Abstract
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.
Highlights
Sri Lanka has a large irrigation canal network to convey water for day to day needs and for irrigation purpose of the people living in remote and drought zones of the country
The bed and banks of these canals are susceptible to wash away by the flowing water constantly and change their topography in the long term. This natural process is known as canal erosion and leads to several other problems such as, scouring of bed and banks making canal inner banks more unstable, deposition of local eroded materials along the canal leading to growth of weeds, increase in seepage and leakages, water logging, and reducing the capacity of the canal system
Based on the experimental observations from the model testing, the Manning’s coefficient for test model gabion lining varies in the range between 0.00633 m-1/3s - 0.00693 m-1/3s for the flow velocity ranging between 0.30 ms-1 to 0.37 ms-1 with the fair level slope as 0.00035 m/m and the predicted roughness coefficient “n” value ranging for the prototype indicates 0.0075 m-1/3s < n < 0.0082 m-1/3s ; a lower value range than that for other linings specified in Chow’s studies even under uneven surfaces like stones and rubble linings including riprap
Summary
Sri Lanka has a large irrigation canal network to convey water for day to day needs and for irrigation purpose of the people living in remote and drought zones of the country. Most of these canals are natural or man-made unlined earthen canals. Due to this nature, the bed and banks of these canals are susceptible to wash away by the flowing water constantly and change their topography in the long term. Canals are needed to be protected against the erosive forces developed by flowing water and as a solution, canal lining may be used [11]
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