Po (river)
The Po is the longest river in Italy. It flows eastward across northern Italy, starting from the Cottian Alps. The river's length is, or if the Maira, a right bank tributary, is included. The headwaters of the Po are formed by a spring seeping from a stony hillside at Pian del Re, a flat place at the head of the Val Po under the northwest face of Monviso. The Po then extends along the 45th parallel north before ending at a delta projecting into the Adriatic Sea near Venice.
Draining a basin of, the Po is characterized by its large discharge. It is, with the Rhône and Nile, one of the three Mediterranean rivers with the largest water discharge. As a result of its characteristics, the river is subject to heavy flooding. Consequently, over half its length is controlled with embankments.
The river flows through many important Italian cities, including Turin, Piacenza, Cremona and Ferrara. It is connected to Milan through a net of channels called navigli, which Leonardo da Vinci helped design. Near the end of its course, it creates a wide delta at the southern part of which is Comacchio, an area famous for eels. The Po Valley was the territory of Roman Cisalpine Gaul, divided into Cispadane Gaul and Transpadane Gaul.
Geography
The Po has a drainage area of in all, of those being in Italy, of which is in montane environments and on the plain. The slope of the Po's river valley decreases from 0.35% in the west to 0.14% in the east, a low gradient. Along its path lie 450 standing lakes. Almost all of the rest of the non-Italy basin is in Switzerland, primarily in the canton of Ticino, which is essentially drained by the river Ticino rising in the Gotthard Area, and includes Lake Maggiore and Lake Lugano. A small part of the canton of Grisons drains to the Po, partly via the Ticino. The Simplon Valley in the canton of Valais is drained by the Diveria.A minute section of the Po basin belongs to France in the running from Mont Thabor to the Italian ski resort of Bardonecchia. Although in France, Vallée Étroite is so remote it is essentially administered by Italy. Further minuscule parts of the Po's basin within France are found in the form of small streamheads forced into France by the 1947 Peace Treaty of Paris as a punitive measure against Italy. These can be found on the Mont Cenis and Mongenevre passes. The former contains a reservoir dammed at the Po end and so technically constitutes part of its basin, although it contributes little to the water flow as the water is, by definition, retained by the dam. The Po is the longest river in Italy; at its widest point it is across.
Po Valley
The vast valley around the Po is called the Po Basin or Po Valley ; the main industrial area and the largest agricultural area in the country - accounting for 35% of Italian agricultural production. In 2002, more than 16 million people lived in the area, at the time nearly one-third of the population of Italy.The two main economic uses of the valley are for industry and for agriculture. The industrial centres, such as Turin and Milan, are located on higher terrain, away from the river. They rely for power on the numerous hydroelectric stations in or on the flanks of the Alps, and on the coal/oil power stations which use the water of the Po basin as coolant. Drainage from the north is mediated through several large, scenic lakes, commonly referred to as the Italian Lakes, and shared with Switzerland. The streams are now controlled by so many dams as to slow the river's sedimentation rate, causing geologic problems. The expansive, moist and fertile flood plain is reserved mainly for agriculture and is subject to flash floods, even though the overall quantity of water is lower than in the past and lower than demand. The main products of the farms around the river are cereals including – unusually for Europe – rice, which requires heavy irrigation. The latter method is the chief consumer of surface water, while industrial and human consumption use underground water.
Tributaries
The Po has 141 tributaries. They include :- Pellice
- Varaita
- Maira
- Chisola
- Sangone
- Dora Riparia
- Stura di Lanzo
- Malone
- Orco
- Dora Baltea
- Stura del Monferrato
- Sesia
- Rotaldo
- Grana del Monferrato
- Tanaro
- Scrivia
- Agogna
- Curone
- Staffora
- Ticino
- Versa
- Tidone
- Lambro
- Trebbia
- Nure
- Adda
- Arda
- Taro
- Parma
- Enza
- Crostolo
- Oglio
- Mincio
- Secchia
- Panaro
The longest tributaries of the Po are Adda, Oglio, Tanaro and Ticino.
Po Delta
Active delta
The most recent part of the delta, which projects into the Adriatic between Chioggia and Comacchio, contains channels that connect to the Adriatic and therefore is called the active delta by the park authorities, whereas the fossil delta contains channels that no longer connect the Po to the Adriatic. The active delta was created in 1604 when the city of Venice diverted the main stream, the Po grande or Po di Venezia, from its channel north of Porto Viro to the south of Porto Viro in a channel then called the Taglio di Porto Viro, "Porto Viro cut-off". Their intent was to stop the gradual migration of the Po toward the lagoon of Venice, which would have filled up with sediment had contact been made. The subsequent town of Taglio di Po grew around the diversionary works. The lock of Volta Grimana blocked the old channel, now the Po di Levante, which flows to the Adriatic through Porto Levante.Below Taglio di Po the Parco Regionale Veneto, one of the tracts under the authority of the Parco Delta del Po, contains the latest branches of the Po. The Po di Gnocca branches to the south followed by the Po di Maestra to the north at Porto Tolle. At Tolle downstream the Po di Venezia divides into the Po delle Tolle to the south and the Po della Pila to the north. The former exits at Bonelli. The latter divides again at Pila into the Busa di Tramontana to the north and the Busa di Scirocco to the south, while the mainstream, the Busa Dritta, enters Punta Maistra and exits finally past Pila lighthouse.
Despite the park administration's definition of the active delta as beginning at Porto Viro, there is another active channel upstream from it at Santa Maria in Punta, where the Fiume Po divides into the Po di Goro and the Po di Venezia.
Fossil delta
The fossil Po is the region of no longer active channels from the Po to the sea. It begins upstream from Ferrara. The Fiume Po currently flowing to the north of Ferrara is the result of a diversion at Ficarolo in 1152 made in the hope of relieving flooding in the vicinity of Ravenna. The diversion channel was at first called the Po di Ficarolo. The Fiume Po before then followed the Po di Volano, no longer connected to the Po, which ran to the south of Ferrara and exited near Volano. In Roman times it did not exit there but ran to the south as the Padus Vetus exiting near Comacchio, from which split the Po di Primaro exiting close to Ravenna.Before 1152 the seaward extension of today's delta, about, did not exist. The entire region from Ravenna to Chioggia was dense swamps, explaining why the Via Aemilia was constructed between Rimini and Piacenza and did not begin further north.
Protected areas
The Po Delta wetlands have been protected by the institution of two regional parks in the regions in which it is situated: Veneto and Emilia-Romagna. The Po Delta Regional Park in Emilia-Romagna, the largest, consists of four parcels of land on the right bank of the Po and to the south. Created by law in 1988, it was managed by a consortium, the Consorzio per la gestione del Parco, to which Ferrara and Ravenna provinces belong as well as nine comuni: Comacchio, Argenta, Ostellato, Goro, Mesola, Codigoro, Ravenna, Alfonsine, and Cervia. Executive authority resided in an assembly of the presidents of the provinces, the mayors of the comuni and the board of directors. They employed a Technical-Scientific Committee and a Park Council to carry out directives. In 1999 the park was designated a World Heritage Site by UNESCO and was added to "Ferrara, City of the Renaissance, and its Po Delta." From 2012 the park is managed by the Ente di Gestione per i Parchi e la Biodiversità - Delta del Po, composed by the comuni of Alfonsine, Argenta, Cervia, Codigoro, Comacchio, Goro, Mesola, Ostellato and Ravenna. The of the park contain wetlands, forest, dunes and salt pans. It has a high biodiversity, with 1,000–1,100 plant species and 374 vertebrate species, of which 300 are birds.Geologic history
The Mediterranean Basin is a depression in the Earth's crust caused by the African Plate slipping under the Eurasian Plate. Typically in geologic history the depression is filled with sea water under various geologic names such as Tethys Sea. In the last period of the Miocene Epoch, the Messinian, the Messinian salinity crisis, a near drying of the Mediterranean, was caused by the sea level dropping below the sill at the Strait of Gibraltar and the equilibrium between evaporation and replenishment shifting in favor of evaporation. At that time the Po Valley and the Adriatic depression were a single canyon system thousands of feet deep. On the southwest the Apennine Mountains bordered a land mass termed Tyrrhenis geologically. Their orogeny was just being completed in the Miocene. On the north the Alpine Orogeny had already created the Alps.At the end of the Messinian the ocean broke through the sill and the Mediterranean refilled. The Adriatic transgressed into all of northern Italy. In the subsequent Pliocene sedimentary outwash primarily from the Apennines filled the valley and the central Adriatic generally to a depth of to but from to off the current mouth of the Po, with pockets as deep as. At the start of the Pleistocene the valley was full. Cycles of transgression and regression are detectable in the valley and the Adriatic as far as its centre and in the southern Adriatic.
From the Pleistocene alternation of maritime and alluvial sediments occur as far west as Piacenza. The exact sequences at various locations have been studied extensively. Apparently the sea advanced and receded over the valley in conformance to an equilibrium between sedimentation and glacial advance or recession at 100,000-year intervals and to fluctuation of sea level. An advance began after the Last Glacial Maximum around 20,000 years ago, which brought the Adriatic to a high point at about 5,500 years ago.
Since then the Po delta had been prograding. The rate of coastal zone progradation between 1000 BC and 1200 AD was 4 m/yr. Human factors, however, brought about a change in the equilibrium in the mid-20th century with the result that the entire coastline of the northern Adriatic is now degrading. Venice, which was originally built on islands off the coast, is most at risk due to subsidence, but the effect is realized in the Po delta as well. The causes are first a decrease in the sedimentation rate due to the locking of sediment behind hydroelectric dams and the deliberate excavation of sand from rivers for industrial purposes. Second, agricultural use of the river is heavy; during peak consumption the flow in places nearly dries up, causing local contention. As a result of decreased flow, salt water is intruding into the aquifers and coastal ground water. Eutrophication in standing waters and streams of low flow is on the increase. The valley is subsiding due to the extraction of ground water.