Hello all,

When designing water networks and harnessing resources, it is usual to be told that population estimates should be for a 20 year target period. In my experience and opinion, however, there are several reasons why it is necessary to look beyond a 20 year study period. The actual implementation of a major project (trunk mains or a system of service reservoirs, not to mention a dam) may not start before 5-10 years after inception of the project. By the time the project is completed, it is found that the services provided has already reached its useful capacity ( as designed 20 years ago ). i.e. even before it starts operation, it is already underdesigned!

It is in this respect that it is sometimes useful to look at least 50 years ahead, (in any case beyond 20 years) bearing in mind that
- a pipe is still in useable condition 50 to 70 years after its laying,
- reservoirs and dams structures have a similar lifetime, and
- economic analysis tends to taper off beyond a 50 year lifetime.

Of course, it cannot be foreseen what type of new technology will come along in the future. Thus going too far ahead in the future could tend to become wishful thinking. But this exercise has one big advantage. It immediately lays down the nature of investment required in terms of infrastructure and water conservation for meeting future possible development scenario as well as indicating what may be the natural constraints.

Hope this stirs in some ideas,
Regards,
Virendra