Author(s): Mohd Rizal Shukor, Shanker Kumar Sinnakaudan, Munyati Mohammed, Siti Isma Hani Ismail, Mohd Sofiyan Sulaiman
Linked Author(s): Mohd Rizal Shukor
Keywords: Roughness coefficient, mountain river, coarse-bedded river, discrepancy ratio test
Abstract: At present state of knowledge, the selection of roughness coefficients, n for natural rivers are remains a major doubt among engineers and practitioners. In common practice, roughness values are obtained either by referring to the typical tabulated values listed in any hydraulic textbooks or handbook manuals or by using empirical equations. However, the values obtained are mostly unfit for all river morphologies. Various studies has been reported to quantify the Manning's n values for diverse river conditions, however similar studies are still limited in Malaysia particularly for mountain river reaches. Thus, the present study evaluates the applicability of the existing roughness coefficient equations to the Mountain Rivers of Malaysia. 12 selected roughness coefficient equations were tested in present study whereby 4 equations are developed locally. The roughness value recommended by DID (2012) also included in the analysis for comparison purposes. Selected roughness coefficient values were used to predict the velocity for 178 sets of data from 27 Mountain Rivers in Malaysia. The accuracy of existing equations was assessed by discrepancy ratio analysis whereby predicted and measured velocities from field are compared. It was found that none of local equations can predict more than 50% of total number of data. So far, Jarrett (1984) equation has shown satisfactory prediction of flow velocity over Malaysian Mountain Rivers with 63% of data lies within the acceptable discrepancy ratio (0. 5 to 2. 0)
Year: 2017