Arda (Maritsa) in the context of "Upper Thracian Plain"

The Maritsa, known in Greek as the Hebros and in Turkish as the Meriç, is a river that runs through the Balkans in Southeast Europe. With a length of 480 km (300 mi), it is the longest river that runs solely in the interior of the Balkan peninsula, and one of the largest in Europe by discharge. It flows through Bulgaria in its upper and middle reaches, while its lower course forms part of the border between Greece and Turkey. Its drainage area is about 53,000 km (20,000 sq mi), of which 66.2% is in Bulgaria, 27.5% in Turkey, and 6.3% in Greece. It is the main river of the historical region of Thrace, most of which lies in its drainage basin.

It has its origin in the Rila Mountains in Western Bulgaria, its source being the Marichini Lakes. The Maritsa flows east-southeast between the Balkan and Rhodope Mountains, past Plovdiv and Dimitrovgrad in Bulgaria to Edirne in Turkey. East of Svilengrad, Bulgaria, the river flows eastwards, forming the border between Bulgaria (on the north bank) and Greece (on the south bank), and then between Turkey and Greece. At Edirne, the river meets its two chief tributaries Tundzha and Arda, and flows through Turkish territory on both banks. It then turns towards the south and forms the border between Greece on the west bank and Turkey on the east bank all the way to the Aegean Sea, which it enters near Enez, forming a river delta. The upper Maritsa valley is a principal east–west route in Bulgaria. The unnavigable river is used for hydroelectric power generation and for irrigation.

Rudozem (Bulgarian: Рудозем [rudoˈzɛm]) is a town in southern Bulgaria, near the Greek border, located in the Rhodope Mountains, where the Elhovo and Chepino rivers flow into the Arda, and is part of Smolyan Province. It is the administrative centre of the homonymous Rudozem Municipality. As of December 2009, the town had a population of 3,583.

The name Rudozem is a compound word made up of Bulgarian ruda (руда) meaning "ore"; and the root zem (зем) meaning "land". It refers to the wealth of the area in mineral resources. Its former name is Palas. During the rule of the Ottoman Empire, it was part of the Ottoman İskeçe sanjak in Edirne vilayet between 1867 and 1912.

Ivaylovgrad (Bulgarian: Ивайловград, "city of Ivaylo", Greek: Ορτάκιοϊ, Turkish :Ortaköy, "Middle Village") is a town in Haskovo Province in the south of Bulgaria set near the river Arda in the easternmost part of the Rhodope Mountains, and is the administrative centre of the homonymous Ivaylovgrad Municipality. The border with Evros, Greece is around two miles from the town centre.

The Studen Kladenets Reservoir (Bulgarian: язовир „Студен кладенец“, meaning "cold well") is the third largest reservoir by volume in Bulgaria after Iskar Dam and Kardzhali Dam. It is situated on the river Arda, and is created behind the Studen Kladenets dam, 30 km south-east of the town of Kardzhali. There are another two dams of the Arda - Kardzhali Dam to the west (upstream) and Ivaylovgrad Dam to the east (downstream). The dam is operated by the Bulgarian National Electric Company, NEK EAD.

The reservoir has a total volume of 388 million m and a drainage basin of 3,706 km and is 29 km long. It is situated at an average 227 m above sea level, its dam being 338 m long and 67.5 m high. The top of the dam consists of nine spillways, each one being 10.5 by 5 m."Studen Kladenets" Hydroelectric Power Plant is situated appr. 1 km downstream of the dam. Initially the HPP had four Francis-type turbines, 15 MW each. А project for reconstruction and upgrading the HPP with another 16 MW turbine and a smaller eco-turbine underwent and after the completion, the total output reached 85 MW with annual production of 165 GWh of electricity.