construction and refurbishment of earthen irrigation channel banks

8. Earthen Irrigation Channels8.1 DescriptionIrrigation systems require large volumes of water to be conveyed from storages to farms.Pipelines are an efficient means of water conveyance, but on economic grounds, channelssupply the large irrigation systems in Australia, and most of these channels are of earthenconstruction.An earthen channel is defined as an open channel excavated and shaped to the requiredcross-section in the natural earth or fill along a pre-determined route and of a predeterminedgrade. Earthen channels are either classified as unlined or lined depending onthe treatment of the wetted perimeter.Water is often distributed within an irrigation scheme through a network of earthenchannels because they can be constructed more economically than other availablemethods. The availability of water has been a determining influence in Australia, shapingthe pattern of human settlement and economic development. Australia has large areas ofland that have only been able to be used for irrigation through the construction of longlengths of earthen channels to transport and deliver water.Main carrier channels are large channels which transport water to an irrigation area fromthe headworks. Distribution channels have smaller capacities and they distribute waterdirectly to each farmer’s land.The design of earthen channel systems are based on functional requirements and thephysical aspects of earthen construction. Earthen channels are generally designed with atrapezoidal cross section. This approximates the stabilised shape generally taken bynatural streams and lends itself to construction and maintenance with equipment that isreadily available.If the channel bed is above the natural surface level, then the channel will be placedentirely in fill. When the entire excavation is below natural ground level, then thechannel is in cut.A typical cross-section of irrigation channel is shown in Figure 8-1 below:CrestCrestNatural SurfaceBankBedWaterwayBattersBankFigure 8-1Typical Irrigation Channel Cross-Section8.2 Length of Earthen Irrigation Channels in AustraliaThe length of earthen irrigation channels in Australia was surveyed during the researchproject for the Guidelines with an update from a more recent survey of irrigationConstruction and Refurbishment of Earthen Channel Banks August 2002 – Edition 1.0 8-1