Model Study to Determine the Manning’s Coefficient for Gabion Lining against Canal Erosion

Canal erosion often happens in unlined canals due to high velocity water flows. Because of this natural phenomenon, numerous problems occur in canal systems and finally change the topography of the canals in the long-term. Canal lining is the method adopted worldwide, to prevent canal erosion using different lining materials available such as concrete, rock masonry, brick or clay, with the modern practice being gabion nets filled with rubble. Considering several factors such as, economy, stability, material availability and manpower requirement, gabion lining is a suitable canal lining method compared to other prevention methods used at present.

To make the gabion lining method very effective, economical and feasible in canal lining applications, the surface roughness or the Manning’s coefficient (n) value of gabion linings needs to be experimentally determined first, as this value is unknown at present and will be useful for the scientists and engineers in design stages later on.

A 300 mm x 300 mm rectangular field channel was selected as the prototype to model it dimensionally in a laboratory hydraulic flume. The Manning’s formula, which applies to uniform flow conditions in open channel flow, was used to determine “n” experimentally.

Present experimental observations indicate a value range of 0.05044 m^-1/3s to 0.0552 m^-1/3s as Manning’s coefficient for the test model study and that of 0.0597 m^-1/3s to 0.0654 m^-1/3s for the prototype.