Hidden Nature

the shortest and straightest route to the sea, the more the flow

of water weighs into the bends, the longer its path and the

more destructive and the worse the water will become.^1

The variations in the temperature of the water-body are so subtle,

within a range of 0.1 °C to 2.0°C (0.04°F to 0.08°F), that contempo-

rary hydraulic engineering practice has never felt they were signif-

icant. Viktor Schauberger, however, considered the temperature

variation absolutely essential for all natural water resources man-

agement. He insisted that no artificial constraints on the river could

ever be successful unless these variations were taken into account,

since whether a river removes, transports or deposits its sediment

is dependent upon the water temperature and the temperature gra-

dient predominantly active along its course.

Creating a positive temperature gradient

When water descends a gradient, in the course of flow under natural
conditions, it rhythmically first heats up and then cools down. The
degree of heating depends on the amount of friction with the
riverbed, the external temperature and the extent to which the water
is directly exposed to the Sun. Only a minute change in temperature
is required for water to pick up, transport or deposit its sediment, but
the type of temperature gradient prevailing determines the action. A
negative temperature gradient causes the deposition of sediment,
and a positive temperature gradient provokes its removal. The tem-
perature gradients alternating too suddenly can, however, cause the
scouring or deposition of gravel to become chaotic.

Fig. 11.1. Alternate heating and cooling

(breathing) rhythms in river flow.

Friction with the river bed gradually warms the

river (negative temperature gradient) so that it

starts to deposit its suspended sediment. When

this reaches its maximum, an overfall occurs,

producing a horizontal barrel vortex that cools the

water (positive temperature gradient), until the

river gradually warms up again. Schauberger

likened this to the river 'breathing.'

11. RIVERS AND HOW THEY FLOW