construction and refurbishment of earthen irrigation channel banks

Photos\inside batter\CG7channel2armour.jpgPhoto 18-4 20mm diameter rock armour placed in 1992Photos\inside batter\CG7channel3armour.jpgPhoto 18-5 75mm diameter rock armour placed in 1992Whether, batter erosion is identified as a potential problem at the design stage of a newchannel or develops into a problem on an existing channel, a layer of rock armour can beused to protect the batters.Gravity alone holds the rock in place, the protective layer is flexible, local damage or losscan be easily repaired by the addition of rock and wave run-up is reduced.The technique has been used in Canada and Queensland, and trialed in Victoria toprovide protection and stability to eroding batters. It works effectively and is relativelylow cost, provided suitable rock material is available locally.18.4.1 General Design Considerations18.4.1.1 Extension of Bank LifeRock armour slope protection can be relatively expensive, but on a life cycle costbasis, it is likely to be economically attractive if suitable rock material is availablelocally. Rock armour can stop or reduce the erosive impacts of dispersive soil,bank slumping, wind and wave action and yabbies and carp.In Alberta Canada, which has an extensive network of earthen irrigation channels,most rehabilitated channels have rock armour protection. The irrigationauthorities have been using rock armour slope protection for over 30 years andthey believe that rock armour at least doubles the life expectancy of a channelbank.18.4.1.2 Batter SlopeThe rock must be on a stable batter slope so that no sliding down the face willoccur.Where the friction between the rock and the face of the batter is less than theinternal friction of the rock mixture, partial or complete failure of the rock armourcan occur where the rock slides down the batter slope.Overseas studies have been carried out to determine what batter slopes should beused for rock armour, and it has been found that 1:2.5 (V:H) is the optimumslope.A batter slope of 1:3 (V:H) was found to be better, but only marginally and at ahigher cost. A slope of 1:2 (V:H) may work satisfactorily on smaller channels,but on larger channels the potential for failure at 1:2 (V:H) was found to beunacceptably high.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 18-8