23

Key Elementsof Flood Disaster Management

2

24

2.1 Risk Management and Flood Plain Delineation

A change to proactive management ofnatural disasters requires an identification ofthe risk, the development of strategies toreduce that risk, and the creation of policiesand programmes to put these strategies intoeffect. Risk management is a fundamentalactivity geared to the evaluation of schemesfor reducing but not necessarily eliminatingthe overall risk, as in may cases risk cannotbe entirely eliminated. Figure 8 provides aschematic of the steps associated with riskassessment and management. It includesassessing the potential for a hazard to occurand a vulnerability analysis to provide anunderstanding of the consequences shouldan event of a certain magnitude andfrequency occur. Based on this initial work,various mitigation measures can beevaluated to assess their ability for reducingrisk exposure. Based on a thorough riskassessment, disaster management plans andspecific mitigation measures can be

identified. Efforts would then be undertakento implement the selected mitigationmeasures.

For flooding events, there is a need tocalculate the probability or likelihood that anextreme event will occur and to establish andestimate the social, economic andenvironmental implications should the eventoccur under existing conditions. Maps of theflood-prone areas should be prepared anddetailed impacts outlined. A participatoryprocess should be invoked, leading to thedevelopment of an acceptable level of risk.Measures can be evaluated and implementedto meet this level. This overall process assiststhe community in better understanding thevarious actions that can increase or decreaserisk exposure, and can lead to greatercommunity participation in the developedsolutions to the flooding problem.

Figure 8

Framework for Flood Risk Assessment and Risk Management

Source: Adapted from WMO, 1999

Natural System ObservationsInventory

AccountingData

Thematic Event Maps

Establish FloodHazard PotentialStreamflow versus

Probability of Occurrence

Risk AssessmentRisk = function (Hazard, Vulnerability, Value)

Planning / Mitigation Measures

Reduce Risk Through Best PossibleManagement Practices

> Land use Planning (Flood Plain Mapping)> Structural Measures (Dams, Building Codes)> Flood Forecasting and Warning Systems

Assess VulnerabilityValue (Material, People)

InjuriesResiliency

Protection Goals / Risk Acceptance

Unacceptable Risk Acceptable Risk

Implementationand

Periodic Review

25

Guidelines for Reducing Flood Losses

There may be a necessity to define severalzones within the flood-prone area, dependenton the velocity of the river and other physicalfactors. As an example, the flood-prone areamay be broken down into floodway and floodplain components. Figure 9 shows aschematic of the designated floodway andflood plain for a hypothetical community.

Delineation of the flood-prone area

In order to map and delineate an areaaffected by floodwaters, there is the need toselect a "design" event. Various approachesfor estimating the design event exist, basedin essence on "acceptable" risk, although atthe time of their adoption, the concept ofacceptable risk was not explicitly recognized.These approaches include using a historicalworst-case scenario that happened in thebasin or could plausibly have happened,which is referred to as storm transposition.Another approach is to theoreticallymaximize the meteorological factors thatcould happen in an area leading to the worstpossible storm producing the worst possibleflood. These are termed the Probable

Maximum Storm and Probable MaximumFlood, respectively. The third approach is touse a probability-based analysis whereinsystematic records and historical informationon past flooding are used to develop arelation of probability of occurrence versusmagnitude. It is becoming popular to adoptthe concept of acceptable risk rather thanadopting preset levels of protectionassociated with a specific probability ofoccurrence (e.g., the 100-year flood). Acommunity and its government may wish tomove to more extreme design levels whenfaced with the reality of future loss-of-lifeand extreme economic hardships when thefuture event occurs.

The frequency based approach is thepredominate method used in most floodplain delineation studies when the potentialfor loss of life is considered negligible interms of historical floods. The peak flooddischarge and corresponding water level areestablished for various frequencies ofoccurrence or return periods of events suchas once in 25 years (1:25), 1:50, and 1:100.Associated estimated damages are

Designation of floodplain and floodway components

Sour

ce: E

nvir

onm

ent C

anad

a

Figure 9

26

established for each probability. Manyjurisdictions have set their design level tothe "100 year flood". Statistically it is quitepossible to have more than one "100 yearflood" within a 100-year period, and a moreextreme event can also occur at any time. Areasonable length of streamflow record isrequired to ascertain with some accuracy theprobability of an event occurring.

When using a known historical flood todefine the flood-prone area, various effortsare required to delineate the flood plain. Thisapproach can at times rely on surveyinformation collected during or immediatelyafter the historical flood event. These datacan be used to verify hydraulic modelinformation to ensure accurate delineation ofthe flood plain. In cases using historicalfloods, care should be taken to adjuststreamflow and water levels to reflect thepresent levels and possibly projected levels ofdevelopment in the basin or other physicalchanges in the waterway. When a historicalstorm is transposed, hydrological models areused to transform rainfall to streamflow, andhydraulic models are, in turn, used todelineate the flood plain.

A shortcoming of using a known extremeflood event is the difficulty of assigning afrequency of return for evaluation of risk.However in data-short areas or when theevent can cause catastrophic results, it isprobably the preferred approach. It is alsouseful in establishing acceptable levels ofprotection.

These approaches tend to assume that eventsin the future are predictable based on theexperience of the past. If changes in land useare occurring, this may not be true, and thechanges should be reflected in the analyses.Similarly, the impacts of climate change orvariability are not typically being incorporatedin the analysis. If possible, such factorsshould also be taken into account in thedelineation of flood-prone areas.

Floodway and flood plain

The floodway is that portion of the flood-prone area that is required to pass the designflood event without a significant rise inwater levels compared to undevelopedconditions. "Significant" is normally definedas a rise in the range of 25 to 40 cm. Thefloodway is delineated using the floodfrequency or extreme event informationcombined with a hydraulic analysis.Normally the floodway can be characterizedas that part of the flood-prone area havinghigh velocities, high potential for erosion,and high exposure to significant flow ofdebris. Often the floodway encompasses thenormal river channel and some expandedhigh water area. No structures, other thancritical infrastructure such as bridges,should be allowed in the floodway. Insimple terms, the floodway is reserved forthe river, not for humans.

The flood plain is the residual area outside ofthe floodway where the water velocities areless and flood protection and flood-proofingmeasures can be considered. When both thefloodway and flood plain are identified, this ittermed a two-zone approach. A simplified orone-zone approach is, at times, used whenthere is no existing incompatible developmentin the floodway and no new incompatibledevelopment will be allowed in the future. Insuch cases, only one designation of zone isused, and the entire area is treated as a floodplain. Under such circumstances, care wouldbe taken to ensure that no new incompatibledevelopment occurs in the zone.

Figure 10 shows a section of a map for a one-zone application where the flood plain isdesignated in its entirety. The map showshomes, businesses, and institutions at risk at a1:2,000 scale. Land contour information at 1-metre resolution is provided. Implications onexisting and future land use (e.g., residential,parkland, industrial) would be set throughpolicy and would be reflected in local zoning.

27

Guidelines for Reducing Flood Losses

Implications on existing investments wouldalso be set by policy, which could consideroptions such as relocation of incompatibleuses, adoption of flood-proofing measures, orchanges in designation of vacant or unusedlands.

Areas beyond the defined flood plain may besubject to flooding by even rarer events,which are events that exceed the design event.Efforts should be made to ensure that"critical facilities" are flood proofed againstthese rarer events. Critical facilities includehazardous materials production, storage andwaste facilities; essential utilities such as waterand wastewater facilities and power plants;essential services such as hospitals, schoolsand airports; and emergency services such asfire stations or major computer centres. Forexample, if the 100-year flood is used todefine the flood plain for zoning purposes,then critical facilities could be flood proofedto higher standards as if they were in the 500-year flood plain.

Vulnerability analysis

A vulnerability analysis considers thepopulation and structures at risk within theflood-prone area. The analysis evaluates thepotential costs of flooding in terms ofdamages to buildings, crops, roads, bridgesand critical infrastructure, such as utilities.Normally the analysis is carried out forvarious probabilities of floods, and anelevation-damage curve is developed.

A vulnerability analysis, because it identifiesthe population at greatest risk, can also beused to identify the emergency responsesthat may be required, including the need fortemporary shelters and evacuationrequirements.

The analysis is also valuable for making adecision on the level of flood protection. Thedecision is based on knowledge of the degreeof cost effectiveness of various options.However it should be a public process that

Sour

ce: E

nvir

onm

ent C

anad

a

Section of map showing designated flood plain areaFigure 10

28

establishes the "acceptable level of risk" thatleads to the return period appropriate for thedelineation of flood-prone areas. The analysismay also generate information useful indetermining the benefits of flow forecasting.

Flood risk mapping

Mapping defines the area at risk and shouldbe the basis for all flood damage reductionprogrammes and subsequent actions. Themaps often have a legal connotation in termsof zoning and other structural and non-structural measures undertaken, so theyneed to be accurate and credible.

The mapping is normally based on afrequency of flood event determined bypublic consultation and reflected in policy,which may be based on a vulnerabilityanalysis that is site specific. If regional ornational flood reduction programmes are inplace, there are advantages to a commonmapping standard. If the historical flood isused, then some attempt should be made toassign a return period to the event forcommunication and design purposes.

Maps become the common element in termsof identification of flood-prone areas,identifying the risk to individuals andlending institutions, preparation ofemergency response plans, and design offlood protection and flood proofing

measures. Perhaps their greatest value is asan educational and communications tool,and they should be readily available to thepublic as well as to emergency responseagencies at all levels of government.

Through modern computational systems,inundation maps can be generated in real-time and be part of the hydrological forecastsystem. These can greatly assist incommunication to residents in areas ofpotential risk, and in planning responseactions and assistance.

Protecting flood-prone lands

Policies and programmes to keep futureflood damages from rising are based on thedelineation and mapping of flood-proneareas. Generally the resulting programmeswill mean some form of control over newdevelopment in the flood-prone areacombined with measures to reduce damagesto existing development. Such programmesare needed to curb the rising social andeconomic losses that results from floods.

Alternate use of flood-prone land should beconsidered where possible. It is better tohave the land zoned and used for purposessuch as parks, nature areas or ecologicalreserves than to try and ensure that futuredevelopment is flood proofed. Zoning andflood proofing measures can be used tocontrol development and reduce future flooddamages, but the effectiveness of suchmeasures is highly reliant on enforcementand maintenance. Local authorities aresubject to developmental pressures andstandards have a tendency to "slip" as thememory of a flood event fades.

Climatological forecasting

Climatological or seasonal forecasting hasnow advanced to the point of being a usefultool in reducing the risk of flooding.Extreme events are correlated to major

Pho

to: I

nter

natio

nal A

ssocia

tion

for C

hrist

ian

Actio

n, I

taly

29

Guidelines for Reducing Flood Losseschanges in atmospheric and oceancirculation patterns, and once suchpatterns have been identified, thepotential for a lesser or greater degree ofstorm activity can be forecast. Thisinformation can then be used to increasethe degree of readiness of emergencyresponse and forecasting agencies.

In certain cases the climatic forecasts canalso be used to increase the availability ofstorage in reservoirs, to influence watermanagement decisions and to create anawareness of the potential for flooding.All of these measures can reduce theseverity of flooding, if it occurs.

When the probability of the extremeflooding event is greater than normal,then activities such as the stockpiling ofsandbags, emergency food and watersupplies, and the evacuation of highvalue stored crops or goods from flood-prone areas can be undertaken. It is agood time to create awareness in thepublic as to the potential for flooding,highlight the actions that the public andothers should take, and to carry outemergency response exercises to test thedegree of readiness. In some casesemergency measures such as temporaryraising of flood protection works may bewarranted.

China, Yangtze River, 1998

The photograph depicts Chinese soldiers and civilians struggling tomaintain weakened levees during the summer floods of 1998.

It has become almost an annual occurrence: China'smighty Yangtze River swells under torrential rains, thensurges downstream, flooding dozens of communities andleaving thousands homeless. During the summer of1998, more than 2,000 people were killed, and thefloods, which began in early June when seasonal rainsarrived earlier and were heavier than usual, left 14million homeless. For the fifth time that summer, theYangtze hurled a massive flood crest toward the tens ofmillions of people who make their homes along its centraland lower stretches. Earlier that week, a fourth floodcrest was thwarted by millions of weary soldiers andcivilians drafted into the flood-fighting campaign. Moreimportantly, weakened levees that have withstood an earlyconstant assault by the river remained largely intact.

Pho

to: X

inhu

a N

ews A

genc

y

30

2.2 Supportive Technologies

A number of tools are available to array anddisplay information for the use of technicalexperts, to explain programmes of flooddamage reduction to the decision-makers,and to communicate real time forecasts andwarnings to the public. In general the toolsshould be interactive in the sense that theinformation can be easily updated, andflexible enough to develop scenarios, and toprovide visual and quantitative informationregarding the state of conditions during theforecasted event.

Geographic information systems

Geographic Information Systems (GIS)provide a computer-based information andmanipulation system useful in support offlow forecasting and emergency response.Information from a variety of sources andscales can be combined as a series of layers,provided that the information can beidentified in terms of the commondenominator of location. For example,information on vegetative cover can becombined with soils and land slopeinformation to estimate infiltration rates forforecasting purposes. Similarly layers ofutility, land use, flood plain delineation, andstructures information can help in thedevelopment and updating of emergencyresponse plans.

A good representation of the basintopography is an important asset in floodforecasting, emergency action andmitigation. A digital elevation model(DEM) or digital terrain model (DTM) forthe basin should be developed as part of anyGIS. Technologies exist that enable theconstruction of a "seamless best available"DEM. In other words the DEM isconstructed from whatever topographicinformation is available. Parts of the basinor certain features may be very accurate

while others may be quite basic. The DEMcan be improved with time.

The development of inexpensive globalposition indicators has made GISinformation easier to obtain. For example,data network sites, buildings or physicalfeatures can now be easily located withprecision and at low cost. Land use,vegetative cover or soils information is alsoeasier to assemble.

Mapping

Maps of areas at risk from natural disastersare valuable information and communicationtools. They can be used for a wide variety ofpurposes ranging from flood plaindelineation, zoning and land use planning topresentation of information at publicmeetings.

Zoning maps, however, are static and mayrequire updating with time as changes occur.For static information, such as the delineationof the flood-prone area, frequent updating isnot required, and maps are a useful referencetool for a wide variety of users.

Visualization techniques

GIS and other computer-based informationsystems allow for a wide range ofpresentational material to be easily generatedand tailored to the target audience. Three-dimensional displays, zoom and scan, androtational techniques can be combined withother informational material such aspictures, overheads or slides. As anexample, a GIS flood inundation map canbe generated based on hydraulic modelderived information. The map can beconveyed to residents in the flood plain andis useful for depicting the probable impactof the approaching flood.

31

Guidelines for Reducing Flood LossesThis tailoring of technical information intodisplays that are more readily understood isvaluable for explaining programmes todecision-makers, informed experts, and thepublic at large. Highly visual information isparticularly valuable for public meetings oropen houses, but must be tailored carefullyfor the audience. In particular, the

2.3 Flood Plain Management

Management of activities within the flood-prone area can significantly reduce flooddamages to existing development and preventthe amount of damages from rising in thefuture. The most desirable approach is toprohibit new development in the flood plainand to flood proof existing structures, or toreplace the existing development byalternative usage of the land. However,where the amount of present development issubstantial or the flood plain is essential forthe production of food or other key economicactivities, alternate strategies such as floodproofing and protection can be considered.

A. Structural Measures

Construction of dams/diversions/storm channels/levees

Construction of protective works such asflood storage reservoirs, diversion of waterto side channel storage or other watersheds,construction of storm channels to carrywater around the area to be protected, andlevees along the floodway provide tools toreduce flood damages. Such works can beconstructed to various levels of protection,usually based on: 1) minimum standardsfor flood protection; 2) the optimum levelof costs and benefits based on an economicanalysis; or 3) to meet established levels ofacceptable risk.

Protective works should be consideredwhen major infrastructure has already beendeveloped and costs to protect existinginvestments are far less than those relatedto reconstruction, lost economic activity,disaster assistance, or relocation of existingstructures and activities. For example, floodprotection measures for the city ofWinnipeg, Canada, were completed in thelate 1960s at a cost of $US 92 million. Arough estimate of damages prevented infive large floods since then is approximately$US 2.0 billion.

Protective works have a tendency toincrease the level of development in flood-prone areas, as the assumption is made thatit is now safe to build and invest in areasthat are protected. However, it must berecognized that at some point in the futurethe design event will likely be exceeded andcatastrophic damages will result. Leveesand storage dams are particularlydangerous when design thresholds areexceeded in that unexpected failure canresult in a rapid rise in water level andmake evacuation and emergency protectionextremely difficult. Diversions or stormchannels are less prone to catastrophicfailure and the level of protection cantemporarily be increased by emergencymeasures if the lead-time of the floodwarning is sufficient.

information must be credible and easilyunderstood.

The above techniques, combined with theflood forecast, provide a very effectivemeans of delineating areas at risk and forcommunicating this to the decision-makers,emergency response teams, and the public.

32

Flood control storage may be onecomponent of a multi-purpose reservoirdevelopment. Over time the operation ofthe reservoir could be altered to enhanceother beneficial uses of storage to thedetriment of flood control. A commitmentto "designated flood storage" and toreservoir operation procedures to achievethat storage is needed.

Inspection, rehabilitation andmaintenance

Structural works require a periodic andsystematic inspection, rehabilitation andmaintenance programme to ensure that thedesign capabilities are maintained. Forexample, levees may be subject to weakeningdue to erosion during a past flood event, bythe actions of burrowing animals, or theconstruction of utility lines through thelevee. Of particular importance is aninspection programme and responsibilityassigned for rehabilitation and maintenance.

Structures such as dams should be subjectto a dam safety programme, usually at thenational level, to ensure that the specializedexpertise required is available for theinspection of all structures. Dam safetyprogrammes are carried out in manycountries and standards or guidelines arereadily available.

Flood proofing of new and existingstructures

Any new construction permitted in theflood plain should be flood proofed toreduce future damages. Building codescan be developed that minimize flooddamages by ensuring that beneficial uses ofbuildings are located above the designflood elevation. For example, buildingscan be raised above the design flood levelby placement of fill; stilts or piles used toelevate the structure; and building utilitiescan be located above the flood level (see

Figure 11). Ground floors can bedesigned in a way that little flood damageoccurs through use of masonry materialsand specifying that contents must beremovable.

If any new development is allowed withinthe flood-prone area, then the impact ofthat development must be taken intoaccount to ensure that flood levels do notrise significantly due to the additionalconstriction to flow. Hydraulic analysescan be undertaken to ascertain the impactsof potential activities and to keep the riseto within acceptable limits.

Flood proofing of existing structures isdifficult and expensive. One successfulstrategy is to link flood disaster assistanceavailable after a flood event to methods ofreconstruction that minimize future flooddamages. This approach often requiresadditional funding over and above apayment for damages, but can be cost-shared between various levels ofgovernment and the owner. This strategyis particularly useful when flooding isfrequent and future disaster assistance canbe expected as part of disaster policies.

Flood proofing of existing structures caninclude raising of structures to preventdamage, relocation of utilities, changedbuilding use, installation of protectivewalls and waterproof closures, and use ofmaterials that are not damaged by waterand can be easily cleaned after the floodevent. Relocation of existing buildings andstructures to an area that is not flood-prone is also an option.

Buyout and relocation programmes for aparticularly vulnerable development shouldform a component of flood proofinginitiatives. In many cases it may be moreeconomical to buy out and relocate theexisting use than to protect it.

33

Guidelines for Reducing Flood Losses

A number of critical services such aswater lines, power pylons and telephoneservices often cross the flood plain.These utilities can be protected againstthe ravages of flooding at relatively lowcost through additional depth of burial,a higher design standard for exposedcomponents, and raising of componentsabove design flood levels.

Water supply and treatment plants areparticularly vulnerable. They are oftenlocated on the flood plain yet are criticalfor the protection of human healthduring and after a flood event. Suchstructures need to be protected againstextreme events and designed to preventcross-contamination from floodwaters orsewers.

Bridges and roads

Bridges generally constrict the flow of water,and they can act as artificial dams if debrisjams on the structure. In all cases, theirhydraulic characteristics must be considered atthe design stage to prevent an unacceptablerise of water levels upstream of the structure.

Bridges are important in terms ofmaintaining access for evacuation anddelivery of medical and other emergencyservices. Key transportation corridorsshould have high design standards that willwithstand extreme flooding events.However not all bridges require a high levelof protection, and the design criteria can beto a lesser standard that takes intoconsideration the possibility of overtopping.

Figure 11

Flood proofed dwelling

Pho

to: E

nvir

onm

ent C

anad

a

34

Bridges are expensive, and difficult toreplace quickly after a flood event. Analternative strategy is to design the approachroads to be the weak link in the chain so thatextreme events wash out the road but do notdamage the bridge. Approaches can bequickly repaired after a flood event andtransportation corridors restored.

Road design, either parallel to the river orleading to bridges, must be given carefulconsideration. There is a temptation to raiseroads that have been overtopped by floodevents without giving adequateconsideration to the number and size ofopenings necessary to pass local drainage ortributary inflow. In such cases the road canartificially raise water levels upstream andcause additional flood damage. Roads canalso act as levees when they are parallel tothe river. This is a two-edged sword: whileflood protection is provided, the water levelupstream can increase, resulting inadditional flood damages there. Hydraulicstudies must be undertaken before roads areraised to fully establish the impacts of theseactivities.

Enforcement of standardsand codes

The enforcement of standards and codes forflood-prone areas is as important as their

initial development. There is a tendency tobend the rules as the memory of a floodevent and its catastrophic consequencesgradually fade away with time.

Enforcement procedures and penalties needto be built into the process, and emergencyresponse drills undertaken to ensure thatflood prevention measures such aswaterproof closures still work. An auditprocedure should be performed by higherorders of government with participation ofall interested parties to ensure broad nationalstandards are being met and that codes andrules are being suitably followed andenforced.

Governments should consider introducingrequirements such as surveyor certificates toverify that design elevations have been met,or inspector reports that flood-proofingmeasures have been implemented. Lendingand insurance institutions could usefully beinvolved in this process, as they have avested interest in ensuring that theirinvestments are protected.

B. Non-structural Measures

Non-structural measures are particularlyapplicable to flood-prone areas that are notyet developed. As such, they are acomplement to structural approaches inareas where additional development mayoccur, and they also represent anindependent approach where some controlover flood plain development can beexercised at low cost. Non-structuralapproaches do not mean "no use", but rather"wise use".

Land-use planning

Land-use planning at the local or municipallevel can be a useful tool in reducing futureflood damages. Consideration should begiven to ensuring that there are conforminguses in flood-prone areas as part of master

Pho

to: D

. Ray

ner,

Geo

Res

ourc

es

In the days and weeks following Hurricane Mitch, people struggledto find even the basic needs such as clean, safe water.

35

Guidelines for Reducing Flood Lossesplans. The land along a river is highlydesirable for parks and recreational uses, aswell as for ecological reserves. Supportiveinfrastructure such as washrooms, picnicfacilities and changing rooms can be floodproofed. Private development of conforminguses such as golf courses can also beconsidered. The important point here is tointegrate the land-use planning for flood-prone lands into the broader plans for theurban and surrounding area.

Zoning of flood-prone lands

The best way to reduce future flood damagesis to prevent development from occurring onflood-prone lands. Zoning of such lands isan effective approach, but generally should becoupled with the broader land-use planningmentioned above so that the land has adefined use.

Zoning can be used to reduce damages fromflooding and be flexible enough to recognizethat other forms of land use are compatible.An example is agricultural use of lands inflood-prone areas where water velocities arelow enough not to cause serious erosion.Flood-prone lands can continue to be usedfor agricultural purposes, particularly incountries where the amount of agriculturalland is limited and self-sufficiency in foodsupply is a national goal. It is important,however, to ensure that the supportinginfrastructure such as buildings and housesare located away from the flood-prone area orare flood proofed. It is also important thatlivestock, machinery or stored crops can beevacuated quickly from the area in the eventof a flood. This underscores the importanceof a flood forecast, warning and responsesystem.

Zoning of flood-prone lands as ecologicalreserves or protected wetlands can often helpto meet broader environmental or biodiversitygoals. In addition, such lands often play animportant role in sustaining the fishery, and

they can also act as temporary storage andinfiltration areas. Riparian buffer strips alsoreduce the movement of agriculturalchemicals and nutrients into the aquaticsystem.

Redevelopment of flood-prone areas

A major flood disaster is sometimes anopportunity to correct the planning errors ofthe past. Removal of flood-pronedevelopment and conversion of the land to aconforming use is an option to consider. Itmay be less expensive in the long run tophysically relocate flood-prone development,buy it out as part of a disaster assistanceprogramme, or include its purchase in longterm planning. The success of the latterapproach can be enhanced by measures suchas prohibiting improvements not required forhealth and safety, placing caveats on the landtitle, and by obtaining rights of first refusalon resale.

Compensation and incentives

Compensation as part of disaster assistanceshould always have as a goal the reductionof future flood damages. Rather thansimply paying for damages, the fundsshould be focused on flood proofing,buyout, relocation and public education onthe risks and consequences of living onflood-prone lands.

Pho

to: M

ing

Pres

s

36

In a similar manner, incentives can bedeveloped that encourage flood proofing orrelocation, and these can be financedthrough cost-shared programmes. Here thecost of flood proofing can be shared inproportion to the benefits to the variouslevels of government of not having tocompensate for future flood damages.Property owners should also be expected topay a reasonable share in view of theenhanced value of a flood-proofed structureand the reduced inconvenience after a flood.

Land exchange programmes can be used asan incentive to relocate from flood-pronelands. In such cases a public entity makesalternate land available and disasterassistance is generally used to pay forrelocation or replacement of structures,depending on the costs and benefits.

Incentives can also take the form ofpenalties. For example, if an individual isaware of the risk of flooding through suchprogrammes as flood plain delineation, orcaveats on land titles, and still decides tobuild on flood-prone land, then that personshould bear the consequences of his/heractions and not be eligible for disasterassistance. However this is difficult toenforce and is reliant on strong political willat the time of announcing disaster assistance.

Insurance

Flood disaster insurance forms part of thesuite of responses to reducing flood lossesin the United States of America. When aprospective homebuyer seeks to purchase aproperty in a designated flood-prone areawith funds obtained through a federally-insured or regulated institution, the lender

is required to notify the borrower of theneed for flood insurance. The lossescovered by flood insurance are paid fromthe accumulated premiums of policyholdersrather than disaster assistance funds.There are some weaknesses in thisapproach, as not all homeowners in flood-prone areas purchase insurance, and thereis the necessity for public funding if lossesexceed the accumulated premiums. Floodinsurance schemes have been utilized inother countries, including parts ofGermany, with varying degrees of success.

For insurance schemes to be successful,there needs to be a clear definition of therisk, as premiums should reflect the degreeof risk at a given location. It is alsodesirable for governments to promote or,when possible, mandate universal insurancecoverage and guarantee funding whenpayouts exceed premiums. Such schemesshould be designed to be self-sustainingover the long term. An additionalproblem concerns the information base,which is seldom sufficient to define thedegree of risk adequately. It is alsodifficult to effectively make insurancemandatory. Often those most at risk due toflooding are the least able to pay, or theyrefuse to pay because of high premiums.

The United States has an advantage froman insurance perspective in that 20,000communities are at risk from flooding; withsuch a large number of flood-pronecommunities, the financial risk can bespread more easily than in smallercountries. Insurance is an option thatneeds to be considered, but is probably notfeasible in many developing countries atthis time.

37

Guidelines for Reducing Flood Losses

2.4 Watershed Management

The water storage effect of vegetation, soil,shallow groundwater, wetlands and drainagehas a direct impact on the flood level indownstream areas. Each of these storagemedia retain certain quantities of water forvarious periods of time and can influencethe timing of tributary flows and hence theircontribution to a flood event. The storageeffect can be likened to a sponge and isdependent on the antecedent conditions andthe magnitude of the flood.

Impacts of land-use changes

The impacts of land-use changes on floodevents can be both positive and negative, sopredictions are hard to make for a specificwatershed. Generally the removal of forestand other natural cover, and the conversionof land to agricultural uses, compacts thesoil and reduces infiltration rates, leading tohigher flood peaks. Deforestation isbelieved to have been a significant cause ofthe catastrophic flooding in the YangtzeRiver basin in China and in CentralAmerica from Hurricane Mitch, both in1998. Deforestation and other land-usepractices can also lead to greater incidencesof landslides and mud flows.

Natural water storage is also generallyreduced due to the gradual loss of organicmaterial and soil erosion, once an area isconverted to agriculture. Additionally,natural vegetation may transpire moisture tothe atmosphere at a greater rate thanreplacement crops, thereby affecting both

the amount of storage available in the soiland the amount of local rainfall.

Drainage of wetlands and marshescontributes directly to changes in the timingof runoff, the amount of natural storage inthe basin, and the vulnerability of thechannel to the erosive forces of water. Evenroad construction can contribute directly toincreased runoff rates through improveddrainage as well as the effect of reducedinfiltration through the road surface.

By far the greatest impact of land-usechange is associated with urbanization itself.The paving of surfaces significantly reducesinfiltration, natural storage is reduced byimproved drainage, and streams are oftenconstricted by development or crossings. Acity will frequently have significant floodingproblems that are local in nature, but willalso be impacted upon by major flood eventson larger streams or lakes that are not withinthe urban zone.

A general rule is that the impacts of land-use change will be greater for smaller basinsthan for larger ones. Increases in flood peakand runoff volume in the range of 15-25%for medium-sized basins (>5000 squarekilometers) have been estimated intemperate climates. However, more detailedstudies are required before makingpredictions for specific basins and theirconditions. Scaling small basin results up tolarger basins and vice versa remains a majorscientific challenge.

38

2.5 Climate Variability and Change

There is growing concern about the impact ofchanging concentrations of greenhouse gaseson our current climate system and theramifications these changes might have onwater availability. It is believed that furtheralterations of atmospheric chemistry could leadto increased abnormalities in climaticparameters such as temperature, precipitationand evapotranspiration and might well lead tomore dramatic impacts on streamflow patternsand extreme conditions. Some analyses ofstreamflow over the last 30 to 60 years haveshown evidence of increasing and decreasingtrends in the low flows, with markedgeographic patterns to these trends. Thus far,there has been less evidence of trends in annualflood data for natural pristine basins. However,based on scenarios of projected futureatmospheric conditions, it is anticipated thatthere might be more pronounced alterations tothe streamflow regimes in various regions ofthe world. If these projections are correct,more severe or extreme conditions may prevail.

Climate impacts on extreme events

A number of studies on the potential impacts ofclimate change on flooding have been carried outas part of the work of the IntergovernmentalPanel on Climate Change (IPCC). Thesestudies indicate potential future increases in floodpeaks of approximately 15% in temperate zonesdue to increased storm activity and overallincreases in depth of precipitation.

At this point in time, it is not possible to predictpotential increases in flood peaks due to climatechange for specific basins with the degree ofcertainty necessary for their incorporation intothe design and planning process. However, thefreeboard on levees and other works canprobably accommodate the potentialmodifications in extremes due to climate changethrough modified operating procedures ofcontrol structures.

Sea level rise and storm surge

Coastal communities must also deal with theimplications of sea level rise, tsunamis, andocean storm surge in preparing for floodingevents.

Sea level rise due to climate change will resultin decreased river slopes in reaches abovewhere the river enters the ocean, therebyreducing the capacity of the channel to passflood flows. This increases the elevation offloods in coastal cities. While the rate of sea-level rise is slow, most protective works orflood plain delineation exercises are sufficientlylong term in scope to warrant consideration ofthe predicted rise.

Some studies have indicated that there ispotential for increased frequency of stormsurges, which result from high winds andincreased barometric pressure. Tsunamis canalso be devastating natural disasters and mustbe considered in a manner similar to flooding.Forecasting and emergency responses to theseevents must be based on the same principles ofacceptable risk and advance planning.

ENSO events

The El Niño Southern Oscillation (ENSO),related to changes in sea-surface temperaturesin the Pacific Ocean, can profoundly changethe weather patterns in Central and SouthAmerica. The number of hurricanes that canbe expected in a given season is also related.Climate predictions of above or below normalstorm activity during El Niño and La Niñaevents can assist with the regulation ofreservoirs and other water managementactivities that can reduce the magnitude ofpeak storm runoff. Flood forecasting andemergency response activities should also beperiodically tested to ensure they meetappropriate levels of readiness.

39

Guidelines for Reducing Flood Losses

2.6 Development of Policies, Strategies and Plans

The development of policies, strategies andplans to combat the risks associated withnatural disasters should be based on acomprehensive risk assessment. Thisrequires an integrated approach whereby awide range of mitigation measures should beconsidered. For example, mitigationactivities such as hazardous land mapping(i.e., flood plain mapping plus landslide-and mudslide-prone areas) should bedesigned so that considerations of otherdisaster types lead to sounder overall land-use plans. In essence, there would be verylittle purpose in moving people and goodsfrom one risk zone to another, especially ifthe other hazard is equally or more apt tooccur under the prevailing conditions suchas torrential rain. Within this overallprocess, full consideration needs to be givento the social, environmental and economicimpacts of policy and programmedevelopment. This chapter providesguidance on aspects of flood hazards thatneed to be considered within the overallplanning process. The aspects containedherein are meant to complement othermaterials in this guide, such as thedevelopment of a flow forecasting andwarning system, which are important toolswithin the range of options to be considered.

Basin wide planning

Reduction of flood losses must beconsidered, using the basin as the basicplanning unit. It is absolutely essential tohave knowledge of water uses, diversions,storage, and management practices in allparts of the basin, as well as the antecedent,present, and forecasted meteorological andhydrological conditions.

Transboundary basins represent a specialchallenge in that international collaborationis required. In such cases consideration

should be given to expanding existingbilateral or regional arrangements forexchange of data and information and to thenegotiation of treaties or agreements.Agreements can also include the option ofprojects of mutual advantage funded by allthe countries involved, includingconstruction of flood storage or other floodpreventative measures at the mostadvantageous locations in the basin as awhole.

Multijurisdictional issues

Basin-wide planning for reduction of floodlosses can involve government at the local,provincial/state and national levels. As suchit is desirable to have the nationalgovernment develop strategies and policiesthat ensure a consistent framework whereverthey are applied. This can extend to matterssuch as installation and maintenance of datanetworks, design standards for protectiveworks, flood proofing standards, costsharing arrangements, and incentive andinsurance programmes.

In general the national level of governmentshould take the lead in bringing the partiestogether, but should delegate planning of thedetails and delivery of the emergencyresponse programmes to the local level.Generally the national and provincial/stategovernments will play some direct role inoperation of forecasting centres, and theywill need to provide for emergency responsethat exceeds the capability of the local level.There should also be a role of higher ordersof government in auditing enforcement ofpolicy measures by local levels.

Inter-agency collaboration

Reduction of flood losses will involve anumber of government agencies and often

40

the private sector if, for example, reservoirsare operated by energy utilities.Development of common objectives anddefinition of a clear role for each of theplayers can be a major challenge. From aland-use planning perspective, landdevelopers must also be directly involved inthe solutions.

Normally some form of inter-agency bodywill need to be established, and theleadership role assigned to the agency withthe greatest involvement or to a strongcentral agency. There is probably no idealmodel for such a structure, as circumstancesare quite different in every country.

An independent agency is an attractiveoption, but in general it is probably better totry and build on the strengths of existingagencies so that supportive resources can bemarshalled quickly in case of extreme events.However, within this diverse model, it isimperative that one agency be given theoverall lead, and that that agency be heldaccountable for the overall process.

International collaboration

There are a number of United Nationsspecialized agencies and programmes thatcan be of assistance to a country establishinga programme aimed at reducing the lossesthat result from flooding. Some of these aredescribed herein and could be contacted byinterested parties.

The UN Department of Economic andSocial Affairs (UNDESA) has been activelyinvolved in providing advice to governmentson water resource management duringextreme hydrological events in a wide rangeof environmental and climatic settings fromthe drought-prone upland plateaus of centralAfrica through large river basins and aquifersystems in Asia to vulnerable groundwaterlenses on Pacific atolls. If one principallesson is to be learnt, it is that managing

water resources under conditions of climaticvariability and extreme events involves nospecial approach; it is simply sound waterresource management. To this extent,climate change should involve relatively fewsurprises, and should not be an excuse forpoor management. It is only possible toundertake sound management practices,however, if the appropriate and accuratehydro-meteorological data are available toresource managers on a regular basis. Oneof the critical issues in this area is thebreakdown in hydro-meteorological datacollection systems and analysis. As fundingfor water resource organizations declines,monitoring networks and the capacity tocollect, store and analyze data break down.Ironically, it is only in times of drought orsevere flooding that the political will to fundthese activities is revived, by which time it isoften too late.

Water resources assessment is a core issuethat the UN system is addressing throughits technical cooperation activities and theWorld Water Assessment Programme.UNDESA's technical cooperation withdeveloping countries and economies intransition uses state of the art technologiesand software for the assessment of waterresources availability as a basis for short-term and long-term planning horizons.National capacity has been developed toperform and continue these assessments incountries such as Bahrain, Burkina Faso,Cape Verde, China, Jordan, Madagascar,Mali, Mauritania, Niger, Senegal, andYemen. This is of particular importance inwater-scarce countries, where water hasbecome a limiting factor for economic andsocial development.

UNDESA has been collaborating withgovernmental organizations to enhancenational capacity to address the problems ofwater quality assessment and overall watermanagement. Guidelines andrecommendations concerning water quality

41

Guidelines for Reducing Flood Lossesprotection and management are alsoprepared for national and regionalorganizations, dealing with monitoring andprotection of environment.

The United Nations DevelopmentProgramme (UNDP) has a programme forstrengthening national capacities related toflood mitigation, prevention andpreparedness in developing countries.UNDP works in flood reduction andrecovery through practical application at theregional and country levels. UNDP hasdevoted special attention to reducing socialand economic vulnerability and loss of lives,and to protecting livelihoods and broad-based development gains.

The World Meteorological Organization(WMO), a specialized agency of the UN,was established in 1950 to facilitateworldwide cooperation in meteorology,hydrology and climatology for the benefit ofhumanity. WMO promotes the followingtypes of activities: the establishment of thenetworks of stations for acquiringmeteorological, hydrological and relatedgeophysical observations and thestandardization of observationalmethodologies; establishment andmaintenance of systems for processing andexchanging data and information; activitiesin operational hydrology, such as floodforecast and warning systems; multi-agencyand interdisciplinary programmes on waterresources, climate change, natural disasters,and other environmental issues; andresearch and training.

The International Strategy for DisasterReduction (ISDR) was launched by theGeneral Assembly of the United Nations inJanuary 2000, to provide a globalframework for action with the objective ofreducing human, social, economic andenvironmental losses due to natural hazardsand related technological and environmentalphenomena. The ISDR aims at building

disaster-resilient communities by promotingawareness of the importance of disasterreduction as an integral component ofsustainable development. The GeneralAssembly established two mechanisms forthe implementation of the ISDR: the Inter-Agency Secretariat and the Inter-AgencyTask Force on Disaster Reduction(IATF/DR).

The ISDR Secretariat serves as a focal pointwithin the United Nations system for co-ordination of strategies and programmes fordisaster reduction and to ensure synergybetween disaster reduction activities andthose in the socio-economic andhumanitarian fields. The ISDR Secretariatalso serves as an international clearinghousefor the management and the disseminationof information, in particular on currentknowledge and status of disaster reductionthrough the publication of its Global Reviewof Disaster Reduction Initiatives. It developsactivities such as advocacy campaigns topromote wider understanding of naturalhazards, as well as risk assessment andmanagement to motivate a worldwidecommitment to disaster reduction. TheISDR Secretariat has a facilitating role,bringing agencies, organizations anddifferent disciplines together, and providinga common platform and understanding ofthe scope of disaster risk reduction. In thisregard, one main function of the Secretariatis to support the Inter-Agency Task Forcefor the development of policies on naturaldisaster.

In particular, the ISDR Secretariat supportsactivities, such as the development ofguidelines, related to reducing the risk fromwater-related hazards. This requires, on theone hand, support for the development ofcapacities to monitor the magnitude,duration, timing and location of hazards,such as floods and droughts, as well aslandslides, storms, earthquakes, and volcaniceruptions. All of these latter hazards also

42

have impacts on freshwater resources andinfrastructure. On the other hand, this alsorequires promoting the assessment andreduction of the vulnerability to suchextremes. This requires decision-making onissues such as development and planningcontrol, legislation and land-use,environmental management and financialtools (e.g., insurance).

The ISDR, with its focus on disaster andrisk reduction, draws its relevance fromprevious practices in the disastermanagement fields, where traditionally the

focus has been on preparedness forresponse. Political authorities, professionalsfrom many different fields, commercialinterests, public organizations, educationalinstitutions and local community leaders areincreasingly recognizing the essential publicvalue of sustained efforts to reduce thesocial, economic and environmental costs ofdisasters. There is now increased emphasisplaced on risk, and a growing acceptancethat disaster, development andenvironmental problems are inextricablylinked.

2.7 Emergency Preparedness and Response

The most critical element in the suite ofactivities associated with flood-loss reductionis emergency preparedness and responseactivity. The response to a natural disasterwarning must be immediate, comprehensive,and demonstrate very clear lines ofcommand. There must also be a mechanismin place to quickly draw upon externalresources available at higher levels ofgovernment, or even internationally, whenthe local level of response will not besufficient. Many countries have systems inplace where a provincial/state wide ornational disaster can be declared to bring inthe resources needed. The keys to effectiveemergency response are advance planning,ability to mobilize sufficient resourcesquickly, and periodic exercises to identifyweaknesses and problems.

Collaboration and coordination

Emergency planning and preparedness isfirst a local responsibility, but one thatrequires collaboration and coordination with

others in a growing circle of like-mindedand expert groups that can be drawn uponas events unfold. In particular, there mustbe strong and reliable communicationlinkages to storm warning and forecastcenters so that the emergency responseactions taken are appropriate to themagnitude of the probable event.

The network of linkages from the local levelupward must be established in advance and,more importantly, key players mustperiodically meet to exchange informationand become comfortable working together.Information sharing should be bi-directional, both upward and downward,between the levels of government. Practicedrills are important.

Emergency response must include inputfrom the community and political levels butcannot become a collective responsibility.There must be clear lines of authority, evenif the lead agency changes dependent on themagnitude of the event.

43

Guidelines for Reducing Flood LossesThe community and individuals must have agood understanding of what is expected ofthem. A good example would beevacuation. Information that definesevacuation routes, identifies emergencyshelters, and specifies actions to be takenbefore leaving, such as removing mobileequipment and removing personal goodsand furniture, must be available in advance.

Preparedness and response plans

Detailed response plans need to be preparedin advance and reviewed with all of the keyagencies and players. There is no one"common" response plan as the linkages willbe different in each case. The response to atoxic chemical spill is very different from theresponse to a major fire or flood.

Not only must the plan be in writing andavailable to those that will be responding,but also it must be continually reviewed andupdated. Some of the key pieces ofinformation are: which agency andindividuals have the specific responsibility;whom to contact for expert advice; andwhere to go for information on backupcommunication systems. This informationis constantly changing and needs to beverified periodically and tested in exercises.Multiple contact points need to beestablished as the emergency may occur on aweekend, holiday, or after regular businesshours.

Mechanisms for coordination must beincluded in the plan, including the structureof response committees, where they willmeet and sources of resource informationavailable to them. Often this takes the formof something equivalent to a "war room"where maps, plans, other material andsupport staff are available immediately.

Inventory of resources

A key component of any emergencypreparedness plan is an inventory ofresources that can be accessed. In the caseof flooding this could include items such asemergency vehicles, buses and trucks,earthmoving equipment, pumps, plastic,plywood, emergency generators, supplies ofgravel and sand, sandbags, and mobilecommunications equipment. The inventoryshould also include access to expertise suchas surveyors, levee or slope stability experts,forecasting specialists, the media andcommunity leaders.

Emergency shelters should be designated inadvance, their individual capacity definedand plans made for obtaining sufficientsupplies of water, food, medicine andmedical/social assistance.

If local resources are not sufficient, then theavailability circle must be expanded toinclude adjacent communities, theprovincial/state and national governmentlevels.

Triggering emergency action

Advance warning is the key to effectiveresponse. It is possible to set up a series ofwarnings in advance of an actual extremestorm event that can be used as alerts. Thiscould start with long-term climatologicforecasts or more immediate hurricaneforecasts that identify potential danger. Forspecific basins an alert could be issued basedon antecedent precipitation and rainfallintensity data in advance of an actual floodforecast. A more detailed forecast wouldthen be issued when all of the data andinformation required to make a floodforecast became available.

44

The emergency response to such alerts isvery site-specific and should be included inthe plan. If, for example, emergency actionssuch as temporary levees are necessary, thenthe work could begin based on an alertrather than the specific forecast. The samemay hold for emergency evacuation.

The response to an extreme flood forecastshould be immediate, and with no uncertaintyas to what actions and activities should betaken. The public expects governments to actquickly and in a professional manner undersuch circumstances. Community leadersshould be visible, informed and active rightfrom the start.

Training and response exercises

Emergency response teams need to be welltrained in advance and their skills constantlyupgraded. Once the disaster strikes, it is toolate to train or try to find missing expertise.Trained staff should know theirresponsibilities, have immediate access toresponse plans and other criticalinformation, and already have built aworking relationship with colleagues inother organizations.

The only meaningful way to test responseplans is to carry out periodic emergencyexercises. These exercises are meant tosimulate real emergency situations and testall aspects of the plan. Costs are significant,but have real payback in an actualemergency. Often critical gaps are identifiedand appropriate backup strategies developedas part of the exercise.

Advance preparation

Assuming that there is advance warning of amajor storm event, a number of steps can be

taken to increase readiness. Such stepsinclude: construction of temporary floodprotection works; placing emergency responseteams on high alert; distribution of criticalmaterials such as stockpiled sandbags totargeted locations; and preparation ofemergency shelters and hospitals prepared foroccupation.

The population at risk can be informed ofwhat is expected of them in the actuality of anextreme event. As the event becomes morecertain, actions such as evacuation of people,goods and machinery can begin. Even if theevent is not as extreme as predicted, thesepreparations help test emergency responseplans and inform the public as to the nature ofnatural hazards.

Media and public information sessions helpset the stage as well. The media are keyplayers in the link between public officials andthe public. It helps if they are familiar withthe terminology used in warnings andforecasts and know whom to contact for moredetailed information during an actual floodevent.

After the flood event

The emergency response does not end withthe event, but continues through cleanup andresettlement stages. People will want to knowwhat assistance will be made available, who isresponsible, and how to go about seeking thatassistance.

Senior levels of government should developclearly defined response policies andprogrammes in advance. In the absence ofsuch policies, the response is often ad hoc,politically and emotionally motivated, and setsprecedents that are not wise in the longer run.Often the response is incomplete in that the

45

Guidelines for Reducing Flood Lossesobvious and immediate requirements areaddressed, but fundamental changes inthinking and sustainable strategies areignored.

After a major flood it is beneficial to conductan assessment of the causes and effects of theflood and to make recommendations thatwould improve preparedness for the nextevent and reduce future flood losses. Such anassessment can also lead to improvements inflood plain management policies.

The long-term economic and socialimplications of flooding become evident in thepost-disaster period. Governments need todemonstrate leadership and sometimes takebold steps to restore employment, addresssocial issues and move the economy in a newdirection. In that sense, natural disasters canbe a positive motivator for change.