A drive-over bank separating bays. Water flows into the field through the small channels either side of the bank from a main channel across the horizon that has no bank on the field side.

Irrigators trying to improve the efficiency of their surface irrigation systems should consider the option of bankless irrigation, according to NSW Department of Primary Industries (DPI) irrigation officer at Griffith, Iva Quarisa.

Bankless irrigation is a system of overflowing the head ditch into a paddock with the grade running in the opposite direction to a typical raised bed irrigation and syphon system.

The excess water then drains back into the head ditch and on to the next bay.

“Many irrigators have not only installed the beds in a bankless channel layout, but in many cases they have also modified it to best suit their situation, soil types and crops,” Ms Quarisa said.

“One such modification has been made on a Murrumbidgee Irrigation Area property at Whitton, between Griffith and Leeton.

“A terraced bankless channel system has been developed which has short irrigation runs of 170 metres.

“But with the use of drive-over banks, they have crop runs of up to 1.2 kilometres, for ease of sowing, spraying and harvesting.”

Ms Quarisa said each bay in the farm plan (left) is flat, with zero fall in any direction.

“Each bay also has a main bankless channel 450 millimetres below paddock height which feeds smaller bankless channels,” she said.

“The smaller bankless channels have a grade of one in 333. Water is pushed up the smaller bank-less channels which in turn feed each furrow from both ends.

“Once the water has met in the middle, the main door is pulled so that water can flow into the bay below.

“Due to a minimum terrace step of 150 millimetres between each bay, when the lower bay is full, there is minimal residual water in the upper bay.”

Designer of the system Mike Naylor said the layout could be easily modified for rice growing.

“The aim of this design was to get irrigations as low as half a megalitre per hectare while maintaining reasonable uniformity and hopefully get irrigation and drainage times to around six hours,” he said.

“This should minimise deep infiltration, maximise soil air and plant performance, but will require more frequent irrigation.”

NSW DPI is planning to gather data on the efficiency of different bankless irrigation layouts to help irrigators assess the efficiency of system.

Bankless irrigators willing to be involved with this evaluation project should contact John Lacy at Yanco office of NSW DPI on (02) 6951 2738.

Contact Iva Quarisa, Griffith, (02) 6960 1331