The Tiber embankments

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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 island.
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