On the basis of a project prepared by the Tbilisi Branch of the Gidroproekt Institute (Tbilgidroproekt), the Zhinvala hydraulic development is being constructed in a picturesque canyon of the Aragvi River. This project is of great national-economy importance for supply of power and water to the city of Tbilisi, suburban health resorts, and localities, and for land irrigation in the canyons of the Aragvi, Iori, and Kura Rivers.The approved scheme (Fig. 1) contemplates construction in the lower course of the Atagvi River over a 60-kmIong stretch, in two stages, of two divided-faLl hydroeleetric plants-Zhinvala and Mtskheta, with a total capacity of 415,000 kW and an annual output of 738 million kwh. For the Zhinvaia plant, with a capacity of 130, 000 kW, use is made of the stretch of the Aragvi River between the villages of Ananuri and Bulachauri, with a drop of 188 m. and for the Mtskheta plant, with a capacity of 285, 000 kW, use is made of the stretch between Misaktsieli and Mtskheta, with a drop of 131 m.The Zhinvala plant site is characterized by a moderately warm climate, with a mean monthly minimum temperature of -2"C, a recorded minimum of-23"C, and a maximum of 38*C. The mean annual precipitation is 712 mm, the number of days with precipitation is 102, and the maximum depth of the snow cover is 1.0 m. At the Zhinvala site, the mountainous Aragvi River, which is 100-km long and empties into the Kura River, has an annual runoff of 1.4 km 3 and an annual sediment load of over 1.3 million m s. Its mean annual flow is 44 m3/sec, the maximum recorded is 1120 mS/see, and the minimum recorded is 6 m3/sec. The Aragvi River canyon has a flat-bottomed flood plain over 1.0-kin wide, with afforested steepslopesup to 35* in inclination. An exception is a 600-m-long stretch at the village of Zhinvala, where the flood plain is significantly narrowed, the rock outcrops, the slope steepness increases, and favorable conditions are present for construction of a high dam. Upstream from this stretch, the Aragvi River canyon bifurcates (Fig. 2), and two rivers join the Argavi-Mtiuletis and Pshavis. This favors the construction of a large reservoir with a total capacity of 520 million m s with the river level raised 94 m to elevation 410 m. For a reservoir level drop of 40 m, the useful capacity is 3"/0 million m~; at the normal pool level, the reservoir area is 11.5 km z, and in the Mtiuletis-Aragvi canyon the backwater extends 10 km and reaches the foot of the Ananuri fortress.The reservoir basin consists of impervious Cretaceous softs covered with soils of Quaternary origin. Minor slides, which do not affect the reservoir volume, may occur only at its tail portion. Bank transformation to any significant scale is not expected, because of the small thickness of the deluvlal layer (to 5 m, on the average) covering the rock in the reservoir. The main structure of the hydraulic development is a 101-m-high embankment dam (Fig. 3) made of shingle, witha 490-m width at the base and with a crest length of 415 m; the shingle required fo...