running north-south roughly through the centre of Lulu Island. Flood Hazard - The potential damage that would be done by flooding. Flood Risk - The probability that flooding will occur. Level of Protection - The probability of occurrence of a flood event that dikes or other flood control structures are designed to withstand. These' probabilities can be expressed as either an annual probability of occurrence or a return period. (.005 annual probability of occurrence is equivalent to a 1 in 200 year return period.) Low Pressure Systems - Weather systems characterized by low barometric pressures and high winds. The highest tidal levels around Lulu Island result from severe low pressure systems occurring during the winter months. vi i i Normal High Tide - Any high tide that occurs from the gravitational pull of the sun and the moon alone, rather than in conjunction with a low pressure system. MCE - Maximum Credible Earthquake - The largest earthquake that can be expected to occur in an area. Morbidity - The average number of people sick at any one time. Mortality - The expected number of deaths per thousand in a population. For example, the mortality of males from 45 to 54 is the number of deaths that can be expected to occur in a group of 1000 males 45 years old before they reach 55 years old. PMF - Probable Maximum Flood - A hypothetical flood derived from physical criteria that is the largest flood that could reasonably be expected to occur. Ponding - The filling of a diked area to the level of water entering through a dike breach, characterized by deeper water levels than would have occurred without the dikes and a loss of velocity through the breach. In effect, the diked area becomes a pond with the dikes as banks. Primary Care - The type of health care first sought by patients as opposed to health care delivered as a result of a referral by a physician. Typical examples of primary care are the family physician and hospital emergency wards. River Stage - A river level with respect to a known datum or elevation. ix
Spring Freshet - The high river levels caused by the spring
snowmelt.
Tidal Relief - The drop in water levels around Lulu Island that
occurs during low tide. Full tidal relief occurs when the
water level at low tide is lower than the land level inside
the dikes. 1
INTRODUCTION
This is a study of the flood hazards and flood risk in the
Municipality of Richmond, specifically Lulu Island. The
Municipality of Richmond is located primarily on Lulu Island, south of the City of Vancouver, in the Province of British
Columbia.
For a flood hazard to exist, two conditions must be met: there must be development that can be damaged by inundation and there must be a path for water to inundate the development.
Richmond's location and geology have been excellent for the development of a flood hazard.
The Province of British Columbia is mountainous and contains relatively little flat or agriculturally productive land. The existing flat land is concentrated in river valleys.
Most of the rest of the province is made up of steep, forested land. As a result, most of the land outside of settled areas is uninhabited. The Atlas of British Columbia describes and explains the population distribution this way:
"Three features characterize the distribution of population in British Columbia - heavy concentration in the southern coastal lowlands, valley oriented lines of settlement with larger clusters along them in the southern and central interior and large areas of unpopulated land.
"The essentially unpopulated areas are those which by reason of topography, climate, soil conditions, vegetative cover, or relative isolation have offered little inducement to settlement."(Farley, 1979, p. 4)
In a province with this type of topography and population distribution, it is no surprise that a flat area with a mild climate, prime agricultural soil, and located within easy 2 commuting distance of Vancouver (metropolitan population 1.2 million) has attracted development. Between 1950 and 1960 Richmond's population growth was more than 5% per annum. Since then the growth rate has slowed, but it is still approximately 4% per annum. Monetary value of flood damages was last estimated for Richmond in 1971. At that time, the population was 62,000 and potential flood damages were estimated at $100 million. Since 1971, the population has increased to 104,000. In addition, Richmond has been more closely integrated into the Greater Vancouver Regional District's economy and has become a major shopping and warehousing area. Over $500 million of building permits for commercial developments have been issued since 1971. Assuming that flood damages would increase proportionately with population and inflation, the maximum flood that the dikes were designed for, would cause about $500 million in damage today (1986). Since, as was mentioned above, the character of development has changed, these assumptions are probably conservative. Lulu Island is a low lying island located in the mouth of the Fraser River estuary. It is susceptible to flooding from both the ocean and the Fraser River. If there were no diking system, flooding over the whole island to the 2 foot level would occur from a 1 in 10 year recurrence period flood. High tides could be expected to flood parts of the island on several days each month. 3
To protect against this flooding, 30 miles of diking have been built. The earliest dikes on Lulu Island were built in 1876. Since then the dikes have been expanded to entirely surround Lulu Island. The dikes have been periodically raised and widened. The last time the dikes were raised was under the Federal-Provincial Agreement of 1968. Under this agreement, the dikes were raised to provide .6 meters of freeboard above the level of a flood with a 1 in 200 year recurrence period. This level of protection was chosen because the 1 in 200 year flood approximates the largest flood of record. Incidentally, in several areas of the Fraser Valley, soil conditions make it technically difficult (but not impossible) to build dikes any higher. (Wester, 1986, personal comm.) Although cost benefit studies were done to determine which areas should receive money to upgrade their dikes, the design standard for the dikes was set primarily for political and technical, rather than economic, reasons. The design standard sets the risk of flooding at .005 per year and is now the standard for flood protection throughout British Columbia. There are several factors that make the flood situation on Lulu Island worthy of study at this time. The first has already been discussed. There is a large (and growing) flood hazard in Richmond. In fact, it is the largest flood hazard in Canada and one of the largest in North America. The second factor is that a new technology of risk assessment has been emerging over the last decade. This technology has been developed mainly to deal with issues related 4 to the nuclear and hazardous chemicals industries. Spin-offs of this research have been applied to dam safety and are applicable to flood control. The main thrust of this research is to determine "How safe is safe enough?" This question is clearly germane, given the somewhat arbitrary way in which the current design standards were arrived at.
The third factor is that there is concern that the risk of flooding is increasing. This concern arises from the trend toward higher levels of carbon dioxide in the atmosphere. It is felt that the increased levels of carbon dioxide will cause atmospheric warming, which in turn will melt parts of large ice sheets such as the Greenland ice sheet. It is predicted that the water thus released could increase sea level by about 1 metre within the next 50 years.
The fourth factor is that some concern has been expressed that the flood risk has been underestimated because of the possibility that an earthquake could liquefy, and thus damage, the dikes. This concern was triggered by the earthquake which struck Niigata, Japan. Niigata has similar soil structures to those found in Richmond. Both cities are built on poorly compacted sands and silty sands. During the Niigata earthquake, widespread soil liquefaction occurred and some dikes failed as a result.
The final factor is that the British Columbia government is in the process of revising its flood control policies. This makes the timing of this thesis fortuitous. 5
In an overall sense, the management of the flood situation in Richmond has been successful because no significant flooding has occurred since Lulu Island was developed. The combination of a large and growing hazard and both technical and political difficulties in reducing the risk make it worthwhile to study this situation.
This thesis reviews the contemporary trends in flood and other hazard protection and examines the flood hazard situation
in Richmond in the light of these trends. 6
LITERATURE REVIEW
The literature applicable to this thesis has come from several different areas. Since the early 1970's, a considerable body of literature has grown up that is specifically concerned with risk assessment. Works will be reviewed from this area on the subjects of risk perception, risk analysis in general, and risk analysis applied to water resources projects in particular. Another relevant area is the cost/benefit analysis which has been used to evaluate flood control projects in the lower Fraser Valley. The final area applicable to this thesis is the hydrology and geology of Richmond. Specifically, works reviewing the earthquake hazard, the river flood hazard, and the ocean flood hazard will be reviewed.
Vancouver International Airport Sea Dykes Rehabilitation - Hay and Company (1985) This report discusses the design of dikes to protect Sea Island. Sea Island is within the boundaries of the Municipality of Richmond, but is north and west of Lulu Island, the main subject of this thesis. The section on hydrologic background of this report gives a good description of the ocean-based flood hazard faced by Lulu Island. The report states that: "Without the dikes about 85% of Sea Island would be inundated during normal high tides, and would subsequently be exposed at low tides. The natural ground levels of the low lying areas range from .9 to 1.5m GSC, just over a metre above the mid-tide level of 0.0m GSC" (Hay and Company, 1985, p. 13).
* GSC - Geodetic Survey of Canada. 7
The report also calculates the effect of a 200m breach, lasting 1 tidal cycle, in Sea Island dikes. The calculation, done under worst case conditions, shows that 7.4 million cubic metres of water would enter Sea Island, resulting in flooding to a depth of .7m on agricultural land. 85% of Sea Island is agricultural land. The final applicable part of this study discusses ocean waves. The report states that 2.8 to 3.4m waves would be generated under 85kph winds blowing across the Strait of Georgia for a minimum of 6 hours. It then states that this maximum wave height is reduced by 82% across Sturgeon Banks as a result of bottom friction. This means that a 3m wave would be reduced to ,6m by the time it approaches the dikes across Sturgeon Banks. Because Lulu Island is close to Sea Island, much of the description is applicable. It should be noted that Sea Island tides are slightly higher. Large portions of Lulu Island, including almost all heavily developed areas, are located at elevations from .9 to 2.0m GSC. The building code in Richmond requires that all urban development on Lulu Island be built at or above ,9m GSC. The report gives mean high tide level as 1.4m GSC and low tide level as -3m GSC. The Municipality of Richmond puts the mean high tide level at the slightly lower level of 1m for Lulu Island. It should also be noted that the time it would take to flood Lulu Island from a storm-caused breach would be somewhat longer because Lulu Island is 8.5 times as big as Sea Island. If no ponding occurred, then flooding to an average depth of 6cm 8 per tidal cycle could be expected from a similar dike breach.
Deeper flooding could be expected in the lowest areas nearest the dikes, but it is clear that as long as the duration of ocean flooding is kept to 1 or 2 tidal cycles, the flood damage would be kept to acceptable levels.
Finally, while Lulu Island is near to Sea Island, it is. far less exposed to wave action because almost all of Lulu Island's western coast is protected by Sturgeon Banks. In fact, the reduction in wave action caused by Sturgeon Banks has made it unnecessary to rip-rap Lulu Island sea dikes to protect them against wave action.
The Role of Perception in Flood Control - Gordon Shanks (1972)
This work provides an excellent summary of the river hydrology around Lulu Island. It correctly points out that the largest flood hazard facing Richmond is the one caused by the spring freshet involving a dike breach in the eastern end of
Lulu Island. In addition, Shanks provides detailed descriptions of the attitudes and perceptions toward the flood hazard of both the government officials concerned with flood control and the public living on Lulu Island.
HYDROLOGY OF LULU ISLAND
Lulu Island is located in the Fraser River Estuary. The
river branches and forms several channels around Lulu Island.
The eastern end of Lulu Island is totally in a riverine environment, while the western end, fronting on Georgia Strait,
is in a marine environment. The general east-west dividing line
separating areas under riverine and tidal based flood hazard is 9 shown. The areas under tidal influence are not treated in this work.
Flooding from a dike breach during the spring freshet is identified as the largest flood hazard. The work correctly states that a major dike break, from this cause, would flood the whole island. It also states that flooding would occur to the same level as if there were no dikes. The average flooding level for a 1 in 200 year flood is given as 4 feet (1.2m).
DIFFICULTIES WITH DIKING SYSTEMS
Several difficulties in the dependence on diking systems to protect urban areas from flooding are described. These include:
- The difficulty in building dikes high enough to provide
complete protection from overtopping.
- The impossibility of building dikes that are completely
safe from extreme flooding events. Problems from
boils, undercutting, piping, and underseepage can
occur even with well maintained dikes during these
extreme events.
- The impossibility of maintaining dikes to 100% of
standard. Dikes settle, are damaged by bank erosion
and other less obvious factors such as burrowing
animals over time. As a result, constant repairs are
necessary.
- The fact that a major break in the dikes would cause
flooding of the whole island making the dikes useless. 10
- The tendency for development to grow up behind dikes. When dikes fail, the damage is greater than it would have been if dikes had not been built. PROBABILITIES OF FLOODING When this work was written the design standard for Richmond dikes was the 1948 flood plus two feet of freeboard. It is stated that the probability of overtopping is .005 per annum. The author points out that, over a design life of 50 years, the probability of overtopping the dikes under these conditions is .22. PERCEPTION OF FLOOD HAZARD The discussion of flood hazard perception is divided into 2 parts: the perception of involved government officials and the perception of the public living in Richmond. It was found that there is a large variation in how serious the flood hazard was perceived to be among government officials. A gradation in concern was noted from federal officials to municipal officials. Shanks writes: "Federal officials who have the least direct input consider the present hazard to be a significant one. On the other hand, the municipal level officials who are the most directly involved with implementation of flood management policies fail to perceive the flood hazard as being significant." (Shanks, 1968, p. 94) Officials perceived diking as the most suitable adjustment to the flood hazard and upstream storage as the next most suitable alternative. These measures control the flood risk, not the flood hazard. There was little support for solutions that control the flood hazard such as floodproofing and land use restrictions. 11
This work found that the public recognized the possibility of flood damage (52% of respondents), but did not expect to experience flooding in their lifetime (85% of respondents). The author states that this is a low level of flood hazard perception. This work found that the public is essentially indifferent to the flood hazard and that, by default, policy is made by the professionals in flood control. As the author states:
"Indications are that public support would not be a decisive factor in affecting flood adjustments." (Shanks, 1968, p. 108) Since this study was performed, the dikes have been raised to the 1 in 200 year level plus 2 feet of freeboard. It is probable that raising the dikes decreased public awareness of the flood hazard. It should be noted that the probability of no flooding occurring in the next 40 years is 82%.* In view of the length of time people can be expected to live in one place, the public's lack of concern about the flood hazard does not seem unreasonable. The sense of the author's argument is that if government officials find that different flood control methods such as floodproofing or stricter zoning are necessary, the public probably would not object. Finally, Shanks was unable to explain why federal officials were the most concerned about the flood hazard while provincial * The probability of no flood occurring in 40 years given annual probability of flooding is .005 is (1 - .005)40 = .818 . 12 officials were less concerned and municipal officials were the least concerned. No attempt was made to correlate the level of responsibility for payment of flood damages with level of concern about flooding.
Earthquake Design in Richmond, B.C. - Peter M. Byrne and Donald L. Anderson (1983)
This work documents the earthquake hazard faced by
Richmond. Richmond is located in the circumpacific belt well known for its earthquake activity. It outlines the role of the underlying soils in creating the potential for high earthquake hazard. It is stated that water-saturated loose- to medium-dense sands and silts are prone to strength loss through liquefaction when exposed to strong shaking.
This paper describes the process of liquefaction
of sand as follows:
"If all the load is transferred to the water, the soil loses all of its strength and behaves like a liquid and is said to have liquefied. The high water pressures can lead to expulsion of water and sand at the ground surface in the form of miniature volcanoes and the loss of strength can result in large movements of structures and services founded in or above the liquefied zone. Such behaviour has been noted repeatedly during earthquake shaking where the underlying soils are comprised of loose saturated soils (Youd, 1975). Resulting earthquake damage has generally been much more severe in areas underlain by such soils." (Byrne, 1985, p. 3)
The essential points made in this paper with respect to flooding in Richmond are:
- Richmond soils are loose to medium dense sands and silts.
- The dikes around Richmond are made of the ..same materials. 13
- The high water table in Richmond ensures that the dike
foundations and the lower part of the dikes are
constantly saturated.
- The soils found in both the surface soil layers and the
dikes are of the type that is likely to liquefy in a
strong earthquake.
- An earthquake likely to cause liquefaction would have a
return period of 475 years.
- The upper portions of the dikes are only saturated during
extreme high tides or the spring freshet. Consequently
the probability of liquefaction of the total height of
the dikes is quite small.
- Even if only the base of the dikes and the foundations
liquefy, longitudinal and transverse cracks could
occur in the dikes.
- The flooding that would occur under the most likely
conditions would be from tidal sources. The tidal
relief during low tide would allow repairs to be made
to the dikes under dry conditions. If repairs to the
dikes were not completed quickly, serious flooding
would result.
- The probability of an earthquake occurring during the
high water levels of the spring freshet is so small
that the possibility can be considered negligible. 1 4
Estimating Flood Damages in the Fraser River Basin - Archie N. Book and Romeo Princic (1975)
This work contains the methodology and results of the last comprehensive estimate of potential flood damage in the Fraser
River Basin (including Richmond). As this study is concerned only with estimating potential flood damages, no guidance is given in this report as to what appropriate levels of flood protection are. It is noted, however, that flood control structures are typically designed to protect against a "design flood" and that the size of the design flood is usually determined by methods other than economically rational criteria.
A major problem with the results of this study is that it is now
15 years old. Much development has occurred in Richmond in the intervening years. In particular, $500 million of building permits for commercial uses have been issued since 1971.
This study identifies 4 types of flood damage: loss of property and income, risk-taking, intangibles, and restrictions on the use of the floodplain.
MEASUREMENT OF RISK-TAKING
Risk-taking is measured as the difference between the level of protection specified by political decree and the level that would be optimal on the basis of marginal analysis. Intangibles are given only minor consideration.
INTANGIBLES
This report lists intangible damages as loss of life, injuries, psychological disturbances, and social upheaval. Loss of life and injuries are discounted because deaths and injuries normally do not result from flooding in the Fraser Valley and it 15 is unclear that structural flood control measures prevent either deaths or injuries. Given the slow rise in river levels that occurs in the Fraser Valley, these observations about the likelihood of deaths and injuries are reasonable.
Psychological disturbances and social upheaval are not considered because they are difficult to determine in monetary terms.
COST OF RISK-TAKING
The cost of risk-taking is defined as the premium people are willing to pay to avoid very large losses in a catastrophic flood. The report suggests that this premium equals the excess in protection levels specified, over what would be specified by setting marginal costs of protection equal to marginal benefits from protection.
PROPERTY AND INCOME LOSSES
The main focus of this report is on property and income losses.
Three types of floodplain usage were found to contribute significantly to potential flood damages:
- Residential usage. - Commercial and industrial usage. - Agricultural usage. Residential Usage
This study found that slightly less than half of all potential flood damages in the Fraser Valley are from residential losses. For Richmond, it was slightly more than 50%.
Given the 2/3 increase in Richmond's population since 1971, the potential for this type of damage has certainly increased. 16
Commercial and Industrial Usage
Extensive surveys were performed to determine potential commercial and industrial flood damage. Commercial activities were grouped to facilitate calculation of flood damage. Each
industrial activity was surveyed to determine potential flood damage. These activities accounted for 16% of potential damages
in the Fraser Basin and 23% in Richmond. It is clear from the value of building permits issued that commercial activity has
increased greatly in Richmond since 1971. It would be necessary, however, to repeat the extensive survey reported in this work to determine an accurate figure for these usage types.
Agricultural Usage
The report lists the probable agricultural flood damages as:
"crop and equipment losses, reductions in productive capacity of livestock, premature slaughtering of poultry, and the costs of extra feed to replace that lost during a flood" (Book and Princic, 1975, p. 62).
This type of activity accounted for 16% of potential flood damage in the Fraser Basin, but only 5% in Richmond.
SUMMARY
Because of the urbanized nature of development on Lulu
Island in 1971, a large flood hazard was identified. The trend
toward urbanization, has if anything, increased since 1971. The
increasing levels of urbanization since then can only have
increased the hazard. As a thorough documentation of the size of
the Lulu Island flood hazard, the authors' work is relevant to
this thesis. 1 7
The major limitation of the report is its treatment of
intangible and risk-taking costs. By defining risk-taking cost as the premium people are willing to pay over what marginal cost analysis would suggest, the report neglects the possibility that
the aversion felt against extremely large losses occurs because
these losses would lead to social upheaval and disruption.
Safety of Dams: Flood and Earthquake Criteria - Committee on Safety Criteria for Dams (1985)
This work reviews current practices in designing dams to
resist extreme hydrologic and seismic events. It clearly
identifies two types of failure during extreme flooding events:
reservoir failure and dam failure.
Reservoir failure occurs when there is insufficient
reservoir capacity to store inflow waters behind a dam. To
protect the dam and prevent a sudden release of all the water
stored behind the dam, water is routed over a spillway. Extreme
hydrologic events can cause the release of sufficient flows over
the spillway to cause flood damages approaching or even
exceeding those that would have occurred if the dam had not been
built.
Dam failure occurs when the spillway capacity is
insufficient to prevent overtopping and/or breaching of the dam.
A dam failure can cause flood damages much greater than would
have been experienced if no dam had been present. A rare and
large magnitude event can cause either type of failure. This
work is mainly concerned with dam failure rather than reservoir
fa ilure. 18
This report makes several useful points concerning how much safety should be designed into a dam. It states the design objective as follows:
"The objective should be to balance the benefits of making dams safer against the cost of the increased safety and to reduce any risks to acceptable proportions." (Committee on Safety of Dams, 1985, p. 9)
It states that government must decide what is an acceptable
level of risk for involuntary hazards where it acts as the agent
for groups of people.
Several factors are cited that have made it difficult for
government to decide what is an acceptable risk. These include a
lack of precision and accuracy in the prediction of large magnitude hydrologic events, the inability to easily factor in
intangibles such as loss of life into calculations, and the
possibility that future downstream development might
significantly increase the hazard after a dam is built.
This work, also, suggests that the costs of safety relative
to total project cost are important in making design trade-offs:
"For example, if only a tiny addition to the cost of building the dam would be required to design to a higher standard, this greater standard makes sense. Similarly, if the cost of designing to the PMF and MCE are very large in relation to a slightly less stringent design, careful consideration must be given to whether the more stringent design is needed." (Committee on Safety of Dams, 1985, p. 14)
The current design practices reviewed by this work show
that most jurisdictions use a relatively simple hazard
classification scheme to decide on appropriate risk levels. (See
Table I at the end of this thesis). Minimum discharge
*PMF - Probable Maximum Flood. MCE - Maximum Credible Earthquake. 19
capacities, which are usually quite stringent, are set. This
work describes several situations under which these conditions might be relaxed to a less stringent discharge capacity. These
situations include re-evaluation of existing high hazard dams
and evaluation of low and intermediate hazard dams.
It is suggested that risk analysis techniques be applied to
determine required discharge capacity in these situations and
two distinct types of risk analysis are described.
The first technique involves determining the costs of
various spillway designs and the associated long term damages
(risk cost). The spillway capacity chosen would be the one with
the lowest total cost. It was proposed that costs associated
with loss of life be translated into monetary amounts based on
recent court decisions.
This approach has not been widely accepted because:
- There is reluctance to place a monetary value on human
life.
- The present value calculations in an economic analysis
are dependent on the interest rate selected. It is
felt that the choice of interest rate is arbitrary.
- Estimates of average annual risk costs are dependent on
the flood frequency curve adopted. Estimates of the
frequency of rare flood events are inaccurate. (The
frequency for a given size event has been observed to
increase over time as more data is collected).
... The second technique involves choosing the flood flow for
which failure of the dam would cease to create significant 20 additional damage downstream. This technique is more in line with current legal and professional practice, in that it ensures that damage would be no greater than if the dam had not been built.
One problem mentioned, with this approach, is the possibility that increased downstream development after the dam is built could make the expected spillway capacity inadequate.
This technique is particularly applicable to the review of existing high hazard dams. For these dams it is often found that the spillway is inadequate to pass the probable maximum flood because the size of the probable maximum flood has been revised upward.
For low hazard and intermediate hazard dams this report appears to relax the criteria further:
"Safety evaluations for intermediate- and low-hazard dams are primarily concerned with the economic effects of their potential failures. However, a continuing problem with such evaluations is the actual or potential development of the area downstream from the dam after the dam is constructed and the consequent change in the hazard ratings for the project." (Committee on Safety of Dams, 1985, p. 102)
The low- and intermediate-hazard dam break evaluations are not very far removed from the natural flood control evaluation.
Some differences do exist, however. The principal difference is that all dam breaks involve higher hydraulic head, higher water velocities, deeper flood waters, and rapid flooding. All of these factors make the probability of loss of life high if any development exists immediately downstream of a dam. This is not the case with most flood situations. In particular, loss of life is not probable from the flooding of Lulu Island. A second 21 difference is that dams are built and operated by someone. If a dam fails, whoever built it can expect to have to account for resulting flood damage. Finally, the building of dams does not necessarily act as a catalyst to development on the floodplain.
The possibility that future development might increase the hazard is especially important for flood control because, unlike most dam projects, flood control projects increase the hazard by fostering development.
Another important point with respect to flood control is the high incremental costs when efforts are made to reduce the risk of flooding to very small probabilities. This is not true for dams where the cost of a spillway per unit discharge decreases as the capacity of the spillway increases. The differing cost structures make it expensive to avoid the task of assessing risks for the flood hazard by making those risks very small.
On the other hand, there are many similarities between the two situations. Both result in flood damage. In both cases not all flood damage can be calculated. In particular, the social upheaval from a natural flood is difficult to quantify. Both are subject to the inaccuracies in determining frequencies of rare flooding events. Finally, although no one is responsible for natural flooding, governments usually take some responsibility for aiding flood victims.
On the whole, dam breaks are a more serious hazard than natural flooding, but the two hazards are similar enough that 22 the methods used to evaluate dam breaks can be applied, with some modifications, to natural flood hazards.
Modelling the Societal Impact of Fatal Accidents -
Paul Slovic, Sarah Lichtenstein, and Baruch Fischoff (1984)
This article considers two models of how fatal accidents are perceived. The first model suggests that the social cost of
N lives lost is a function of Na. It is commonly suggested that a single large accident is perceived to be more serious than many small accidents producing the same number of fatalities, implying that a > 1.
The second model suggests that the seriousness with which an accident is perceived is not necessarily related to the number of fatalities. The article instead suggests that the seriousness of an accident can be attributed in part to the fact that accidents are signals of future trouble. It states that:
The societal impact of an accident is determined to an important degree by what it signifies or portends. An accident that causes little direct harm may have immense consequences if it increases the judged probability and seriousness of future accidents." (Slovic et. al., 1984, p. 464) To support this model, the authors cite several studies in which people were asked to characterize the risks from several sources - including nuclear power. It was found that the results of these studies could be explained by two factors, unknown risk and dread risk. Unknown risks are those which are: not observable, unknown to those exposed, delayed in their effects, new, and unknown to science. Dread risks are those which are: uncontrollable, global catastrophic, fatal, not equitable, of 23 high risk to future generations, not easily reduced, increasing,
involuntary, and personally affect the respondent.
The risks associated with nuclear power were found to be quite high in both of these catagories. This article does not
specifically cover the flood hazard, but it does consider the
risk from large dams. Large dams are perceived to be known but
dread risks. As the same technology is used to contain floods as
to build dams, but the probability of fatalities is less during
most flooding than during a dam break, floods should be
classified as non-dread, known risks. Thus, this model suggests
a slightly risk-prone attitude toward flooding.
Shank's finding that people in Richmond are at most
indifferent to the flood hazard supports this view. The federal
government's policy that all flood control works be strictly
cost justified also supports this view.
In effect, this policy states that expected flood damages
(net benefits) must exceed the amount spent to avoid the damages
(expected project costs). In addition, because of the fixed
level of protection provided in British Columbia (all flood
protection is designed to protect up to the 1 in 200 year
level), benefit-cost ratios have been higher for urban areas
than rural ones. A flood in an urban area such as Richmond would
cause far more damage than a flood in a rural area having far
less population and development. Current policy spends less for
each dollar of damages in areas with higher expected flood
damages than in areas with lower potential damages. Current
policy is, in effect, risk-prone toward larger flood risks. 24
Risk Perception: A Systematic Review of Concepts and Research Results - Ortwin Renn. (From "Avoiding and Managing Enviromental Damage from Major Accidents") (1985)
This paper reviews the state of the art knowledge in risk perception. It presents a number of concepts that are useful in assessing attitudes to the flood hazard.
It states that, generally, people do a good job in assessing risks that are familiar. Low risks, however, tend to be underestimated while high risks tend to be overestimated.
When a risk is outside of normal experience, few people have the ability to determine even the order of magnitude of the risks
involved. Examples given include:
- The number of lives likely to be lost in a catastrophic
event that occurs once in a lifetime. Either all risks
are graded almost uniformly or exorbitant estimates
are made.
- Disasters expected at long intervals (80 to 100 years).
An important finding reported in this paper is that presumed loss rates are practically independent of risk perception. In other words, people do not assess hazards according to presumed losses per year. Expected losses per year have only slight explanatory value in predicting risk percept ion.
The minimal predictive value of expected losses on risk perception is partially explained by the fact that most people are not familiar with the rationale of probability estimates.
When probabilities are not intuitively understandable, the perceived riskiness is likely to be related to the worst 25 imagined accident. Media coverage sensationalizes the worst imagined accident: i.e., tends to make it seem more probable and more serious than it is.
Another point made in this article is that people do not perceive risk directly. They see options or possibilities that have benefits and risks attached to them. If an option benefits them directly, people will accept more risk than if the option distributes benefits and risks equally throughout society. If the option does not benefit them, but imposes risks on them, people will perceive the risk very stongly.
Hazards that pose a pending danger are perceived as more serious than hazards that come at predictable times. This is so because the dangerous situation could occur at any time.
Two other factors which influence risk perception, after the debate on a hazard has been politicized, are mentioned.
A person's value orientation and general attitudinal system will influence risk perception. This is especially true if the debate on the hazard has become politicized.
In addition, the credibility of normal sources of information can be destroyed in a politicized situation. When this happens, people will pay more attention to counter- information highlighting the risks than to reassuring information and will demonstrate risk averse behaviour to be on the "safe side."
The final point made in this article is that risk perception and risk analysis are not the same thing. 26
A number of the points made in this article are important in assessing the perception of the flood hazard on Lulu Island. First, people cannot be expected to have an accurate perception of the flood hazard because the 1 in 200 year return period used for flood protection is outside of the range of normal experience. Second, the use of a worst imagined accident is important in analyzing the flood hazard because knowledge about the flood hazard is quite good. The worst imagined flood in Richmond is something people would rather not live through. It would cause a lot of property damage and disruption. However, unlike the worst imaginable nuclear accident or hazardous materials spill, a flood is not likely to kill large numbers of people. A flood is, thus, something that people are not extremely afraid of. People are especially afraid of risks that are not well known and which could have catastrophic and long lasting consequences. Flooding in Richmond is a well known hazard, and would likely cause few casualties and no long term effects. Third, the point that people do not perceive risk directly, but rather, perceive options with risks and benefits attached is also important. The decision to locate an activity in Richmond has many benefits for the people taking the risk, including flat fertile land, access to a major metropolitan area, and access to water transportation. Finally, it should be noted that the flood hazard in Richmond does not fit the definition of a pending danger. Current flood forecasting systems give several days warning that 27 a dangerously high river level will occur. In addition, 8 to 12
hours would elapse after a dike break before flooding became
deep enough to immobilize road transportation.
This summary of risk perception gives no indication that
risk averse behaviour toward the flood hazard in Richmond can be
expected. Who Shall Live? - Victor Fuchs (1974)
This work analyzes the health care system in the United
States in the early 1970s from an economic point of view. It is
important to this thesis because it is one of the earliest
examples of a risk-benefit analysis. The methodology used in
this work is applicable to risk analysis, in general, and flood
control, in particular.
It consists of the following steps:
- Identifying the hazards.
- Identifying a standard which can be used to judge the
effectiveness of money spent to reduce the hazard.
- Using economic analysis to examine various options that
will not increase hazards.
- Choosing the least cost option that does not increase the
hazards.
The problems identified in the U.S. health care system were
increasing costs, difficulty in access, and mounting health
problems.
COST PROBLEMS
This work breaks cost problems in health care into average
cost problems and unusual cost problems. Average cost problems 28 refer to the fact that the average cost of health care in the U.S. increased at a greater rate than the rest of the U.S. economy from 1963 to 1972. The unusual cost problems arise for a small number of people who use large amounts of medical services because of major illness. ACCESS PROBLEMS Two types of access problems are identified: general access problems and special access problems. General access problems occur with respect to primary care, emergency care, home care, and care outside of customary working hours. These types of care do not require the higher levels of skill found in medical specialists. In many cases, they could be provided by para-medical staff working under the guidance of a general practitioner. Special access problems affect specific groups of people, such as the poor, ghetto dwellers, and rural populations. HEALTH PROBLEMS This work.points out concerns that health levels are not as high in the U.S. as in other developed countries and that health levels vary greatly among different groups. A disturbing trend noted in this work is the decline in health levels among U.S. males (with the exception of infants and the very old) between 1963 and 1972. HOW IS HEALTH JUDGED? The measure of the general level of health used by this work is mortality. (The percentage of a population of a given 29 age which can be expected to die before a later age). It is argued that other measures of health are highly correlated with mortality. An implicit assumption throughout the book is that changes to the health care system which would lead to an increase in mortality would not be acceptable. Conversely, changes that do not lead to an increase in mortality are judged on their economic merits. ECONOMIC ANALYSIS The thrust of this work is that mortality and health care costs are loosely connected. "The connection between health and medical care is not nearly as direct as most discussions would have us believe." (Fuchs, 1974, p. 6) This work discusses mortality in different age groups to examine the potential*effect of increased medical expenditures. Infant mortality The first age group discussed is infants -(0 to 1 years). It notes that most of the decline in infant mortality, since 1800, has occurred as a result of higher living standards. As nutrition, shelter, quality of drinking water, and improved sanitation have become available to the general population, infant mortality has dropped from-the very high rates (200-500 per 1000 live births) found in 1800. This rise in living standards has been very effective in reducing the mortality rate in the 2-month to 12-month age group. It has been so successful that most infant deaths occur between birth and 1 month of age. Reduction of the death rate in this age group has proved very difficult. It is suggested that the mother's nutrition, smoking 30 habits, and age (very young or very old) are more important than medical intervention in achieving further reductions in infant mortality.
Childhood
The tremendous advances in medical care since the 1930's are noted. These advances drastically reduced the death rate, from childhood diseases, through the use of drug and immunization therapies. Deaths from childhood diseases are relatively rare and mortality in children between 1 and 15 is quite low. There is little more that increased medical expenditures could do to lower mortality in this age group.
Young Adulthood
For young American males, 3 out of 4 deaths occur by means of violence, including automobile and other accidents, suicide, and homicide. Behaviour-related mortality such as this cannot be reduced by medical care.
Early Middle-Age
For male Americans in early middle age, the leading causes of death cited are heart disease, cancer, accidents, suicide, cirrhosis of the liver, and homicide. Lifestyle, including diet, exercise, tobacco consumption, alcohol consumption, and the propensity for violence are the chief contributors to mortality for this age group. Again, increased medical expenditures will not significantly decrease the death rate in this age group.
Late Middle-Age
For males in late middle-age, heart disease and cancer dominate as causes of mortality. As these diseases are lifestyle 31 related, increased medical expenditures will not significantly decrease mortality.
In summary, this work presents a convincing case that mortality in the United States is relatively invariant once a basic level of health care has been attained. This basic level of care is far lower than the levels normally available for most
Americans when the work was written. This finding allows considerable scope to consider alternative methods of providing health care that reduce cost and increase access.
On this basis the rationale for current expenditure patterns is examined. This author states:
"Although it is the patient rather than the physician who has the major influence on his health, the opposite is true regarding the cost of medical care."(Fuchs, 1974, p. 6) The work goes on to point out that the importance of the physician in determining health costs results from the physician's control of medical procedures, hospitalizations, and drugs prescribed. The suggestion that overpayment of physicians, because of their monopoly position, is a significant cause of high health care costs is rejected. The argument that providing more physicians is a feasible method of improving access to the health care system is examined. The problems with this approach are the impossibility of training sufficient physicians to provide all of the primary care access required and the high cost of using highly trained physicians for this purpose.
It is suggested that people want access to the health care system 24 hours per day, 7 days per week for primary and emergency care. Further, they want the person attending them to 32
be familiar with their case history. It is clear that the provision of more highly trained specialists is not the way to
fill this demand.
By carefully examining the problem with access to the health care system, this work made it clear that less expensive
options exist than simply expanding the system.
Special access problems and unusual cost problems were
discussed in conjunction with methods of paying for health care.
The point is made that, no matter how health care is financed,
if more health care is desired, the cost will be higher.
However, it is noted that payment on a fee for service basis by
the patient effectively excludes the poor from the health care
system and leaves everyone open to the possibility of extremely
high costs from unusual demands for health care services. It is
also noted that fee for service payment provides little
incentive for the physician to minimize the usage of health
care.
For these reasons, universal health insurance based on a
fixed payment per person is advocated. It is interesting to note
that despite the fact that most of the analysis in this work is
economic in nature, major factors in making this recommendation
are value judgements. The importance of equality of access and
protection from unusual financial risks are both value
judgements.
Several other recommendations are made to reduce the cost
of health care, without adversely affecting health care. These
include: decentralized health care delivery systems, more 33 flexible use of health resources/personnel, matching physician supply with demand, and matching hospital capacity with demand.
In summary, this work found that, beyond a fairly minimal level of availability of health care services, the effect of the health care system on improving overall health is minimal.
Improvements in health will likely come from medical research or from changes in human behaviour. It also found that considerable scope exists for reducing the costs of the health care system and improving access to the system without endangering health.
Major differences exist between the flood control problem and the health care problem. In particular, the effectiveness of the health care system can be measured by average numbers of deaths and average amounts of sickness (mortality and morbidity respectively). Because deaths and illness happen frequently, this work did not consider the advisability of providing a health care system to handle infrequent events that would affect large numbers of people.
In designing flood control systems, infrequent, catastrophic events must be considered. The amount used to evaluate flood control projects, expected annual flood damages, will probably never occur in any year.
Notwithstanding these differences, the methodology presented in this work is extremely useful in evaluating the flood hazard. This work is relevant because it presents a method of integrating tangible and intangible factors to evaluate policy options. The methods presented in this work are applicable to a wide range of problems including flood control. 34
THE FLOOD HAZARD
Lulu Island is 12000 hectares of flat land in a mountainous province, located within easy commuting distance of the downtown of a major metropolitan area. It is, also, a low-lying island located in the Fraser River estuary. Lulu Island is made up of poorly consolidated sandy soils in the most tectonically active area of Canada. All of these factors have led to the creation of a flood hazard on Lulu Island.
Its proximity to the city of Vancouver and flat topography have created a social and economic opportunity. Flat land is excellent for the development of residential, agricultural, commercial and industrial properties. The mountainous nature of
British Columbia's topography and of the Vancouver area has meant the supply of flat land for these purposes is limited.
The opportunity to fulfill demands for flat land for residential, commercial, and light industrial development on
Lulu Island has been recognized for at least 20 years.
In 1966, virtually the whole western half of Lulu Island was zoned for urban uses, despite the fact that large parts of the urban zoned areas were in agricultural use.
The opportunity has been and is being realized by the growth of an urban municipality with a population of over
100,000 and property assessed at $6 billion. Population has grown by 2/3 since 1971 and is still growing. Residential, commercial, and industrial development have grown with the population. The growth of commercial development has been especially notable (see table III) since 1971. 35
It is important to keep in mind the magnitude of the economic and social opportunity presented by the development of
Lulu Island in evaluating the flood hazard there. The possibility of potential flood damages, even extremely large potential flood damages, has not been sufficient to cause any hesitation in realizing this opportunity.
The high level of development that has occurred on Lulu
Island is a necessary prerequisite for a large flood hazard to exist. If Lulu Island were undeveloped, no flood hazard would exist.
Conversely, if there is development, but no possibility of flooding, then there is no flood hazard. Two sources of flooding exist around Lulu Island: the Strait of Georgia and the Fraser
River. To protect against flooding from these sources a system of dikes has been built around Lulu Island. Several possible mechanisms exist which could cause these dikes to fail and result in subsequent flooding.
These mechanisms include winter storms, the spring freshet, and earthquake damage to the dikes. Conceivably, combinations of these events could also cause flooding, but as shown in table
IV, the probabilities of combined events are small.
To understand the nature of these mechanisms and to evaluate the seriousness of a dike failure caused by each mechanism, a good understanding of the topography, tidal ranges, expected flood depths, expected flood warning, and geology on
Lulu Island is necessary. In addition, an understanding of the 36
ease of repairing a dike break under each of the failure mechanisms is necessary.
TOPOGRAPHY
Lulu Island is essentially flat. The standard measurement scale used for elevations is based on geodetic zero elevation
(GSC). Zero metres GSC is set at mean sea level. For the rest of this discussion all elevations cited are relative to zero metres
GSC.
Elevations on Lulu Island vary from Om to 4.0m over a length of 21 km. Even this relatively narrow range overstates the elevation differences for flood control purposes. All structures on Lulu Island must be on ground that has been built up to at least .9m and only 10% of the total area is above 2.1m.
Further, almost all of the more heavily developed commercial and residential areas are between .9 and 2.1m. So it can be seen that "flat" is an apt description of Lulu Island's topography.
A major implication of this flat topography is that a major break in the dikes, anywhere on Lulu Island, could flood the western half of the island, where most urban development is concentrated, and probably would flood the whole island.
TIDAL RANGES
Tidal levels are inherently variable phenomena. The major determinants of tidal levels are the gravitational effects of the moon and sun, atmospheric pressure, and wind speed and di rect ion.
The gravitational effects of the sun and moon produce high and low tides twice a day. In addition, the gravitational pull 37 of the moon produces two tidal cycles per month (lunar day). The combined effect of solar and lunar gravity usually produces a
single highest tide for each month and for each year. The highest tide for each year due to gravitational forces is called
the highest normal tide.
Tide levels vary inversely with atmospheric pressure. In
effect, the Strait of Georgia acts as an inverse barometer. When
there is a high pressure system over the Strait of Georgia,
water levels are depressed. Conversely, a low pressure system
causes increased water levels.
High winds that last over a period of several hours cause
large waves. This wave set up adds to any tidal effects or surge
resulting from changing atmospheric pressure.
In practice, the highest velocity winds and lowest
atmospheric pressures occur during winter storms. These storms
occur from November to March.
Comparing Table V to the land elevation on Lulu Island, it
can be seen that most of the island is at elevations equal to or
greater than the normal high tide level. This means that only
severe tide surges during winter storms present a flood risk.
All of the island is above low tide level.
CLIMATOLOGICAL CHANGE
In recent years, there has been increasing speculation that
ocean levels are not stable. The Atmospheric Environment Service
has predicted a rise of up to 1m in sea level in the next 50
years, as a result of a world-wide warming trend. The results of
this rise in sea level would put most of Lulu Island below 38
normal high tide level, but would still leave the island well above the.low tide level.
EXPECTED FRASER RIVER STAGES
The Fraser River only poses a flood hazard during the
spring freshet. The spring freshet is caused by the annual
snowmelt in the mountainous areas of the Fraser River Basin. A
number of factors determine the stage which will be reached
during the spring freshet. These include:
- The amount of snow occurring during the course of the
winter. Heavier snowfall produces the potential for a
higher peak runoff.
- The suddenness and intensity of spring warming. A sudden
hot spell after a cool spring increases the chance of
high water.
- The geographical distribution of spring warming. If the
whole basin warms simultaneously, higher runoff will
result.
- The co-ordination with which the tributaries of the
Fraser River reach their peak discharge. If flood
peaks from tributaries occur so that they are
superimposed on each other, then the peak reached will
be higher.
- The occurrence of intense rainfall that coincides with
peak run-off from snowmelt.
If enough of these factors occur in a given year, the peak
river discharge can be very high. The normal peak discharge is
5600 to 8500 m3/s. The highest known discharge is 17,000 m3/s. A 39 discharge greater than or equal to this one has a .005 probability of being exceeded in any one year. Accurate river stages have not been calculated for river discharges higher than 17,000 m^/s. River stages for this discharge slope downward from 3.7m at the eastern end of Lulu Island to 2.5m at the western end. At the lower (western) end of Lulu Island these levels are .4 to 1.6m above 90% of the island. At the upper (eastern) end they are above virtually the whole island. GEOLOGY Lulu Island is located in the area of greatest tectonic activity in Canada. It is composed of loosely compacted silty sands and sandy silts. The design earthquake acceleration has a .0021 annual probability of occurrence. When Lulu Island's soils are dry they are stable under the design earthquake acceleration. However, because Lulu Island is a low-lying area, the water table is always high, ensuring that soils are saturated. Under these conditions, Lulu Island's loosely consolidated soils are likely to liquefy to a depth of 6-9m. The increased pore pressure that results when liquefaction occurs, leads to the expulsion of sand and water from the ground. The expulsion of sand and water can lead to differential settlement, causing cracking in flat areas and slumping in areas loaded with fill and on steeper slopes. As the dikes fit these criteria, significant damage to them would occur. A comparison of normal tide and river levels with elevation on Lulu Island shows that most areas of the island would be at 40 or above high tide or river levels as long as the earthquake did not occur during the spring freshet or an extreme high tide.
It should be noted that the predicted 1m rise in sea level from climatological change alters this situation. Under the assumption of a 1m rise in sea level, tidal levels would be higher than most of Lulu Island during any high tide.
The dikes surrounding Lulu Island are made of the same types of soils as the rest of the island. During extreme events, the dikes are saturated and could be expected to liquefy.
Greater damage could be expected to the dikes if they, rather than just the underlying soils, are saturated. During extreme events, river and tide levels are higher than most of Lulu
Island. For both of these reasons, the combined event (which is extremely unlikely) of earthquake and high tide or high river flows could produce severe flooding.
DIKE REPAIR
A key consideration in assessing the seriousness of any of the foregoing flood hazards, is the ease with which a breach in the dikes can be repaired. Many organizational issues affect the capability to repair dikes under emergency conditions. At this point, adequate organizational preparations will be assumed.
Given adequate flood fighting capabilities, the most important determinant of the ease of dike repair is the velocity with which water moves through a breach.
If the water is moving very slowly (or preferably not at all), dike repair is relatively straight forward. If the area behind the dikes is dry enough that equipment can work in the 41 breach, dike repair is even easier. On the other hand, if water is pouring through the dike at 2 m/s dike repair can be a very difficult task.
The easiest conditions for the repair of dikes are those in which it is dry behind the dikes and in the dike breach. Under these conditions, it is possible to work along the full length of the breach simultaneously and any easily accessible, reasonably suitable material can be used to make the necessary repairs. Under these conditions, access to sufficient quantities of sand and earth moving equipment would be the limiting factors in effecting repairs. Repairs made after an earthquake could probably be made under these conditions.
Somewhat more difficult conditions occur when there is water in the dike breach, but it is moving at extremely low velocity. Under these conditions it would not be possible to work behind the dikes because wet and/or muddy conditions would prevent access. Any reasonably suitable material could be used in repairing the breach, but it would be necessary to end dump material into the dike breach from on top of the dike at either end of the breach. The limiting factor in making repairs would be the logistics of maneouvering trucks to and from the ends of the dike breach along the top of the relatively narrow dikes.
Repairs made after a severe winter storm would probably require this technique.
The most difficult conditions occur when water pours through a breach at appreciable velocities. A breach during the spring freshet could result in velocities of 2 m/s. Water moving 42 at this velocity is capable of moving 5 cm diameter rock. Larger rock would be desirable for repair work; and would be necessary for the final stages of closure. The ends of the breach would be unstable and any smaller materials (such as sand) dumped into the breach would be swept away by the water pouring through the breach. Several strategies have been suggested to deal with this situation. They include: - Catch the breach early before it has a chance to enlarge. End dump rock into the breach to close it. This strategy was successfully applied in Chilliwack for a small breach in 1948. Other breaches opened to over 100m in only a few minutes during the same flood. This strategy can only be expected to work for a limited number of breaches. - Build a ring dike around the breach. This approach will work as long there aren't multiple breaches. It is, however, slow because because it requires several times as much dike to be built as the length of the breach. A considerable amount of flooding can occur while the ring dike is being built. - Let the water inside the dikes pond up to the level of the river outside of the breach. When this happens the velocity through the breach will drop to near zero and the breach can be directly repaired. As flood damage is largely determined by depth of flooding, ponding on 43
Lulu Island would result in greater damage than if no
dikes existed.
- Deliberately breach the dikes on the downstream end of
the island to let the water drain off the island. This
approach would prevent ponding. The use of this
strategy would probably mean that flooding would last
until the river level dropped close to the bankful
level.
From the foregoing discussion, it is clear that a breach with water continuously flowing through it is the most difficult type to repair.
TIDAL RELIEF
Implicit in the foregoing discussion of dike repair is the concept of tidal relief. During low tide, there is a reduction in the velocity of water flowing through a breach. This provides an opportunity to repair dikes under much less difficult conditions. These conditions make dike repair much faster and, hence, limit the amount of the resulting flooding. While it is true that any tidal relief is welcome in a flood situation, to provide a real opportunity to repair the dikes, low tide must reduce water levels to level with or below the bottom of the breach for several hours during each tidal cycle. As can be seen from Fig. 3, significant tidal relief occurs for the western half of Lulu Island. Tidal relief from the spring freshet is not great enough to fit this condition in the eastern half of Lulu
Island. 44
It is reasonable to assume that all dike breaks on the western half of Lulu Island, from any source, can be repaired in. under 24 hours. On the other hand, the least that could be expected from a major dike break on the eastern end of the island from the spring freshet is several days of flooding.
FLOOD DEPTHS
Predicted flood depths vary for the different types of hazard. The major determinants of flood depth are the length of time to repair the dikes, the difference in elevation between the water outside the dikes and the ground inside, and the size of any dike breaches.
The length of time to repair a breach is determined by the size of the breach and the techniques that can be applied to effect repairs. An extremely large breach would take longer to fix because more material would be required. The techniques that could be applied to repair, a breach depend mainly on the presence or absence of tidal relief. Without tidal relief, water is constantly moving across a breach, making the task more difficult.
The elevation difference across a breach determines the volumetric flow rate through the breach. The elevation difference can be expected to be greatest for a breach on the eastern end of Lulu Island. A breach from earthquake damage not associated with an extreme hydrological event would have a much smaller elevation difference. 45
The width of a dike breach is essentially random. One thing is clear, a wider breach will allow more water through than a narrower one.
The deepest flood depths would result from a breach on the eastern end of Lulu Island from which the water ponded to either the level of the inflow water or the level of the dikes
(whichever is lower). Expected flood depths under these conditions would be 2.3m.
If no dikes existed or deliberate breaches were made in the dikes in the western end of Lulu Island to prevent ponding, expected flood depths would be 1.2m. It should be noted that for a major breach in the dikes in eastern Lulu Island, a similar length breach would have to be opened downstream to prevent ponding above the 1.2m level.
Flooding from a winter storm could be expected to increase by 6 cm per tidal cycle. As this sort of flooding would be subject to tidal relief it should be possible to repair any damage within 24 hours. Damage from this level of flooding would probably remain within acceptable bounds.
Flooding from earthquake damage in the absence of an extreme hydrologic event would be limited in extent because most of Lulu Island is above normal high tide. However, if sea level rises over the next 50 years due to climatological change, serious flooding would result if repairs were not made quickly.
Potential damage from this source is not a serious risk and may not materialize unless the predicted rise in sea level does, in fact, take place. 46
FLOOD WARNING Of the various types of flooding, the spring freshet is the only one for which accurate warnings could be issued before a breach occurs. Approximately four days warning could be expected for this type of flooding. These warnings would only predict high water levels and the danger of flooding. They would allow sufficient time to set up dike patrols, flood fighting crews, and to move some property to higher levels. It is doubtful that a full scale evacuation would be ordered on this basis. From the description of tidal flooding, it is clear that ample opportunity would exist to evacuate Lulu Island (should it be necessary) before flood depths were sufficient to cripple road transportation. Flooding from the spring freshet in the eastern end of Lulu Island would almost certainly require the evacuation of Lulu Island for all except the smallest of breaches. Water levels would be less than .3m for 12 hours after a 200m breach. For a 400m breach, only 8 hours would elapse before the .3m level was reached. As evacuation would be much more difficult at flood depths above .3m, 8 to 12 hours provides an outside limit to the time available for orderly evacuation. Beyond this time, the highway system would be impassable and evacuation would have to be carried out by boat or helicopter. RATING OF FLOOD HAZARDS Three mechanisms were identified which could cause the dikes to fail: winter storms, the spring freshet, and earthquake damage. It is clear from the foregoing discussion that the depth 47 and duration of flooding from these mechanisms makes the spring freshet the most serious hazard. Flooding caused by winter storms is a serious hazard only if no efforts are made to repair the dikes. Flooding from earthquake hazard is more a matter of concern than a danger at current sea level. If sea level rises, flooding from earthquake damage would be a hazard on the same order as flooding from winter storms. No studies have been done to determine the economic cost of tidal based flooding. The low depth of flooding, however, precludes large scale economic damage. Extensive studies were done on the flood damage from the spring freshet as part of the Fraser River Upstream Storage Report (1976). By updating these studies to account for inflation and population increase, flood damage has been estimated at roughly $500 million (see Table VI) Factors not- taken into account in this estimate include: the large increase in commercial development that has taken place on Lulu Island since the study was done, the trend toward building better quality houses, and the trend toward developing basements. These factors could make the actual flood damage considerably higher than the above estimate. Finally, this estimate does not include intangible costs from flood damage. The social upheaval of shutting down a community, of 100,000 population, for over a month and disrupting the life of that community for the next 6 months while repairs are made, is difficult to quantify, but should not be neglected in determining flood protection levels. 48
RISK ANALYSIS AND PERCEPTION
In addition to knowledge of the extent of a hazard, knowledge of the likelihood of occurrence is necessary to judge what constitutes an appropriate response. The overall response to a hazard can be determined intuitively or by the use of statistical modelling. If the response to a hazard is judged intuitively, the process is called risk perception. If statistical modelling is combined with quantitative measures of the extent of a hazard to determine an appropriate response, the process is called risk analysis.
Both risk analysis and risk perception can be used to determine the appropriate level of protection against flooding in British Columbia. In essence, both methods try to answer the question "How safe is safe enough?". There is, however, no guarantee that both methods will arrive at the same answer.
The judgement of what constitutes an appropriate level of protection is a problem that has no calculable solution. All costs of flooding are not economically quantifiable. The following description of the Pearl River flood in Jackson,
Mississippi in April of 1979 describes the social upheaval from a flood.
"As the flood waters receded the dimensions of the residential property damage became apparent. Flood damages are particularly depressing. Not only have people suffered losses, but they also must endure an excruciating clean up process. The house is normally a mess. It smells. The water may be contaminated. The electricity is usually damaged meaning one must toil in the dark. Snakes can be present. Cherished family belongings have to be discarded into a growing trash pile."(Anderson and Weinrobe, 1979, p. 5) More detail is provided on the next page. 49
"The loss of furniture, fixtures, and personal belongings produced the most tortuous losses. Wallboard and carpeting are impersonal and can be replaced. The loss of family photographs, a favorite table, the dining room set or piano goes well beyond the monetary value of these items. The piles of these and other objects that accumulated in front of damaged houses was one of the sadder sights observed in Jackson."(Anderson and Weinrobe, 1979, p. 6) In addition, not all costs of flood protection are quantifiable. In particular the environmental costs of flood control measures are often quite difficult to determine. It has, also, been made clear over the years that not all decisions concerning flood control are made on a purely economic basis. The economics of damming the Fraser at Lillooet (250 kilometers northeast of Vancouver) were never considered in detail because of the negative impacts of the dam on the salmon fishery. RISK PERCEPTION Recent research into risk perception has shed some light on an important component of the determinant of appropriate protection levels. The perception of risk is important because the intuitive assessment of a hazard influences both individual and collective reaction to risk. Behaviour with respect to risk can be classified as risk prone, risk neutral, or risk averse. (Slovic et. al., 1984). - Risk prone behaviour would pay more to avoid many small accidents than to avoid one large one causing the same amount of damage. 50
- Risk neutral behaviour would pay the same amount to avoid
many small accidents as to avoid one large one causing
the same amount of damage.
- Risk averse behaviour would pay more to avoid one large
accident than many small accidents causing the same
amount of damage.*
Research into risk perception has shown that people determine their response to risk based on a number of qualities of the risk. These qualities have been resolved into two factors: dread risk and unknown risk as shown in Fig. 2. Flood risk has been drawn onto Fig. 2 as an open circle based on the fact that the same technology is used to predict dam failures as dike failures, but dam failures are more serious hazards. Dam failures involve deeper water moving at much higher velocities, and carrying larger debris. For these reasons dam failures are more likely to cause fatalities than the slow rising flood waters typical of the Fraser River.
The position of the flood hazard in the lower left quadrant of Fig. 2 leads to the hypothesis, based on risk perception, that response to the flood hazard is risk prone.
*It should be noted that this definition of risk averse behaviour differs from the definition of risk averse behaviour put forward in Book and Princic during the Fraser River Upstream Storage Report. In that work, risk averse behaviour was defined as the direction of more resources toward avoiding a hazard than the optimum level of expenditures derived from cost benefit analysis using expected costs and benefits would warrant. This is similar to the conventional definition from decision theory. Practical problems occur with this latter definition because it is impossible to separate unmeasured intangibles from the amount that can be assigned to risk aversion. 51
The current flood control policy was not justified on economic grounds. This fact was recognized in the last economic analysis of the flood hazard on Lulu Island: "The most common practice is to build a structure so as to protect against some large "design" flood determined more by political decree or arbitrary selection than by any stated economically rational criterion."(Book and Princic, 1975, p. 5) The design flood for all flood protection works in British Columbia is a flood that has a .005 annual probability of occurring. This flood is also referred to as the 1 in 200 year flood. Setting all hazards to the same probability of occurrence is, however, a risk prone strategy. The level of protection for both Lulu Island and Dewdney Diking Area, a small agricultural area 80 kilometers east of Vancouver, has been set to the same level. Dewdney Diking Area, a small and lightly populated area, is a smaller flood hazard than Lulu Island. Because the level of protection is the same for the two areas, more is spent to avoid each dollar of flood damage for the smaller hazard in the Dewdney Diking Area, than for the larger hazard, Lulu Island. Thus it can be seen that this method of determining levels of protection is risk prone. Presently, the expected flood damage for Lulu Island, after allowance has been made for the protection afforded by the dikes, is $15 million annually (see Appendix C). Funding was refused for Westham Island under the federal provincial cost sharing program because protection would not have been cost 52
justified at the 1 in 200 year level.* More flexibility in
setting the level of protection is necessary.
The gap between the current level of protection, based on collective risk preception and the expected costs of flooding
Lulu Island is particularly serious. It should be especially worrisome to the federal government because the federal- provincial cost sharing formula for flood damage allocates 90%
of the costs of flood damage in British Columbia over $10 million to the federal government.
RISK ANALYSIS
The other methods suggested in the literature for
determining levels of protection are based on risk analysis.
They are:
- Set levels of protection to minimize the expected costs
of flood damage plus the costs of flood prevention
measures.
- Use a rule of thumb system to match flood protection with
the size of the flood hazard.
Setting protection to minimize costs is a variant of the
risk-benefit analysis applied to the provision of health care
services. The analysis applied to health care suggested ways to
minimize the costs of providing health care without increasing
the expected number of deaths.
A similar method of setting flood protection levels is also
limited by the restriction that the chance of loss of life not
* The provincial government has subsequently provided protection for Westham Island to a lower standard than the 1 in 200 year level. 53
be increased in order to minimize costs. For flood control on
Lulu Island this limitation is not very severe because there would be adequate time to evacuate the island before or after a breach in the dikes occurred.
This method is theoretically attractive because it provides an optimum level of protection that can be used. However, some practical problems exist in applying this method.
It does not take into account intangibles. Intangibles exist in determining the costs of flood protection works and the costs of flood damage. The environmental damage that can be done when constructing flood control works can be both great and difficult to measure. Similarly, the costs of development that doesn't occur because of zoning or floodproofing requirements and the costs of social upheaval resulting from a major flood are difficult to measure.
Even where it is possible to quantify the costs and benefits, the analysis to determine them is difficult and expensive. Field surveys are required for industrial, commercial and residential properties. Engineering work must be done to determine costs of flood protection at varying levels of protection. The extra cases that must be considered, make the analysis of a flood control project more difficult and require more time.
The final problem with this approach is that it is heavily dependent on the assumptions made about the course of future development in the area to be protected. Predicting growth over a 50 year period is an inherently inexact process. 54
This approach is theoretically optimal, but, especially for smaller diking districts, is expensive and cumbersome to apply.
The results for a large diking district such as Lulu Island would be worthwhile and probably enlightening.
Another approach that has been widely applied to the evaluation of dam safety is to use a rule of thumb system to roughly match the protection level to the hazard level. An example rule of thumb system has been derived from the one used by the United States Army Corps of Engineers, and is presented in Table VIII.
There are several disadvantages to the use of a rule of thumb chart. It does not attempt to identify an optimal level of protection and it does not take into account differing costs to provide protection to given level.
In terms of the second point, the costs of flood protection are affected by expected water levels, the shape and size of the diking area, and the method used to achieve flood protection.
Circular diking areas are less expensive per hectare enclosed than long, thin, banana-shaped diking areas. The costs of building dams for flood protection have proven extremely high in
British Columbia.
Notwithstanding these problems, this method should not be dismissed out of hand. This method provides a better fit in assigning protection levels to areas with different hazard levels than is provided by the single province-wide level of protection in use today. 55
It is easy to implement from a procedural point of view.
The table fits on one piece of paper and can be easily memorized. Combined with professional judgement, it can take intangibles and future growth patterns into account. Where appropriate and justified, economic modelling and detailed engineering design could be used to adjust these guidelines.
The advantages of this method are that it is easy to implement and allows the flexibility of professional judgement to be applied in resolving issues involving uncertainty and difficulties in quantification. It cannot, however, be applied without taking the implicit cost base into account.
From the foregoing discussion, each of the methods suggested has drawbacks. The following method draws on the strengths of all three methods that have "been discussed:
- A minimum level of protection be set for extremely low
hazard areas. An event with .02 annual probability of
exceedence seems reasonable.
- A rule of thumb chart be used for all but the largest
diking areas or areas in which there is a clear
probability of loss of life.
- Formal risk benefit analysis be done for the largest
areas and those in which loss of life is a factor.
The problems with the current method of setting protection levels for Lulu Island have increased with the amount of development on Lulu Island. The expected damage increases with development and decreases as levels of protection are increased.
Since the last upgrade to the dikes, development has increased 56 the flood hazard on Lulu Island, but political decree has held the level of protection, and hence the risk, constant. The result has been increased expected flood damage. As development on Lulu Island is continuing and the policy for determining the level of protection has not changed, the trend will be for expected flood damage to continue to increase. Eventually, it will be necessary to increase the level of protection. ACCURACY OF HYDROLOGICAL PREDICTIONS Throughout this paper, the statistical predictions of the probabilities of hydrological events have been taken as a given. For the Fraser River Basin, predictions of events with annual probabilities as low as the design standard of .005 are reasonably well supported. Attempts to predict probabilities of events that happen less frequently than the design events are less well supported. The lower the probability of occurrence, the greater the uncertainty that must be attached to estimates of the probability of occurrence. This uncertainty comes from two sources. First, given a set of values from which a probability distribution is estimated, only one of a wide range of distributions could plausibly be the correct distribution. Second, it is possible that events with extremely low probabilities of occurrence do not fit the distribution derived from available data because they are caused by different processes than those that caused known events. 57
The use of probabilities with this level of uncertainty in conjunction with accurate cost estimates to produce a single expected flood damage amount is methodologically unsound.
A second area of uncertainty is the probability that a dike will fail at a given water level. It is unreasonable to expect dikes to be safe up to the design level and fail as soon as the water level passes the design level.
Whether a dike withstands water levels below, up to, or above design levels depends on many factors including flood duration, underseepage, piping, boils, vegetation and animal burrows in the dike, and the effectiveness of flood fighting efforts. From this list, the level of maintenance is an important determinant of dike stability.
The level of maintenance that a dike will receive is extremely difficult to predict before the dike is built.
Instituting a nominal higher levei-of protection by raising the dikes will do nothing to ensure adequate maintenance. It is, in fact, possible that the maintenance of higher dikes will be worse because flooding will be less frequent.
OTHER STRATEGIES
The above discussion suggests that other strategies to reduce the risk than raising the dikes be pursued. The strategies that will be proposed will be aimed at reducing or providing for the hazard rather than reducing the risk levels.
The first strategy involves sectioning Lulu Island by raising key parts of the road system above flood levels. In many 58 ways this suggestion is an adjunct of contingency planning and will be discussed in the next chapter.
The second strategy is to accept that flooding will occur on an infrequent basis and to set up a contingency fund to defray the costs of such flooding. In effect, this is a flood insurance program and will be discussed in the chapter on flood insurance. 59
CONTINGENCY PLANNING AND OTHER MEASURES TO REDUCE DAMAGE
While much has been written about how to prevent flooding and how to design dikes to prevent breaches from occurring, almost all information on repairing breaches is contained in engineering lore. It has always been assumed that a dike breach resulting from the spring freshet would be impossible to contain. For this reason, efforts have always been directed toward ensuring that no dike breaches occur. This approach has its drawbacks. Past experience has shown that techniques to reduce the flood risk below current levels are expensive to implement and conflict with other uses of the river basin. In particular, these techniques conflict with fishery and recreational uses.
Some policies have been suggested that would diminish the flood hazard by limiting development on the floodplain or designing floodplain structures to resist flooding. These policies have not been particularly effective in controlling the flood hazard. The opportunity to develop Lulu Island as an urban community has far outweighed any pressures to limit development to the low density agricultural and recreational uses that would limit the amount of potential flood damage. Designing structures to withstand flooding has proved to be too expensive for widespread acceptance.
A "safe-fail" policy that would allow some flooding without causing catastrophic losses and would be economically feasible would be attractive. 60
CURRENT POLICY
Before suggesting "safe-fail" policy, it is necessary to review current planning for limiting flood damage after a dike break occurs. Current planning is to requisition personnel, earth moving equipment, and repair materials to repair the breach as quickly as possible. In addition it is recognized that a major breach from the spring freshet would require evacuation of the entire population of Lulu Island.
FLOOD FIGHTING MATERIALS
No specific stock piles of rock and other materials are kept for dike repair. However, several building materials suppliers operate on Lulu Island. These suppliers should have sufficient materials on hand for dike repair. At least some of this material is accessible from the dike and so could be used to repair dikes after flooding has occurred.
FLOOD FIGHTING EQUIPMENT
Equipment for dike repair can be requisitioned from the municipality or private contractors. On short notice it has been found that less trucks were available than were needed. For a freshet based flood there would be several days notice of the existence of flood danger. Advantage should be taken of this notice to procure any needed equipment and personnel. Formal agreements with equipment suppliers or even a municipal by-law to give priority to emergency flood fighting equipment demands over other demands would also be good practice. 61
EVACUATION PLANNING Total evacuation of Lulu Island could be accomplished in 6- 8 hours. This estimate depends on the highway system remaining open. Modeling done in the course of this study suggests that it would take 8-12 hours for flood levels to reach the .3m level from a moderate to large dike breach. Low lying areas would reach this level more quickly than higher areas. As ,3m or 1 foot of water would make the road system impassable, these areas should be identified and evacuated first. ACCESS TO LULU ISLAND There are no special provisions to keep access routes open. The George Massey Tunnel would collect water very quickly because it is below the level of the island. All bridges are above flood levels, but access roads are not. It is reasonable to expect that the approaches would stay open as long as the rest of the road system. SUMMARY OF CURRENT CONTINGENCY PLANS The current approach shows a good practical grasp of the situation and is certainly adequate for tidal based flooding. Flooding from the spring freshet is a more difficult problem. From the previous discussion of dike repair techniques, it should be clear that for all but the smallest of breaches, the feasible techniques available are: build a ring dike, let the flood waters pond before repair, or breach the downstream dikes to prevent ponding. The option that would effect dike repairs the most quickly, building a ring dike, would probably take a minimum of 48 hours to complete. After 48 hours of flooding, 62 flood levels could be 1.2 to 1.8m. Large amounts of property damage would result. It is clear that current contingency plans would not be particularly effective in reducing flood damage after a dike breach occurring during the spring freshet.
SUGGESTIONS FOR CONTINGENCY PLANNING
An option, that has been alluded to but has never been pursued, consists of segmenting the island to prevent a single breach from causing flooding throughout the island. Probably, the most feasible way to approach segmentation would be to raise parts of the road system so that they are effectively out of the flood plain.
If designed correctly, this approach could be effective in cutting the risk of a catastrophic flood. The probability of both the dikes and the raised portion of the road system failing would be extremely small. The areas that would be flooded would be lightly populated and have agricultural development. By allowing flood waters to pond against the raised roads, dike repairs could be made more quickly. It would ensure access to the island was maintained, both for evacuation purposes and to move flood fighting equipment and materials.
One alignment that appears promising is shown in Fig. 4. If a dike breach occurred west of the proposed alignment, tidal relief would be available to limit repair time. Development is relatively light east of the alignment so that flooding from a breach there would cause relatively little damage. The rapid ponding that would occur in this case would make it possible to repair the dikes quickly. 63
The one disadvantage of segmenting the island that should be noted is that segmetation would make flooding worse in the areas flooded. The preponderance of development on the western end of Lulu Island makes segmentation a good trade-off because worse flooding in lightly populated areas would be more than offset by protection of large amounts of urban development.
OTHER RECOMMENDATIONS
In addition to raising road levels on Lulu Island, provision should be made to ensure bridge and tunnel access routes remain passable. The entrances to the George Massey
Tunnel should be diked on both ends or the tunnel will fill with water.
All bridges are above flood level but access roads are not.
The level of bridge access roads should be raised above flood level. Ensuring access routes to the island are passable will aid in evacuation and rescue operations and will allow personnel, equipment, and material to be brought onto the island for dike repairs.
Another consideration is to make provision to rapidly close off any underpasses, culverts, or other holes in the raised portions of the road system. Failure to do this would result in flooding in the developed areas.
As evacuation times will be tight, the lowest areas should be identified and evacuated first. Low lying portions of the road system (below .3m geodetic) should be identified to ensure that they do not block any evacuation routes. People not involved in flood fighting should be encouraged to leave Lulu 64
Island and to store their possessions above flood levels when it becomes apparent that high flood stages will be reached.
Care should be taken that adequate supplies of materials be stockpiled and accessible from the dikes. Alternate supplies of materials should be located off Lulu Island as a back up.
Formal agreements should be made with trucking companies or a municipal by-law should be drawn up to ensure adequate equipment is available for flood fighting.
On the whole, contingency planning is adequate as long as
large amounts of flood damage are acceptable from flooding caused by the spring freshet on an infrequent basis. On the
other hand, raising the level of selected parts of the road
system would be an effective method of reducing this hazard and
should be considered. 65
FLOOD INSURANCE
At the present, time flood insurance is not available in
Canada. Several factors make it an attractive idea at this time.
The large but infrequent nature of flood costs make some sort of
financial protection worthwhile for all floodplain users. The senior governments, both federal and provincial, already provide what amounts to flood insurance in that damages have
traditionally been compensated. The large, and growing, expected damage from a major flood represents a deferred, but real income
transfer from outside of the floodplain to floodplain users. The current policies do not provide local officials in the
Municipality of Richmond sufficient feedback to make rational
decisions about what levels of protection to request, what
design measures are appropriate for .flood plain structures, what
zoning measures are appropriate, and what residual amounts of
expected damage should be left to be paid as flood insurance
premiums.
THE NEED FOR FLOOD INSURANCE
A major flood on Lulu Island would cause a great deal of
damage. Repair costs for a typical residence would range from
1/5 to 1/3 of the value of the residence. A burden such as this
would cause financial hardship. On the surface it seems like a
natural area for the private insurance industry to sell
insurance to spread the risk of flooding.
The situation, however, differs from a normal insurance
situation. Usually insurance is issued when it can be expected
that only a small proportion of those covered will claim in any 66 one year, but that claims will come in continuously. This enables the insurance company to offset a continuous stream of claims against a continuous stream of premiums.
The situation with flood insurance is that for any given river basin, claims can be expected to come only rarely. When there is a flood, however, everyone covered by the flood insurance can be expected to claim at once. From the insurers' point of view, flood insurance spreads the risk over time, not over a group of policy holders at any one time.
GOVERNMENT INVOLVEMENT IN FLOOD INSURANCE
Because of the damages caused by flooding and the lack of involvement on the part of the private insurance industry, the provincial and federal governments have agreed to share the costs of flood damages. For large flood damages (above $4 per capita) the federal government pays 90% of eligible flood damages (See Table VII).*
Therefore in the primitive sense of sharing a risk among many, the provincial and federal governments do provide flood insurance.
* It should be noted that there is no legal requirement for either the federal or provincial governments to pay flood compensation and that not all types of damage are eligible for compensation under the federal provincial flood damage cost sharing formula. Normal practice is to set up a board of inquiry to determine whether flood damages are eligible for compensation and to set a deductible amount.
Notwithstanding these limitations on flood compensation, the type and extent of potential flood damages on Lulu Island make the approval of compensation a near certainty. 67
OTHER FUNCTIONS OF INSURANCE
Insurance is not just a primitive risk-sharing tool. It also provides feedback on how well a hazard is being managed and
provides a powerful way of modifying behaviour toward a hazard.
It has been shown that residual expected flood damages on
Lulu Island is $15 million per annum. Recent costs of building
dikes on Sea Island were estimated at about $1 million per
kilometer. As Lulu Island has 56 kilometers of dikes, it is
clear that some improvement in protection levels could be
justi f ied.
This discrepancy between the expected damage, as calculated
on economic criteria, and current policy based on risk
perception represents an income transfer to the floodplain
users. If the whole burden of the residual excess value of flood
damages was added to Richmond municipal taxes it would add
approximately 2.5 mills to property taxes. As was pointed out
above, it would be economically efficient to reduce this burden
by increasing structural flood protection.
The point is not, however, that the Municipality of
Richmond should be forced to upgrade structural protection, but
that information should be given to the municipality so that
their perception of the costs of expected flood damage matches
the actual expected costs. It is not fair for policies to be
pursued which create higher expected flood damage than is
economically justifiable and to expect an income transfer from
society to cover that damage. 68
IMPLEMENTATION OF FLOOD INSURANCE
Because of the possibility of a catastrophic flood occurring before enough premiums have been collected to cover
it, flood insurance would have to be implemented as a government program. Because costs are averaged over time rather than over a
risk group, coverage should be mandatory and premiums should be
segregated from general revenues in a sinking fund.
It is suggested that premiums be collected as part of municipal taxes based on the assessed value of property, type of property, level of flood risk, specific design measures to
resist flooding, and an initial study to determine expected
flood damage. Tying premiums to assessed value would provide a
deferent to inappropriate development. As the character of the
flood hazard may change over time the flood damage"study should
be repeated periodically.
SUMMARY
In summary, adoption of a flood insurance plan along these
lines will allow diking disticts to make rational decisions
about development, building design, and flood protection levels
to request. It will provide senior governments with information
about the priority with which to implement flood control
projects. It will make explicit what subsidy, if any, is
provided to flood plain users. Finally, it will provide
resources to repair the massive amounts of flood damage that
would occur if Lulu Island were flooded. 69
CONCLUSIONS
In the course of this thesis, several conclusions were reached. They are:
- There is an increasing flood hazard on Lulu Island
because its location and topography make it highly
desirable for development as an integral part of the
greater Vancouver Regional District. Property on Lulu
Island is assessed at $6 billion.
- The three mechanisms that could cause flooding, in order
of seriousness of the hazard, are the spring freshet,
winter storms, and earthquake damage to the dikes.
- The probability of coincidental occurrence of combined
events is too small to require consideration in
planning flood protection for Lulu Island at current
protection levels. If future policy decisions raise
protection levels significantly, consideration of
combined risks may be required.
- The current method of setting levels of protection is
risk prone. It spends more per dollar of expected
flood damage to protect against small flood hazards
than for large flood hazards.
- Expected costs of flooding on Lulu Island can be expected
to increase as long as the current policy of a fixed
level of protection is followed and development on
Lulu Island continues.
- The accuracy of prediction of the size of hydrological
events greater than the current design events is not 70
sufficient to be used with confidence in risk benefit
analysis.
- Current contingency plans are adequate for storm based
flooding. However, these plans would not be effective
in reducing flood damage should there be a breach near
the eastern end of the island during the spring
freshet.
- An implicit income transfer to floodplain users on Lulu
Island is currently taking place as a result of the
expected flood damage, residual, after current
protection levels are taken into account.
- While the earthquake hazard is a danger that should not
be minimized, it should not cause significant flooding
if earthquake damage to the dikes were repaired
quickly.
- As the total pumping capacity on Lulu Island is 1 million
U.S. gallons per minute or less than 100 m3/s the
pumping system would be of little use in pumping out
water from a dike breach. The pumps are there to
maintain drainage and pump out water resulting from
rain with the dikes intact. 71
RECOMMENDATIONS
The following recommendations follow from this study:
- Flood risk levels should be set to be roughly risk
neutral. Methods of setting risk levels include a rule
of thumb hazard chart and risk benefit analysis.
- The option of segmenting Lulu Island by raising selected
parts of the road system should be considered as an
effective method for reducing the flood hazard from
the spring freshet.
- A government sponsored flood insurance program that is
mandatory should be set up to defray the costs of
flood compensation and to encourage rational decision
making about the flood hazard. Premiums should be set
based on assessed value and the level of risk of
flooding.
- The flood hazard on Lulu Island is not static. As long as
development continues, periodic review of the size of
the hazard should be undertaken to ensure that the
residual expected damage is not excessive. A complete
flood damage study should be undertaken once per
decade.
- Rising sea levels will necessitate raising the level of
the sea dikes to accomodate higher tide levels, but
will not change the character of the storm based
flooding hazard. They will change the character of the
hazard from earthquake damage to.the dikes because
flooding would result from a normal high tide. For 72
this reason, before the dikes are rebuilt, the best
available evidence regarding a rise in sea level
should be considered. If a rise in sea level is
confirmed the dikes should be built to withstand
earthquakes.
- Action should be taken to ensure that bridge and tunnel
access to Lulu Island would not be cut during a flood.
- A priority, should a severe earthquake occur, should be
to perform a careful survey of the dikes to locate any
damaged areas. As time would be limited and surface
transportation would be disrupted by an earthquake,
the most feasible way to perform this survey is by
air. 73
BIBLIOGRAPHY
Air Pollution Control Association. Avoiding and Managing Environmental Damage from Major Industrial Accidents: Proceedings of an International Conference Held in Vancouver, B.C. November, 1985. Air Pollution Control Association. Pittsburgh, 1985. Algermissen, S. T. and T. Hardings. The Puget Sound Washington Earthquake of April 29, 1965: Preliminary Seismological Report. U. S. Coast and Geodetic Survey. Rockeville, Maryland. 1965. Anderson, Dan R. and Maurice Weinrobe. Effects of a Natural Disaster on Local Mortgage Markets: The Pearl Flood in Jackson, Mississippi - April, 1979. Natural Hazard Research Series Institute of Behavioural Science #6. University of Colorado. 1979. Beak Consultants (K4350).Proposed Improvements to the Fraser River Shipping Channel: Preliminary Report for Public Works Canada. Vancouver, B.C. 1979. Book, A. N. Problems Arising From Flood Control Benefit Studies. Environment Canada, Planning Division, Water Planning and Operations Branch. 1971. Book, A. N. and R. Princic. Estimating Flood Damages in the Fraser River Basin. Environment Canada, Inland Waters Directorate, Water Planning and Management Branch. 1975. B. C. Ministry of Environment, Rivers Branch. Liquefaction Program Committee Papers. Unpublished. Byrne, P. M. and D. M. Anderson. Earthquake Design in Richmond, B.C. Soil Mechanics Series No. 75, Department of Civil Engineering. The University of British Columbia. Vancouver. 1 983. Clark, E. M. Lower Fraser River Dyke Survey: Liquefaction. Canada Department of Northern Affairs and National Resources, Water Resources Branch. Vancouver, B.C. 1963. Clark, E. M. Report on Flood Frequencies, Elevations, and Durations in the Sumas Lake Area. Environment Canada, Engineering Division, Water Planning Branch. 1972. Committee on Safety of Dams. Safety of Dams: Flood and Earthquake Criteria. National Academy Press. Washington, D. C. 1985. Crippen and Associates Ltd. Estimate of Capital Costs, Fraser River Storage, System 'E' Projects. Unpublished. 1971. 74
Crosson, Robert S. Earthquake Hazard Evaluation in the Pacific Northwest: Open File Report. File 81-965. U. S. Geological Survey. 1981.
Deal, Terrence E. and Allan A. Kennedy. Corporate Cultures: The Rites and Rituals of Corporate Life. Addison-Wesley. Reading, Massachusetts. 1982.
Farley, A. L. Atlas of British Columbia. The University of British Columbia Press. 1979.
Finn, Liam. Behaviour of Earth Dams During Earthquakes. Commission Internationale des Grands Barrages. Neuvieme Congres des Grand Barrages. Istanbul. 1967.
Finn, Liam, R. G. Capanella, and Y. Aoki. Seismic Testing of Soil Models. Department of Civil Engineering, Soil Mechanics Series No. 8, The University of British Columbia. 1969.
Finn, Liam and Byrne, Peter M. The Liquefaction Potential of the Vedder Canal Dykes. Unpublished. 1970.
Flavell, D. R. and R. 0. Lyons. Probable Maximum Floods for the Fraser River at Hope and Mission. Environment Canada, Inland Waters Directorate. 1973.
Flavell, D. R. and Lyons, R. 0. Compile and Extend Flow Data. Environment Canada, Inland Waters Directorate. 1973.
Fraser River Board. Final Report of the Fraser River Board on Flood Control and Hydroelectric Power in the Fraser River Basin. Fraser River Board. Victoria, British Columbia. 1 963.
Fraser River Joint Advisory Board. Fraser River Upstream Storage Review Report. Fraser River Joint Advisory Board. Victoria. B.C. 1976.
CBA Engineering Ltd. Fraser River Flood Control Project No. 3 - Township of Richmond. Survey Control Monuments and Benchmarks. Unpublished. 1971.
Fraser River Flood Control 1968 Agreement. Project No. 3, Township of Richmond, Contract No. 1, Sea Dyke Improvements. 1973.
Fraser River Joint Program Commission. Liquefaction Problems of the Lower Fraser Valley Dykes. Unpublished. 1970.
Isfeld, E. 0. Fraser River Upstream Storage Review Task No. 57 - Navigation Studies. Department of Public Works Canada. 1973. 75
Fischoff, B., S. Lichtenstien, P. Slovic, S. L. Derby, Ralph L. Keeney. Acceptable Risk. Cambridge University Press. Cambridge, Massachusetts. 1981.
Fuchs, Victor R. Who Shall Live?: Health, Economics and Social Choice. Basic Books Inc. New York. 1974.
Hay and Company. Vancouver International Airport, Sea Island Dykes Rehabilitation. (For Transport Canada Air, TP 6335 E). 1985.
Hodgson, J. H. Earthquakes and Earth Structures. Prentice-Hall, Englewood Cliffs, New Jersey. 1964.
Hourston, W. R. Serpentine-Nicomekl Proj. 10 Sea Wall Proposal - Mud Bay. Comments of Department of Fisheries and Forestry. Unpublished. 1971.
Howard, Terry R. ed. Seismic Design of Embankments and Caverns. Proceedings of a symposium sponsored by the ASCE Geotechincal Engineering Division. American Society of Civil Engineers. New York. 1983.
Inland Waters Branch, Engineering Divsion, Pacific Region. Liquefaction Problems of the Vedder Canal Dykes. Unpublished. 1970.
Inland Waters Directorate, Pacific and Yukon Region. Economic Analysis of Dyke Improvement for Westham and Reifel Islands. 1982.
Inspector of Dykes. Correspondence on Earthquake Studies February 1970 to August 1985. Unpublished.
Jones, W. C. Stability of Dykes in Lower Fraser Valley.. Department of Mines and Petroleum Resources. Victoria, B.C. 1963.
Kanakami and Asoda. Damage to Ground and Earth Structures by the Niigata Earthquake of June 16, 1964. Soils and Foundations. Vol. VI, No. 1, pp. 14-30. January, 1966.
Luternauer, John L., Genesis of Morphological Features on the Western Delta Front of the Fraser River, British Columbia - Status of Knowledge. Geological Survey of Canada, Paper 80- 10. 1980.
Lyons, R. 0. Fraser River Upstream Storage Study Spillway Design Floods for System E Reservoirs. Environment Canada, Inland Waters Directorate. Vancouver, B.C. 1975.
McBean, Edward, Michael Fortin, and Jack Gorric. A Critical Analysis of Residential Flood Damage Estimation Curves. 76
Canadian Journal of Civil Engineering. Vol. 13, No. 1. February, 1983.
Midwest Research Institute. Earthquake Risk and Damage Functions. An Integrated Preparedness and Planning Model Applied to New Madrid. U. S. Department of Commerce National Technical Information Service. Springfield, Virginia. 1979.
Milliman, John D. Sedimentation in the Fraser River and Its Estuary, Southwestern British Columbia, Canada. Geological Survey of Canada. Vancouver, Canada. 1979.
Milne, W. G. Letter to C. H. Maartman of June 15, 1970: with Results of Chilliwack and Vedder Canal Earthquake Simulation. Unpublished.
Pavol, Peter. Canal and River Levees. Elsevier Scientific Publishing Company. 1982.
Plazak, David J. Flood Control Benefits Revisited. Journal of Water Resources Planning and Management. American Society of Civil Engineers Water Resources Planning and Management Division. Vol. 112, No. 2. April, 1986.
Princic, R. Economic Analysis of Flood Control Measures on the Vedder River. Inland Waters Directorate, Pacific and Yukon Region, Vancouver, B. C. 1977.
Ripley, Klohn and Leonoff International Ltd. Richmond Dykes - Remedial Treatment for Fraser River Joint Program Committee. Unpublished. 1969.
Ripley, Klohn and Leonoff International Ltd. Vedder Canal Dykes; Preliminary Liquefaction Studies. Fraser River Joint Program Committee. 1970.
Seed, H. B. and I. M. Idriss. Ground Motions and Soil Liquefactions During Earthquakes. Earthquake Engineering Research Institute. Berkeley, California. 1982.
Seed, H. B. Landslides During Earthquakes Due to Soil Liquefact ion. ASCE Journal of the Soil Mechanics and Foundations Division. September, 1968.
Seed, H. B. Turnaqain Heights Landslide, Anchorage, Alaska. Journal of the Soil Mechanics and Foundation Division. ASCE. Vol. 93, No. 5. July, 1967. pp. 325-353.
Shepard, F. P. and W. H. Mathews. Sedimentation of Fraser River Delta. The American Associations of Petroleum Geologists, August, 1962. 77
Shanks, Gordon Ross. The Role of Perception in Flood Plain Management. UBC Master's Thesis. 1972.
Slovic, Paul, Sarah Lichtenstein, and Baruch Fischoff. Modeling the Societal Impact of Fatal Accidents. Management Science, Vol. 30, pp. 464-475. 1984.
Statistics Canada. Table 5 - Population by Sex, and Proportion of Males to Females, for Census Metropolitan Areas With Components. 1971-1985.
Statistics Canada. Time Series Retreival of Consumer Price Indexes for Vancouver and Canada. Jan. 22, 1986.
Statistics Canada. Table 10 - Building Permits Issued in Metropolitan Areas. 1971-1985.
Togashi, Hiroshoyoshi. Study on Tsunami Run-up and Countermeasures. Doctor of Engineering Thesis, Tohoku University, Sendai, Japan, 1976. (trans. 1981).
Varzeliotes, A. N. T. Fraser River Upstream Storage Study: River Regime and Sediment Studies. Inland Waters Directorate. Vancouver, B. C. 1974.
Wallis, Douglas. Ground Surface Movements Due to Earthquakes. Master's Thesis, University of British Columbia. 1979.
Western Canada Hydraulic Laboratories Limited. Feasibility Study: Development of a Forty-Foot Draft Navigation Channel New Westminister to Sandheads. Final Report Hydraulic Model Studies for Public Works Canada April, 1977. 1977.
Western Canada Hydraulic Laboratories. Hydraulic and Related Studies and Review of Existing Oceanographic, Hydraulic and Geotechnical Information on Sturgeon Banks for B.C. Hydro and Power Authority. Unpublished. 1980.
Yamada, G. Damage to Earth Structures and Foundations by the (Niigata Earthquake, June 16, 1964). Soils and Foundations. Vol. VI No. 1. Jan, 1966. pp. 1-13. APPENDICES
Appendix A - Tables
Appendix B - Figures
Appendix C - Calculation of Expected Flood Damages 79
Appendix A - Tables
Table I - Terms for Classifying Hazard Potentials (Committee on Safety of Dams, 1985, p. 130) Loss of Life
Category (Extent of Development) Economic Loss
Low None expected(no Minimal (undeveloped to permanent structures occasional structures or for human habitation) agriculture)
Signi f icant Few (no urban Appreciable (notable developments and no agriculture, industry, more than a small or structures) number of inhabitable structures)
High More than few expected Excessive(extensive casualt ies community, industry, or agriculture)
Table II - U. S. Army Corps Engineers Hydraulic Evaluation Guidelines: Recommended Spillway Design Floods (Committee on Safety of Dams, 1985, p. 132)
Hazard Size of Dam Spillway Design Flood
Low Small 50- to 100-yr frequency Intermediate 100-yr to 1/2 PMF Large 1/2 PMF to PMF
Significant Small 100-yr to 1/2 PMF Intermediate 1/2 PMF to PMF Large PMF
High Small 1/2 PMF Intermediate PMF Large PMF 80
ulldinq 1^1 f ! . g Permits for Commercial Purposes (Statistics Canada Table 10 - Building Permits Issued in Metropolitan Areas, 1971-1985)
Year Value (OOP's) 1 971 8,174 1972 17,380 1 973 15,700 1974 23,352 1975 25,997 1 976 37,455 1977 34,219 1 978 17,891 1 979 145,447 1980 38,518 1 981 52,071 1982 34,255 1 983 21,311 1 984 22,096 1985 38,452
Total 532,318
Table IV -—Annual Probabilities of Combined Flood Hazards
Freshet Winter Earthquake Storm
Freshet .005 0.0 • less than .00083
Winter Storm 0.0 .005 .00014
Earthquake less than .00014 .0021 .0083 81
Table V - Predicted Changes to Tidal Levels (Levels Given in Meters GSC)
Current Levels Predicted Levels
Normal Low tide -2.6 -1 .6
Mean Tide 0.0 1 .0
Normal High Tide 1 .0 2.0
Design Tide 2.7 3.7
Yearly High Tide 2.2 3.2
Minimum Dike Height 3.0 4.0
Table VI - Flood Damage Estimate for Lulu Island
1971 Estimate by Category (Book and Princic, 1975) (000's) Residential 61,831 Commercial 17,905 Industrial 8,888 Agricultural - Crop 5,661 - Other 561 Industrial 2,378 Transfer Costs and Secondary Income Losses 2,408 Miscellaneous 15,034
Total 114,666
Change in Consumer Price Index (Statistics Canada, 1986) - High 2.98 - Low 2.68
Population Growth 1.67 (Statistics Canada. Table 5 - Population etc.,1971 -1985)
Combined Inflation/Population Factors - High 4.97 - Low 4.47
Flood Damage Estimates - High $570,646 - Low 51 3,199 82
Table VII - Federal-Provincial Flood Damage Cost Sharing Formula
Damage per Capita Federal Share Provincial Share
Less than $1 0% 100%
$1.00 to 2.00 50% 50%
$2.00 to 4.00 75% 25%
Above $4.00 90% 10% 83
Table VIII - Example Rule of Thumb Flood Protection Level Chart
Flood Hazard Classification
Low Medium High
Flood Depth < .3m ,3m to 1.4m > 1.4m
Flood Duration < 1 day 1 to 5 days > 5 days
Flood Warning > 48 hrs > 12 hrs None
Flood Damage Exposure Potential
Very Low Uninhabited or strictly rural with little rural development.
Low Rural with some small communities.
Moderate Medium sized communities. Parts of large communities where the parts at risk are comparable in population to a medium sized community.
High Large urban communities or possibility of loss of life.
Very High Possibility of loss of large numbers of lives.
\ 84
Table VIII(cont.) - Recommended Levels of Flood Protection
Hazard Level Description Protection Level
Very Low Very low damage potential or Low damage potential and low depth, duration and warning None
Low Low damage potential, medium depth, duration, warning or Moderate damage potential, low depth, low duration, medium warning 1/100
Moderate Moderate damage potential, 1/100 to depth, duration, warning 1/2 PMF
High High damage potential, medium depth, high duration, medium warning or low damage potential, high depth, high warning 1/2 PMF to PMF
Very High Moderate damage potential, high depth, high warning PMF 85
Appendix B - Figures
List of Figures
1. Map of the Western End of the Lower Fraser Valley
2. Risk-Hazard Perception Rating Chart
3. Map of Full Tidal Relief Zone
4. Raised Road Alignment PORK. • «*i * ^ITIXLL'
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enters • Unamaitrr Csmt • tlactric IHr i feci (flrri)_ _ *Co«l Mining Accieents • III S»1i«9» „ , • Span raraoaitai tac taanega) • General Aviation Electric H1r « Appl (Shock)* ticycles* Motorcycles* • Hioh Construction Iriaoes* • Rinreae Ccllfiioni Alcohol Acctoeats coa. Alalia. Ftreaorts* #
*A*te laciaa. 4 • MMam a) Dynaattc Factor 2 ROT OBSERVABLE iftotam TO TKOSE EXPOSES EFFECT DELATED REV tm COKTRXLAILE (ISO IHOOMK TO SCIERCC •MOWTKIUAiLE •OT DREAD OREAD KT B.OSAL CATASTROHIC ftOBAL CATASTROPHIC eOMEOUEKCES KIT FATAL ORSEOUEICES FATAL EQUITABLE ROT tOu;TABLE IRDIV1DUAL CATASTROPHIC Factor 1 LOU list TO FUTURE MICt list TO FUTURE KXEUTIOKS HHEUTIOXS EASILY REDUCtO ROT EAS1LT (EDUCED RISK OECRSASIRS s 11 SIC lRCSEASlUS •DLuVIARY WVOLU»TA«T HCSR'T AFFECT FC tmm TC THOSE EIFCSED AFFECTS ME EFFECT IMMEDIATE OLD RJSt 11 SU DOrX TO SCIERCE Figure 2- HAZARD LOCATIONS ON FACTORS I AND 2 DERIVED FROM THE INTERRELATIONSHIPS AMONG 16 RISK CHARACTERISTICS. EACH FACTOR IS MADE UP OF A COMBINATION OF CHARACTER ISTICS.AS IS INDICATED BY THE LOWER DIAGRAM. (FROM SLOVIC et al.,1984) Figure 3' RICHMOND-AREA OF TIDAL RELIEF. Figure 4= RICHMOND - ROADS WHICH COULD BE RAISED TO SEGMENT AREA SUBJECT TO FLOODING. 90 Appendix C - Expected Flood Damage Calculation for Lulu Island August 12, 1986 Assumed Rate of Damage Increase 0.04 Effective Interest Rate 0.08 Flood Stage at Mission (feet) 24 25 26 Est. Flood Damage (000's) $275,000 $500,000 $510,000 Probability of Flooding .005 .01 .005 Growth Expected Present Year Factor Damage Value 1 1.0000 8925000 8925000 2 1.0400 9282000 8594444 3 1 .0816 9653280 8276132 4 1 .1249 10039411 7969608 5 1 .1699 10440988 7674438 6 1 .2167 10858627 7390199 7 1.2653 11292972 7116488 8 1.3159 11744691 6852914 9 1.3686 12214479 6599103 10 1.4233 12703058 6354692 1 1 1.4802 13211180 6119333 1 2 1.5395- 13739627 5892691 1 3 1.6010 14289213 5674443 1 4 1.6651 14860781 5464278 15 1 .7317 15455212 5261898 1 6 1.8009 16073421 5067013 1 7 1.8730 16716358 4879345 18 1.9479 17385012 4698629 19 2.0258 18080412 4524606 20 2.1068 18803629 4357028 21 2.1911 19555774 4195656 22 2.2788 20338005 4040262 23 2.3699 21151525 3890622 24 2.4647 21997586 3746525 25 2.5633 22877490 3607765 26 2.6658 23792589 3474144 27 2.7725 24744293 3345472 28 2.8834 25734065 3221566 29 2.9987 26763427 3102248 30 3.1187 27833964 2987350 31 3.2434 28947323 2876708 32 3.3731 30105216 2770163 33 3.5081 31309424 2667564 34 3.6484 32561801 2568766 35 3.7943 33864273 2473626 36 3.9461 35218844 2382010 37 4.1039 36627598 2293788 38 4.2681 38092702 2208833 39 4.4388 39616410 2127024 40 4.6164 41201066 2048245 41 4.8010 42849109 1972384 42 4.9931 44563073 1899333 43 5.1928 46345596 1828988 (cont inued next page) 91 Growth Expected Present Year Factor Damage Value 44 5.4005 48199420 1761247 45 5.6165 50127397 1696016 46 5.8412 52132493 1633200 47 6.0748 54217793 1572712 48 6.3178 56386504 1514463 49 6.5705 58641965 1458372 50 6.8333 60987643 1404358 Cumulative Present Value 204461692 Yearly Budget $15,475,262 92 Calculation of Expected Flood Damages Flood Damage Estimates from Book and Princic (1975) Flood level at Mission 24 25 26 (000's) (000's) (000's) Damage Estimates by Category Residential 32647 61831 61831 Commerc ial 881 4 17905 17905 Industr ial 5109 6946 8888 Agricultural - crop 4228 5603 5661 Agricultural - other 404 548 561 Primary Industrial 1401 21 44 2378 Transfer costs 1 486 2207 2408 Miscellaneous Damages 7365 14465 15034 Total 61 454 111649 114666 Population Growth Factor 1 .67 1 .67 1 .67 Total Adjusted for Pop. Growth 102628 186453 191492 Inflation Factors - low 2.68 2.68 2.68 - high 2.98 2.9'8 2.98 Low estimate $275,044 $499,696 $513,199 High estimate $305,832 $555,632 $570,647 Annual Probability of stage 0.05 0.02 0.005 Prob. of Failure given stage 0.1 0.5 1 Combined Prob. of Failure 0.005 0.01 0.005 Expected Annual Cost in 1986 Dollars - low $11,504 - high $12,792 93 Formulas Used in Calculating Expected Flood Damage The formulas used to calculate expected flood damage are as follows: Growth Factor = (1 + Rate of Damage Increase)Year Expected Damage = Growth Factor * (Flood Damage at 24 feet * Prob Flood at 24 feet + Flood Damage at 25 feet * Prob Flood at 25 feet + Flood Damage at 26 feet * Prob Flood at 26 feet ) Present Value = (Expected Damage)* (!/(1+Interest rate)