Resistance to flow in gravel-bed rivers

Abstract

An emphasis is placed on the importance of understanding the processes responsible for resistance to flow and on the necessity of critically reviewing the assumptions and limitations associated with the methods that are commonly adopted to evaluate resistance to flow in gravel-bed rivers.A commonly applied technique is first presented for estimating the local effective boundary roughness, ks, by the use of data from a vertical velocity profile. Then methods of estimating bulk measures of resistance to flow in a river reach are outlined. Resistance equations in terms of the friction-factor parameter, [Formula: see text],are classified into three main types: dimensional power equations, nondimensional power equations, and nondimensional semilogarithmic equations. The results of seven independent studies are considered when recommending tentative equations for each of the three defined classes of resistance equations. The bulk flow equations are considered to be applicable for the case where d/D50 is greater than 10, there is no bed-load transport, and the flows are in-bank flows. Finally, a brief summary of the problems of estimating resistance to flow for an ice-covered channel is presented. Key words: resistance, flow, hydraulics, rivers, gravel-bed, velocity, friction factor, equations, Manning, Keulegan, classification.

Closure relations for mobile bed debris flows in a wide range of slopes and concentrations

“…(13)), while the following values for the rough wall resistance were obtained: b o ¼ 3:85 and n o ¼ 0:25. The order of magnitudes of these parameters are similar to those of the formula proposed by Daver [12] in low submergence flows on fluvial gravel bed. We also carried out experiments with material of the same average size, d 50 , but with a different size distribution, but we did not observe any effect of size dispersion (variance of the distribution) on the formula of hydrodynamic resistance.…”

Flow resistance in steep mountain streams

“…These values compare to a best-fit roughness length (k s ) value of 6·8 D 50 reported by Bray (1982).…”

Uniform Flow Development Length in a Rough Laboratory Flume

“…Roughness height is defined in various ways. Bray (1982), for example, found k s = 3.1d 90 , 3.5d 84 , 5.2d 65 , and 6.8d 50 where i in d i is the percentage of sediment finer than the size given by d i . Yen (2002) lists additional relationships between k s and various measures of particle size.…”