Remedial works at two Victorian embankment dams to allow safe passage of the probable maximum flood

Strines reservoir in South Yorkshire is constructed across a tributary of the River Loxley and lies in cascade above Dale Dike and Damflask reservoirs. It is an earth embankment dam completed in 1869. Agden reservoir is situated on an adjacent valley to Strines and was also completed in 1869, following a redesign after the failure of the original Dale Dike dam in 1864. Following recent recommendations made in the interests of safety at both reservoirs, hydraulic models of the spillways were constructed for the probable maximum flood (PMF) outflow of 150 m3/s at Strines and 135 m3/s at Agden. The models showed that there would be significant out-of-channel flow from the spillways, which could pose a threat to the embankments. The models also showed that the peak stillwater flood level was above the embankment crest at both reservoirs such that the existing wave walls would have to retain the PMF flood rise. This paper describes the design and construction works that were carried out at both reservoirs between 2006-2009, which included new wave walls and significant spillway modifications. The solution for each site was unique owing to site constraints and topography. A number of innovative construction solutions were used including a masonry effect formliner used on in situ concrete walls, and precast concrete wave wall sections that were then clad with existing masonry. The challenges of delivering a cost-effective solution were met while complying with the aesthetic requirements of the Planning Authority.