Difference between man made and natural lakes?

Both, natural as well as manmade lakes represent a water storage located in a

topographic depression. Both receive inflows from usually more than one source.

The outflow, however, differs considerably:

- in natural lakes the outflow is dependent on the lake water level which in turn

is a function of the stochastic natural inflows. There is usually only one lake

outflow.

- in manmade lakes - mostly created by dams - we usually have at least two

different outflows, both of which are regulated by man. One outflow is

following the natural river course downstream of the dam, the other

represents withdrawal of water from the storage for various purposes.

These purposes are in many cases competitive which calls for compromise

solutions. We distinguish between a single reservoir and reservoir groups as well

as between single purpose and multipurpose reservoirs. Fig. 1 shows the mutual

relationships. The simplest system would be a single-purpose single-unit

reservoir; the most complex a multi-purpose multi-unit reservoir system.

While in a natural lake the hydrology within the lake as well as downstream

of the lake represents one natural interdependent process we find in manmade lakes "two hydrologies", one dealing with processes within the lake, the other with

those downstream of the lake. These two hydrologie processes - in the lake and

downstream of the lake - are conditioned by man's reservoir operation and can

be made independent to a large extent.