Dewatering for opal springs powerhouse excavation

Planning and execution of dewatering for a deep excavation in coarse alluvium containing cobbles and boulders are discussed. A deep well dewatering system was installed and had to be supplemented with extensive sumping due to inflow from large natural springs, and seepage through a rock fill river diversion embankment. The value of a flexible dewatering plan and provision for backup power are illustrated. Important details of well design are provided. Good engineering, in the form of pumping tests, and design that considers construction requirements are shown to be important contributors to dewatering success.