APPROXIMATE RELIABILITY AND RESILIENCE INDEXES OF OVER-YEAR RESERVOIRS FED BY AR(1) GAMMA AND NORMAL FLOWS

Approximate storage-reliability-resilience-yield (S-R-R-Y) relationshi ps are derived for over-year water supply systems fed by autoregressiv e lag one Gamma and normal inflows. It is shown that a two-state Marko v model may be exploited along with S-R-R-Y relationships to describe the general behaviour of over-year water supply systems. The two-state Markov model is also used to relate the probability of n-year no-fail ure operations (the concept of reliability used in the USA) to the ste ady-state probability of a system failure (the concept of reliability used in Australia and elsewhere) yielding a unified view of system rel iability. Resiliency criteria are introduced which indicate whether or not a reservoir system is likely to return to normal operations once a failure has set in. These criteria indicate that the resilience of a n over-year water supply system is generally independent of its steady -state reliability. The conditions under which finite reservoir system s behave like semi-infinite reservoir systems are also documented, and a factor is derived which describes the impact of the serial correlat ion of the inflows on the derived S-R-R-Y relationship.