P. Galvanin, A. Socci –
Alpina Spa
According to the last review
of the Global World Urbanization Prospects, issued by United Nations:
“55 % of the world’s population lives in urban areas in 2018; by
2050, 68 % of the world’s population is projected to be urban”.
Urban growth is closely
related to three dimensions of sustainable development: economic,
social and environmental. For sure water is the most immediate and
critical limiting factor to both human and environmental well-being.
For this reason, since ancient
times, men were engaged in construction of big aqueducts for water
supply: the ancient Romans built engineering and architectural
masterpieces for water transport, like - for example - the 400 km of
underground channels in Naples, excavated in the yellow tuff,
connecting monumental tanks, among which the spectacular
Piscina Miarabilis or the
Cisterna Imperiale.
The Piscina Mirabilis built by
Romans
The Cisterna Imperiale,
Ancient Romans underground tanks Nowadays, as in the past, engineers
are involved in construction of aqueducts for megacities: tunnelling
still plays a crucial role for development of water infrastructures.
There are roughly 40 cities in
the world with more than 10 million inhabitants: Metro
Manila in the Philippines is
one of them, while Nakuru City in Kenia is an example of a rural
area, experiencing a rapid growth of the resident population
with approximately 5 million inhabitants within 2050.
The municipality of Metro
Manila is investing billions to improve the reliability of the raw
water transmission system towards the city, including seismic hazard
mitigation. One of the most important projects is the so called
AWTIP (Angat Water Transmission Improvement Project) which
involves the Angat river, whose water is conveyed from IPO
dam to Bigte through 3 existing tunnels. The project includes a new
intake structure at Ipo Dam reservoir and the New tunnel n.°4 -
having a total length of roughly 6,4 kilometres and an
internal diameter of 4,2 m. The tunnel, conveying aminimum flow rate
of 19 mᶟ/s, is excavated for its entire length with a double shield
Tunnel Boring Machine (TBM).
The Itare Dam next to Nakuru
City for the new water supply system © Alpina Archive
In Kenya, next to Nakuru city,
a new giant aqueduct is under construction: this project is aimed at
improving water supply in the Nakuru Municipality and its environs:
Molo, Elburgon, Salgaa and Njoro towns. The integrated water system
for the supply of the potable water from the new Itare Dam to the
villages of Nakuru is mainly composed by a dam with a total storage
volume of 11,6 Mm3, a free surface water transfer tunnel - having a
3,2 m internal diameter and a total length of roughly 12 km -and a
more than 130 km long treated water pipeline. The machine chosen for
the tunnel excavation is a dual mode “crossover” EPB/TBM, capable
to excavate in hard or soft rocks.
The internal diameter - only
3.2 m - can be considered quite huge for an aqueduct, but very small
for a modern tunnel. A width not so different from tunnels excavated
beneath Naples by ancient Romans: admired engineers of the past, who
are still teaching to young and modern enginers.
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