Landslide and flood hazard from the lago sirino, basilicata, italy

Abstract

The Sirino lake or Lago Sirino in Basilicata, Italy, is possibly a disaster waiting to happen, in some ways similar to the situation at Vaiont in the months and years leading up to the landslide there in October, 1963, with both precursor movements and expert opinion dismissed and not acted upon. The lake is retained in a basin, which is entirely contained within a fault-bounded and displaced block of Jurassic-age rocks, thought to be Schisti Selice. The lake is fed by precipitation on the adjacent mountainside (Monte Sirino), which rises to approximately 2000 m a.s.l. A significant proportion of the precipitation is snow melt. The natural dam retaining the lake moves from time to time, creating fissures down which some of the lake disappears. Lake water level is usually maintained by spring via a stream, and this water also infiltrates the rock mass, and later issues downslope in a series of copious springs that feed a further series of streams. These downslope streams are exploited for water supply and irrigation. This lake is approximately circular in plan with a diameter of about 200 m, and a maximum depth of about 12m. The maximum lake level is controlled by an overflow weir and discharge tunnel. Downslope of the natural dam and the lake which it impounds, there are numerous small settlements, and at a distance of 2.5 km and some 370-400 m lower in elevation, there is the town of Nemoli which has over 1600 inhabitants. Any breach of the natural dam would lead to a flood down the natural channel to Nemoli and beyond. While the town centre is not directly threatened, there are numerous houses on the edge of the town that are. Around the rim of the lake, which despite its potential for mayhem, is rather attractive, is an array of houses, hotels, restaurants and bars, as the local community relies on the existence of the lake and its considerable visual attractions for a lively tourist business. This paper describes the geological setting of the lake, with some accounts of past movements and water losses, but in the absence of. detailed subsurface investigations, the short description that follows is mainly geomorphological in character and no further prognosis of the behaviour of this system is possible.