Incontro sul Piano degli Interventi sul Rio S. Girolamo (II parte) - Le osservazioni dei convenuti In this second part we report the comments and proposals made by the people who participated in the Works Plan developed by the Agency for the District Hydrodata Hydrographic Sardinia.
Hydrodata He wonders if the company, based in Turin, has completed inspections of territory to verify directly the situation. It is reported that company representatives were present at random in Cagliari on the day of the flood and were able to attend in person to the current events. In addition, to carry out the study, were responsible for the technical inspections.
It is noted that the Plan of Action does not provide assistance to the mountain environment .
In particular, the section SG01, including nearly one third of the entire surface of the basin, where they originate most of the rainfall and probably of debris going to flow downstream in the basin, there is no type of intervention . The study highlights the fact that in this stretch there are no critical because there are no human settlements or activities vulnerable. In reality, there are critical, but the sections as targets valleys.
It also calls for a thorough study is conducted here and it is expected, as is already done in other parts of Sardinia, the realization of dams and large-scale intervention to restore the vegetation cover . It is thought that the straps are not necessary in masonry, but according to techniques used today may be in timber or silting and to conduct any of their function. The dams require regular maintenance to remove debris accumulated over time.
The Cliffs mass : do not protrude from the floor and did not campaign to stem the full function but bank protection from erosion. Anchoring and the consolidation of the same, as well as materials such as concrete and earth, especially in northern Italy where this practice is widely used, is guaranteed by planting willow seedlings, fast growing and highly developed roots. In our climate, less rain, the rooting of plant species (even if local) is difficult and requires special constant irrigation (ie staff and funds for maintenance), otherwise it will inevitably face the cliffs and with inadequate anchorage. Many express particular disappointment
for the proposed construction, with major expense of bank protection for the building Hydrocontrol . It is believed that this measure is totally unnecessary, because the building being built nell'alveo river (even dangerously restricts the course) and the model simulations carried out by Hydrodata show that the building will still be exposed to flooding for flood lower that in October 2008, no employee shall be presumed, would be willing to have her as their place of work. It is proposed to save the most useful works for the € 800,000 needed.
Many expressed doubts to the allegation contained in the schedules of the Plan Hydrodata the alleged action took place dalle piscine di Poggio nella deviazione delle acque verso la casa più a valle che è stata interessata dalle acque in piena e verso il ponte. E' opinione comune che le piscine non costituissero ostacolo alle acque e che l'erosione spondale che ha colpito l'abitazione di un socio della Cooperativa Poggio dei Pini sia stata causata dalla scomparsa dell'abbondante vegetazione presente in alveo, in conseguenza di un incendio.
Si manifestano perplessità anche sul fatto che lo studio Hydrodata, in questa fase, abbia definito degli interventi senza aver compiuto le opportune indagini sugli affluenti in destra idrografica che hanno avuto un ruolo molto significativo soprattutto nel determinare l'entità del trasporto solid, knowing where, probably, the choices on interventions (eg Hydrocontrol) could have been different.
is expressed considerable concern that the amplitudes of the riverbed and bridges in this first stretch of the river are large (70 m for the bridge at Hydrocontrol and 110 m for the pool deck Poggio), while downstream where the flow of the river water is much higher, the river and bridges shrink drastically in passing through the village of Rio San Jerome. According
Hydrodata, access to the pool deck Poggio should be through the road 24 (road to schools Poggio). This road, as well as complicate the path, has a width adequate to withstand the impact of traffic through and from Cagliari to Poggio Capoterra (the most difficult point where you have a lot in the road narrows to pass between four houses that are within 5 to 10 meters from the road and where there is a slope in the granite rocks that would be necessary to kill to be able to expand, the road is also regularly used by pupils to return home on foot and supports its passage already difficult for schools and the means for collection of municipal waste, ed.)
One wonders whether it is possible to move the bridge a bit 'further downstream, while maintaining and possibly retracing the existing access road to the left idrografica.
Si manifestano dubbi sull'effettiva utilità del canale di derivazione che escluderebbe il lago di Poggio dal corso principale del Rio San Girolamo. Se il canale è dimensionato per un tempo di ritorno di 200 anni (circa 100 m3/s di portata), esso può funzionare solo in regime normale, mentre in caso di piena pari a quella del 22 ottobre 2008 il canale non potrebbe contenerla e l'acqua potrebbe di nuovo tracimare dalla diga. L'unico effetto che se ne otterrebbe sarebbe quello di portare a morte lenta il lago.
Ci si chiede se non sia possibile, invece, fornire ad esso uno sbocco adeguato alla piena del 22 ottobre, possibilmente anche con un certo margine di sicurezza, scavando nel granito in hydrographic left to stretch properly line overflow of the lake and to get a rock in the deep channel enough to accommodate such a volume of water to put the dam away from new overflows. A solution of this kind has already been proposed in a technical report on the stability of the dam, which is not part of the study Hydrodata commissioned an expert in the field.
It highlights again the importance of the lake as well identity of resident communities in the area and as a key strategic resource of water in case of fire.
We were asked the reason for the choice of removing the concrete cross the lake small: it is considered that the choice is justified by the fear that a rise in water level at this point may interfere with the structure of the earth dam upstream, causing damage to the structure.
It expresses deep disappointment with the choices made in ' urban area of \u200b\u200bRio San Gerolamo . E 'of particular concern to the decision not to make any relocation of buildings, apart from the nursery. It is noted that the provision of two systems of levees in contour of entire residential areas would create a sort of ghetto-like neighborhoods, with access roads on them.
It is noted that the height and layout of the levees not guarantee that the water can not override or circumvent and especially does not guarantee that the water can flow, with the risk of a dangerous effect "tank" which would bring the waters to stagnate at its landlocked areas "protected".
It is noted that the two banks in the project are arranged in opposition to the flow coming from the River. The waters to flow out, should get around and move in a narrow gap between them. E 'be expected that, unlike the days of the flood, when all was able to flow freely between the houses on a broad front towards the estuary, the water may now accumulate upstream of the dams, an increase that could exceed the level of 'height of 2 meters (the water level was observed on October 22 from 1.5 to 1.8 m).
Preoccupa anche la velocità raggiunta dalle acque il giorno della piena: lo studio Hydrodata ha calcolato una velocità elevatissima, pari a 7 m/s, alla sezione del lago di Poggio. In condizioni di maggiore velocità delle acque è molto più probabile un accumulo in corrispondenza di eventuali ostacoli.
Il superamento degli argini da parte delle acque potrebbe inoltre causare dei franamenti improvvisi degli stessi, con la formazione di locali ondate di piena che potrebbero investire le abitazioni circostanti.
Molti si sono espressi in favore della delocalizzazione di un numero significativo di abitazioni in modo da lasciare al fiume lo spazio necessario the flow of water in flood. The inhabitants of the areas affected by the flood of 2008 live in a situation of constant stress and must have the courage to relocate where possible. The writer has expressed the need to relocate all buildings in Rio S. Jerome affected by the flooding of October 22, plus a wide range of buildings of golden fruit II at the mouth (about 130 buildings in total).
Among other considerations, expressed the need for a hydrogeological study also basin Masoni Olla study, which also damage has occurred, and which helps to increase the volumes of water at the mouth of the Rio S. Jerome. It
notes that the bridge provided in the most valley are heavily understaffed, with the exception of the viaduct on 195. It is noted that
€ 35 million can not be spent to carry out works to the full sized assumed for the return period of 200 years, because such works are likely to be useless if not harmful, while any money saved could contribute to the relocation Housing.
It highlights the fact that the evaluation of return periods of floods is made according to strict algorithms certainly, but the historical database on which these calculations are made can not be considered adequate. In these conditions, the payback can be a useful reference for defining the priorities and actions be regarded as forecasts can lead to big errors in sizing entire operation.