floods

Floods

AKBAR ALI KHAN 25 Bijoygamar, Dacca 2, Bangladesh

1. INTRODUCTION The recommendations of the Mar del Plata Action Plan on food loss management were based on the optimistic assumption that floods are not part of nature’s order, something that has to be endured as a part of life. The technical expertise for reduction of flood losses is readily available. However. adequate resources and appropriate institutional structures for mitigation of flood hazards are still lacking. The action plan therefore emphasized the need for decreasing flood losses “by comprehensive structural and non- structural precautions and by organization of emergency services, including expanding the hydrological services to aid in forecasting flood and rclated events”.’ The conference also noted with concern the tragic losses of life and crippling damages caused by floods that frustrated the efforts of many dcveloping countries to break the vicious cycle of poverty. In this context it was observed by the conference that “the negative economic impact of water related natural disasters in developing countries was greater than the total value of all the bilateral and mutilateral assistance given to these countrics”.’

2. THE IMPACT AND MANAGEMENT O F FLOODS ACCORDING TO

DIFFERENT LEVELS OF DEVELOPMENT Though the techniques for minimization of flood losses are well known, the frequency and intensity

of floods since Mar dcl Plata Conference have not changed significantly. According to one survey, at least 133 significant flood events involving loss of human life occurred in 4.5 countries during the period 1977-1984 (Table I). This estimate does not includc floods which merely damaged property but did not cause any death. On average, 16.6 significant flood events occur annually; the range varies between 10 and 26 (Table I).

Flood damage in dcveloping countries consti- tutes a higher pcrcentage of GNP than in the developed countries. Thus, tloods cause more hardship in the developing countries than in the industrial societics.

In addition to floods caused by natural conditions, e.g. melting of winter snows, storms, etc., floods result from the activity of man.

2.1 FLOOD$ AS A

CONSEQUENCE OF 1 I U M A N ACTION

All floods are not natural Some floods are caused by human action and others are aggravated by such interference. Catastrophic floods often result from the collapse or failure of storage dams. Since the Mar del Plata Conference in 1977 several floods have been caused by dam failures. On 6 November 1977 a 3.5-year-old earthen dam in Toccoa. Georgia, USA, weakened by several days of heavy rainfall, collapsed. It unlea5hcd a 30-foot wall of water that killed 39 people. August 1979 witnessed a major dam disaster in India. The Machhu TI dam in the industrial town of Morvi,

Dr. Ali Khan is a member uf the Directing Stulfuf the Rungludesh Public Administration Truining Centre. A more extensive version of this paper was prcsented at the llnitcd Nations Symposium on Improved Efficiency in the Management of Water Resources. Ncw York, January 1087.

Natural Resources Forum @ United Nations, New York. 1987.

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TAULL I Number of Jignificantflood event7 involving loss of life, by continents, 1977-1984

Year

1977 1978 1979 I Y X O 1981 1982 1983 1984

Total -

Asia

- > Y 6 8

1 1 6

14 Y

68 I S

(Source: Appcndix 1 . )

which was completed in 1978, collapsed. A 20-foot wall of water inundated the town and killed more than 5000 people. The published account of the incident suggested that hydrological factors might have been responsible for this. The collapse of this dam underscores the need for better flood prediction and better dam design.

Dams are very often erroneously considered to be foolproof guarantees against floods. This leads to large-scale settlement in the floodplains pro- tected by dams. It is often forgotten that if design limitations of a dam are exceeded. then there will be flooding. To avoid such disasters the public should also be educated about the design limitations of dams.

Floods are also aggravated by deforestation, which is continuously taking place in different parts of the globe as a result of land hunger and fuel shortage.

Taking into account the adverse effects of deforestation, the Mar del Plata Action Plan recommended to improve catchment areas for the retention of flood waters and soil erosion control and encourage local participation in the implementation of such measures.' Despite its harmful effects , deforestation continues unabated, especially in ecologically sensitive areas. During the period 1977-1983 about 1.37% of forests and woods in the world was cleared. Approximately 9.5 million hectares of land are deforested annually. The rate of deforestation has, however, fallen slightly in recent years. During 1971-1977, an average of about 14 million hectares of land were deforested annually. This is approximately 33% higher than the rate of deforestation during

the period 1977-1983. The situation varies from region to region. In Europe the area under forest incrcased from 150.10 million hectares in 1971 to 155.29 million hectares in 1983. In Asia and North America there was also a slight improvement during the period 1977-1983. Despite some improvement in afforestation in Asia as a whole, there was large-scale deforestation in certain critical areas such as Nepal, India, Bangladesh and the Philippines. During thc period 1977-1983 the forest area in Africa decreased by 2.47%, in South America by iibout 2.75%. The adverse effects on the ecology of the deforested areas are likely to be pronounced in the coming years.

2.2 PATTERNS OF POPULATION

The most compelling reason for deforestation is the rapid growth of population in recent years. The world population has increased from 4212 million in 1977 to about 5000 million in 1986.4 In the last 9 years the population of the world has increased by 717 million. The adverse effects of this large population growth are not confined to deforestation alone. They have also forced larger numbers of people to live in the hazardous floodplains too close to the path of annual floods. The higher density of population in the floodplains not only exposes increasing numbers of people to flood hazards, but also aggravates the problem of flood by posing obstructions to the movement of flood water. 2.2.1 Urbanization and its impact offloods In recent years there has been an increase in urbanization in most flood-prone countries of the

SEITLEMENT AND THEIR IMPACT O N FLOODS

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world. The share of agriculture as a percentage of GDP has decreased in all of the flood-prone countries during the period 1965-1983. The number of cities with population over 500,000 in 20 f-lood-prone countries increased from 122 in 1960 to 257 in 1980. Most of these new cities are located in floodplains. The Percentage of urban population in India increased from 18 in 1965 to 24 in 1983; in China from 18 to 21; in Bangladesh from 6 t o 17 and in Nepal from 4 to 7. Consequently more people in dcveloping countries are now exposed to flood hazards, and the economic losscs on account of flood are mounting.

The available evidence suggests that floods which are primarily produced by natural phe- nomena are becoming increasingly destructive as a result of undesirable human interference. This is particularly true of the densely populated developing countries. A recent World Bank report rightly analysed the flood problems of the Gangetic floodplain in the following manner: “As testimony to the effects of population growth, the severity of flooding has increased exponentially over the past twenty years, even though the annual rainfall has hardly changed”.’

2.3 ECONOMIC IMPACT OF FLOODS

It is extremely difficult to quantify the economic effects of floods. First, only a few countries collect data on flood losses systematically. Secondly, data on disastcrs like floods are col- lected in highly emotional circumstances, and

tend to be exaggerated. Data are often manipu- lated by local administrators t o secure adequate disaster relief. It is not unlikely that flood-damage estimates of doubtful accuracy and debatable value are often prepared to justify expenditures on flood-control projects.‘

The available evidence suggests that deaths on account of floods have decreased since the last United Nations Water Conference. On average about 7232 pcople died in floods annually in the world during 1947-1970. The annual death rate has decreased substantially since the Mar del Plata Conference, owing to better warning systems and evacuation measures. During the period 1977-1984, the average number of deaths per annum due to floods in the world was 3370 (Table 11). However, there is no detailed global estimate of economic losses caused by floods. The available qualitative cvidence suggests that flood losses have mounted in recent years.

An analysis of deaths resulting from floods indicates that Asia is the worst-affected conti- nent. During 1947-1970, 88.96% of all flood deaths occurred in Asia. Asia’s share of flood casualties was 81.7% during the period 1977-1984 (Table 11). Lately, however, floods have been less fatal in Europe. From the point of view of the loss of life, floods have become more devastating in South America, Central America and North America. There was no appreciable changc in Africa and Australasia.

2.4 GEOGRAl‘lilCAL DISTRIBUTION OF FLOODS

TABLE I1 A comparison of average annual loss of life iii floods between 1947 and I970 and I977 and I984

~~~ ~

Area Average irnnuul Perceiiroge of’ Average annual Percentage of loss of life I1ve.s lost loss of life lives losi 1947-1 970 unnunlly 1447-1 970 1977-1 984 utmuully 1977-1984

-

Australasia 2.3 0.03 3.3 0.10 Asia (excluding USSR) 6433.7 88.96 2749.0 81.57

(excluding USSR) Europe 339.2 6.08 25.0 0.74

Africa 112.0 1.54 108.3 3.21 South America 124.6 1.79 266.3 7.90 Central America and 92.0 1.27 157.2 4.66 the Caribbean North America 28.4 0.39 61.2 1.82 World 7232.5 100 3370.2 100

(Sourcc: UN, Guidelines f o r Hood Loss Prevcnriotz wid ibluntrgement iti Develupitzg Courztries, p. 78, and Appendix I .)

NRF VOL. 11, NO. 3,1987 262 A. A. KHAN

Economic losses due to floods appear to be increasing in Asia. Flood Iosscs have increased in India and China. During the period 1961-lY70 India used to losc on an average 0.33% of her GNP annually due to flood damage (Table 111). Floods reduced India’s GNP by about 1.01%~ annually during the period 1982-1 984. Compared with the 1 9 6 0 ~ ~ India’s flood losses in the 1980s as a percentage of GNP have increased by about 300%. In 1983 India’s flood damages stood at US$2538 million - a maximum over the last 30 years.7 In China 2.28 million hectares were flooded in 1980. of which 680,000 ha were seriously affected.x In 1981 flood loss was csti- mated to be more than US$1100 million i n t h e Sichuan Province of China alone. Flood losses are also significant in Bangladesh, Indonesia. the Philippines and Sri Lanka. Exccpt in Japan. flood risks in Asia have not diminished substantially.

In North America annual losses on account of floods are mounting. This may be attributed to the intensified use of land in flood-prone areas. Simulation on the expected losses from natural hazards in the USA suggests that damages will increase from $22,300 million per year in the early-1980s to $37,700 million (in 1980 constant US dollars) in the year 2000.’ If the present trends continue, then flood damages will increase in absolute terms in North America in the next two decades.

Flood damage in Central and South America is also steadily increasing. During the last decade devastating floods have occurred in Argentina, Bolivia, Brazil, Colombia, Ecuador, Honduras.

Mexico, Nicaragua, Paraguay and Peru. This trend may be attributed to large-scale deforestation and widespread floodplain encroachment.

The expericnce of Africa is similarly sad. Floods have plagued South Africa. Mozanibique and Swaziland. Human interference with thc delicate ecological balance largely contributed to these floods. However, in Africa there is rela- tively little increase in flood loss in the rural areas, but flood losses are mounting in areas ex- periencing rapid urban development and high- way construction in agricultural floodplains.”

There was no appreciable irnprovernent in the flood situation in Australasia. The performance of Europe is, however, mixed. In certain countries of Western Europe, such a s Italy. France, Greece, Spain and the Federal Kcpublic of Germany, floods inflicted considerable damagc. In 1982 there was a report of floods from the Georgian SSR in the USSR. However, there was a significant fall in the number of deaths resulting from floods in Europe. Despite flood-mitigation measures. flood-loss potential has not decreased substantial I y .

2.5 EFFECI s ON H U M A N

Floods bring in their trail serious health hazards. Sometimes, floods cause dislocation to existing public health services such as water purification plants, sewage treatment plants and water-supply pipelines. In destructive floods thousands are rendered honielcss. Apart from injuries and loss of life, floods m a y compel people to go without

HEAL’I 11 A N D WFI.L-BEING

TABLE I11 A comparison of unnual flood damage in India hetwetw 1961 and 1970 and I977and I984

Period+erir Annual flood Anniiril awruge Rurio of toicil tlumage (millioti fluod datncrge titimuge 10 G N P

USSF) per c.crpirt1 A vcragr Maximum ( 0 6 ) (%)

1961-1967 207.30 0.42 0.33 0.61 1981 1768.XO 2.46 0.94 - 1983 2.538.70 3.46 1.33 - 1984 1528.70 2.03 0.98 - 1982-81 1935.40 2.65 1 .01 1.33

(Sources: Estimates of flood damage. 1961-19h7 obtained f r o m L’N Guicldine.\ for Floucl Loss Prercvitiorz r m f 12lanagemenr in Developing Coimtrie~ and estimates of flood damage 1982-1984, obtained from the ilririrral Reports of Department of Irrigation, Ministry of Irrigation and Power, Governmcnt o f India. Estimates of pcipulation and per capita income drawn from World Bank’s World DPvdoprnetit Rep0rt.Y.)

_ _ _ _ ~ ___I__________ ___ ___ ~ _ _ _ _ _ ~

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shelter under severe climatic conditions. New hazards arise when flood waters start receding. A UN Conference on flood damage prevention listed them as follows:"

1 . Floods arc generally accompanied by the contamination of water sources by various organic residues present on the surface of inundated soil. This creates conditions con- ducive to the outbreak of epidemics.

2. The migration of wild rodents to human dwellings during floods in some cases create the prerequisites for the outbreak among human beings of such dangerous diseases as plague, tularaemia, etc.

3. The formation of numerous stagnant pools of water during floods creates suitable sites for the breeding of the mosquito vectors of such diseases a s malaria, etc.

3. Finally, in all natural calamities, including floods. there is always an increase in general morbidity, especially among children and persons of advanced age. as a result of the changes in many of the ordinary factors of the environment.

The harmful effects of floods are not confined to disease and epidemic only. Floods also pose serious threats of malnutrition. hunger and famine in developing countries. Floods inundate and damagc existing food supplies, destroy agricultural crops and causc death to livestock. The poor and assetless, especially, suffer from flood damage. The 1974 famine in Bangladesh is a case in point.

3. CURRENT INSTITUTIONAL STRUCTURES AND MANAGEMENT

APPROACHES

Floods pose complcx challenges to administrators. Effective flood management must take into account not only technical and economic, but also social, administrative, political and legal factors. There are four stagcs to a rational flood management programme:

Pre-disaster mitigation. This includes measures to reduce the impact of or prevent a flood event. Examples range from structural measures to public education. Prc-disaster preparedness. At this stage a

response plan for the flood is developed in advance; a warning system for flood is installed and the people responsible for implementation of prcparedness are trained; the institutional mechanism for implementation is specified. Response. This includes activities which are undertaken during and immediately after flood, such as emergency aid and assistance and taking measures for minimizing secondary damage and recovcry operations. Post-flood recovery. At this stage support is provided for a return of vital life-support system to minimum operation levels, which is continucd until the community returns to normal life. These stages are, however. interrelated. For

example, recovery programmes may be related to pre-disaster mitigation in the future. Mobilizution of emergency supplies on an ad hoc basis Despite the urgcncy of an effective flood- management approach, ad hoc measures are taken in most of the developing countries to cope with floods. Flood management very often consists of crisis-driven responses. Floods do not occur regularly. The occurrence of a flood therc- fore provokes an immcdiate crisis. However, as the memory of the crisis fades away, the preparations of flood management also disappear.

Most o f the developing countries respond to floods with ad lzoc measures. The main reasons for the failure to adopt a comprehensive and effective flood-management policy in these countries may be summarized as follows:

In most of thc developing countries, adequate funds for undertaking mitigation, warning, preparedness and recovery programmes are not availablc. Thus the response to floods is always ad hoc and half-hearted. Political and economic costs are considered to be disproportionate to the benefit of a comprehensive management programme. Policy-makers are busy with pressing day-today problems and cannot take a long-term view . "Constituencies and advocacy groups support- ing hazard management policy do not repre- sent a powerful political force, except perhaps after a disaster occurs. Thus legislation tends to

264 A. A. KHAN NRF VOL. 11, NO. 3, 1987

be enacted in the immediate wake of a disaster often under urgent circumstances and on the basis of incomplete Flood problems are technically complex and uncertain. It is difficult to justify flood- mitigation measures on economic calculus alone. Inter-governmental and inter-organizational rivalry. jealousy, distrust and contlicts under- mine integrated response to flood events.

3.1 S.1 KCIC‘I’UKAL MCASUKLS T O PREVENT FLOODS

There is a persistent demand for flood-prevention measures. Historically, structural measures for altering flood patterns were known as “flood- control projects”. However, i t is now realized that absolute control over floods is rarely feasible, either physically or economically. There is now a growing understanding that “zero risk” is not a possibility and “safe” is not the equivalent of “risk-free”. Such structures are therefore now described as “flood damage mitigation measures” or “flood management measures”.

Structural measures can be divided into five categories:

storage reservoir or detention basin; retarding basin; levees and flood walls; channel improvement; and floodways or flood diversion through by- passes.

From the administrative point of view, there are major constraints in the construction and operation of flood mitigation structures. The first problem is the delineation of t h e area for flood mitigation. From thc theoretical point of view, the ideal solution is corn rehensive planning for an entire river basin.‘ However, such an approach is not always feasible, either because of lack of funds or because of political obstacles. In the case of shared water resources the optimal solution lies in joint efforts of the co-riparian states. Examples of fruitful international co- operation for flood control may be cited from the USA and Mexico, Hungary and her neighbours, and Canada and the USA.14 However, collabor- ation is not always politically feasible. The second

problem is the lack of adequatc resources for the construction of flood mitigation structurcs. The problem is not mcrcly financial. The construction of earthen embankments necessitates the acqui- sition of considerable areas of cultivatable land. Thus, thc structural measures not only reduce the area of total cultivatable land but may also render small and marginal farmers landless.

3.2 WARNING SYSTEMS

Damages multiply when floods come un- announced. Timcly flood warnings may reduce a significant part of the damage and suffering caused by floods. Early alert facilitates the evacuation of people, personal property and livestock from flood affected areas. Sometimes flood warning may make it possible to harvest valuable crops before the onrush of flood-watcr. Early warnings arc useful for gearing-up emergency evacuation and relief operations. They are also useful for taking precautionary measures to ensure thc safety of flood control works. This is why Mar del Plata Action Plan recommended to “develop flood forecasting and warning systems as well as flood fighting and evacuation measures to minimize the loss of livcs and property in case of flooding”. l 5

3.3 ORGANIZATIONAL INTEGRATION OF WARNING AND RELIEF MEASURES A N D OF

STRUCTUKAL A N D NON-STRIJCTURAL ALTERN A n VES

Flood-loss prevention and management consists of a spectrum of interrelated activities in a wide variety of sectors in the economy. No single activity by itself is adequate to provide risk-free protection against floods. Flood-loss prevention and management therefore calls for a comprchcn- sive and integrated approach. There are several impediments to the operation of an integrated organizational structure for this purpose. First, in some countries thc responsibilities for flood-loss management are diffused over various levels of government. Secondly, different types of skills and expertise will have to be combined in an integrated organization. For example, flood mitigation and recovery involve technical, policy. political and fund-raising skills, whereas in flood preparedness and response the emphasis is on

NRF VOL. 11, NO. 3, 1987 FLOODS 265

decision-making, communication, direction and control skills.

The first step of a rational flood-loss management programme is the execution of flood- mitigation mcasures. Such measures include structural and non-structural measures. Very often structural and non-structural measurcs are not complementary; they are compctitive either from the technical or from the economic point of view. The correct mix of structural and non- structural measures cannot be selected on consid- erations of flood loss only. It should be based on comprehensive planning within the water sector. Similarly, i t is not sufficient to issue flood warnings only; these should be supported by preparations for evacuation.

3.4 LACK OF INFRASI.KUC'TURE FOR PRFVF.NTIOP* OF FLOODS AND FOR

C'AKKYING O U T RELIEF ACTION

The flood mitigation measures taken in most of the developing countries are inadequate when compared with needs. For example, the total flood-prone areas in India stands at 40 million hectares, of which 32 million hectares can be provided with a reasonable degrec of protection. Up to 1984 only 12.75 million hectares had been covered by flood-mitigation measures." This implies that only 39% of flood-vulnerable areas had been givcn some sort of protcction. In Bangladesh only 32% of the flood-vulnerable areas are covered by protective ~neasu res . ' ~ In China there arc more than 1500 rivers. So far China has succeeded in providing some form of protection in the basins of seven big rivers; however. most of the medium-sized and small rivers have not yet been brought under control." Despite massive investments, the USA still has areas vulnerable to flooding. Most of the areas susceptible to flooding lie in major conurbations.

If floods cannot be prevented, then attempts should at least be made to minimize flood losses. However, the infrastructure for emergency action and relief is in most cases less developed than flood mitigation structures. There arc two reasons for neglecting the machinery for relief. First, because it is difficult to justify investments for emergency relief on the basis of traditional economic calculus, most donors preferring con- spicuous flood mitigation structures to humdrum

evacuation and relief activities. On the othcr hand, most of the developing countries cannot provide adequate resources for preparation of flood cmergencies. Secondly, there is an administrative lag in flood emergencies. Floods do not occur regularly, the machinery for co-ordinating such emcrgencies falls into limbo as soon as the emergency that originally activated it passes away. Flood losses can be considerably reduced if the physical and organizational infrastructure for flood mitigation as well as relief and evacuation are kept in readiness.

4. ALTERNATIVE MEASURES FOR IMPROVEMENT IN THE MANAGEMENT

OF FLOODS Since time immemorial there h a w been two types of adjustments to floods. At one extreme the dwellers in floodplains have become accustomed to living with floods. This is the practice today in some areas of South and South-east Asia. The City of Song Phi Nong in Thailand, where people live at ground level when floods recedc and on the first floor when floods occur, is a case in point. At the other extreme the construction of protective works such as levees and storage reservoirs has a history extending to ancient times. With the rapid expansion of population. flood mitigation is gradually becoming inescapable in most of the floodplains. However, the range of choice is now wider and a number of techniques for the adjustment to floods are available.

Broadly speaking, there are four structural approaches to flood protection.

Impounding of cxcess run-off by dams and reservoirs. Confining flood-waters within areas immediately adjacent to the river by lcvccs or sea wal I s . Increasing channel capacity by channel improvement and removing obstructions to flow. Diverting excess flows through by-passes or floodways. Dams and reservoirs are nceded not only for

flood protection, but also for other purposes such as generation of power and provision o f irrigation facilities. Thus, dams and reservoirs are very often constructed as a part of multi-purpose projects. Reservoirs do not only reduce the flow

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of water in t h e flood season, but also augment flow in the rivers in the dry season. The Mar dcl Plata Action Plan therefore recommcnded to “provide the maximum feasible scope for flood mitigation in reservoir design and operation having regard, however, to the main function of the particular reservoir”. “)

The most popular method of flood mitigation is the construction of embankments or levees. The main attraction of embankments is that embankments arc cheap and easy to build. The embankments often provide reasonable protection against flood. Howcvcr, embankments are mixed blessings. Embankments tend to produce a number of undesirable side effects. First, the confining of flood flows within embankments leads to a rise of flood levels in the channel. This exposes downstream areas and the strip between the channel and embankment to higher floods. Secondly, the river channels have to transport more sediments than before embankments were constructed. In most cases this leads to a rise of the river bed.20 The continuous aggradation of river beds undermines the effectiveness of embankments. Thirdly, embanking may produce an increased meandering or shifting of the river channels because of increascd flood velocities in embanked channcls. This contributes to frequent erosion of embankments. Thus, embankments have to be continuously retired. Fourthly, if adequate measures are not planned in advance embankments may lead to the problem o f interior drainage. In some embanked arcas there is an acute shortage of water in the beginning of the dry season. There are reports of unauthorized cutting of embankments by farmers in Bang- ladesh for interfering with traditional methods of cultivation. Fifthly, embankments obstruct the flow of silts into fields. In some areas of Bangla- desh there are also reports of moisture deficiency and hardening of the soil.21 Sixthly, embankments may adversely affect the production of fish and dislocate the traditional navigational routes. Seventhly, the change in natural hydrology in certain areas may also create health hazards to the human as well as the livestock population. Finally, the embankment fosters increased floodplain occupancy. When a flood of greater magni- tude than the design flood occurs, much greater damage is done than if n o embankment had becn

constructed at all, Levees requirc rcgular inspec- tion and continuous maintenance. During floods levees become particularly vulnerable and flood- fighting or continuous patrol is needcd to main- tain the effectiveness of levees.

Levees are often supplemented by channel improvement. However, such measures arc essentially local protection measures which may lead to an increase of flood magnitudes downstream. In some cases channel improvement may cause bank erosion. Finally, the maintenance of improved channels in silty rivers is very costly.

Floodways are often helpful for flood rniti- gation. However, opportunities for the construc- tions of floodways are limited by the topography of the area and the availability of low-value land which can be used for the floodway. Moreover. unless regularly used, floodways tend to aggrade, resulting in significant increase in the cost for maintenance.

In short, none of the flood protection measures is sufficient for absolute flood mitigation. Most of these measures are calculated risks and serve only limited purposes. Specifically, three measures should be taken to increase the cffcctivcness of flood mitigation structures. First, the structures should be undertaken on the basis of an intcgratcd master plan for the entire river basin. Secondly, they should be supplemented by other measures to modify the flood and the damage- susceptibility. Lastly, the construction of flood mitigation structures should not be allowed to generate a false sense of security among floodplain occupants.

Watershed management can play a significant role in flood abatcmcnt. Therc arc various techniques of watershed management. The most common conservation practices are terracing, contour ploughing, strip cropping, planting cover- crops or farm ponds.

However, there is considerable controversy regarding the efficacy of watershed management. This controversy is often referred to in the literature as “the upstream-downstream controversy” or “the conflict between big dams or little darns”. According to one school, deforestation and devegetation are major causes of flood and watershed management is the only effective means of flood control. The exponents of the other school are of the opinion that watershed

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management is not at all adequate for flood mitigation, and floods downstream can not be controlled without structures.

Thcre are, however, several obwcles to efficient watershed management. First, land in the watershed may bc owned by a large number of farmers. It will not be sufficient to motivate a few farmers to alter thcir cropping patterns or to undertake bank stabilization programmes. It is difficult to motivate all or a majority of farmers to undertake flood-abatement measures. The work can be expedited by the government through extension work and financial assistance. Sec- ondly, watershed management by itself may not be useful for minor floods and small streams. This is borne out by the fact that major floods used to occur long before deforestation was caused by modern civilization. Finally. watershed nianage- ment may contribute either to low-flow aug- mentation or to flood reduction, but rarely to both. Thus, watershed management may not always be adequate for flood reduction.

However, the bcnefits of watershed management should not be evaluated in terms of flood reduction capacity alone. Watershcd management also helps to improve the quality of the environment. This is why some countries have already enacted laws for the preservation of vegetation cover. Malaysia’s Land Conscrvation Act of 1960 and Japan’s Forest Law and Soil Conscrvation Law may be cited as examples of such legislations.

4.1 MODIIWATION OF

Flood losses can be reduced by modifying the vulnerability of life and property in the floodplain to damages from flood-waters. Thesc measures do not eliminate flood losses, they merely reduce them. Two methods are used to attain this objective: floodplain management and structural change.

Floodplain management seeks to minimize flood losses by discouraging those activities which would not remain economically viablc if the “natural tax’‘ exacted by flood is taken into account. This is usually enforced through land- use regulations. There arc several advantages to this method. First, floodplain management costs much less than flood-protection measures.

SUSCEPTIRILITY TO FLOODS

Moreover, it reduces the burden on the public exchequer by passing the costs of protection from the government t o those who benefit from floodplain encroachment. Secondly, land-use regulation, by providing adequate space for the passage of flood-water, reduces the probability of flooding. Thirdly, land-use regulation may be useful to promote watershed management which is ben- eficial both from an environmental and from a flood-mitigation point of view. Finally. it encour- ages careful weighing of the costs against the benefits of floodplain occupation.

Land-use regulations have proved to be effective in reducing flood losscs in a number of developed countries such as Canada, France, Japan, the UK and the USA. Though the Mar dcl Plata Action Plan recommended: “to develop flood-risk maps as a basis for public information programmes and actions by government to reg- ulate development in flood prone arcas”, the progress in identifying flood hazard zones in the developing countries has been very slow. In part this is because enforcement of land-use regulations cannot be ensured without an elaborate administrative machinery. Unfortunately, the enforcement capability of most of the developing countries is very limited.22 Moreover, such regulations cannot be enforced without the spon- taneous support of local people. It is extremely difficult to enlist the support of local people in areas where land-use regulations are in conflict with the traditional settlement patterns.

4.2 MINIMIZATION OF L O S S ~ S

Even if floods or susceptibility to floods cannot be modified, flood losses can be minimized cither by emergency action, or by spreading the incidence of the burden over a larger segment of the community or spreading it more evenly over time.

4.2.1 Emergency measures Broadly, there are five types of emergency measures:

flood warnings and evacuation from flood areas; flood-fighting ; flood-proofing ; rescheduling of operations; and relief and treatment of health problems.

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In some communities evacuation from the affected area is the most effective means for minimizing flood losses. Evacuations are usually made on the basis of flood forecasts. Flood- fighting involves both collective and individual action. Collectively existing levees may be guarded or new temporary dykes may be built. Individuals may remove goods and equipment to higher ground. Flood-proofing is based on the adoption of certain measures that can be taken as soon as a flood warning is received. Among the various methods o f flood-proofing are the installation of removable covers over equipment. doors or windows, and the installation of sump pumps and elevated outlet pipes to remove water which seeps into buildings. Moreover, in flood- prone zones activities may be rescheduled to avoid flood losses. For example, goods which would be damaged may be moved from thc flood-prone areas at the time when flooding is expected. Relief operations include life-saving operations, the provision of temporary shelter and the ncccssities of life, health care facilities and water supply, ;is well as rehabilitation and reconstruction.

The main problem with flood emergency action in developing countries is that the entire cost has to be borne by the government. There is hardly any participation in meeting the cost by the local people. This lack of financial participation. on the one hand, impedes the mobilization of local resources; on the other hand, i t impairs the effectiveness of emergency actions.

5 . CONCLUSIONS The overwhelming majority of the world’s population is exposed to thc hazard of floods. Floods cause loss of life. damage property and crops. and bring in their wake diseases, famine and pauperization. In the developing countries they are the most difficult obstacle to moderniz- ation of traditional agriculture. Floods are not in tion of traditional agriculture. Floods are not i n the least new, there have always been floods which impaired man’s strugglc to win a living from the earth. Two lessons can he drawn from mankind‘s protracted and tortuous struggles against floods. First, no dramatic solution for the problem of flood is available. There are some

palliatives; there is, however, no curc. Floods will continue to be problems for a long time to come. They cannot be tamed by ad hoc or short-term measures. It is therefore neccssary to draw up long-term plans for the mitigation of floods. Second, the problems of floods are compounded by myopic human action. Unless the undesirable human interference with nature is halted. then the intensity and frequency of floods are likely to increase.

To minimize flood losses, the machinery for flood warning, evacuation and relief need strengthening to include:

(i) increasing the forecast lead time by strengthening the flood forecasting and warning system through the installation of effective equipment for collection of hydrological and meteorological data, and through adequate training for related personnel;

(ii) setting up an efficient system for the dis- semination of flood warnings;

(iii) encouraging the introduction of zoning laws, especially in urban areas and areas covered by newly-built water-control structures;

(iv) education of the public about flood hazards, especially through the development of flood-risk maps; the inclusion of disaster relief and preven- tive health measures in development programmes;

(vi) the encouragement of the introduction of flood insurance on an experimental basis; and

ture for emergency relief operations.

(v)

(vii) the maintenance of an effective infrastruc-

At the institutional level, bccause the threat of floods cannot be eliminated overnight, it is essential to undertake long-term research for the minimization of flood losses. In this connection research and technical co-operation in the following areas should be encouraged and intensified by inter-governmental and international organiz- ations:

(i) weather modification as a means of flood abatement;

(ii) reduction of the hazards of “greenhouse effects”;

NRFVOL. 11, NO. 3,1987 FLOODS 269

(iii) collection of adequate hydrological data and (v) models for flood forecasting; continuous monitoring of dynamic changes in flood-hazard occurrences; projects; and

environmental changes occurring in the emergencies. water sector;

(vi) appropriate technology for flood mitigation

(iv) legal and economic issues associated with (vii) institution-building for handling flood

NOTES 1. Reportof the UriitediVutions Witter Cotifrrence. UN Publication, Sales No. E.77.II.A.12, p. 39. 2. Ibid., p. 112. 3. Report of the United Nations Water Conference. UN Publication, Sales No. E.77.TI.A. 12, p. 39. 4. The cstimates of 1971 population obtained from ESCAP Statistical Yrrtrhook fur Asia and the Pacific

5. World Bank. World Devrlopmetir Report, 1984. Oxford University Press, New York, 1984. p. 95. 6. Guidelines for Flood Loss Prevention arid Mutingemrnt in Developing Countries. UN Publication, Sales

7. Department of Irrigation, Ministry of Irrigation and Power, Government of India, Annual Report

8. Government of the People's Republic of China. China Economic Almanac, 1981, pp. 424-425. 9. W.J. Petak, Op. cit., p. 3 . 10. Report of the United Nations Interregiotzal Seminar on Ffood Damage Prevention Measures and

1984. The estimates of 1986 are based on estimates of 1985 Britannica Book of the Year.

No. E.76.II.A.7,p. 72.

1984-85, p. 16.

Management. UN Publication STITAOISER.CI144, p. 10. 11. Ibid., pp. 11-12. 12. W.J. Petak, U p . cit., p. 5 . 13. See, for example. UN Guidelines , for FIood Loss Preveritiott nnd Managemerir iti Developing Countries.

14. Experiencfs in the llrvelopmenf urid Muncigetnfnt uf Internutional R i i w and Lake Basins. UN

15. Report of the United Nations Water C'oriferencr. UN Publication. Sales No. E.77.11.A. 12, p. 40. 16. Government of India, Department of Irrigation, Ministry of Irrigation and Power, Annucd Report,

17. Government of thc People's Republic of Bangladesh: Third Five Year I'lan. Planning Commission,

18. Government of the People's Republic o l China, Chinu Eroriuniic Almannc. 198 1, p. 422. 19. Report of the United Nations Writer Conference. U N Publication, Sales No. E.77.11.A. 12, p. 39. 20. A. Volker 1983. Integrated development of the delta and upland portions of a river basin. In River Basin

21. Joseph F. Stepanek 1979. Banglrrlesli-E~~~iitable Growth? Pergamon Press. New York, p. 123. 22. Gunnar Myrdal 1970. The Challenge of World Poverfy. Penguin, Hammondsworth, pp. 21 1-251.

UN Publication, Sales No . E.76.IT.A.7, p. 16.

Publication: Sales No. E.82.II.A.17, pp. 197-203. 204-216, 349-358.

1981-85, p. 1 .

Dhaka. 1985, p. 181.

Development M . Zaman et al. ( 4 s ) . Tycooly International Publishing. Dublin. p. 42.

floods

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