Internal erosion is one of the main causes of incidents at dams in service, accounting typically for around 50% of dam failures. This article describes the status and content of forthcoming International Commission on Large Dams (ICOLD) bulletins on internal erosion.
The European working group on internal erosion was first set up in 1993 under the chairmanship of Andrew Charles (2002), with this passing in 2004 to Jean Jacques Fry at a time when a significant research programme commenced in France.
An inception report was published of the Aussois workshop in 2005 (Fell and Fry, 2007) with annual workshops thereafter, including an interim report at the European conference at Freising in 2007 (ICOLD European Working Group, 2007) and an article on the workshop in St Petersburg in 2009 (Brown and Bridle, 2009). The work of the working group has now been developed into two bulletins, the first on ‘Internal erosion of existing dams, levees and dikes, and their foundations’ and the second on ‘Testing, monitoring and case histories of internal erosion’. Rodney Bridle and Alan Brown gave an evening meeting to present the forthcoming bulletin at the British Dam Society (BDS) in London on 3 October 2011, with a record of the meeting available as a video on the meetings page of the BDS website.
Key features of the bulletin will comprise
description of the four types of internal erosion (concentrated leaks, backward erosion, contact erosion, suffusion) and how they could progress to breach
the importance of consideration of all three factors of material properties, hydraulic conditions and stress state in determining whether internal erosion can occur
how to examine the internal erosion threat at existing dams, including screening to decide if the level of threat warrants attention by safety works or monitoring to various degrees of rigour
evaluating whether the properties of the dam will allow erosion, if initiated, to continue or whether erosion will be prevented by the filtering capabilities of the dam fills or foundation materials.
Although the annual meetings of the working group have included sessions on risk assessment, it has been decided that the bulletin will be limited to providing tools for an engineering assessment of the vulnerability to internal erosion, with summaries of methods of estimating probability of failure, including rate of erosion, to be given elsewhere.
It is anticipated that the first bulletin would be published in 2012, with the second bulletin on testing and monitoring a year later. If anyone would like copies of the draft bulletin, or papers from the annual workshops of the working group (often available online from the organisation hosting the workshop) they should contact either Rodney Bridle (rodney.bridle@damsafety.co.uk) or Jean Jacques Fry (jean-jacques.fry@edf.fr).
