Bed roughness coefficients for natural channels in Malaysia / Dr. Shanker Kumar Sinnkaudan ... [et. al].

Although much research has been done on Manning's roughness coefficient (bed roughness), n, for stream channels in overseas, very little has been done to derive the verified roughness values for streams in Malaysia. All hydraulic computations involving flow in open channels requires an evaluation of the roughness characteristics of the channel. At the present state of knowledge, the selection of roughness coefficients for natural channels remains chiefly an art and merely done by referring typical tabulated values according to factors that affect roughness listed elsewhere in the hydraulic text books (Chow 1959, Henderson, 1966, Barnes, 1967 and Streeter, 1971 or Storm Water Management Manuals (DID 2000) without proper selection justification for Malaysian river condition. However, it is sometimes difficult to convince either the layman or the scientist that consistently reliable roughness coefficients need to be selected by trained engineers on the basis of sound judgment and experience. Furthermore, there are no resistance diagrams or quantitative relationships available similar to those used for steady flow in uniform pipes or for the frictional resistance of ships (Barnes, 1967). Consequently the ability to evaluate roughness coefficients for natural channels representing a wide range of conditions must be developed through experience. The experience necessary for the proper selection of roughness coefficients can be obtained in several ways, namely (1) to understand the factors that affect the value of the roughness coefficient in Malaysian river conditions, and thus acquire a basic knowledge of the problem, (2) to consult a table of typical roughness coefficients for channels of various types, and (3) to examine and become acquainted with the appearance of some typical channels whose roughness coefficients are known. Photographs of channels of known resistance are thus useful in estimating the roughness characteristics of similar channels. Familiarity with the geometry, appearance, and roughness characteristics of these channels will improve the engineer's ability to select roughness coefficients for other channels. To the untrained beginner, the selection of a roughness coefficient can be no more than a guess; and different individuals obtain different results. Thus, there is an urgent need to come out with such a reference material for Malaysian rivers by compiling photographs and bed roughness coefficient data which covers a wide river range conditions in Malaysia.