Determination of Manning's roughness coefficient for concrete catchment

• Main Author: Ahmad Abul Hassan
• Other Authors: Wong Sai Wai, Tommy
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Civil engineering::Water resources
• Online Access: http://hdl.handle.net/10356/16097
• Institution: Nanyang Technological University

Manning’s roughness coefficient is one of the parameters in the Manning equation used to find uniform flow depth in an open channel. Essentially it refers to the resistive force against the flow of fluid. The determination of Manning’s roughness coefficient (Manning’s n) is a process that has been empirically derived in the past for different surfaces and flow conditions. To determine the coefficient for a concrete catchment that is subjected to natural rainfall, the use of computer model is essential. The Kinematic Wave Model (KWM), a physically-based model which is a proven method to predict runoff, is employed. To develop such a model, the physical characteristics of the catchment, rainfall data, Manning n and a loss model needs to be specified. To evaluate the Manning’s n for simulating runoff hydrographs; the hydrograph-fitting technique is used. In this study, rainfall and runoff data obtained from an experimental concrete catchment comprising of two overland planes and one rectangular channel were used. A selection process based on a set criteria was used to select seven events that were used for the evaluation of Manning’s n. The findings in this study showed that the simulated hydrographs of the seven events showed a close fit to the observed hydrographs. The range of optimal Manning’s n values of the seven selected events ranged from 0.005 to 0.010 and the recommended Manning’s n value to be used in this model is 0.007. The range of Manning’s n values that were obtained in this study will prove to be useful to any user of the simulation model and the user will be able to obtain good simulated hydrographs using the recommended Manning’s n value for a concrete catchment.