Assessment of rice hydraulic loading impacts on groundwater and salinity levels

Abstract This paper describes the impact of ricehydraulic loading (percentage area under rice crop) ongroundwater levels and salinity in the Murrumbidgee irrigationarea (MIA), Australia using a MODFLOW-basedmodelling approach. The model simulations show that thegroundwater levels will be in equilibrium after a fall ofapproximately 1 m under most of the areas, however, thegroundwater salinity levels will rise by more than 1,000ls/cm in most parts of irrigation area. If the rice growingarea is reduced by 50 and 75%, there can be a net decline ingroundwater levels during the first 2 years and then a newquasi-equilibrium will be established. To downscale theseresults at the farm level, SWAGMAN Farm model inconjunction with groundwater outflow rates obtained froma three-dimensional MODFLOW model was applied fordetermining net recharge rates under rice for different areaswithin the MIA. The highest net recharge during 2005'2006 season was 0.84 ML/ha (84 mm) in parts of theirrigation system, whereas the average net recharge due torice hydraulic loading for the whole MIA during 2005'2006 season was estimated as 0.34 ML/ha (34 mm).