Toddbrook: the independent government review a forensic approach to causality

Abstract

The Toddbrook embankment dam was constructed in 1840. A concrete auxiliary spillway chute was added to its crest and downstream slope 50 years ago in 1970. On the 31 July 2019 the auxiliary spillway discharged a significant flood. The following day, as flows died down, the chute progressively collapsed. The author was the all reservoirs panel engineer and member of the independent governmental review team, charged with establishing the cause. The paper describes the forensic approach adopted and how that identified the immediate causal mechanism to be the injection of large quantities of water through cracks on the chute due to flows impacting rocks embedded on the chute invert and developing stagnation pressures. It also concluded that many factors such as poor design, deterioration, poor maintenance and some aspects of poor construction, all probably contributed to weakness in the chute which facilitated crack development.