Viktors Articles.

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From "Our Senseless Toil"

More energy is encapsulated in every drop of good springwater than an average-sized power station is presently able to produce.  These energies can be generated effortlessly and almost free of cost if we follow the path which Nature constantly shows us and abandon the blind alleys of conventional technology.
Happiness and health are available to us just as near cost-free as unlimited energy, if we but once realise that in water dwell Will and its Resistance, Life.  We struggle so hard for these today, because in all our endeavours we constantly rob the bearer of all Life (water) of its noblest possession, its soul.  The Will of Nature serves all things and expresses itself in growth by way of atomic dissociation and transformation.  It is only through our obsession with atom-destroying work and our selfish over-exploitation of her resources that we encounter Nature's resistance.
The only possible outcome of the purely categorising compart-mentality, thrust upon us at school, is the loss of our creativity.  People are losing their individuality, their ability to see things as they really are, and thus their connection with Nature.  We are fast approaching a state of equilibrium impossible in Nature.  This equilibrium must force us into total economic collapse, for no stable system of equilibrium exists. The principles upon which our actions are founded are therefore invalid because they operate within parameters that do not exist.
Our work is the embodiment of our will.  The spiritual manifestation of this work is its effect.  When such work is properly done it brings happiness, and when carried out incorrectly it assuredly brings misery. 


                                    Viktor SchaubergerHotwordStyle=BookDefault; , 1933

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TURBULENCE

Concerning the Movement of Water and its Conformity with Natural Law
   
Wien, 1930
   
The influence of water temperature has been dismissed as too insignificant for the purposes of stream management, and therefore for flood mitigation, timber floatation and rafting operations, water supply and dam construction in general, and also for the whole realm of hydroelectric technology.  Documented variations in temperature yield values arithmetically too small for any noteworthy effect on the results to be inferred.
It must be emphasised that the internal variations in water temperature are a result of the differences between the temperature of the water and the medium surrounding it. 
If internal variations in water-temperature are ignored, then the significance of differences between water and air or external temperature and therefore the cause of the water cycle, will likewise be negated. No word can truly express the vital role of the water cycle for all life on the Earth.
Of equal importance, if less obvious, are the effects of variations in temperature within the water itself, as will be shown later.  Up to now such variations have been disregarded as immaterial for the purposes of all hydraulic calculation.  Observations over many years, practical experiments and correctly carried-out measurements have proved that it is absolutely imperative to take internal variations in water temperature into account.  Their very exclusion - elimination is out of the question - makes all practical use and exploitation of water impossible.  The understanding alone of the important effect of these variations compels the reappraisal and revision of the fundamental bases of currently-held theories relating to the whole sphere of river engineering.
A new, hitherto neglected, but extremely vital factor is now added: the changes induced in the inner state of water through the stratification resulting from differences in temperature. Were this factor to be integrated into conventional theory, we would have to learn to reformulate our ideas about fundamental principles.

There is another omission in contemporary theory about the formation of many springs.  Apart from commonly-known seepage springs where water above impervious strata is brought to the surface by gravity, there are also springs, lying far above any possible accumulation of water, which, breaking all known laws, surface rather like artesian wells much higher than the main water table.  An example is a spring on the High Priel, which rises about 100m (330ft) below the summit, at an altitude of over 2,000m (6,500ft), and discharges water all year round.

To return to the actual theme - the effect of internal variations in water temperature on the movement of the water itself: It must be pointed out that these differences in water temperature would appear totally to preclude any state of rest in the water-body itself.  Even in apparently motionless water very considerable movements occur - they are able to set large quantities of logs in motion.  If an ostensibly still stretch of water is exposed to the Sun on one side only, then an inclined plane (thermocline) is formed through the warming of the water surface in the insolated area, which induces a flow towards the colder side and results in the formation of circulating currents.  Therefore, even without a bed-gradient movement of the water takes place.
When water, comprising strata of different temperatures and therefore of different densities, flows down a riverbed gradient, these layers travel alongside and above each other for a long period without mixing.  The movement of every single particle of water down a given gradient is linked to a very particular velocity, which corresponds to its specific weight.  If its specific weight is altered by the gradient (greater velocity, greater friction, increase in volume), then the water is unable to adjust itself readily to the new velocity without a transitional phase.
The same thing happens when the specific weight is modified by outside influences, such as solar radiation.  The water breaks, or in more common parlance, becomes turbulent, which is the activation of a hitherto-unrecognised precision brake in moving water, which operates with marvellous automaticity and which is normally actuated by the external temperature.  The greater flow-velocity in cool weather and during the night suffices to change the waters volume and weight.  The temperature of all the water filaments approaches +4?C, and hence density 1.  As a result their specific weight ought to conform to the increase in velocity - in which case a constant increase in the rate of flow should occur.  However, through the increase in flow velocity, the friction between water particles themselves and between water particles and channel surfaces will be intensified, resulting in a rise in temperature and a consequent increase in volume.
The picture thus emerges that:
?   on the one hand an increase in flow-velocity occurs, and on the other a decrease in specific weight;
?   the water filaments rupture and the water becomes turbulent;
?   the forward motion of the water will be resolved into the formation of vortices. 
The greater the velocity of forward motion, the greater or more intense the formation of vortices.  At a certain velocity this assumes such a violent nature that water can actually be atomised in the water-body itself, a phenomenon that manifests itself as a cloud-like formation.
In summary it can therefore be stated that turbulence is the interruption of the forward motion of flowing water.  It occurs in the axis of flow (the position of greatest increase in velocity) in conformity with natural law, and arises due to the fact that in water each and every specific weight corresponds to a particular velocity.  Turbulence therefore represents the automatic activation of a compensatory motion.  It is the automatic and double-safe brake in all flowing water and in every channel.
Through knowledge of the spring and the way it comes into being, and with a clear understanding of the function of turbulence, every possible way to make use of water practically in accordance with natural law, and therefore without limitation, is made available to humanity.


Deriving from above are the following guiding principlesHotwordStyle=BookDefault;  and basic propositions and with them the compelling necessity  for the restructuring of the whole body of water resources management.

Everything flows, and
   all processes in the atmosphere
      are reflected in the interior of the Earth

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Guiding principles

The body of water passing through a channel profile is never a homogeneous mass, but always exhibits strata of different temperatures.

In all channels the relation between flow-velocity and bed-gradient is primarily dependent on the thermal stratification of the water.

The channel profile affects the flow velocity to the extent that its form and composition exert an influence on the differences in the temperature of the individual water-strata.

The profile is a product of the processes that take place within the flowing body of water itself.
                             
                                             Viktor SchaubergerHotwordStyle=BookDefault;

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TEMPERATURE AND THE MOVEMENT OF WATER I

An article by Viktor Schauberger, published in "Die Wasserwirtschaft", the Austrian Journal of Hydrology,
Vol. 20, 1930

To the Editor of Die Wasserwirtschaft:

Mr. Viktor SchaubergerHotwordStyle=BookDefault;  has sent me the attached treatise concerning temperature and the motion of water.  Since this has aroused my keen interest, due to the entirely new points of view it presents, which will not only be fruitful but pioneering in relation to dam construction and river regulation, I consider it to be in the public interest that this work be made known to a wider readership and the scientific world.  With this in mind, I recommend the publication of this interesting article.
Yours faithfully,  FORCHHEIMER ,  m.p.

                                             ForchheimerHotwordStyle=BookDefault;  m.p.


Contents   

?  The importance of the temperature-gradient in the             
   movement of waterHotwordStyle=BookDefault;
? The accretion of groundwaterHotwordStyle=BookDefault;
? The drainage of water over the ground surfaceHotwordStyle=BookDefault;
? Some comments on river regulationHotwordStyle=BookDefault;
? The importance of the groundwater for agricultureHotwordStyle=BookDefault;

Preamble 

The increasing frequency of catastrophic floods in recent years, and the constantly increasing aridity in many areas, raise the question as to whether, in conjunction with other measures inaugurated by human hand, arbitrary systems of water resources management are not in part to blame for these evils.  We are here concerned primarily with two factors, which need to be examined with this in mind: contemporary methods of river regulation and the increase in forest clearance.
   
Before addressing the theme itself, attention should be drawn to a very important factor hitherto ignored in all hydraulic engineering practices: the temperature of water in relation to soil and air temperature as well as the internal variations in temperature (temperature gradients) in flowing or standing water.  Since even small differences in temperature suffice to bring about obvious changes in the state of aggregation of water (solid, liquid and gaseous), it is quite easy to understand that larger variations in the internal temperature of flowing or standing water must have a decisive influence on its movement in and over the Earth.

In the following section the hitherto-neglected interrelations between temperature and the movement of water will be addressed, and those errors will be identified which have arisen through disregard of this vital interaction.


I. Temperature Gradients - Full & Half Hydrological Cycles
   
The movement and distribution of water returning to the ground surface from the atmosphere is conditioned by the prevailing rainwater temperature and by the temperature of the surrounding air and ground strata.

If the temperature of the incident water is higher than the ground strata supposed to absorb it, then through cooling and becoming specifically heavier as a result, rainwater will readily be able to infiltrate the interior of the Earth.  After having attained a temperature of +4?C (+39.2?F - also its condition of greatest density) and by sinking further, the water eventually arrives at strata of higher temperature, and by accommodating itself to these temperatures it becomes specifically lighter.
   
The further it sinks due to the pressure from the heavier water above, the greater its inherent resistance to downward movement, owing to its constantly reducing specific weight.  Finally a state of equilibrium is established through which the all-important height of the groundwater tableHotwordStyle=BookDefault;  is regulated.  Under very particular conditions of pressure, a water stratum with a temperature of +4?C (the centre stratumHotwordStyle=BookDefault; ) is formed within the general body of groundwater. 

In the case described above we are concerned with a positive temperature gradient , which is the rate of change per unit length between the temperature of the incident rainwater and that of the ground, expressed arithmetically.

This case also represents the full cycle of waterHotwordStyle=BookDefault; , the full hydrological cycle. In reiteration of what has been stated earlier, this is characterised by the following phases:
 
   infiltration of water into the Earth;
   passage through the +4?C centre-stratum of the groundwater;
   purificationHotwordStyle=BookDefault;  at this temperature;
   further sinking into subterranean aquifers due to its own weight;
   transition to a vaporous state due to strong geothermal influences;
  rising again towards the ground-surface with a simultaneous uptake of        nutrients;
   cooling of the water and deposition of nutrients;
   draining away over the ground-surface;
   evaporating and forming clouds;
   falling again as rain, and so on.

In warm soils the +4?C groundwater stratum is missing.  Hence the counterweight to the upward pressure from below is also absent.  If the temperature of rainwater is lower than the uppermost ground-stratum, then the water initially sinks to a certain depth and there becomes warmed and specifically lighter.  Finally it is forced up to the surface again by the pressure from below and, provided it does not evaporate immediately, drains away along the riverbed-gradient.
   
In this case we are concerned with a negative temperature gradient  (water temperature lower than the surface-temperature of the ground).  The full cycle no longer develops, but only a half cycleHotwordStyle=BookDefault; , namely precipitation of water earthwards, surface run-off, evaporation, cloud formation and re-precipitation as rain.

The following may throw more light on the temperature gradient and help in better understanding what is to be discussed later:
When an initially-negative temperature gradient  (warm earth, cold rain) is coupled with a simultaneous drop in atmospheric temperature, the ground can be cooled to such a degree that the temperature gradient  ceases to exist.  The same thing can also happen with an initially-positive temperature gradient, if the infiltrating water is of sufficient quantity to warm the ground.  In both cases, when a zero temperature gradient occurs, the drainage is conditioned by the actual riverbed-gradient until such time as the temperature gradient is reinstated through the action of friction and other factors.  It is necessary in each instance to re-establish the required temperature gradient through the addition of water of the right temperature in order to brake the waters free and almost resistance-less flow down the inclined plane of a riverbed.



II. The Groundwater Table 
   
The height of the groundwater table fluctuates according to the temperature of the ground strata , which are also affected by the temperature of infiltrating water-masses.  Air temperature also plays a major role.
   
Where localised impoundment of water-masses occurs, cold bottom-water influences the temperature of surrounding ground strata .  These are cooled, and in this way a stable, positive temperature gradient is created, since in this instance rainwater will always be warmer than the colder ground.  These are the preconditions for the infiltration of rainwater.  As a result, the groundwater table will not only be raised, but the absorptive capacity of the soil will also be increased laterally and vertically.

The previously-described +4?C centre stratumHotwordStyle=BookDefault;  in the groundwater will be displaced downwards owing to increased pressure from over-lying water-masses, thus overcoming the resistance to further downward penetration of warmer and specifically-lighter water lying below the centre stratum.  This leads to the formation of a natural subterranean reservoir, a retention basin, which inhibits rapid surface drainage and gives rise to the full hydrological cycle.  The release of water from this reservoir then follows.  As will be described later, the lateral expansion of the centre stratum (formation of springs) can also occur due to pressure acting on it from above and below.  Fig. 1aHotwordStyle=BookDefault;   below, schematically illustrates a cross-section through a groundwater reservoir. This depicts how not only the lateral but also the upward flow of the centre stratum (under the greatest pressure from all other strata) can come about.

In contrast, as described in section 1HotwordStyle=BookDefault; , high surface temperatures permit hardly any water to infiltrate into the ground at all.  The accretion of groundwater ceases, or it only accumulates in small quantities at great depths.  Through evaporation of small residues of groundwater still present, the ground becomes increasingly incapable of absorption.  Due to the effect of too high a ground temperature, percolating water will develop into surface run-off, leading to rapid re-evaporation connected with it (a half-cycle)HotwordStyle=BookDefault; .  In this case no accretion of groundwater in the previously-described sense therefore comes about.  In such districts hot springs frequently make their appearance, forced up to the surface through fissures by upward pressure from below, for which no counter-pressure exists due to the lack of over-burdening groundwater.

The absorptive capacity of the ground is thus dependent on the conditions of temperature which give rise to the regulation of the groundwater table as described above, and hence on the existence and height of the groundwater-table (sketchHotwordStyle=BookDefault; )

In summary it can be stated:

A positive temperature gradient is the pre-condition for the soils ability to absorb, for the accretion of groundwater and for the creation of the full hydrological cycles associated with it

A negative temperature gradient prevents the accretion of any groundwater and gives rise to half-cyclesHotwordStyle=BookDefault;  only.



III. The Drainage of Water
   
The drainage of water below the ground surface (groundwater-flow) occurs as a result of pressures exerted from above and below in conjunction with temperature variations obtaining in the groundwater and the surrounding ground strata.  What alone has been construed as groundwater flow up to now was merely the drainage of groundwater overlying an impervious layer - drainage which moves down its inclined surface until it is re-integrated into the full cycle.  Water is able to discharge over the ground surface under two conditions:

1.   With a negative temperature gradient  (as described in section I.) this occurs immediatelyHotwordStyle=BookDefault; !
2.   With a positive temperature gradient it takes place only after saturationHotwordStyle=BookDefault;  has occurred, and the groundwater table rises towards the surface under the influence of the SunsHotwordStyle=BookDefault;  heat.

This also explains a phenomenon often observed in the mountains: rainfall over several days causes no appreciable increase in the flow of water in the associated receiving streams.  The rainwater is almost completely absorbed by the ground. 
Only after the onset of warmer weather does a flood-discharge enter receiving streams.  Cold groundwater rises to the ground surface, which by this time has been warmed by the Sun and warm air.  The earlier positive temperature gradient is transformed into a negative one; the water flows away.  Country folk say the mountain is "pissing?.
   
In case 1 above, the preconditions for the creation of floods are far greater and all the more so, if as a result of the direct run-off of water resulting from an initially negative temperature gradient in the ground (cooler higher strata, warmer lower strata), a positive temperature gradient is developed (effect of friction), when the water tends to infiltrate the ground gradually, loosening and carrying away boulders and pebbles.  A thermal surface-gradient is now added to the physical riverbed-gradient.  A further increase in run-off velocity and the power to shift pebbles, gravel and sediment ensues.  Once the present positive temperature gradient again becomes negative, bends in the river are formed in the lower reaches through turbulence, and thus a mechanical deceleration in the rate of flow occurs.  Suspended sediment is deposited and the oncoming water-masses become backed up.  The result: flooding.
   
In case 2, if saturation of the groundwater basin occurs as a result of a stable positive temperature gradient , then groundwater (springwater) that now surfaces is colder than the ground strata  lying directly beneath it.  The temperature gradient  has been reversed and has become negative again.  Rapid drainage of the heavy water-masses follows.  As a result of relatively low temperatures in the ground, cold, heavy, excess water from the Earths interior now drains off, achieving a positive condition only gradually, because the specifically-heavier water warms up very slowly.  Since in the upper third of the catchment area the slope of the riverbed is usually extremely steep, turbulence is created, and hence bends in the more horizontal parts of the river are formed. 
The further transition from a negative to a positive temperature gradient therefore takes place very slowly, and the incidence of strong turbulence again leads to excessively sharp horizontal bends and to the deposition of boulders, pebbles and sediment, the gouging of pot-holes and the dislocation of the channel bed through mechanical action.  The immediate result of this type of discharge is a widening of the channel, a heaping up of broad banks of boulder-gravel, and evaporation or subsidence of water in the churned-up riverbed.  In this process the riverbed has again been exposed to the influence of external temperature (already typical of alpine flow-regimesHotwordStyle=BookDefault; , and always associated with an asymmetrical profile - a deepened bed on one side and a gravel shoal on the other).  The discharge of water takes place immediately in exactly the same way as in case 1.  The rupture of the riverbank is the result.  In times of flood mechanical braking is effected by the bends thus formed, and banks are breached even further.  The situation is even worse than before and again the result is flooding. 

In order to avert the danger of flooding completely it is necessary to eliminate both extreme cases 1 & 2 artificially.

By building dams incorporating appropriate provisionsHotwordStyle=BookDefault; , thermal conditions and rate of discharge can once again be regulated - where these have been altered inappropriately owing to the shift in the temperatures and the associated temperature gradient of the ground strata . The discharge conditions of these regulating dams can be automatically adjusted thermally and quantitatively to the prevailing daytime temperature.  In this way both of these extreme cases will be avoided and will also be modified automatically so as to fall within the intermediate temperatures of the discharge.  With increasingly finer adjustment of the simple apparatus proposed for these dams, temperature gradients suited to the mean seasonal temperature are progressively developed in the river, and in this way it is possible to reduce the danger of flooding at its inception and gradually to avert it.
There is no danger of flooding because, by adjusting the temperature of the discharge to the mean annual temperature, the correct ground temperature gradient can be re-established.  This results in the restoration of the absorptive capacity of the ground, the proper regulation of the groundwater table and with this, the formation of the vitally important retention basin.  Through appropriate adjustment of discharge conditions allows an orderly further drainage of water over the ground surface.  No localised evaporation takes place, and because of this no rapid succession of rainfall occurs, restricted to a limited area.  In other words, the well-ordered conditions of the full cycle are re-established.

Where de-watering or drainage of the ground is desired, it is likewise possible to make unwanted, stagnant water disappear by creating a temperature gradient (positive temperature gradient) conducive to this situation.

It is therefore possible to produce a full cycle or half-cycle at will.  However, dams that have been constructed so far have only produced half-cycles.
In this connection the meaning of full and half-cycles should again be clarified: 
The full hydrological cycle involves the entry of water into the interior of the Earth, the creation of the necessary groundwater body, the detention of run-off water and thereby to forestall or reduce the danger of flooding.  Cold springs are also continuously formed, whose waters reduce the temperature of receiving streams and help to inhibit over-rapid evaporation downstream.

With the half-hydrological cycle, by comparison, a familiar condition occurs where rising water vapour is produced almost uninterruptedly.  In other words, a continuous contribution is made to the mass of atmospheric water and the recurrent precipitation associated with it.  One flood therefore gives rise to the next.



IV.  Basic Principles of River Regulation 
   
It is vitally important to achieve the proper conditions of discharge not only in the above sense, but also in the regulation of waterways and the formation of their banks.  The aim of contemporary river-regulation practice is to effect the fastest possible drainage of water, through bank-rectification and bank-stabilisation with artificial structures.  This type of regulation, however, is thoroughly one-sided and does not fulfil its purpose.
   
It cannot and should not be the task of the river-engineer to correct Nature.  Rather, in all watercourses requiring regulation, his job should be to investigate Natures processes and to emulate Natures examples of healthy streams.  Here again the most crucial factor is the interrelation between water and air temperature, which cannot be disregarded in any regulation.
   
The natural regulators of the drainage of water are forests and lakes.  By cooling the ground in their immediate vicinity, forests create a permanent positive temperature gradient, resulting in the formation of groundwater reservoirs which have a delaying effect on rainwater discharge.  Once again, cold springs issuing from these groundwater reservoirs quickly enter receiving streams, cool the main body of water and thereby inhibit premature evaporation as the water flows along the channel. 
The cyclical movement of water - the transfer of water from the ground to the atmosphere - will be slowed down and distributed spacially along the length of the watercourse.  These cycles do not take place over relatively small areas, so that one fall of rain or one flood does not necessarily give rise to the next.
   
Where forests have been felled and natural lakes are absent, it is necessary to create a substitute: an artificial impoundment of water, which must be correctly built and properly operated.  Only then can it bring about the specified functions of groundwater-recharge, detention of run-off and the creation of a proper temperature gradient.

Indeed, impounded lakes are often built to enable the orderly management of water resources.  However, these have not always proved satisfactory and have often achieved the opposite of what was desired.  To be more specific: as constructed and operated today, impounded lakes are nothing more than storers of water.  They collect the water and fulfil the function of rainwater detention, but almost always produce a half-cycle.  The water remains on the ground surface (no infiltration) or evaporates soon after its release.

Precipitation in the vicinity of existing reservoirs becomes irregular and increases or decreases according to the orientation (wind direction) of the valley.  The normal flow of water in the middle and lower reaches diminishes, the groundwater table also sinks in the middle and lower reaches for the same reason and the productivity of the soil in these areas noticeably declines.  This happens for the sole reason that a thoroughly one-sided temperature gradient  is created in the downstream flow-regime because of the way reservoirs are constructed and through the continuous release of either specifically-heavy or light water, depending on whether water is released directly from the bottom of the reservoir or via a spillway from the top.  Both types of discharge lead to the extreme cases outlined earlier and thus to the generation of half-cycles, with their well-known detrimental effect in the spawning of floods and the resulting damage.

It is therefore the purpose of a properly-constructed reservoir, equipped with the requisite discharge-control systems and starting at the dam itself, to regulate the temperature gradient of watercourses continuously in such a way that these depredations can be avoided with certainty. 

With this method of regulation of the temperature gradient, expensive but usually inadequate installations in the channel itself become unnecessary.

Correctly-constructed reservoirs, as such, are those in which the movement of the water, though slight, will be enhanced by the development of a strong temperature gradient .  Thus, by means of the proposed equipment, cool water strata will continuously and automatically reach the water surface, significantly reducing excessive evaporation - with its unwelcome consequences - which has occurred over these reservoirs up to now.
   
Dangers of flooding can only be prevented in a practical way if, with the use of naturalesque methods of control, water is not returned to the atmosphere as rapidly as possible - as has hitherto been the case -, but is able to fulfil its true function.  This is the establishment of the full cycle in its roundabout route through the Earth, and with it the supply of nutrientsName=supply of nutrients; HotwordStyle=BookDefault; note=See chapter "Temperature&Water movement 6";  to the soil.  It is evident that to date two cardinal errors have been committed: by draining water too rapidly over the ground surface, it is returned to the atmosphere too quickly, thereby causing renewed precipitation and flooding.  More importantly, the water was thus robbed of its most important purpose of infiltrating into the ground.  By inhibiting the full cycle, the supply of nutrients to the soil was also cut off.

River engineering carried out without consideration of the temperature gradient, and concerned exclusively with drainage of the water-masses down the riverbed-gradient, ultimately leads to disturbance of the proper sequence of temperature gradients, or to development of a one-sided temperature gradient  - and hence to catastrophes and inundations.  In France, for example, these must now occur with increasing intensity.  Moreover they will also become common further south until the current misguided practices cease.


Handcolored sketch (original)HotwordStyle=BookDefault;
Handcolored sketch (translated)HotwordStyle=BookDefault;


V.   The Interrelationship between Groundwater & Agriculture

In the preceding section attention was drawn to the mistakes that have been made in the execution of hydraulic engineering projects and indications were given as to how they can be avoided.  In the following the devastating consequences that ensue from the incorrect management of water resources  are to be given special emphasis.

Through mismanagement of waterways, not only are riverside communities exposed to a direct and acute threat but, what is far worse, they are also threatened by an insidious evil, a reduction in soil productivity.

This manifests itself in the retreat of groundwater or its other extreme, swamp development.  If we note the changes that have occurred in areas under food production within the space of a single generation, and if we consider that today (1930) in Austria hardly any grass grows where once our grandfathers enjoyed rich farmland, it is clear to us how fast the productivity of the soil is declining.  For example, the areas under wheat and rye cultivation have fallen from 273 million hectares to 246 million over the last 30 years. 

This decline in yield is particularly marked in mountainous regions, which naturally are the first to feel the full force of the retreat of groundwater.  On alpine pastures, where previously the raising of 100 head or so of cattle was of no consequence, today those with grazing rights squabble over the fodder required for a single beast.  The previously almost inexhaustible, pastureland is today insufficient even for a fraction of its former carrying capacity.

The reason for this decline in soil fertility is purely and simply that the groundwater table has subsided and is continuing to sink further.  The soil, which ought to produce a good yield, must be replenished constantly with additional ingredients required by the plants for growth.  The carrier and distributor of these substances is the groundwater, which in its internal cycle constantly brings up fresh nutrient salts from the interior of the Earth.  If the groundwater recedes, then the natural supply of nutrients ceases.  Artificial fertilisation and redoubled effort constitute only a temporary and incomplete substitute for the natural supply of material.  Atmospheric precipitation only moistens the ground and contains no nutrients for the plants. 

Nature herself is not responsible for the constant increase in the dessication of the Earths surface caused by the sinking groundwater table. Rather, since time immemorial, it has been the unconscious hand of humans that is to blame for the constant lowering of the water table, and with it the withdrawal of natural nutrients.

The reason why water has been generally mistreated is because the importance of the temperature gradient for the movement of water according to inner law has been unknown until now.  In consequence  water was generally mistreated.  In exploiting waters inherent energy for electricity generation, for example, arbitrary structures have been installed in channels which in many cases have affected the water destructively.  Attempts have been made to regulate rivers by their banks, naturally producing negative results.  No thought was ever given to the re-establishment by other means of the rivers equilibrium, which was disturbed by structures in the river itself and through forest clearing. 

The method referred to here - artificial re-establishment where necessary of temperature gradients that under normal circumstances come into existence naturally - is the only correct solution to the problem of bringing about natural drainage of water or its retention in the ground.  Only by pursuing this course or by making use of these findings can further subsidence of groundwater be prevented, and a further drop in soil fertility avoided.  Only in this way will it also be possible to avert the devastation of floods, and to transform water once more into what it always was and always must be: the Giver of Life.

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TEMPERATURE AND THE MOVEMENT OF WATER II

Fundamental principles of River Regulation
With Due Regard To The Status Of Temperature In Flowing Water.

An article by Viktor Schauberger published in "Die Wasserwirtschaft",
the Austrian Journal of Hydrology,
Vol. 24.  1930

Contents:
   
Turbulent phenomena in flowing water
Temperature gradient, streambed slope and riverbend formation
Influence of geographic situation and Earth-rotation on the watercourse
General objectives of river regulation
Regulation of the temperature gradient

The most important factors affecting a waterway will now be addressed in broad outline and the techniques will be presented for regulating waterways in ways that correspond to Natures laws.  Questions of detail will not be dealt with here.

I. Turbulent Phenomena in Flowing Water.

When an ideal liquid flows down an inclined plane without friction, individual filaments of the current ought to move along parallel to each other.  Moreover, according to the law of gravity, this motion ought to accelerate uniformly.  This never happens in Nature, however, since friction occurs between liquid and channel surfaces and between particles of the liquid themselves.  As energy is dissipated in this process, motion is no longer accelerated, but is uniform - if pulsations and other irregularities are discounted. 
In the case of a non-ideal, viscous liquid, as long as water-movement is stratified (laminarHotwordStyle=BookDefault; )  - surface friction for the moment excluded - a certain amount of energy is transformed into heat.  At a particular velocity, which varies according to water temperature, laminar motion transfers into a vorticose, turbulent one.  With turbulent motionHotwordStyle=BookDefault;  a certain amount of energy is also converted into heat, as was demonstrated by Barnes and Cokers experiments, and a further amount of energy is dissipated through exchange of momenta.  In this context Forchheimer states that  ...in vortical motion the more central flow is not only transformed into heat but also into vortices, and conversely an acceleration of the more central motion can also possibly occur through a reduction in vortical activity, although no experimental evidence for this is available?.  The authors own observations reveal that:
   
1. Turbulence is at a minimum at a water temperature of +4?C (+39.2?F) under equal conditions and in identical profiles;
   
2. Turbulence and the associated decrease in velocity become more pronounced the more the water temperature diverges from +4?C;
   
3. It is possible to achieve an acceleration in the central flow by inducing a decrease in water temperature towards +4?C. 
   
Fig. 2HotwordStyle=BookDefault;  shows the exceptionally strong occurrence of turbulence and vortices where a hot spring flows into the Tepl near Karlsbad (Karlovy Vary).  If the hot spring water is blocked off temporarily , the water in the Tepl flows downstream with considerable velocity due to the pronounced slope of the stream-bed at this spot.  After re-introduction of hot spring water, this is reduced immediately to an extraordinary degree.


The enormous effect of water temperature on turbulence and velocity can also be observed at a log-flume in Neuberg (Steiermark).  Here in a half-round, 2km (1.2 miles) long wooden flume, measurements of temperature and velocity were made during the floatation of timber.  In the morning when the water temperature was roughly 9?-10?C (48.2?F - 50?F), a block of wood required about 29 minutes to cover the distance.  At midday, with a water temperature of 13?-15?C (55.4?F-59?F) and under otherwise equal conditions, it took 40 minutes.

A further example of this concerns water supply to the turbines of a board mill in North Austria.  The water supply consists of two 2km long concrete channels.  One draws its water from the so-called Cold Murz, the other from the warmer Still Murz.  The former flows towards their common intake along the shaded side of the valley, the latter on the sunny side.  With the canal profile at full capacity the normal flow of water from the Still Murz amounts to about 860 litres/sec (189gals/sec).  According to the observations of Mr Br?ckner, the factory director, and Mr. Patta, the works manager, on occasions when the water temperature of the Still Murz approaches that of the Cold Murz, and the temperature gradient in the supply canal from the Still Murz becomes positive, under certain circumstances (such as at night) the volume of water increases to 1,800 litres/sec (396 gals/sec).  Despite the constriction of the intakes above the turbines, the output of the turbines increases, resulting in an increase in power generation equivalent to the thermal output of one wagonload of coal per night.



II. Temperature Gradient, Riverbed-slope and River Bend Formation
   
The formulae applied today to the calculation of flow-velocity in channels encompass geometrical profile of the channel, roughness of channel wall-surfaces and gradient (riverbed-gradient, slope of the water surface or energy lines).  What these formulae do not take into account are the physical properties of water, such as viscosity and specific weight, which vary with temperature.  However, it is important to take note of the temperature regime in the direction of flow - the temperature gradient or rate of change in temperature per unit length in the direction of the downstream flow. 

The temperature gradient is described as positive when the water temperature approaches +4?C in the direction of flow, and in the opposite case, as negative.
   
If for example the temperature at point A of a channel is t1?, at a lower point B is t2?, and if t1>t2 (positive temperature gradient ), then along this stretch an increase in velocity occurs due to a reduction in turbulence.  Horizontal transverse vortex-trains and turbulent formations become smaller.  In the opposite case, where t1<t2 (negative temperature gradient ), the incidence of turbulence increases owing to a rise in temperature and an ensuing loss in kinetic energy, which expresses itself as a decrease in velocity.  The tractive force becomes less and deposition of transported sediment  follows.

In the section relating to tractive force and the movement of sediment, Robert Weyrauch states in his book, Hydraulic Calculation: 
So [boundary shear force] is dependent on the provenance of the sediment, and is therefore constant for a relatively short stretch of river without the presence of affluent streams.  In the case of longer stretches without affluent streams it diminishes in a downstream direction.?
   
In the above example the reason for this is obvious - a case of negative temperature gradient.  Where secondary streams exist (which reintroduce colder water into the main stream and thus usually effect an increase in flow-velocity through a reduction in turbulence), weakening of the tractive force does not occur.  Tractive force is maintained or increases with a positive temperature gradient and decreases with a negative temperature gradient.

This phenomenon becomes all the more important when studying changes in the riverbed.  Assuming a uniform discharge of water, the bed-gradient remains constant, or will become greater with a positive temperature gradient and smaller with a negative temperature gradient . 

Where the volume of water increases in conjunction with a negative temperature gradient, the morphology of the riverbed itself is not substantially altered, whereas under these conditions ruptures of the bank do occur as the central axis of the current oscillates from one side to the other.  With an increase in the volume of water and a positive temperature gradient, the riverbed will be attacked and deepened.  The watercourse straightens out and river bends previously formed through deposition of sediment will be evened out. 

Under certain circumstances, with a sudden drop in temperature and atmospheric pressure (such as clear skies after a flood), especially at night, the descending flow of water can become even more dangerous than quantitatively greater masses of water under a negative temperature gradient in warm, rainy weather conditions.

The mean central riverbed gradient which develops over the course of time is affected by the mean annual discharge and the temperature gradient corresponding to the mean annual temperature, wherein the mean annual temperature and the amount of rainfall are to a certain extent interrelated.  In those years where larger fluctuations in the mean annual temperature occur, there will also be relatively greater changes to the riverbed.

Measurement of temperatures in the same river cross-section indicates that temperatures vary according to location.  Also, during the course of a day the place of the greatest flow-velocity (flow-axis, central core of the current) also changes its position within the profile laterally as well as vertically.  While the lowest temperature is always to be found in the central core of the current, it increases to a greater or lesser extent towards the periphery.  During the day the line of the central axis of flow lies closer to the shaded bank, since that is where the heavy water accumulates, whereas the lighter water flows along the sunny side.  At night, due to the enlargement of the heavy water side, the current core migrates towards the centre of the channel.  With a negative temperature gradient, the current core lies close to the water surface, and with a positive temperature gradient, deeper down.

During the floatation of timber the following phenomenon can be observed: if the temperature of the surroundings is lower than the water temperature (temperature gradient decidedly positive - water cools during flow), floatation takes place with the greatest of ease.  The logs stay in the middle of the channel and float down the clearly-defined central axis of the current. On warmer days, especially towards midday, timber becomes stranded.  Log-jams happen easily, because the flow axis wanders about (transverse currents due to turbulence) and does not keep to a centralised course for a prolonged period, as it does with a positive temperature gradient .
   
In section 1-1?HotwordStyle=BookDefault; , in the stretch of river shown in fig. 2HotwordStyle=BookDefault; , the axis of the current still lies in the middle of the river.  If the values of the mean flow-velocities in each vertical of the river profile are plotted vertically, and an energy-line is drawn, then as is to be expected, the energy falls off to a greater or lesser extent towards the rivers edge.  If this decrease exceeds a certain limit, then it is obvious that this condition can only be unstable and even small causes will suffice to alter the status quo.

If, for example, the bank at 1 HotwordStyle=BookDefault; is shaded (see sketchHotwordStyle=BookDefault; ) and the bank at 1? exposed to the Sun, then at 1? the water will be warmed, becoming specifically lighter, and due to increased turbulence will flow more slowly here than at 1.  As a result of this heavy water flowing along the left bank will advance more rapidly, already initiating the first beginnings of circular motion, shown in fig. 3HotwordStyle=BookDefault; .


In this instance the point of rotation lies beyond the profile of the river.  A new condition of equilibrium is established (profile 2-2?HotwordStyle=BookDefault; ).  This circular motion continues until the respective temperatures and velocities of the heavy and light waters have reached equilibrium.  The temperature gradient in the cross-section itself, which in cross-section (2-2?HotwordStyle=BookDefault; ) was previously negative from the left bank to the right, is reversed and becomes negative from right to left - for with the constant increase in the inward curvature of the current-axis towards the right (fig. 3HotwordStyle=BookDefault; ) a flow of lighter and slower water of a higher temperature is created to the left.  At the point in the cross-section where the temperature gradient reverses, a ford (cross-section 3-3?HotwordStyle=BookDefault; ) is established through the weakening of the tractive force (due to transfer of energy from the heavy water to the light water on the right bank). 

If the profile of the river is compared with the respective energy line, it can be seen that both contours are similar.
The formation of river bends occurs mainly where greater fluctuations in temperature, enhanced by climatic conditions, occur within short periods of time - as in the case of the debouchment of a river from mountains onto the plains.  On the other hand, a straight stretch of river with regular, bilateral deposition of sediment is formed where the temperature gradient remains positive over long stretches of river for the greater part of the year.

Fig. 4Name=Fig. 4; HotwordStyle=BookDefault; note=Reproduction is impossible, due to the bad quality of the original;  shows a stretch of the River Tepl shortly before it flows into the Eger.  In this stretch the temperature gradient is always positive, because the water, previously heated upstream by the inflow of hot springs, cools off en route.  Over this stretch the Tepl in every respect exhibits a straight course with regular bank-formation on both sides.

Handcoloured sketch (original)
HotwordStyle=BookDefault; Handcoloured sketch (translated)



III. The Influence of the Geographical Situation and the Rotation of the Earth 
   
Apart from the influence of terrain and temperature gradient outlined above, the geographical location and the rotation of the Earth (geostrophic effect) also decisively affect the development of a waterway. 

By and large, the influences arising from geographical location are expressed in the development of the temperature gradient. 

In Sweden [far north], for example, the regular climate favours a positive or only weakly-developed negative temperature gradient.  The flow of water in rivers is uniform, as is the transport of sediment.  The riverbed is perfectly regular, and in most cases trough-shaped (see fig. 5HotwordStyle=BookDefault; ).  Heavy water-masses only adjust slowly to climatic conditions of valley floors, and water temperatures are preserved for a long period.  Such conditions are also to be found in other mountain streams flowing through cool ravines or forests.  Despite enormous fluctuations in the amount of water discharged and the generally steep gradients, moss attaches itself to the stones in such streams.  The moment such a channel is exposed to direct light, the covering layer of moss disappears from the stones, which subsequently will be dislodged, and breaches in the riverbank will occur: the channel immediately assumes the character of channels whose temperatures fluctuate continuously.

The earlier a watercourse is exposed to direct sunlight (through clear-felling and clearance), the faster the time and the shorter the distance in which the equalisation of temperature occurs.  As a result, the water-masses decelerate abruptly in sharp brake-curves, and transported sediment is deposited prematurely (loss of energy and velocity with the rapid transition from a positive to a negative temperature gradient).  Very wide channel-beds are formed so that the water flowing through them under normal conditions is increasingly exposed to the effects of higher temperatures.  The immediate result is excessive evaporation and over-saturation of the atmosphere with water vapour, which promotes protracted rainfall or sudden catastrophic downpours with the onset of low temperatures.

Venetian rivers enter the upper Italian plain from a steep and almost sheer range of high mountains.  Because of this they are subjected to extraordinarily large and abrupt fluctuations in the temperatures of their immediate environment for the greater part of the year.  As long as the river continues to flow in the mountains, the water and its surroundings are maintained at a uniformly low temperature.  Fluctuations occur only within narrow limits.  The morphology of the riverbed exhibits no particular deviations.  This all changes the moment the river enters the plain, which for the greater part of the year is warm, periodically hot, and is prone to sudden, strong fluctuations in temperature.  Daytime and night-time temperatures also vary by up to 10?C (50?F).  The profile of the stream-flow takes on a very characteristic form; a very flat bed with deeply incised gutters (or even two or more gutters in very wide beds) - a pronounced double-profile (see fig. 6HotwordStyle=BookDefault; ). 
As a rule the gutters in the torrente are very deep.  However, since the stream-bed gradient is slight, the velocity of the water in the gutter keeps within normal bounds.  Since forestry in the Italian Alps is in a very poor state - whole areas are barren due to neglect over hundreds of years - when the snow melts, great quantities of cold water reach the hot plain without a transitional phase.  The ensuing almost instantaneous reversal of the temperature gradient provokes the deposition of large banks of boulder-gravel, which is ejected mechanically by the massive volume of water in the stream-bed - and where the channel is insufficiently wide, this causes considerable flooding.

Rivers in western parts of the upper Italian plain have a completely different appearance, although topographical conditions are the same as the Venetian.  The rivers exhibit no torrente character, but flow in a regular profile at a uniform velocity towards the river Po.  This regularity is caused by the large reservoirs of the upper Italian lakes, which detain the snow meltwater and release it at a temperature already more suited to the plain, so that the formation of such extreme negative temperature gradients, which occur with the torrente, can no longer happen

In northward-flowing alpine streams, conditions are similar to those described above, but not as pronounced as those of the torrente, because the northern slope of the Alps is gentler and fluctuations in temperature are smaller.  Here, after leaving the mountains, the streams exhibit an asymmetrical deepening of the channel with a build-up of shallow gravel beds on the inside curve (likewise a double-profile) - also a result of the negative temperature gradient present in the longitudinal and transverse sections for the greater part of the year (fig. 7HotwordStyle=BookDefault; ).

In the above, two extreme cases (Sweden and Italy) were discussed.  Between them there is of course a wide range of intermediate stages which would take too long to elaborate here.  It should be mentioned, however, that rivers which flow into the sea under a positive temperature gradient (those flowing into the Arctic Ocean) carry their sediment far out into the sea (promontory or haff formation), whereas rivers discharging into the sea under a negative temperature gradient deposit their sediment prior to reaching it (formation of deltas).

In the case of a westeast direction of flow, the former rivers migrate laterally northwards due the constant enlargement of the heavy water side and the migration of the stream-flow axis towards the northern bank.  In the latter case the rivers are widened perpendicularly to the direction of flow in proportion to the decrease in tractive force.

Through the formation of the previously-described heavy water and light water sides, and as a result of helical inversion of the respective water-strata, centrifugal effects are induced.  These are either strengthened or weakened by the Earths rotation (geostrophic effect) according to the direction (orientation) in which the discharge of water occurs.  Channels flowing in an eastwest direction have a different character to those whose flow is westeast, northsouth or southnorth.  In a westeast channel the transport of sediment will be distributed evenly over the whole cross-section, whereas in southnorth and northsouth channels the transport of sediment is mostly one-sided.  Westeast and eastwest channels will generally be fertile on both banks (although in the latter case both banks will eventually become barren).  Southnorth and northsouth channels in the main are fertile on one side only and typically exhibit an asymmetrical deepening of the channel bed.



IV. The General Tasks of River Regulation 
   
In connection with the previous explanations, the following factors are decisive in the formation of the channel cross-section, the development of
the longitudinal profile and the horizontal course of a river:

1.    the topography
2.    the temperature gradient
3.    the geographical location
4.    the rotation of the Earth
   
The topography is dictated by Nature.  Where it is essential to protect objects of cultural value, it is possible to use minor retaining walls, although it would be wrong to attempt to regulate a river by means of its banks - in other words, merely to combat the effects, but not the causes themselves. In particular, bank-rectification in the form of straight, smooth walls is often dangerous, since the ensuing increase in velocity along the smooth walls will produce the circular motion described Temperature Gradient, Riverbed Slope and River Bend Formation, figs. 2HotwordStyle=BookDefault;  & 3HotwordStyle=BookDefault; , promoting breaches in the riverbank in a downstream location.  A more promising direction for river engineering is a priori to regulate the temperature gradient, for with the regulation of the temperature-gradient with only minor subsequent assistance from the riverbank itself, the geographical constraints can to some extent be catered for.
   
In the execution of river regulation works, the prime objective is the harmless drainage of water, so that human life and cultural assets will be protected with all certainty from the effects of flooding. 
The following factors must be taken into account in all river engineering:
   
a): the longitudinal profile and the horizontal course must be brought into harmony;
b): the channel profile must be so constituted as to enable the faultless discharge of a certain maximum quantity of water in a manner suited to local conditions;
c): precautions must be taken to ensure that water from catastrophic rainfall in the catchment area does not immediately become surface run-off;
d): endeavours must be made to regulate the transport of sediment in such a manner that deposition or removal only happens where desired.

In connection with a); Over the course of time a bed-gradient will be established in a river, related not only to the mean annual discharge, but also to the temperature gradient corresponding to the mean annual temperature.  This mean streambed-gradient can then be maintained or engineered through the regulation of the temperature gradient appropriate to prevailing climatic (temperature) conditions. 

Furthermore, when modifying longitudinal profile to suit the actual situation, care must be taken to ensure that the sequence of river bends is correct and that, for example, a left-hand bend does not occur where Nature demands a right-hand one.
   
Referring to b); the channel profile must be adapted to the local conditions and must be capable of an orderly discharge during periods of low and high water flow.  The phrase `suited to local conditions` will be used to mean: in those stretches of rivers which exhibit, and whose nature is favourable to, a natural positive temperature gradient for the greater part of the year, a simple trough-shaped profileHotwordStyle=BookDefault;  would be appropriate.  However, where strong fluctuations in temperature occur a profile should be selected which, due to its shape, contributes to the longest possible maintenance of low temperatures in the flowing water.  A profile possessing these characteristics is the type of double-profile (fig. 6HotwordStyle=BookDefault;  and fig. 7HotwordStyle=BookDefault; ) which rigorously follows the prevailing conditions.  In this a natural separation between heavy and light water occurs - therefore drainage of water will be orderly and lateral oscillations of the central axis of the current will be reduced to a minimum, since this will be displaced from the surface down to the deeper part of the channel. 
Through the distribution of weight vertically instead of laterally the flow of water at the bends is consistent with that of a healthy channel.  It prevents a change in temperature gradient within the cross-section, as was described in section 2 .HotwordStyle=BookDefault;   Heavy water flows in the lower part of the profile, local conditions permitting, and light water in the upper part.  At the interface between the fast-flowing heavy water and the slower-flowing light water, a train of vortices with horizontally-disposed axes is formed, which acts counter to the direction of the current (fig. 9aHotwordStyle=BookDefault; ).  This train of vortices distributes the suspended sediment evenly to the right and left of the heavy water core (fig. 9bHotwordStyle=BookDefault; ). 
The light water flowing above the heavy water protects it from excessive direct heat.  Through this the temperature gradient is maintained for as long as possible in the flowing water.  The advancing cold-water core is braked mechanically due to the increasing velocity of the heavy water core, the vortex-train is enlarged and the cold water core diminished, automatically reducing its translatory energy.  Conversely, with a decrease in the riverbed gradient the translatory velocity slackens, causing a reduction in the magnitude of the vortex-train and its braking effect.
   
The correct positioning of this vortex-train is extremely important.  The mechanical formation of the transverse profile is dependent on it.  In healthy waterways, apart from slight variations in river bends, the axis of the vortex-train lies horizontally, while under abnormal conditions it is sharply inclined or even vertical, giving rise to irregularly-shaped profiles.  The appearance and power of such vortices at the interfaces between different velocities are described by Forchheimer:
"Where a shallow strip borders on a deep bed, as is often the case where the flow overtops the riverbank, the unequal velocities create vortices with vertical axes.  These vortices can excavate longitudinal gutters in the upper riverbed close to the edge of the deeper bed, which have the appearance of pipeline trenches." 
During the flood of 14th July 1913, a longish gutter 0.3m-1.5m (1-5ft) wide and 0.2m-1.5m (7in-5ft) deep was formed in this way in the Leonardbach at Graz, by a vertical vortex about 30cm (12in) away from the edge of the deep bed (see fig. 10HotwordStyle=BookDefault; ).

If it is impossible to implement a double-profile (because of too high a cost, for example), then by means of a properly-operated reservoir the discharge in the channel can be structured automatically in such a way that the temperature gradient becomes positive or only weakly negative along the stretch of river in question.  In this case heavy water always moves down the centre of the river and the even deposition of sediment and suspended solids on both sides acts to build up the riverbanks, as was mentioned earlier in the case of the Tepl.  In this instance the water carves out the appropriate profile unaided, and in the course of time a correctly-positioned double-profile (endowed with the previously described characteristics favourable to the discharge of water) will come into being automatically, a process which naturally takes quite a long time.

In connection with c); the essential measures for preventing rapid stormwater run-off have already been addressed in section 1.3HotwordStyle=BookDefault; , so that any further comment here would be superfluous.
   
Regarding d); the tractive force, the sediment transport of a river and their relation to the temperature gradient have already been covered during this discussion.  Through the orderly introduction of the colder energy-water present in affluent streams the positive temperature-gradient and thus the tractive force can be maintained in the main channel - an objective which can also be achieved through the after-release of low temperature bed-water from the dam.  The intensity of the effect, however, will depend on the ratio of the after-flow water to the scouring-force-deficient main-channel water.
   
The temperature gradient at the confluence of a secondary stream with a main stream must be properly established, otherwise unwelcome phenomena may occur in the main stream in the same way that incorrect regulation of the secondary flow can also play the most appalling havoc in the main channel.
   
In this connection attention should also be drawn to phenomena related to the tractive force in unhealthy rivers.  As was previously seen in the case of the torrente, when cold water-masses reach a warm valley floor, then the longitudinal profile shown below comes into being.  This is due to the temperature gradient which at this point has become negative.  From A to B the temperature gradient is negative with a major accretion of sediment at B, the point where the tractive force is weakest (see fig. 11HotwordStyle=BookDefault; ).
Here the water has attained its highest temperature.  Due to the back-up at B caused by the deposition of sediment, an overfall with potholes and a train of horizontally-disposed vortices (barrel vortices) is formed immediately downstream from B, creating areas of low temperature (pockets of heavy water) which are clearly identifiable.  When the light water passes over the top of this colder heavy water it will be cooled from below and the temperature gradient  will become positive over the short stretch up to C and from here the whole process is repeated.
   
For a regulation to be carried out successfully, the alternation of temperature gradients must now be extended over a greater distance, resulting in a more regular movement of sediment and the re-formation of the stream-bed into gentler wave-forms.

Handcolored sketch (original)HotwordStyle=BookDefault;
Handcolored sketch (translated)



V. The Regulation of Temperature Gradient   
   
The establishment of the correct temperature gradient is only possible under two conditions:
   
1) regulation of the temperature gradient through the construction of an impounded lake
2) maintenance of the temperature gradient through the correct form of profile 
   
On the first point: where topographical conditions permit and there are no problems with water rights, it is preferable to construct an impounded lake in the highest part of the river catchment area.  With sufficient depth the lakewater becomes stratified according to its specific density, the lower-temperature water below and the higher-temperature water above.  At the point of out-take, the dam wallName=dam wall; HotwordStyle=BookDefault; note=See Patent Nr.: 136 214;  can be so constructed that water of the required temperature can be drawn from the reservoir through the automatic mixing of water of different temperatures taken from various levels.  This is made possible by means of a movable sluice gateHotwordStyle=BookDefault; , activated automatically by a floating caissonHotwordStyle=BookDefault;  directly exposed to the Suns radiation and the external air temperature, and which will thus automatically release a greater or lesser cross-section of the deeper water-strata.

In this way bottom-water can be mixed with surface water as circumstances demand. To this end, final adjustment of the floating caisson will be carried out after examination of climatic and other conditions, so that at all times the water leaves the dam at a temperature approximating the prevailing air temperature. 
Taking this factor into account, the temperature gradient in the sector of the channel decisive for regulation of the whole watercourse (usually the upper reaches) will become positive, with only a gradual and unavoidable transition to a negative temperature gradient .  The point of transition and the progress of the change-over can thus be effected at the desired location, which will be selected such that mechanical influences will produce no adverse effects.  The reversal of  the temperature gradient no longer takes place over short distances, but over a desired longer stretch - and deposition of sediment will also no longer be precipitate, but will be distributed evenly along this greater length.  Through the evening-out of the temperature gradient achieved in this way, only gentle modifications to the riverbed will occur instead of the haphazard dislocation of the channel geometry described previously, and conditions will be created which very closely approximate the mean annual temperature gradient and discharge.

In connection with the second condition above: where impounded lakes cannot be built for some reason or other, attempts must be made to maintain a low water temperature for as long as possible - decisive for a positive temperature gradient - through the correct choice of channel profile.  Such a profile was described in section 2.4HotwordStyle=BookDefault; .  The greatest attention must be paid to the horizontal development of the watercourse (sequence of river bends).  For this reason the deeper part of the double-profile must be correctly positioned in relation to depth and handing (left or right) at the river bend in order to maintain the central axis of the current and the proper alignment of the axes of the vortex-train.  If the lower, decisive portion of the profile is properly established, then it also maintains its form and position in loose gravel, as is demonstrated by the gutters in the torrente.

Conclusion 

These are very generalised illustrations of the difficult problems encountered in river engineering and river regulation, when the decisive factors and temperature gradient are taken into account.  Detailed explanations an only be applied to specific and individual cases and conditions and cannot be given here.
   
The perception that mathematical formulae alone are an inadequate basis for the execution of river engineering works, was aptly expressed by the hydrologist Robert Weyrauch - namely, that for the carrying out of river engineering projects, "an especial gift for hydraulics, an exceptional feel for what is hydraulically possible or impossible is necessary.  This is only acquired with difficulty, and even the most experienced repeatedly suffer disappointments.?