The Atbashi hydroelectric station with an installed capacity of 40,000 kW was put into operation in early 1970; the total capacity of its reservoir is 9.58 million m s, the useful capacity is 4.34 million m 3 at the normal pool level (NPL) of 154 m, and the dead storage level (DSL) is 145 ms The structures of the hydrostation include [i]: a gravel--pebble earth dam with a height of 79 m with a grouting gallery and grout curtain (Fig. !), operating tunnel spillway Qdes = 330 m3/sec, intake and power tunnel d = 5 m, I = 300 m, powerhouse with four units, grouting adits in the rock walls located at two levels ( Fig. 2), access adits, and a diversion tunnel. The hydrostation is located in the high-mountain region of Central Tien Shan on the Atbashi River, a left-bank tributary of the Na~/n River.The region of the hydrostation site has complex toBographic and engineering-geologic conditions: the foundation and bank abutments of the dam are composed of marmorized limestones whose permeability is characterized by permeability coefficient 0.2-0.01 m/day.The numerous fractures in the limestones are mainly of a tectonic origin. The bank release fractures with an open width to 50 cm, usually filled with sand--clay material or calcite, extend tens and hundreds of meters~The developed ancient karst has cavities from several millimeters to tens of meters.The groundwater level is 15-18 m below the water level in the river. The seismicity of the region is intensity 8. The climate is markedly continental: the mean annual air temperature is +2.5~ with an absolute maximum of +34 ~ and minimum of --38 ~ The mean annual discharge of the Atbashi River is 32.8 m3/sec, the sediment load varies from 0.I to 5.8 million m31yr, and the volume of runoff of shuga reaches 5.6 million m3/yr. At the present-day level the minimum storage of the reservoir for daily and weekly regulation needed for the Atbashi hydrostation to eliminate the weekly nonuniformity of the load is 1o7 million m 3. Since the volume of sediment and shuga [spongy ice lumps] far exceeds the indicated quantity, for providing operation of the hydrostation it was necessary to specify --for the first time in our country for a reservoir on a mountain river --deep (more than 40 m) annual flushing with complete drawdown of the reservoir during recession of the flood and brief stopping of the hydrostation.Such flushing was planned in stages with alternation of a partial rise of the water level in the reservoir and discharge of the clarified water for washing out the deposits formed in the lower pool during flushing into the Naryn River (a distance of about 4 km).Periodic deep flushings are supplemented by constant flushings in the su~er and fall by discharging surplus water at the 145-m DSL.For deep flushing, the inlet structure of the operating tunnel spillways has a number of special features (Fig. i): the sill of the radial gate is located 42 m below the NPL and the three-level intake openings, in the event of clogging of the lower opening by sediments, make it possible to flush ...
The basin of the Malaya Almaatlnka River is located in one of the most active mudflow regions of the USSR. In the high-mountaln part of the basin mudflows of local Character are formed almost annually. Disastrous mudflows occur as a result of cloudbursts and outbreaks of morainal lakes during rapid melting of glaciers. They occur considerably more rarely (recorded in 1888, 1889, 1921, 1956, and 1973), but inflict great damage on the economy.To retain the mudflows formed in the greater part of the basin of the M. Almaatlnka River it was decided in 1964 to construct a mudflow-control dam at Medeo. Construction was by the method of directed massive blasting with subsequent additional rock filling to the design profile. The height of the dam is 115 m, crest width 20 m, gradient of the upstream slope from 1:1.6 to 1:2.2 and of the downstream 1:2. A loam facing with an impervious blanket was placed along the upstream slope. The total volume of fill was 3.8 million m 3.The dam project called for a discharge tunnel calculated for a discharge of 30 mS/sec with right-and left-bank intakes. The design of the first provided a discharge from elevations up to 1830 m, the second provided discharge from any elevation in the storage basin. An open emergency mud spillway with a discharge capacity of 230 mS/sec was provided for use in the event of overfilling of the mud storage.The construction work on the dam was completed in 1972, the discharge tunnel was ready by the time of the first directed blast in October 1966, and withstood the dynamic impact of the blast waves well. For a number of reasons construction of the main left-bank water intake and emergency mud spillway was not completed by the time of passage of the mudflow that formed on July 15, 1973.The temporary channel and right-bank intake and the dam'as a whole withstood the power of the mud-stone flow that moved toward the city at a velocity in the order of i0 m/sec --the mud-storage dam held it all. The mud-storage basin was filled to elevation 1835.5 m, i.e., to a depth of 60-70 m, with a total volume of mud of 4 million m s. This was about 2-3 times greater than the 1921 mudflow, which, having reached the streets of the city, caused great damage and loss of llfe. The dam at Medeo prevented a disaster of a considerably greater scale, if one considers the unprecedented magnitude of the mudflow and denser present-day development of the city. The mudflow was retained, but it plugged the inlets to the discharge tunnel. The water level began to rise and the serious threat of reservoir overfilling appeared.To keep the residual reservoir volume left after accumulating the mudflow (2 million m 3) from being filled by the natural streamflow, it was decided to pump out the water. This de---
The Atbashinsk hydroelectric station earth dam [1], designed for a head of 76 m, has antiseepage provisions of original construction. The antiseepage curtain ( Fig. 1) in the body of the darn was designed in the form of a diaphragm whose composition varies along its height. Within the confines of the narrow lower (canyon) part, to aheight of 40 m, the diaphragm comprises 8 m of riher-bed alluvial deposits and 14 m of sand-gravel soil laid down in water, sealed with clay-cement mixtures, and a 17-m-thick concrete plug surmounted by an access gallery, bridging the upper canyon part of the river bed. The upper part of the diaphragm consists of a polyethylene film, which is fixed at its base to the concrete of the gallery and the plug and at the sides to concrete cut-offs up the abutments. The diaphragm of the dam is joined to the grout curtain along the foundation and abutments at the site.
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