Despite the large number of theoretical and experimental works devoted to consideration of the effect of sediment transport on hydraulic resistance in a uniform flow [3, 4, 7, 8, I0], this problemhasstill not been conclusively solved~ Some investigators consider that a flow saturated with suspended solids does not spend additional energy on transporting the suspended material, others support the opposite viewpoint.To assess the effect of sediments on hydraulic resistance, we will use certain general principles of diffusion and gravitation theory [4,5], as well as of works [3,6].Let us examine a compartment of length s Of a uniform flow having slope J. At a certain point inside the compartment let the volume concentration of the solid phase be s and the velocity of the liquid phase be v. If the densities of the liquid and solid phases are respectively ps and 0s and F is the cross-sectional area of the flow, then we can write the following expression for the work of the gravitational force applied to the compartment during time:i0 5., + s Strictly speaking, we should take the account fluctuations of s, v, and Vs, having added to (i) the corresponding term I.However, consideration of such details at the current stage of study of the motion of a two-phase flow is impossible.Therefore, physically it is completely natural to consider Vs = v, as is assumed hereinafter.Work (I) is spent on overcoming the hydraulic friction and on moving the sediments.The expenditures on friction 9 Xlv~t,where v is the average flow velocity; X is its wetted perimenter; T is the average shear stress on the wall.Suppose that the investigated compartment stopped.Then the i particle with volume V i will begin to settle under the effect of the force V~ (Ips--p @ g(3)of the difference of its weight and Archimedean buoyant force, If wi* is the velocity of fall of a particle, then the work of force (3) during time At will be Vi~P's-'-P-)gwl*At-The total work for all stopped particles in the compartment will be N (%-%) gst ~ v~*. ~=I

626.31:532.543 For the design and construction of canals for redistributing runoff with discharges of 1000-2000 m3/sec, it is necessary to study processes of unsteady channel deformation in existing canals with variation in water discharges within prescribed limits.Special attention should be paid to an investigation of the structure of the flow and morphology of the canals during formation of the channel and creation of the conditions of hydrodynamic stability, and also to a study of the hydraulic regime of the clarified flow in a canal retaining a stable channel shape.Several methods are used in the practice of hydraulic calculations of stable channels: the method of hydromorphologic equations (abroad it is called the "regime theory"), method of permissible velocities, and method of tractive force.Two main forms of static stability are examined in these methods: total or limit static stability and one of the forms of hydrodynamic stability.Different forms of stability of the slopes and bed of the channel are observed during formation of a stable channel of complex shape for the same hydraulic characteristics of the flow in cross section.Since it is difficult to record the instant of transition from one form of stability to another, the solution of this problem in the method of permissible velocities issimplified byexamining mainly two characteristic flow velocities, noneroding vo and shearing v s, between which exists the relation v s = (1.3-1.5)vo [i].In the presence on the nonerodible bed of local irregularities of critical size Acr-(7-10)dso the flow velocities causing transport of particles are about 30% less than the velocities transporting these same particles in a channel without such irregularities.Usually, in the channel of an earth canal there are macroroughnesses of a size much greater than Acr and, therefore, the formation of dunes or ripples is characteristic for natural conditions, even if the flow velocity is considerably less than the noneroding for the given sediment.At a velocity exceeding the noneroding, one of the characteristic phases of bed-load transport occurs in a canal with bed macroroughnesses which were transformed into ripples or dunes, and a relatively hydrodynamically stable form of the canal channel can resuit.The inhomogeneity of the sediments over the perimeter of the canal cross section and the variation in the forms of the macroroughness can be the cause of loss of stability of the canal.Therefore, during the initial period of operation of large earth canals alignment works may be required over the entire route to overcome the unstable state of the flow leading to loss of hydrodynamic stability by the channel.The following klnematic-morphologic relations can be used for determining the width B, average depth hav, and mean velocity v of the flow in large earth canals composed of noncoheslve soll in the presence of various types of channel processes [i]:a o r,+xp ~.% ; 2.5+x (g/) P dav'~-3"~p ! 3tp Q2.5 +3.Xp (12 ~--3.t:p hay= AI= O5 (i) (2)

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The skill of six well-known formulas developed for calculating the longshore sediment transport rate was evaluated in the present study. Formulas proposed by Bijker [Bijker, E.W., 1967. Some considerations about scales for coastal models with movable bed. Total rate and distribution of longshore sand transport. Proceedings of the 23rd Coastal Engineering Conference, ASCE, 2528-2541] were investigated because they are commonly employed in engineering studies to calculate the time-averaged net sediment transport rate in the surf zone. The predictive capability of these six formulas was examined by comparison to detailed, high-quality data on hydrodynamics and sediment transport from Duck, NC, collected during the DUCK85, SUPERDUCK, and SANDYDUCK field data collection projects. Measured hydrodynamics were employed as much as possible to reduce uncertainties in the calculations, and all formulas were applied with standard coefficient values without calibration to the data sets. Overall, the Van Rijn formula was found to yield the most reliable predictions over the range of swell and storm conditions covered by the field data set. The Engelund-Hansen formula worked reasonably well, although with large scatter for the storm cases, whereas the Bailard-Inman formula systematically overestimated the swell cases and underestimated the storm cases. The formulas by Watanabe and Ackers-White produced satisfactory results for most cases, although the former overestimated the transport rates for swell cases and the latter yielded considerable scatter for storm cases. Finally, the Bijker formula systematically overestimated the transport rates for all cases. It should be pointed out that the coefficient values in most of the employed formulas were based primarily on data from the laboratory or from the river environment. Thus, re-calibration of the coefficient values by reference to field data from the surf zone is expected to improve their predictive capability, although the limited amount of high-quality field data available at present makes it difficult to obtain values that would be applicable to a wide range of wave and beach conditions. D (M. Larson). www.elsevier.com/locate/coastaleng Coastal Engineering 44 (2001) 79-99 Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of informat...