Hi Mitch -

Not exactly the same thing, but maybe close. This was for an irrigation project in Turkey back in the 60s - our crew did not have access to a computer but had a bunch of alternative water supply sources and alternative irrigation service areas to sort out. We derived a "typical year" of monthly streamflow values, based on the geometric mean rather than the arithmetic mean of our meager data. The arithmetic mean was too distorted by outliers. Then we also had a low water supply year case to test with. Each alternative was described with a (real paper) spreadsheet with water allocations, costs, etc.

The computerized approach outlined by Giles and followed up with several years of simulation is a good one. Applying the Turkey case would suggest using geometric means for monthly precip. The several years of simulation should include dry, typical, and wet years for a comprehensive presentation of project behavior under different conditions. This approach assumes that over-year storage is not a significant aspect of the system.

Ron Kilmartin
ronkilmartin@attbi.com