Observations from initial evaluation trials of Bankless Channel Irrigation Systems M.K. Grabham 1,2,3 , J.W. Hornbuckle 1,2 , S.R. Raine 1,3 , R.J. Smith 1,3 1 CRC for Irrigation Futures, Darling Heights, QLD, Australia 2 CSIRO Land and Water, Griffith, NSW, Australia 3 University of Southern Queensland, Toowoomba, QLD, Australia Abstract Increasing community pressure for efficient water use, competition for water resources and rising production costs mean it is important to optimise all aspects of irrigated production. Bankless channel surface irrigation systems are a relatively new and increasingly popular method of irrigation for broadacre cropping systems. Motivation for the installation of these systems is attributed to labour efficiency gains, improved machinery access and the versatility of the system to irrigate a wide variety of crops. While bankless channel irrigation systems may enhance the performance of many aspects of irrigation production, no water-related design, management or evaluation criteria exist for optimising the irrigation performance of the system. This paper presents initial observations of an irrigation evaluation aimed at developing a tool to measure and improve the irrigation performance of bankless channel irrigation systems. These initial observations concentrate on the advance and elevation variation within the evaluated system. These observations demonstrate that, under the described flow conditions, water depth appears to have a small influence on the advance of water and that soil and furrow properties have a substantial effect on irrigation advance. This initial field data will be used to develop and/or validate suitable hydraulic simulation models to improve the design and operation of bankless channel irrigation systems. Introduction Australian bankless channel systems operate in a similar way to American “drain back level basins” (Dedrick 1989) albeit with larger dimensions and higher flow rates. Australian systems were developed in the 1990's to improve water management and production performance in rice based farming systems. Subsequently, hills or beds and furrows were added to the system enabling the production of row crops within a rice based farming enterprise. These adjustments not only provided cropping alternatives, but also increased operational and labour efficiencies while decreasing occupational health and safety (OHS) risks and, though largely anecdotal, water use efficiency improvements over conventionally siphon fed systems (Grabham and Williams 2005; Hood and Carrigan 2006). Row-crop focussed enterprises recognised the advantages of the system over traditional siphon irrigated methods and the system is now used in a number of areas outside the rice based farming enterprises of southern NSW. Bankless channel systems consist of a series of terraced bays which, while irrigated separately, are connected by a bankless channel (Figure 1). Each bay is irrigated by backing-up water behind a closed gate in the bankless channel, causing water to spill into the adjacent bay. Once the bay has been sufficiently inundated, the gate in the bankless channel is opened allowing both supply water from the channel and drainage water from the bay to flow into the next bay in the series. This process is repeated until all bays are irrigated. The bankless channel delivers the water to the bay, distributes water across the inlet width of the bay and also acts as a drain for the bay.