Flood studies and physical model tests demonstrated that the original overflow and spillway facilities at the Ogden Impounding Reservoir were unable to pass the Probable Maximum Flood (PMF) without overtopping onto the main earth embankment with a consequent risk of failure due to the destructive action of out-of-channel flows.
The main purpose of the project was to improve the overflow and spillway facilities at Holden Wood and Ogden Reservoirs allowing PMF flows to be safely routed through the Grane Valley cascade and return the reservoirs to their normal operating levels.
PaSCoE were commissioned by Eric Wright Civil Engineering to provide both permanent and temporary works design.
Prior to the works commencing it was necessary to undertake a stability assessment of the embankment dam in order to manage the site works such that they would not unduly affect the stability of the dam.
Throughout the construction phase the stability was reassessed and, where necessary, restrictions placed on the weight of plant operating on the dam or on the extent of open excavations.
The detailed analysis was used to justify the use of much larger plant than would normally be acceptable on the crest of a Pennine Dam by the implementation of aluminium track mats and observational monitoring. The analysis was also used to demonstrate that a small mobile crane could be used on the part constructed apron on the upstream slope of the dam; a novel technique that simplified the construction and mitigated the risk and cost of employing a larger static crane.