Stochastic modelling of the effects of reservoir operation

Reservoir operation can often significantly alter the mean level of the monthly average flows downstream from a dam. For instance, flows may be increased downstream from the dam during a previous dry season before reservoir construction and decreased when there is abundant runoff. Intervention analysis is a stochastic technique that can be used to model and statistically describe the effects of reservoir operation on the seasonal average downstream flows. The mathematical theory of intervention analysis is explained, followed by the identification, estimation and diagnostic check stages of model development. An intervention model is developed to model the effect of the operation of the Gardiner Dam on the downstream average monthly flows of the South Saskatchewan River at Saskatoon, Canada. It is shown how the percentage changes in mean flows are calculated from the estimated transfer function parameters. Because the standard errors are known for the estimated parameters, confidence intervals for the flow changes can also be obtained.