Application of new solutions for groundwater mounding to irrigation mosaics

Irrigation mosaics, consisting of patches of irrigated area, may offer advantages when compared to traditional contiguous irrigation schemes (Figure 1). Irrigation mosaics could reduce water table rise, water logging and salinisation associated with large irrigation schemes. The water table mound that builds up under an irrigated patch due to increased recharge is examined using both a new analytical solution and a numerical solution. The rise in water table is examined in both dimensional and nondimensional parameters with the analytical solution. This solution was developed by Cook etal. (2007a) and is computationally efficient. The use of non-dimensional variables allow us to examine a very large range of possible solutions.A solution for water table rise with a square array of circular irrigation patches is developed and used to examine these arrays. These results are supplemented by numerical simulations using MODFLOW (McDonald & Harbaugh, 1988). The MODFLOW calculations allow for periodic recharge and also irrigation arrays that are limited in spatial extent.Results show that the maximum water table rise(in the centre of the irrigated patch) is strongly dependent on the size of the irrigation patch. This water table rise is linear with time initially but the rate of rise reduces with time as the mound spreads. The irrigation arrays show that if mosaics are to be introduced that the size and spacing will have a large effect on the maximum water table rise. The numerical results show that periodic recharge will result in a periodic time rise of the water table and that this is likely to approach the water table rise calculated with an average steady recharge rate over longer time.Results suggest that irrigation mosaics of correct size and spacing could reduce water table rises relative to traditional irrigation systems while still irrigating the same total area.