Hydraulic works on the River Nera to secure the areas at risk of flooding in the Conca Ternana (3rd functional section, Lot I)

The planned works are included in the urban section of the city of Terni, between Ponte Allende and the RFI Terni-L’Aquila railway bridge, and had as their object the adaptation of the embankment levels of the River Nera, on the hydrographical right and left, to the francs required by the Province of Terni. In order to raise and cross the embankment, reinforced earth embankments were used, which were able to guarantee higher inclinations of the walls on the country side and compatible with the expropriation and subjugation restrictions established in the final design phase. On the crowns of the compacted earth embankments, walkable and vehicular towpaths were built for future maintenance activities. Along the section of the embankment on the left bank there is a gravity concrete bank defence wall, which was built to protect a production area. The raising of the crown of the existing defence wall, also for the purpose of mitigating the visual impact, was designed by entrusting the containment of the TR = 500 flood tie-rod to a watertight COR-TEN steel bearing parapet. In compliance with the prescriptions issued by R.F.I., the executive project provided for works to protect the Nera River crossing infrastructure. The deck protection device for the deflection of the floating material and the absorption of accidental impacts consists of a spatial lattice gantry structure made of steelwork, which also serves as a footbridge. The impact protection element consists of a COR-TEN steel sheet casing. Upstream and downstream of the bridge, on the hydrographical right and left, the project envisaged the construction of grazing defence works aimed at ensuring a regular hydrodynamic connection of the flood current. The project was completed by the construction of greenable reefs made of natural boulders placed at the foot of the embankments in order to counter erosion phenomena and, in order to increase the liquid area available upstream of the bridge for flood transit and contain the backflow induced by the local narrowing of the section, the reprofiling of the riverbed to remove overflow deposits.