624.131.6:627.8 and L. A. Molokov Hydroelectric projects, reservoirs, and large canals are the largest objects created by man, and their effect on the environment extends over considerable territories and encompasses the basins of large rivers or wide zones along canals, i.e., has a regional character. With the existing scale and rate of constructing hydraulic structures (at present about i0,000 reservoirs with a volume of more than 0.i km s have been constructed worldwide, of which more than 250 are in the USSR) [i, 13], the damage inflicted by these structures on the environment is becoming comparable to the reserves of certain natural resources.For example, just the losses from flooding or depreciation of the quality of lands as of 1974 amounted to about 85,000-95,000 km 2 [4], which is comparable to the land reclamation plan in the country (draining and irrigation) up to the year 1990 [9].A specific feature of the construction of hydraulic structures is, in particular, that it is practically impossible to eliminate its adverse effect on the environment and, as a rule, it occurs imreversibly {e.g., flooding of lands), although many types of it can be~regulated and the problem usually reduces to the compilation of economic evaluations of the environmental damage from constructing the structures and the corresponding cost to prevent it. Some of these evaluations are rather conventional (e.g., the cost of various soils, forests, etc.); others in the near future can change substantially, and it is difficult to predict the extent of the change.Therefore, a study of all parameters of the environment and the most complete possible evaluation (at least in a physical expression) of the remote consequences of constructing large hydraulic structure are now becoming the top-priority problem.In itself this problem is not new, but now, compared to the 1950s when the country acutely needed first and foremost a boost of the energy base, its urgency has increased sharply. Moreover, before the 1950-1960s, when there we=e few large reservoirs and their cascades, our knowledge about their effect on the environment was rather scanty and largely theoretical. Now the situation has changed substantially: for many types of effects and certain particular processes there are quantitative evaluations or studies based on long-term experience in operating large structures and cascades of =eservoirs.During this same period environmental damage has increased markedly also from other human engineering and economic activities (the mining and processing industry, cities, irrigation systems, etc.) and therefore at present it is necessary to examine the adverse effect of constructing hydraulic structures against the background of the overall anthropogenic impact in this direction [8]. At present there are no quantitative total and branch (of the economy) evaluation of the indicated adverse impact on the environment, and therefore it is extremely difficult to assess the "contribution" of the construction of hydraulic structures proper:to thi...

The hydropowCrdevelopment at As-Saurah in Syria has a multiple purpose (average annual production of 1.6 billion kwh, irrigation of 640,000 ha) and is one of the largest hydraulic structures in the Near East.It was designed, constructed, and is being operated under unique engineering-geological conditions related to the wide development in the given region of Oligocene chalks covered by Neogene dolomites.The latter in the zone of the main structures of the development are completely cut through by the valley of the Euphrates River and only here and there have been partially preserved on the valley floor in the cores of synclinal folds.In the foundation of the powerhouse of the hydroelectric station and floodplain--channel dam (with the exception of a very small stretch near the left bank) occur only Oligocene chalks covered by a thin layer of modern alluvium (10-15 m), which was removed both in the zone of the foundation pit for the powerhouse and from under the central part (cutoff wall) of the earth dam. Thus, Oligocene chalks had paramount importance for the main structures of the development and had to be studied thoroughly. The thickness of the chalk strata exceeds 200 m and the entire active zone of even the heaviest structures does not fall outside its limits.Since the practice of constructing large hydraulic structures on chalks at the time of planning the Tabqa hydroelectric station project was limited mainly to the experience of constructing four dams in the USA [6], project surveyors, designers, and builders were at once faced with a number of complex problems which had to be solved for the given case.The structure, composition, and properties of the rocks of the Oiigocene chalk strata have been elucidated in detail in published works [1][2][3][4][5], and here we need note only that the greatest complications were caused by the presence in them of two thin (1-3 cm) interlayers of bentonite clays (B I and B2) , the distance between which in the section was about 70 m, and several interlayers of clayey marls with a thickness from 3 to 15 cm (marker horizons O, P, Q, R, S). The presence of the interlayers and the characteristics of the composition, particularly the clay content of the deposits, made it possible to some extent to draw an analogy between the Oligocene chalks of the middle course of the Euphrates and the Turonian--Coniacian chalks of the Missouri b~sin.This permitted using as starting points certain data and technical ideas realized when constructing dams in the Missouri basin.It is natural that the particular structure of the Oligocene chalk strata and all characteristics of their composition and properties were thoroughly studied and investigated directly at the construction site.In particular, of greatest importance was a study of the tectonics and jointing of the chalk mass, which made it possible to find a sufficiently favorable site for the powerhouse. Within its limits the upper bentonite interlayer (B1) was eroded and the lower --by virtue of the cosedimentation development of the st...