Exploitation and reduction Background Sevan was recognized as being a major potential water resource in the 19th century. Its high altitude location relative to the fertile
Ararat plain and limited energy resources attracted engineers to explore ways of usage of the lake's water. In his 1910 booklet, Armenian engineer Sukias Manasserian proposed using Sevan's water for irrigation and
hydroelectric power generation. He proposed draining the lake by . Major Sevan would completely dry out, while Minor Sevan would have a surface area of .
Implementation Manasserian's proposal was adopted by the Soviet authorities in the 1930s when, under
Joseph Stalin, the country was undergoing rapid
industrialization. Works on the project started in 1933. The riverbed of
Hrazdan was deepened through excavation. A tunnel was bored around under the lake's surface. The tunnel was completed in 1949 and thereafter the Sevan's level began to drop significantly, at a rate over per year. The water was used for irrigation and the
Sevan–Hrazdan Cascade of six hydroelectric power stations on Hrazdan River.
Effects During the second half of the 20th century, the ecological condition of Lake Sevan underwent tangible changes and vast degradation due to reduced water level, increased
eutrophication, and detrimental impact of human activity on the biological diversity of the lake. According to Babayan et al. the lake level dropped by by 2002, while the volume decreased by 43.8% (from ). Due to the water level decrease, the quality of the water deteriorated, natural habitats were destroyed that meant
loss of biodiversity. Vardanian wrote that drop of the lake level and the economic development in the basin brought about the change in hydro-chemical regime of the lake. The quality of the water deteriorated, water turbidity increased. The inner circulation of the water constituents as well as the circulation of the biological substances altered.
Reversal and recovery Arpa–Sevan tunnel By the time of the
Khrushchev Thaw, "it had become evident that the ecological and economic consequences of extensive exploitation of the water of Lake Sevan were too undesirable to continue in the same way." Soviet Armenian leaders soon agreed that "the best way to solve the issue would be to construct a canal to divert water from Armenia's
Arpa River into the lake." To support this project, Yerevan needed assistance from the all-union budget. On
Victory Day (9 May) 1961, Armenian officials, led by First Secretary
Yakov Zarobyan, together with Marshal
Ivan Bagramyan, met with
Nikita Khrushchev at the lake to discuss the Arpa-Sevan proposal. Guided by advice from Khrushchev's close ally
Anastas Mikoyan, the Armenian leadership managed to persuade Khrushchev to support the project, "estimated to be 480 million rubles (in old price values)." The plan for the Arpa-Sevan tunnel was approved on 12 August 1961 by the
Council of Ministers of the Soviet Union. It envisioned diverting water from a reservoir of the Arpa River near
Kechut through a long tunnel to the lake near
Artsvanist. Armenian authorities "moved to begin the implementation of the project" on 29 August 1961. The tunnel was eventually completed in 1981 and continues to bring up to of water to Sevan per year. However, it is estimated that due to
climate change, the outflow of the Arpa river will decrease by 22% by 2030.
Vorotan–Arpa tunnel Since the water level in the lake did not rise as fast and as much, on 20 April 1981 the
Council of Ministers of the Soviet Union made a decision for the construction of the Vorotan–Arpa tunnel. Due to the
Nagorno-Karabakh conflict and the
1988 earthquake in northwestern Armenia construction was halted. The tunnel was inaugurated on 26 April 2004. The Vorotan–Arpa tunnel brings an additional to the lake annually. It reached in October 2010. The government committee on Sevan forecasts that the level will reach by 2029. Water level stood at 1900.44 m in November 2019. == Population ==