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 theGeography
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 their 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.Middle course
The middle section of the river spans from the city of Bihać to the town of Novi Grad and its confluence with the Sana.Lower course
The lower section of the river spans from the town of Novi Grad to the river mouth. After exiting the town of Novi Grad, the river flows in a general northeast direction until its confluence with the Sava river near Jasenovac. Major towns and villages on the river in this section are Novi Grad, Kostajnica and Kozarska Dubica on the right bank in Bosnia and Dvor na Uni, Hrvatska Kostajnica and Hrvatska Dubica on the left bank in Croatia. The waterfalls, rapids and tufa rock that were common in previous sections are almost completely nonexistent in the lower section as the Una takes up the characteristics of a mature river, meandering through alluvial plains and having a low gradient. Near its confluence with the Sava exist a couple of oxbow lakes colloquially called Stara Una (lit. "Old Una"). After a total length of about 212 km, the Una flows into the Sava river near the Croatian village of Jasenovac. The total length of the river between Novi Grad and Jasenovac is around , with a gradient of 0.041% and drop of .Hydrography
Watershed
The watershed of the Una river has a total area of , of which 79% () belongs to Bosnia and Herzegovina, and 21% () to Croatia. It borders the watersheds of the Korana, Glina and Sunja to the northwest, the Adriatic watersheds of the Lika, Zrmanja and Cetina to the southwest, the watershed of the Cetina to the south and the watersheds of the Vrbas and Jablanica to the east. The shape of the watershed itself is very irregular, but roughly triangular. Due to strong karst influence in the area, the watershed is poorly developed with few large surface streams. The karstification coefficient for the entire watershed is 0.244, which means that 24.4% of the surface area in the watershed lacks proper surface streams and drainage. The karstification coefficient up to Bihać is 0.43, up to Novi Grad 0.28 and up to Kostajnica 0.26. The average air temperature in the area of the watershed is , and the average amount of annual rainfall is . 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 relatively small differences in the average monthly discharges (the driest month August has 37% of average yearly discharge while the wettest month April has 155%) and minimal daily and monthly discharges also show a very small difference. Low discharges last a relatively long time and high discharges appear quickly due to sudden rainfall and snowmelt and last a comparatively short amount of time. High discharges and water levels are present in April and December, and low discharges in August and January. There are multiple measuring stations in Bosnia and Herzegovina on the Una, and their data is show in the tables belowTributaries
The Una river has a relatively weakly developed network of tributaries, owing to its karst geology. Most of the tributaries are shorter rivers, albeit with strong sources and relatively large discharges. There is also a number of karst springs located directly at the main channel of the river. The right tributaries of the river are the Krka, Unac, Krušnica, Vojskova and Sana rivers, and the left tributaries are the Dobrenica, Drobinica, Klokot and Baštra rivers.Sana
The Sana river is the longest and most important tributary of the Una river, with a watershed size of and average discharge of over . Its source is located under Lisina mountain, 420 m above sea level. The longest headwater of the Sana is the Korana, whose source, Dobra Voda, is located at an elevation of 870 m above sea level, but is relatively insignificant in terms of discharge () when compared to the main source of the Sana river. The mouth of the Sana is located in Novi Grad, at an elevation of 117 m above sea level. The Sana has a high karstification coefficient of 0.43 at the Ključ measuring station, which has the consequence of the Sana watershed being relatively undeveloped and having few surface streams. The tributaries of the Sana river are the Banjica (53 km2 watershed area), Gomjenica (776 km2 ). Kozica (120 km2), Ribnik (447 km2 ), Sanica (468 km2), Kijevska rijeka (64 km2), Dabar (111 km2), Zdena (65 km2), Blija (133 km2), Majdanuša (60 km2) and Japra (355 km2). The Sana flows through both entities of Bosnia and Herzegovina. Its source is located inUnac
The Unac river is the longest headwater of the Una, and, at their confluence, has a larger discharge and a larger watershed. The longest headwater of the Unac, Šatorski potok, flows out of Šator lake under the Šator mountain at an elevation of 1460 m above sea level. The largest town on the Unac isKlokot
The Klokot is a short river with watershed area of about 94 km2 and a length of 4,5 km. It flows out of a very strong karst spring around 5 – 6 km west of Bihać and has an average discharge of 14 – 15 m3/s.Krka
The Krka is a right tributary of the Una, and, for the entirety of its length, forms the border between Bosnia and Croatia. It's 4 km long and forms a small canyon. It has a watershed area of 119 km2 and is part of the Una National Park.Krušnica
The Krušnica is a right tributary of the Una. Its source, a strong karst spring with an average discharge of 7 – 8 m3/s, is located 6 km south of Bosanska Krupa. It is around 7 km long and has a watershed area of 301 km2. One interesting thing to note about the river itself is the fact that a small branch of the Una river flows into the Krušnica first, before the Krušnica flows into the Una. A small hydroelectric power plant is also located near the river source.Economy
Hydropower
Due to the rivers's steep gradient, especially in the upper course, 942 MW of electrical energy could be produced if all the potential energy of the watershed was used, and currently, less than 1% of the river's hydroelectric potential is put into use. There have been multipleTourism
The entire watershed of the river has a very large potential for the development of tourism. Notable areas include the upper section of the river, with the Una National Park and its waterfalls, the cities of Bihać and Bosanska Krupa and the surrounding countryside. The tourism sector experiences steady growth, and the number of visitors to the national park has increased every year since its founding in 2008.Rafting
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 ofCities 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 theBosanska 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. The river enters the town from the west, just after having exited its large canyon, and continues to flow through the city, turning north. The river, just like in Bihać, forms multiple cascades and smaller islands connected by bridges. Downstream of Bosanska Krupa, the Krušnica river flows into the UnaNovi Grad
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 10 120, and the municipality has a population of 27 115. The river enters the town from the southwest and after exiting the town continues to flow northeast. The confluence of the Una and its largest tributary, the Sana, is located in the town itself, and the town also divides the middle and lower portions of the river.Kostajnica
Main articles: Kostajnica and Hrvatska Kostajnica Kostajnica and Hrvatska Kostajnica are two towns on opposing banks of the river, in Bosnia and Croatia respectively. 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 3 834, and the municipality has a population of 5 977. The river enters the towns from the west and after exiting the town continues to flow east. Hrvatska Kostajnica is the largest town in the Hrvatska Kostajnica municipality in the Sisačko-moslavačka županija and the administrative center of said municipality. The town has a population of 2 746.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. The river enters the town from the west and after exiting the town continues to flow northeast.Environmental issues
The Una river, with the quality of its waters, unique landscape, rare tufa deposits and waterfalls, rapids, river islands and other aesthetic, geomorphological, hydrological and biological characteristics represents a unique environment in need of protection. The largest current threats to the river and its ecosystem are pollution and proposed hydropower projects.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. In the cities and towns located on the river banks, most of the local population lacks any sort of ecological consciousness, which, combined with the lack of public trash cans and the ongoing migrant crisis, leads to a large amount of trash being thrown onto the river banks and into the river itself. Commons sites where large amounts of trash can be found are bathing sites, especially more obscure ones, the intake of the hydroelectric power plant in Bihać, publicly accessible river islands, and the shallower parts of the river. Completely destroyed trash cans, park benches and vandalized bridges are not an uncommon sight, especially in more obscure, badly lit parts of the cities. Some of the vandalized bridges on the river even required complete reconstruction. 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
References
External links