Hydrodynamic forces and repairs to stepped masonry spillways

Major collapses occurred at two masonry spillways in the UK, in 2005 and 2007. The UK Environment Agency subsequently funded an extensive research project, led by the author, into the possible causes of the collapses. It was discovered that vortex forces had acted on the side walls of the spillways, causing individual masonry elements to be plucked out in a way which eventually led to the complete collapse of the walls. The author is now assessing the condition of a number of other masonry dam spillways, and advising on the most appropriate means of repair and maintenance. This paper gives some background to the testing and hydrodynamic forces involved in the deterioration and focuses on how these are then used to develop the most appropriate repair and maintenance methods. Lessons learned are presented, leading to general guidance which could be applied in similar cases.