Cascade of Middle Chirchik hydroelectric stations in the Uzbek SSR

Abstract

Development of the water resources of the Chirchik River in the Uzbek SSR, the main tributary of the Syt~darya River in the middle course, is being accomplished by constructing a cascade of Middle Chirchik hydroelectric stations.Xn 1941 the construction of the diversion works of the Chlrchik (Tavak and Komsomol) hydrostations made it possible to divert waters of the Chirchik to the Boz-Su waterway and to construct on it by 1954 a cascade of 16 hydrostations with a total capacity of 320 MW. The upper course of the Chlrchlk remained unused for a long time.The cascade of Middle Chirchik hydrostations (Fig. I), consisting of three--Charvak, Khodzhikent, and Gazalkent --using the drop of the upper course of the Chirchlk and mouth reaches of the Chatkal and Pskem rivers over a length of 45 km to the diversion works of the Chlrchikhydrostatlons with a total drop of 215 m. Below the confluence of the Chatkal and Pskem rivers the Chirchlk flows into the Charvak Gorge, where the Charvak hydrostation has been constructed. Below there the Chirchikvalley has a gorge structure and the river flows in a narrow rocky canyon up to 40 m deep cut into the Intermontane valley. Within this stretch the Khodzhikent hydrostation has been constructed and the Gazalkent hydrostatlon is under construction. The average slope of the rlverln this stretch is 3.2 m/km.Within the stretch being considered one comparatively large tributary, the Ugam River, accounting for 9% of the total runoff of the Chlrchik, and several small mudstream tributaries (KaranJul'sal, etc.) empty into the Chlrchik from the right below the site of the Charyak hydrostation. The normal runoff of the Chlrchlk at the site of the Charvakhydrostation is 6.5 km s and at the sites of the Khodzhikent and Gazalkent hydrostations 7.2 km3; 80% of the annual runoff passes in the s,,--,er (April-Septomber).The average winter natural discharges at the site of the Charvak hydrostation are 70-80 mS/sac and at the Khodzhlkent and Gazalkent hydrostations 75-85 mS/set. The maximum observed discharge at the Charvak hydrostation is 1600 mS/sec and at the Gazalkent hydrostation 1960 mS/set. The annual sediment discharge of the Chirchlk under natural conditions at the Charvak hydrostation is 2.9 million tons, and of the Ugam River about 0.3 million tons, which determine the long period of silting of the dead storages of the reservoirs, viz., Charvak about I00 years, Khozhikent and Gazalkent more than 50 years.The structures of the Charvak hydrostatlon are of the first class and of the Khozhikent and Galzalkent of the second. For the Charvak hydrostation the maximum design flood discharge for extreme operating conditions with a probability of 0.01% is equal to 2400 me/set. With consideration of storage of part of the runoff in the reservoir the design discharge of the structures is 2150 mS/sec. The surplus flood works for the construction period were calculated for discharges with 1% probability of 1410 mS/set (the increased probability was used in connection with the fact that the structures we...