Discussion by A. Goubet, France.
Water reuse is a relatively new subject, on which most work has been done in the last 10 years. It is
true that the world consumption of electricity has doubled in 10 years, that waste heat from central
generating stations has kept pace with power generation and that the prospect of massive nuclear
power stations is likely to lead to a further doubling of power production in the next decade.
The research work in progress to study the problems arising from thermal pollution may be
classified as (1) biological effects, which are not necessarily harmful, and (2) physical studies arising
from mixing of warm with cold water, and the cooling of water.
The biological studies, because of the complexity of the phenomena involved in receiving rivers and
the variety of the objectives of such work, are not yet capable of predicting results with any great
accuracy, except perhaps where high temperature discharges are involved.
Mixing studies on heated water discharges have likewise made little progress. We know that mixing
is poor and that heated water tends to remain at the surface but we are comparatively ignorant as to
what will happen in an estuary or how recirculation currents will affect a discharge, although some
progress has been made by the use of models.
However, so far as the study of temperature effects in rivers is concerned, principally the mixing of
heated water, satisfactory progress has been made.
Several groups have worked independently and reported their results recently. In 1966 the mathematical model of Berger and Schmitz constituted the best of its kind in Europe if not the world, both
as a contribution to research in this field and as a tool for the study of an actual problem.
These models express generally that the temperature of a river depends upon phenomena such as
evaporation, condensation, radiation, convection etc., that have long been known although they also
depend upon the use of coefficients or laws that may be insufficiently well defined, e.g., the influence
of wind velocity. Furthermore, the calculations require the use of meteorological values that ought to
appertain to the actual situation but which in reality only apply to the perhaps distant meteorological
station where they were obtained.
For these reasons the use of such physical laws in theoretical studies may introduce inaccuracies. It
is desirable that mathematical models relative to temperature, like all other models, may be compared
with the results of actual situations. I do not think that the authors' model has been subjected to this
sort of proof.
It also seems desirable that the model permits a probability study to be made of the reuse of water
with a view to obtaining information about the maximum temperature likely to be obtained, expressed as a probable occurrence in terms of frequency per day or per annum. This would presuppose
the availability of meteorological data daily or weekly and the use of such data in the model. The
introduction of such data does not appear to be capable of being achieved in Berger and Schmitz's
model, nor in any other described in 1966.
A model also ought to take account of the fact that it is possible for several heated discharges and
many effluents to be discharged to a long river. This clearly was not the problem before the authors,
who limited their investigation to one point (the city of Basle), the section of the Rhine situated
between two points receiving an important effluent. It would be useful if models recently put forward
would provide answers to questions arising from the complex problem of multiple discharges.
Thus, the model can be adjusted to agree with actual observations; what is the possibility of
obtaining day to day temperatures based on true meteorological data, and what is the possibility of
the model being used to represent complicated situations, particularly where several central power
stations occur and variable additions of non-heated effluents may be made?
Reply
The correctness of the model was actually proven by observations. In these cases flowtime-distance
relations of the stream were measured with the aid of fluorescent dye, water temperatures were
recorded over a restricted period of time and likewise global radiation, total radiation budget, temperature and water vapor content and wind velocity above the surface of the water at a certain distance.
These studies were made at the Rase River, near Gottingen, Germany, a small stream deriving from
a karst spring pool at a constant temperature of 9°C, on two occasions, one representing a cloudless
summer day, the other during 24 hours on a bright and very cold day in winter. The first situation
resulted in warming, the second one in cooling the water flowing out of the spring.
Further studies were made in the Madison River at Yellowstone Park, U.S.A. The stream drains hot
geyser effluents and therefore has summer temperatures above the equilibrium temperature. The
cooling effect on the water whilst flowing downstream is remarkable because of the high altitude of
the area. The temperatures observed in the streams were in good conformity with those ones computed from the observed meteorological data. Deviations for certain ranges of the Madison River could
be explained by the penetration of ground water into the stream through the river bed or by shading
effects of forests closely bordering the river banks.
Mixing of the geyser effluents in the Madison River was complete in the cross section. Mixing of
21
Water reuse is a relatively new subject, on which most work has been done in the last 10 years. It is
true that the world consumption of electricity has doubled in 10 years, that waste heat from central
generating stations has kept pace with power generation and that the prospect of massive nuclear
power stations is likely to lead to a further doubling of power production in the next decade.
The research work in progress to study the problems arising from thermal pollution may be
classified as (1) biological effects, which are not necessarily harmful, and (2) physical studies arising
from mixing of warm with cold water, and the cooling of water.
The biological studies, because of the complexity of the phenomena involved in receiving rivers and
the variety of the objectives of such work, are not yet capable of predicting results with any great
accuracy, except perhaps where high temperature discharges are involved.
Mixing studies on heated water discharges have likewise made little progress. We know that mixing
is poor and that heated water tends to remain at the surface but we are comparatively ignorant as to
what will happen in an estuary or how recirculation currents will affect a discharge, although some
progress has been made by the use of models.
However, so far as the study of temperature effects in rivers is concerned, principally the mixing of
heated water, satisfactory progress has been made.
Several groups have worked independently and reported their results recently. In 1966 the mathematical model of Berger and Schmitz constituted the best of its kind in Europe if not the world, both
as a contribution to research in this field and as a tool for the study of an actual problem.
These models express generally that the temperature of a river depends upon phenomena such as
evaporation, condensation, radiation, convection etc., that have long been known although they also
depend upon the use of coefficients or laws that may be insufficiently well defined, e.g., the influence
of wind velocity. Furthermore, the calculations require the use of meteorological values that ought to
appertain to the actual situation but which in reality only apply to the perhaps distant meteorological
station where they were obtained.
For these reasons the use of such physical laws in theoretical studies may introduce inaccuracies. It
is desirable that mathematical models relative to temperature, like all other models, may be compared
with the results of actual situations. I do not think that the authors' model has been subjected to this
sort of proof.
It also seems desirable that the model permits a probability study to be made of the reuse of water
with a view to obtaining information about the maximum temperature likely to be obtained, expressed as a probable occurrence in terms of frequency per day or per annum. This would presuppose
the availability of meteorological data daily or weekly and the use of such data in the model. The
introduction of such data does not appear to be capable of being achieved in Berger and Schmitz's
model, nor in any other described in 1966.
A model also ought to take account of the fact that it is possible for several heated discharges and
many effluents to be discharged to a long river. This clearly was not the problem before the authors,
who limited their investigation to one point (the city of Basle), the section of the Rhine situated
between two points receiving an important effluent. It would be useful if models recently put forward
would provide answers to questions arising from the complex problem of multiple discharges.
Thus, the model can be adjusted to agree with actual observations; what is the possibility of
obtaining day to day temperatures based on true meteorological data, and what is the possibility of
the model being used to represent complicated situations, particularly where several central power
stations occur and variable additions of non-heated effluents may be made?
Reply
The correctness of the model was actually proven by observations. In these cases flowtime-distance
relations of the stream were measured with the aid of fluorescent dye, water temperatures were
recorded over a restricted period of time and likewise global radiation, total radiation budget, temperature and water vapor content and wind velocity above the surface of the water at a certain distance.
These studies were made at the Rase River, near Gottingen, Germany, a small stream deriving from
a karst spring pool at a constant temperature of 9°C, on two occasions, one representing a cloudless
summer day, the other during 24 hours on a bright and very cold day in winter. The first situation
resulted in warming, the second one in cooling the water flowing out of the spring.
Further studies were made in the Madison River at Yellowstone Park, U.S.A. The stream drains hot
geyser effluents and therefore has summer temperatures above the equilibrium temperature. The
cooling effect on the water whilst flowing downstream is remarkable because of the high altitude of
the area. The temperatures observed in the streams were in good conformity with those ones computed from the observed meteorological data. Deviations for certain ranges of the Madison River could
be explained by the penetration of ground water into the stream through the river bed or by shading
effects of forests closely bordering the river banks.
Mixing of the geyser effluents in the Madison River was complete in the cross section. Mixing of
21