Tanaro

The name Tanaro can be associated with the Celtic theonym "Taranus" and the British "Taran" (temporal, thunder, god of temporal) or to a hydronimic prelatina root "Tan".^[6][7] See also the French Tarn (fiume).

Tanaro was born at the south-western end of the Piemonte bordering Liguria, in the Ligurian Alps. It is formed in fact to the confluence of the Tanarello and Negrone streams on the border between the municipal territory of Ormea (CN) and that of Cosio d'Arroscia (IM).

More precisely the Tanarello is born from Mount Saccarello (2.201 m), the highest peak of Liguria, and flows for about ten kilometers - of which the first 4 km in Piedmont and the remaining in Ligurian territory (common of Cosio di Arroscia) - in a valley with typical Alpine counties, then reaching 4 km upstream of the village of Ponte di Nava (fraction of Ormea), where it receives from left the contribution of Negrone, a stream that is born instead in Piedmontese territory from Cima Missun (2356 m), not far from Punta Marguareis (2.651 m). Del Negrone also needs to remember the characteristic of some resurrections at the foot of the karst massif of Marguareis-Mongioie, where in tunnels and tunnels we collect rainwater, which then flows with imposing waterfalls in the throat of the Fascettes and the Vene del Tanaro.

From this confluence between Tanarello and Negrone upstream of Ponte di Nava the river doubles in size and changes name becoming Tanaro, thus heading towards the north-east as a foaming Alpine river in a narrow and wooded valley and acting for a few kilometers as a border between Piemonte and Liguria. Once the town of Ponte di Nava was bathed and received from the right the Rio dei Boschetti (or Rio Nava), the river definitively enters Piedmontese territory reaching Ormea where it receives various tributaries such as the Rio Chiappino, the Armella stream, which originates from the Pizzo d'Ormea lake, and the Rio Peisino. The water flow in this stretch suffers some drops due to artificial withdrawals (the annual average is around 6.9 m³/s).

Further downstream, after wet the municipality of Garessio receiving from the left the Rio Inferno and the Rio Luvia and from the right Rio Bianco and the Rio Malsangua that flows between two bridges, the one of the mid-nineteenth century red bricks («corticato» from the flood of November 1994, then demolished in 2020^[11]) and that of the Amitiè at the end of the twentieth century (overwhelmed by the waters and rebuilt with a higher arch), the river then begins to flow for a few kilometers in a large flat basin surrounded by the peaks of the Ligurian Alps, shortly reaching the municipality of Priola and then that of Bagnasco where an evocative medieval stone bridge crosses it (it was partly destroyed by the aforementioned flood and then rebuilt thanks to the «Maurizio Costanzo Show»); its flow rate is now 9.1 m³/s.

From here onwards the valley narrows again and the river turns sharply towards north-west, first entering the suggestive ingola stretch of the Gorge of the Rocchini and then wet, once outside, the town of Ceva, where it receives from the right the river Cevetta. From this point onwards, the Tanaro applauds its race by losing part of the famous torrents, and the Alpine aspect of the valley changes deeply because it is the same river now that the Langhe hilly complex has been lambire.

From here the river continues towards the north, creating a gap between rough hills reaching the centre of Castellino Tanaro with an average flow of 12.40 m3/s. In this section his bed is deeply recessed between the reliefs of the Langhe and theMonregalese plateau, digressing in a very irregular way and creating, now on one bank, now on the other, suggestive gullies of erosion and also changing the color of its waters (up until now transparent) which now become muddy due to the clayey nature of the valley's soils.

Once in Lesegno receives the first important left tributary: the torrent Corsaglia (average over 10 m3/s) after which, disembarked from a dam, yields all its scope for hydroelectric purposes, remaining completely dry for about 1 km. Recaptured the water flow, another dam near Niella Tanaro drains again the river for a few kilometers. In Bastia Mondovì (an average annual flow of 29 m3/s), another dam once again subtracts all the water to the river for a few kilometers. At the same time, various tributaries come to the river, including the Hella (average 5 m3/s), the Pesio (media 10 m3/s) and the Mondalavia which increase the volume of Tanaro water.

In Clavesana the river is still a remarkable water loss twice in a few kilometers: first it is partly drained to supply a channel that once fed the local oil mill, after which, regained the entire flow of water through a large discharge mouth, is again disembarked a few hundred meters downstream from a big dam to bulk for food. For a few kilometers his bed returns almost dry.

The same scenario is resurfaced more downstream several times as near Farigliano, where the river now has an annual average flow of 38.70 m3/s, for a short stretch in Monchiero, up to the confluence of the Rea stream (average 1.7 m3/s) and, even further downstream, in Narzole where the water is held by a large dam. Despite the massive use of its waters, the Tanaro takes on more and more the characteristics of the river itself, continuing northwards with winding trend and increasing its bed.

Once in Cherasco with an average annual flow of 41 m3/s, the river bends eastward and flows the Stura di Demonte, a very rich river of water (average 36 m3/s), its main left tributary (115.4 km). From here onwards the Tanaro changes its appearance with its valley that becomes very wide (also 3–4 km) and its bed which expands considerably, sometimes branching out into various secondary arms; the water flow doubles by touching the 80 m3/s; in this section the river wet Pollenzo, formerly a Roman city of which some vestiges remain, and, disembarked from the eternal dam, goes to feed the Canal of Verduno.

Once in Alba receives both from right and left the contribution of modest torrents: the Rio de la Gera, the Mellea and the Riddone from the modest heights of Roero, Talloria (1.8 m3/s), Cherasca (0.7 m3/s) and Seno d'Elvio, coming instead from the Langhe. With a wide and pebbly bed the river reaches Castagnole delle Lanze And San Martino Alfieri by entering so into Astesana (and also in province of Asti): here it crosses the southern outskirts of the Asti receiving from the left the Borbore (9,5 m3/s), the Rio Valmanera and the Versa (3,5 m3/s), water streams draining all the astigian portion of the basin.^[12]

In short wet the centers of Castello di Annone And Rocchetta Tanaro, after which it enters province of Alessandria the municipalities of Masio (where it receives the stream from the right Tiglione) e Felizzano, where a last large dam exploits its waters, thus beginning its plain course closed between two high embankments.

At the Villa del Foro from the right the hipposes before the Belbo (95 km and annual average of 8.1 m³/s) and the Canal Carlo Alberto (which drains a small part of the waters of the Bormida) after which it is preparing to cross the city of Alessandria, with an average annual flow close to 90 m³/s, also receiving the last albeit small tributary on the left: the Rio Nuovo di Loreto.

Arrived at Pavone d'Alessandria, fraction of Pietra Marazzi, a few kilometers downstream from the city of Alessandria, the river laps at the base of the last offshoots of the Monferrato creating a very suggestive scenario made of harsh erosion walls on the left bank, lanche, large tree-lined golenes, fields cultivated in the right bank.

Here the Tanaro receives its greatest tributary of right: the Bormida (154 km and over 33.2 m³/s annual average) which, excluding a small portion to the west of its upper basin in the province of Savona, drains almost the entire Apennine part of its large basin.

After this last confluence the average annual module of the river increases again reaching values among the most important among the tributaries of the Po (116,2 m3/s), comparable almost to those of the Oglio and lower only to those of Ticino and Adda, all rivers however of Alpine origin.

From the confluence the river continues lazy with wide meanders, lapping the feet of the hill Montecastello. We are now in the open plain, even if the river almost does not seem to want to completely "abandon" the Monferrato hills, stubbornly continuing to lap them on the left bank. Here it becomes navigable up to the mouth by small boats (except in summer).

Finally, the scope of the municipality Rivarone the Tanaro passes under the bridge Bassignana and with a last effort it covers the last kilometre course and then flows into the Po, without immediately being able to confuse its limacciose waters with the grey-green ones of the latter.

The large Tanaro basin includes numerous tributaries (in brackets the place of confluence of each of them):

About 100,000 years ago the Palaeo-Tanaro in its valley section of Ceva headed north and flowed into the Po in the area where today stands Carignano (TO). The subsidence of the astigiano-Alessandrin area and erosive action of small watercourses flowing between Asti and Bra stretched up the basin of the latter, capturing the river and moving its confluence into the Po in the present position, located near the Bassignana (AL).^[14] This phenomenon of capture gave, among other things, the area of Rocche del Roero, characterized by spiers and gullies elsewhere rather rare in Piemonte.^[15]

The Tanaro differs from the other tributaries of the Po being characterized by a complex regime, practically halfway between the counties of the Alpine and the Apennines rivers, being its basin distributed partly on the mountain chain and in part on the Apennines.

The river has two peaks full during the year (the spring and autumn attic) with the late spring-spring greater than the autumn (common feature of the Alpine rivers) and two peaks of lean (summer and winter) with the summer much more accentuated than the winter (as happens instead for the Apennines rivers).

In any case the Tanaro basin is very vast and therefore has many different water characteristics depending on the various sections of its course:

• 1st Section: source (Alpi Liguri) - Ceva

In this section, the river has a nearly alpine regime, with rich flowing in late spring for melting snow on the Ligurian Alps and summer and winter magre. Differences between full and lean flow are not exemplary.

• 2nd Section: Ceva - Cherasco

In this portion, however, the Tanaro regime becomes pluvio-nival with maximum flow rates in autumn (due to strong rainfalls that during this period affect the Monregal plateau and especially the Langhe) and in spring (for melting of snow) with the spring peak slightly greater than the autumn.
The magre instead follow the typical trend of the Apennines rivers, with the summer lean much more marked than that winter.

• 3rd Section: Cherasco - mouth in the Po

In this last portion the river, while greatly increasing its flow, has a pluvious-nival regime even more accentuated with 2 peaks of full year:

autumn (October-November), mainly due to the contributions of the aforementioned medium-upper section of the river and the many torrents and streams coming from the reliefs of Langhe, Roero and Monferrato (Rio della Gera, Mellea, Riddone, Talloria, Cherasca, Seno d'Elvio, Borbore, Versa, Tiglione...), affected in this period by heavy rainfall.
In the short final stretch from Alessandria to the mouth in the Po the autumnal floods are even more frequent and imposing due to the further contribution of the Belbo and especially of the Bormida (both rivers with pluvial character, with basins arranged almost totally on the highly waterproof lands of Langhe and high Monferrato).

Late spring (May-June), is much higher than the autumn one (it can even reach values of 300–400 m³/s) and is largely due to the contribution of the Monregalese rivers and above all to the very substantial one of the Stura di Demonte following the melting of the snow from Colle della Maddalena.
The most important are in winter (December-February) and especially in August where, especially in the downstream section of the confluence with the Stura di Demonte, the flow is reduced almost to a 1/4 of the annual average, once again as in the Apennine rivers.

The Tanaro is characterized by the imponence of its full seasonal ones that can easily reach values of 2.000 m3/s.

The same river also has a remarkable erosive and transport capacity with relatively short travel times (if compared to the considerable length of the main auction) in case of heavy rainfall: in case of formation of a full upstream wave (Ormea area) it is necessary 24-28 hours before the latter reaches the mouth in the Po a Montecastello.

From this it is evident how the whole basin of the river is rectified by a very fragile balance as distributed on extremely delicate territories from the hydrogeological point of view, often subject to remarkable phenomena of dissect (smottings, landslides, erosions, washing...).

The situation then becomes even less comforting, including the process of urbanization to say little savage occurred in the seventies along the banks of the river characterized by artificial channellings of wide sections of river and its tributaries, occupation of much of the gorge territories and uncontrolled sbanking of the gravel from the river bed.

Several times over the centuries Tanaro and its tributaries have caused more than one problem to human settlements located along their shores as in the autumn of the 1948, of 1968, of 1994, of 2016, of 2020.

Among the species that go up this river to reproduce there is cheppia (Alosa fallax).

• Eugenio Perrone, Tanaro, Cecchini, Rome, 1916 (description and study on hydraulic driving power)
• Giovanni Rapetti, I pas ant l'èrba (edited by Franco Castelli), Alessandria, All'Insegna del Moro, 1987
• Luciano Cortevesio del Tanaro, Legend runs on the river, Gribaudo, Cavallermaggiore (CM), 1990
• Giuseppe Aldo di Ricaldone "Monferrato tra Po e Tanaro" Gribaudo Lorenzo Fornaca publisher, Asti 1999
• Richard Motta, Tanaro, Bormida and the collective unconscious of Alessandria, Maxmi Publisher, Castelnuovo Scrivia, 1995
• Ugo Boccassi, Alessandria by boat - When the Tanaro Canottieri remava, in "Nuova Alexandria" Year III N° 10, Ugo Boccassi Editore, Alessandria 1997
• Fulvio Basteris, Garessio, yesterday and today, B&B Editions, Cuneo, 2003
• AA.VV., Tanaro: a river, its world... once, Edizioni i Grafismi Boccassi for the Ethnographic Museum of Alessandria "Once Upon a Time", Alessandria, 2005
• Massimo Arattano, Fabio Brunamonte, Fabio Luino: Alluvial event of 5-6 November 1994 in Piemonte: considerations on the vulnerability of some inhabited centres. Proceedings of the 1st Conference of the National Group of Applied Geology, Giardini Naxos (ME), 11-15 June 1995, pp. 89–108, Publ. No. GNDCI: 1231, 1995
• Massimo Campora, Renato Cottalasso, Ornella Dura, Marco Grassano, The Tanaro. Illustrated guide to the landscape, flora and fauna of the Tanaro river, Muzio publisher, 2007
• Laura Calosso and Laura Nosenzo, Tanaro, the friendly-enemic river (edited by Daniela Piazza Editore) Turin
• Marina Marengo, Alta Val Tanaro. Methods and paths of construction of a mountain territory, Pacini, Ospedaletto (PI), 2011
• Roberto Moriani, To the sources of Tanaro - Between history and legend. Fusta Editore, Saluzzo 2022