Contents preface (VII) introduction 1—37

5.14.7. Failure of Lining
The main causes of failure of lining are the water pressure that builds up behind the lining material due to high water table, saturation of the embankment by canal water, sudden lowering of water levels in the channel, and saturation of the embankment sustained by continuous rainfall. The embankment of a relatively pervious soil does not need drainage measures behind the lining. In all situations requiring drainage measures to relieve pore pressure behind the lining, a series of longitudinal and transverse drains satisfying filter criteria are provided. A typical arrangement of longitudinal filter drain is as shown in Fig. 5.24.

Coarse sand blanket

Graded filter 0.30 m thick laid in two layers of 0.15 m each

C.C. Lining

Longitudinal
filter drain

Fig. 5.24 Longitudinal filter drain

CANAL IRRIGATION

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The growth of weeds on canal banks and other aquatic plant in channels may not result in failure of the lining but would affect the conveyance of channels which may be lined or unlined. Weeds and aquatic plants consume water for their growth and thus the consumptive use of irrigation water increases. Weed growth increases channel roughness and, hence, reduces the flow velocity thereby increasing evaporation losses. The cleaning of channels having excessive weed growth is, therefore, a vital maintenance problem. Cleaning operations can be carried out manually or by mechanical devices, such as used in dragline excavation and tractor-drawn cranes. Commonly used methods are pasturing, mowing, burning, and applying chemical weed killers.