Analytical Model of Excess Shear Stress and Riparian Vegetation in Determination of Optimal Dimensions of Gravel Bed Rivers

Document Type : Research Article

Author

Abstract

Extremal hypotheses without bank stability constraint typically over-predict and under-predict alluvial channel width in large rivers and natural streams, respectively. While this process may appear inversely for the depth. In general, results obtained from unconstrained extremal hypotheses are indicative of inappropriate agreement between computed and observed dimensions of the rivers. Such discrepancies between regime model predictions and observed channel widths have been used to argue that optimizations such as MSTC do not describe the behavior of alluvial systems. However, extremal hypothesis models that explicitly consider bank stability exhibit no such bias and can predict alluvial channel widths quite accurately. One of the important factors in disparity of the data may be lack of appropriate relationship to assess bank vegetation of the rivers. For this reason, a modified analytical model has been developed to reduce the effect of bias by considering boundary shear stress, bank stability and vegetation. The model takes into account channel shape factor, bed load equations in the form of excess shear stress and vegetation quantification (i.e. using bank material friction angle) which enables one to predict optimal channel geometry dimensions. Finally, developed model was calibrated using the field data of the rivers in the United Kingdom and Iran. In addition to indicating the effect of bank stability and vegetation on estimation of the geometric characteristics of the channel, the results obtained also confirmed the efficiency of the constrained model in comparison to the unconstrained one.

Keywords


جوهری، ر. و مجدزاده طباطبایی، م. ر؛ (1392). مطالعه صحرائی تغییرات مکانی ضریب مسلح‌شدگی و تأثیر پارامترهای هیدرولیکی بر آن، پایان­نامه کارشناسی ارشد، دانشکده مهندسی آب و محیط زیست، دانشگاه شهید بهشتی.
دستورانی، م. ت. و رجبی محمدی، ف. (1391). "تعیین اثرات مکانیکی و هیدرولوژیکی گیاهان کنار رودخانه بر پایداری کناره رودخانه (مطالعه موردی: رودخانه حنا)"، سومین همایش ملی مدیریت جامع منابع آب، دانشگاه علوم کشاورزی و منابع طبیعی.
کرمی، م. و مجدزاده طباطبایی، م. ر. (1388). "توسعه مدل تحلیلی اثر پوشش گیاهی در تعیین هندسه پایدار رودخانه­های شنی"، نشریه مهندسی عمران و نقشه­برداری- دانشکده فنی، دوره 43، شماره 1، ص.ص. 105 - 115.
ASCE Task Committee on Hydraulics, (1998), “Bank mechanics and modeling of river width adjustment, 1: processes and mechanisms”. J. Hydraul. Eng. ASCE, Vol. 124, No. 9, pp. 881-902.
Chadwick, A. J. and Morfett, J. C., (1995), Hydraulics in civil and environmental engineering. Champman & Hall.
Darby, S. E., (2005), “Refined hydraulic geometry data for british gravel-bed rivers”, Journal of Hydraulic Engineering, Vol. 131, No. 1, pp. 60–64.
DuBoys, P., (1879), Le Rhone et les rivieres a lit affouillable, Annales des Ponts et Chaussees, Vol. 18, pp. 141–195.
Eaton, B. C. and Millar, R. G., (2004), “Optimal alluvial channel width under a bank stability constraint”, Geomorphology, No. 62, pp. 35-45.
Eaton, B. C., Church, M., and Millar, R. G., (2004), “Rational regime model of alluvial channel morphology and response”, Earth Surf. Processes Landforms, Vol. 29, pp. 511 – 529.
Einstein, H. A., (1950), “The Bed-load function for sediment transportation in open channel flows”, U.S. Department of Agriculture, Soil Conservation Service,  Technical Bulletin no. 1026.
Flintham, T.P. and Carling, P.A., (1988), “The prediction of mean bed and wall boundary shear in uniform and compositely rough channels”, in White, W. P. (Editor): River Regime, John Wiley and Sons, pp. 267- 287.
Henderson, F. M., (1966), Open Channel Flow, Macmillan Pub. Co., New York. 522.
Hey, R. D. and Thorne, C. R., (1986), “Stable channels with mobile gravel beds”, Journal of the Hydraulic Engineering, ASCE, Vol. 112, No. 8, 671- 689.
Huang, H. Q., (2010), “Reformulation of the bed load equation of Meyer-Peter and Müller in light of the linearity theory for alluvial channel flow”, Water Resources Research, Vol. 46, No. 9, pp. 1-11.
Huang, H. Q. and Nanson, G. C., (2000), “Hydraulic geometry and maximum flow efficiency as products of the principle of least action”, Earth Surface Processes and Landforms,Vol. 25, pp. 1–16.
Kirkby, M. J., (1977), “Maximum sediment efficiency as a criterion for alluvial channels. In River Channel Changes”, Gregory KJ (ed.).Wiley: Chichester; pp. 429-442.
Knight, D. W., (1981), Boundry shear in smooth and rough channel, Journal of the Hydraulics Division, ASCE, Vol. 107, No. 7, pp.839-851.
Knight, D. W., Demetriou, J. D. and Hamed, M. E., (1984), “Boundary shear in smooth rectangular channels, Journal of the Hydraulic Engineering”, ASCE,Vol. 101, No. 4, pp. 405-422.
Knighton, A. D., (1998), Fluvial Forms and Processes, Edward Arnold: London.
Lacey, G., (1958), “Flow in alluvial channels with sandy mobile beds”, Proceedings of the Institute of Civil Engineers, London, 9, Discussion, Vol. 11, pp. 145–164.
Lane, E. W., (1955b), “The design of stable channels”, Trans, ASCE, Vol. 120, No. 2776, pp. 1234-1279.
Leopold, L. B. and Langbein, W. B., (1962), “The concept of entropy in landscape evolution”. U. S. Geol. Survey, Prof. paper 500-A.
Manning, R., (1891), “On the flow of water in open channels and pipes”, Transactions of the Institution of Civil Engineers of Ireland, Vol. 20, pp. 161-207.
Meyer-Peter, E. and Muller, R., (1948), “Formulas for bed load transport”, In Proceedings of the 3rd Meeting of IAHR Stockholm, pp. 39–46.
Parker, G., (1979), “Hydraulic geometry of active gravel rivers”, Journal of the Hydraulics Division, ASCE, Vol. 105, pp. 1185–1201.
Pickup, G., (1976), “Adjustment of stream channel shape to hydrologic regime”. Journal of Hydrology, Vol. 30, pp. 365-373.
Van Rijn, L. C., (1984), Sediment transport, part I-bed load transport. Journal of the Hydraulic Engineering, ASCE, Vol. 110, No. 10, pp.1431–1456.
Yang, C. T., (1971a), “Potential energy and stream morphology”, Water Resources Research Vol. 7, pp. 311-322.
Yang, C. T., (1996), Sediment transport: theory and practice, McGraw-Hill.