of urbanization

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Hydrological effects of urbanization

Report of the Sub-group on the Effects of Urbanization on the Hydrological Environment,

of the

Co-ordinating Council of the International Hydrological Decade

Prepared under the chairmanship of

M. B.

McPherson

The Unesco Press

Paris 1974

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I

Studies and reports in hydrology 18

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TITLES IN THIS SERIES

1. The use of analog and digital computers in hydrology: Proceedings of the Tucson Sympo- sium, June 1966 / L’utilisation des calculatrices analogiques et des ordinateurs en hydrologie: Actes du colloque de Tucson, juin 1966. Vol. 1 & 2. Co-edition IAHS-Unesco / Coédition A I S H - Unesco.

2. Water in the unsaturated zone: Proceedings of the Wageningen Symposium, June 1967 / L’eau dans la zone non saturée: Actes du symposium de Wageningen, juin 1967. Edited by /Edité par P.E. Rijtema & H. Wassink. Vol. 1 & 2. Co-edition I A H S - U n e s c o / Coédition A I S H - Unesco.

3. Floods and their computation: Proceedings of the Leningrad Symposium, August 1967

1

Les crues et leur évaluation : Actes du colloque de Leningrad, août 1967. Vol. 1 & 2.

Co-edition IAHS-Unesco- W M O / Coédition A I S H - Unesco.OMM.

4. Representative and experimental basins: A n international guide for research and practice.

Edited by C. Toebes and V. Ouryvaev. Published by Unesco.

4. Les bassins représentatifs et expérimentaux : Guide international des pratiques en matière de recherche. Publié sous la direction de C. Toebes et V. Ouryvaev. Publié par l’Unesco.

5. *Discharge of selected rivers of the world / Débit de certain cours d’eau du monde.

Published by Unesco / Publié par l‘Unesco.

Vol. I: General and régime characteristics of stations selected / Caractéristiques géné- rales et caractéristiques du régime des stations choisies.

Vol. II: Monthly and annual discharges recorded at various selected stations (from start of observations up to 1964) / Débits mensuels et annuels enregistrés en diverses stations sélectionnées (de l’origine des observations à l’année 1964).

Vol. III: Mean monthly and extreme discharges (1965-1969) / Débits mensuels moyens et débits extrêmes (1965-1969).

6. List of International Hydrological Decade Stations of the world / Liste des stations de la Décennie hydrologique internationale existant dans le monde. Published by Unesco /Publié par 1’ Unesco.

7. Ground-water studies: An international guide for practice. Edited by R . Brown, J. Ineson, V. Konoplyantsev and V. Kovalevski. (Will also appear in French, Russian and Spanish / Paraîtra également en espagnol, en français et en russe.)

8. Land subsidence: Proceedings of the Tokyo Symposium, September 1969 / Affaisement du sol : Actes du colloque de Tokyo, septembre 1969. Vol. 1 & 2. Co-edition IAHS-Unesco

1

Coédition A I S H - Unesco.

9. Hydrology of deltas: Proceedings of the Bucharest Symposium, M a y 1969 / Hydrologie des deltas : Actes du colloque de Bucarest, mai 1969. Vol. 1 & 2. Co-edition IAHS-Unesco / Coédition A I S H - Unesco.

10. Status and trends of research in hydrology / Bilan et tendances de la recherche en hydrologie. Published by Unesco / Publié par l’Unesco.

il. World water balance: Proceedings of the Reading Symposium, July 1970 / Bilan hydrique mondial : Actes du colloque de Reading, juillet 1970. Vol. 1-3. Co-edition IAHS-Unesco-

W M O

I

Coédition A I S H - U n e s c o - O M M .

12. Results of research on representative and experimental basins: Proceedings of the Wellington Symposium, December 1970 / Résultats de recherches sur les bassins représentatifs et expérimentaux : Actes du colloque de Wellington, décembre 1970. Vol. 1 & 2. Co-edition I A H S - Unesco / Coédition A I S H - Unesco.

13. Hydrometry: Proceedings of the Koblenz Symposium, September 1970 / Hydrométrie: Actes du colloque de Coblence, septembre 1970. Co-edition I A H S - Unesco- W M O / Coédition A I S H

U n e s c o - O M M .

14. Hydrologic information systems. Co-edition Unesco- WMO.

15. Mathematical models in hydrology: Proceedings of the Warsaw Symposium, July 19711 Les modèles mathématiques en hydrologie : Actes du colloque de Varsovie, juillet 1971.

Vol. 1-3. Co-edition IAHS-Unesco- W M O / Cogdition A I S H - U n e s c o - O M M .

16. Design of water resoyrces projects with inadequate data: Proceedings of the Madrid Sym- posium, June 1973

1

Elaboration des projets d’utilisation des resources en eau sans données suffisantes : Actes du colloque de Madrid, juin 1973. Vol. 1-3. Co-edition U n e s c o - W M O - I A H S / Coédition Unesco- O M M - A I S I I .

17. Methods for water balance computations. An international guide for research and practice.

Published by Unesco.

18. Hydrological effects of urbanization. Report of the Sub-group on the Effects of Urbanization on the Hydrological Environment. Published by Unesco.

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Published by The Unesco Press

Place de Fontenoy, 75700 Paris Printed by La Néogravure, Paris

The designations employed and the presentation of the material in this publication

do not imply the expression of any opinion whatsoever on the part of the publishers concerning the legal status of any country or territory, or of its authorities, or concerning the frontiers of any country or territory.

ISBN 92-3-101223-1

0

Unesco 1974 .

Printed in France

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Preface

The International Hydrological Decade (IHD) 1965-74 was launched by the General Confer- ence of Unesco at its thirteenth session to promote international co-operation in research and studies and the training of specialists and technicians in scientific hydrology. Its purpose is to enable all countries to make a fuller assessment of their water resources and a more rational use of them as man's demands for water constantly increase in face of developments in population, industry and agriculture. In 1974, National Committees for the Decade had been formed in 108 of Unesco's 131 Member States to carry out national activities within the programme of the Decade. The implementation of the programme is supervised by a Co- ordinating Council, composed of thirty Member States selected by the General Conference of Unesco, which studies proposals for developments of the programme, recommends projects of interest to all or a large number of countries, assists in the development of national and regional projects and co-ordinates international co-operation.

Promotion of collaboration in developing hydrological research techniques, diffusing hydrological data and planning hydrological installations is a major feature of the programme of the IHD which encompasses all aspects of hydrological studies and research. Hydrological investigations are encouraged at the national, regional and international level to strengthen and to improve the use of natural resources from a local and a global perspective. The programme provides a means for countries well advanced in hydrological research to exchange scientific views and for developing countries to benefit from this exchange of information in elaborating research projects and in implementing recent developments in the planning of hydrological installations.

General Conference authorized the Director-General to collect, exchange and disseminate information concerning research on scientific hydrology and to facilitate contacts between research workers in this field. To this end Unesco initiated two series of publications; Studies and Reports in Hydrology and Technical Papers-in Hydrology.

is aimed at recording data collected and the main results of hydrological studies undertaken within the framework of the Decade, as well as providing information on research techniques.

Also included in the series are proceedings of symposia. Thus, the series comprises the compilation of data, discussions of hydrological research techniques and findings, and guid- ance material for future scientific investigations. It is hoped that the volumes will furn- ish material of both practical and theoretical interest to hydrologists and governments participating in the IHD and respond to the needs of technicians and scientists concerned with problems of water in all countries.

As part of Unesco's contribution to the achievement of the objectives of the IHD the

The Studies and Reports in Hydrology series, in which the present volume is published,

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45 69 95

11 3 137

153

177

193

273

275

278

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Foreword

Among the numerous studies undertaken by the International Hydrological Decade was an invest- igation initiated in 1965 by the Working Group on the Influence of Man on the Hydrological Cycle and supported by the Food and Agricultural Organisation (FAO) I charged with agricultural and urbanization aspects of the subject. The Coordinating Council in 1970 decided to form a Sub-group on the Effects of Urbanization on the Hydxological Environment, supported by Unesco, to assist the Working Group and :o investigate more intensively industrial and urbanization aspects.

1973. Members were:

The Sub-group met in three sessions, 28-3C dune 1971, 2-5 May 1972 and 12-13 November Professor S Inokuti* (Japan)

Dr V V Kuprianov* (USSR) Professor G Lindh (Sweden) Mr M B McPherson (USA), Chairman Mr T Waldmeyer (UK)

Mr R Zayc, 1971-1972; and Dr H Massing, 1972-1973 (Federal Republic of Germany) Ir. F C Zuidema* (Netherlands)

The Sub-group was assisted Gy Mr J Jacquet (France), who represented the IHD Working Group on Representative and Experimental Basins. Mr N A Bochin of Unesco/IHD served as Technical Secretary of the Sub-group through its first two sessions, and was succeeded by Mr F H Verhoog in that capacity.

The Sub-group provided the IHD Coordinating Council with a Summary Statement on the Hyd- rological Effects of Urbanization in 1971, assisted the Working Group on the Influence of Man on the Hydrological Cycle on the part of its 1972 report dealing with urbanization through Ir. F C Zuidema, and prepared the report which follows.

In 1972 the IHD Secretariat circulated to all national committees for the IHD, a quest- ionnaire on research and development needs.

Respondents, identified in Annex I, were among the participants at an International Workshop on the Hydrological Effects of Urbanization held in Warsaw, Poland, 8-10 November 1973, Sponsored by the Polish Academy of Sciences , U.S. National Science Foundation, Unesco/IHD, and the American Society of Civil Engineers.

al Summary', was reviewed at the Workshop and the many invaluable observations and suggest- ions made by participants have been taken into account in the following report.

participants are identified in Annex II. Annex III contains definitions of terminology used throughout this report.

Part II of the report contains 'Case Studies' for Sub-group members' countries and Part III is a group of 'Illustrative Special Topic Studies' prepared by individual members and associates from their countries.

This report is a result of the wise decision of the IHD Coordinating Council to give a greater attention than originally planned to the effects of urbanization. With the rapid growth of urban areas and associated industrialization around the world, present and projected, this attention is particularly appropriate. One of the major findings of this report is that the field of urban hydrology is almost devoid of modem research investment and there has been relatively little study to date of the effect of urban man upon natural hydrological conditions, in spite of the significant economic and environmental importance of urban settlements in nearly every nation.

extensive research and development in individual countries and the formulation of improved mechanisms for international cooperation on research subjects of widespread general interest.

questionnaire respondents, so many similarities were found in problems and effects that it is concluded that the findings of this report are more universally representative than the small sample of nations involved would suggest.

Responses are summarized later in this report.

A draft of Part I of this report, 'Internation- Workshop

It is earnestly hoped that this report may inspire more While only relatively few nations were represented by the Sub-group, as augmented by

* Members also of the FAO/IHD Working Group on the Influence of Man on the Hydrological Cycle.

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Part I

International summary

by the

IHD/Unesco Sub-Group on the Effects of Urbanization on the Hydrological Environment

as revised by the

International Workshop on the Hydrological Effect of Urbanization, Warsaw, 8-10 November 1973

and as completed by the Sub-Group in Warsaw 12-13 November 1973

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CONTENTS

1-1 Iritroduction

13 1-1.1 Purpose and scope

1-1.2 Urbanization

1-1.3 Environmental effects 1-1.4 Urban hydrology

1-1.5 Urban hydrological research and development 1-2 Summary of findings

1-2.1 Urban hydrological system 1-2

-

2 Urbanization indices 1-2.3 Climatic effects

1-2.4 Changes in surface and groundwater flows 1-2.5 Water supply and water conservation 1-2.6 Water quality and pollution effects 1-2.7 Other hydrological implications 1-2.8 Conclusions

1-3 Research and development

i6

29 1-3.1 General status, conclusions and recommendations

1-3.2 Current activities

1-3.3 Inquiry on research needs

1-3.4 Major research and development needs 1-3.5 International co-operation

1-3.6 Recommendations for international action 1-4 References

I

37

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Introduction

I

-

¹INTRODUCTION

1-1.1 Purpose and scope

The objectives of this report are to describe the effects of urbanization together with its environmental impacts on the hydrological cycle aqd to recommend research needed by the managers of all types of water systems to minimize the environmental stresses. This report is primarily directed to researchers in hydrology. and a special summary is directed to water managers.

Man's impact on the hydrological regime is, on the whole, nowhere more intensive than in urban areas. The effects of urbanization on the human environment transcend by far the considerations of the hydrological cycle. Expected massive increases in urbanization over the next several decades clearly suggest that present problems will probably be alarmingly compounded. Although water is a necessity, an economic reality, an amenity, and an aesthetic component in urban settlements, research on urban water resources has lagged behind large catchment research in nearly every nation. Needed research is complex and will take considerable time , with much larger financial commitment than previously encountered.

Satisfactory assessment of contemporary hydrological effects is thwarted by a dearth of suitable information. Therefore, it has been necessary to use indirect means in this report to define principal effects and to identify necessary research.

was simply not feasible. As an expedient, extensive case studies were made for a few countries, to highlight both similarities and pronounced differences, complemented by supplement- ary information from other countries, and a canvass was made of a much larger sample of nations to determine relevant current research anã to identify outstanding research needs.

to account. The case studies reported in Part II are from economically and technologically advancea countries, and hence the hydrological effects identified here have been experienced in countries of that type.

moving in the same direction, the observations offered may be regarded as precursors of occurrences that may be expected sooner or later almost everywhere. The findings from the selected case studies are summarized in the next chapter. It is hoped that they will give impetus to case studies in developing nations and that such case studies will focus upon the special needs and interests of such nations.

topics in urban hydrology, with the purpose of indicating what has been accomplished and documenting justification for much of the more urgently needed research and development recommended in this report. Some of the findings from these special studies are incorporated in the next chapter.

It is important to note that this report largely pxovides information and does not include an analysis of existing international publications.

Terminology used in this report is defined in Annex III of Part I.

While surveys of scores of nations would surely have been desirable and appropriate, this

An advantage of the case study approach is that inherent interrelations can be taken in- However, because most of the developing nations appear to be

Part III explores in detail, via state-of-the-art studies, some of the most important

1-1.2 Urbanization

'The movement of people from rural to urban areas tends to proceed concomitantly with the mechanization of agriculture. The pressure of the surplus population, the extension of employment in industry, and better education, medical facilities, and culture in the cities have led to a growing migration to the urban and industrialized areas in developing and developed countries alike. It has coincided with an unprecedented increase in world population , thus putting an almost insuperable burden on metropolitan areas.

Africa, Asia and Latin America) , the main problem is urban.

. . ..

.

-. '

(WHO Expert Committee, 'Although both rural and urban areas suffer because of this rapid change (especially in 1965a)

-

Industrialization is included in urbanization because the latter can be reqarded as human activities involving change in land occupancy and use resulting from the conversion of rural lands to industrial uses and to urban, suburban and industxial communities. Also, there are instances where the effects of water pollution from large-scale mining operations are comparable to those from industries. Urban areas affect, and are affected by, such sometimes distant human activities. Among the obvious effects are increased population

13

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Introduction

densities and increased concentrations of residential, industrial and commercial buildings and facilities, with resultant increases in areas that are impervious (impermeable to infiltration). Hydrological impacts then include the effects of these changes on the natural drainage, runoff, groundwater, sediment, water quality, water demands, and on measures utilized for the disposal of wastes and surplus waters and for the supply of water,

Kammerer, 1961) Among the hydrological problems associated with urbanization are the cont- inually increasing demands for water for various uses, changes in the physical environment that alter the natural water balance, and the disposal of wastes that may contaminate streams and groundwater. Of course, there are wide differences in both the distribution of population density and of natural water occurrences around the world.

by a continuous increase in the ratio of urban to rural dwellers, and it is expected that by the year 2000, half of the world's population will be urban. (United Nations, 1967). By then, three-quarters of the world's population will be in the less-industrialized countries.

In the interval, urban growth is likely to be at least twice as rapid as total population growth, and to house this population will require building in one generation more structures than have been built in the whole of human history.

Paradoxically, the land occupied by urban population in nearly all countries is only a small fraction, often of the order of less than 5%, of the total land area. The geographic concentration of human activities in urban agglomerations intensifies local competition and conflict over all resources, including water in its many aspects.

its per capita income. (Davis, 1965) 'In general, the later each country became industrialized, the faster was its urbanization'..

. . . . .

It is the underdeveloped countries

-

^'repres-

enting three-quarters of humanity

-

that are mainly responsible for the rapid urbanization now characterizing the world as a whole'... and in these countries, 'it is virtually impossible to create city services fast enough

...

It is even harder to expand agridult- ural land and capital fast enough to accommodate the enormous natural increase on farms.

The problem is not urbanization, not rural-urban migration, but human multiplication. It is a problem that is new both in its scale and its setting, and runaway city growth is only one of its painfull expressions,

'

(Davis, 19651,

national population in urban places.

influence on the environment than ever before.

urban development and partly as a consequence of the stronger relationship between the urban and the rural worlds. Communication between the different urban concentrations increasingly opens up the countryside. Intensification of land use and increasing exploitation of natural resources are also directly related to the urbanization process.

...

In economically advanced societies, each individual today requires five to ten time more space for housing, employment and recreation than he did in 1900.' (Benthem, 1971)

Australia. Although Australia is a large continent of some 7700-million square kilometers with a population of only 13-million people, it is highly urbanized in some areas.

of its population live in urban areas and two-thirds of these people are concentrated in only 12 urban centres. The question of the effect of urbanization on the hydrological cycle in Australia is therefore an important one.

(S'avini and

(FAO, 1973)

On a world-wide scale, total population growth during this century has been accompanied

Currently, the degree of urbanization of a country reflects directly the magnitude of

A large majority of the countries of Western Europe have a large part of their total 'Urbanization in its present form has a much greater

This is partly due to the large amount of

The concentration of large populations in a small national space is exemplified by Over 83%

1-1.3 Environmental effects

Urban settlements are characterized by an accelerating concentration and growth in man's activities, such as energy consumption, modification in land occupancy, traffic congestion, public demands for services and use of water. As a consequence, the natural environment is essentially changed.

ative and qualitative aspects of the water cycle. These changes are leading to an increasingly critical situation.

A man-made environment evolves with subsequent changes in the quantit-

Hydrological effects of urbanization which are discussed later, include:

-

The agglomeration of settlements and industries is accompanied by rising water needs

-

Growing amounts of waste waters place a burden on rivers and lakes and endanger the-r which often exceed the natural resources in these areas;

ecology ;

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Introduction

-

Conversion of only 20% of a natural catchment can result in a doubling of the peak rate of runoff for that area;

-

Replacing natural ground surfaces with impervious coverings reduces the infiltration of rain water;

-

Extensive use of groundwater lowers the water table

,

adversely affects agriculture and forestry, diminishes the base flows of streams and aggravates the pollution problem;

-

Changes in the local micro-climates of cities have been observed;

-

Increasing amounts of all kinds and varieties of wastes resulting from urbanization and and the increasing lack of places for their disposal complicates the water quality problem.

'The crisis of human settlements stems from man's failure to understand the effects of urbanization, from indifference to the consequences of his intervention in the natural environment , or from his inability to take the necessary preventive or corrective actions, '

(Secretary General

,

UN , 1971).

centrated and profound influence on man, (Secretary General, UN, 1971).

health and urban-specific diseases to a change in social behaviour.

tries (united Nations, 1971) , therefore, the less industrialized countries should note the difficulties experienced in developed countries in more comprehensive planning of their developnient that takes into account environmental considerations.

the future health and well-being of humanity,

'

concludes that all growth projections end in collapse and that a possible remedy would be an all-out effort to end exponential growth, and this prescription is independently supported by a group of some of the most distinguished scientists of the United Kingdom (Anon, 1972).

On the other hand, assuming that for every scarce material a substitute can be found, that new technology can keep pollution under control and that an infinite energy source can be developed, recalculation of Club of Rome scenarios indicates that the world would come to a rather acceptable steady state (Boyd, 1972). It therefore appears that there are possibilit- ies ranging between stability and collapse, but it is clear that attainment of stability will require conscious effort and is unlikely to emerge as a product of chance.

plentiful materials for scarce materials , strive for still higher productivity

,

reduce the amount of material wasted in processing, and reduce power consumption per unit of production.

However, the fundamental ecological problem is how to protect the environment without unduly interfering with economic growth. One of the most vexing difficulties is in attempting to internalize the costs of pollution abatement within the cost structure of goods and services.

Also, improved technology is not necessarily without flaws because new developments have a nasty habit of creating unforeseen side effects.

In most countries , economic growth, population growth, non-agricultural water use and pollution are intertwined. Water in its many manifestations plays a vital role in the

extremely complex processes of urbanization

,

and thus affects national health and growth.

For example, in some countries the demand for water-based recreation is literally exploding, placing heavy stresses on facilities that are currently available.

1-1.4 Urban hydrology

In turn, it is in urban settlements that the overburdened environment has its most con- These influences have physical, psychical and social effects ranging from endangered Problems of urban settlement are common to industrialized and less industrialized coun-

'The reduction and ultimate elimination of these problems is an essential condition for A study (Meadows , Meadows, Randers and Behrens , 1972) conducted for the Club of Rome

(United Nations, 1971)'

Meanwhile , as conditions of scarcity increase , industries can be expected to substitute

Urban hydrology is a distinct branch of the broad field of hydrology because the complex interactions of human activity in concentrated settlements , with air

,

water and land must be collectively taken into account. That is, the impact of man on the water cycle is greatest per unit of area in urban places. Man is capable of transforming his local environment in an almost endless variety of ways, over a matter of a few years , whereas nature moves largely on a timetable of eons. Thus, urban hydrology contends with the dimension of dynamic change because urban development everywhere has been in continuous states of expansion and flux.

Urdan water resources management utilizes the social and biological sciences as well as the

15

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Summary of findings

natural sciences. The impact of 'urbanization may extend beyond urban boundaries.

1-1.5 Urban hydrological research and development

Problems of urban hydrology have been of world-wide concern for several years, but there have been few compilations of background information and even fewer comprehensive investigations of specific urban situations. Although the general outlines of the effects of urbanization on the hydrological cycle can now be described in part, there is an urgent need for improved understanding, in detail, of interactions between urban stresses on the environment, the water regime, and the efforts made to manage, conserve, and improve our water resources.

to obtain them. In the meantime, water managers face the need to make immediate working decisions on a day-to-day basis. Consequently, while there is the need for new and expanded research in the future, there is also an urgent need to make the best possible use of existing information-and data. Careful analysis of the existing data will provide a useful mea- sure of information needed by water managers throughout the period before results are available from new and more rationally organized research programmes.

Chapter 3. It should be noted that none of the recommendations is for strictly new areas of research. Each of the areas recommended is an extension of work that has already been begun.

It is the synthesis of the information and data in these earlier stuäies, regardless of how inadequate they may seem at this time, which should proceed simultaneously with the initiat- ion of newer investigations based on improved understanding of data requirements, improved concepts , and improved instrumentation.

One of the major observations made during the preparation of this report is that the problems of urban hydrology are remakably similar in all parts of the world. Three important deductions may be made from this observation. The first is that data requirements and anal- ytical and integrating procedures will be similar in many investigations, with due allowance for local conditions.

Opportunity to intensify regional

,

continental, and world-wide cooperation among water scientists and water managers concerned with urban problems.

apparent to institutions concerned with these problems that their problems will be resolved much more readily to the extent they expedite and implement the exchange of information among those working in the field. In this connection it is necessary to remember that the instit- utional arrangements for dealing with water in many countries are complex and fragmented, making it difficult to develop rational comprehensive water research programmes. This frag- mentation makes it even more important to emphasize the need to encourage the widespread exchange of information.

was a need for research to establish the nature of the effects of urbanization on basic hydrological processes. Today, the broad nature of these effects is beginning to be understood.

However, just as it was more than a decade ago, more research and investigations are needed to better our understanding of the detailed effects of urbmization on order to facilitate and improve

providing urban areas with the basic water they require.

However, no matter how vital it may be to have new information and data, it takes time

A detailed discussion of additional research and development needs is given in Part I,

The second is that such similarity of effort provides an excellent The third is that it should be,

More than a decade ago (Savini and Kammerer, 1961) , it was possible to say that there

the adequacy of planning to alleviate or prevent undesirable consequences while 1-2 SUMMARY OF FINDINGS

The contents of this chapter are based on selected national case studies, which are collected in Part II. The following points will be described: urban hydrological system; urbanization indicators; climatic effects; changes in surface and groundwater flows; water supply impact and water conservation; water quality and pollution effects and other hydrological implications.

1-2.1 Urban hydrological system

A schematic representation of the hydrological cycle is given in Figure 1. Because agrarian activity has only a modest effect on the hydrological cycle, Figure 1 has been designated as the 'pre-urban hydrological system' in order to visualize the water components for a typical large sector of the land prior to its urbanization. The complexities imposed on the system

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17

(15)

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18

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Surmnary of findings

of Figure 1 by urbanization can be appreciated by comparing it with Figure 2, an 'urban hydrological system'. The latter illustrates the local water balance changes brought about by the drastic changes in land use that accompany urbanization.

Figure 2 is a simplified summary of a particular hydrological system.* Representation of water quality aspects

,

not shown in Figure 2 , would be still more complicated.

Of considerable hydrological importance is the relative location of an urban centre in the river basin of which it is a part, as well as the degree and character of its hydrological overlap with other urban centres, and their distance from a large lake or an ocean.

Because early commerce utilized waterways for transportation , the great majority of metropolises are located on or near major water bodies. Hence, they frequently occupy low-lying ground, and tend to be located near estuaries of major streams or the junction with their tributaries

,

or along a coast. The advantages of superior water transport, water supply and waste-assimilation capacity through self-purification afforded by many of these locations have since been partly offset by increases in flooding damages and pollution that have accompanied more intensive urbanization. Further , growth in water-using industries and in mining enterprises has strained capabilities for enlarging community water supplies , and aggravated thermal and chemical pollution. Because total water withdrawals for domestic and industrial uses are expected to climb dramatically over future decades, present problems can be regarded as merely a prologue of what is to come. Also, in some locations , such as Kobe, Yokohama and Southern California, the sprawl of urban development into the steep foothills of nearby mountains has posed a new set of special problems there and at points 'downstream'.

1-2.2 Urbanization indices

The findings summarized here are based mainly on the five national case studies in Part II and only to a limited extent on some of the special topic studies of Part III. A draft of this chapter was distributed to participants of the 1973 Warsaw International Workshop on the Hydrological Effects of Urbanizatior, and their comments on this chapter have been taken int.0 consider ation.

In feudal times, the limits of urban areas were clearly bounded by the walls of cities and towns, which formed fortresses for defence against invaders. These and newer communities today are characterized by a seemingly endless sprawl beyond their densely occupied commercial centres

-

Population density tends to diminish exponentially with the distance from urban centres and the cessation of urban densities and the beginning of rural densities can be only subjectively defined. Additionally , the peripheral populations around two or more centres may overlap, and even nearby but separated urban areas may have obvious economic or cultural ties. Such complications have plagued demographers and economists in their attempts to specify definitions of 'urban areas' , 'metropolises' , 'megalopolises' and related features of urbanization. Each country has its own definitions, which best describe that nation's demography

.

lations. The case studies include whatever data are available for around 1970 and expect- ations for about the years 1980 and 2000. Population is generally reported for communities of 50-thousand or more, 100-thousand or more, a half a million or more, and one million or more persons , together with total national populations. Where appropriate, available data on population density are also reported, and comparisons are usually drawn between the coll- 'ective size of urban areas and the total national area. Also where appropriate, qualitative The five case studies in Part II are all of nations that have predominantly urban popu-

*Notes: In Figure 2, 'Water Systems' is intended to include treatment and distribution facilities of community systems and self-supplied industrial process systems. Because usually only a small percentage of industrial cooling water is from groundwater sources, only surface water withdrawals and returns of this type are represented. Provision of flow-detention storage for overland runoff is considered to be a part of 'Storm Drainage'. The term'Mani- pulated'

,

used twice in Figure 2, would include: runoff management, such as in the deliberate provision of local storage, of the 'Urban Land Surface' ; and recreation, transportation, flood control measures and property-value enhancement in connection with 'Bodies of Surface Water'. Water-borne carriage of human wastes is assumed. Management of seawater intrusion is not included. Some connections/functions shown are not necessarily typical of a particular metropolis.

19

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S m a q

of findings

divisions into principal national climatic-topographic regions have been made for existing and expected communities with populations exceeding about 50-thousand persons.

The immediately preceding parameters were selected as indicators of urbanization for the purpose of putting the national case studies in Part IL on a reasonably common demographic footing.

1-2.3 Climatic effects

Localized climatic changes produced by larger urban settlements have been noted (Secretariat , WMO, 1971), but knowledge of effects is limited, (Chandler, 1970). These effects are often

called micro-scale phenomena and are unplanned or inadvertent as opposed, for example, to deliberate attempts to modify precipitation, (Neiburger, 1969)

.

Some climatic changes , for example thermal inversion , can make life unpleasant on occasions.

electricity is only part, coupled with changes in land heat-transfer characteristics due to urban development, have resulted in measurable and even rather large differences in the micro- climates of cities compared with their environs

-

The tremendous growth in the rate of total energy consumption, of which generation of

Four physical mechanisms contribute to the micro-climates of urban areas:

1.

2. Built-up areas are obstacles to the wind, changing the natural flow and turbulence 3. The water vapour balance in A city is upset by the change from moist to dry surfaces;

4. The city emits heat, water vapour and pollution to the atmosphere. In addition, Evaluation of climatic changes in urban areas can be made by analysis of the following A. Air temperature. This climatic element has higher values for urban areas than for the country. The difference for the annual average temperature varies between 0.5 and 2OC, (Alison, Drosdow, and Rubenstein, 1956). This is caused by the following factors :

1. A much smaller latent heat flux;

2. The different physical properties (such as the albedo, the specific heat and the thermal conductivity) and the different structures of the urban surface;

3. The energy generated by combustion processes (house heating, factories , auto- mobiles and human metabolic heat). For Vienna the artificial heat supply pes annum is one-sixth to one-fourth that provided by direct solar radiation, and for Berlin and Amsterdam, the ratio is one-third (Kratzer, 1956 and Zuidema, 1974). At Amsterdam it is found that in Winter the energy generated by human activity exceeds the solar energy (Zuidema, 1974)

-

The pall of dust and carbon dioxide over a city influences not only the incoming solar radiation (especially the shorter lengths of the spectrum such as the ultraviolet rays) by additional flux divergence, but also reduces the net out- going longwave radiation. For Boston the city values of solar radiation aver- ,

aged 15% lower than those in the suburbs. The solar radiation in Toronto, Canada averaged 3% higher on Sundays than on weekdays. In Winter the ultraviolet radiation in the centre of Leicester, England, amounts to 70% of that on the outskirts (Mann, 1966). The characteristic warmth of a city is called the urban heat island, the size and intensity of which changes fram day to day. It is at a maximum at night and as for most climatological elements there is evidence of a weekly cycle. A 1968 international symposium on urban climates

(Secretariat, WMO , 1970) discussed the interrelations between micro-scale phenomena and noted characteristics such as the 'heat island' effect and difference in precipitation between cities and their environs.

The natural radiation balance is disturbed by chan*ges in the properties of the under- lying surface.

of the air;

Vegetation is replaced by large areas of concrete and brick;

traffic is a source of local turbulence.

elements :

4 -

B. The water vapour content of the air. The urban water v a p u r pressure is mostly below the value of the country because the precipitation is quickly discharged.

Because the air temperature is normally higher, it can be understood that the relative huniidity will be smaller. However, in the night the vapour pressure is often higher in the city. Por American cities it has been found that the difference amounts to 8% in summer and 28 in winter because of the emission of water vapour by

(18)

Swmnary of

findings

C.

D.

E.

combustion processes (Zuylen , 1971). Due to the relatively large area of open water near Amsterdam, no difference has been found between the city and the surrounding rural area (Zuidema, 1974).

Fog.

roundings , due to an increased amount of condensation nucleii, Pollution and fog vary from city to city, but fog frequency is lower in relatively clean cities, due to a higher temperature.

Cloudiness and precipitation. It may be stated that due to an abundance of condensation nucleii , turbulence and convection , an increased cloudiness has been observed in urban regions. However, it is questionable whether this increased cloudiness is sufficient to cause an increased precipitation. Results of research into this problem appear to be very contradictory. Several investigators have found a weekly

cycle that must be related to human activities. For instance, for Paris (Zuylen, 1971; Zuylen, 1973; Dettwiller, 1970) and for Rochdale, England (Alisson , Drosdow, and Rubenstein, 1956) there is convincing evidence that the amount of precipitation during working days exceeds that of weekends. At Amsterdam, rainfall is higher than the surrounding area, and this is distributed evenly throughout the year.

The wind. Because of the high aerodynamic roughness of urban development, the mean wind velocity in the city is smaller than in the country. For Moscow the city values of the yearly wind velocity averaged 0.9 m/sec. lower than that of a nearby rural station. The disturbance manifests itself through locally distributed turb- ulent movement. Moreover, during periods of calm weather the city heat island may cause a local low inducing a country breeze and by consequence upward currents over the city itself.

In very polluted urban regions the frequency of fog is higher than in the sur-

Although average changes in climatic elements caused by urbanization have been quantified, Table 1, there is, as yet, insufficient evidence to draw any firm conclusion in regard to these various factors.

Table 1. Average changes in climatic elements caused by urbanization (Landsberg, 1970) El emen t Comparison with rural environment

Contaminants

-

condensation nucleii and particles 10 times more gaseous admixtures

Cloudiness

-

5 to 25 times more

Cover 5% to 10% more

fog, winter 100% more

fog, summer 30% more

Precipitation

-

totals

days with less than 5 mm snow f al 1

winter summer Radiation

-

Relative Humidity

-

5% to 10% more 10% more 5% more 2% less 8% less

global 15% to 20% less

ultraviolet , winter 30% less

u1 tr avi ole t , s umme r 5% less

sunshine duration 5% to 15% less

annual mean to 1 C more

winter minima (average)

10

to 20c more

he at degree -days 10% less

annual mean 20% to 30% less

extreme gusts 10% to 20% less

calms 5% to 20% more

Temperature

-

O O

Wind Speed

-

21

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Summary of

findings

Heat releases into the atmosphere and into water bodies ‘are to a large extent (perhaps two-thirds) concentrated in the densely populated urban areas that constitute only a fraction of the land area of the world ... The effects of urban and regional heat sources on continental and global climate are uncertain‘

,

(Anon,, 1971).

I-2.4 Changes in surface and groundwater flows

Urbanization substantially alters precipitation-runoff relations compared with those €or natural drainage. Despite a number of studies that have been made, the time/space relationships of the urban runoff process are still not very well quantified. As a result, generalizations can be made only at extreme hazard and those that follow are offered as tentative observations.

The increase in the impervious area that accompanies urbanization tends to reduce the volumes of infiltration and evapotranspiration of a catchment. Surface detention storage characteristics can be drastically changed, as street runoff ‘collection arrangements and underground drainage conduits facilitate rapid removal of water from the surface of the ground. i d 1 these factors collectively change the surface runoff regime, a change which is often reflected in an alteration in the amount of groundwater recharge.

receiving streams can be diminished as a consequence of the increase in impervious area div- ersions and bed recharge, and can be raised by the discharge of effluents that originated as imported water. Local runoff can also be increased as a result of the greater local precipitation produced by urbanization. Over-exploitation diminishes the overall yield of groundwater supplies as water levels and pressures in groundwater reservoirs progressively decline.

Evapotranspiration can be reduced in respect of impervious surfaces and increased where cultured ground-growth is extensively irrigated. \iater yield can be enhanced by human intervention, such as groundwater recharge, successive multiple reuse, desalination and weather modification. The yields of portions of aquifers may be increased by leakage from water distribution systems or be decreased by drainage into foul, storm and combined sewers.

surfaces, means for collecting drainage at the surface, and underground conduits for artificial drainage, are thought to result in the faster, greater runoff peaks than would normally be experienced in the absence of urbanization. The cumulative effect of increased surface water volume and localized flood peaks may be to accentuate mainstream flooding. Flooding can be aggravated by the occupance of flood plains and associated flood-prone areas by dwell- ings and other structures.

that urbanization results in increases of surface runoff volumes and peak flows and decreases in base flows.

A management problem that occurs in many coastal countries is the intrusion of salt water into well fields subjected to heavy groundwater withdrawals ; serious intrusion have occurred along seacoasts and estuaries.

ial plains composed of geologically young deposits, where serious land subsidence has occurred as a consequence of intensive groundwater withdrawal for industrial and municipal use and/or natural gas exploitation, (Anon, 1970). Areas of subsidence are more susceptible to inun- dation from surface runoff, aggravated by high tides in coastal areas. Probably the best- known incidence of subsidence related to groundwater withdrawal is the sinking of Venice.

Subsidence of half a metre to a metre have occurred in some Swedish cities (Lindh, 1972).

Because no a priori data exist, it is not possible to evaluate the role of impermeable urban surfaces in lowering groundwater levels by way of reduced natural recharge, but this reduction must have a bearing on subsidence occurrences.

90% of their volume when drained.

‘Related phenomena are the acceleration of sinkhole development in certain limestone areas from groundwater withdrawal, and those landslides induced by slipping of ground that previously had stable slopes. Soil collapse and a resulting land subsidence can be facilit- ated when water is added in large amounts, particularly in loess deposits.

Land reclamation causes drastic changes in the immediate hydrological vicinity, (Zuidema, 1974). The outstanding example is the polder development in the Netherlands, where a large inland bay has been separated from the North Sea by a dam, divided i-ito parts by dikes, arid drained for agricultural and urban uses. About one-third of the Netherlands is at an eleva-

Both local runoff and catchment annual discharge are generally increased. Base flows of

The volume of flood runoff increases as the degree of urbanizatiori increases. impervious

ïn several countries, including Sweden (Ernfors and Isgard, 1970) , it has been observed

As elsewhere, many of the large cities and their environs in Japan are located on alluv-

I-’eat formations, for example, may lose

(20)

Summary

of

findings

tion below the normal range of tides, and another third extends only 10 m above this level.

Lust about every conceivable water management problem is encountered in polder development, from defence against salt water intrusion to the control of groundwater and surface water pollution.

i-2.5 Water supply and water conservation

Water availability has affected the viability of ancient civilizations and the economic vit- ality of modern nations. In general, there appears to be a loose relationship between the extent of urbanization and the abundance of national water supplies.

domestic purposes , (Peixoto and Kettani, 1973)

.

uses are given in Table 2.

nation, the Federal Republic of Germany expects an increase from 540 m3 in 1970 to 820 m in the year 2000, for domestic, industrial and agricultural uses.

Flater is a necessity for development, though only a small portion of it is used for Recent estimates by the USSR State Hydrological Institute, of principal global water As an indication of growing demands per capita in cubic metres/year in a developed

3

Table 2. Present and projected water use, cubic kilometres

1 9 7 0 2 0 0 0

Continent

Domes tic Indus tri al Agricultural Domes tic Indus tri al Agricultural

Europe 30 160 125 77 32 4 320

Asia 40 50 1300 200 360 2 300

Africa

?

3 120 42 50 2 60

North America 40 267 206 77 9 20 300

South America 4 12 64 40 170 120

Australia and Oceania 1 8 12 4 22 40

Totals 119 500 1827 4 40 1846 3340

Table 2 indicates that the water demand of the more developed continents will increase less than those of continents which include most developing countries. Table 3 shows the relative increase of water consumption in the period 1970-2000 for domestic and industrial use.

Table 3. €%elative increase of water demands to the year 2000 (1970=100) for mostly developiilg and mostly advanced continents.

Domestic Indus trial Mostly developing continents 500-1050 700- 17cO Mostly advanced continents 200- 400 200-350

Table 3 suggests Large increases and the redistribution of the four principal water uses (domestic, industrial, agricultural and cooling water) by the year 2030 compared with an esti- mated total global runoff of 47 O00 km3/year.

municipal, most energy and the majority of industrial needs are in or near urban areas, strong- ly indicates a massive acceleration in the hydrological effects of urbanization, especially in developinq countries. Perhaps over 40% of the reauirements in the year 2000 or over 2300 km3/

year, will be for urban areas, which would represent a four-fold increase over requirements in 1970.

above figures.

water resources will have to be improved, such as by more extensive re-use, in certain regions of a number of nations.

(Lvovich, 1974). This plus the fact that all

A growing competition between urban and agricultural water uses is also suggested by the Farming efficiences will have to be raised (Penman, 1970)and husbandry of urban

23

(21)

Summary

of

findings

On a local scale, the intensive concentration of large numbers of people in urban areas is characterized by water demands exceeding the yields of the parts of catchments in the immediate vicinity.

affected in the acquisition of its water supply.

water from distant sources, but little is known about the effects of such water transfers on the regional water balance and associated water quality,

'Urban water supply is a critical factor in public health and economic development in m s t parts of the world, particularly in the developing countries.

water resources a high priority should therefore be given to metropolitan use', Committee , 1965b) .

Figure 3 illustrates the subsystems involved in waste water re-use and emphasizes the environmental impacts beyond the water system.

ment of urban water resources can be significant.

ponding increase in the volumes of waste water.

posal problem parallels that of the water supply problem.

Noting the continuously changing composition of urban waste waters and resultant alter- ations in the character of receiving waters, the need for more water re-use is foreseen in the U.K. 'The combined effect of increasing abstractions from and discharges into our rivers is to accelerate the rate at which the quality of their water is being changed. If these trends continue unabated, and at present we see no indication otherwise, we shall before the turn of the century be compelled to re-use water much more than we do now. Concurrent with these changes is a greater use of our rivers, estuaries and inland lakes and reservoirs for recreation and as general amenities'. (Department of the Environment, 1971). The report also notes existing and potential adverse effects on groundwater quality. It expresses the uni- versal concern on the public health implications of the increasing variety and incidence in water supplies for community use, of heavy metals and other trace elements, and exotic organic substances , to which could be added pathogenic organisms.

Reclaimed waste water has been used directly as a potable water supply in South Africa, (Cillie, VanVuuren, Stander and Kolbe , 1967; Henzen, VanVuuren and Stander, 1973) as a source o5 recreational water in the USA (Parkhurst, 1967) , and for industrial water supply in Japan (Kubo, 1973). In the UK there axe instances of water shortage being alleviated by supplying high quality effluents to industry. Artificial recharge with treated waste water effluents to augment groundwater supplies is widely used ,

Sciences, 1973). However, a variety of pollution problems can be encountered (WHO Expert Committee, 1968) that offset the advantage of recharge. In addition, the natural dissolved mineral content of water tends to increase in concentration with each successive re-use unless removed prior to each re-use.

questionnaires to experts in many countries throughout the world

,

requesting information on re-use of waste water practices. Replies from 30 countries were received. An analysis of the replies indicates that re-use of waste water for agricultural purposes is by far the largest use (18 countries), while the re-use of waste water for industrial purposes is on the increase , particularly for cooling purposes. Increased re-use of treated waste water is also being practiced for recreational purposes, such as fishing, and even bathing, as well as for irrigation of public parks, golf courses, etc. The only example of direct re-use to supplement domestic water supplies is reported from South Africa.

There are significant public health implications in the re-use of reclaimed waste water (WHO, 1973; Shuval, 1969). If waste water is to be used to supplement domestic water supply, the most stringent quality requirements , both chemical and bacteriological , must be applied and enforced. (WHO , 1973 , Anon. , 1972a) . Furthemore , it is recommended that extensive research be carried out on the possible health effects of consuming reclaimed waste water.

This will make possible the establishment of acceptable criteria for the re-use of effluents for potable purposes , (WHO , 1973)

.

Too often overlooked as measures for conserving water are reductions in user waste, the possibility of metering , and leakage reduction in water transmission and distribution systems.

It can be stated that judiciousl-y applied 'conservation' measures will make it possible to use water of first quality for domestic purposes, while waters of secondary quality can be used for other purposes. In any event, the adequate treatment of waste water is imperative both The larger an urban complex the greater the hydrological region that may be

Large demands often are met by bringing (Lindh , 1972)

.

In the allocation of (WHO Expert hs competition for water grows, the practice of re-use will necessarily increase sharply.

The role of waste water reclamation in the manage- As water abstractions for domestic and industrial uses increase there will be a corres-

That is, the scale of the waste water dis-

(International Association of Hydrological

Tñe World Health Organization (WHO Expert Committee, 1968; WHO, 1973) submitted informal

(22)

25

(23)

Summary of findings

for pollution control and for supplementing water resources for other beneficial use ( M O , 1973) .

Because water is qenerally regarded as a 'free good' , the price charged for it too sel- dom reflects true total cost and , except for outright shortages, incentives for conservation do not often exist. 'In most countries the price charged for water is well below its real cost to the economy, in contrast to other production inputs, in which, with some notable exceptions , real costs still regulate man's economic behaviour

.

No wonder, therefore

,

that the introduction of water-conserving facilities and of water substitutes has never risen to an economically justifiable level' , (Wiener, 1972).

1-2.6 Water quality and pollution effects

Major streams pass through many metropolitan areas. Advances in relevant methods of runoff analysis were considered at the International Symposium on Mathematical Models in Hydrology at Warsaw, Poland, in July, 1971, and earlier by Dawdy and Kalinin (1970). Some streams are estuarine when they reach metropolitan areas, and methods of analysis in this situation have also progressed considerably in recent years, particularly with regard to water quality parameters (Orlob, 1972). Progress in stream water quality analysis has been greatly enhanced by the growing use of automatic monitoring (WHO, 1971). In some areas where groundwater is used for water supply, deterioration of its chemical quality has been recorded due to overpumping, especially in coastal aquifers where sea water intrusion takes place.

Major causative sources of water quality degradation in urban areas include: agricul' tural storm runoff; soil erosion; combined sewer overflows; industrial process effluents;

heated effluents from electric power plants; community waste water treatment plant effluents;

natural drainage from marsh lands; leakage from septic tanks and cesspools; urban storm runoff; contamination from surface of roadways , spills and leakage from oil and chemicals;

contamination from mining activities; and waste water discharged because of inadequate or malfunctioning systems of sewerage. Such degradation inhibits and/or makes more costly:

use and re-use of urban surface water and groundwater supplies; water-oriented recreation;

waterfront use , aesthetic improvements; aquatic life; commercial fisheries; shipping and navigation; waterfowl and sport fish propagation; and a number of other uses and cervices.

'In the absence of careful planning, urban centres are particularly susceptible to communicable diseases , particularly those which may be water-borne.

. . . .

. . The lack of sewerage and sewage-treatment facilities in many metropolitan areas of the world is a major cause of communicable diseases , including cholera , typhoid, diarrhoea, dysentery , filariasis , haemorraghic fever , infectious hepatitis , etc. , (WHO Expert Committee , 1965) .

elements and from myriad synthetic organic chemicals disposed of by industries also pose serious threats to public health. For example, mercury residues have been reported in many types of agriculturally produced food and in wildlife , including fish, (Ackefors , Lofroth and Rosen, 1970). High levels of mercury were found in algae collected at a site on an estuary flushed by fresh river water, whereas no mercury was detectable in algae from a fully marine sector beyond (Jones, Jones and Stewart, 1970). An extensive bibliography (with abstracts) of the worldwide literature on metals as pollutants was given by Sinha (1972).

While residuals from synthetic detergents in domestic waste waters (even after treatment) have caused problems of foaming and excessive enxichment of receiving waters, these effects are not as menacing as the possibility that these substances, even in very low dosages, can stimulate the entry of various other chemicals from the intestine into the blood of a human being; this raises the potential toxic effect of the other chemicals, (Mozhaev, Osintseva, Yurasova, Lin'kov and Litvinov, 1972).

Most developing countries are situated in tropical and semi-arid regions

.

. . . .

.

the developing countries are those that have the greatest rate of population growth and a very high rate of urbanization and industrialization. Since water pollution is caused by the activities of man, it occurs to the greatest extent where urban populations are growing rapidly and where water resources are limited' , (WHO Expert Committee, 1968). This is not to suy- gest that developed nations have solved their water pollution problems

-

far from it. For example, the Rhine River, which drains a major portion of the heart of Europe in its 1300 km journey to the North Sea, is subjected to many types of pollution that have defied acceptable international control for decades, (Montgomery and Merklein , 1972)

.

^According

As noted in the preceding section', water pollution from heavy metals and other trace

lLJidespread and serious water pollution has occurred in developing countries.

. .

.

of urbanization

Hydrological effects of urbanization

Report of the Sub-group on the Effects of Urbanization on the Hydrological Environment,

of the

Co-ordinating Council of the International Hydrological Decade

M. B.

The Unesco Press

Paris 1974

1

1

I

1

0

Preface

Contents

45 69 95

177

275

278

Foreword

Part I

International summary

-

i6

37

-

. . ..

-. '

-

. . . . .

-

-

...

'

...

-

-

Introduction

-

-

-

,

-

-

,

'

,

,

,

Summary of findings

,

0

-- +-+

N'd330 1

z

!x

a

c!

. .

I I I I

I

I I I

c

I I

k-1

I

I

I

i-l

Surmnary of findings

,

,

-

.

,

S m a q

.

-

-

findings