Drava

The Drava or Drave (Drau, ; Drava ; Drava ; Dráva ; Drava ), historically known as the Dravis or Dravus, is a river in southern Central Europe. With a length of 710 km, or 724  km, if the length of its Sextner Bach source is added, it is the fifth or sixth longest tributary of the Danube, after the Tisza, Sava, Prut, Mureș and likely Siret. The Drava drains an area of about 40,154 square kilometers. Its mean annual discharge is seasonally 500 m³/s to 670  m³/s. Its source is near the market town of Innichen, in the Puster Valley of South Tyrol, Italy. The river flows eastwards through East Tyrol and Carinthia in Austria into the Styria region of Slovenia. It then turns southeast, passing through northern Croatia and, after merging with its main tributary the Mur, forms most of the border between Croatia and Hungary, before it joins the Danube near Osijek, in Croatia.

Name
In ancient times the river was known as Dravus or Draus in Latin, and in Greek as Δράος and Δράβος. Medieval attestations of the name include Dravis (c. AD 670), Drauva (in 799), Drauus (in 811), Trauum (in 1091), and Trah (in 1136). The name is pre-Roman and pre-Celtic, but probably of Indo-European origin, from the root *dreu̯- 'flow'. The river gives its name to the dravite species of tourmaline.

Carpis
The Carpis (Greek: Κάρπίς) was a river which, according to Herodotus, flowed from the upper country of the Ombricans northward into the Ister (Danube), whence it has been supposed that this river is the same as the Dravus.

Geography
The Drava (along with one of its tributaries, the Slizza) and the Spöl are the only two rivers originating in Italy that belong to the Danube drainage basin. Its main left tributaries (from the north) are the Isel (contributes 39 m3/s), the Möll (25 m3/s), the (22 m3/s), the Gurk (30 m3/s) and the Lavant (12 m3/s) in Austria, and the Mur (166 m3/s) near Legrad at the Croatian–Hungarian border. Its main right tributaries (from the south) are the Gail (45 m3/s) in Austria, the Meža (12 m3/s) and Dravinja (11 m3/s) in Slovenia, and the Bednja (? m3/s) in Croatia.

Mean discharge is for the last station in the country mentioned in the source.

Course
The sources of the Drava are located at the drainage divide between the market town of Innichen/San Candido and neighbouring Toblach/Dobbiaco in the west, where the Rienz River rises, a tributary of the Adige/Etsch. At Innichen itself the 16+ km, originating near the Sextener Rotwand, joins the ~2 km long source creek. The river than flows eastwards and after 8 kilometres crosses into East Tyrol in Austria. At Lienz it flows into the Isel, sourced from the glaciers of the Venediger and Glockner Groups. The Isel (average discharge 39 m³/s) is almost three times larger than the Drava (14 m³/s) where they meet and, starting from the source of its tributary under the Rötspitze, the Isel (ca. 64 km) is also longer than the combined Drava and Sextner Bach (ca. 60 km) to that point.

The river then flows east into Carinthia at Oberdrauburg. The river separates the Kreuzeck range of the High Tauern in the north and the Gailtal Alps in the south, passes the Sachsenburg narrows and the site of the ancient city of Teurnia, before it reaches the town of Spittal an der Drau. Downstream of Villach, it runs along the northern slopes of the Karawanks to Ferlach and Lavamünd.

The Drava passes into Slovenia at Gorče near Dravograd, from where it runs for 142 km via Vuzenica, Muta, Ruše, and Maribor to Ptuj and the border with Croatia at Ormož. The river then passes Varaždin, Belišće and Osijek in Croatia, and Barcs in Hungary. It is navigable for about 90 km from Čađavica in Croatia to its mouth.

The hydrological parameters of Drava are regularly monitored in Croatia at Botovo, Terezino Polje, Donji Miholjac and Osijek.

Discharge
The Drava's mean annual discharge (Q) at Drávaszabolcs (Hungary, 77.7 rkm). Period from 1995 to 2022.

Hydroelectric power plants
Currently, there are 22 hydroelectric power plants on the Drava. The power plants are listed beginning at the headwaters:

The Drava is one of the most exploited rivers in the world in terms of hydropower, with almost 100% of its water potential energy being exploited. As the region of the river is a place of exceptional biodiversity, this raises several ecological concerns, together with other forms of exploitation such as use of river deposits.