Characteristics, impacts and causes of the Carntogher bog-flow, Sperrin Mountains, Northern Ireland

A large bog-flow was triggered on the slopes of Carntogher, in the Sperrin Mountains of Northern Ireland, on the 10th September 1993, following a period of above average monthly rainfall and a high magnitude rainfall event on the preceding day. It is believed that high pore-water pressures were established in the peat mass as a consequence of this antecedent rainfall and the transfer of additional wafer to the site by drainage ditches and seepage. The humified basal peat liquefied and breached the surface mat of fibrous peat. Disturbed peat extended 1 km downslope and a further 1.5 km along the floodplain of the stream into which the flow became confined. A significant amount of water was released by the flow, as demonstrated by hydrographs for a gauging station 23 km downstream. Rough grazing ground and fencing were destroyed by the bog-flow and a number of sheep were kilted. Hydro-electric power to a linen mill, and fish stocks were also affected, with a total fish kill for a distance of 8 km downstream. Since the event, fish have partially recolonised this reach of the river by spawning.