Hidden Nature

In Fig. 11.1, for example, from A to B the temperature gradient

is negative. From A to B the water gradually heats up and in the

process is unable to retain the sediment in suspension and drops it

progressively as the water becomes warmer. At B, the zone of maxi-

mum deposition, the accumulated material results in an overfall

that, in turn, creates a horizontal barrel vortex immediately down-

stream. This vortex, however, cools the water and therefore from B

to C the temperature gradient becomes positive. The sediment is

once more picked up and transported. Upon reaching C, the effect

of the positive temperature gradient gives way to its negative coun-

terpart and the suspended matter is again dropped, reaching a max-

imum at D.

This pulsation or alternation is like breathing; a positive tem-

perature gradient representing the inbreath, the absorbing, mate-

rial-collecting movement; the negative temperature gradient

representing the outbreath, where the energetically transformed

matter is exhaled from the system and deposited. In order to reg-

ulate a river naturally and successfully, it is essential to study the

alternating sequence of the temperature gradients. A stretch of

river with a positive gradient is less likely to flood, since only

minor sediment deposition will occur. If the danger of flooding is

to be reduced then a positive temperature gradient must be recre-

ated or its duration extended. This can be done in four principal

ways:

1. By shading and cooling the river through the replanting of
   trees, particularly at the bends, where the friction and therefore
   the warming tendencies are greatest. Tree species with a high evap-
   oration rate should be planted. Through evaporation the sap in the
   tree is cooled and circulates down to the roots under the river bed,
   cooling the water as well. This kind of tree therefore acts like a
   refrigerator.
   In order to maintain the health of the river, there should be a belt
   of trees 500 to 1000 metres wide. Rivers flowing through cleared,
   barren countryside should be reforested in order to re-establish
   healthy flow conditions, restore the nutrient supply and recharge
   the groundwater table in its vicinity (Fig. 11.2).


2. By the construction of appropriately designed dams in which
   the temperature of the discharge can be controlled according to the

HIDDEN NATURE