Environmental Engineering Reference
In-Depth Information
was appreciated by the ancient Egyptians. If the river flood level was at twelve ells there
was insufficient water for crops, and hunger or famine prevailed. As water levels rose the
harvest was likely to improve, so that with a sixteen-ell flood there was abundance.
However, the diagram also demonstrates the delicate balance between too little and too
much water. With flood levels above eighteen ells the river would burst its banks and
cause disaster.
The methods of extracting water from the river varied. As the river level would
normally be lower than the land on which the crops were being grown, there had to be
some method of lifting water. It might not be necessary in mountainous areas where
water could be extracted at higher levels, then allowed to flow naturally down channels to
the irrigated areas, but in lowland areas like Egypt, Iraq and Niger devices to lift water
had to be invented. There are four traditional methods of lifting water (Figure 27.7).
Although useful, they are still small in comparison with the amount of water and the
height of lift which can be achieved by a diesel engine. On the other hand they are simple
to operate, cheap to run and require little maintenance - important considerations in
countries where technical skills are scarce.
Figure 27.6
A Nile gauge, or nileometer. Carved on
stairways down to the river in ancient Egypt, the gauges
measured the height of the annual flood and indicated the
probable impact of the various levels on society. One ell = 45
in., or 1ยท1 m.
