Tundzha

The Tundzha (Bulgarian: Тунджа [ˈtund͡ʒɐ]; Turkish: Tunca [tund͡ʒa]; Tonsus in antiquity) is a river in southeastern Bulgaria and northwesternmost Turkey, a left tributary of the Maritsa. With a length of 390 km, of which 350 km are in Bulgaria, it is Maritsa's longest tributary, though in terms of discharge it is second after the Arda. Tundzha Glacier on Livingston Island in the South Shetland Islands, Antarctica is named after Tundzha River.

The Tundzha springs at an altitude of 2,083 m some 250 m south of the summit of Yurushka Gramada (2,136 m) in the central Balkan Mountains. Its source lies about two kilometers east of Botev Peak (2,376 m), the highest summit in the mountain range. It flows south in a deep valley with steep slopes and a large longitudinal gradient. The riverbed is rocky with gravels. Its water current is high, reaching velocity of 1.5–2 m/s.

At the town of Kalofer the Tundzha turns east and then enters the western reaches of the Kazanlak Valley, where the river valley widens to 3–4 km at the village of Aleksandrovo and then narrows to one kilometer. In that section it flows closer to the northern slopes of Sredna Gora and has steep right slopes. The river meanders, the riverbed is 20–25 m wide and 0.7 m deep. The bottom consists of sand and fine gravel. The velocity of the current is 1–1.5 m/s; the gradient is 1.5‰. The river valley narrows further between the villages of Viden and Buzovgrad, reaching several dozen meters at the village of Koprinka, where the dam of the Koprinka Reservoir has been constructed; it then again widens to one kilometer. The riverbed in that section is 28–30 m, the current is 1 m/s; the bottom consists of sand and gravel.

Downstream of Buzovgrad the valley widens significantly, reaching 5–7 m; the river forms several strongly curved meanders, especially between the villages of Yagoda and Zimnitsa. The gradient in that section is 1.5‰. Just downstream of the town of Nikolaevo the Tundzha enters the Tvarditsa Valley and then the Mezhdenik Gorge, where the river valley narrows, at places to 60–100 m; in the narrowest section is the dam of the Zhrebchevo Reservoir. It exits the gorge at the village of Binkos and enters the Sliven Valley for the next 70 km. There, the river valley reaches a width of 2–3 km, the gradient decreases to 1,0‰; the Tundzha forms numerous meanders. Further east, the river valley widens to more than 7 km.

Southeast of the village of Zhelyu Voyvoda the river turns south and maintains that general direction to its mouth. Before the city of Yambol, the Tundzha passes through a short and wide gorge and receives its largest tributary, the Mochuritsa. Downstream from the city the river enters the Yambol Field. The river valley in that section is vaguely pronounced, reaching a width of 10–40 km; that is the section with the most meanders in its entire course. At the village of Konevets the river enters the elongated Elhovo Field, where the riverbed is 40–50 m wide and the average depth is 1–1.5 m; the gradient decreases to 0.7‰. Its banks are low, gently sloping and overgrown with willows. The bottom is sandy.

Downstream from the village of Knyazhevo the Tundzha enters the long picturesque Srem Gorge between the Sakar mountain range to the west and the Dervent Heights to the east. The gorge is narrow, reaching some 100–200 m, with steep bare slopes and rocky uneven riverbed. There is a small widening of 0.8–1 km between the villages of Srem and Ustrem, after which the gorge narrows again with deforested slopes and in places almost canyon-like. In that section the river is about 60 m wide with an average depth of 1–2 m. Shortly after exiting the gorge the river forms the Bulgaria–Turkey border for about 10 km. East of the village of Matochina the Tundzha leaves Bulgaria and enters Turkey, where it flows into the Maritsa at an altitude of 32 m in the city of Edirne.

Its drainage basin covers an area of 8,429 km² or 15.9% of the Maritsa's total. Of them 7,884 km² are in Bulgaria, encompassing territory of seven provinces — northern Stara Zagora Province, central Sliven Province, over 80% of Yambol Province, eastern Haskovo Province, northwesternmost Burgas Province, as well as small areas of Plovdiv and Gabrovo Provinces. The remaining 548 km² are in Turkey's Edirne Province. About 33% of the catchment area is forested, or 2,613 km².

Beginning from the right bank of the Tundzha mouth the boundaries of its basin head northeast through the southern outreaches of the Sakar mountain range, enters Bulgaria, follows Sakar's main ridge to its highest point Vishegrad (856 m), turns north, runs through the ridge of the Manastirski Heights, descends to the easternmost limits of the Upper Thracian Plain and then ascends the ridge of the Svetiiliyski Heights. Continuing north, the boundary again descend to the Upper Thracian Plain and north of the village of Staro Selo reaches the main ridge of the Sredna Gora mountain range, where it turns west. South of Kalofer, the boundary heads north again and via Strazhata reaches the main ridge of the Balkan Mountains at the summit of Yurushka Gramada. In that section the river basin borders the drainage systems of the Kemal (in Turkey), Kalamitsa, Levchenska reka, Golyama reka, Sazliyka, Omurovska reka, Brezovska reka and Stryama, all of them left tributaries of the Maritsa.