1887

# n Journal of the South African Institution of Civil Engineers - Rational estimation of bend resistance in meandering channels : technical paper

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### Abstract

Resistance to flow in a channel is substantially increased by the secondary circulation induced by bends or curves. Existing empirical methods for accounting for this effect in meandering channels are either unreliable or lack generality. The development of secondary circulation through a bend can be described analytically, and Chang has presented a comprehensive but computationally intensive model that predicts the associated resistance reliably. Chang's analysis has been adapted to describe uniform flow through a sequence of identically repeated meanders. The model is then applied to a wide range of hypothetical conditions to explore the effects of varying channel and flow characteristics on resistance. The results are used to formulate a friction factor adjustment to account for bend losses in prismatic, approximately rectangular, meandering channels. This adjustment is simple, but accounts for all the relevant variables and has a sound theoretical basis.

Weentand teen stroomvloei in 'n kanaal word vergroot deur sekondere sirkulasie wat deur boe en draaie veroorsaak word. Huidige empiriese metodes wat die effek in draaiende kanale aanspreek is of onbetroubaar, of nie algemeen genoeg nie. Die ontwikkeling van sekondere vloeisirkulasie deur 'n bog kan analities beskryf word, en Chang het 'n omvattende maar berekeningsintensiewe model ontwerp wat die geassosieerde weerstand betroubaar kan voorspel. Chang se ontleding is aangepas om egalige stroomvloei deur 'n reeks identiese kronkelinge te beskryf. Die akkuraatheid van die model is vasgestel deur die vergelyking van stroomdiepte-vloeivoorspellings met laboratoriumdata. Die model is later op 'n bree stel hipotetiese gevalle toegepas om die effek van veranderlike kanaal- en stroomvloeieienskappe te ondersoek. Die bevindings hiervan word gebruik om 'n wrywingsfaktorverstelling te formuleer wat die bogverliese in prismatise, byna reghoekige, kronkelende kanale kan verklaar. Hierdie verstelling is eenvoudig, maar verantwoord vir elkeen van die toepaslike veranderlikes en het 'n gesonde teoretiese basis.