1994 Tanaro flood

It is possible to characterize the event through three successive phases, phases that have concerned distinct territorial areas (ARPA Piemonte). The first phase, which took place on 4/11, was characterized by strong rainfall in temporal character and mainly affected the southernmost sectors of Piedmont and Liguria: the maximum intensity of rain was reached in the night between 4 and 5 November with hourly values of more than 35 mm/h and a peak of 55 mm/h around midnight (Cairo Montenotte, Acqui Terme). Then, on day 5 (second phase), rainfall extended to the areas of Astigiano and Cuneese. In many places in the basins of Tanaro, Bormida and Belbo have been exceeded 200 mm of rain in 24 hours. The maximum accumulated on two days was in Levice (CN) with 293,8 mm; the maximum for 1 day was always recorded at Levice with 264,6 mm (Luino, 1999). In the third phase of the event, the most intense rainfalls affected the prealpine belt between the Pellice valley, the Sesia valley, in the afternoon and on the evening of day 5, to attenuate in the morning of 6. On day 6, rainfall has practically ceased in the southern part of the region, while it continues in the middle-seventh district, with modest hourly intensity, but still with daily totals.

After a few days of continuous rain, the Tanaro grew at frightening levels. A full wave formed on 5 November at the top of Ormea and, running downstream, devaded with unhearded fury all its course and dozens of inhabited centers along its banks until it reached the confluence in the Po at the first hours of the day 7 November.^[1]

During the alluvial event, Tanaro touched record values never achieved in the century:

• at the Farigliano hydrometer the river touched the exceptional height of 9 meters (well 3 meters above the previous historical level) with a flow of 3,400 m3/s.;
• in Alba, Asti And Alessandria the width of the full was between 4,000 and 4,200 m3/s;
• to the hydrotro Montecastello, a few km before the confluence with the Po, the Tanaro reached 5,000 m³/s with a hydrometric level of 8.50 m.

Particularly shocked by the alluvial event, the whole stretch between the municipality of Ormea and the confluence with the Stura di Demonte near Cherasco, where Tanaro almost totally destroyed most of the civil artifacts present (inhabitations, bridges, roads, etc.), changing also for large stretches in a definitive way the physiognomy of its bed and the valley floor.

The municipalities involved in the flood were:

• Ormea, Garessio, Priola, Bagnasco, San Michele Mondovì, Nucetto, Santo Stefano Belbo, Ceva, Bastia Mondovì, Clavesana, Farigliano, Piozzo, Monchiero, Narzole and Alba in the province of Cuneo;
• Asti, Canelli, Castello D'Annone, Cerro Tanaro And Rocchetta Tanaro in the province of Asti;
• Solero, Felizzano, Alessandria And Pietra Marazzi in the province of Alessandria.

The cities of Ceva, Alba and Asti, flooded for 1/3 of their surface and above all Alessandria, submerged almost for 50%, where 14 people lost their lives.

In those 3 days of rain (more than 200 mm in 24 hours only on the day of November 5), the creek swollen to dismeasure touching Santo Stefano Belbo exceptional values of 1,330 m3/s and to Castelnuovo Belbo of almost 1000 m3/s (respectively 220 and 167 times the normal flow), thus transciting for the entire length of its course and brutally devastating almost all its valley bottom.

Particularly shocked by the fury of the waters were the municipalities of Rocchetta Belbo, Cossano Belbo, Santo Stefano Belbo, Canelli (the most affected center which also counted 3 victims) e Incisa Scapaccino; only Nizza Monferrato was spared by the disaster while suffering heavy damage to the adjacent roads to the water course and flooding of some basement.

Due to the intense rains the river level grew considerably, and besides the damage caused by the intake of Tanaro downstream, upstream the river enlarged by the contribution in particular of the tributaries Orco and Dora Baltea overwhelmed in various areas causing huge damages and extensive flooding.

The area was very affected by Chivasso, where the confluence with the Orco created a flood that caused the bridge on the Po to collapse in the night between 5 and 6 November, and Trino, where the entire city center was submerged and damages were recorded in the former nuclear power station Enrico Fermi.

Other affected or submerged areas were Verolengo, Crescentino, Palazzolo Vercellese and Morano sul Po.