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Current issues and future needs in urban storm drainage
Water Res. Vol. 17, No. 9, pp. 1067 1071, 1983 Printed in Great Britain.All rights reserved
0043-1354/83 $3.00+0.00 Copyright © 1983PergamonPress Ltd
CURRENT ISSUES AND FUTURE NEEDS IN URBAN STORM DRAINAGE* PETER J. COLYERI+ and BEN CHIE YEN2~ 1Hydraulics Research Station, Wallingford, Oxon, England and 2Department of Civil Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A,
(Received July 1982)
HIGH LEVEL OF INTERNATIONAL ACTIVITY
INTRODUCTION This paper derives from discussions and observations of a conference on urban storm drainage which took place at the University of Illinois at Urbana-Champaign in June 1981. It was the Second International Conference on Urban Storm Drainage and was sponsored by the International Association for Hydraulic Research (IAHR) and the International Association on Water Pollution Research and Control (IAWPRC). The conference was organised by the International Liaison Group on Urban Storm Drainage--an informal group of interested people. As indicated towards the end of this paper, initiatives proposed at the conference led eventually to the formation of a Joint Committee on Urban Storm Drainage under the auspices of IAWPRC and IAHR. It is pleasing to report on this addition to the growing range of IAWPRC activities, and the Association's increasing collaboration with other international organisations. One of the requirements of IAWPRC conference sponsorship is that organisers must supply a technical report on the event for publication by the Association. This paper therefore has a number of purposes. It is a technical report on the conference, as required, but also a succinct overview of the state of the art in urban storm drainage. At the same time it reports on a major activity of one of IAWPRC's newest specialist groups.
*Prepared and submitted to IAWPRC and IAHR on behalf of the Advisory Committee of the Second International Conference on Urban Storm Drainage. The paper was reviewed by the committee members. The committee members are: Dr M. Desbordes, Professor R. S. Engelbrecht, Mr R. Field, Dr N. S. Grigg, Professor P. Harremo~s, Dr P. R. Helliwell, Dr R. K. Price, Professor T. Sueishi, Professor A. Sj6berg, Professor M. P. Wanielista, Dr W. O. Wunderlich and Professor B. C. Yen. tSecretary, IAHR/IAWPRC Joint Committee on Urban Storm Drainage. :~Chairman, IAHR/IAWPRC Joint Committee on Urban Storm Drainage.
A number of phenomena have recently combined to produce renewed international interest in urban storm drainage, including: the development of mathematical techniques for flood routing and hydrological prediction which may be transferred, with various degrees of modification, from natural catchments to artificially drained urban catchments; the increasing availability in many countries of powerful computing facilities, which are essential for the solution of extensive network calculations and sophisticated management techniques; the recognition of storm runoff as an important source of water pollution; the awareness of environmental and hydrological changes due to the urban rainfall-runoff process. The simultaneous emergence of these phenomena has led to the creation of several nationally co-ordinated research and application projects. These projects recognise the large expenditure necessary to produce well-drained urban areas, and the environmental and health problems which could arise from improper practice. A casual observation reveals geographic variation in the perceived problems in urban storm drainage. With few exceptions, major efforts in North America have tilted in recent years towards storm runoff quality problems. Great Britain focuses mainly on hydrological, quantitative aspects, whereas in Western European countries various attempts have been made to solve runoff quantity and quality problems. In Japan urban storm drainage is almost exclusively the environmental engineers' domain. Activities in developing countries which would benefit most from improved urban drainage are, regrettably, relatively isolated and lacking. The limitation of the achievements so far must be recognised. The wider application of new principles of urban storm drainage is still awaited, often in parts of the world most in need of improvements in living conditions and human health. Moreover, the exist-
1067
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PETER J. COLYER and BEN CHIE YEN
ence of a nationally co-ordinated research programme does not guarantee, in any country, that better environmental and cost-effective practices will be implemented by drainage authorities actually responsible for construction work and operation. Evidence suggests that getting the research results adopted in general practice is a much harder task than obtaining the results themselves. URBAN HYDROLOGY AND HYDRAULICS--DO WE KNOW ENOUGH? Often it is claimed, particularly in North America, that sufficient basic knowledge is available about the hydraulics and hydrology of urban storm drainage. The papers and discussions in the conference indicated the contrary. For instance, very little is known about the temporal and spatial variations of storm rainfalls. Even less is known about the critical storms that should be used for the design and simulation of future operational conditions of drainage facilities. Only recently have attempts been made to justify scientifically the conventionally used design return period concept on the basis of benefit-cost and risk considerations. In the hydraulic aspects, present knowledge is equally, if not more, inadequate. For example, a practical and reliable routing technique for unsteady sewer flow has not been proven, despite the common knowledge that the Saint-Venant equations can sufficiently (although not exactly) represent the flow. For the approximate techniques such as the various kinematic wave models the significance of the backwater effects have not been systematically assessed. Much less is known about the hydraulics of transition between gravity and surcharge flows in a sewer and about the quantitative hydraulic effects of the manholes and junctions. These and other similar fundamental hydraulic phenomena ought to be understood to ensure the appropriateness of the simplified techniques and models which would be more suitable for practical applications. Neither is enough known about the overland flow. To account for the unsteady nature of the flow and to achieve improvement over Manning's or similar simple formulas, kinematic wave equations have recently been very popular despite the fact that the equations are actually applicable only to rather simple and homogeneous surfaces without significant backwater from downstream. It is now known that for shallow overland flows Manning's roughness factor is far from being constant and the flow resistance is significantly affected by the rainfall. However, little information is available on the quantitative changes of the flow resistance. Worse still, rainfall abstractions, particularly infiltration which is a significant component in determining storm runoff, are often modelled in a rather subjective manner. Urban storm drainage problems were solved, albeit rather primitively and in a less sophisticated fashion,
more than a century ago and earlier, before the development of the rational method. Today with increasing complexity of the drainage and pollution problems of storm waters and improved computational tools, how much should be known and what degree of sophistication is required? MODELLING CAN BE ACCURATE AND SOPHISTICATED--DOES IT HAVE TO BE BOTH? The process of storm rainfall, surface flow, pollution entrainment and transport and unsteady flow in sewers lends itself in a particularly attractive way to mathematical simulation. Each part of this process can be represented by complex mathematical or statistical sub-models, and the more ambitious packages attempt to combine these phenomena into a coherent representation of the total catchment response. Several such packages were presented at the conference, originating in the United States, the United Kingdom, Denmark, Sweden, Turkey and Japan. Although apparently modelling the same phenomena these packages show considerable divergence in their treatment of details and there was, for the user, a somewhat alarming lack of agreement among mathematical modellers about even fundamental aspects of flow routing in pipes. Particular problems occur with handling backwater effects in free surface flow conditions, the representation of head and pressure changes in surchaged flow and the solution of looped networks. Evidently the last work on these subjects has not yet been said. However, alongside this trend towards sophisticated modelling another trend was clearly discernible; towards simplification, a view that many of the mathematical niceties may be irrelevant when it comes to engineering practice and construction. So the conference was also presented with design approaches based on classical unit hydrograph theory, simplified kinematic wave routing and the rational method. The last word on these traditional solution methods has not been said either. Several lessons may be learnt from these apparently contradictory trends. Firstly the requirements for designing new drainage systems are totally different from those for the management and optimum performance of existing systems. The performance criteria for new systems (for example a specified frequency of pipe full flow) may be only loosely defined on the basis of very general socio-economic considerations. High accuracy of discharge prediction may therefore be unnecessary because of the large uncertainties in other aspects of the design process. Consequently the simpler methods are of adequate accuracy. Drainage management, however, may require detailed knowledge of the hydraulic performance of existing systems under specified rainfall conditions. This will probably demand computer modelling of
Current issues and future needs in urban storm drainage surcharged networks. All presentations on this subject referred to high demands for computer storage and time, and difficulties in obtaining numerical stability in representing a process which in reality varies very rapidly. A second lesson is that the computer does not meet all the needs of drainage engineers. At one extreme many designs are still based on manual calculation methods and even in highly developed countries access to digital computers is still limited to the larger design organisations. At the other extreme even medium sized computers are sometimes unable to provide sufficient core for the more complex models of surcharging or water quality phenomena. A third lesson is that with present computer capability and knowledge of the physical, chemical and biological aspects of storm runoff, the development of a single, universal, all-capable computer-assisted mathematical model is most unlikely and impractical, despite the extreme strong temptation to develop such an "all-powerful" model. In addition to the computer limitations, such an "all-powerful" model would have so many options and require so many data that an engineer would be very confused and frustrated in trying to sort out the maze to identify and use the part that he needs. Fourthly the work of the "simplifiers" is based upon a fundamental question: are the field data good enough to support the sophisticated models? Indeed, any model, irrespective of its level of sophistication and objective, should be adequately verified over the entire range of conditions of its intended uses before being introduced for applications. Practically all the presently existing models share the general criticism of inadequate testing and verification. But it is unfair to lay the blame totally on the model developers because very few good data are available to verify even limited aspects of the models. Data requirements were a persistent theme of the conference.
1069
ments which will not have to be repeated as the data bank increases during subsequent years. Secondly a long period of catchment monitoring is necessary to collect data on the low frequency events and to obtain a good knowledge of the flow frequency relationship. This is becoming increasingly important as urban drainage studies are moving into the area of flood-frequency prediction on a statistical basis. Statistical analysis techniques can, of course, increase the benefit of even a relatively short record, but on the whole nothing is as good as an extended data base. Discussions in the conference also illustrated three different aspects of data collection: the temporal extent of the data collection; the spatial extent of the data collection; the type of storm water quantity and quality data to be collected. A distinction may be necessary between funding for research and funding for data collection. A long-term commitment to data collection may be best undertaken by a statutory drainage authority whose future existence and interest can be guaranteed. In this way long term records could be assembled by a permanent central authority for the benefit of both present and future research projects. Maximum use should be made of the data which are obtained at such difficulty and expense. International exchange of urban rainfall-runoff data has already proved beneficial in both Europe and North America. Problems of parameter definition and other aspects of compatibility inevitably arise; the issue of data standardisation is one which the newly formed committee (see below) will have to attend to. S T O R M WATER Q U A L I T Y - - W H A T T O MEASURE AND H O W T O GENERALISE OBSERVED RESULTS
A repeated question on storm runoff water quality is what parameters are important in urban drainage
DATA C O L L E C T I O N - - P A I N F U L BUT ESSENTIAL
Discussion about data collection systems revealed that these are frequently part of a relatively short term research project (2 5 years). Since the first year or more may be consumed in painful experience of instrument malfunctions or incorrect location, it is evident that good data are only becoming available towards the end of the funding period. The data collection exercise may well be terminated just as it is producing its most useful results. Two arguments for changing this situation should be considered. Firstly urban rainfall-runoff data collection projects have very high initial costs; not only the capital costs of instruments and laboratory procedures for, e.g. pollutant identification, but also high initial costs of catchment land use analysis and network surveys. These initial activities yield extremely valuable information about monitored catchw.K
17/9
H
pollution problems and what representative parameter or parameters can be used to indicate the water quality during the storm runoff process. Current and past storm water data collection and analysis projects are site-orientated, isolated cases. Clearly there is a need to categorise and characterise the pollutants based on the rainstorm properties, catchment characteristics, properties of the pollutants and geographic locations. It is possible that through systematic categorising and eharacterising of a sufficient amount of data, perhaps with the aid of regression and dimensional analyses and parameter normalisation, a generalised pollution prediction method can be developed to be used for ungauged or future urban catchments. D O N O T D I S T U R I ~ - I S IT POSSIBLE?
Increasing awareness of the effects of environmental disturbances are apparent. Topics presented included
1070
PETER J. COLYER and BEN CHIE YEN
rainfall acidity, suspended solids and heavy metals, pollution from streets, gullies (catch basins) and storm water overflows, impact on receiving waters and groundwater quality in urban areas. Little was discussed quantitatively on the levels and damages of urban flooding. Increased use of detention storage and semi-permeable urban surfaces were among the methods suggested for tackling the problems of pollution and flooding. Remedy measures usually can restore only a limited range of the original environemnt. It is evident that environmental considerations will have to play a larger part in future drainage design.
FUTURE TRENDS AND NEEDS
Any prediction of the future trends and needs is only conjectural but several trends appear to be evolving. Firstly, storm drainage problems will be attacked in a more complex and comprehensive context than in the rational method era. The new techniques probably will consider both flood mitigation and pollution control, minimising negative environmental impact while maximising the environmental and economic improvement. This new approach may require the incorporation of risk analysis and optimisation techniques in problem solving. Secondly, use of computers in solving drainage problems will be increased. There will be computerbased mathematical models of different levels of sophistication for different objectives of design as well as for simulation, planning and management and suitable for computers of different sizes ranging from pocket computers to large full-size computers. Thirdly, there will be continuous efforts in the collection of good urban storm runoff data of appropriate temporal and spatial resolutions. These data will be used for evaluation, calibration, verification and selection of mathematical models. Systematic and scientific analyses of these data will also provide useful information for applications. Fourthly, with improving living standards, increasing attention to urban storm drainage will be paid in the developing countries where design and development of new drainage systems will continue to be the main concern. Conversely, for developed countries, deterioration, inadequacy in capacity due to urban expansion, and insufficient handling of runoff pollution in existing drainage systems will increasingly become problems. Possibly and ideally urban storm drainage will be considred within the context of a regional water resources development and management programme. A list of some of the more specific topics needing additional research and development in the near future is given randomly as follows: Collection of ;torm water quantity and quality data with well planned programmes in the temporal and spatial domain.
Analyses of the data for characterisation and generalisation and for evaluation of mathematical models. Development of accurate and efficient unsteady flow routing schemes and critical evaluation and comparison of routing schemes. Critical, quantitative and objective evaluation of urban storm drainage mathematical models. Studies on surcharged flow and the transition between surcharged and free surface flows. Studies of the hydraulics of junctions, manholes and gulley pots (inlet catch basins/. Development of improved methods for overland runoff simulation, including two-dimensional surface and gutter flows and better representation of the land surface and of the resistance coefficient for unsteady shallow water flow under rainfall. Development of improved methods to account for abstractions from precipitation, especially infiltration. Studies of the temporal and spatial distributions of rainfalls pertinent to the urban environment. Identification of the representative water quality parameters in urban storm water pollution and characterisation and normalisation of these parameters from local data for general use. Investigation of the need for and significance of modelling the biological and chemical processes in urban storm water transport. Studies of the transport of sediment in urban storm drainage systems. Studies of the storm water overflow and its impact on receiving water quality. Evaluation of the effectiveness of various pollution and flood control measures such as detention storage and porous surfaces. Investigation of the performance and preferability of combined or separate storm sewer systems under different conditions. Collection of data on the costs of construction, damage, and operation and maintenance of drainage facilities and analysis and normalisation of such data for general uses. Incorporation of risk analysis and optimization techniques in the design and management of urban storm drainage. Investigation of operational and maintenance needs of urban storm drainage and consideration of these needs in the design and management of urban drainage. Financial and professional support should be given to all three stages of urban storm drainage technology development, namely, the stages of research, development and evaluation, and implementation. It is almost universal that support of research is difficult to obtain, partly because urban storm drainage is seldom a life-threatening, news-media sensational item. It is equally difficult to find knowledgeable, good and objective evaluations of new techniques or models. It is, unfortunately, even more difficult to receive support for technology transfer of worthwhile new tech-
Current issues and future needs in urban storm drainage niques to practising engineers for field applications. There is a need for coordination and mutual support among research institutions, public agencies and private industries to ensure sufficient support for all the three equally important stages from research and development to implementation of new techniques. FUTURE INTERNATIONAL COOPERATION
Future international cooperation in urban storm drainage consists of several aspects: coordination and exchanges of experiences in the implementation of new technologies; national and international cooperation in data collection; national and international coordination and cooperation in research and development projects; rapid and free exchanges of research experience and technical development among researchers, engineers and scientists at national and international level. The United Nations has declared the 1980s as the International Drinking Water Supply and Sanitation
1071
Decade. UN should be persuaded to include urban storm drainage as a major theme of the Decade and lend itself, its sister interational organisations and member nations to full support of international cooperation and development in urban storm drainage. In order to promote actively international cooperation in urban storm drainage the Urbana conference proposed that an urban storm drainage committee be established under the joint auspices of the International Association of Hydraulic Research (IAHR) and the International Association on Water Pollution Research and Control (IAWPRC). This has now been achieved and an IAHR/IAWPRC Joint Committee on Urban Storm Drainage has been established. The current chairman is Professor B. C. Yen (U.S.A.) and Mr P. J. Colyer of Hydraulics Research Station Ltd, Wallingford, Oxfordshire, England is the secretary. The Third International Conference on Urban Storm Drainage will be held at G~teborg, Sweden from 4 to 9 June 1984. Further details from IAWPRC in London. The proceedings of the Urbana conference are available from: Water Resources Publications, P.O. Box 303, Littleton, CO 80522, U.S.A.
0043-1354/83 $3.00+0.00 Copyright © 1983PergamonPress Ltd
CURRENT ISSUES AND FUTURE NEEDS IN URBAN STORM DRAINAGE* PETER J. COLYERI+ and BEN CHIE YEN2~ 1Hydraulics Research Station, Wallingford, Oxon, England and 2Department of Civil Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A,
(Received July 1982)
HIGH LEVEL OF INTERNATIONAL ACTIVITY
INTRODUCTION This paper derives from discussions and observations of a conference on urban storm drainage which took place at the University of Illinois at Urbana-Champaign in June 1981. It was the Second International Conference on Urban Storm Drainage and was sponsored by the International Association for Hydraulic Research (IAHR) and the International Association on Water Pollution Research and Control (IAWPRC). The conference was organised by the International Liaison Group on Urban Storm Drainage--an informal group of interested people. As indicated towards the end of this paper, initiatives proposed at the conference led eventually to the formation of a Joint Committee on Urban Storm Drainage under the auspices of IAWPRC and IAHR. It is pleasing to report on this addition to the growing range of IAWPRC activities, and the Association's increasing collaboration with other international organisations. One of the requirements of IAWPRC conference sponsorship is that organisers must supply a technical report on the event for publication by the Association. This paper therefore has a number of purposes. It is a technical report on the conference, as required, but also a succinct overview of the state of the art in urban storm drainage. At the same time it reports on a major activity of one of IAWPRC's newest specialist groups.
*Prepared and submitted to IAWPRC and IAHR on behalf of the Advisory Committee of the Second International Conference on Urban Storm Drainage. The paper was reviewed by the committee members. The committee members are: Dr M. Desbordes, Professor R. S. Engelbrecht, Mr R. Field, Dr N. S. Grigg, Professor P. Harremo~s, Dr P. R. Helliwell, Dr R. K. Price, Professor T. Sueishi, Professor A. Sj6berg, Professor M. P. Wanielista, Dr W. O. Wunderlich and Professor B. C. Yen. tSecretary, IAHR/IAWPRC Joint Committee on Urban Storm Drainage. :~Chairman, IAHR/IAWPRC Joint Committee on Urban Storm Drainage.
A number of phenomena have recently combined to produce renewed international interest in urban storm drainage, including: the development of mathematical techniques for flood routing and hydrological prediction which may be transferred, with various degrees of modification, from natural catchments to artificially drained urban catchments; the increasing availability in many countries of powerful computing facilities, which are essential for the solution of extensive network calculations and sophisticated management techniques; the recognition of storm runoff as an important source of water pollution; the awareness of environmental and hydrological changes due to the urban rainfall-runoff process. The simultaneous emergence of these phenomena has led to the creation of several nationally co-ordinated research and application projects. These projects recognise the large expenditure necessary to produce well-drained urban areas, and the environmental and health problems which could arise from improper practice. A casual observation reveals geographic variation in the perceived problems in urban storm drainage. With few exceptions, major efforts in North America have tilted in recent years towards storm runoff quality problems. Great Britain focuses mainly on hydrological, quantitative aspects, whereas in Western European countries various attempts have been made to solve runoff quantity and quality problems. In Japan urban storm drainage is almost exclusively the environmental engineers' domain. Activities in developing countries which would benefit most from improved urban drainage are, regrettably, relatively isolated and lacking. The limitation of the achievements so far must be recognised. The wider application of new principles of urban storm drainage is still awaited, often in parts of the world most in need of improvements in living conditions and human health. Moreover, the exist-
1067
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PETER J. COLYER and BEN CHIE YEN
ence of a nationally co-ordinated research programme does not guarantee, in any country, that better environmental and cost-effective practices will be implemented by drainage authorities actually responsible for construction work and operation. Evidence suggests that getting the research results adopted in general practice is a much harder task than obtaining the results themselves. URBAN HYDROLOGY AND HYDRAULICS--DO WE KNOW ENOUGH? Often it is claimed, particularly in North America, that sufficient basic knowledge is available about the hydraulics and hydrology of urban storm drainage. The papers and discussions in the conference indicated the contrary. For instance, very little is known about the temporal and spatial variations of storm rainfalls. Even less is known about the critical storms that should be used for the design and simulation of future operational conditions of drainage facilities. Only recently have attempts been made to justify scientifically the conventionally used design return period concept on the basis of benefit-cost and risk considerations. In the hydraulic aspects, present knowledge is equally, if not more, inadequate. For example, a practical and reliable routing technique for unsteady sewer flow has not been proven, despite the common knowledge that the Saint-Venant equations can sufficiently (although not exactly) represent the flow. For the approximate techniques such as the various kinematic wave models the significance of the backwater effects have not been systematically assessed. Much less is known about the hydraulics of transition between gravity and surcharge flows in a sewer and about the quantitative hydraulic effects of the manholes and junctions. These and other similar fundamental hydraulic phenomena ought to be understood to ensure the appropriateness of the simplified techniques and models which would be more suitable for practical applications. Neither is enough known about the overland flow. To account for the unsteady nature of the flow and to achieve improvement over Manning's or similar simple formulas, kinematic wave equations have recently been very popular despite the fact that the equations are actually applicable only to rather simple and homogeneous surfaces without significant backwater from downstream. It is now known that for shallow overland flows Manning's roughness factor is far from being constant and the flow resistance is significantly affected by the rainfall. However, little information is available on the quantitative changes of the flow resistance. Worse still, rainfall abstractions, particularly infiltration which is a significant component in determining storm runoff, are often modelled in a rather subjective manner. Urban storm drainage problems were solved, albeit rather primitively and in a less sophisticated fashion,
more than a century ago and earlier, before the development of the rational method. Today with increasing complexity of the drainage and pollution problems of storm waters and improved computational tools, how much should be known and what degree of sophistication is required? MODELLING CAN BE ACCURATE AND SOPHISTICATED--DOES IT HAVE TO BE BOTH? The process of storm rainfall, surface flow, pollution entrainment and transport and unsteady flow in sewers lends itself in a particularly attractive way to mathematical simulation. Each part of this process can be represented by complex mathematical or statistical sub-models, and the more ambitious packages attempt to combine these phenomena into a coherent representation of the total catchment response. Several such packages were presented at the conference, originating in the United States, the United Kingdom, Denmark, Sweden, Turkey and Japan. Although apparently modelling the same phenomena these packages show considerable divergence in their treatment of details and there was, for the user, a somewhat alarming lack of agreement among mathematical modellers about even fundamental aspects of flow routing in pipes. Particular problems occur with handling backwater effects in free surface flow conditions, the representation of head and pressure changes in surchaged flow and the solution of looped networks. Evidently the last work on these subjects has not yet been said. However, alongside this trend towards sophisticated modelling another trend was clearly discernible; towards simplification, a view that many of the mathematical niceties may be irrelevant when it comes to engineering practice and construction. So the conference was also presented with design approaches based on classical unit hydrograph theory, simplified kinematic wave routing and the rational method. The last word on these traditional solution methods has not been said either. Several lessons may be learnt from these apparently contradictory trends. Firstly the requirements for designing new drainage systems are totally different from those for the management and optimum performance of existing systems. The performance criteria for new systems (for example a specified frequency of pipe full flow) may be only loosely defined on the basis of very general socio-economic considerations. High accuracy of discharge prediction may therefore be unnecessary because of the large uncertainties in other aspects of the design process. Consequently the simpler methods are of adequate accuracy. Drainage management, however, may require detailed knowledge of the hydraulic performance of existing systems under specified rainfall conditions. This will probably demand computer modelling of
Current issues and future needs in urban storm drainage surcharged networks. All presentations on this subject referred to high demands for computer storage and time, and difficulties in obtaining numerical stability in representing a process which in reality varies very rapidly. A second lesson is that the computer does not meet all the needs of drainage engineers. At one extreme many designs are still based on manual calculation methods and even in highly developed countries access to digital computers is still limited to the larger design organisations. At the other extreme even medium sized computers are sometimes unable to provide sufficient core for the more complex models of surcharging or water quality phenomena. A third lesson is that with present computer capability and knowledge of the physical, chemical and biological aspects of storm runoff, the development of a single, universal, all-capable computer-assisted mathematical model is most unlikely and impractical, despite the extreme strong temptation to develop such an "all-powerful" model. In addition to the computer limitations, such an "all-powerful" model would have so many options and require so many data that an engineer would be very confused and frustrated in trying to sort out the maze to identify and use the part that he needs. Fourthly the work of the "simplifiers" is based upon a fundamental question: are the field data good enough to support the sophisticated models? Indeed, any model, irrespective of its level of sophistication and objective, should be adequately verified over the entire range of conditions of its intended uses before being introduced for applications. Practically all the presently existing models share the general criticism of inadequate testing and verification. But it is unfair to lay the blame totally on the model developers because very few good data are available to verify even limited aspects of the models. Data requirements were a persistent theme of the conference.
1069
ments which will not have to be repeated as the data bank increases during subsequent years. Secondly a long period of catchment monitoring is necessary to collect data on the low frequency events and to obtain a good knowledge of the flow frequency relationship. This is becoming increasingly important as urban drainage studies are moving into the area of flood-frequency prediction on a statistical basis. Statistical analysis techniques can, of course, increase the benefit of even a relatively short record, but on the whole nothing is as good as an extended data base. Discussions in the conference also illustrated three different aspects of data collection: the temporal extent of the data collection; the spatial extent of the data collection; the type of storm water quantity and quality data to be collected. A distinction may be necessary between funding for research and funding for data collection. A long-term commitment to data collection may be best undertaken by a statutory drainage authority whose future existence and interest can be guaranteed. In this way long term records could be assembled by a permanent central authority for the benefit of both present and future research projects. Maximum use should be made of the data which are obtained at such difficulty and expense. International exchange of urban rainfall-runoff data has already proved beneficial in both Europe and North America. Problems of parameter definition and other aspects of compatibility inevitably arise; the issue of data standardisation is one which the newly formed committee (see below) will have to attend to. S T O R M WATER Q U A L I T Y - - W H A T T O MEASURE AND H O W T O GENERALISE OBSERVED RESULTS
A repeated question on storm runoff water quality is what parameters are important in urban drainage
DATA C O L L E C T I O N - - P A I N F U L BUT ESSENTIAL
Discussion about data collection systems revealed that these are frequently part of a relatively short term research project (2 5 years). Since the first year or more may be consumed in painful experience of instrument malfunctions or incorrect location, it is evident that good data are only becoming available towards the end of the funding period. The data collection exercise may well be terminated just as it is producing its most useful results. Two arguments for changing this situation should be considered. Firstly urban rainfall-runoff data collection projects have very high initial costs; not only the capital costs of instruments and laboratory procedures for, e.g. pollutant identification, but also high initial costs of catchment land use analysis and network surveys. These initial activities yield extremely valuable information about monitored catchw.K
17/9
H
pollution problems and what representative parameter or parameters can be used to indicate the water quality during the storm runoff process. Current and past storm water data collection and analysis projects are site-orientated, isolated cases. Clearly there is a need to categorise and characterise the pollutants based on the rainstorm properties, catchment characteristics, properties of the pollutants and geographic locations. It is possible that through systematic categorising and eharacterising of a sufficient amount of data, perhaps with the aid of regression and dimensional analyses and parameter normalisation, a generalised pollution prediction method can be developed to be used for ungauged or future urban catchments. D O N O T D I S T U R I ~ - I S IT POSSIBLE?
Increasing awareness of the effects of environmental disturbances are apparent. Topics presented included
1070
PETER J. COLYER and BEN CHIE YEN
rainfall acidity, suspended solids and heavy metals, pollution from streets, gullies (catch basins) and storm water overflows, impact on receiving waters and groundwater quality in urban areas. Little was discussed quantitatively on the levels and damages of urban flooding. Increased use of detention storage and semi-permeable urban surfaces were among the methods suggested for tackling the problems of pollution and flooding. Remedy measures usually can restore only a limited range of the original environemnt. It is evident that environmental considerations will have to play a larger part in future drainage design.
FUTURE TRENDS AND NEEDS
Any prediction of the future trends and needs is only conjectural but several trends appear to be evolving. Firstly, storm drainage problems will be attacked in a more complex and comprehensive context than in the rational method era. The new techniques probably will consider both flood mitigation and pollution control, minimising negative environmental impact while maximising the environmental and economic improvement. This new approach may require the incorporation of risk analysis and optimisation techniques in problem solving. Secondly, use of computers in solving drainage problems will be increased. There will be computerbased mathematical models of different levels of sophistication for different objectives of design as well as for simulation, planning and management and suitable for computers of different sizes ranging from pocket computers to large full-size computers. Thirdly, there will be continuous efforts in the collection of good urban storm runoff data of appropriate temporal and spatial resolutions. These data will be used for evaluation, calibration, verification and selection of mathematical models. Systematic and scientific analyses of these data will also provide useful information for applications. Fourthly, with improving living standards, increasing attention to urban storm drainage will be paid in the developing countries where design and development of new drainage systems will continue to be the main concern. Conversely, for developed countries, deterioration, inadequacy in capacity due to urban expansion, and insufficient handling of runoff pollution in existing drainage systems will increasingly become problems. Possibly and ideally urban storm drainage will be considred within the context of a regional water resources development and management programme. A list of some of the more specific topics needing additional research and development in the near future is given randomly as follows: Collection of ;torm water quantity and quality data with well planned programmes in the temporal and spatial domain.
Analyses of the data for characterisation and generalisation and for evaluation of mathematical models. Development of accurate and efficient unsteady flow routing schemes and critical evaluation and comparison of routing schemes. Critical, quantitative and objective evaluation of urban storm drainage mathematical models. Studies on surcharged flow and the transition between surcharged and free surface flows. Studies of the hydraulics of junctions, manholes and gulley pots (inlet catch basins/. Development of improved methods for overland runoff simulation, including two-dimensional surface and gutter flows and better representation of the land surface and of the resistance coefficient for unsteady shallow water flow under rainfall. Development of improved methods to account for abstractions from precipitation, especially infiltration. Studies of the temporal and spatial distributions of rainfalls pertinent to the urban environment. Identification of the representative water quality parameters in urban storm water pollution and characterisation and normalisation of these parameters from local data for general use. Investigation of the need for and significance of modelling the biological and chemical processes in urban storm water transport. Studies of the transport of sediment in urban storm drainage systems. Studies of the storm water overflow and its impact on receiving water quality. Evaluation of the effectiveness of various pollution and flood control measures such as detention storage and porous surfaces. Investigation of the performance and preferability of combined or separate storm sewer systems under different conditions. Collection of data on the costs of construction, damage, and operation and maintenance of drainage facilities and analysis and normalisation of such data for general uses. Incorporation of risk analysis and optimization techniques in the design and management of urban storm drainage. Investigation of operational and maintenance needs of urban storm drainage and consideration of these needs in the design and management of urban drainage. Financial and professional support should be given to all three stages of urban storm drainage technology development, namely, the stages of research, development and evaluation, and implementation. It is almost universal that support of research is difficult to obtain, partly because urban storm drainage is seldom a life-threatening, news-media sensational item. It is equally difficult to find knowledgeable, good and objective evaluations of new techniques or models. It is, unfortunately, even more difficult to receive support for technology transfer of worthwhile new tech-
Current issues and future needs in urban storm drainage niques to practising engineers for field applications. There is a need for coordination and mutual support among research institutions, public agencies and private industries to ensure sufficient support for all the three equally important stages from research and development to implementation of new techniques. FUTURE INTERNATIONAL COOPERATION
Future international cooperation in urban storm drainage consists of several aspects: coordination and exchanges of experiences in the implementation of new technologies; national and international cooperation in data collection; national and international coordination and cooperation in research and development projects; rapid and free exchanges of research experience and technical development among researchers, engineers and scientists at national and international level. The United Nations has declared the 1980s as the International Drinking Water Supply and Sanitation
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Decade. UN should be persuaded to include urban storm drainage as a major theme of the Decade and lend itself, its sister interational organisations and member nations to full support of international cooperation and development in urban storm drainage. In order to promote actively international cooperation in urban storm drainage the Urbana conference proposed that an urban storm drainage committee be established under the joint auspices of the International Association of Hydraulic Research (IAHR) and the International Association on Water Pollution Research and Control (IAWPRC). This has now been achieved and an IAHR/IAWPRC Joint Committee on Urban Storm Drainage has been established. The current chairman is Professor B. C. Yen (U.S.A.) and Mr P. J. Colyer of Hydraulics Research Station Ltd, Wallingford, Oxfordshire, England is the secretary. The Third International Conference on Urban Storm Drainage will be held at G~teborg, Sweden from 4 to 9 June 1984. Further details from IAWPRC in London. The proceedings of the Urbana conference are available from: Water Resources Publications, P.O. Box 303, Littleton, CO 80522, U.S.A.