Revised equations for Manning's coefficient for Sand‐Bed Rivers

The procedure for selecting values of Manning n is subjective and requires judgment and skill which are developed primarily through experience. Government agencies and private sectors in developed nations such as the USA are still doing research on predicting n values for rivers. Since flow and boundary roughness vary with river conditions, such research is therefore pertinent for rivers in Malaysia where floods are one of primary concerns. Research on Manning n value was started by River Engineering and Urban Drainage Research Centre (REDAC), Universiti Sains Malaysia (USM) since 2000 at the Kinta River catchment. Further data collections were later made at two other major rivers i.e. Langat River and Kulim River. Two new equations are proposed for determining Manning n for sand‐bed rivers in Malaysia based on 163 data collected from these three rivers. On average, both equations have an error less than 10% in predicting flow discharge for all 163 data.