UDINE. The Tagliamento is the river of Friuli, because in geological times it shaped the mountain with its tributaries and generated, with the floods, the great plain. Its drainage basin embraces the entire mountain area (the Carnic and Julian Alps) and presents an extraordinary beauty, especially where the riverbed is wide, with the water channels that intertwine and run after each other.
But so much harmony and beauty, on the occasion of strong weather events, quickly turn into nightmares for the coastal populations. In fact, the entire catchment area presents both natural and human-induced fragility.
The most disastrous floods recorded in the hydrometric stations of Venzone and Latisana in the last hundred years show a tendency to reach ever higher flow rates. From the disastrous flood of 1882 to that of 1940, worsened in 1965, to reach its maximum in 1966, with an estimated flow rate (at the Pinzano squeeze) of 4500 cubic meters per second, causing breakage of embankments and the flooding of various centers inhabitants (in particular of Latisana).
The flood of November 1966 finally led the authorities to take into consideration the hydraulic danger of the “Great River”.
The main proposals for hydraulic defense works of the plain (1970, National Commission chaired by Professor De Marchi) provide, in addition to the hydraulic-forestry arrangements for landslides and instability, a reservoir for flooding at the Pinzano strait. In this locality the river subtends a catchment area of about 2 thousand square kilometers, or almost four fifths of the entire basin.
The barrier structure was foreseen in concrete with fixed spans (the principle of the bathtub with the exit hole), with an accumulation of about 100 million cubic meters of water, with which it was believed to be able to guarantee, Latisana, a flow not exceeding 3 thousand cubic meters per second, without danger of flooding.
The De Marchi Commission also hypothesized the expansion of the Cavrato spillway, which had proved useful in the floods of 1965 and 1966. This channel is located on the right bank, about 5 kilometers south of Latisana, therefore not able to safeguard the inhabited centers upstream adequately. But, to fulfill this last function, it was planned to create a new truncated spillway (called pre-Cavrato), upstream of Latisana, or rather at the height of San Giorgio al Tagliamento.
But none of these works was carried out due to the opposition of the population of the municipalities that would have been submerged by the project.
Further studies, in 1998, by the National Basin Authority of the rivers flowing into the Upper Adriatic, hypothesized the construction of expansion tanks downstream of the Pinzano strait: in summary, it was planned to exploit the width of the existing bed between the bridge of Pinzano and that of Dignano (where the riverbed is about 2 kilometers wide); the accumulation, on the orographic right of the riverbed, of about 30 million cubic meters of water was planned, divided into three expansion tanks, which would come into operation in sequence with the arrival of the flood wave.
Even this project, strongly opposed by local populations and administrations, has not been implemented. It certainly entailed a high environmental impact due to the embankment heights of the coffins and the permanent narrowing of the riverbed, as well as a high cost.
At this point (as history has taught us since ancient times), when there are complex problems and there is no political will to expose themselves with the choice of a solution, we opt for the appointment of a study commission.
In 2010, with the decree of the President of the Friuli Venezia Giulia Region, the Regional Commission “Laboratorio Tagliamento” was born, made up of representatives of administrative and technical authorities.
The commission examined a substantial dossier of studies, memories, models – both mathematical and physical – and design hypotheses. The members of the commission presented an additional 14 design solutions alternatives to expansion boxes (which we do not list for the sake of brevity).
The final collegial indications of the “Tagliamento Laboratory” can be summarized as follows: 1) urgently intervene in adapting and reinforcing, with diaphragms, the embankments made of loose material, from Mount Latisana to Cavrato; 2) deepen the design hypotheses of the junction node of the Cavrato spillway channel and arrange the channel itself, which presents an entire route lying in the Veneto Region; 3) define the flood flow arriving at the Pinzano strait, to be mitigated with a low environmental impact rolling beam (which comes into operation only in the event of exceptional floods): 4) confirm, with the planned interventions on the embankments and the recalibration of the riverbed, the maximum flow rate arriving at the incile del Cavrato.
The commission also evaluated the opportunity to investigate further integrative solutions with feasibility studies, which are omitted for the sake of brevity.
The conflicts between the state and regional authorities, as well as with the local ones, the opposition of the riparian populations and environmentalist associations, have so far, in fact, paralyzed every decision regarding the interventions briefly illustrated.
The only works carried out so far, for which part of the funds allocated have been spent, have been: 1) inserting reinforced concrete diaphragms from Latisana and downstream, inside the embankments; 2) raise the bridge of the Trieste-Venice railway; 3) recalibrate some sections of the riverbed; 4) plan the elevation of the Latisana-Portogruaro road bridge.
In conclusion, many studies have been carried out for the Tagliamento, but the interventions actually carried out were few and not conclusive. If these are the premises, all that remains is to invoke the goddess Hope, so that our king of the Alpine rivers has clemency and spares men from its devastating power. –
* naturalistic and cultural operator Friulian Alpine Society
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