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Flood Damage Reduction
a
b
c
Kersi S. Davar , John M. Henderson & Brian C. Burrell
a
IWRA, University of New Brunswick , Canada
b
IWRA, Consultant, New Brunswick , Canada
c
Department of the Environment and Local Government , Fredericton, New Brunswick,
Canada
Published online: 19 Oct 2010.
To cite this article: Kersi S. Davar , John M. Henderson & Brian C. Burrell (2001) Flood Damage Reduction, Water
International, 26:2, 162-176, DOI: 10.1080/02508060108686901
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International Water Resources Association
Water International, Volume 26, Number 2, Pages 162–176, June 2001
Flood Damage Reduction
Kersi S. Davar, Member IWRA, University of New Brunswick, Canada, John M.
Henderson, Member IWRA, Consultant, New Brunswick, Canada, and Brian C. Burrell,
Department of the Environment and Local Government, Fredericton, New
Brunswick,Canada.
Abstract: A fundamental conflict occurs when a floodplain, fluvio-morphologically formed by the
river for draining its high flows, is occupied and developed by humanity. Consequently, damages are
experienced that are the inevitable costs of occupancy of the floodplain. A systematic methodology is
suggested for formulating an optimal scheme for addressing any flood situation with its own unique
characteristics. This methodology embraces all available measures, structural and non-structural, tradi-
tional and modern, in evolving the best scheme. Diverse flood situations in New Brunswick (Canada), the
Nile River Basin and Bangladesh exemplify three flooding situations radically different in origin and
character. Finally, some important conclusions are drawn and recommendations are made for approaching
solutions to major flood problems.
Keywords: Flood(s), floodplain(s), flood risk, flood damages, floodplain management, river(s).
by tidal phenomena. The hydraulic characteristics of a
Introduction
flood situation are governed by location along the river
This paper examines the general problem of floods in course. However, a regional storm could affect only the
rivers and the related occurrence of damages in occupied contiguous river reaches, and a very large storm and/or a
river valleys and offers suggestions for systematically basin-wide snowmelt event can impact the entire river
developing an optimal solution scheme for reducing dam- system.
ages in each case, with its own unique characteristics.
Three examples are briefly reviewed.
Three main factors govern the dynamics and devel-
opment of a natural flood event in a river valley: (1) in-
Among natural hazards afflicting mankind, river tensive storm rainfall and/or rapid snow melt; (2)
floods occupy a major role. To address the problem of watershed characteristics and prevailing conditions in-
floods it is important to clarify the characteristics of flood- fluencing the runoff regime (the type of basin, vegetal
ing. For this purpose floods may be viewed from a natural cover and its modification, and very importantly, the an-
(hydrological and ecological) perspective and a human tecedent soil moisture content); and (3) river channel and
perspective. floodplain conditions (channel constrictions, obstructions
What is a flood? Viewed from a hydrological perspec- on the floodplain; in cold regions the often sudden oc-
tive, a flood may be described as an abnormally high stage currence of ice jams). Also, there may be special occa-
in a river channel and its floodplain. The type of flood sions, such as an upstream dam failure rapidly releasing
situation varies with location along the river’s course. In enormous volumes of water.
the upstream reaches the channel is narrow, the slope is
From the human perspective of those that have occu-
steep, and velocities are high; this combination results in pied and developed the floodplain, a major flood event is
the flood flows being confined mainly in the channel. In one that at high river levels results in extensive damages
the main stem and lower valley, the river normally has a (economic), general disruption of human activities and
relatively wide channel and a well-developed floodplain. consequent disbenefits (social effects), and intense trauma
During flood stages, the river rises above the channel and (psychological). The attractiveness of a river floodplain
spills into the floodplain, which it has fluvio-morphologi- during non-flood seasons leads to its occupancy and de-
cally formed over time. During major floods, the river velopment by humans. In the context of current envi-
occupies the channel/floodplain system for natural drain- ronmental and ecological concerns, these important
age of large volumes of water. In the lower estuarine interactions within a flood situation have also to be care-
reaches the river generally has an extensive network of fully addressed.
meanders and interconnected channels traversing a rela- While this paper deals mainly with the flooding prob-
tively undefined floodplain, where it is strongly influenced lem in rivers, flooding problems also occur for other spe-
162

Flood Damage Reduction
163
cial situations. Among them are dam break generated ests of the people by an authority acting on their behalf,
floods, coastal zone tsunamis, tidal surges in bay areas, the action can be considered as for the good of the public.
volcanic induced floods, debris flows, and unusually high Measures or circumstances affecting a community or
groundwater. However, it is suggested that the systematic group of people can be considered in terms of public good.
methodology presented herein for deriving an optimal so- Flood damage reduction measures should benefit people
lution strategy can be adapted to any of these special situ- and therefore be for the public good.
ations.
Equity
Flood damage reduction strategies should be based
Basic Precepts for Flood Damage Reduction
on equity, or a system of rules based on fairness and well-
founded and reasonable exercise of authority aimed at
Evaluation of Potential Benefits
In understanding the severity of a flooding problem, protecting people and the public good while respecting
it is necessary to evaluate the damages resulting from past the rights of the property owner. Equity depends upon
floods. Any assumption made has to be documented and context (social, legal, and political) and a realistic assess-
supportable on the basis of past experiences and evidence. ment of the flooding problem. Equity implies that no stake-
Average annual damages can be expected to increase with holder should endure unfair physical, social, or economic
population, development, and rising economic values of hardship resulting from the application of flood damage
investment in flood hazard areas. Regardless of the level reduction measures, which should be reasonable and non-
of detail in estimating the damages that could result from discriminatory, and not totally prohibitive (Burrell and
future floods, having an appreciation of potential dam- Stelling, 1991). It is the responsibility of decision-mak-
ages is important to justify funding for, and to reduce ers to include equity and fairness as criteria in the overall
speculation in the process of planning and implementing process of evaluating flood damage reduction strategies.
flood control works and floodplain management.
The “Policy Statement of the Government of Ontario
One would be remiss in discussing the damages due on Planning for Floodplain Lands” (Ontario Ministry of
to floods and not to mention that there are often benefits Natural Resources and Ministry of Municipal Affairs,
arising from floods. For example, flooding frequently re- 1982) has provided several principles that should be ap-
sults in the deposition of fertile silt on floodplains making plied to introduce equity into floodplain management pro-
them more productive for agriculture. Periodic flooding grams: (1) floodplain management policies must be based
may also be essential for sustaining certain ecosystems. on an evaluation of all relevant social, economic, physi-
When considering net flood damages, the benefits of flood- cal, and environmental factors; (2) floodplain manage-
ing should be subtracted from the damages, to the extent ment policies must take place within an overall coordinated
feasible using a common scale of values.
land use and watershed planning framework; (3) when-
The extent of an action should relate to the severity ever feasible, existing development within floodplains is to
of the problem and the capability to lessen the problem. be protected against major flood losses; (4), future land
Flood damage reduction activities should be related to, uses that will be susceptible to significant flood damages
and must be justified on the basis of the expected reduc- or that will increase flood damages to existing uses must
tion in net flood damages that would result from the ac- not be permitted within the floodplain; and (5) floodplain
tivities. Management decisions have often been predicated management policies must be developed and administered
on the amount of risk to life and property acceptable to in a manner that promotes public understanding and ac-
the particular circumstances of an area or community. ceptance.
Indirect benefits from flood damage reduction may also Equity also suggests that management should prevent
occur; for example, increases in land value, and reduc- development that results in the transfer of risk to vulner-
tions in disruptions to business and societal activities.
able persons. For example, emergency evacuation of the
occupants of hospitals, nursing homes, schools, and places
of confinement because of flooding or a failure of struc-
Public Good
The benefits of flood damage reduction are the esti- tural flood control measures could result in considerable
mated savings resulting from flood damage reduction ef- hardship, injury or death. Therefore, government policy,
forts, that is the difference in potential net flood costs planning ordinances, and other legislated land use restric-
(
direct and indirect) without flood damage reduction mea- tions should be used to prevent the construction and use
sures and the potential net flood and implementation costs of such facilities in vulnerable areas.
associated with flood damage reduction measures.
Flood damage reduction must not be considered in- Environmental Compatibility
dependent of the human experience. The effect of flood-
Use of floodplain lands should be compatible with
ing on people must be a primary consideration in the planning the interdependent biological and physical factors of an
and development of flood damage reduction. When ben- environment that comprises an ecosystem, which is a com-
eficial action is taken with due consideration of the inter- plex web sustaining flora and fauna. It must be remem-
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164
K.S. Davar, J.M. Henderson, and B. C. Burrell
bered that humanity itself is part of the fabric of life within encountered in river valleys occupied by people.
the environment.
Floodplain ecosystems are productive. Because of the Flood Damage Reduction Techniques
relative abundance of water, floodplains provide habitats
Over time and with much experience, humanity has
for a multitude of plant and animal species, and the en- developed and practiced a variety of defensive measures
ergy and nutrients from the healthy functioning of flood- in response to the periodical threat of floods. Often, these
plain ecosystems are passed along to organisms in adjacent
and downstream areas (University of Colorado, 1992).
approaches have been used in combination in response to
the needs of a specific flooding situation. The appropri-
The technological control which humankind is now ateness and effectiveness of these measures as commonly
able to exert over the environment is so great that the employed have not been demonstrated conclusively, par-
power of the environment over humanity is easily over- ticularly with respect to eco-environmental concerns. New
looked, and public perception becomes that any environ- innovative approaches to the overall problem need to be
ment, modified and conditioned by human activity, must sought continuously.
be inevitably suited for human life (Calvin, 1970). Un-
Techniques for flood damage reduction encompass
planned and uncontrolled development, and industry in structural and non-structural measures that reduce or elimi-
particular, can mar a natural landscape, destroy a habitat, nate flood hazard and the potential for future flood dam-
and affect the flow of energy and materials crucial to ages; these measures are listed in Table 1. Structural
sustainability of an ecosystem.
measures to reduce flood damages, often referred to as
Flood damage reduction measures may include pro- flood control works, include levees, ring dykes and
visions that allow all or part of a floodplain to be left polders, floodwater diversion channels, and storage res-
undeveloped. From an ecological standpoint, leaving ervoirs. Generally, these measures are feasible only when
floodplains undeveloped will sustain biological produc- used to protect a highly developed floodplain where the
tivity, preserve wildlife habitats, protect vulnerable or en- savings on potential flood damages (combined with other
dangered species, and maintain natural biodiversity. benefits from multi-purpose projects) are great enough to
Additional environmental benefits that could be derived justify the expenditures for construction, operation, and
from leaving floodplains undeveloped include improved maintenance of such structural systems. Structural mea-
water quality, less land erosion, and increased groundwa- sures can often be very effective in reducing flood dam-
ter supply.
ages. The examples include the levees at St. Louis,
Missouri, USA, during the Great Mississippi River Flood
of 1993, the flood water diversion channel around the city
Feasibility
Appropriate legislative authority, financial resources, of Winnipeg, Manitoba, Canada, during the Red River
and a favorable socio-political climate must exist to make Flood of 1997, and the High Aswan Dam since 1972.
any measure to reduce flood damages effective in the short However, American and Australian experience has shown
term and sustainable in the long term. It is also necessary that structural flood control measures frequently give a
to consider program implementation and operation dur- false sense of security, which leads to continuing devel-
ing the early stages of program development.
opment on the floodplain. As a result, extensive flood
damages have occurred when design flood conditions were
exceeded or when structural measures failed. Non-struc-
tural damage reduction includes floodplain management
and flood forecasting/warning services. The emphasis is
Flood Damage Reduction
The Fundamental Conflict
A river’s channel and floodplain system have evolved on wise use of the floodplain rather than on attempts to
fluvio-morphologically for a natural drainage function. control floods.
Periodically, the river system will be subject to very high
stages resulting in floods.
Flood proofing consists of any combination of site-
specific structural and non-structural additions, changes
The attractiveness of the river and its floodplain leads or adjustments to existing structures and utilities, which
to occupancy and development by people. During large eliminate or reduce the potential for flood damages. Flood
floods, societal, economic, eco-environmental, and psy- proofing may be an economically viable means of reduc-
chological damages are inevitable and must be consid- ing the potential for flood damages, especially in areas
ered the price of occupancy, on a long-term basis. Hence, where protection provided by structural flood protection
a perpetual conflict exists in the river valley, people ver- works is inadequate or where alternative means of flood
sus the river.
damage reduction are technically or economically unfea-
Damages that have historically occurred worldwide sible (James F. MacLaren Limited, 1978). Several publi-
have been documented and reported, for example, Major cations on flood proofing are available (Alberta Municipal
Flood Disasters of the World, Table 3-29, in The Water Affairs, 1987; Federal Emergency Management Agency,
Encyclopedia (Van der Leeden et al., 1991). Such infor- 1986; Office of the Chief of Engineers, 1982).
mation conveys the immense scale of flooding problems
Flood damage reduction must be based on potential
IWRA, Water International, Volume 26, Number 2, June 2001

Flood Damage Reduction
165
Table1. Flood Damage Reduction Measures
risks and associated net costs, which vary in time and
place. The extent of social and community disruption brought
on by flooding, and the cost of flood damages depend on
several factors (New South Wales Government, 1986): These
include: (1) the magnitude of the flood, (2) the depth and
velocity of the flood water, (3) the land use pattern, (4)
flood awareness, (5) the effective warning time, (6) the
rate of rise of the floodwaters, (7) the evacuation or res-
cue procedures that are in place, and (8) flood-borne de-
bris and sediment.
Structural Measures
Flood diversion
Floodwater diversion channels
Floodwater/ice/debris storage areas
Channel structures
Storage dams and reservoirs
Diversion dams and barrages
Ice or debris control structures
Flow retardation basins
Flood barriers
Ring dykes and polders
Levees and floodwalls
The Role of Floodplain Management
Structural floodproofing
Permanent floodproofing
requiring no action prior to flood)
A distinction exists between flood damage reduction
practices and floodplain management. The definition of
the latter is limited to the non-structural measures under-
taken to influence, regulate or control the uses of flood-
plain land. Floodplain management can thus be considered
a subset of an overall flood damage reduction strategy.
The successful application of floodplain management
activities to the problems of a particular floodplain de-
pends upon the selection of appropriate measures based
upon:
(
•
elevation of structure on fill or col-
umns
berms, cut-off walls
•
•
floodproofing of utilities flow
(
e.g., check valves on sewers)
water-resistant materials and con-
struction
•
Contingency floodproofing
requiring action just prior to flood)
(
•
•
watertight doors
flood shields
Non-Structural Measures
• consideration of the characteristics and severity of the
flood problem,
Emergency measures
Flood advisories
Flood fighting/emergency/floodproof-
•
the physical features and morphology of the water-
shed,
ing (e.g., placing sand bags)
Evacuation
Disaster relief services
• the nature and extent of development (existing and
proposed) on the floodplain,
(
e.g., water and food distribution)
•
•
the economic and social conditions of the region,
the political and environmental concerns of the com-
munity, and
Flood alerts (based on long-term and
seasonal information)
Flood warnings (based on upstream ob-
served/predicted conditions)
Flood forecasts (based on hydrologic
analyzes/modeling)
• existing and planned flood control works.
Effective floodplain management provides the follow-
ing general benefits (United States Water Resources Coun-
cil, 1981):
Floodplain management
Public education and awareness pro-
grams
Flood plain delineation
•
•
•
flood mapping
flood plain area demarcation
past flood level indicators/signs
•
•
•
reduction in loss of life, injury, and hardship due to
floods,
reduction in public expenditures for construction of
flood control works,
emergency action, and post-disaster assistance (com-
pensation), and
Financial measures
•
•
financial incentives and disincentives
flood insurance
Direct change
• preservation and enhancement of natural floodplain
values with their attendant benefits of groundwater
recharge, water quality conservation, and reduced ero-
sion and sedimentation.
•
•
relocation
use conversion
Regulation of land use/activities
•
•
•
•
•
national/state/provincial legislation
regional or municipal zoning by-laws
building convenants and restrictions
subdivision controls
restrictions on issuance of develop-
ment permits
watershed management to reduce
flood volumes and runoff rates
other land use controls and planning
Land use planning is a major component of flood-
plain management. Land use planning and controls for
floodplains are based on the widely held belief that de-
velopment of the floodplain should be discouraged by
public policy because the private market would encour-
age inappropriate development (Milliman, 1984). It is
therefore imperative that interactions of floodplain man-
•
•
IWRA, Water International, Volume 26, Number 2, June 2001

166
K.S. Davar, J.M. Henderson, and B. C. Burrell
agement are considered with other aspects of land use plan- ban settlements, the number of buildings in the floodplain
ning, and that proper planning principles are applied through- that would have to be removed may be large and devel-
out.
opment pressures may make abandonment of the flood-
Floodplain management activities include: (1) flood- plain economically unjustifiable, unless combined with
plain delineation; (2) direct land use changes; (3) regula- well-financed programs of urban renewal or public facil-
tory controls; (4) development discouragement through ity construction.
incentives and disincentives; (5) flood insurance; and (6)
public information activities.
Regulatory Controls of Land Use
Regulation of land use is a tool to provide for the
wise use and development of a floodplain if development
Floodplain Delineation
Floodplain delineation is the identification of areas pressure occurs (Minnesota Department of Natural Re-
that have been flooded or which may be flooded during a sources, 1981). Regulatory controls include, but are not
future flood event, so as to influence future development. limited to, special floodplain regulations, zoning bylaws,
The identification of flood prone areas on maps is often subdivision controls, environmental laws and sanitary
the initial step of floodplain management, serving as the ordinances, and building codes enacted by governments
basis for legislated programs and also as an effective and planning authorities upon land use and development
means of informing the public of the flood hazard. Four in flood hazard areas. To be successful, regulatory con-
common means of floodplain delineation are: (1) the trols must have a sound legal basis, be well administered,
hydrotechnical approach using engineering science (ap- and be adequately enforced. The principal advantages of
plied hydrology, hydraulics, hydrodynamics) in detailed regulatory controls include flexibility in integrating a
studies to provide a flood line with an assigned frequency broad range of economic, social and environment values,
of occurrence based on statistical analyses; (2) the past and faster and less expensive implementation compared
flood approach based on information for a single past flood to structural flood damage reduction. Regulations have
event for which a flood frequency may or may not be the greatest potential benefit in avoiding future flood dam-
assigned; (3) the flood documentation approach involving ages to new development, not in preventing flood dam-
the use of information on past floods to develop a maxi- ages to existing development.
mum flood profile that does not have an assigned frequency
of occurrence (Burrell, et al., 1989); and (4) a biophysical Development Incentives and Disincentives
approach in which delineation of a flood risk area is based
Government agencies often attempt to discourage, but
on differences in types of vegetation, types of soils, and not control, development on floodplains. Although prob-
channel shape. The successful completion of any flood ably less effective, this less direct approach may be more
risk mapping project requires the integration of this infor- politically acceptable than regulation of floodplain uses.
mation onto mapping (Burrell and Keefe, 1989).
The onus is on landowners to decide what action is to be
It is not possible to precisely delineate areas subject taken in order to protect their property based upon the
to flooding, but the law in many jurisdictions permits the information provided.
imposition of regulations based on less than perfect in-
A restriction of financial assistance is one means of
formation (Dingman and Platt, 1977). American legal re- discouraging development on flood prone land. By re-
search has revealed that statutory requirements do not stricting funds available for flood-susceptible develop-
require using the best available methods nor do they man- ment, governments not only curtail their support for such
date the development of new and improved methods. development but also influence the availability of funds
However, the data upon which the regulations are based from the private sector. Restrictions on financial assis-
must not be arbitrary and capricious. The National Flood tance are key elements of the Canada Flood Damage Re-
Insurance Act (USA) requires only that the flood eleva- duction Program (Bruce, 1976). Other techniques
tion determination not be scientifically or technically in- commonly used to discourage floodplain development
correct (Mrazik, 1983).
include the preparation and dissemination of public in-
formation materials, the use of flood warning signs and
markers, the recording of flood hazard, and the control of
Direct Land Use Changes
This approach involves changing the use of land or infrastructure development.
buildings to make them less susceptible to flood dam-
Financial incentives to develop on, or relocate to, land
ages. The characteristics of the flood events remain un- not prone to flooding, in the form of grants, low interest
changed. Direct land use changes can be accomplished loans or tax adjustments are another means of reducing
by public acquisition, relocation or conversion, as justi- development on floodplains.
fied by reasons of public safety, or reduction in future
flood disaster expenditures. However, as a means of flood Flood Insurance
damage reduction, this approach is mainly applicable to Insurance against flood damage helps offset the fi-
isolated flood-prone buildings in rural areas. In large ur- nancial burden that may result if a property is flooded,
IWRA, Water International, Volume 26, Number 2, June 2001

Flood Damage Reduction
167
but does not lessen the possibility of flooding or flood
damages. In the United States, the Flood Disaster Act of
973 (U.S. Congress) requires the purchase of flood in-
1
surance after March 2, 1974, or one year after a commu-
nity is identified as being flood-prone, as a condition for
receiving federal financial assistance for acquisition and
construction purposes in an identified floodplain area of
communities participating in the National Flood Insur-
ance Program (Waananen et al., 1977). As with all insur-
ance, there must be an evaluation of risk, and uncertainty
increases the difficulty of obtaining insurance.
Public Information Activities
Maintaining an awareness of the flood hazard among
all sectors of the general public is necessary if flood dam-
age reduction efforts are to be effective. A direct benefit
is the avoidance of flood prone land by potential devel-
opers and users because available information illustrates
an unacceptable risk to lives and/or property. A second-
ary benefit is increased public support for government
action and expenditures once the flood hazard is known
and understood. A failure of many public information
activities lies in the ineffective, untimely, or insufficient
dissemination of materials to those who would benefit
from them. Like other activities to reduce flood damages,
public information activities must be properly planned,
implemented, and monitored to achieve the success de-
sired.
Figure 1. A schematic procedure for developing an effective strategy
against flood problems. Note: See text for clarification of items in the
boxes.
ness on basis of benefits and costs, feasibility for co-
ordinated implementation, and political acceptability,
for all cases considering direct, indirect, and intan-
gible items).
Strategy Development and Implementation
Strategy Goal
The general strategy can be simply stated: maximize 4. Selection of an optimal scheme (best meeting the cri-
the benefits of river valley occupancy and development, teria prescribed in step 3).
and minimize attendant damages from floods over a long 5. Periodical re-evaluation (as affected by changes in
time frame. The important question is how to best achieve
this goal with a comprehensive vision spanning the entire
spectrum of available methods while embodying an inte-
grative approach.
occupancy and development, innovative technology,
and political priorities).
Following this procedure is fraught with difficulties
but it is greatly facilitated by experienced guidance. In
most cases, the amount of information that can be used
Developing an Optimal Strategy
There are many varieties of flood problems, each with by decision-makers can be enhanced with the appropriate
its own features, which must be carefully considered in use of geomatics and information technology.
developing an approach strategy specifically for any situ-
For example, stipulation of the benefit-cost criteria is
ation. The procedure for evolving an effective scheme desirable as a measure of economic effectiveness of funds
for combating adverse effects of floods consists in the spent. In analyzing costs and benefits, the assessment of
following five fundamental steps as given below and costs is relatively direct; however, benefits are interpreted
shown step-wise in Figure 1:
as “damages saved” by the scheme. The estimation of
damages saved” is done by frequency analysis, a pro-
. A clear statement of the flood problem (identification cess sensitive to the time span of the flood records and
of objectives, constraints, type of flood situation). reliability of surveys conducted to assess damages, par-
. Formulation of alternative combinatorial schemes (of ticularly for extraordinary floods of rare occurrence. At
different scope, scale, funding, and integrating differ- best, such benefit-cost criteria must be viewed as mea-
“
1
2
ent practices in each alternative).
sures of relative competence among several alternative
3
. Examination of alternative schemes (criteria include: schemes as viewed in the current time frame. Intangible
social impacts, eco-environmental impacts, effective- effects escape such quantifiable analysis, however, their
IWRA, Water International, Volume 26, Number 2, June 2001

168
K.S. Davar, J.M. Henderson, and B. C. Burrell
important consequences need to be carefully assessed.
and flood insurance schemes. Geomatics includes four
Present techniques for assessing environmental-eco- principal technologies: mapping and photogrammetry,
logical impacts, as well as social impacts, are mostly semi- Geographic Information Systems (GIS), Global Position-
quantitative; a large measure of subjectivity is inherent in ing Systems (GPS), and remote sensing. Geographic In-
these processes, even if well-informed. Thus, to some formation Systems (GIS) can be used to delineate the flood
extent, controversy is inescapable, but informed judgements prone area, to identify flood susceptible uses within the
can be considered best guides for appropriate action.
delineated area, to extend the capability to analyze the
Fighting floods in the modern context requires coordi- nature of flooding problems, and to carry-out floodplain
nation among several government agencies, trained seg- management activities. For example, the flood prone area
ments of the public and effective leadership. These can be related to property ownership databases or over-
elements of coordination are vitally important for suc- lain on property mapping to determine which properties
cessful implementation of any scheme for mitigation of would be subject to certain provisions of floodplain man-
adverse flood effects. Without them even a well-conceived agement, such as financial restrictions. Global Position-
scheme may not be successful.
ing Systems (GPS) can be used for rapid demarkation of
Finally, it is to be remembered, that the major com- the limits of flooding or positioning of ice jams during an
ponents of any strategy for addressing flood problems are actual flood event. Remote sensing is a potential source
likely to be politically very sensitive. Informing, educat- of information on hydrological phenomena, as the dy-
ing, and involving people in the process is indispensable. namic nature of hydrologic phenomena often necessitates
The destiny of any scheme for alleviating adverse effects the acquisition and analysis of environmental informa-
of floods in a region will be eventually governed by po- tion over a wide area on a timely basis.
litical decisions; its success will depend on leadership at Trained Personnel: Flood damage reduction requires
the top and cooperation among those likely to be affected trained staff. For comprehensive management, it is desir-
by the consequences.
able to form multi-disciplinary teams. These teams may
include, for example, hydrologic engineers for floodplain
delineation, civil engineers and architects for designing
Program Implementation Considerations
General: A flood damage reduction strategy or plan structural measures, community planners for land use
must be capable of successful implementation. Organi- regulation, hydrologic modelers for flood forecasting, and
zational constraints may inhibit the development of such ecologists for environmental assessment and monitoring.
plans. Implementation of a new program may have sig-
Two concerns of managers should be staff commit-
nificant implications for administrative practices within ment and productivity. As floods do not occur on a regu-
organizations and thus may require new administrative lar or periodic basis, an effort should be made to help
practices that threaten the existing power structure within staff understand and adhere to long-term management
the organization.
objectives. Continuing professional development is nec-
Indecision due to a lack of program clarity or direc- essary due to changing technology and changing envi-
tion, and inconsistencies in program delivery due to prob- ronments (for example, economic shifts in developing
lems with organizational structure or multi-agency countries, urbanization, political change, and new man-
cooperation will substantially weaken the delivery of a agement approaches). Staff must have the training that
management program. This may also result in detrimen- allows them to be in a state of ongoing preparedness.
tal effects such as the delay of appropriate development
or use of floodplain lands, unnecessary hardship to indi- Program Operation Considerations
viduals, and needless expenditures by the agencies respon-
sible for flood damage reduction.
Ongoing program financing is essential to ensure a
program’s effectiveness. Secured funding for several years
Information Collection and Use: The quality of de- allows floodplain managers to plan and undertake projects
cision-making is dependent upon the availability of the of longer duration. Secured funding also allows for flood-
relevant information, which is the basis for decision-mak- plain managers to be retained over a period of several
ing and action. With respect to floodplain management, years, thus allowing them to develop greater awareness
hydrometric and river channel information are important of the nature of the flooding problem, the characteristics
in determining flood elevations, and can be used with to- of the floodplains, and the problems encountered by de-
pographic information in delineating flood risk areas, velopers and floodplain residents.
which can then be used with flood damage/property in-
formation in determining appropriate floodplain manage- menced, it will be ineffective unless there is public sup-
ment activities. port and compliance. Voluntary compliance based on
After a floodplain management program has com-
Geomatics, or the science, technology, and manage- public appreciation of the flooding problem requires a
ment of geographic information, is especially useful in public education program with an understandable mes-
non-structural flood damage reduction activities such as sage aimed at creating acceptance of the floodplain man-
floodplain delineation and mapping, regulatory controls, agement plan. In most cases, public information must
IWRA, Water International, Volume 26, Number 2, June 2001

Flood Damage Reduction
169
point out the benefits to the individual property-owners
of compliance with the floodplain management strategy.
Some property owners might fail to respond volun-
tarily to the flood hazard and continue to put themselves
or others at risk. When measures for voluntary compli-
ance do not work, various controls can be created to en-
sure that management objectives are met. Regulations can
be enforced by means of negotiation with the offender,
court action, financial penalties, and other action to en-
sure that the intent of a floodplain policy is fulfilled. En-
forcement measures should have a sound legal basis, be
equitably applied and be fair to the individual. Imposed
penalties must relate to the situation and be reasonable.
For example, charging fines may not work if no comple-
mentary action is taken to mitigate the flood risk or if
individuals do not have the financial resources to pay the
fine. If there is active enforcement of a regulation, there
should also be a mechanism for an appeal based on estab-
lished criteria.
Management strategies should be subject to review
every 10 to 15 years, and after every major flood, to de-
termine whether original program objectives are still valid
and the objectives are being met. Revision of manage-
ment plans may be necessary if structural flood damage
reduction measures have eliminated or greatly reduced
the need for non-structural flood damage reduction mea-
sures, development is no longer at risk, the severity of
flooding has been reduced due to changes in land use prac-
tices, or major changes have occurred in the socio-politi-
cal, regulatory, planning, or economic setting. Deficiencies
may exist due to some impediment to implementation, im-
proper design of a measure, or changes from original con-
ditions. The review should provide the basis for
strengthening operations, modifying measures, or adding
new measures to enhance overall performance. Once a
program has outlived its usefulness, it should be termi-
nated.
Examples of Diverse Flood Situations
The three examples outlined below represent very
different situations. One is in a developed country, one in
a large international river basin in which the downstream
nation has a history of thousands of years of increasingly
sophisticated irrigation, and the third in a developing coun-
try with a flood problem so great it seems unsolvable.
The three examples are intended to emphasize the impor-
tance of differences in the origin and nature of flood situ-
ations, and are examples of flood situations applicable to
the suggested approach to floodplain strategy develop-
ment.
New Brunswick, Canada
New Brunswick, one of Canada’s three Maritime
2
Provinces, has an area of 73,440 km , and is roughly rect-
Figure 2. Features of flooding and damages in the province of New
angular in shape (about 240 km from east to west and 320 Brunswick, Canada.
IWRA, Water International, Volume 26, Number 2, June 2001

170
K.S. Davar, J.M. Henderson, and B. C. Burrell
km north to south). It has a humid continental temperate ever, during the following six months, opposition grew, and
climate with cool summers and no dry season. Mean an- by early 1997 citizens had organized meetings to oppose
nual precipitation is in the range of 900 mm to 1,400 mm. adoption of the floodplain policy. Concerns over property
Snowfall over the winter months (December to March) values and use of flood-prone land were raised during these
constitutes a major portion of total precipitation, varying meetings. Eventually, other priorities occupied the atten-
from 2 m (200 mm of water equivalent) in the south to 4 tion of the government agencies, and further development
m in the north (Acres Consulting Services Limited, 1977). of a floodplain policy was postponed.
The features of flood events in New Brunswick are
At the end of March 2000, the federal-provincial Gen-
presented in Figure 2. Snowmelt, ice jams, and rainfall eral Agreement Respecting Flood Damage Reduction
are the principal causes of flooding in New Brunswick, expired. This ended the program of flood risk mapping
which result in average annual direct flood damages of and financial deterrents with respect to new floodplain
approximately $CDN 4 million. Floods involving ice jams activities. At the time of this writing, New Brunswick did
tend to be more destructive than open water events, par- not have an effective Province-wide flood damage reduc-
ticularly to bridge structures. For example, during the tion program. However, some municipalities have taken
flood of February 1970, which featured a series of ice the initiative from the program to implement some as-
jams in six rivers, 32 bridges were destroyed and another pects of floodplain management.
1
24 were damaged (Environment Canada, circa 1986). Gray and Burrell (2000) suggested some reasons why
In March 1976, New Brunswick became the first Ca- efforts (to date) to develop a floodplain management
nadian province to enter into an agreement with the fed- policy for New Brunswick have not materialized. The
eral government aimed at reducing flood damages by reasons they give are as follows:
means of flood forecasting, flood risk mapping, and re-
strictions on government activity and development sup- • Flood damage reduction is long-term whereas floods
port in the form of financial assistance. During the period
976 to 1992, as flood risk mapping and flood forecast-
ing were being carried out, there were several attempts to
are short-term. Public concern fades once a flood event
is over and political priorities shift once public con-
cern fades.
1
create more comprehensive management of flood risk • Different government agencies have been responsible
areas, but these attempts were generally unsuccessful.
Burrell et al. (1995) provide a more detailed account of
the evolution of floodplain management efforts in New
Brunswick.
The latest attempt at floodplain management resulted
from a recommendation of the Commission on Land Use
and the Rural Environment (CLURE), which was estab-
for land use planning and water resources planning.
Water and land use planners often have differing pri-
orities and approaches, i.e., to many planners, water
is water and land is land. (Recent re-organization of
government departments has resulted in the placement
of community planners, water resource planners and
hydrologists in the same department.)
lished in 1992 by the provincial government to address • The public does not consider flood risk a high prior-
problems related to the management of land and water
resources. Pursuant to CLURE’s recommendations, a task
group with representation from several departments was
established to prepare a draft policy for consideration by
government. By mid-1995, a draft policy had been essen-
tially completed (Savard and Burrell, 1995). The land use
ity. In New Brunswick, flooding has resulted in only
few deaths and usually short-term hardship or incon-
venience. Flood disaster assistance mitigates the con-
cerns of landowners.
Landowners’ interests sometimes conflict with the
controls outlined in the draft policy were linked to exist- public good. Land use controls reduce some benefits of
ing floodplain mapping: a collection of maps at different land ownership while enhancing others. Floodplain de-
scales and contour intervals and depicting one or more lineation and land use controls are perceived as reducing
flood risk zones depending on the means of floodplain property values.
delineation. If an area had been delineated identifying two
A province-wide, comprehensive flood damage re-
zones, new development in the higher risk zone (flood- duction program may still be desirable. Flood-susceptible
way) would be restricted to flood-compatible uses and development is likely to continue to increase as develop-
certain types of public infrastructure. In the lower risk ment continues to follow past settlement patterns and
zone (floodway fringe) or an area with only one identi- transportation routes, which were along rivers, and be-
fied flood risk zone, additional development, including cause waterfront property is highly valued. Such devel-
flood-proofed single-family residential buildings, could opment will put more people at risk, increase the amount
be built.
of environmental contamination during floods, and exac-
During the summer of 1996, a public consultation erbate flooding and flood damages. Furthermore, climatic
process was undertaken. Response was limited and it was change is expected to increase the frequency of flood
first assumed that public response was favorable. How- events.
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Flood Damage Reduction
171
Figure 3. The Nile River Basin
Nile River Floods
Flood Characteristics
periodic floods cause great damage is in Khartoum and its
vicinity where the Blue Nile and the White Nile join to
The almost legendary floods of the Nile have carved form the Main Nile.
a valley 2,500 km long out of rock, built an extensive
The origins of these floods can be identified in the
floodplain and delta, and created an environment that fos- unique characteristics of the basin, which are illustrated
tered the growth of a great civilization. The Nile has also on Figure 3. The Nile River Basin comprises five distinct
periodically inflicted devastation on the inhabitants of the climatic-hydrological regions which can be distinguished
valley and delta, both by being excessive and by being on the map from headwaters to the Mediterranean Sea,
inadequate.
Two other regions in the Nile River Basin have histo-
they are as follows:
ries of flood problems. In the early 1960s, the water level
of Lake Victoria slowly rose by about 2.5 meters, caus-
The Lake Plateau
This is not a homogeneous region, climatically or to-
ing considerable damage to shoreline installations. Since pographically, but its sub-regions are similar enough for
then the water level has gradually receded, but has not the purposes of this analysis. The rainfall pattern tends to
yet returned to its previous level. The cause of this be bi-modal with peaks in November and March. Aver-
anomaly has not been determined. The other area where age monthly precipitation seldom exceeds evapotranspi-
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172
K.S. Davar, J.M. Henderson, and B. C. Burrell
an average of about 10 percent of its flow to evaporation
and seepage. However, in both the Saharan region, which
may be defined as extending to the High Aswan Dam,
and the Nile Valley in Egypt, there are run-off channels
that deliver flash floods occasionally, perhaps only once
in 10 or 20 years. These floods can have two effects. First,
people forget about the flood risk and settle in the flood-
plains of these torrent channels. When a flash flood even-
tually strikes, settlements are destroyed and there may be
fatalities. Second, the flash floods transport large amounts
of rock and sand which may impede the flow of the river
and create a new navigation hazard (Hurst et al., 1959).
The Nile Valley and Delta
It is in this region that in ancient times the Nile floods
led to the development of one of the first irrigation civili-
zations. The Nile, because it receives no additional water
in this region, and because it carried a large silt load dur-
ing the high flow period, was an aggrading river: that is,
its bed gradually became raised above the floodplain, so
that when its bank was over-topped, the overflow spread
over a large area. Early Egyptians planted their grain and
vegetables in the soaked soil and usually got a crop. Over
Figure 4. Normal monthly mean discharges of the Nile and is princi-
pal tributaries in millions of cubic meters per day 1912–1936.
Source: The Nile Basin, Volume V, Hurst and Phillips.
ration, but there is, in general, no pronounced dry season. time, they learned how to control and channel this natural
Average annual precipitation is fairly generous, ranging flooding and the science of hydraulics and irrigation was
from 1,000 mm to over 1,600 mm (FAO, 1984). It is also born. Of course, occasional large floods would cause great
a region of enormous natural storage, and consequently damage and loss of life, or exceptionally low floods would
is subject to huge evaporation losses. The result can be not overtop the river banks or enter the canals, and fam-
seen in the average monthly flows of the Victoria Nile, ine would ensue (Hurst et al., 1966).
the Bahr-el-Jebel and the White Nile at Mongalla, as
shown on Figure 4 (Hurst and Phillips, 1938).
The geographic differences between these regions
explain the flow patterns, including the floods and
droughts, of the Nile. The first three regions contribute to
the discharge of the Nile, the fourth and fifth consume
The Sudd/Bahr-el-Ghazal Region
This region is like another great lake basin, which in- most of its water.
deed it may have been. The Sudd itself is a huge swamp
fed from three sources, overflow from the Bahr-el-Jebel,
spill-over precipitation from the Congo River Basin to
the west and south, and runoff from the Bahr-el-Ghazal situations with regard to flooding. One large sub-basin
Flood Control
The Nile River Basin illustrates three very different
basin in western Sudan (Hurst and Phillips, 1938).
contains enormous natural storage and consequently con-
tributes little, if anything, to the flood characteristics of
the main river. The other major sub-basin contains very
The Ethiopian Highlands
The highlands of Ethiopia, ranging in altitudes from little storage and is the source of nearly all the flooding
,500 to over 4,000 meters, experience a pronounced uni- experienced by Sudan and Egypt. A third type of flood,
1
modal rainy season, during which precipitation greatly the relatively rare and local flash flood, is found in the
exceeds evaporation. There is only one lake and it pro- desert areas where rainfall seldom occurs but, when it
vides little storage and contributes only a small percent- does, can be devastating. Each of the flood situations in
age of the flow of the Blue Nile. Three rivers drain this the Nile River Basin could be analyzed using the method-
huge area into the Nile: the Sobat, the Blue Nile, and the ology presented in this paper, probably with positive results.
Atbara. Together they contribute 85 percent of the flow The international nature of the Nile River basin makes
of the main Nile River, almost all of its flood characteris- the establishment of a comprehensive or even a local flood
tics, and almost all of its silt (Hurst et al., 1959).
protection program extremely difficult. The problem ex-
perienced in Lake Victoria probably arose more from a
constriction in the outflow of the Lake than excessive rain-
The Sahara Desert Region
From the junction of the Atbara to the Mediterranean fall over its drainage basin. Due to the infrequency of the
Sea, a distance of 2,700 km, the Nile receives no tributar- flooding occurrence in Lake Victoria, it is unlikely that
ies. In the Saharan region, it is estimated, the river loses there will be any move to introduce flood damage reduc-
IWRA, Water International, Volume 26, Number 2, June 2001

Flood Damage Reduction
173
tion measures in the lake plateau region in the foresee-
able future.
The Sudd area is occupied by tribes that benefit from
the regular flooding. The human ecology is attuned to the
hydraulic system. An environmental impact analysis was
undertaken of the Egyptian-Sudanese plan to save water
for downstream use by bypassing much of the Sudd
through the Jonglei Canal. The analysis evidently did not
adequately consider the social aspects of the proposed
canal because the local people halted its construction by
force in the early 1980s.
The flood problem in the Khartoum area is not ame-
nable to structural solutions within Sudan, and interna-
tional efforts have not been mounted to attempt to create
Figure 5. Bangladesh and the Ganges, Brahmaputra and Meghna river
basins.
significant storage in Ethiopia. At some future time it may Mountain chain to the south and north, respectively. The
be possible to undertake an integrated international water Meghna is a short river but it drains one of the highest
management study of the Blue Nile Basin which will in- rainfall areas in the world. It rises in the Meghalaya and
clude measures to reduce flood damages in the Khartoum Tripura States of India. At Cherrapunji, the average an-
area. A combination of structural and non-structural mea- nual precipitation is 11,016 mm and the mean monthly
sures will likely be required.
rainfall for May, June, July, August, and September are
Egypt solved its own problems of flood damages by 1,341 mm, 2,671 mm, 2,524 mm, 1,812 mm and 1,129
constructing the High Aswan Dam (HAD) which contains mm, respectively (FAO, 1987).
over-year storage. However, the HAD studies were car-
Rainfall averages over 2,000 mm per annum over most
ried out in the 1950s and 1960s without any environmen- of the deltaic region, and about 4,000 mm in the Sylhet
tal impact assessment. Although the HAD has created a region in the Meghna watershed. Eighty percent of the
number of negative side effects, the benefits of full flood precipitation occurs during the monsoon season, which is
control, including generating 10,000 Gigawatt-hours an- June through September. Average monthly rainfall at
nually of electrical energy, and bringing approximately Dhaka during June, July, August, and September is 420
half a million hectares of new land under perennial culti- mm, 405 mm, 324 mm, and 256 mm, respectively. Even
vation, seem to outweigh the detriments of the High these figures do not give the full picture; the Bay of Ben-
Aswan Dam.
gal is an area which generates huge tropical cyclones,
International cooperation, combined with a thorough many of which drive northwards through Bangladesh caus-
understanding of the geographical and human parameters ing great damage and flooding.
of the flood regimes, are essential if flood damages and
The topography is unusually low. Much of the coun-
benefits are to be optimized in the Nile River Basin. Flood try is lower than 10 meters above sea level (m.a.s.l.), and
management strategies for the Nile River Basin could be the highest areas in the north of the country are only about
analyzed using the methodology presented in this paper. 100 m.a.s.l. The Brahmaputra system flows about 560
kilometers through Bangladesh to the Bay of Bengal. The
Bangladesh
slope through the delta is very slight (United States Gov-
Bangladesh probably suffers more flood damage per ernment, 1989).
person or per square kilometer than any other country in
All these features combine to create an extremely
the world. The reasons are geographic, social, and eco- flood prone country (Figure 6). Floods are of several types:
nomic. The country covers only 144,000 square kilome-
ters and contains approximately 120 million people, or • monsoon floods from the major rivers,
8
30 people per square kilometer (8.3/hectare). Bangladesh • local flooding due to heavy and intense rainfall,
lies at the northern end of the Bay of Bengal, and consists • flash floods in the eastern and northern rivers, and
of two, almost separate lobes; the smaller is the Chittagong • floods due to storm surges in the coastal area.
Hill Tracts, occupying the eastern shore at the head of the
Bay. The larger portion comprises a combined delta of
Floods in Bangladesh are normally categorized by the
three great river systems: the Brahmaputra, the Ganges, extent of the area flooded rather than by river stage. The
and the Meghna. The delta region lies at the head of the seriousness of the flood risk is illustrated by the fact that
Bay of Bengal. The rest of this discussion will be limited on average 22 percent of the country is flooded each year
to the delta.
and about 60 percent of the country is flooded in a 100-
The drainage areas of the great rivers that converge year flood (The World Bank, 1989).
in the Bangladesh delta are shown on Figure 5. The Ganges Many flood studies have been completed for
and Brahmaputra drain a large part of the Himalayan Bangladesh, but after two of the most severe floods on
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174
K.S. Davar, J.M. Henderson, and B. C. Burrell
The Action Plan has been analyzed and discussed by
Wescoat et al., 1992, who appear mainly to doubt the
wisdom of the structural approach. However, James and
Pitman (1992), make it clear that an entirely non-struc-
tural approach to the specific flood problems of
Bangladesh would not be feasible. In discussing the po-
larization between “embankers” and “non-embankers” the
authors make the point that the greatest challenge is to
overcome ideologies and find a way to better the lives of
the poor and suffering people.
Referring to flooding problems on the Brahmaputra
River in India, Bhattacharyya, and Bora (1997) conclude
that “management of the floodplain and reduction of flood
hazards . . . need to be approached through properly
planned, designed, and implemented flood management
activities that in turn may be the key factor in socioeco-
nomic development in the Brahmaputra Valley.”
The analytical methodology presented in this paper,
it is suggested, could contribute to finding the right com-
bination of structural and non-structural interventions,
area-by-area, to satisfy both human and hydrological
needs.
Figure 6. Area of flooding in Bangladesh.
record occurred in 1987 and 1988, the Government of
Bangladesh determined to undertake a systematic flood
protection program. This started with preparation of an
Conclusions and Recommendations
It is emphasized that the following conclusions and
Action Plan for Flood Control. The World Bank agreed recommendations pertain mainly to river valley floods;
to help coordinate international efforts of assistance for special types of flood situations may require different
this objective. In December 1989, the Action Plan was solutions, but a similar systematic methodology should
published. In the preparation of this plan, there was on- be employed.
going debate about the relative merits of structural and
non-structural approaches to flood damage reduction. It
was recognized that periodic flooding in Bangladesh is
largely unavoidable, and that the measures required to
Conclusions
Every river system flood problem is unique; its causes
eliminate flooding in some areas are technically and eco- and effects must be individually addressed. There is no
nomically infeasible, and that they may cause as many universal solution to flood problems, as shown in the three
problems as they solve. On the other hand, it was widely examples. For extraordinary flood events, adequate pro-
believed that the country cannot be at the mercy of floods tection is rarely feasible. The appropriate approach is
forever and that the rivers must be contained so that floods through an early warning system on the basis of which
safely pass to the ocean. The Government, in general, fa- emergency measures can be undertaken, including deploy-
vors a structural approach, with elements of non-struc- ment of national defence services and volunteer public
tural efforts.
efforts. The complete elimination of floods is neither fea-
The structural solutions in the Bangladesh Action Plan sible nor always desirable, especially when environmental
include extensive embanking along the main rivers to and ecological conditions interrelated with the geo-fluvial
contain flood waters and compartments around cities and system are considered. The current climate of justifiable
other vulnerable areas to keep flood waters out. The lat- environmental and ecological sensitivities is averse to any
ter also requires drainage systems to release water from major changes in the river regime and the floodplain char-
direct rainfall from the compartments. In addition, flood acteristics unless very clear and strong benefits can be
water diversions are planned, utilizing several of the del- demonstrated.The final decision in adopting a scheme for
taic channels to greater effect than under natural condi- relief from floods is largely a political one, taking into ac-
tions. Non-structural efforts include a flood forecasting count economic, social, and cultural values, as well as likely
and early warning system and a flood preparedness pro- environmental and ecological consequences. Institutional,
gram. The Plan is supported by many relevant studies. administrative and international cooperation and coordi-
The practical approach to floodplain management may nation are essential for effective development and imple-
involve a combination of structural and non-structural mentation of flood damage reduction strategies and
measures.
programs, especially for international river basins.
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Flood Damage Reduction
175
Recommendations
References
In developing a strategy to attain an optimal solution Acres Consulting Services Limited. 1977. Regional Flood Fre-
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Dr. Kersi S. Davar joined the
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America, including the Caribbean. Email:
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IWRA, Water International, Volume 26, Number 2, June 2001