2013 – Hydrological considerations for design of fuseplug spillways for Keepit Dam safety upgrade

Nanda Nandakumar and Stephen Farrelly

Fuseplug auxiliary spillways are used to increase the discharge capacity in dam upgrades for flood security. Hydrologic level-pool routings are used to determine the size and trigger levels for fuseplugs. In the level-pool routing, the water surface from the body of the storage to fuse bays is generally assumed to be horizontal and any drawdown effects on the water level are neglected. This paper assesses the validity of this assumption using the CFD model results for Keepit Dam. It is shown that equal spacing of trigger levels can result in premature activation, and the drawdown effects need to be taken into account in determining spacing of trigger levels. It was also shown that the design water levels for the intermediate AEPs are underestimated.
A comparison of inflow and outflow frequency curves showed that peak outflows can exceed the peak inflows due to fuseplug operations, but the downstream impact is expected to be negligible due the size of the flood in which the peak outflow will exceed the peak inflow.