The issue of the need for the complex use of the Sevan waters has been studied before the establishment of the Soviet rule in Armenia. In 1910, engineer-constructor Sukias Manaseryan, who participated in rescuing works of the Aral Sea from disaster, published a work proposing to reduce the level of evaporation from Lake Sevan, which made 88 percent of the lake's waters revenue, so to use the saved water for irrigation and energy purposes. Manaseryan suggested that the level of the lake should be lowered by 50 meters, as a result of which the Big Sevan would dry up, and the depth of the Small Sevan would decrease up to 50 meters. As a result, the surface of the lake would be reduced 7 times, respectively, bringing to the essential reduction of the evaporation.
The problem raised by Manaseryan later became known as the "Sevan problem" and was realized with the establishment of the Sevan-Hrazdan Cascade.
The first stage of the project, which would have lasted for 50 years, included the mentioned artificial lowering of the lake level by 50 meters. On the second stage, the use of centuries-old water resources would have to be stopped, and a new, stable water balance of Lake Sevan with an annual outflow of 700 million cubic meters would have to be established.
According to that, in the 1920s, a two-stage technical project for the use of the lake was developed, i.e. the "Sevan-Hrazdan Irrigation-Energy Complex".
It was foreseen that as a result of the program, the irrigated lands of the Ararat Valley and foothills would have increased by at least 100 thousand hectares, and the republic would have received more than 2 billion kWh of electricity per year.
The program was launched in 1933. In 1933-2000, the level of the lake decreased by 19.6 meters due to the industrial exploitation, and the volume was reduced from the previous 58.5 billion cubic meters to 32.5 billion cubic meters. 65% of 26 billion cubic meters of the used water was spent for energy production, and 35% - for irrigation purposes. An area of 25,000 hectares was cleared from the bottom of the lake.
Tens of thousands of hectares of dry lands have been irrigated thanks to the system of irrigation canals built during those years. For these and other purposes, 1,200 million cubic meters of water have been released annually from the Sevan water, as a result of which the level of the lake has been gradually decreasing.
| Indices | 1936 | 2000 | Difference |
| Maximum depth (m) | 98.7 | 79.7 | -19% |
| Average depth (m) | 41.3 | 26.8 | -35% |
| Area (sq.m) | 1,416.2 | 1,238.8 | -12.5% |
| Volume (cubic meters) | 58.48 | 33.20 | -43.2% |
| Level (m) | 1915.97 | 1896.65 | -19.32 m |
The negative consequences for the natural environment have started to be outlined in parallel with the implementation of the project. The essential change of the natural regime of the lake has led to a serious disturbance of the ecological balance of the physical geographical phenomena of the lake and its water-catchment basin established for the millennia.
A special, permanently operating Transcaucasian expedition headed by geologist-academician F. Yu. Levingson-Lessing has been created for in-depth and comprehensive research of the issue. The latter has provided with the rich material on the possible changes of the natural environment, i.e. climate, hydrology, water balance, surface alignment, lake bottom soils, basin soil and plant coverage a result of the lowering of the level of lake Sevan.
Taking into account the possible dangers of the lowering of the level of the lake, thermal power plants working with gas or other fuels have been built in the republic, which significantly reduced the flow from the lake for energy purposes. It became necessary to feed the lake from other sources for the stability of the level of Lake Sevan and for the improvement of the minimum energy and irrigation requirements. A decision was made to build the Arpa-Sevan tunnel, through which it was foreseen to transfer annually 250 million cubic meters of water from the Arpa River to Lake Sevan.
The construction of the Arpa-Sevan complex began in March 1963 by the decision of the Central Committee of the Communist Party of Armenia and the USSR Ministry of Energy and Electrification. This unprecedented structure (48.3 km) in the history of domestic tunnel construction, i.e. the Arpa-San tunnel, was put into operation on March 21, 1981. This stopped the lowering of the lake’s level, and the lake entered the next stage of its development.
Since 2002, the water balance of the lake has been generally positive on an annual basis, and the process of the continuous increase of the lake’s level has started.
The volumes of water release from Lake Sevan with the purpose of the irrigation-energy purposes have been reduced in parallel with the program of the increase of the water level.
The law adopted by the RA National Assembly in 2019 prohibits the releases of more than 170 million cubic meters of water per year from Lake Sevan, except during the drought years.
The volumes of electricity production by the Sevan-Hrazdan Cascade have decreased, correspondingly, in average making annually about 400 GWh, instead of the projected 2,300 GWh. Nevertheless, the Sevan-Hrazdan Cascade continues playing an important role for the entire energy system of Armenia, ensuring the stability of the system and producing about 7-10% of the total useful electricity supply in the republic./p>
The Sevan-Hrazdan Cascade consists of 7 hydro power stations located along the Hrazdan River.
The Hrazdan River originates from Lake Sevan and has a large fall. Originating from an altitude of 1900 meters, it flows towards the city of Yerevan. Near the town of Hrazdan it receives the Marmarik tributary from the right side. Reaching the village of Qaghsi, the fall of the river gradually increases, it enters a deep gorge and leaves the Ararat valley. The length of the river is 146 kilometers, it joins the Araks river at an altitude of 800 meters above the sea level. Thus, the river has a fall of more than thousand meters, thus the favorable conditions from the point of view of the construction of hydro power plants are conditioned by that.
The Yerevan 1st and 2nd hydro power plants built in 1926 and 1929 were the first steps to absorb the hydro-energetic potential of the Hrazdan River. These HPPs satisfied the demand of the small production enterprises of Yerevan of that time. These plants were built on the Artashat irrigation canal originating from the Hrazdan River.
However, the demand for greater quantity of energy raised in parallel with the growth of industry. The construction of the Sevan-Hrazdan energy system has been promoted by the irrigation and energy program of Lake Sevan, which, on the one hand, would provide the necessary electricity and, on the other hand, would give raise to the receiving of the high and stable harvest of agricultural crops in the Ararat Valley. The fertile soil here and the favorable climatic conditions in a short time could create great opportunities for the development of agriculture. Only the issue of irrigation of the lands of the Hoktemberyan region was solved in those years, and the other regions of the Ararat Valley had a shortage of irrigation water. The receiving of the harvest mainly depended on the climatic conditions, the sequence of dry and wet years.
The extended outflow of waters from Lake Sevan along the Hrazdan River has started since 1933. The average annual flow of the Hrazdan River increased about 14 times. A number of irrigation canals have been built during that time, the construction of the Kanaker HPP has started, which was completed in 1936. The installed capacities of the Kanaker HPP have been significantly expanded later. The Kanaker HPP was once the highest pressure plant in the Soviet Union.
The construction of the headquarter plant of the Cascade, i.e. the Sevan HPP began in 1940, which being stopped during the years of the Great Patriotic War, was completed in 1949. The junction of the penstock structures of the Sevan Lake Underground Hydro Power Plant is a complex and original hydro technical structure that regulates the distribution of water to all the power plants and irrigation canals.
The Sevan HPP with its unique structure is considered as one of the magnificent and sightseeing structures of the Republic of Armenia. 320 stairs descending to the underground lake hydro power plant and the elevator lead to a three-storied underground plant. The turbines are located on the bottom floor, on above, and the control room is located on the upper floor.
The construction of the penstock structure was completed in 1948, before that the waters of Lake Sevan, bypassing the newly built lake HPP, flowed into the Hrazdan River. When the construction of the plant was completed in the first half of 1949, these waters were diverted to the plant's turbines.
According to the initial program, the Sevan HPP had to operate only during the first stage of the "Sevan-Hrazdan Irrigation and Energy Complex" program. The plant's turbines had to be replaced with smaller ones after the implementation of a 50-meter fall of the lake's level.
The largest HPP of the Cascade, i.e. the Argel HPP (formerly Gyumush), was put into operation in 1953. It was one of the largest hydro power plants of the Soviet Union. The construction of the Arzni HPP over a rock-cut plant was completed in 1956. Prior to the launching of this plant, in the second tunnel, the Hydro-Energy Institute of the Armenian SSR calculated the coefficient of smoothness of the concrete surface of the tunnel, during which the aerodynamic method was used for the first time in the Soviet Union. The engine of LI-2 airplane was launched in the tunnel for this purpose.
The rests of the plants have been built consistently: the Hrazdan (Atarbekyan) HPP in 1959, the Yerevan-3 HPP - in 1960, and the new Yerevan-1 hydro power plant in 1962. The construction of another three hydro power plants (Verin Argavand, Nerkin Argavand and Noragavit HPPs) was planned in the 1960s, but these plants have not been built.
The Artashat, Lower-Hrazdan, Nork, Kotayk, Arzni-Shamiram, Alapars and other irrigation systems were built on the basis of the waters of the Sevan-Hrazdan Cascade. The waters flowing from the river Hrazdan and released from Lake Sevan totally irrigate about 70% of the cultivated lands of Armenia.
