It was shown in [i] on the basis of actual data that the main working formulas for the Chezy coefficient do not correspond to the character of the hydraulic friction of earth canals and as a consequence it is impossible to generalize on their basis the actual data for canals belonging to the same category even in a comparatively small range of hydraulic radii R = 0.10-2.60 m.In view of the fact that the standard recommendations on hydraulic calculation of earth canals are constructed on criticizable formulas, a comparison of these standards with the actual data is also important.These standards amount to a recommendation of the working formula of the Chezy coefficient and value of the roughness factor n. In many USSR standards, N. N. Pavlovskii's formula is recommended as the main one C=Rv/n, where R is the hydraulic radius, and the exponent is determined by the relation (1) y= 2.5 VY--0,13 --0,75 VR (V~--0,10).(2)The recommended roughness factor depends on the "conditions of upkeep and repair" and on the value of the hydraulic radius or discharge of the canal. The standards of the USSR Ministry of Construction of Electric Power Stations (MSES) [2]for assigning the roughness factor recommends a table which represents a selection from Pavlovskii's complete table [3], which is the basic one in Soviet design practice and in the reference literature.If the selection given in [2] is supplemented by the line concerning "small" canals, also taken from the complete table, then for "large" and "small" earth canals under "average conditions of upkeep and repair" we will have values of the roughness factor equal respectively to n = 0.025 and n = 0.0275, and under conditions greater than the average, n = 0.0225 and n = 0.025. The MSES standards, just as all other current guides to hydraulic calculations, do not elaborate the concepts "large" and "small" canals from the viewpoint of assigning the roughness factor. Resorting to [3], where these concepts were first introduced, for an explanation of this we find that canals with R = 0.5-3 m are assigned to "medium" and "large" canals and consequently canals with R < 0.5 m should be assigned to "small."The standards of the USSR State Construction Committee (Gosstroi) [4] associated the roughness factor with the discharge and for canals in cohesive and noncohesive soils and peat under "normal" conditions for discharges Q > 25.0 ma/sec, 25.0 > Q > 1.0 m3/sec, and Q < !.0 m3/sec, recommend values of the roughness factor equal respectively to n = 0.02, 0.0225, and 0.025.Since we will compare the results obtained on the basis of the preceding recommendations with the actual data on earth canals of Central Asia which have already been used and described in more detail in [I], we will confine ourselves here to brief information about these data concerning canals in cohesive soils (foams, loamy sands) and silted sands, which are united also by the following common features: the channels are practically straight, maintained in a satisfactory condition, not overgrown or with negligible ve...

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slightly at the exit with increase of the the height of the discharge openings to h < 0.6d c and for Dtw >_ 3d c it decreases. When h > 0.6d c the height of the throughgoing flow is constant and at the exits is about (0.55-0.6)h for Dtw = 4d o (0.27-0.35)h for Dtw = 3dc,)h for Dtw = 4d c.During operation of the discharge openings full section (h ___ 0.3), an increase of the tower diameter is accompanied by an increase of nonuniformity of the distribution of velocities over the height of the openings; the opposite picture is observed with the occurrence of separation of the flow from the sill, i.e., for h > 0.3. 2. In the pump operating regime for a height of the openings h _> (0.5-0.6)dc, the intakes/outlets with an outside diameter of the discharge openings Dtw = 2d c have smaller values of the resistance coefficients (by 0.02-0.06) than for Dtw > 3d c, and for h < (0.5-0.6)d c intakes/outlets with a tower diameter Dtw > 4d c are preferable with respect to head losses.3. In a turbine regime without trash racks, smaller head losses are observed in intakes/outlets with Dtw >__ 3tic; a decrease of the tower diameter to Dtw = 2d c leads to a considerable increase of the head loss coefficient: by 0. 05-0.18 in the range of heights of the openings h = (0.6-0.3)dc; the presence of trash racks of the same height leads to an increase of the resistance coefficient of the intake/outlet with Dtw = 2d c. 4. With consideration that with a change in the outside diameter of the discharge opening, the increase of the head loss coefficient with increase of their height in the pump regime changes in magnitude and signt and also that investments in construction depend on the outside diameter of the discharge openings (tower), the final choice of the size of the intake/outlet can be made only on the basis of a technicoeconomic comparison of variants with the use of the results of the studies presented in this article. LITERATURE CITED M. M. Nosova, "Resistance of entrance and exit pipes with a shield," Promysh. Aerodin., No. 7 (1956). I. E. Idel chik, Handbook of Hydraulic Calculations tin Russian], Mashinostroenie, Moscow (1975).It was established on the basis of data of laboratory and prototype investigations of flow in smooth-walled flumes and precast reinforced-concrete canals [1] that the regularities of hydraulic resistance of tranquil and nonaerated uniform rapid flows in the indicated categories of channels are completely different, rapid flows being characterized by a special variety of mixed resistance, which for A = const, v = const is analytically described by O. M. Aivazyan's formula whereK< 0, x< 0, z < 0.With representation of the Nikuradse graphs in traditional coordinates, the unknown characteristic of the hydraulic resistance of rapid flows [1] is expressed in an increase of the coefficient ~ with increase of R for Re = const, A --const.

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