Trends and directions in hydrology

189 Pages·1986·18.95 MB·English

Collected Reprint Series
Trends and Directions in Hydrology
American Geophysical Union
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Copyright 1986 by the American Geophysical Union
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CONTENTS
Chapter 1: Trends and directions in hydrology
Stephen J. Burges .................................................................................................................................................1S
Chapter 2: The emergence of global-scale hydrology
Peter S. Eagleson ..................................................................................................................................................6S
Chapter 3: Scale of fluctuation of rainfall models
Ignacio Rodríguez-Iturbe ...................................................................................................................................15S
Chapter 4: Catchment-scale evaporation and the atmospheric boundary layer
Wilfried Brutsaert ...............................................................................................................................................39S
Chapter 5: Looking for hydrologic laws
James C. I. Dooge ..............................................................................................................................................46S
Chapter 6: Classification of seasonal snow cover crystals
S. C. Colbeck .....................................................................................................................................................59S
Chapter 7: Modeling alluvial channels
David R. Dawdy and Vito A. Vanoni ..................................................................................................................71S
Chapter 8: The “physics” of soil water physics
Garrison Sposito ................................................................................................................................................83S
Chapter 9: Water flow and solute transport processes in the unsaturated zone
D. R. Nielsen, M. Th. van Genuchten, and J. W. Biggar .......................................................................................89S
Chapter 10: On the simulation of nonaqueous phase organic compounds in the subsurface
George F. Pinder and Linda M. Abriola .............................................................................................................109S
Chapter 11: Statistical theory of groundwater flow and transport: Pore to laboratory,
laboratory to formation, and formation to regional scale
Gedeon Dagan ................................................................................................................................................120S
Chapter 12: Stochastic subsurface hydrology from theory to applications
Lynn W. Gelhar ................................................................................................................................................135S
Chapter 13: Use of systems analysis in water management
Peter P. Rogers and Myron B. Fiering ................................................................................................................146S
Chapter 14: Flood estimates: How good are they?
Ray K. Linsley ...................................................................................................................................................159S
Chapter 15: Bridging the gap between flood research and design practice
David H. Pilgrim ..............................................................................................................................................165S
Chapter 16: Dilettantism in hydrology: Transition or destiny?
V. Klemeš .........................................................................................................................................................177S
WATER RESOURCES RESEARCH, VOL. 22, NO. 9, PAGES 1S-5S, AUGUST 1986
Trends and Directions in Hydrology
STEPHEN J. BURGES
Departmento f Civil En(cid:127)lineerin(cid:127)lU, niversityo f Washin(cid:127)ltonS, eattle
INTRODUCTION The first paper, by Peter Eagleson,d ealsw ith the emergence
During my last year as coeditoro f Water ResourceRs e- of global-scaleh ydrology, a study that is possibleo nly because
searchI, undertooka projectw hichc ulminatedin this volume, of advancesm ade in the last 40 years in computational devices
the first comprehensivsep eciails suein the 22-yearl ife of the and in broad-scale observational instruments that can record
journal. The decisionto preparea speciali ssueo f invited selectedh ydrologic and vegetals tatesr emotely. Eagleson[ this
papersr esultedfr omd iscussionwsit h a numbero f individuals issue] points out that for the last century the developmento f
and my assessmentht at a need existedt o provide greater hydrology has been largely the results of efforts by civil and
coherenceto the study of hydrology.T here have been other agricultural engineers.T he nature of the problems addressed
attemptsin the lastd ecadeto places pecifiacs pectos f hydrol- by those groups, water supply and hazard reduction, dictated
ogy into perspectivOe.n e notablee ffortw asb y Myron Fier- the catchment scalea s the unit for study. This scale has been
increased to distances on the order of 10 3 km now that electric
ing, who askedc olleaguetso write on the scientificb asiso f
water resourcem anagemen[tU .S. NationalR esearchC ouncil, energy production interties are practicable.E ngineersn eed to
198(cid:127)].W hilet hep apercso ntaineidn thec urrenvt olumed o considerd rought phenomenaa nd effectsa t widely spacedl o-
not have as extensivea subjectb ase as those in the earlier cations.P rogressi n this area has been realized through exten-
work, they do addressm any importantt opicsi n hydrology. sion of traditional approaches (see, for example, Leytham
The 19 authors who have contributedt o the 15 papersi n this [1982]). Eaglesone mphasizesth e needt o examinep henomena
volume have, collectively,o ver 500 years of professionael x- at this and larger scales using complex land surface-
atmosphericc oupled systemst hrough a perspectiveo f global
perience.
From time to time we have all had the pleasureo f attending scale that is more in accord with the traditional view of a
a stimulatingl ecturet hat placeda n entire disciplinei n per- geophysicisrt ather than that of a problem solvingp ragmatist.
spectiveO. ften the publishedv ersionso f suchp resentationsA strong case is made for use of global climate models for
have had limited circulationa nd many who could have bene- examining,a t least in a qualitative sense,t he impact of large-
fited from readingt hemh aven ot had that opportunityT. his scalea nthropogenicc hange,p articularly to ground cover. His
issue of Water ResourcesR esearchc ontains papers of this observations,c oupled with his detailed work on climate-soil
generasl tyle.W e hopet hat thisi ssuew ill be read widelya nd vegetation systemso ver the past decade, might provide the
servea s an inspirationt o newcomertso hydrologya s well as basis for a union of climate models and satellite images of
to colleaguesw ho undertaker esearche nquiry remotef rom vegetative cover time-spacev ariations on a continental scale.
their previouss tudiesa nd expertise. The spatial resolution of climate models remains crude, reflec-
When I invited contributions, I indicated that I was not ting restricted data collection and recording capability as well
as limitations of the computing power of sequentialv on Neu-
concernedw ith overlap becaused iffering assessmenwt ould
add to the overall richnessA. ll participantsw ere invited to be mann computers. Spatial representationl imits will become
philosophicala nd reflective,a nd to share personali nsights lessi mportant with the advent of enhancedr emote measuring,
imaging, and recordings ystemso f precipitation and evapor-
that may, admittedly,s till be speculativeT. he commentst hat I
receivedf rom most reviewersi ndicated that they thought of ative fluxesa nd vegetalc over and use of sophisticatedp arallel
processorc omputer architecture.E aglesonh as made an elo-
the papersa s "review papers."I believet hat thesep apers go
quent statemento f researchn eedst hat presenta challengef or
well beyondn ormal reviewp apers.
Severals ubfieldso f hydrology are not included.N everthe- generationso f hydrologists.
The second paper, by Ignacio Rodriguez-Iturbe, con-
less,I anticipatet here is much food for thought for the spec-
trum of readers of the journal. Since no specifict heme was centrates on precipitation modeling at different scales.
Progressi n this endeavor,c ombinedw ith progressi n depict-
adopted, each author was invited to write on any subjecto f
ing the other major atmospherich ydrologic flux (evapotran-
his or her choice. Each paper reflectst he individual experi-
enceso f its authors, who have tended to emphasizea reas of spiration), is essentialf or improvement in predicting hydro-
enquiry or activity that have occupiedt hem for significant logic phenomena throughout a catchment. Mathematical
treatmento f rainfall fieldsr ather than analysiso f rain gouge
periods.
data alone is a relatively recent activity by researchh ydro-
SUMMARY OBSERVATIONS logists.R odri(cid:127)luez-Iturbe[t his issue]p lacesi n perspectived e-
velopmentst hat have occurreds incea bout 1980 in temporal
The order chosenf or presentationo f the papersf ollows an
approximate systematich ierarchy that encompassessc ale in point rainfall models,a real storm rainfall models,a nd three
dimensionals pace-times tructureso f rainfall fields.T he latter
hydrologice nquiry,t ies researcha reast ogether,c ommentso n
the state of practice,a nd finally, indicatest he need for a clear topic buildso n the pioneeringw ork of Waymiree t al. [1984].
Rodriguez-Iturbep resentsa strong case for organizing the
identity for hydrology.
mathematicalr epresentationo f rainfall structuret o reflectn at-
Copyright 1986 by the American GeophysicalU nion. urally occurringh ierarchiesfr om small mesoscalea reast o rain
bandsto synoptidci sturbancHese. emphasiztehsa t desired
Paper number 6W0342.
0043-1397/86/006W-0342505.00 measurementso f the physical phenomenono f interest are by
2S BURGES' STATUS AND DIRECTIONS OF HYDROLOGY
necessityi ndirect. Becausev alidation of suitable models of David Dawdy and Vito Vanoni examine one of the most
precipitation phenomenaw ill be based on indirect observa- difficult subjectsf aced by hydrologists,g eomorphologistsa, nd
tion, a new and difficult classo f inversep roblemsm ay await engineers't he modeling of alluvial channels.W hile the plan
US. form of river channelso ccupiesa bout 1% of a catchment's
Evaporativef luxese qual some6 0% of the influxest o catch- area, river channels are the hydrologic concentration center
ments, but seldom are measurementsm ade at catchment scale. for the catchment, where water and sediment yielded by the
From the perspectiveo f soil moisture changes,e vaporation catchmenta ccumulate.T ime scalest hat require hydrologic
phenomenaa re a low-frequencyp henomenonr elative to rain- (mass conservation)t reatment throughout the bulk of the
fall influxes.S ignificanti mprovementsi n our ability to model catchment become small enough to require fluid mechanic
catchmentr esponsetso precipitationw ould resultf rom en- treatment of the water-sediment mix that constitutes channel
hanced understanding,e stimation, and measuremento f evap- flow. From fluid mechanicc onsiderations,s ediment transport
orative fluxes.W ilfried Brutsaerte xaminesr egionala nd catch- in rivers is a demandinga rea of representation.T he flow phe-
ment scalea spectso f techniquesfo r estimatinge vaporationI.n nomena are three dimensional in space and the air-water
keeping with the first two papers in this volume, Brutsaert interface introduces additional complications. The nonfixed
posest he questiono f what scaleo f parameterizationo f evapo- channel,waterb oundary and the mixture of sedimentw ith
ration phenomena, consistentw ith available and measurable water createsa s complicateda problem as one might envision.
data, is appropriate. Brutsaert [this issue] demonstratest he Variations in river bed form, particle size distribution and
limitation of point processe stimation schemesa nd recom- shape, and the nonuniformity of channels complicate the
mends exploration of appropriate integrative schemes.H e problem further. Dawdy and Vanoni [this issue] examine
arguesf or atmosphericb oundary layer schemesth at require modelsth ath aveb eend evelopefdo r thep urposoef predicting
more completeu nderstandingo f turbulent transport mecha- sedimentt ransport. Most suchm odelsw ere developedf or en-
nismst han is available currently. Brutsaert'sr equirementsf or gineeringd ecisionm aking and reflectt hat backgroundr ather
improved representationo f catchment-scalee vaporative flux than integrativeg eophysicanl eeds.D awdy and Vanoni stress
are neededf or advancesi n hydrologicd escriptiona nd predic- that fundamental improvementsi n understandings ediment
tion. motion, bed armoring, and net scour and fill at a channel
Dooge [this issue] makes extensiveu se of analogy to ex- sectiona re neededa nd ultimately shouldb e incorporatedi nto
plore one area of fundamental concern: the searchf or hydro- models.A ppropriates chemesfo r representingb ank erosiona s
logic laws. Dooge leads us through physics,c entral tendency well as hydraulica nd sedimentf lux boundaryc onditionsa re
statistics, Weinberg's laws for complex systems, and ap- critical to successfusl edimentt ransport models.T he authors
proachest o the study of water where he considerst he impor- hope that a modelw hichi ncorporatesth e essentiapl hysicso f
tance of scale and the search for hydrologic laws at mac- each part of the sedimentt ransport processc, onsistentw ith
roscale.B y way of illustrating the searchf or hydrologicl aws, ability to obtain relevant field data, will provide improved
he examinesd evelopmentsin flood hydrology and particularly sedimentt ransportp redictivec apability.
the need for estimation of extreme floods, beginning with In contrast to the first six papers,w hich discussis suesr elat-
suggestionsm ade by O'Connell [1886]. Doog½n otes that the ing to surface hydrology, the next five are concernedw ith
state of our understandingo f underlying ½atchmentl aws is subsurfacep henomena.G arrison Sposito starts his paper on
similar to that of thosec oncernedw ith pipe or open-Channel "soil-water physics"w ith a delightful quotation from Nobel
flows before development of Reynolds and Froude criteria. laureatep hysicistR ichard Feynman;i t setst he tone for his
More effort needst o be directed toward determinationo f hy- treatment of soil water physicsf rom the formal beginningso f
drologic criteria, similar to those of fluid mechanics,w hich the subjecat s studiedb y Edgar(cid:127) Buckinghamin 1905t o the
have so far eludedu s but are necessaryfo r hydrologicc lassifi: present.W ater movementi n the unsaturateds oil zone and the
cation schemes. sta. te of the unsaturated zone dictate many hydrologic flux
Colbeck[ this issue] presentsa classifications chemef or sea- phenomena.M anagement of the water in this zone has enor-
sonal snow cover crystals. Snow hydrology practice relies mous economici mpactsf or agriculture;t he partially saturated
heavily on empirical relationshipsw, ith surrogatei ndicese m- zone dominatess ilviculture.D espite the economics ignificance
ployed to estimates nowmelto r ablation. Problemsr elated to of this zone, Sposito[ this issue]n otes,i n his review of histori-
scale in describingp recipitation fields may be comparable to cald evelopmenints t hed escriptioonf thep hysicosf fluidf low,
those neededf or describings now accumulation,m elt, and ab- that most of the applicable physical phenomenah ad been
lation. Point processi ntegration methods that might be used formalized mathematicallyb y Richards in 1931. Sposito indi-
in snow hydrology are complicatedm arkedly by topographic cates that fundamental issuesr elated to Richard's equation
variations,s now morphologicalc hanges,a nd energyi nput po- remain to be exploreda nd identifiesf our areas that require
tential variations throughout snow-coveredc atchments.M any detailed study to aid in unifying this broad field; they are
schemesc an be used to classifys now cover crystals;i t is un- similarity, internal energy balance consistentw ith Richard's
likely that any one scheme will gain universal acceptance equation,c oupledh eat and water flow representationth at is
among geophysicistsh, ydrologists,a nd engineersT. he scheme self-consistenatn d verifiablee xperimentally,a nd relationships
proposedb y Colbeck shouldp rove to be versatile,p articularly between microscopic( molecular behavior) and macroscopic
as remotely sensedp roperties of snow cover are used to de- soil water transporte quations.T heseq uestionsr epresentb asic
scribes pecificf eatureso f the state of a snowpacka nd thus for levelso f enquiry,a nd demandc onsistenat nd rigorousi nvesti-
predicting melt and ablation. Two levels of classificationa re gations.
provided' one for simple,p ractical classificationa, nd a second, While SpositoI -thisi ssue]c onsideredc oupledt hermal-water
more general classification,t hat meets the needs of both re- flow in the partially saturatedz one, Donald Nielsen, Rein van
search and practice. Colbeck notes that the classification Genuchten,a nd JamesB iggar considerw ater flow and chemi-
scheme will need to be revised as knowledge of snow meta- cal and biological transport in the unsaturated zone. Their
morphism increases. perspectivea nd theme [Nielsen et al., this issue] is
BURGES: STATUS AND DIRECTIONS OF HYDROLOGY 3S
to many other aspectso f hydrology; specificd isciplinaryr e- and provides a unified statistical approach to describe flow
searchb y hydrologistss, oil scientistsg, eochemistss,o il micro- and transport at these three levels. The major differences
biologists,a nd others has precludede ffectivei nterdisciplinary among the three scales are elucidated through use of the
approachest hat might have led to better representationsa nd theory of spatial random functions. Dagan concludes by
prediction of flow and transport in the vadosez one. The nub noting that the statistical approach to porous media flow is
of the problem is groundwater hydrologistsh ave tended to now a comprehensivet heory in its own right that should re-
treat the vadose zone as the zone that suppliesg roundwater, ceive greater use for determiningf ield data collection sched-
microbiologistsh ave tended to concentrateo n the root zone ules and for managing aquifer systemsa nd waste disposal
region, and geochemistsh ave tended to use equilibrium chem- sites.
istry for their predictions.A ll need to define system bound- Lynn Gelhar demonstratesh ow developmentsi n stochastic
aries more carefully to encompassth e full extent of the vadose subsurfacefl ow theory may be applied in practice.G elhat [this
zone if migration of pollutants from the land surface to issue] points out that few applications of the stochastica p-
groundwater is to be better understood. Nielsen et al. [this proach have been made and that those contemplatingu se of
issue] have described the need for integrated studies that the technique may be overwhelmed; therefore he identifies
shouldl ead to improvedp redictionso f chemicalt ransport and areas in which results from the theory are applicable. He em-
soil-water biological activity in the vadose zone. While they phasizest hat heterogeneityi n aquifersl eadsn aturally to prob-
have consideredp henomena deterministically,t hey recognize abilistic rather than deterministic approaches to describe
the utility of stochasticr epresentationsa nd recommendc lose variability in flow and transport. By means of an hypothetical
study of Dagan [this issue]. example, abstractedf rom a field case,G elhar showsh ow re-
Increasedi nteresti n the detectiono f the presenceo f organic sultsf rom the stochastict heory can be used to estimatel arge-
substances( often in trace amounts) that have been added to scalea quifer parametersa nd to judge the adequacyo f a three-
the subsurfacef low domain has created a need for improved dimensional,d eterministicf low model. In his concludingc om-
descriptionso f their transport and fate. Analytical treatments ments, he notes that results from groundwater models can
of these complex transport patterns have been relatively now be interpretedq uantitatively with predictionsg iven as a
recent. George Pinder and Linda Abriola provide a compre- likely range rather than as unsupportablep oint estimateso r
hensivet reatment of one facet of this subject area: movement scalars.L ike Dagan, Gelhar recognizesa major challengei n
of nonaqueous phase organic liquids (NAPL). Pinder and applying the researchf indingso f the stochastict heory to sig-
Abriola [this issue] have treated NAPL movements in nificant applied problemso f environmentalm anagementa nd
saturated-unsaturatedg roundwaters ystemsu sing a determin- aquifer development.
istic approach. Constitutive relationshipsa re establishedf rom Almost three decadesa go activity began in what is now
thermodynamics supplemented with experimental data. known as "systemsa nalysis" or the "systemsa pproach" to
Pinder and Abriola presenta n example simulation for an hy- problems in water resourcesp lanning, management,a nd hy-
pothetical NAPL contamination situation that reflectsc urrent drologice nquiry and application.T hat activity continuesw ith
modeling capabilities.T hey emphasizet hat much needs to be apparent dominant interest in the selectiono f measuresa nd
done even for assumedh omogeneousi,s otropic aquifersb efore mathematical procedurest hat permit optimal representations
prediction of multiphasem igration of contaminantsb ecomes of hydrologic interactions for water resourcesp lanning and
practicable. The problem posed by preferential migration managementa ctivities.P eter Rogersa nd Myron Fiering, who
pathways of NAPL (fingering)t hat occur in relatively homo- were among the earliestd eveloperso f this field, discussth e use
geneousl aboratory settings must be addressed.F ormidable of systemsa nalysis in water management. What many re-
problemsa re to be anticipateda s natural heterogeneitiesa re searchw orkers hoped would prove to be a widely embraced
consideredi n future developmentso f this work. approach to resourcem anagementi s shown by Rogers and
In 1935 C.V. Theis provided a means for hydrologistsa nd Fiering [this issue] to have had limited utility in the total
engineerst o estimatet ransient head changesf or a singlew ell systemsc ontext where the methodologyc ould have influenced
pumping in a confineda quifer of infinite areal extent. Schema water resourcep roject design.R ogers and Fiering point out
based on that broad principle (mass conservationc ombined that "If used to identify a range of acceptableo ptions, and
with Darcy's law) formed the basis for most treatments of then to examine thesec loselyu nder stochastici nfluences,t he
groundwater flow for a 40-year period. Most problems of techniqueo f 'systematica nalysis'h as the potential of signifi-
groundwater flow were treated deterministically,a nd parame- cantly improving water resourcesp lanning and management."
ters of models were obtained by solution of inversep roblems. Their commentaryb uilds on an early statemento f a system-
With increasingn umberso f observationsg, reater awarenesso f atic approach,d evelopeda nd usedb y Arthur Morgan in 1913.
probabilistic treatments of natural phenomena,a nd the ready His approach," inclusivee ngineeringa nalysis"[ Morgan 1951,
availability of impressivec omputational power, efforts were 1971], while not using optimization methods, led to plans for
made to study groundwater flow and transport processess to- exceptionale ngineeringf acilitiest hat have been in place since
chastically. the early 1920s. The formalization of approachess imilar to
In the past decade much has been written concerning sto- thosed evelopeda nd usedb y Morgan seemt o have had much
chastic treatment of groundwater flow. The scales at which lesse ffect in the three most recent decades.R ogersa nd Fiering
particular phenomena are representedd ictate the level of sto- urge that optimization methodsb e directed toward systematic
chastic treatment appropriate to their description. Gedeon analysis consistentw ith Sirnon's[ 1957] concept of "satisfic-
Dagan placest hesed evelopmentsin perspectivea nd provides ing." By extension, approaches used by Morgan, Roebling,
coherencet o an area of enquiry that has developedr apidly. Eiffel, Eads, and other engineers would be contained within
Dagan [this issue]c onsidersg roundwaterf low and transport their envisionedu se of systematica nalysis.W hile Rogersa nd
phenomenaf rom pore scalet o regionals cale.H e characterizes Fiering find few reported instancesw here use of systems
flow domainsb y the length scaleo f their spatial extent,i denti- analysisl ed to final engineeringp lans,t hey showp athwaysf or
fies three fundamentals cales:l aboratory, local, and regional, the professionto considert o take advantageo f the
4S BURGES' STATUS AND DIRECTIONS OF HYDROLOGY
The last three papers deal with improving professionalh y- solutions.B ox [1976] provides a concises tatement of this in
drologic practice. Two authors, Linsley [this issue] and Pil- describingt he importance of the work of Sir Ronald Fisher,
grim [this issue], discusst he practice of flood hydrology. The who was first and foremost a scientist who eschewed "mathe-
final author, Klerne(cid:127) [this issue], reminds us that hydrologic matistry." Nielsen et al. [this issue] suggestt hat progressw ill
engineeringa nd practice need a clearer focus. be made in studying the vadose zone when workers from the
Numerous papers and reports over the last decade have many disciplines who have interests in portions of it choose
been written about ways to estimate probabilities of uncom- common system boundaries.A more comprehensiveo bserva-
mon floods.O ne indicator of the level of activity over a 4-year tion is that progressw ill be realized when lateral rather than
period is provided by Greis [1983], who cites approximately vertical thinking (see,f or example,d e Bono [1967]) is adopted.
150 papers and reports relating to some aspect of flood hy- Lateral thinkers recognize the need to explore broadly rather
drology. Linsley [this issue] points out that despitee xtensive than "digging the same hole deeper." The observations of
effort by theorists to improve estimates of flood flows, the Nielsen et al. and Philip [1975] are applicable to all aspectso f
dominant method in practice is based on Mulvaney's [1851] human enquiry and activity. Progressi s made by those who
paper. Linsley observest hat marked differencesb etweent heo- take as broad a view as possiblea nd recognizet he totality of a
retical and applied flood hydrology predictors indicate our problem rather than a fragment.
information transfer mechanisms do not work well. He invites A vital considerationi n approaching any area of enquiry is
educatorsa nd practicing and researchh ydrologistst o remedy establishmento f relevant systemb oundaries.E aglesonh as in-
this unsatisfactorys ituation. troduced an important classo f problems where the scaled ic-
David Pilgrim usesf lood hydrology to illustrate his theme tates study of boundaries that include catchments en-
of bridging the gap between researcha nd hydrologic design compassingv ery large areas.A hierarchicals ystematicv iew is
practice. His paper is based on his extensivew ork in Australia needed' both "bottom up" and "top down" approachesw ill be
as leader of the team whose mission was to revise "Australian required. For instance, a global climate model will require
Rainfall and Runoff," the guide for practitionersi nvolved in elementsa s part of its formulation that will be determineda t
flood estimation in Australia. Australia is the driest of the medium and small catchment scales. There are other scales on
continents and exhibits variation of hydrologic extremes of the order of a few meters where fundamental enquiry is
floods and droughts beyond those experiencede lsewhere.P il- needed.
grim [this issue] discussest he aspects of flood hydrology It is too easy for us to adopt one or a few objectivesw hen
where gaps occur between existing information and research determining the boundaries and scale at which problems
emphases.W hile his arena is Australia, many of his observa- should be approached. Most of the authors of our set of
tions possessw orld-wide validity and reinforce Linsley's[ this papersc omment directly or implicitly on the userso f hydro-
issue] conclusionsP. erhapsi t is the changeds tructure of the logic methods. The best work in hydrology has always re-
researchc ommunity that provides the basis for Pilgrim's ob- sultedw hen a good balanceh as been struck betweent he skills
servations. Research work earlier in this century was per(cid:127) u(cid:127) u(cid:127)c(cid:127) o(cid:127) n(cid:127)ctnou(cid:127) ctnu tnc amount of detail containeu in the
formed by a few scholarso f the first rank who practiced hy- methods. Many have written about this topic; the fact that
drology, whereas most research for the last several decades there seems to be a need to keep reminding the profession
has been conducted by university staff and members of re- about this (see, for example, James and Burges [1982a, b])
search organizations. suggeststh at the concernso f Pilgrim, Linsley, Kleme(cid:127), Dagan,
Vit Kleme(cid:127) takes as his theme the need for a clear identity Gelhar, and Dawdy and Vanoni may persist.
for hydrology as an important sciencei n its own right rather The works of scientistsf rom other fields cited, for example,
than as an appendaget o other disciplinesT. he issuesr aisedb y in the paperso f Dagan, Dooge, and Kleme(cid:127) and evidenti n the
Klemeg [this issue] are central to hydrology as a discipline writings of Billington [1983] emphasizet he need for careful
and must be addressedb y the profession and educators. In observationa nd assessmenot f the suitability of various meth-
part, his paper summarizes observations of other authors in ods. There is a tendencyf or some in the professiont o worry
this volume. His paper also forcesu s to confront squarelyt he too much, for instance, whether fast flow to channels is via
fact that we often engagei n "mathematistry"r ather than sci- Horton, Dunne, or "subsurfaces tormflow" processesF. ield
ence and that we choose to obtain numbers for decision- observationsi ndicate that all these mechanismse xist. Perhaps
making purposesr ather than attempting to obtain deeper un- confusiono f interpretation arisesw hen we becomet oo depen-
derstanding.C ommentsm ade by Rogersa nd Fiering, Linsley, dent upon the outputs of simple mathematical descriptions
and Pilgrim relating to "methods in search of problems" are (which may require formidable computation) of hydrologic
again emphasizedb y Vit Kleme(cid:127). He has presenteda signifi- phenomena.T he remarks of Kernot [1883, 1965] about cor-
cant challenget o all who work in the looselyd efinedd iscipline rect representationso f engineerings ystemsa re equally rele-
of hydrology to work toward improvement and, by extension, vant today.
be willing to examine what Liebman [1976], called "wicked Some aspectso f hydrology are not coveredi n this volume.
problems." Notable omissionsa re hydrology of hillslopes,f orests,r ange-
lands, and agricultural lands. Discussionso f parts of these
CONCLUDING REMARKS important fields are containedw ithin severalo f the papers.I
restrictedt he subjectc overages ucht hat the multiple issueso f
It ain't so much the things we don't know that gets us in trouble.
It's the things we know that ain't so. chemistry and biology of surface and subsurfacew aters are
Artemus Ward not includede xplicitly.T he broad and important areaso f data
collection,i nterpretation,a djustment,m anagement,a nd dis-
The collecteds et of papers addressesn umeroust opics and semination, and resourcem onitoring are not included. Remote
identifies a few of the many remaining problem areas. To a and direct observationd evicesa nd recordingm echanismsth at
great extent, the challengesr emaining in hydrology and hy- make data availabled irectlyf or usei n digital computersw ill
drologic practice have analogs in other disciplines.I n most have an increasing role in hydrology, particularly for
instancesi t seemst hat a blend of both the art of the subject characterizinga tmospherich ydrologicf luxes and recording
area and the applicationo f relevafist ciencceo ntributetso spatialv ariationsi n hydrologics tatest hroughout
BURGES.' STATUS AND DIRECTIONS OF HYDROLOGY 5S
and monitoringt he stateso f streamsl,a kes,a nd estuariesT. he Gelhar, L. W., Stochastics ubsurfaceh ydrologyf rom theory to appli-
cations, Water Resour. Res., this issue.
concernse xpressebdy Leopold[ 1982] aboutc ollectioni,n ter-
Greis, N. P., Flood Frequency analysis: A review of 1979-1982, Rev.
pretation,a djustmenta, nd availabilityo f data must not be
GeophysS. paceP hys.,2 (cid:127)(3), 699-706, 1983.
overlooked. James,L . D., and S. J. Burges,S election,c alibration and testing of
The subjectm atter of hydrologyu suallyi nvolvest oo much, hydrologic models, in, Hydrologic Modeling of Small Watersheds,
or too little water, or undersirable additions to water. Impor- edited by C. T. Haan, H. P. Johnson,a nd D. L. Brakensiek,p p.
435-472, American Society of Agricultural Engineers, St. Joseph,
tant aspectso f hydrologyt hat have receivedt oo little atten-
Mich., 1982a.
tion involve hydrologici nteractionsu nder normal climatic James,L . D., and S. J..Burges,P recipitation runoff modeling: Future
conditions where substantialc hangesh ave been or will be directions,i n AppliedM odeling in CatchmentH ydrology, edited by
made to vegetalc over,t opographyg, roundwaters tates,a nd V. P. Singh, pp. 291-312, Water ResourcesP ublications, Littleton,
Colo., 1982b.
soil water chemistryW. ork needst o be donea longt he lineso f
Kernot, W. C., Lecture to students,1 883, J. Inst. Eng. Aust., 37(6),
inquiry of Moore et al. [1986] and O'Loughlin[ 1986] to pro-
N33-N39, 1965.
vide tools capableo f predictingc hangesi n hydrologics tates Klemeg,V ., Dilettantism in hydrologymTransitiono r destiny?,W ater
that result from such modifications.E nquiries of this nature Resour. Res., this issue.
are needed at all catchment scales.W e cannot separate hy- Leopold, L. B., Field data: The interface between hydrology and
geomorphology,i n ScientificB asiso f Water-ResourceM anagement,
drologyf rom land-vegetasl ystemso r considert he land sub-
pp. 105-108, U.S. National Research Council, Washington, D.C.,
strate to be constant. 1982.
Enormous advancesh ave been made this century in mea- Leytham, K. M., Physical Considerationsi n the Analysis and Syn-
suringf luxesa nd statesa ppropriatef or describingth e natural thesiso f Hydrologic SequencesT, ech. Rep. 76 (NTIS PB83167593),
228 pp., Harris Hydraul. Lab., Dep. of Civ. Eng., Univ. of Wash.,
movement of water in each of its three phases.T he largest
Seattle, 1982.
potentialf or improvemenht asc omew ith developmentisn the
Liebman, J. C., Some simple-mindedo bservationso n the role of opti-
last two decadest hat have combinedt he capability of exten- mization in public systemsd ecision-making,I nterfaces,6 (4), 102-
sives patiala nd temporalm easuremenwt ith the capabilityt o 108, 1976.
store and retrieve summaryi nformation from those measure- Linsley, R. K., Flood estimates:H ow good are they?, Water Resour.
Res., this issue.
ments.T he ready availability of high-speedd igital computers
Moore, I.D., S. M. MacKay, P. J. Wallbrink, G. J. Burch, and E. M.
has made feasiblet he analysiso f enormousq uantitieso f spa- O'Loughlin, Hydrologic characteristicsa nd modelling of a small
tial and temporald ata. Thesec apabilitiesw ill increasefu rther forestedc atchment in southeasternN ew South Wales, Pre-logging
with developmentosf parallelc omputera rchitectureM. inimal condition, J. Hydrol., 83, 307-335, 1986.
Morgan, A. E., The Miami ConservancyD istrict, 504 pp., McGraw-
progreshsa sb eenm adew henm ethodsth at wereu sefubl efore
Hill, New York, 1951.
the availabilityo f computersh aveb eenp rogrammedfo r com-
Morgan, A. E., Dams and Other Disasters, 422 pp., Porter Sargent,
puter use.T he greatespt rogressh asc omef rom and will con- Boston, Mass., 1971.
tinue to come from efforts which recognizet hat computersa re Mulvany, T. J., On the use of self-registeringra in and flood gaugesi,n
machinesth at can augmenth uman minds [Simon,1 977] and making observationso f the relations of rain fall and of flood dis-
chargesi n a given catchment,i n The Transactionsa nd Minutes of
that they are muchm ore than large,f ast calculationd evices.
Proceedingso f the Institution of Civil Engineerso f Ireland, vol. 4,
Kleme(cid:127) [this issue],i n his next to last paragraph,r emindsu s Samuel B. Oldham, Dublin, 1851.
that we cannote xpectt o make significangt ainsb y attempting Nielsen, D. R., M. Th. van Genuchten, and J. W. Biggar, Water flow
to extract much more information from our past measure- and solute transport processesi n the unsaturated zone, Water
Resour. Res., this issue.
ments.I ntegrativem easureso f relevant fluxesa nd measure-
O'Connell, P. P. L., Relations of freshwater floods of rivers to the
mentso f statest hat have previouslyn ot been measurableo r
areas and physicalf eatureso f their basins,P roc. Inst. Civ. Eng., 27,
weres ampleda t inappropriates patiala nd temporals calesa re 204-207, 1886.
necessarayn d are applicablet o progressa t all the scalesa d- O'Loughlin,E . M., Predictiono f surfaces aturationz onesi n natural
dressedin the paperst hat follow. catchmentsb y topographica nalysis, Water Resour. Res., 22(5),
794-804, 1986.
Philip, J. R., Somer emarkso n sciencea nd catchmenpt redictioni,n
AcknowledgmentMs.y debt to all the participantso f this issueo f
Predictioni n CatchmenHt ydrology,e ditedb y T. G. Chapmana nd
Water ResourcesR esearchi s very large. Thank you for giving so
F. X. Dunin, pp. 21-30, AustralianA cademyo f Science1, 975.
much.T he supporta nd encouragemengtiv enb y coeditorsR on Cum-
Pilgrim,D . H., Bridgingt he gap betweenfl ood researcha nd design
mingsa nd Don Nielsenm adet hisp ublicationfe asiblew; e all are in
practice,W ater ResourR. es.,t his issue.
their debt.T he cooperationan d goodc heero f the AGU publications
Pinder,G . F., and L. M. Afriola, On the simulationo f non-aqueous
staff is appreciatedS. pecialt hanksa re due to Diana Leythamw ho
phaseo rganicc ompoundsin the subsurfaceW, ater Resour.R es.,
providede ssentiahl elpt hroughoutt he project.
this issue.
Rodriguez-IturbeI.,, Scaleo f fluctuationo f rainfall models,W ater
REFERENCES Resour. Res., this issue.
Billington, D. P., The Tower and the Bridge, 306 pp., Basic Books, Rogers,P . P., and M. B. Fiering,U se of systemsa nalysisin water
New York, 1983. managementW, ater ResourR. es.,t his issue.
Box, G. E. P., Science and statistics,d . Am. Stat. Assoc., 71(356), Sposito,G ., The "physics"o f soil water physicsW, ater Resour.R es.,
791-799, 1976. this issue.
Brutsaert, W., Catchment-scalee vaporation and the atmospheric Simon,H . A., Modelso f Man, John Wiley, New York, 1957.
boundary layer, Water Resour.R es.,t his issue. Simon, H. A., What computersm ean for man and society,S cience,
Colbeck,S .C., Classificatioonf seasonasl nowc overc rystalsW, ater 195, 1186-1191, 1977.
Resour. Res., this issue. U.S. National Research Council, Scientific Basis of Water-Resource
Dagan, G., Statisticalt heory of groundwaterf low and transport:P ore Management, 127 pp., U.S. National Research Council, Washing-
to laboratory, laboratory to formation, and formation to regional ton, D.C., 1982.
scale, Water Resour. Res., this issue. Waymire,E ., V. K. Gupta,a nd I. Rodriguez-IturbeS,p ectratlh eoryo f
Dawdy, D. R., and V. A. Vanoni, Modeling alluvial channels,W ater rainfall intensity at the meso-scaleW, ater Resour.R es., 20(10),
Resour. Res., this issue. 1453-1464, 1984.
De Bono, E., New Think, Basic Books, New York, 1967.
Dooge, J. C. I., Looking for hydrologicl aws, Water Resour.R es.,t his S. J. BurgesD, epartmenot f Civil EngineeringF,X -10, Universityo f
issue. Washington,S eattle,W A 98195.
Eagleson, P.S., The emergence of global-scale hydrology, Water
Resour. Res., this issue. (AcceptedJ une2 3,
WATER RESOURCES RESEARCH, VOL. 22, NO. 9, PAGES 6S-14S, AUGUST 1986
The Emergenceo f Global-Scale Hydrology
PETER S. EAGLESON
Departmento f Civil EngineeringM, assachusettIsn stitute of TechnologyC, ambridge
Emergingp roblemso f environmentalc hangea nd of long rangeh ydrologicf orecastingd emandk nowl-
edge of the hydrologic cycle at global rather than catchment scale. Changes in atmospherea nd/or
landscapec haracteristicms odify the earth's metabolismt hrough changesi n its biogeochemicacl ycles.
The most basico f thesei s the water cyclew hichd irectlya ffectst he globalc irculationo f both atmosphere
and oceana nd hencei s instrumentali n shapingw eather and climate. Defining the spatial extent of the
environmentali mpact of a local land surfacec hange,o r identifying,f or forecastingp urposest,h e location
and nature of climatic anomaliest hat may be causallyl inked to local hydrologicp ersistencierse quires
global scaled ynamicm odelingo f the coupledo cean-atmosphere-lands urfaceD. evelopment,e valuation,
verification,a nd use of thesem odels requirest he active participation of hydrologistsa long with a wide
range of other earth scientists.T he current state of these models with respect to hydrology, their
weaknessesd,a ta needs,a nd potential utility are discussed.
INTRODUCTION cation first of fire and then of plants and animals [Saga et al.,
For the last centuryt he developmento f hydrologyh as been 1979]. Early civilizationsd estroyed the temperate forests of
largely in the handso f civil and agriculturale ngineersw orking China and the Mediterranean Basin, and modern civilizations
on the classicp roblems of water supply and natural hazard have greatly reduced the temperate forests of Europe and
reduction.T he scaleo f their interesth as been primarily that of North America.
the catchmentw ith the atmosphereb eing considereda n inde- In the last 500 yearst he hand of man has beeni ncreasingly
pendentd river of the hydrologicp rocesses. felt on the biogeochemicalc ycles that control the Earth's
In recent years,h owever,t he important hydrologicp rob- metabolism. Energy production, farming, urbanization, and
lems of the temperatez onesh ave expandedt o a scalec om- technologyh ave alteredt he albedo of Earth, the composition
mensuratew ith that of the atmosphericw ater cyclei n those of its soil and water, the chemistryo f its air, the amount of its
latitudes,a nd interesti s growingi n the tropicsw heret he at- forest,a nd the structurea nd diversityo f the global ecosystem.
mospherica nd catchmenst calesa re comparableH. ydrologists Approximately 40% of the Earth's land area is now under the
are now beingf orcedt o considert he atmospherea nd the land active managemento f man with more than 10% being under
surfacea s an interactivec oupleds ystem,a perspectivew hich cultivation [Olson et al., 1983, pp. 20-21]. Chemical com-
drawsu s closert o the geophysicistv'sie wpointo f globals cale poundsh aving no analogsi n nature are beingi ntroducedi nto
processesIn. this paper I hope to make the casef or a global both air and water at increasingr ates.
scaleh ydrologicp erspective. Most recently the tropical forestsh ave come under attack.
Meyers [1979] estimatedt hat Latin America has lost 37% of
GLOBAL ENVIRONMENTAL CHANGE its original rain forest (largely to agricultural development),
The atmosphereh, ydrospherea, nd surfacel ayers of the SoutheastA sia has lost 38% (principally to logging), and
Earth have arriveda t their presentc haracteristictsh rougha Africa has lost over 50% (primarily to slash-and-burna gricul-
coevolutiono f living and nonlivingc omponentsT.h e picture ture).
as revealedb y paleoclimatologisitss o ne of large-scalen atural The alteration of ground cover affectss urfacea lbedo and
processesu ndergoingc ycleso f dynamic change on a wide runoff, changest he ratio of sensiblet o latent heat transport,
spectrumo f time scales,f rom years to hundredso f thousands alters surfacew inds and erosionr ates, and changest he ther-
of years,a ccompanieds ynergisticallbyy the evolutionaryd e- mal and moisture state of the surface. The microclimates of
velopment of life forms. An example of the evidencef or this foresteda nd cleareda reasd iffer markedly. In tropical regions
natural changei s offeredb y the fossilp ollen record in North sucha s the Amazon basinw here soilsa re typically poor, their
Americas incet he peak of the last ice age 18,000y earsa go as exposure to sunlight may produce chemical and structural
determinedb y Webb and coworkers(W ebb et al., unpublished changes that inhibit either agriculture or reforestation and
manuscript1, 977)s ee,f or exampleB, ernaboa nd Webb[ 1977]) introducee rosioni n the presenceo f the heavy precipitation.I n
and is presentedin Figure 1 as taken from Kerr [1984]. An subtropicalr egions,s ucha s central Africa, where precipitation
increase in summer solar radiation and the retreat of the ice is limited, a foreste cosystema ppearst o be unstable[ Eagleson
sheetc ausedt he oak and northernp ine forestst o withdraw to and Segarra, 1985] and its destruction leads to a stable tree-
the north and at the samet ime developedo ur southernp ine grass savanna. Such has been the fate of 40% of the African
forests. equatoriafol restsa s a resulto f slash-and-bmag'nr iculture
Humansh aveb eena lteringt he environmenot verl argeg eo- [Phillips, 1974].
graphic areas for over 10,000 years through their domesti- The globalc ycleo f water is perhapst he mostb asico f all the
biogeochemicacl ycles.I n addition to its strong influenceo n
the other cycles( e.g.,c arbon,n itrogen,p hosphoruss,u lfur),i t
directly affectst he global circulationo f both atmospherea nd
Copyright1 986b y the AmericanG eophysicaUl nion. ocean and hencei s instrumentali n shapingw eather and cli-
Paper number 5W0749. mate. Planning and/or constructioni s underwayo n various
0043-1397/86/005W -0749505.00 macroengineeringw ater projectsw hich, through their
6S
EAGLESON: GLOBAL-SCALE HYDROLOGY 7S
A 10,000 YEARS B.P. 6,000 YEARS B.P. 500 YEARS B.P.
Oak
Fig. 1. Vegetationc hangei n easternN orth America during the past 10,000 years.C rosshatcheda rea is ice sheet.
Contour is 1% oak. Light stipplingi s 5-20% oak or 20-40% pine. Heavy stipplingi s greatert han 20% oak or greater
than 40% pine. (From Kerr [1984], Climate sincet he ice begant o melt, Science2, 26, 326-327, copyright1 984 by the
AmericanA ssociationfo r the Advancemenot f Science.)
cationso f regionalh ydrology,p romiset o contributet heir own connections,"a s they have come to be called, we cite first the
distortionst o the courseo f environmentalc hange. striking negative correlation between the winter snow cover
One examplei s the drainageo f the immenses wampso f the over Eurasiaa nd the intensityo f the followings ummerm on-
White Nile's Sudd region in order to capturef or downstream soon in India. As was pointed out by Walsh [1984], this in-
usess ome of the water now lost by evapotranspirationT. he verser elation( seeF igure 2) is consistenwt ith the argument
permanenst wampsa re on the ordero f 34,000k m2 in surface that widespreadsn owc overl eadst o lowers pringtimea ir tem-
area and if solelyt he dry-seasone vaporationf rom this surface peraturesa nd hencet o highers ea level pressureso ver south-
could be capturedi t would amount to some 25 x 109 m3 ern Asiaw hicho pposeth e normalm onsoonapl ressurger adi-
annually, which is more than the current annual flow of the ents.O f courset,h e correlationd oesn ot establishca usalityA.
White Nile at Khartoum [Chan and Eagleson,1 981]. The loss similacr orrelatnio h asb eenf oundb otho bservationaalnlyd
of this atmosphericw ater and its associatedla tent heat would with atmospherigc eneralc irculationm odel (GCM) experi-
surelyb e felt climaticallyT.h e first phaseo f this projectt, he mentsb etweend roughti n northeast. Brazila nd positives ea
360-km Jongleic anal,i s nearly complete. surfacete mperaturea nomaliesin the tropicalA tlantic.
Another project is the diversiono f severalS oviet rivers Much similare videnceh asb eena ssembletdo supportt ele-
away from their currentn orthwardf low. The projecth as two connectionsb etweens eas urfacet emperaturea nomaliesi n the
parts: a European portion now under way which will divert easternt ropical Pacific Ocean (El Nifio) and middle-latitude
the Sukhona and Onega Rivers southward, away from the atmosphericc irculationi n the winter hemisphere(s ee,f or ex-
White Sea, to irrigate 2.5 million acres in the northern Cau? ample, Horel and Wallace [1981]), and betweens ea surface
casuasn, da Siberiapno rtionw hichif undertakweno ulds end temperature anomalies in the Atlantic Ocean off West Africa
the Ob and Irtysh rivers to the arid regionsa round the Aral ands ub-Sahardarno ugh[tL amb , 1978].
Seain steaodf i ntot heK araS eaB. yd eprivinthge K araS eao f The climatic effects of anomalies in land surface conditions
a large fresh water inflow, this latter diversionm ay alter the have been establishedo bservationallya t local and regional
ice covera nd thusc hanget he regionala lbedo. scalea s a result of urbanization[ Landsberg,1 974] and irri-
Both the deforestationa nd the proposedm acroengineering gation [Schickedanz1, 976; Stidd, 1975]. At continentala nd
projects act to create anomalous regional moisture and/or globals calet he sensitivitiehsa ve beene stablishetdh rough
heat sources( or sinks)t he effectso f which may, in theory at numericasl imulationsa s summarizedb y Mintz [1984].
least,p ropagatet o distant regionsv ia atmosphericd ynamics The evidencei s overwhelmingt hat regional anomaliesi n
[Webster, 1982]. As possible examples of such "tele- the surfaces tateo f the Earth as givenb y its albedo,