2008 – Working towards design guidelines for outlet works – current practice

Marius Jonker, Mike Taylor and Glen Hobbs

Abstract: One of the activities authorized by organizations such as ANCOLD is the development of guidelines to enhance the ability of organizations to assure that adequate dam safety programs and practices are in place.

However, due to the absence of a single recognized guideline covering the various design aspects of dam outlet works, there is currently great inconsistency in the underlying principles for design and review processes for these facilities. A single, nationally recognized “standard” would lead to greater consistency between similar project designs, facilitate more effective and consistent review of proposed designs, and result in increased potential for safer more reliable facilities.

The need for a design standard is further underscored by the fact that poorly designed and/or constructed outlet works have been identified as a significant contributor to the occurrence of embankment dam failures. The failure of critical components in the outlet works of dams, not leading to an uncontrolled release of water, is generally considered less important due to apparent lesser consequences compared with a dam failure. However, the drought experienced over the past decade in Australia has highlighted the value of water and securing it for the future. The potential impact caused by the inability of a primary storage to supply a town or city, due to a failure in the outlet works, potentially affecting thousands of people and industries, could be devastating.

This paper summarises the current state of practice with regard to outlet works for dams concerning design, construction, inspection and evaluation, as well as maintenance and renovation. It also underlines some commonly occurring deficiencies encountered at existing dams. It provides a basis for further discussions of the state of practice for these topics in order to work towards consistent and unified outlet works design guidelines for dams.

Keywords: outlet works, state of practice, design guidelines