The Una (, ) is a border river between Bosnia and Herzegovina and Croatia and a right tributary of the Sava river. It is part of the Black Sea drainage basin, and its watershed has a size of , of which belongs to Bosnia and Herzegovina, and to Croatia. The total length of the river is . The source of the river is located near the village of Donja Suvaja in Croatia, and its mouth is located near the village of Jasenovac, on the border with Bosnia. The largest right tributaries are the Krka, Unac, Krušnica and Sana rivers, and the largest left tributary is the Klokot river. Its longest headwater is the Unac river. The largest and most important city located on the river is Bihać. Other important cities and towns are Bosanska Krupa, Bosanski Novi and Bosanska Kostajnica. The river is characterized by a multitude of waterfalls, rapids, karst springs and relatively untouched nature. A large part of the upper river is part of the Una National Park.

Etymology

According to local legends, the river was named by the Romans who, after seeing it for the first time, said una (lat. one, as a reference to its unique beauty) to describe it.

Una is a popular female name even in the areas that are not located in the vicinity of the river. One explanation for this is that people that were displaced during the Yugoslav Wars continued to give the name to their children.

Geography

Sources

The source of the Una river is located near the Croatian village of Donja Suvaja and consists of multiple smaller springs. The largest spring by discharge is a large karst spring at an elevation of above sea level, called Vrelo Une, and is considered to be the main spring of the river. The water, originating from great depths, forms a round, calm, bluish green lake, thirty meters by fifteen meters in size, surrounded by forests and steep cliffs of the Lička Plješevica and Stražbenica mountain ranges. The Una river, flowing out of the spring, forms its first travertine cascade roughly 20 meters downstream and another large waterfall 3 – 4 meters in height roughly 100 meters downstream. The spring itself was explored and mapped up to a depth of 248 meters, which makes it the deepest explored spring in the Dinaric karst region and the fifth deepest in the world. Due to its unique aesthetic, ecological, geomorphological and hydrological value, the spring and the surrounding region, totaling an area of , were declared a natural monument in 1968.

The karst aquifer of the Una is located mostly in the territory of Croatia. The aquifer itself takes up a large area from Korana in the northwest to Velika Popina in the southeast. It encompasses the mountainous areas of the Lička Plješevica, Čemernica and Mala Kapela mountains, and the Koreničko, Bijelopolje, Krbavsko and Lapačko polje karst fields. All aforementioned karst fields are directly connected to spring of the river itself, and other nearby springs (Klokot, Vedro Polje, Dobrenica, Ostrovica).

The discharge of the spring varies from a minimal recorded in 1987 to a maximal recorded in 2009, with the average discharge being . The spring seems to have a limited outflow capacity, potentially caused by limited dimensions of the karst outflow channel, water retention in the karst, water flowing under pressure and water overflowing into other watersheds. The total amount of water that flows out of the spring yearly ranges between and . The temperature of the water varies in relatively narrow margins of with an average of , which also leads to the conclusion that the surfacing water spends a large amount of time in the karst underground. The average, minimal and maximal monthly and yearly discharges seemed to have increased in recent times, contrary to a trend of decreasing discharges from other springs in the nearby regions believed to be caused by global warming.

Upper course

The upper part of the river spans from its source to the city of Bihać.

After emerging from its source, the river flows for about 5 km before reaching its confluence with the Krka river, after which it forms the border between Bosnia and Croatia for about 7 km and then enters Bosnia completely for the first time, flowing through the village of Martin Brod where it forms a cascade of waterfalls with the total drop being about . Downstream of Martin Bord, the Una more than doubles in size at its confluence with the Unac. After 9 km the river bends west at the town of Kulen Vakuf where it is joined by the small tributary Ostrovica before continuing to flow in a general northward direction. Downstream of Kulen Vakuf, the river meanders through a valley by the village of Klisa before again meeting the Croatian border after about 8 km. This time, the river forms the border for about 18 km and cuts through a gorge, forming a cascade of rapids and waterfalls, the biggest and most notable being the Štrbački buk. After entering Bosnia completely for the second time, the rivers forms the Troslap and Dvoslap waterfalls, after which it exits the national park and flows through the villages of Lohovo and Račić. After that, the river slowly enters the Bihać field, flowing through the villages of Ripač, Golubić and Pritoka, taking in the waters of the Dobrenica and forming multiple river islands and small waterfalls, before finally entering the city of Bihać after about 70 km of total flow. In Bihać, the river forms multiple islands of varying sizes, often surrounded by small waterfalls, some of which are private property while others are public and often popular bathing sites. The core of the city itself is surrounded by the Una river, and a channel carries water from the river to a small hydroelectric power plant. Another small tributary of the Una, the Drobinica, flows through the city in a regulated channel before merging with the Una. In its upper course, the Una is a youthful river with a steep gradient of 0.232% and a large amount of waterfalls. The total drop is over a distance of . The deposition of carbonate minerals and the formation of porous limestone rock (tufa) and pronounced karst influence is characteristic for this section.

The watersheds of the Una and the watersheds of the Korana and Glina are often grouped together for analytical purposes in Bosnia and Herzegovina.

Discharge

The Una river has an average discharge of at its mouth, with a minimal discharge of .

There are multiple measuring stations in Bosnia and Herzegovina on the Unac, and their data is show in the table below: It has a hydraulic head of 2.6 m and an intake capacity of 9 m<sup>3</sup>/s. The water is directed into the intake by a low, concrete dam, colloquially called "beton" (bos. concrete), that doubles as a walkway and bathing site during low water levels. During high water levels, excess water flows over the dam forming a long waterfall. The power plant along with all other related structures was in 2011. declared to be a national monument of Bosnia and Herzegovina.

The Krušnica hydroelectric powerplant is located near the source of the Krušnica river near Bosanska Krupa and was, like the Bihać power plant, build during the Austro-Hungarian rule in Bosnia, in 1911. It has an installed capacity of 460&nbsp;kW and a yearly electricity production of 400 MWh. The installed capacity of each turbine is 2.35 MW for a grand total of 9.40 MW.

Rafting

Rafting is one of the most popular form of outdoor recreation in Bosnia and Herzegovina, and is important part of the national park offer for the river Una.

Fly fishing and angling

The river Una as well as the Unac are popular fly fishing grounds, and among the largest in Europe. An abundant ichthyofauna, rich in salmonid species, primarily grayling and brown trout, with the Una being also famous huchen destinations. Fly fishing and other angling methods are allowed only in certain sections and under strict rules and regulations of the national park services. This also applies on most tributaries, especially the Unac, Krušnica, and Klokot, while the Krka, like most of the Unac watercourse within the National Park, is completely excluded from all water and underwater activities.

Flora and fauna

Over 170 types of medicinal herbs grow by the Una River; a rare plant called Campanula unensis, the "Una bluebell", was named after the River Una's bright turquoise and green colors.

Ichthyofauna

Twenty eight (28) species of fish live in the Una river, the biggest of which is the huchen (mladica, Latin: Hucho hucho). The river is rich in salmonid fish species, where as the healthy population of endemic huchen, otherwise globally endangered, makes the river Una and its main tributary the Sana, one of Europe's primer habitats and spawning grounds. Other smaller tributaries are also important for this fish, as it enters smaller stream during spawning season to lay eggs.

Cities and towns

Bihać

Bihać is the largest and most important city located on the banks of the Una river and is the administrative center of the Una-Sana Canton in the Federation of Bosnia and Herzegovina and is the center of the Bihać municipality itself. The city itself has a population of 39 690, and the municipality has a population of 56 261. The Una National Park is almost completely located in the Bihać municipality, along with some of the largest waterfalls, canyons, cascades and tourist attractions. Some of the settlements on the Una river in the Bihać municipality are Martin Brod, Kulen Vakuf, Lohovo, Ripač, Pritoka, Golubić and Ostrožac na Uni.

The river enters the city from the south after having formed the large Ribićka otoka island. It continues to flow north towards the Alija Izetbegović bridge and passes by the Midžića jezero lake. The first cascade in the city is located at the end of the low concrete dam of the hydroelectric power plant. After flowing under the bridge, it continues to flow north where it forms the Gradska otoka island. The island is accessible by two pedestrian bridges connecting it to both banks of the river, and another pedestrian bridge connecting it to the smaller Amerikančevo island. After Gradska otoka island, the river splits into multiple smaller channels and forms multiple islands, some of which are private property and are connected to the mainland by bridges and some of which are wild, uninhabited islands. Two additional cascades are located in this stretch. After the individual channels combine, the water flows over a large, V-shaped cascade, after which the river splits into two channels again, forming another island. There are cascades on both sides of the island. The western one is a popular fishing and fly fishing spot and the location where the water flows out of the hydroelectric power plant, and the one on the eastern side is a popular bathing site. After the island, the river channels combine again and the water flows under the second large bridge in the city, the Bakšaiš bridge. After the bridge, the river forms multiple cascades before splitting into two channels again and forming the large Bakšaš island, after which the two channels combine again before forming another large set of river islands called Jotanovi otoci or simply Jotani. The last large cascades in the city are located here. After Jotani islands, the river flows under an old pedestrian bridge just before its confluence with the Klokot river.

Bosanska Krupa

Bosanska Krupa is the largest town in the Bosanska Krupa municipality in the Una-Sana Canton and the administrative center of said municipality. The town has a population of 10 196, and the municipality has a population of 25 545. Another large settlement on the banks of the river in the municipality is the town of Bosanska Otoka.

Kozarska Dubica

Novi Grad is the largest town in the Novi Grad municipality in Republika Srpska and the administrative center of said municipality. The town has a population of 10 544, and the municipality has a population of 21 524.

Pollution

The upper section of the river is, for now, still a relatively untouched and unpolluted part of the river. The main pre-war pollutants, such as the cellulose factory in Drvar and the glue factory in Srb, have stopped operating after the war, and as such the water quality is satisfactory. Currently there are still multiple locations where raw, untreated sewage still flows into the river, and a large part of the sewage system of some of the cities on the river was destroyed during the war, worsening the problem. A current problem is also the exploitation of forests on the river banks and the exploitation of sand and clay from the riverbed, which could lead to erosion that could affect the river basin and the river itself. The Unac river is prone to sudden increases of discharge and water level, which could also lead to additional erosion.

Another large but often overlooked issue is the fact that there are multiple illegal landfills located in the watershed of the river, most notable in the Una-Sana canton. Some of the landfills are located directly above spring which feed directly into the river itself. To this date, there have been no solutions to the problem as the government of the Una-Sana canton is unable to properly organize and find a suitable location for a canton-level landfill.

Hydropower projects

There have been multiple hydropower projects proposed on the rivers itself and its tributaries, including the large Unac, Vrhpolje and Ključ hydroelectric power plants, and the smaller Štrbački buk power plant. There have also been multiple proposals for smaller mini hydroelectric power plants along the smaller tributaries, such as the Dobrenica. Some of those power plants, like the Unac power plant, would have large dams that would flood attractive canyons while other would divert a large portion of river's water to a machine room several kilometers downstream, leaving large parts of the riverbed dry. All of those proposals were met with fierce resistance from the local and international communities for fear of the destruction of the river's unique environment and, eventually, were cancelled.

<gallery class="center">

File:Vrelo Une.jpg|The spring of the Una

File:Martin Brod – Veliki slap.jpg|The Una in Martin Brod

File:Bridge over Una river in Kulen Vakuf.jpg|The Una in Kulen Vakuf

File:Unamameapark2.jpg|The Štrbački Buk viewed from Croatia

File:Bihać noću..jpg|The Una in Bihać at night

File:Una bei Bihac.jpg|The Una river canyon

File:Bosanska Krupa, mestecko na Une.jpg|The Una in Bosanska Krupa

File:Rijeka Una - Novi Grad 21.jpg|The Una in Bosanski Novi

File:Una Hrvatska Kostajnica 2.jpg|The Una in Hrvatska Kostajnica

</gallery>

References

  • Green Visions article about Una
  • Una springs in Lika region, Croatia

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