construction and refurbishment of earthen irrigation channel banks

around the world are typically 20 to 40% of the total water diverted depending on soiltypes and other local conditions.In the recent Benchmarking Report for Australian Irrigation Water Providers for the1998/99 season prepared by the Australian National Committee on Irrigation andDrainage, average distribution efficiencies for mainly open unlined channel systemswas 77%. From the Benchmarking study, reported efficiencies for open channelsystems are Ord River 75%, Burdekin River 87.4%, Coleambally Irrigation 81.2%,Goulburn-Murray Water 74.6%, Murrumbidgee Irrigation 79.7% and MurrayIrrigation 79.5%.Figures for existing earthen channels in northern Victoria located on average clayloam soils are typically leakage 3-4%, seepage 2-3% and evaporation 2-3% ofaverage diversions at the channel offtake.Water loss figures in some literature need to be treated cautiously as some figures arefor seepage only, while others are in fact total conveyance or transmission losses.Conveyance losses through an earthen channel system depend on a number ofphysical, operational and climatic factors, and can include:• operational outfalls and spills• seepage• leakage through banks and at structures• evaporation• over-delivery to irrigators• transpiration from channel weeds• channel filling• theft, as well as• perceived losses due to measurement errors.Average 10 year water balance figures for Goulburn-Murray Water’s open channelirrigation areas are given in Table 22-2.OutflowPercentage ofTotal InflowTotal Deliveries74%Outfalls8%Leakage2%Seepage2%Evaporation2%System Filling2%Domestic & Stock supplies 1%Meter Error3%Unaccounted balance6%Total 100%Table 22-2Average water balance figures for Goulburn-Murray WaterThe figures represent averages and they vary between Areas as well as betweenseasons due to deliver volumes, climatic conditions and other factors. Theunaccounted for balance is mainly attributed to inflow-outflow measurement errors.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 22-8