Gleno Dam

Dam in Bergamo, Italy

Dam

46°00′59″N 10°04′30″E / 46.01639°N 10.07500°E / 46.01639; 10.07500StatusFailed, surviving structure standingConstruction began1916Opening date1923Demolition date1 December 1923Dam and spillwaysImpoundsGleno RiverHeight43 m (141 ft)ReservoirCreatesGleno ReservoirTotal capacity4,500,000 m³ (3,648 acre⋅ft)Power StationCommission date1923Decommission date1923Installed capacity3,728 kW

The Gleno Dam was a multiple arch buttress dam on the Gleno Creek in the Valle di Scalve, northern Province of Bergamo, Italy. The dam was built between 1916 and 1923 with the purpose of producing hydroelectric power. The middle section of the dam collapsed on 1 December 1923, forty days after the reservoir was filled, causing widespread flooding that killed at least 356 people.^[1]

Construction

The dam was proposed and constructed by the Viganò company. A request to construct it was submitted in 1907 and construction began in 1916. In 1920, construction began on the foundation. In September of that year, local officials were warned that contractors were not using proper cement mortar. In 1921, because of lack of funding, the project design was changed from a gravity dam to a multiple-arch type. The revised design was approved: the multiple arch dam would be constructed on top of the gravity dam foundation.

By January 1923, the dam was 80% complete and by October that same year, it was fully complete and its reservoir full after heavy rains.^[1] The dam's power plant had an installed capacity of 3,728 kW (3.7 MW).^[2]

Failure

At 6:30 am on 1 December 1923, a buttress on the dam cracked and subsequently failed. Within minutes, an estimated 4,500,000 m³ (3,648 acre⋅ft)^[3] of water gushed from the reservoir at an elevation of 1,535 m (5,036 ft) to the valley below. The village of Bueggio was flooded first, followed by a partial flooding of Dezzo, part of the municipality of Azzone, and complete flooding of Dezzo, a frazione of Colere and Corna di Darfo. The flood waters stopped when they reached Lake Iseo, which lies at an elevation of 186 m (610 ft). At least 356 people were killed in the disaster.^[1]^[2]

Investigation

The dam was originally permitted as a gravity dam with a slight curvature, but was changed to a multiple arch dam by the client to save money.^[4]

The permit was not revised for this change until after the dam was completed. The failure of the multiple arch dam was attributed to many aspects of its construction, ultimately poor workmanship. The concrete in the arches was of a poor quality and it was reinforced with anti-grenade scrap netting that had been used during World War I.

There were also indications that the dam was poorly joined with its foundation.^[3] Additionally, the concrete was believed not to be completely cured when the reservoir was filling. Reportedly, workers who complained about the construction techniques were fired.^{[citation needed]}

Legacy

The dam's failure was influential in the development of Italian dam design and risk assessment.^[5] As a result of the accident, multiple arch dams fell out of favour.^[4]

A much smaller dam was built spanning the gap left by the collapse, and is still in use today, creating a minor reservoir. A memorial at the site commemorates the tragedy.^[1]

References

^ ^a ^b ^c ^d "The Curious Traveler: Ride II The Ruins of Gleno Dam" (in Italian). Biblioteca Italia Grassi. Retrieved 10 March 2011.
^ ^a ^b "La diga Gleno" (in Italian). Scalve.it. Retrieved 10 March 2011.
^ ^a ^b Ratnayaka, Don D.; Brandt, Malcolm J.; Johnson, K. Michael (2009). Twort's water supply (6th ed.). Oxford: Butterworth-Heinemann. p. 191. ISBN 978-0-7506-6843-9.
^ ^a ^b Herzog, Max A. M. (1999). Practical Dam Analysis. London: Thomas Telford Publishing. pp. 115, 119–126. ISBN 3-8041-2070-9 – via Google Books.
^ Marco Pilotti; Andrea Maranzoni; Massimo Tomirotti; Giulia Valerio. "The 1923 Gleno Dam‐Break: Case Study and Numerical Modelling". American Society of Civil Engineers: Journal of Hydraulic Engineering. Retrieved 10 March 2011.