On the estimation of transport timescales – case study: the Dez reservoir

The purpose of this study is to demonstrate an application of a hydroinformatics methodology for analysis of transport timescales in a large reservoir. Therefore, a laterally averaged two-dimensional numerical model was used to estimate the transit time, flushing times and combination of these two timescales by modeling about 230 scenarios in the Dez reservoir. The model was calibrated using temperature profiles and then executed for a period of two years (2002–2004). A possible characterization of the flushing time as e-folding time was investigated and the results revealed that the e-folding time, which is simpler to estimate, can be used in place of the flushing time in the Dez reservoir. The effects of the location of the outlet on each of these timescales were also investigated. Results indicated that the mean residence and flushing times have their smallest value when the outlet is set in the middle of the Dez dam. The mean flushing times were also less sensitive to thermal structures of the Dez reservoir than the transit times. Finally, the temporal patterns of these timescales were elucidated. It was found that no single transport timescale can be used for all conditions.