Trends in hydrological analysis, by M.A. Kohler

Trends in hydrological analysis, by M.A. Kohler

Introduction

Since this meeting has been organized i n com- memoration of the Tercentenary of Scientific Hydrology, it seems appropriate to cite the first analysis involving a comparison of precipitation and runoff (Perrault,1674).

Though the analysis was simple in concept, the results were of profound scientific significance.Such computations are basic even today,since they provide valuable insight into the hydrology of a catchment.

Unfortunately,there are still many basins throughout the world for which we have only very limited information on precipitation, runoff and the relation between the two.

Hydrology is one of the newer recognized geophysical sciences

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scientists in the field in addition to those involved in the application of hydrology to water management,agriculture etc.

Since the development of hydrology has been so closely tied to practical applica-

tions and the theme of this paper is centred on trends in methods of analysis,a review of problem applications is appropriate.Examples are :

a) Reservoir design

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b) Design flow capacity for bridges, storm sewer systems,etc. ,

c) Predicting effects of land-use changes on streamflow,

d) River and lake forecasts for warning purposes and to meet a host of operational problems,

e) Water supply forecasts for water

management and agricultural operations, f) Recharge and yield of groundwater

aquifers,

g) Effects of influent pollutants on water quality,

h) Flood plain mapping

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specified frequency.

Although Perrault's studies are relevant to estimates of average water supply and evapotranspiration,most problems require analysis of temporal variations in flow, sediment transport,and other elements; of the frequency of occurrence of specified or selected values or events;and of the effects of changes in existing conditions.

The urgent need for solutions to problems such as those listed above with limited data and resources led to the development of some rather simple techniques and

methods which are in some respects ingenious and in some cases are still in use.At the same time,expedience often led to reliance on formulas and techniques having little scientific basis

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Factors affecting trends in hydrological analysis

There are a number of factors which have resulted in changes in analysis techniques in the recent past and will probably continue to do so.The more important are discussed below.

Electronic computers

Perhaps the most important single factor in bringing about changing methods of

hydrological analysis is the introduction of the electronic computer.Since a major part of present-day research relies heavily on computer access,it is obvious that the trend will continue for some time in the future.Both analogue and digital computers are used in hydrological analysis,although use of the latter is and will probably continue to be far more widespread.Analogue computers are used principally in the simulation of flow in groundwater aquifers.

The development and application of most present-day conceptual streamflow models would verge on the impossible were it not for the digital computer.The importance of such models as a research tool is not to be overlooked,but their application is becoming widespread in dealing with an

increasing number of problems.Models are particularly valuable in rendering a fore- cast service;they serve to extend stream- flow records, thus improving the reliability of frequency ana1yses;and they are effective tools for evaluating land use practices, the results of cloud seeding,and other influences of man.

The terms "conceptual hydrological model"

and "catchment model" are usually cons trued to mean a model for simulation of the discharge hydrograph.They normally simulate othereelements such as soil moisture and actual evapotranspiration.Since sediment transport,water temperature,and other aspects of water quality are highly interrelated with stream discharge,flow models become a basic part of more complex models for the simulation of these elements.Computers are required for the development and application of such models.

Traditional methods of streamflow (or storage) routing neglect the dynamic effects on wave movement.Since these methods are sufficiently accurate for most purposes on the typical river reach,they will continue to be used for some time in the future.

There are,however,complex reaches (estuaries, multiple channels,etc.) where the neglect of dynamic effects is not acceptable.The basic concepts involved i n dynamic routing are not new,but their practical application was not achieved until computers became available.Much remains to be done in improving the techniques of application, however.

to hydrological problems was extremely limited until the advent of the computer made possible the development and use of more sophisticated techniqueS.If the esti- mation of design storage for a single reservoir requires 1000 traces of annual flows,each as long as the expected useful life of the project (Burges,1970) ,it is apparent that the analysis must be made on a computer.The reqairement is even more obvious in the case of multiple reservoir systems.Most stochastic analyses to the present time have assumed a Markov process in which any event is dependent only on the event immediately preceding it.Extensive studies (Hurst,l951) indicate that there is long-term persistence in natural time series which negates the Markov pr0cess.A

The application of stochastic methods

number of investigators (Box and Jenkins, 1970; Mejia,et a1.,1972 Mandelbrot and Wallis,1972) have suggested techniques for taking into account the "Huts t phenomenon", but the circumstances under which there is need for doing so are not yet fully estab- 1ished.The issue is raised here only because of the implications regarding future trends in hydrological analysis.

In the past,the operation of most

reservoirs and other water control structures was based on one or two parametere and/or a simple rule curve.It has not been uncommon to find a flood control reservoir operated on the basis of observed inflow at a single upstream station,or the reservoir contents and season of the year.The basis for sched- uling operations frequently has been exceed- ingly unrealistic in terms of optimizing the over-all benefits of the structure(s).The advent of computers has multiplied the possibilities for taking into account rele- vant factors in developing plans of operation and in applying the procedures.With access to a suitable computer and taking advantage of other developments discussed subsequently,

it will be feasible to optimize operations to an extent which was inconceivable in the past (Jamieson,l972).

Concern for preservation of the environment Preservation of the environment is a cause of increasing concern to the peoples in all parts of the world.It was this widespread concern which led to the United Nations Conference on the Human Environment (Stockholm,June 1972) and the subsequent establishment of the United Nations Environ- ment Programme (üNEP)

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Most agencies of the United Nations family have relevant programmes and there is little doubt that international aspects will be pursued at an accelerating rate for many years to come.Nationa1 efforts to minimize the degradation of the environment by man's activities vary from country to country because of circumstances,but many nations now have strong regulations and major programmes to maintain and/or improve water quality in streams,lakes,estuaries and ground-water aquifers.0ther nations will undoubtedly find it necessary to take action along these lines in the near future.

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M. A. Kohler

This trend of concern for the environ- ment has profound implications with respect

to hydrological analysis.Sound techniques are required to determine the environmental impact downstream from any proposed project or plant effluent,and operating schedules must be designed carefully to minimize adverse effects.If water quality is to be controlled,then it must be monitored and predicted along with water quantity,it must be taken into account in project design studies,and a warning service will likely be needed in some cases.

considered to be an aspect of water quality and the discussion in the preceding paragraph is in most respects applicable to water temperature,chemical quality and biological quality.Water temperature has added signifi- cance,however,since it becomes involved in water quantity studies (evaporation) and in studies pertaining to ice.

Water temperature is customarily

SpiraZZing food and energy demands

Much has been written concerning the expand- ing population of the world and predicting major deficiencies of food and energyarn fact, the terms "food crisis" and "energy crisis" cire much used in recent times to describe current conditions in some parts of the world if not for the whole.Dwindltng petroleum and coal supplies,and the fact that these resources will have increased use for purposes other than energy,dictate that any renewable energy resource be used to the maximum faasible extent.

Satisfying the increasing demands for food and energy will most certainly require optimized use of water for power and irriga- tion.There will be Ereat stress on efficient water management th;ough improved science and its application.This wlll lead to increas ed support of hydrological research and ser- vices,and to new and more costly methods of hydrological analysis.

Increasing population and coincident dwindling resources have a secondary impact in that the pursuit of resources and

improved living conditions lead to geograph- ical expansion into environments which are less understood and for which basic hydro- logical and meteorological data are scarce or

reserves on the north slope of North America is a case in point.The establishment of

communities and the construction and operation of pipelines and other facilities in areas with adverse climate and largely void of environmental data presents a host of hydrological problems.The problems are even more formidable if high priority is given to preservation of the environment.There has been substantial stress in recent years on

the development of hydrological analysis techniques for application where basic data are inadequate by usual standards to meet requirements in developing countries.It is evident that such techniques will be required for many years to come as man's activities expa1.d into new areas of the world.

Chanf~ing meteoroZogica

Z

It W ~ I S pointed out that hydrology tended to be dicpersed among the sister sciences in years past.This was particularly true in the case of meteorology,and,in fact, the two sciences are inseparable even today.For example,studies of ptecipitation,snow cover and evaporation are reported in journals of meteorology and hydrology.Weather forecasting and modification are central to the science of meteorology,and it Ps these activities which are treated here ^~

Precipitation and those meteorological elements influencing evaporation and snowmelt serve as input to hydrological models for simulation and prediction of streamflow,water quality,sediment discharge,ice formation,etc.

Any improvement in the reliability of these input data will result in more accurate hydro- logical forecasts and more efficient water management operations.Although discussion of

the possibilities of more reliable weather forecasts is beyond the scope of this paper,

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both in design and operations.With respect to operations,this implies integration or close coordination between meteorological and

hydrological services to facilitate rapid exchange of information.

It is not uncommon , in es timating the

benefits of a proposed water resources project, to assume that the inflow hydrograph is known

scheduled accordingly.0ther aspects of design, such as the spillway capacity ,may assume complete absence of knowledge of impending flows.Al1 aspects of design should reflect operations based on realistic appraisal of forecast accuracy and the advantages in following such practices will increase as skill in the quantitative prediction of weather elements improves.

ant water supply is a principal objective of experimental and operational weather modifi- cation activities today.The degree to which these activities have or can augment natural precipitation or influence the areal distri- bution is still a subject of debate,but we cannot rule out the possibility that future weather modification operations will be sufficiently successful to affect the design and operation of water resources structures and systems.Additionally,hydrological analysis should play a more important role in evaluat- ing the success of weather modification experiments and in determining the environ- mental impact of anticipated effects.

Evaluatiq the impact of grandiose proposals for inducing major climatic changes (such as those pertaining t-o the polar icecaps) will also require sophisticated hydrological analysis if they are to be pursued.

Augmentation of precipitation and result-

€hanging data collection systems

Data collection systems and their impact o n future developments in hydrology are dis- cussed in a companion paper at this symposium (Rodda,1974).It will suffice to cite here the relevant changes in data col- lection systems which are anticipated and discuss the implications with respect to

trends in hydrological analysis.

Improvements in instrumentation and data processing are expected to continue,but they will not have a major influence on methods of hydrological analysis.More accurate observations will,however,enhance the results of the analysis and future develop- ments are likely to facilitate observations under the adverse conditions existing in some areas.The development of instruments for elements heretofore unmeasured could have a decided effect on hydrological analysis,particularly in the area of water quality.It may be noted,for example,

that soil moisture and actual evapotrans- piration are simulated in catchment models in the absence of suitable observations.

Rodda states that real-time networks will provide a wider tange of data more

frequently and from more sites than hitherto.

The implications of this projection with respect to hydrological analysis are of some importance.Justifiab1e detail of analysis tends to increase with station density and frequency of reports,and thus may even influence the selection of a model for application.Improved forecasts should result and forecasts for smaller catchments would become feasib1e.h the future,it will become incumbent on those responsible for the design and operation to take advantage of the benefits to be derived from real- time reports.To do so will require exten- sive,sophisticated analysis.

sending and imaging systems (radar,satellite, aerial surveys) is stili in a preliminary stage of development.The quantitative application of such systems to hydrology is very limited,but this will not be the case in the future.The analysis for application need not be complex,but the development of techniques for compression of immense quantities of data into manage- able proportions and with minimum loss of information is a key requirement.There is also the problem of refining the data to filter extraneous effects.For example,the intensity of the radar return signal is largely a function of precipitation intensity and the time integration of the scope usually yields a reasonably good pattern of storm precipitation.However, the scope brightness is also affected by a number of other factors such as drop-size distribution,attenuation by precipitation along the path traversed,ground clutter and anamalous propagation.Techniques are needed which will automatically integrate the digitize the return signa1,modified to take into account such extraneous effects (Kessler and Wilk,l968;Flanders,l969).Alternatively, the precipitation pattern derived from radar data can be modified on the basis of point measurements.

Hydrological analysis involving remote-

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M. A. Kohler

Basic research

Research across a broad front,including hydrology and other geophysical sciences,will result in new knowledge applicable to the field.It may be expected that continuing research will have a decided influence on trends in analysis.Specu1ation in this regard is not warranted,but it is to be hoped that hydrologists will be diligent in applying

the results of research conducted in other scientific fields.

It was pointed out in the introduction that the development of hydrology has been pursued largely by engineers and others to solve practical problems but that there are growing numbers of scientists pursuing more basic avenues of research.There is a tendency for the engineer to conclude that the results of basic research are not applicable to his problems and for the scientists to complain that the fruits of his research are not being applied.Trends in hydrological analysis will be highly dependent upon the effectiveness of communication between the two groups.

Improved communications and understanding in this regard are necessary if hydrology is to continue to develop and properly serve the needs of the world in the future.

Conclusions and swrunazy of future trends The application of computers in hydrology will continue to increase.This is necessary if w e are to use fully present-day knowledge and to follow indicated avenues of research.

Access to more powerful and versatile compu- ters will lead to the development and applica- tion of models for the simulation of stream- flow,sediment transport,water temperature and other aspects of water quality which are more in accord with scientific concepts.

Models for simulating the full hydrological cycle,thus accounting for the feedback between hydrological and meteorological models now in use,are not beyond the realm of possibility.

Dynamic routing techniques will be further developed and applied,and the same is true for stochastic methods

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Concern for preservation of the environ- ment will dictate that greater emphasis be given to water quality aspects of design and operation.Sound techniques must b e developed and used to evaluate the impact of proposed projects and procedures of operation.

Spiralling food and energy demands will lead to stress on efficient water management through scientific research and application of the best available analysis methods.This will mean that project design must be based on operating plans which take full advantage of advances in real-time networks and fore- cast accuracy,and that operations must optimize the benefits of the system.

sing,storage,exchange,analysís and retrieval of data for water management,certain

conclusions come to light because of inter- relations among the various activities.For optimum benefits from a reservoir,the controlled reseases must reflect the

anticipated inflow,and the downstream flows cannot be predicted until the scheduled releases from the reservoir have been

decided upon.This feedback between forecaster and operator must take place for each point of control in a river basin.

affecting water management operational decisions,and the problem is obviously more complex in the case of multipurpose struc- tures.When a series of reservoirs is operated as a system,it becomes necessary to make successive approximations to the operations schedule and the corresponding predicted

flows.

Taking into account all elements of control and the increasing significance of water pollution,a unified and computerized approach will become annecessity in the highly developed rivers of the world in the

future (Kohler,l970).Arrangements whereby a number of water management agencies make independent operational decisions with no attempt to optimize benefits of the system will be entirely unacceptable in the future.

There must be a centralized data bank and processing complex where hydrological, meteorological and other relevant data are continually updated as rapidly as possible

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where operations schedules are made on the basis of forecasts and "programmed decisions"

In other words,all required coordination would be achieved in the logic of the com- puter programmes and not through discussion at each whim of nature.The analysis and programming requirements under these arrangements for a large,highly developed river system are formidable.

If a broad view is taken of the proces-

There are usually a number of factors

Re ferences Kessler,E.,Wilk,K.E.1968.Radar measurement of Box,G .E .P., Jenkins ,G .M. 1970 .Time series

precipitation for hydrological purposes.

(WMOfIHD report no.5)

analysis :forecasting and control. San Kohler,M.A.l97O,Hydrospheric research leading Francisco,Calif.,USA.,Holden-Day. to improved water management.A century of Burges,S.J.1970.Use of stochastic hydrology weather progress,p.ll-17.Boston,Mass.U.S.A.,

to determine storage requirements for American Meteorological Society.

reservoirs- a critical analysis.Progrm Mandelbrot,B.B.,Wallis,J.P.1972.Com~uter in Engineering-Economic Planning, experiments with fractional Gaussian Report EEP-34.Calif.,USA,Stanford Uni- noises.Water Resources Res.,no.l,p.228-

versi ty

.

for weather radar data.(WMO/IHD report Streamflow simulation: 2-Broken line

110.9). process as a potential model €or hydrologic

simulation.Water Resources Res.,no.4,p.931- reservoirs .Trans.Amer.Soc. Civil Engrs, 941.

p. 770-808.

1-Operating multipurpose reservoir systems for water supply and flood alle- viation. Water Resources Res. no .4 ,p. 899-

903. hydro1ogy.Tercentenazy of Scientific

Flanders , A. F. 196 9, Hydro logical requirements Mej ia ,J * M * ,Rodriguez-Iturbe I ,DawdY l9 ⁹

Hurst,H.E.1951.Long-term storage capactty of

Perrault ,P. 1674, De 2 'orígine des fontaines.

Jamieson,D.G.l972,River Dee Research Programe: Paris.(English translation by A.LaRocque, New York,Hafner Publishing Company,l967).

impact on the future development of fiydrology.Paris,ünecco (in press).

Rodda,J.C.1974.Data collection system and their

Trends in hydrological analysis, by h1.A. Kohler

Abstruct

Perhaps to a greater extent than is the case for most other natural sciences,advances in hydrology have been sporadic.

Hydrology was dispersed among sister sciences for decades, and once generally recognized,its development was largely contingent upon the needs of engineers and others to solve practical problems involving hydrology.Advanced training for hydrologists,per se,is only now becoming available in relatively few countries of the world.

The electronic computer has brought about new approaches to hydrological analysis and has led to the development of conceptual models which treat many of the varied and complex processes affecting the streamflow hydrograph.Grow1ng concern for our environment is now bringing about a new dimension to hydrology

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can lead to more efficient water management,but taking advantage of this opportunity will require new techniques of analysis applicable to project design,hydrological forecasting and operations.

The paper discusses changing requirements and anticipated trends i n hydrological analysis during the next two or three decades.Factors considered in the projections include (a) the role of the electronic computer;(b) concern over preservation of the environment;(c) spiralling food and energy demands;

(d) meteorological aspects;(e) trends in data collection systems;

and (f) basic research.It is concluded that the design of future water resources projects will be more closely keyed to optimized plans of operations,and that forecasts and operation schedules must be derived through an iterative procedure for the highly developed rivers sytems of the future.If these conclusions are substantiated,the analysis and programming requirements are foimidable by the standards of today.

M. A. Koliler

Les tendances de l'analyse hydrologique,

par M.A. Kohler Rt;sLiiizr

Dans une mesure peut-être plus grande que ce n'est le cas pour la plupart des autres sciences naturelleS.les progrès réalisés en hydrologie ont été sporadiques.L'hydro1ogie a été,pendant des décennies,dispersée parmi d'autres sciences qui lui sont proches et,une fois son caractère propre généralement reconnu,son évolution est restée largement dépendante des besoins des ingénieurs et d'autres utilisateurs ayant à résoudre des problèmes pratiques dans lesquels intervient 1'hydrologie.Une formation d'hydrologues au niveau supérieur en tant que telle commence seulement maintenant à être dispensée dans un nombre relativement faible de pays.

L'ordinateur électronique a apporté avec lui de nouvelles manières d'aborder l'analyse hydrologique et a conduit à la mise au point de modeles conceptuels qui permettent de traiter un grand nombre des processus variés et complexes qui inter- viennent dans les hydrogrammes d'écoulement.Les préoccupations croissantes concernant notre environnement donnent aujourd'hui une nouvelle dimension à l'hydrologie

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La présente communication porte sur les modifications des besoins et sur les tendances prévisibles en matière d'analyse hydrologique au cours des deux ou trois prochiiines décennieS.Les facteurs examinés dans ces projections copprennent: (a) le rôle de l'ordinateur électronique;(b) les préoccupations concernant la sauvegarde de l'environnement;(c) l'augmentation vertigineuse des demandes de denrées alimentaires et d'énergie;(d) les aspects météorologiques;(e) les tendances en matiëre de systèmes de rassemblement des données, et (f) la recherche fondamentale.

I1 est indiqué en conclusion que la conception de futurs projets de valorisation des ressources en eau sera plus étroitement axée sur des plans d'opérations optimalisés,et que les prévisions et les programmes d'opérations devront être calculés selon un procédé d'itération pour les systèmes fluviaux hautement développés de 1'avenir.Si ces conclusions sont justifiées,les besoins en matière d'analyse et de

programmation seront immenses par rapport aux normes d'aujourd'hui.

Tendencias del aiidisis hidrológico, por M.A. Kohler

K C9111116'11

Los progresos de la hidrologia se han producido siempre con un caracter mucho más esporádico que el que puede aplicarse a la mayorfa de las demás ciencias naturales .Diirante muchos decenios la hidrología ha estado dispersada dentro de otras ciencias conexas y,desde el momento en que fue considerada como una disciplina aparte,su desarrollo dependi0 de la necesidad que los ingenieros y otros especialistas tenfan de resolver

problemas prácticos relacionados con la hidrologfa.La formación superior de hidrolog<a,como ciencia independiente.so10 se practica actualmente en muy pocos paises del mundo.

planteamientos del análisis hidrológico y ha motivado la creación de modelos conceptuales para estudiar muchos de los variados y complejos procesos que afectan al hidrograma de las descargas.

El creciente interés que se manifiesta por nuestro medio ambiente viene a dar una nueva dimension a la hidro1ogfa:el estudio y predicción de la calidad del agua.Es evidente también que el progreso de los sistemas de elaboración de datos permitirá

La calculadora electrónica ha permitido aplicar nuevos

crear redes automáticas de observación en tiempo real para la ordenación de los recursos hfdricos en gran escala.La

disponibilidad de datos actuales puede traducirse en u n -

aprovechamiento 6 s eficaz del agua,aunque para poder beneficiar- se de esta oportunidad será preciso utilizar nuevas técnicas de analysis que sean aplicables a la elaboración de proyectos, a la predicción hidrológica y a las actividades prácticas.

y tendencias previstas referentes al análisis hidrológico en los proximos dos o tres deceniaS.Entre los factores previstos figuran: (a) la función de las calculadoras electrÓnicas;(b) el interés en conservar el medio ambiente;(c) las demandas de alimentos y energfa; (d) los aspectos meteorológicos: (e) las tendencias de los sistemas de concentraci& de datos; y (f)la investigación b8sica.Se llega a la conclusión de que la elabora- ción de los futuros proyectos hídricos este' dirigida principal- mente a obtimizar los planes de operaciones y de que las

predicciones y programas de actividades han de ser necesariamente deducidos mediante un procedimiento iterativo,en lo que se refiere a los futuros sistemas fluviales mas.desarrollados.Si estas conclusions son correctas,no tenemos mas remedio que admitir que las exigencias de análisis y programmaci& resultan enormes si tenemos en cuenta los criterios actuales.

En este documento se estudian las nuevas necesidades

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M. A. Kohler