Гидротехнический водоводный тоннель протяжённостью около 48 км, перебрасывающий сток реки Арпа в озеро Севан для поддержания его уровня. Строительство велось с 1963 года и завершилось вводом в 1981-м; вход — у Кечутского водохранилища близ Джермука, выход — у села Арцванист на берегу Севана. Один из крупнейших безнапорных гидротоннелей региона.
A hydraulic water-conveyance tunnel about 48 km long, transferring the flow of the Arpa River into Lake Sevan to maintain its level. Construction was carried out from 1963 and completed with commissioning in 1981; the inlet is at the Kechut Reservoir near Jermuk, and the outlet is near the village of Artsvanist on the shore of Sevan. It is one of the largest free-flow hydraulic tunnels in the region.
480 000 000 руб. (в ценах до 1961 г.), в ценах 1961 г.
Wikipedia's Lake Sevan article states the Arpa-Sevan tunnel project was "estimated to be 480 million rubles (in old price values)." The phrase "old price values" refers explicitly to pre-1961 Soviet rubles (before the 1961 monetary reform). The estimate dates to 1961, when the project was approved by the Council of Ministers of the USSR on 12 August 1961. Construction ran 1963–1981. No other independent primary source with a cost figure was located; the figure comes solely from the Wikipedia article on Lake Sevan.