A contribution to the International Hydrological

In this series

1 Perennial Ice and S n o w Masses. A Guide for Compila- tion and Assemblage of Data for a World Inventory.

2 Seasonal S n o w Cover. A Guide for Measurement, C o m - pilation and Assemblage of Data.

3 Variations of Existing Glaciers. A Guide to Internation- al Practices for their Measurement.

4 Antarctic Glaciology in the International Hydrological Decade.

5 Combined Heat, Ice and Water Balances at Selected Glacier Basins. A Guide for Compilation and Assem- blage of Data for Glacier Mass Balance Measurements.

6 Textbooks on Hydrology - Analyses and Synoptic Tables of Contents of Selected Textbooks.

7 Scientific Framework of World Water Balance.

8 Flood Studies - A n International Guide for Collection and Processing of Data.

9 Guide to World Inventory of Sea, Lake, and River Ice.

10 Curricula and Syllabi in Hydrology.

11 Teaching Aids in Hydrology.

12 Ecology of Water Weeds in the Neotropics.

13 The Teaching of Hydrology.

14 Legends for Geohydrochemical Maps.

Légendes des cartes hydrogéochimiques.

Leyenda para mapas geohidroquímicos.

HereHna un« reorHnpoxMMHtiecKHx KapT 15' Research on Urban Hydrology, vol. I.

16 Research on Urban Hydrology, vol. II.

Technical papers in hydrology 18

Urban hydrological modeling and catchment research:

International summary

by M . B . McPherson and F . C . Zuidema

A contribution to the International Hydrological

Programme

unesco

Printed in Unesco's workshops O Unesco 1978

Printed in France

PREFACE

The "Technical Papers in Hydrology" series, like the related collection of

"Studies and Reports in Hydrology", was started in 1965 when the International Hydrological Decade was launched by the General Conference of Unesco at its thirteenth session. The aim of this undertaking was to promote hydrological science through the development of international co-operation and the training of specialists and technicians.

Population growth and industrial and agricultural development are leading to constantly increasing demands for water, hence all countries are endeavouring to improve the evaluation of their water resources and to make more rational use of them. The IHD was instrumental in promoting this general effort. When the Decade ended in 1974, IHD National Committees had been formed in 107 of Unesco's 135 Member States to carry out national

activities and participate in regional and international activities within the IHD programme.

Unesco was conscious of the need to continue the efforts initiated during the International Hydrological Decade and, following the recommendations of Member States, the Organization decided at its

seventeenth session to launch a new long-term intergovernmental programme, the International Hydrological Programme (IHP), to follow the decade.

The basic objectives of the IHP were defined as follows: (a) to provide a scientific fraiBework for the general development of hydrological activities; (b) to improve the study of the hydrological cycle and the scientific methodology for the assessment of water resources throughout the world, thus contributing to their rational use; (c) to evaluate the 'influence of man's activities on the water cycle, considered in relation to environmental conditions as a whole; (d) to promote the exchange of information on hydrological research and on new developments in hydrology;

(e) to promote education and training in hydrology; (f) to assist Member States in the organization and development of their national hydrological activities.

The International Hydrological Programme became operational on 1 January 1976 and is to be executed through successive phases of six years' duration. IHP activities are co-ordinated at the international level by an intergovernmental council composed of thirty Member States.

The members are periodically elected by the General Conference and their representatives are chosen by national committees.

The "Technical Papers in Hydrology" series is intended to provide a means for the exchange of information on hydrological techniques and for the co-ordination of research and data collection. In order to co-ordinate scientific projects, however, it is essential that data acquisition, transmission and processing be conceived in such a way

as to permit the comparison of results. In particular, the exchange of information on data collected throughout the world requires standard instruments, techniques, units of measurement and terminology.

It is believed that the guides on data collection and compilation in various specific areas of hydrology which have been published in the "Technical Papers in Hydrology" series have already helped hydrologists to standardize their records of observations and thus have facilitated the study of hydrology on a world-wide basis.

Much still remains to be done in this field, however, even as regards the simple measurement of basic elements such as precipitation, snow cover, soil humidity, run-off, sediment transport and ground-water phenomena.

Unesco therefore intends to continue the publication of

"Technical Papers in Hydrology" as an indispensable means of bringing together and making known the experience accumulated by hydrologists throughout the world.

TABLE OF CONTENTS

Pape

FOREWORD 1 SECTION 1 - SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 3

SECTION 2 - URBAN WATER RESOURCES 10

Introduction 10 Water Balances 10

Figure 1 - General Urban Area Water Budget for Sweden.. 11

Systems Analysis 13 Figure 2 - Hierarchy of the Water Resources

Management System 14 The Urban Water Resources System 15

Figure 3 - The Physical Urban Water Resources System... 16 Figure 4 - Stormwater and Wastewater Portion of Urban..

Water Resources System 17 SECTION 3 - URBAN RUNOFF, QUANTITY AND QUALITY 18

Introduction 18 Research Status 19 Research Obj ectives 19 An Ideal National Program 20

Figure 5 - Ideal Minimum National Field Data.

Network for Sewered Catchments 21 Figure 6 - Ideal National Urban Runoff Program 22

Role of National Governments 23 A Developing Nation Perspective 26 SECTION 4 - URBAN CATCHMENT RESEARCH 28

Introduction 28 Figure 7 - Urban Stormwater Disposal Physical Subsystem 29

A National Program Example 28 Table 1 - Catchments Investigated in Norway 30

Another National Example 31 Table 2 - New Catchment Investigation Program,

Philadelphia, Pennsylvania, U.S.A 32

Instrumentation 33 Data Collection 33

Figure 8 - Data Transmitting System 35

Special Studies 34 SECTION 5 - URBAN DRAINAGE MODELING 37

Introduction 37 Why Simulation ? 37 Categories of Model Applications 37

Components of Urban Runoff Models 38 Figure 9 - Components of Urban Runoff Models 40

Advantages in the Use of Models 39

Model Limitations 41 Storm Characterization 43 Concluding Remarks 44

SECTION 6 - REFERENCES 46

FOREWORD

This International Summary was prepared under International Hydrological Programme sub-projects 7.1 "Research on Urban Hydrology" and

7.2 "Development of Mathematical Models applied to Urban Areas considering both Water Quality and Quantitative Aspects", within the general framework of Project 7 "Effects of Urbanization on the Hydrological Regime and on Quality of Water".

The Bureau of the Intergovernmental Council of the International Hydrological Programme appointed Mr. M.B. McPherson (USA) as rapporteur of sub-project 7.1 and Mr. F.C. Zuidema (Netherlands) as rapporteur of sub-project 7.2 in 1975.

Since 1975, twelve national reports for the International Hydrological Programme (IHP) have been compiled on the state-of-the-art in urban

catchment research and hydrological modeling, with particular attention given to underground conduit systems. Summarized in this report are their principal commonalities, together with particularly noteworthy observations or advances reported for individual countries. The . . reference reports are for: the U.S.A.,^¹' Australia, Canada

the United Kingdom, ' ' the U.S.S.R., the Federal Republic of Germany'⁶^ Sweden, ^{7 )} France, ^ Norway,⁽⁹⁾ the Netherlands, ⁽¹⁰^ Poland,⁽¹¹⁾ and

India.(12)

The first five of these reference reports have been published by Unesco as Research on Urban Hydrology, Volume 1 (Technical papers in hydrology, no. 15) and the other 7 as Volume 2 (Technical papers In hydrology, no. 15/2) in 1977 and 1978 respectively.

Most of the substantial progress that has been made has taken place in the 1970's. However, to be consistent with the economic and social importance of urban drainage, much more needs to be done everywhere.

Three fundamental research objectives are identified with regard to

urban runoff: determination of the hydrological effects of urbanization;

development of measures that would offset the adverse effects and enhance the assets of urban runoff; and resolution of improved tools of analysis for the planning, design and operation of urban drainage systems.

However, insufficient knowledge has been acquired on crucial characteristics, such as on the processes involved in the accumulation, distribution and

transport of pollutants. This summary report is addressed principally to practicioners in urban hydrology.

This endeavour originated from activities and aspirations of the Unesco Subgroup on the Hydrological Effects of Urbanization of the

International Hydrological Decade (HID) which concluded in 1974. Members of the Subgroup represented the Federal Republic of Germany, France,

Japan, Netherlands, Sweden, U.K., U.S.S.R. and U.S.A. The first writer served as U.S. representative and chairman of the Subgroup and the second

*references are listed in Section 6

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writer servecLas the Netherlands representative. The Subgroup final report is divided as follows: Part I, "International Summary"; Part II, "Case Studies of Hydrological Effects of Urbanization in Selected Countries"; and Part III, "Illustrative

Special Topic Studies". The final draft of Part I was resolved by representatives of over thirty nations who participated in., an International Workshop at Warsaw, Poland, November 1973. ' A very important output from the workshop was the identification of ten crucial international research projects proposed for

inclusion in the Unesco component of the International Hydrological Programme which commenced in 1975 as the successor to the IHD.

The American Society of Civil Engineers (ASCE) took early supportive action by applying for a U.S. National Science

Foundation (U.S. NSF) grant to assist in two of the ten recommended projects, which were later included in the IHP.

R.l. Catchment Studies Report. Prepare a "state-of-the- art" report on research executed in urban catchment areas, which would include instrumentation, data acquired, analysis performed and applications.

R.3. Mathematical Models Report. Prepare a "state-of- the-art" report on mathematical models applied to urban catchment areas and dealing with, for instance, rainfall-runoff relationships and water balances, both with respect to water quantity and

quality.

Of particular significance was the very strong emphasis of the Warsaw Workshop and the Subgroup on the urgency of addressing all such reports to users of research findings. That is, an accentuation of user participation and user orientation of the IHP urban products clearly indicated that facilitation of the

translation of research findings into implementation practice should be a central goal.

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 a nation's health and growth. The most significant conclusion reached by the IHD/Unesco Subgroup is that most urban hydrological problems and effects are similar in technologically and economically advanced countries. Further, many problems confronting the developing nations have at one time or another already been encountered by many developing nations. This strongly suggests

that great benefits would result from exchanging of information and increased international cooperation in research and

development.

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SECTION 1

SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

Summary

For assembly of most of the national reports, a large number of organizations and individuals were contacted in each nation- and reference was made to a multitude of technical reports and publications. Because of limitations in time and funds, none of the national reports can be regarded as

exhaustive. Further, because they are status reports it must be accepted that there is a good prospect that new advances have been made or that additional information has accumulated since they were written. Hopefully, there will be opportunities later in the IHP to update the national reports. This is not to suggest that the national reports are not comprehensive. As a group they are the most informative and revealing collection of information on the subject fchat has ever been made available.

Moreover, while twelve nations are a small sample of the world's total, the many aspects of urban drainage that they share in common very strongly suggest that they are much more representat- ive than their small number would indicate.

Also to be considered is the important background developed during the IHD on the hydrological effects of urbanization.

The twelve national reports have built upon that foundation.

Reference to the broader considerations is exemplified in an introductory portion of the report for the F.R.G. :

"The social process of urbanization, as far as it affects hydrology, manifests itself mainly through the following symptoms:

high local population density; intensified industrial and trade activity; changes in ground surface; heavily increasing water demand; increased energy consumption; physical and chemical changes in the quality of surface and subsurface waters; air pollution; great need for protection from natural phenomena

(e.g. floods); need for the disposal of increasing quantitites of waste of all kinds; and recreational requirements to be met by surface waters.

"Urbanization affects all phases of the water cycle in

settlement areas, with far-reaching changes taking place in precipitation,

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evaporation, évapotranspiration, infiltration and runoff. Urban hydrology is that part of the comprehensive field of hydrology which deals with effects and phenomena in human settlements."

The purpose of the national reports is stated particularly well in the report for the F.R.GS6^:

"As expressly requested by the IHD Subgroup and emphasized by the Warsaw Workshop, this report (for the F.R.G.) is intended for practicioners

in urban hydrology, to give them a concentrated survey of available research results. It is hoped that this will facilitate translation of scientific results into actual practice and communicate unsolved

practical questions and problems to researchers."

On the whole, the status of urban hydrological research in the

Netherlands (10) appears to be quite typical of an economically developed nation:

"In spite of a continuous growth in the population of the

Netherlands (13 million in 1970 with 15.6 million expected in 2000) and an increasing population density (384 inhabitants per square km in 1970, 403 in 1975, 434 in 1985, and 463 in 2000), development in urban water resources research has been rather tardy. However, there is an

enormous diversity among urban hydrological problems, which are solved adequately. For example, while only a few urban catchment studies are going on, mathematical models are used for different goals and at

different levels: models for rainfall-runoff, water quality, comprehensive urban water and water resources management."

Summary. Section 2 - Urban Water Resources

Illustrated are the interrelations, interdependences and interconnections among the elements of the water resources of a metropolis. Such complexity calls for a "systems" approach in analysis. A hierarchical view of the water management system is disaggregated into the physical urban water resources system, from which the stormwater and wastewater portion is further segregated. Recognized is that although drainage, regarded as a subsystem, is currently the least.connected and least dependent of the urban water subsystems, expected more extensive practice of the management of'runoff for beneficial uses will increase its dependence. As a result, management of stormwater, such as for pollution abatement or water re-use, will inevitably become more complex.

This Section commences with a discussion of water balances. Very few water inventories have been made for entire, separate, urban areas, yet this is

the initial step for embarking on a total-system management approach.

A major objective of this Section is to develop a broad base or background to place drainage in its proper context as a part of the total resource. In this way an opportunity is provided to define the scope of coverage of the remainder of the report.

Summary, Section 3 - Urban Runoff

Distinctions are drawn between the convenience provided by underground systems of drainage and the threats to public safety that are offset by flood mitigation measures in natural flood plains. While modern research on urban runoff can be traced as far back as a quarter of a century, present knowledge is

heavily associated with advances made over only about the past ten years.. A primary impetus was the surge of a general public interest in the abatement of water pollution in recent years.

Identified in the national reports are three fundamental research

objectives with regard to urban runoff: determination of the hydrological effects of urbanization; development of measures that would offset the adverse effects and enhance the assets of urban runoff; and resolution of improved tools of analysis for the planning, design and operation of urban drainage systems. These objectives are interrelated and rely for their attainment on the effectiveness and reliability of tools of analysis. In turn, the acceptability and credibility of the tools hinge upon the extent and representativeness of the field data available for their validation. In sum, solutions to problems, tools of analysis and their supporting field data are part of a complicated circle of interdependences.

None of the national reports even implied the existence of an adequate national data base for validating tools of analysis. An ideal minimum national data acquisition program is postulated for the purpose of indicating world-wide deficiencies in a generic sense. Concluded is that despite substantial advances in recent years, attainment of the three goals described above appears to be a long way off in most if not all of the dozen nations for which status reports have been

prepared, despite substantial advances in recent years. However, because recognition of the importance of runoff aspects of urban hydrology is quite recent, we

optimistically expect that more comprehensive national programs will eventually evolve.

Despite the social importance of urban water resources and the substantial investments in associated facilities, we find national, territorial and local

governments involved in a tangle of interests. This, fragmentation is one of the reasons why urban water resources research around the world commonly has suffered from inadequate attention and support and from discontinuous and erratic efforts.

Urban drainage has suffered the raos.t research neglect and technical knowledge of it is the most primitive among the various aspects of urban water resources. On the premise that the manner in which various nations have attempted to overcome the enigma of fractionalized responsibility can be instructive, we have summarized such activities as have appeared in the national reports. Central coordination efforts have been spearheaded by groups ranging between national interagency coordinating groups to voluntary professional groups.

All the national reports but one are for nations that are regarded as economically developed. The sole report from an economically developing nation was for India. Because of the very great importance in the HiP of assisting

economically developing nations by transferring information to them on the positive and negative experiences and progress of more economically developed nations,

selected excerpts from the Indian report form the closure of this Section. The different perspective is both entirely lucid and pointedly direct.

Summary. Section 4 - Urban Catchment Research

Because little would be accomplished by reciting all the urban catchment research detailed in the dozen national reports, we have used examples from among the reports to illustrate the major considerations in such research. Because the national program in Norway appears to be one of the most integrated and

comprehensive in meeting nationwide needs, we have summarized the field research there as an example. We take advantage of this example by pointing out possible

- 5 -

shortcomings, only because they are essentially shared everywhere olse and we

have found no instance of an example that meets minimum ideal criteria. The U.S.A.

is the other example, because it is a much larger nation and thus has engaged in more extensive research activities. This latter example gives us an opportunity to remind our readers of the well-known axiom that a collection of data has no

inherent value, only an unknown potential one, until it has been subjected to thorough analysis and used in some beneficial way. This example also gives us an opportunity to mention a point raised in several reports, that many research stations were installed before the more modern tools of analysis were developed, and hence more recent data needs could not be anticipated, and as a result the data from these older stations is often of limited value.

A general dissatisfaction has been expressed on available instrumentation, particularly for in-sewer flow measurement and for water quality sampling.

Recommended in the report from France is the conduct of an international symposium for the comparison of experiences.

One of the most challenging aspects of data collection is the

synchronization of readings. Automatic data assembly-reduction installations, which overcome the synchronization difficulty, have been described in four of the national reports. Telemetry to a data receiving and processing center are described in two of the reports. We reiterate the truism that data has no inherent value until it is analyzed, and it cannot be analyzed until it has beer, reduced to hyetographs, hydrographs and displays of water quality parameter concentrations versus time.

Special studies are cited in various reports: on roadway drainage, groundwater hydrology and receiving waters. We note that conjunctive analysis of flow and water quality of urban catchments and receiving waters, while highly desirable, is seldom performed, despite a widespread concern over"reducing

stormwater quantities and pollutants entering receiving waters. Interest in the incorporation of retarding or detention storage in urban drainage is noted.

Lastly, mention is made of research on the snowmelt fraction of urban runoff.

Summary, Section 5 - Urban Hydrological Modeling

Discussion centers on the simulation of performance of urban underground- conduit drainage systems. Receiving water modeling is mentioned only where it is conjunctively or conjointly involved with drainage modeling.

This Section opens with reasons for using simulation, among which is primarily the eventual abandonment of established wholly empirical methods. Models are characterized in terms of their applications, and the scarcity of suitable data for the regional validation of such tools of analysis is necessarily emphasized.

Comparisons of various models are mostly inconclusive and hence are controversial.

As an alternative to an innocent entrapment among the scores of models cited in the national reports, we confine our attention to the most comprehensive and flexible tools. These contain capability for routing of rainfall excess over the ground surface to street inlets, routing of runoff (and wastewater in combined systems) through the underground transport conduits, and routing through relevant reaches of receiving waters. Also, conveyance of both water quantities and

pollutants are simulated. With greater comprehensiveness comes increased complexity, and three :iwdels described in some detail in the reports with

capabilities- just described are cited as examples that have enjoyed international application for design and planning purposes. Also cited is a special design model

that is in even wider use.

Advantages in the use of models are drawn from the reports and a recent reference. For example, noted in the report for France is that the introduction of mathematical models made it possible to reduce substantially the degree of empiricism inherent in traditional methods of analysis. Several national reports emphasize the continually escalating costs for new or modified drainage systems, and spiraling investment requirements are particularly evident where urban runoff pollution abatement is an emerging objective. The keen interest in pollution

simulation is quite recent in most countries. That a group of models rather than a single ;nodel is needed for important projects is well argued in the report for Canada.

Among model limitations, the one that particularly stands out is the primitive state of knowledge on the underlying processes in the accumulation and transport of pollutants. A more subtle liability is the fact that just about ill catchment observations have been at a single point, obviating the possibility of validating the spatial performance of models and forcing a reliance on total catchment response as a measure of capability. The report for the U.K. observes that pragmatic p.racticioners are more impressed with tools that can be applied expeditiously than in an assurance that an alternative has a more scientific

foundation. Further, the predictive precision of even the most widely used models may not be inuch greater than for simpler empirical approaches under certain

circumstances.

Control of flooding and water pollution must be based on probabilities of occurrence because of the random nature of precipitation. Little research has . been conducted on the temporal and spatial characteristics of storms that is

applicable to urban drainage systems. Practically all of the national reports cited studies in which a variety of attempts have been made to synthesize suitable storm rainfall for planning and design applications of various tools of analysis. It is concluded that rainfall, the input to runoff models, may become the last element of outright empiricism to be placed on a more scientific footing.

A recurrent opinion expressed in the reports is that advances in modeling capability have surpassed the availability of suitable field data for their

validation. Particularly feared is indiscriminant use of complex models without recourse to local field data for their calibration, a practice that subverts the purpose of such tools and earn3 them an undeserved reputation for impracticality.

This report closes with some important conclusions and recommendations from the report for India. In particular, a need is expressed for identifying tools of analysis suited to urban areas in economically developing nations, and for

determining the type of data needed for the use of such tools in design applications.

Summary, Section 6 - References

The primary entries are the twelve national reports. These are cited for attribution rather than the original references credited in the reports, to avoid duplication and for the sake of brevity.

Most of the other entries are references that have become available since the relevant national reports were written.

Several entries carry an NTIS identification number. For these, copies of the reference can be obtained for a cost-recovery charge from U.S.A. National Technical Information Service, U.S. Department of Commerce, Springfield, Virginia 22151.

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Concluding Remarks and Recommendations

Unesco has published the first five^ ' of the special IHP series of ASCE Program technical memoranda as Volume 1 of Research in Urban Hydrology.' ^ The other seven national reports'^^-12' have already been published ¿s Vwluáe-2 (see

Section 6 - References). '• We are also pleased to note that two of the technical memoranda on which this summary report is based have been reprinted, for national distribution in Canada^¹⁶' and in the Netherlands.(¹⁷' Other indications of heightened interest are: the recent publication in the U.S.S.R. of a book on hydrological aspects of urbanization^¹"' by the author of the technical memorandum for that nation; (5) and announcement of an international conference on Urban Storm Drainage to be held in Southampton, U.K., 11-14 April 1978. In many respects, the numerous papers . presented at the latter conference represent an updating of aspects of several of the national reports^1-12' and extension of related

information to include experiences of some other nations.

Related activities completed under IHP Project 7 have included: a Workshop on the Socio-Economic Aspects of Urban Hydrology, held at Lund, Sweden,

15-19 November 1976 p¹* ' a Symposium on Effects of Urbanization and Industrialization on the Hydrological Regime and on Water Quality held at Amsterdam, Netherlands,

3-7 October 1 9 7 7 p⁰' and a Workshop on Impact of Urbanization and Industrialization on Regional and National Water Planning and Management held at Zandvoort,

Netherlands, 10-14 October 1977.(²¹)

We are of the opinion that the work on urban hydrology under the IHD and the 1975-1977 phase of the IHP has adequately stipulated priority research needs.

On the whole, it remains for individual nations to satisfy these needs, now that they have been internationally documented and recognized. Therefore, we urgently recommend that the next phase of IHP Project 7 should emphasize applications, with Unesco simultaneously continuing to play a vital role in the international exchange of information on research, but with this role extended to include applications.

Development of urban runoff tools of analysis has gone beyond the field- measurement base that supports their validity. There is a need everywhere for more field observations from representative and experimental sewered catchments to

improve the reliability of tools of analysis used in planning, design and operations.

This is particularly true with respect to water quality considerations. The urgent need for a better understanding of the underlying, fundamental processes involved

in the accumulation and transport of pollutants in urban catchments was emphasized at the concluding plenary session of the 1977 Amsterdam Symposium and was recognized among the recommendations of the 1977 Zandvoort Workshop participants. These

expressions of concern reflect the great interest in most nations in recent years on pollution analysis, for the definition of sources of pollutants and their environmental impacts, and resolution of means for effective pollution abatement, all of which require more reliable tools for their analysis than are presently available. Moreover, more reliable tools for water quality analysis are needed

to help resolve the controversy over the merits of separate storm sewer systems vis-a-vis combined sewer systems. Still another reason is the growing interest in

the potential use of storrawater as a supplemental source of water supply.

Among the recommendations of the Zandvoort Workshop was that Unesco should give serious consideration to the establishment of demonstration training- projects on water resources management problems in urban areas situated in different climatic regions, and that these projects should have as one of their long-term objectives the preparation of manuals dealing with local problems of water resources

planning and engineering design. In support of this overall objective, and echoing a viewpoint expressed in several of the national reports summarized here, we

recommend that an international workshop be convened by Unesco on the collection, analysis and use of urban stormwater data, including an exchange of experiences with field instrumentation devices.

In summary, we envision the need for several important forms of Unesco activity over the next few years. To reiterate, these include: the establishment and promotion of demonstration training-projects centering on applications; the promotion of the acquisition of new knowledge, particularly with regard to basic processes underlying urban runoff pollution; the promotion of advances in

technological capability via manuals of practice for various climatic regions;

and facilitation of international exchange of information on both research results and applications. While the IHP may be the most suitable vehicle, for continuing and initiating such activities, we earnestly hope that the IHP together with other branches of Unesco will accord still more attention to urban hydrology issues than

in the past because of the great socio-economic importance of urban areas, their dependence on. water resources for their survival, and the numerous v/a ter-related amenities affecting the quality of life in human settlements. As noted by a leading participant at the Amsterdam Symposium, urban hydrology appears to be a particularly suitable vehicle for interdisciplinary interaction. The effectiveness of Unesco/IHD and Unesco/IHP in stimulating the international and internal-national

interest and activity that has been demonstrated thus far holds at least an equal promise for future projects and programs on urban hydrology..

SECTION 2

URBAN WATER RESOURCES Introduction

Before embarking on any detailed discussion of urban drainage, we will look at the water cycle of an urban area in its conceptual totality. A means for conducting an input-output inventory of water resources is the assembly of water budgets or water balances for a specific geographic entity. We commence our discussion with a collective national annual water balance for all urban areas of Sweden. Illustrated is the comparative isolation of drainage facilities from the remainder of the urban water infrastructure, except where combined sewers are

Lncluded. Examples of water balances for an entire nation or a large portion of a country are noted, but very few metropolitan water balances have been reported.

In order to account for the interrelation, interdependence and interconnection of the water resources of a metropolis it is necessary to adopt some form of a total- resource systems-approach. Having illustrated the use of such an approach for a province of the Netherlands, we point out that water balances are the initial stage of a comprehensive systems analysis. Retaining the total system concept, we next present a schematic representation of the physical aspects of the urban water resources system, and then segregate what may be regarded as the stormwater and wastewater portion, the focus of this report.

Water Balances

Water balances (or water budgets, or water inventories) describe the quantity and quality aspects of the destiny of water from its appearance as

precipitation through its departure from a metropolis as runoff and évapotranspiration.

While very few balances have been made for metropolitan areas, they would provide a basis for better recognition of the interrelation, interdependence, and interconnection of the elements of the water resources of a metropolis.

The collective average annual water quantity budget for urban areas in

Sweden is shown in Figure l.O) The volumes indicated are initial rough approximations that are undergoing continuous refinement. The upper right portion of Figure 1

involves natural processes that occur in urban and non-urban areas alike. However, the remaining portions represent the complex infrastructure introduced to support urban areas. Particularly noteworthy is the limited number of connections between the natural processes and the infrastructure: via combined and stormwater sewers;

via groundwater; and at receiving waters. Thus, urban runoff can be seen to be a rather special part of the total resource.

A preliminary collective average annual water quality budget has also been made for urban areas in Sweden. Initial estimates include the following total

pollution loads from urban areas entering the receiving waters of Sweden, in tons per year: (7)

Pollutant Wastewater Combined Sewer Overflows Stormwater Discharges Sums

BOD7 33 000 3 000 12 000 48 000

P 3 000 100 100 3 200 N 17 000 400 1 200 18 600

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SM01JH3A0 H3Ä3S Q3WSWO0 92

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11

Water is constantly in motion, a fact that can be obscured by averaging quantities over a year. Comprehensive study of water resources would include

development of seasonal balances as well. Water originating solely in an urban area that can be captured is seldom adequate for its water supply. The impact of pollution burdens is often felt in receiving waters well beyond their points of entry. Thus,

to close the water balance of an urban area usually requires accounting for causes and effects that occur some distance away.

National, seasonal water, balances have been achieved for each of two parts of The Netherlands.(10) Projected water balances for numerous sectors are

obtainable from a digital computer model devised for that purpose. Also included are capabilities for modeling salt balances.

Another example of nation-wide water balances is found in Israel, where such inventories are a part of the development of a group of simulation models for optimizing its total water resource.(22./

From the preceding discussion it is evident that a water balance Ls a complete inventory at a given time. A general accounting for the overall movement of water and pollutants can be ascertained by comparing such complete inventories over successive time intervals. (The remainder of this subsection is from the report for the U.S.A.C1)).

Satisfactory evaluation of hydrological effects of urbanization, and

related development of.strategies for resource management and environmental protection, have been hampered around the world because of minuscule research investments despite the economic and environmental importance of urban water resources. Serious obstacles have impeded advances, but progress is being made in a few notable instances.

An ASCE task committee on the hydrological effects of urbanization

highlighted in the conclusions of its final report a need for more comprehensive and more highly systematized investigations of hydrological changes in urban areas. The committer found that available information is of severely limited transfer value, partially as a result of the web of complexities imposed when open land becomes

urbanized. While concluding that useful results will be obtained only via coordinated efforts on a metropolitan scale, the unsolved central problem is the absence of

suitable means for achieving the needed coordination.

The IHD/Unesco Subgroup on the Effects of Urbanization on the Hydrological Environment arrived at very similar conclusions:' -"-T'

More metropolitan-scale water-balance inventories and their analysis should be undertaken as a means for improving overall water resources planning and management, and follow-on inventories should be made periodically to

document change and to provide a better understanding of the hydrological effects of progressive urbanization.

The interrelation and interdependence of water and wastewater and the competition and conflict between multiple jurisdictions have intensified with the growth of metropolitan areas. The variety of uses for water in metropolitan areas are continually enlarging, particularly for recreational purposes and for esthetic enhancement. Thus, hydrological surveys of urban areas should be updated frequently and regularly.

Both the ASCE and IHD groups struggled with the quantification of generic hydrological effects of urbanization on national scales. Despite the fact that most problems and effects are very similar in technologically and economically advanced countries, very few generalities can be drawn. To cite one of the few successful examples, it has been demonstrated in a number of countries that urbanization increases the local contribution of direct runoff volume and that

systems of storm drainage conduits result in greater direct runoff peaks with shorter rise times than for pre-urban conditions. A source of impotence in

generalization is the fact that, world-wide, the field of urban hydrology is almost devoid of modern research investment and that there has been relatively little study

to date of the effect of human settlements upon natural hydrological conditions.

These calls for water-balance inventories are the direct result of a clear recognition of the interrelation, interdependence, and interconnection of the

elements of the water resources of a metropolis. That is, a total resource systems approach is necessary if subsystem phenomena truly are to be identified, because of the complex linkages involved. Also, metropolitan land-use constantly changes, an occurrence which can only be accommodated for a complex system by using a total systems approach.

Systems Analysis

Since 1971 a committee in the Province of Gelderland, The Netherlands, has beer, developing a scientific base for optimal planning and management of available surface vater and groundwater, from the standpoint of both quantity and quality. An approach embodying systems theory is being used, with the water resources management system divided into three types of elements (social, natural and artificial) and into a number of water subsystems. These levels and elements are being

investigated at varying degrees of detail with the aid of mathematical models, mostly by interdisciplinary teams. The water resource^ .management system is regarded as a hierarchy of four strata of elements, Figure 2.

All relevant artificial, natural and social elements are taken into account in the first stratum of Figure 2. Econometric models have been developed for extrapolation of water demands, taking into account various factors that affect such demands.

At the second stratum in Figure 2, the coherence or interrelation betweor.

the natural elements is being studied to establish the interactions among the water subsystems. Models have been developed to simulate the flow of groundwater and surface water and the oxygen dynamics of streams. Quantity and quality aspects have been partially integrated by coupling these models. Moreover, in another model, the natural elements of the first stratum are included in a generalized network format adaptable to numerous surface water and groundwater applications.

By 1976 the usefulness of the modeling efforts undertaken in conjunction with the first two strata had been forcefully demonstrated. More complete coupling of quantity and quality models, and the incorporation of social elements, will complete the third stratum and lead to the fourth stratum, the ultimate goal, an integral water resources management model.

From the standpoint of an individual metropolitan area, it is important to note that the inventory aspects of the artificial and natural elements of the first stratum in Figure 2 are essentially a water balance, described in the preceding subsection. Putting it another way, "the initial stage of a comprehensive systems analysis of the water resources of a metropolitan area is essentially nothing more

than the attainment of a suitable metropolitan water-balance inventory."'^' - 13 -

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The Urban Water Resources System

If we reduce the considerations of the water resources management system of Figure 2 to the physical water-handling aspects, alone, the result is what might be called the.urban water resources system, depicted broadly and schematically in Figure 3. Capability has advanced satisfactorily for the analysis of water supply-treatment-distribution and wastewater collection-treatment-distribution and wastewater collection-treatment-disposal. In Figure 3 it should be noted that storm sewers are almost an isolatable part of the urban water resources system.

Not shown explicitly in the pictorial representation of Figure 3 is the interconnection between wastewater collection-treatment and storm sewers, via combined sewers,

elaborated upon below.

Capability for analysis of urban runoff, particularly drainage, has lagged substantially behind that for other components. In recognition of this fact, the emphasis for the initial phase of the IHP (1975-1977) on urban hydrology was among others on urban drainage research and development. Because simulation models are the basic tools of analysis, they comprised one of the two themes

reviewed. Because field data is essential for the validation of analytical tools, the other theme was catchment research.

Of. \

Figure 4 is a schematic representation that includes the storm and combined sewer subsystem of Figure 3, together with treatment of dry-weather

flows carried by combined sewers. The modeling and catchment research summarized in the present report is mostly in connection with this subsystem, which is a specific portion of the urban water resources system.

- 15 -

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SECTION 3

URBAN RUNOFF, QUANTITY AND QUALITY Introduction

Whereas there is a continuum between the subsystems o£ water supply, water use and wastewater reclamation (Figure 3 ) , stormwater has been historically regarded ás purely a negative good or nuisance and its subsystem (Figure 4) has seldom been deliberately connected to the other urban water subsystems.

The preceding Section closed with a description of the storm and combined sewer subsystem of the-overall urban water resources system. The function of underground drainage conduits is to remove stormwater from urban surfaces (except combined sewers, which' in addition convey wastewater on a perennial basis). The smallest catchment area (on the order of a hectare in size) is that tributary to a street inlet. Flow in storm and combined sewer systems is principally by gravity. Like natural drainage basins, smaller sewer branches unite with larger branches, and so on, until a main sewer is reached.

Thus, a main sewer not only transmits upper reach flow to a receiving watercourse but serves as a collector of surface runoff all along its route.

Human life is seldom threatened by the flooding of underground drainage facilities, except as a health hazard. Because the principal local detrimental effects of flooding are damage to the below-ground sections of buildings and hindrance of traffic, the consequences of flooding range from clearly assessable property destruction to annoying inconvenience. It follows that provision of

complete protection from flooding can only rarely be justified. Instead, facilities are designed which will be overtaxed infrequently. However, because of the marginal level of protection afforded, storm drainage flooding damages are of considerable magnitude. Indirect damages from local drainage flooding are much more extensive

than for stream flooding and generally recur more often, and direct damages are usually much more widely dispersed throughout a community.

Flood control, drainage and the quality of receiving waters are all closely related. Increased volumes of direct runoff from underground drainage conduits

clearly can aggravate flooding of urban flood plains. On the other hand, increased receiving-stream stages can cause or induce flooding of underground drainage systems, because of the intimate hydraulic linkage between them. Moreover, frequently

overlooked is the fact that precipitation cleanses the land surface. However, because pollutants together with aesthetically objectionable materials are washed . off the land and transported to receiving waters in runoff, the result is merely a

transfer of land surface pollution to water pollution despite the benefits accruing to the land. Considering that urbanization increases the rates and volumes of runoff delivered locally to receiving waters, it is evident that the conveniences of surface cleansing and land drainage are obtained at the expense of higher stages and greater pollutant burdens in receiving waters.

Most forms of pollution enter receiving waters continuously or at least seasonally. Because the entrance of stormwater is spasmodic but comparatively

violent, the effects of its pollution are both comparatively dramatic and transient, and its impact depends on the season of occurrence and ambient levels of non-storm associated pollutants in receiving waters. According to Figure 1, Section 2, the estimated annual volume of stormwater runoff for urban areas of Sweden is slightly greater than the annual volume of wastewater, and according to similar estimates

it is about half as large for the F.R.G.^6' The impact of such large quantities

• entering receiving waters over very brief periods is only beginning to be

appreciated. There seems to be a consensus of opinion supporting the contention that the abatement of pollution from combined sewer overflows and storm sewer discharges could well be more cost-effective than the adoption of increased levels of treatment of wastewaters in certain circumstances. Recent papers on research

in the U.K./2 7) Australia^28) and the U.S.A.^29) tend to support this contention.

One of the difficulties in evaluation of such trade-offs is that little is currently known "about either long-term or short-term toxic effects of urban runoff in a

variety of receiving waters and ecosystems".^29-) Research Status

Among the earliest comprehensive field data research programs were those of the Road Research Laboratory in the U.K.^-' and The Johns Hopkins University in

the U.S.A. ,(•*•} initiated over a quarter of a century ago. These programs were conducted as means for improving knowledge on underground drainage system rainfall- runoff relationships. Generally speaking, a broad interest in the water pollution aspects of runoff did not emerge until the I960's, in connection with suspected significant pollution from combined sewer overflows. One thing led to another, and by the early 1970's there was a broad interest also on pollution from discharges from separate stormwater sewers.

Australia, which has no combined sewers, illustrates the recently emerged interest noted immediately above. It could be said in 1976 that:

"water quality measurement programs in urban areas were not integrated with the rainfall-runoff data collection programs until the last few years. This was probably due to the dispersed nature of responsibilities

for measurement of rainfall, runoff and water quality. It was also in part due to a lack of awareness of the magnitude of pollutants in stormwater runoff and their effects on receiving waters. With the move towards the removal of nutrients from sewage effluents in some Australian cities, more attention has been devoted to the contribution of urban stormwater runoff to problems caused by excessive amounts of nutrients or other pollutants reaching, rivers, lakes, bays and estuaries."(²'

Research Objectives

Identified in the national reports are three fundamental research objectives with regard to urban runoff:.

. determination of the hydrological effects of urbanization;

. development of measures that would offset the adverse effects and enhance the assets of urban runoff; and

. resolution of improved tools of analysis for the planning, design and operation of altogether new drainage systems and for the improvement and extension of existing drainage systems.

These three objectives are intimately related, and all.rely on the effectiveness and reliability of the tools of analysis. In turn, the acceptability, credibility and reliability of the tools hinge upon the extent and representativeness of the

field data available for their validation.

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None of the national reports even implied the existence of an adequate national data base for validating tools of analysis. Little, if anything, would be gained by probing the shortcomings of these dozen cases. Rather, an ideal minimum national data acquisition program will be suggested, and reported advances

in knowledge will be reviewed in terms of that ideal.

An Ideal National Program

Schematically portrayed in Figure 5 is an hypothesized ideal minimum national field data network for sewered catchments. Assumed is the existence of four major national climatic zones, realizing that there are countries with only one recognizable zone and others where there would be more. Field data should be obtained in a sample metropolitan area of each major climatic zone. In each sample metropolitan area, about a half-dozen catchments should be selected for rainfall-runoff-quality observation, each representing a different major type of land-use. Land-use of a given catchment should be fairly uniform because that catchment is considered to represent that particular type of land use in its meti-opolis. In order to validate the multiple components of modern tools of analysis, flow measurements should be made, and water quality samples should be taken, not only at the outlet from the catchment (terminus of outfall sewer) but also within conduit branches below major tributary junctions and within some street inlets and at the roof leaders of some individual buildings in a subcatchmentc (Also, at least one raingage should be installed in each catchment).

A specialist in urban hydrology would be justified in criticizing the Figure 5 representation as being extremely sparse, or worse. However,' the minimum data network depicted in Figure 5, using the individual catchment shown as an example of the average case, calls for 192 flow-measurement and water quality- sampling stations, ranging from a flume installation at an outfall sewer exit to a small device in a roof leader. In the hope that zonal differences might be small, the national program could be started with half as many stations, for the most disparate climatic zones (e.g., two of the four in Figure 5 ) . Even so, none of the national reports reviewed here described anything that came anywhere near the ideal minimum. It is not just that not as many catchments were involved.

Practically all observations have been at catchment outlets and water quality

samples have been collected at only a minority of stations. (More about this later).

Figure 6 contains the essential elements of an ideal national urban runoff program. The uppermost element is the sewered catchment field data network described in Figure 5. Attempts to generalize results of analyses of mixed urban catchments (viz., small streams fed by sewered sectors) have been

inconclusive because too many variables are Lnvolved, which is a pity because there appears to be more of this kind of station than for sewered catchments. Thus, urban stream data is segregated in Figure 6, but it should be understood that what is intended is stream stations where upstream sewered sectors would also be observed.

A crucial consideration is the concurrent collection and analysis of field data, activities that could be essentially completed in as short a time as a three-year period of concentrated effort.

The sole purposes of the data collection and analysis phase is to derive national guidelines for planning and design and national indicators of effects of urbanization, by major climatic zones. Prerequisite to the attainment of these goals is: the elucidation of water quality processes (cause and effect relations);

determination of zonal parameter values for tools of analysis; and resolution of linkages with receiving water tools of analysis. An intermediate phase would

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INDIVIDUAL METROPOLITAN AREA (IN ZONE TS)

MAJOR NATIONAL CLIMATIC ZONES

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L E G E N D - F L O W M E A S U R E M E N T A N D WATER QUALITY SAMPLING STATIONS'- XD - At Terminus of Catchment Outfall Conduit

x = Within Catchment Conduits (Storm or Combined Sewers) A = Within Inlets of Subcatchments

o = At Roof Leaders of Individual Buildings in Subcatchments

FIGURE 5-IDEAL MINIMUM NATIONAL FIELD DATA NETWORK FOR SEWERED CATCHMENTS

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NATIONAL SEWERED SYSTEM FIELD DATA ACQUISITION ZONES K AND ET

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FIGURE 6 - IDEAL NATIONAL URBAN RUNOFF PROGRAM

include: the simulation and economic analysis of land-water management strategies (such as diffused detention storage in sewered catchments, on-site management practices for reducing stormwater pollution, etc.); and evaluation of significant historical storm data, by major climatic zones, to place the provision of protection from flooding and abatement of runoff pollution on a probabilistic footing.

We regret to say that, despite substantial advances in recent years, attainment of the goals described appears to be a long ways away in most if not all of the dozen nations for which status reports have beer, prepared. On the other hand, the ideal national program outlined in Figure 6 would require a substantial, concentrated, coordinated, well-managed effort spanning perhaps a minimum of a total of five years for its completion. Because recognition of the importance of the runoff aspects of urban hydrology is quite recent, we optimistically expect that more comprehensive national programs will eventually evolve.

Role of National Governments

We have noted that around the world the 3izing of storm and combined sewers had long been, and mostly still is, determined by wholly empirical methods.

Various versions of what is sometimes called the "rational method" are in common use.

This simplistic procedure yields only a peak flow rate unless the empiricism is further extended to synthesize a hydrograph. The persistence of such a nebulous tool can be credited to a lack of adequate field data for validating more realistic procedures. However, as the next Sections of this report will indicate, catchment research.over the past several years, coupled with development of new tools of

analysis, is gradually leading to the adoption of more realistic methods. The impetus for change in some countries has been a new concern over water quality coupled with an interest in more widespread use of detention storage; and both issues require employment of full hydrographs for their explication.

In nearly all great metropolises around the world, every important level of government participates in each major public service category; the proliferation of single-purpose agencies dealing with specialized public services has been

continuous; and the most common type of metropolitan institution throughout the world, by far, is the independent district, corporation, or authority.^³⁰) Thus, despite the social importance of urban water resources and the substantial

investments in associated facilities, we find national, territorial and local governments involved in a tangle of interests. This fragmentation is one of the reasons why urban water resources research around the world commonly has suffered from inadequate attention and support and from discontinuous and erratic efforts.(*3) In addition, few local agencies can support hydrologie research that will yield

results transferable to other metropolitan areas, or even from one jurisdiction to another in the same metropolis. Noted earlier was that urban drainage has suffered the most research neglect and technical knowledge on it is the -.nost primitive among the various aspects of urban water resources. An important contributing factor is undoubtedly the conventional isolation in the past of the urban drainage subsystem from the total urban water system, discussed in Section 2. New interest in urban drainage performance has arisen at least partly because of a desire to integrate the urban drainage subsystem with other subsystems, such as for water pollution abatement or water re-use.

The manner in which various nations have attempted to overcome the sr.igma of fractionalized responsibility can be instructive. The remainder of this

subsection is devoted to a summary of such activities as have !>eeⁿ. described in the national reports, and the order of their citation follows the numerical order of their release.

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