Two centuries i ie between the publication of Euler's 'Principes gdndraux du ntouve,ment des fluides' and the wide-spread application of nlathenatical models. Dudngthis time. enginee$ - who had in the course of more than a thousand yearsacquired a large practical know-how and learned to design by rules of experience ,.gradually began to appreciate the theories introduced by mathemaricians. IJandin hand with this abstract treatment of water movement. a need arose for series ofsystematic experiments. This need was satisfied by the work of many scientists.

As well as adapting theories for practical purposes and making luli use of thetools at fus disposal, the engineer is faced by another, new challenge: that ofexecuting modern works of advanced technology for an increasingly crit icaj societyin which scientists of many disciplines ponder over issues which have previouslybeen the uncontested territories of the engineer. The authors of this book recog-nize this challenge because each of t iem has participated in mulddisciplinaryproject teams, created ad hoc to solv€ a particuiar set of problems. They have not,however, gone into questions ofan interdisciplinary naturet they have restrictedthenrelves to the compilation of design tools which have not yet been presentedin a comprehensive manner.

The authors have tried to present the current state of affai n on the transport ofsediment and the morphological implications thereof and to indicate dre applic,abil it), of these theories for the river engineer, In addition it was felt that Ln situmeasurements and the processing of these measurements were indispensable toolswhich required new presentation. Mathematical modeis and scale models (some-times called physical models) have also been treated. Finally, the practical rivefengineer who has to use models for specil ic projects wil l hnd solutions to a nunrber

in the last part of this book.

t Introduction

s tare o f a r i ver and lhe use tha t i s ro be made o f r r a te se ldonr in

'1,harmony, the more so when advanced society increases its demands on nature. Asa result river works are car ed out to change the various aspects of a river so thatmore benefit - or less damage - can be achieved. The works cause changes in thenver bed i^clucjJlg the banks, changes in the discharge or changes in the walerlevel. T\ese three main groups of river works are treated in Part 5, preceded bytheoretical considerations in the other palts of this book.

Changes to the river bed are invariably made to help solve erosion or sedimenta-tion problems in particular areas. These problems may concern lengths of a fewmeters or hundreds of kilometers. The plocess oferosion or siltation may takehouls to take effect or it may take centudes to reach an equil lbrium. The area mayconcern a river bank or bridge pier to be protected against erosion, a channel ro bedeepened for navigation, a bifurcation to be altered to gjve a different djstributionof water over lts channels, the degadation of an entire river behind a largereservoir, etc. All these problen"rs are concerned with the morphoiogy of the riverbed. The river works that are associated with their solution - if they can besolved * can be split into temporary or repeated works and permanent w(xks. Anexample wil l i i lustrate the distinction. Suppose that the depth in a particularsection of a river has to be increased. Dredging may solve tire problem. However,

N T R O D U C T I O N ]

after a few montts or maybe a year, the area wil i probably have silted up again

and the remedial measure will have to be repeated. On the other hand the bed

could be confined by goynes to achieve a permanent deepening of the channel. Ir'

this case a new equilib um - at other widths and depths than before the measure

was carded out - will be reached between the confined river stretch and the

unchanged upstream parts, whereas in tlte former case the difference in sediment

tlansport capacities between the dredged section - where the sediment transport

capacity decreases because of the larger profile - and the upstream dv€r means

that the river will eventually revert to its original state. Both for repeated opera-

tions and for permanent work it is necessary to know the amount of sediment

tuanspoded by tlle river, the transport capaoity in various profiles and the time it

takes for a change to occur. It is also important to know to what distance, and by

what time, the disturbarce caused by the temporary or permanent work wil l travelin the upstream and/or in the downstream direction.

Much the same questions have to be answered for the other two goups of river

worls: those conceming the changes in discharge or in water level. Both groups of

measures have to deal with the natural dependence of the river waters on rainfall.Because the patterls of rainfall and runoff seldom coincide with human require'

ments, systerns of regulation are devised, for example: the control of f loods by

temporary storage in reseruoirs; the increase of water depths by construction of a

series of wein, The immediate effects of these works on discharges and/or water

levels are apparent, but the morphological consequences, not only in the vicinity

of the works, but also further upstream or downstream, must also be appreciatedand quantified.

In addition to these three goups of works the river engineer is increasingly

confronted with quality aspects of the water, and sometimes of t}le sediment.There is little he can do when confronted with the actual situation at a particular

river section ur ess he can take measures at the source of the pollution: sewage

a.nd other wastes. For a general understanding of pollution problems and the

mechanics of water-bome organisms Mth respect to substances carried by water,

relevant sections have been included at various places in the book. They are, how'

ever, restricted in size and depth because the book is p marily concemed with the

three types of riyer works mentioned above.lce problems are not treated in this book and the reader is referred to IAHR-

PIANC (1974), I-aszioffy (1956) and C. P. Will iams (19 59, 1970). Vegetation or

sudd problems - of which some aspects are similar to ice problems - are not dis'

cussed either.Tlrc uses or purposes of a river and the messures needed to achieve this usage,

or an improvement for an existing usage, have been summarized in Table i i '1.

The table is not exhaustive, neither in 'use' nor in 'measure', its main purpose being

to introduce the rcader to vadous aspects of riveJ engineedng treated in this book.

As shown in the table, th'ere is sometimes mo6lhan one measute which can be

used to achieve a particular purpose or palt of it. Sotrle measures are also of

secondary importance to the purpose (labelled 2) a0d,some measures (labelled 3)

may be necessary as a result of the operation. A fewrcomments on the table follow:

(i) Defensive measures against floods are not 'uses' of a river in a strict sense,

but the meaning wil l be undentood. It is obvious that one either has to build a

levee - which must be protected against scour and/or do something about the

flood height.(i i) Rectif ication of the channel includes the cutting of meanders; rectif ication

in the flood plain includes measures to increase storage and/or f low capacity

(i i i) For navigation quite a number of improvement5 are shown They vary in

degee of effectiveness and cost.(iv) Hydropower requires the avaitabil ity of sufficient discharge, preferably in

quantit ies which can be adjusted, and the creation ofhead.(v) Irrigalion and water supply withdraw water frorn the river; part of it may

retum elsewhere, usually changed in quality. For large amounts, large in compari-

son with the river discharges, discharge control may be necessary. A weir may also

be required at the point of withdrawal. The point of withdrawal itself must be

4 INTBODUCTO B Y MATTERS

Table l. l- l River uses and measures to achieve themI Measure to achieve the required use2 Measure of secondary importance for the use3 Measure which might be necessary as result ofthe operation

Dscharge and water Qualitylevel regulation controiBed regulation

3

o_

1 'l ll iT 2

33

o l 95 u

6 - o h :g = 5 s : : E & sa j _ - o d = _ 2 a =€ , V ; = , , i o 6 e A E- o - 3 : : i ,

' - ' F = 62 > i 6 d o o x o E 3 ai a . : ; . E : E ' ! E 5 ' : cL E * : E X a € e i : 9E E 5 e ; ; € 5 € E ! ;

3

I3 2

3

L\e of iverFlood control\ari gaiionHl dropowerlrrjgation and water supplyWasre dischargeBank protectionCooling waterCommercial sand dredgingRrver crossingsControl of sea water intrusions

stable and bank pratection may be necessary. Sediment problems in the river irself(sudden decrease of sediment transport capacity because of water withdrawal,and/or after the vrithdrawal pqint (sand traps may be necessary) have to be solved.

(vi) CooLing water and some other uses mentioned hereafter have been ljsredseparat€ly, mainly to show that t l lere are more uses than the four big ones mentionedabove- Temperature problems, which are expected gradually to become serious 1nsome ri!€rs, are, ofcoune, a particular type of waste discharge problem.

(vii) A peculiar river use is large-scale commercial sand dredging which occursin some countdes - as far apart as the Netheriands and Japan to the extent thatremedial measures have to be taken.

(vii i) For bddge pien anti-erosion measures are usually required. They fall underthe heading river crossings, to which pipelines across a river channel also belong.For pipeline construction it is useful to know how long (in time) a dredged trenchperpendicular to the river axis wil l last.

(ix) With the increasing use made of fresh water, the intrusion of sea water intoestuaries becomes a problem which is sometimes aggravated by channel deepenjngfor navigation purposes. Remedial measures against intrusion are often b)-productsof other river works such as discharge controi works and/or water level controlworks. It usually happens that more than one purpose is served, particularly whendischarge control or water level control works are carried out. However, not alluses require compiementary measures and sometimes a choice between conflictinsinterests has to be made.

In order to describe the necessary'measures'and flnd an engineering solution itis necessary to know the behaviour of both water and sedjment. The engineer usedto rely on rule ofthumb and later on on experimental laws based on the statisticalevaluation of numerous obsewations. To a large extent the expedmental laws aresti l l his main tools. This book, however, tdes ro point our the physical basis olwater and sediment behaviour in Part 2; this is translated into mathematical des-criptions which are further elaborated in Part 4.

I N T R O D U C T I O N 5