Surge Tank Design for Flexible Hydropower

Research output: ThesisDoctoral Thesis


Surge tanks are structural components that allow safe and flexible operation of water conduits with pressurized flows that contain significant water inertias for power generation in high-head hydropower plants and pumped storage hydropower plants. Surge tanks allow safe and flexible controllability of the hydraulic machines and reduce the impact of pressure surges.
The ongoing and demanded transition of the energy system towards a renewable energy system requests for capable and sustainable renewable energy production and vast energy storage systems, utilising minimal resources by maximising the economic output. Hydropower schemes are built increasingly larger and more flexible in sense of power capacity. This aspect demands for several issues for improved surge tank design.
Several specific surge tanks were tested by means of 1D and 3D-numerical simulations as well as physical model tests. A specific large surge tank facility was investigated and compared with prototype measurements. The focus of the investigations is the hydraulic design of surge tanks with respect to the mass oscillation, discussing and stating a safety philosophy to provide robust facilities. Special focus of the work are waterfalls in surge tanks, that occur due to water outflow of upper chambers. These may intrude considerable amounts of air into the water, what needs to be controlled. The development of a specific waterfall-damping device is investigated on the basis of a physical model test and the realised prototype. Storage-tunnel surge tanks and semi-air cushion surge tanks as further improvements for surge tank design are investigated. Hydraulically optimized surge tanks show minimised excavation volumes and low coefficients of inertia for water hammer reflections. They are very robust and constructed without moving parts for operation, to allow safe and effective maintenance. To dampen the mass oscillation for large surge tanks for flexible hydropower schemes, passive differential effects such as hydraulic throttles and upper chamber effects show high effectiveness for safe and economic designs.
Original languageEnglish
QualificationDoctor of Technology
Awarding Institution
  • Graz University of Technology (90000)
  • Zenz, Gerald, Supervisor
Award date7 Feb 2013
Publication statusPublished - 7 Feb 2020


  • Surge Tank
  • High-Head Hydropower
  • Pumped-Storage Hydropower
  • Transient Hydraulics

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