Inclusion of the technical session D "Deposition in Estuaries and River Mouths" in the program of the 14thCongress of the IAHR was due to a number of circumstances closely related to the economic utilization of the regions of river mouths and seashores. In connection with the trend toward an increase in the size of shil~ , especially tankers, the ixoblem of cow'trolling deposition in the approach channels is becoming exceptionally urgent. Mud-botZom channels subjected to tidal currents are of particular interest.In recent years problems of the hydrodynamics of fiver mouths and shores have also acquired importance in connection with the creation of large reservoirs for power purposes on rivers emptying into the sea, since the retention of sediments in reservoirs causes intense wave erosion of the shore. To forecast the consequences of streamflow control by re.~rvoirs with respect to the stability of the seashore, it is necessary to have a clear idea of the disrribution of sediments within the estuatine shore, which requires the development of the hydrodynamics of river mouths and shores.Finally, the prediction of changes in the hydrologic regime of rivers in connection with diversion of the runoff from the basin to another for the purpo~ of maintaining a sanitary condition of the river mouths, supplying drinking and industrial water and for reclamation, fisheries, etc., also requires a more comprehensive study of the hydrodynamic regime of river mouths and estuaries.At technical session ]3, 28 reports were presented: six from the USA, four each from the USSIL France, and Great Britain; two from Holland; and one each from India, Turkey, Portugal. Japan. Brazil. Mexico, Canada. and West Germany. These reports can be divided into the following groups according to the character of the investigations: a) theoretical methods of predicting the deposition of sediments in estuaries and transformation of the shore in the region of river mouths (reports 1, 5, 10-14, and 19); full-scale investigations of deposition in river mouths (reports 4, 13, 16, 21, and 28-28); c) experimental study of sediment transpcet in rivers and estuaries on physical and mathematical models (reports 2, 3, 6-9, 11, 12, 17, 18, 20-24, and 26). The brief content of these reports, of interest to Soviet hydraulic engineers, is given below.A. Harrison and M. Owen (D.I,~" England) investigated the transport of fine sediment in estuaries as a recurring cycle of four processes: erosion, transport of suspended sediment, its deposition and consolidation. Each of these processes depends on the hydraulic regime of the flow and characteristics of the sediment and can be expressed only by empirical formulas Qith constants obtained in the laboratory and in full-scale observations. The report discussed the prediction of deposition in the ship channel on the Pleit River located perpendicular to the stream.S. C-oul, Z. Tarapor, and S. Brahme (D.S, India) presented a method of predicting deposition in harbors and channels based on an analysis of full-scale, model, and...
Problems of calculating unsteady transport of suspended sediments and dissolved admixtures in streams arise upon an abrupt increase of water turbidity near an intake structure during a flood.It is suggested that water intakes be equipped with curtain walls or regulating gates providing a steady flow in the tailwater channel.An abrupt change in the concentration of suspended sediments at the inlet to a stream leads to a redistribution of their concentration over the length and to disturbance of the dynamic equilibrium between the bottom sediments and suspended sediments.The solution of the stated problem is especially important for diversion power canals, since an increase of the sediment concentration in the forebay of penstocks leads to wear of turbine blades.For irrigation canals calculation of the distribution of the concentrations of suspended sediments over the length of the canal and in time with entry of an increased sediment concentration through the intake works is important for determining the volumes of transport to the fields together with the suspension of trace elements sorbed on them, which are necessary for plants, as well as for estimating the rate of siltation of the main and distributary canals.For canals of domestic potable or industrial water-supply systems these problems are solved for establishing the parameters of settling structures and for preventing clogging of filters.The one-dimensional equation of mass transport has the form [i, 5] (OlOt) (s~) + (o/~x) (sQ) = = O~ (O~s/dx ~)-WBS~-( 1 ) --Dz~B (Os/az) ~ ,where s is the average concentration of sediments over the cross-sectional area ~; Q is the water discharge; D x is the coefficient of dispersion in the longitudinal direction; B is the top width of the canal; ~ is the thickness of the bottom layer; D z is the vertical turbulent diffusion coefficient; W is the settling velocity.Forsteady longitudinally homogeneous transport of a suspension the relationshipholds and since (~s/~z)~ < 0, condition (i) indicates that in this case the convective flow of sediment particles suspended in water due to the settling velocity W is compensated by the diffusion flow of sediments (directed upward) due to their concentration gradient over the thickness of the "diffusion bottom layer."Within the "diffusion layer" 6 the gradient Ss~ is represented by the relationshipwhere s, = ~NV62/h is the so-called roiling turbidity [2], determined by A. V. Karaushev's formula; 8 = 5.7 x i0-~; N = MCc'g ; C C is the Chezy coefficient; M = 0.7C C + 6; V 6 is the flow velocity at height ~ (bottom velocity).We note that s, ~ does not depend on the concentration of the suspension.
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