Vízügyi Közlemények, 1970 (52. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

stability and permanency of the channel have been derived which are commonly utilized in designing a stable stream channel. In river regulation the correct alignment of the channel is of paramount importance, and it is thus understandable that many theories have been developed. It seems logical to follow an approach according to which the alignment of the channel should be based on factors expressing the interrelationships between the two basic media, namely soil and water. A fundamental requirement in selecting the alignment is to remember that natural streambeds consist of a sequence of bends and neither the straight sections between two subsequent bends can be considered as stable. According to this approach the problem in river regulation is to select the stream alignment at which the regulated river is capable of meeting —i under a given set of hydrological, hydraulic and morphological conditions — the requirements calling for interference. Of these requirements navigation and various diversions and discharges should be mentioned first. The rules introduced by Fargue are familiar, according to which the apex of the bend and the width of the inflexion should vary between 7/6 and 4/3. These rules can be utilized by applying potential, two dimensional flow. If the angle subtending to the tangents of the bend is a, then according to the complex-variable function the stream- and potential lines will form hyperbolae, their equation being Naturally the family of hyperbolae applies only to the potential flow of an ideal fluid and it should be modified appropriately in accordance with the physical properties of water and the type of actual flow resulting therefrom. The development of river bends and meanders is obviously not a random play of Nature. In natural watercourses local irregularities and obstructions give rise to changes in the direction of flow. Actually, however, the development of bends is not a direct result of these. According to one approach, during the development of bends the sum of squared changes occurring in direction must be a minimum, corresponding at the same time to the theorem that total work in the bend should also attain a minimum value. This particular feature of bend development is well demonstrated by the bending of a thin steel wire fixed at two points which is free to assume different configurations between the two fixed points without changing its given length. The steel wire will logically strive towards uniform curvature at the changes of direction without any abrupt turns. Consequently the wire assumes configurations at which the w = zn/a (1) (p + i yj = (x + i y)n/a (p = хя/а — уя/а ip = — 2 xy (2) (3) (4) 10