Gleno Dam Failure
It is 1923 and Victor Emmanuel III of Italy is exploring the site of a disaster.
As the king casts his gaze along the ruined homes downstream from the Gleno dam the question
of how must have crossed his mind.
This Dam was only just built, no?
Usually you’d only want a king to visit the successful completion of a project.
Instead he is roaming the after effects of a catastrophic dam failure, this is not good.
Today we are looking at the gleno dam failure.
My name is John and welcome to plainly difficult.
Background
Our story starts here and the beauty of the Scalve valley in the province of Bergamo in
Lombardy (northern Italy).
In the early years of the 20th century a proposal was put forward to exploit the Gleno River
for hydroelectric power.
The region was home to the Viganò textiles company, and they wanted some of that juicy
electricity for their factories.
This would result in a proposal being put forward in 1907, for a dam across the Gleno,
to create and hold a new reservoir.
This would In turn be used to power a hydroelectric power station.
It would take nearly 10 years from proposal to Project commencement, when in 1916 clearing
works began preparing the site for the foundations.
The original plans submitted in 1913 were for the dam to be a masonry gravity type.
These plans would change in 1917 not long after the stone masonry basement close to
the lower part of the valley was constructed.
It turned out that a gravity dam would have cost a bit more than anticipated as such it
was reinvisioned as a narrow reinforced concrete arch type.
It would be a 220m long structure which when seen from top down looked like an S shape.
The central curved section was 70m and in total the dam had 25 arches with a height
of 45 m, here are the measurements in freedom units.
The newer design was to make use of the first plan's gravity dams foundations, as well as
placing piles directly into the bedrock of the valley.
When you look at pictures of it, like many Italian projects, it's pretty impressive and
pretty well pretty.
However, its beautiful facade was hiding some worrying ugly defects.
As early as 1920 concerns were raised about the quality of the mortar used on the dam.
The concrete was also not the best and in a strange form of recycling the steel reinforcement
made use of surplus anti grenade nets from the First World War.
This would hardly create uniform strength throughout the structure.
Although allowed the change from gravity to a multiple arch design didn’t actually have
its permits reviewed.
The Concrete wasn’t given enough time to cure, and if that wasn’t enough of a concern,
any worker who raised these deadly points were politely asked to piss off.
Even though the construction had issues at the start of 1923 roughly 80% of the dam had
been built.
Water had begun to collect in what would become the Gleno reservoir and by completion in October
some 4,500,000 m3 was being held back by the dam.
The whole reason for the construction was for the generation of electricity and as such
the associated power plant had a capacity of 3,728 kW.
The new dam and reservoir now offered many generations of power for the region, electricity
modernity what’s not to like, well until it all came crashing down.
The disaster
By December the dam and lake were complete, for 40 days the reservoir was full testing
the strength of the structure.
At roughly 06:30 am on 1 December 1923the dam began to shift, this was noticed by a
worker.
Just 45 minutes later a 80m long breach was formed in the central portion of the dam,
within seconds the now compromised sections disappeared.
Within a blink of an eye the 45 m tall central section was gone, a torrent of water battered
it’s way down the valley.
The first victims was the village of Bueggio, which was almost completely obliterated, then
Dezzo, a frazione of Colere, as well as Corna di Darfo.
Povo and Valbona power stations were also hit, together with a bridge and the chapel
of Colere.
Water would pummel the valley as the lake emptied its some 4,500,000 m3, to add further
destruction the flooding like what we’ve seen before picked up debris along the way,
smashing buildings and other infrastructure.
The flow of debris and water reached speeds up to 45kmhr.
In the ensuing chaos officially 356 people lose their lives although this figure is thought
to be much higher with some estimates up to over 600 as many hundreds were reported missing.
The reservoir was at an elevation of 1,535 m (5,036 ft), and the flood waters would finally
settle at Lake Iseo, at an elevation of 186 m (610 ft), the water had dropped over a kilometer
in elevation in less than an hour.
the flood had destroyed three villages, five power stations, as well as multiple other
businesses and factories.
Although happening in the 1920s hundred of photographs would be taken of the aftermath,
the Italian public fascinated and shocked by the disaster bought newspapers in droves
to get as much information on the gleno dams failure.
Now clearly the dam didn’t work as Intended and with a rather large death toll and several
villages smashed up a large question had to be asked how did the gleno dam fail?
Investigation
Almost as soon as the water settled and casualty numbers were calculated engineers started
picking through the rubble of what remained of the gleno dam.
It wouldn't take long to see that construction methods and materials were shall we say a
bit shit.
The Granade nets were seen and the poor quality of mortar and concerete were pretty apparent
upon initial instructions.
During the foundation construction it was found that pretty much anything was thrown
in amongst the concrete, this included tar, scrap metal, wood and the usual junk of waste
food cigarette buts and newspapers.
This didn’t give the concrete a proper base to adhere to, eyewitness reports stated that
the sand used wasn’t washed properly resulting in Chunky and more importantly crumbly concrete.
Mortar was found to be more porous allowing water from the reservoir to seep in between
the joints.
Even the fact that the reservoir was filled to quickly was a cause as the vital concrete
hadn’t been given enough time to cure.
Investigators also found inadequate checks by the Civil Engineers Board; lack of qualified
technical staff during work; poor management of the workers; and a conspiracy of silence
created by most workers fearing dismissal if they raised concerns.
All of these poor design and construction choices meant that the dam was too weak to
hold back the reservoir; this was caused by water seepage into the foundations which eroded
any bonds between the structure and its base.
It was just a matter of time before failure occurred, the disaster essentially doomed
any future arch style dam in the country.
Although the style wasn’t the cause but the bodge job, as any other style would fail
if as poorly built as Gleno.
On Dec. 30, 1923, the public prosecutor charged those in charge of the dam construction and
the engineer.
They were accused of causing disaster through negligence and with multiple counts of manslaughter.
The trial would last a few years taking place between Jan. 1924 and July 1927.
It ended up with the conviction of the managing director of the concessionary firm and of
the designer, both were sentenced to 3 years and 4 months imprisonment.
This would be reduced to 2 years.
They were also ordered to pay compensation but this was overturned.
But these would not be the last of the dam failures in Italian history, but maybe these
will be the subject for a future video.
I'm going to rate this disaster as Dumpter fire….
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https://www.researchgate.net/figure/The-Gleno-dam-after-failure-Dec-1923_fig3_264540093