Shallow surface drainage improves the performance of border-check irrigation systems

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Waterlogging and poor irrigation uniformity can limit the yield potential of border-check irrigation systems. In northern Victoria where border-check is the main irrigation system used, soils have very low infiltration rates. As a result, excess water applied to an irrigation bay drains very slowly to the foot of the bay. This means the bottom of the bay is inundated for much longer than at the top of the bay. New research has shown that shallow surface drains within each border-check irrigation bay can improve irrigation performance by equalising inundation duration over the entire bay.

Figure 1: Shallow drain down length of bay

Farmers who have modified irrigation bays with shallow drains believe their pasture production is consistently higher and more uniform in the modified bays. These farmers report that improved drainage of bay surfaces allows grazing within 48 hours after irrigation and winter rainfall is removed quickly, reducing damage by livestock.

Shallow drains are installed with a tractor mounted rotary digger. The drains, spaced 10-15 meters apart, run parallel with check-banks and extend from the paddock drain at the foot of the bay to between 10 and 20 metres from the top of the bay. Drains are only 1 to 2 cm deep and about 20 cm wide.

Figure 2: Tractor mounted rotary digger

An efficient farm drainage and reuse system is essential when shallow drains are installed. When compared to a conventional bay, the drained bays will increase surface runoff from a given irrigation because less water remains ponded on the bay surface and some water completely bypasses the bay surface in the surface drains. The peak runoff flow rate will also be higher because drainage from the bay surface is much faster.