P12. The performance of Grimwith Dam

The level of Grimwith Reservoir, near Grassington, North

Yorkshire, has been raised 20 metres by the construction of a

49 metre high embankment dam. The embankment (Fig. 1) has

an entirely new rolled boulder clay core and incorporates the

original dam, which was completed in 1864, in its upstream

shoulder. The upper 20 metres of the core has a central

configuration but below this level the core had to be inclined

downstream against the shoulder of the original dam. The

shoulders are largely constructed of shale fill and contain

intermediate drainage blankets. A clay blanket links the top

of the puddle clay core of the original dam with the new core.