Mori-Torbole tunnel

The Mori-Torbole Tunnel (Italian: Galleria Adige-Garda) is a diversion tunnel completed in 1959 between the Italian towns of Mori and Nago-Torbole to connect the Adige river with Lake Garda.

Its function is to reduce water levels in the river upstream of the province of Verona by discharging excess water into the lake. The tunnel reduces the risk of flooding in Verona and environs from once every seventy years to once every two centuries.

To increase the level of Lake Garda by 1 cm, the tunnel must divert about 3,700,000 m³ of water.

When the tunnel is open, the lake's turbidity increases. The sudden influx of the Adige's water, which is both appreciably colder and more polluted than the lake's, causes a considerable heat shock and significantly worsens the habitat for fish. For these reasons the tunnel is used only on the rare occasion when there is a flood risk in the Veronese basin.

After the great floods of the second part of the 19th century (the last in 1882), defense of the city of Verona from Adige floods was deemed urgent. Using an idea already established in the 18th century, Venice's Water Magistrate proposed constructing a diversion tunnel to Lake Garda that would alleviate flooding by conveying that part of the Adige's flow exceeding the river's carrying capacity. The lake's surface area, equal to about 370 km², would allow the diversion of huge volumes of river water with only a modest increase in the lake's level. The most appropriate solution was considered to be a tunnel originating on the right bank of the Adige near Ravazzone (a subdivision of Mori) and terminating at Lake Garda to the south of Torbole. The depth of the lake at that location would allow solid material that might be transported by the water to be deposited without damage. Construction began under the fascist government in March 1939, was suspended for the war in 1943, then resumed in 1954 to finish in May 1959.

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