A) HISTORY
The exceptional flooding on December 1870 occurred just
few months after the annexation of Rome to Italy
Kingdom; of course this could not be allowed for the
town that was becoming the Kingdom Capital. Immediately
the Ministry of Public Works appointed a Commission to
face and solve the problem.
"... esaminare sul luogo le condizioni del fiume
Tevere e dei suoi principali affluenti; di studiare
quali cause accidentali e permanenti determinano i
disalveamenti del fiume a Roma; e finalmente di
proporre come si possono risolvere, indicando i
provvedimenti e quelle opere d'arte che valgano a
migliorare il sistema del fiume per lo scopo
suaccennato"
["... to examine on site the conditions of Tiber river
and its main tributaries; to study which accidental
and permanent causes determine the river to flood out
the riverbed in Rome; and finally to propose how to
solve them, suggesting the measures and restoration
works suitable to improve the river system for the
above mentioned scope"].
This is the chronology of the main events:
| 1870, dec. 29th
|
Exceptional
flooding: 17.22 m at Ripetta. |
|
1871,
jan.1st
|
Study
Commission appointment. |
| 1875, january
|
The
Commission work has not yet produced any result.
|
| 1875, may 26th
|
Giuseppe
Garibaldi, come back to Rome on January as a
Member of Parliament, intervenes in the Assembly
submitting a law proposal to consider all the
works to preserve Rome from the flooding as a
public benefit and showing his project for
complete diversion of Tiber and its tributary
Aniene out of Rome area. |
| 1875, july 6th
|
Approval
of the Law proposed by Garibaldi and financing
of the study completion. The Commission starts
again its works. |
| 1875, sept. 23rd
|
Commission
works completion: the preferred project is the
ing. Canevari one that foresees, among other
things, to eliminate the Tiberina isle by earth
filling of the river left branch; the Garibaldi
project is definitively rejected. |
| 1875, nov. 29th
|
The
High Council approves the Canevari project with
some modifications and the prescriptions (11 points)
of the works to be carried out among
which, at point 5, the preservation of the
Tiberina isle. |
| 1876, dec. 3rd
|
The
Government, taking into consideration Commission
decision, let out on contract the first lot of
the works. |
| 1900, dec. 2nd
|
Exceptional
flooding of Tiber river: 16.17 m at Ripetta. The
banks are near to be completed and the water
flow is contained by the embankments; but,
during the water ebb, a 125 m piece of bank at
the right of the isle, between Garibaldi and
Cestio bridges, falls down. |
| 1900, dec. 15th
|
Appointment
of an Investigation Commission. New proposals
are discussed among which, again, the
elimination of the Tiberina isle by earth
filling the left branch. |
| 1901, june 24th
|
The
Ministry of Public Works definitively rejects
the isle elimination.
The engineer Luigi Cozza states that the wrong
water distribution in the branches at isle sides
is the cause of the embankment erosion and
falling down; he rebuilds the damaged part,
reactivates the isle left branch, actually
filled, and builds two "bridles" under the
Cestio bridge side arches and the threshold
under the central one, restoring the flow
equilibrium between the two isle branches.
|
| 1915, febr. 25th
|
Exceptional
flooding of Tiber river: 16.08 m at Ripetta. No
problem for the banks. |
| 1926 |
Completion
at Rome Town Council care of the last part of
the embankments just below the Aventino hill. A
plaque with verses from Virgilio's Eneide
located on the left bank, in front of the Ripa
Grande port, celebrates the event.
|
In a recent study have been calculated the
equivalent hydrometer levels, referred at
Ripetta, respectively before and after the
embankments erection [P.Frosini]: |
| Before |
After |
Reduction |
The embankments
erection clearly caused a lowering of the
flooding levels referred at Ripetta but an
increasing of the levels as measured
downstream due to the obstructed river
flooding dowstream St.Paolo, contained by the
new banks. It is so explained that at Tiberina
isle the plaque indicating the 1870 flooding
level (17.22 at Ripetta) is located about 40
cm lower than the 1937 one (16.90 at Ripetta).
|
13 m
14 m
15 m
16 m
17 m |
12.22 m
13.13 m
13.96 m
14.87 m
15.81 m |
0,78 m
0,87 m
1,04 m
1,13 m
1,19 m |
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B)
THE CANEVARI PROJECT
The Commission preferred the Raffaele Canevari project
to the less expensive one proposed by Possenti, the
Commission's President. Possenti proposed to lower the
main flooding levels by shortening the river route by
means of "drizzagni" [straightenings]
disregarding to eliminate the normal flooding of the
lower town areas; this did not supply the same
guarantees than the Canevari project that was based on
the principle to contain the river stream between two
continuous bank walls, high enough to exceed the 1870
flooding level (17.22 m at Ripetta), the highest of
the last two centuries.
Therefore Canevari disregarded the maximum historical
levels, as the 1598 one, considering them unrepeatable
due to the changed conditions of the Tiber source
field during the last centuries; the embankments were
therefore designed 18.45 m high above the Ripetta zero
level.
The project stated a constant width of 100 mt at the
embankment foot and 110 m at the top; the wall slope,
stated either vertical and at 45% sloping, was
frequently modified during the erection.
Two platforms were foreseen at the wall foot to
delimit the meagre riverbed: they were designed 8 m
wide, passable and accessible by means of suitable
stairs (see pict. C4).
The problem of sewers overflow in the lower areas of
the town, that occurred in addition to the river
flooding (see pict. C1), was faced and solved
by means of two sewer
headers, grounded at the embankments side (see pict.
C4), to collect the sewers discharge conveying them
downstream the town where the river level is lower.
On the top of the embankments, at both sides, two
vehicles streets was foreseen, the so-called "Lungo
Tevere" [along the Tiber], that still at the present
are very important arteries of the urban traffic (see
pict. C4).
The original project still stated to eliminate one of
the two river branches at the Tiberina isle side (see
pict. C3); this solution was definitively rejected by
the Commission that finally saved the isle; the width
of the left and right river branches at the isle was
fixed at 60 and 70 m respectively.
In order to reduce the construction schedule and costs
as the design calculations as the material selection
were rather approximate (see pict. C6); the 8 m wide
platforms foreseen in the project at wall foot were
built only partially: as a consequence of this the
wall foundations proved to be weakened and exposed to
water erosion. The platforms were resumed only on 1901
by Cozza after the fall of the wall, undermined by
water erosion, at the right bank facing the isle
(1900).
The embankment construction, very criticized for the
deep alteration of the characteristic and evocative
tiberine landscape (see pict. C7), has anyway in short
solved the flooding problem in Rome; however the
combined effects of the riverbed regularization
downstream the town and the reduction of the sediments
transport due to the construction of hydroelectric
plants upstream the town produced erosion and lowering
of the riverbed, two effects that have still to be
completely solved.
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C) THE IMAGES
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D) BIBLIOGRAPHY
[1]
Pietro Frosini "Il Tevere - Le inondazioni di
Roma e i provvedimenti presi dal Governo
Italiano per evitarle" - Roma - Accademia
Nazionele dei Lincei - 1977
[2] M. Bencivenga, E. Di Loreto & L. Liperi
"Il regime idrologico del Tevere, con
particolare riguardo alle piene nella
città di Roma" In: "La geologia di
Roma. Il centro Storico". Memorie descrittive
della Carta Geologica d’Italia, 50,
125-172 - 1995
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