Estimating hydraulic parameters for a surface irrigation model from field conditions

Abstract

Border-check irrigation is the most common method of irrigating pastures in Northern Victoria. To make the best use of a border-check irrigation system, consideration needs to be given to the irrigation schedule and irrigation event management. Surface irrigation models can provide an inexpensive and rapid method for identifying optimal irrigation event performance. The most common difficulty encountered when using surface irrigation models is determining appropriate hydraulic parameters. Two experiments were conducted to investigate the relationship between hydraulic parameters of the Analytical Irrigation Model and easily observable field conditions. The field experiments were performed at Tatura, Victoria, on 12 irrigation bays characterised by a Lemnos loam, a red duplex soil, sown to perennial pasture. For each experiment, 3 replicates of 4 treatments were applied. The first experiment found a linear relationship between field soil water deficit, approximated by crop water use less effective rainfall, and the initial infiltration depth. The second experiment found no relationship between pasture height and the model surface roughness parameter. An alternative to estimate the surface roughness parameter is suggested, which involves making an early observation of irrigation advance and solving for the unknown roughness parameter. The parameter estimation method developed in this paper can assist in improving the management of border-check irrigation on Lemnos loam soil, which covers about 125 000 hectares in the Goulburn Valley. However, field-testing of the approach on commercial farms and other soil types is required.