Following suspected incipient failure of the 84-year old earth-fill dam of Lambieletham Reservoir, Fife, the entire impounding basin was emptied in late November 1984. A culvert was constructed in the reservoir’s by-pass channel to permit access for heavy plant to remove the dam. A survey of sediment thickness variations enabled a long term yieldof 2. It km-2 yr-1 to be estimated from the 2.3km2 catchment which is of arable land (including rotational grass). During 21st–23rd September 1985, stormrain fell almost continuously for 57 hours in the area with recorded intensities reaching over 3.5mm hr-1. The culvert maximum discharge rate was exceeded and the water backed up and overflowed into the now empty 6.4×l04m3 basin which filled to overspill within 12 hours. There was now a great danger of dam failure and the basin was again emptied with the aid of pumps. A coarse debris fan formed beneath the inlet channel and a layer of sandy silts covered the lower part of the basin. The 104t of sediment introduced represents c.33% of the deposits accumulated during the previous 84 years.