On the ancient Venecian Hydrography

Extracted from: Antonio Averone, Ing. Capo del Genio Civile, Magistrato per le acque delle province Venete e di Mantova (1911) Sull’antica Idrogrfia veneta.

There were huge floods and damages in Veneto On May 1905. On the same year On. Fortis, the President of the Italian Cabinet, called for the creation of a unifying authority in charge for the water management of the area. Whit a specific legislation on the 5^th of May 1907, he created the Magistrato delle Acque, literary “the minister of waters” for Veneto and Mantova. This institution was a new edition of a very old and respected office of the ancient Vencian Republic.

Ing. Averone was appointed the first Magistrato of the modern time. He started with the collection of all possible information, maps, documents and material about the Lagoon and its surrounding rivers. These were located in several archives and they documented the continual evolution of the ever changing lagoon.

From the ages of Roman Empire until now a light motive can be found: on one hand the constant efforts to save the lagoon from being covered by rivers sediments and on the other hand the necessity to protect surrounding lands from river and/or sea flooding. Moreover, other complementary objectives are clearly stated by the lows of all time, for instance: keeping the various rivers suitable for navigation.

The natural environment of the lagoon and Venice is particularly instable and ever changing. It is a very large sedimentary area with the tendency to sink under sea level because of natural rearrangement of the soil. Rivers coming from the alps can bring devastating floods, and the natural high tide low tide cycle can submerge vast are areas including large portion of Venice. Here, an ever lasting fight is in place between man and waters.

Averone started looking back into the past and reconstruct the evolution, let say the genealogy of the current hydro-geological and topographical setting. Useful sources were found in Plinio and Strabone in his Geografia, Marco Cornaro (1440) and Professor Schiapparelli in the 19^th century.

The streets of ancient Roman construction can bring useful information, for that reason they were searched all along the centuries and many are still visible today. The general assumption is that Romans would not build on wetlands so that those street can mark a first geographical border. The places where cities and military rocks were built can give to the modern researcher an idea of the dimension of the lagoon in the ancient time.

More recent documents, from the time of the Serenissima, testify the great effort that have been done across centuries to divert rivers outside the lagoon. This was done to avoid submerging the free waters with sediment and therefore transforming a navigable sea in wetlands.

Many have been the theories and conjectures about a large amount of natural phenomena observed in this ever changing environment: the sea level oscillations, the origin and nature of the fresh waters in the middle of the sea, the natural shifting of the river path, and so on.

Professor Schiapparelli, in the 18^th century solved on of the greatest mysteries. He proved that a measured rising of the water of about 10cm per hundred years can be attributed to the movement of the earth axis. In fact, even a small movement of the hearth axis northward will carry a consequent movement of the equatorial belt northward, and given that the heart is spherical a greater centrifugal force is applied at the lowest latitude where the heart radius is the larger, the sea water will tend to accumulate and rise. That’s why the water are rising of about 10cm verey 100 years.

Please notice that this is was a valid theory in the 1911 the year in which Avarrone is writing.

Something else can be extracted from this document, the ancient organization of the Magistrato delle acque. Meaning, how ancient people used to organize administrative function of the waters of the lagoon and how do they perceived and allocated the tasks and problems. Much more can be said about that, here I just mention that the Magistrato was supported by 3 consiglieri: one for the rivers; one for the arbores; and one for the costal lines.

That’s all for now, to be continued.