Quantifying Impact Of Rainfall On Shallow Groundwater Table In The Wakool Irrigation District, NSW

Abstract

Water table rise and salinity are major threats to the sustainability of agriculture in the Wakool area. In order to improve groundwater and salinity management in the Wakool area, it is necessary to quantify impact of both climate and management on shallow groundwater table. Rainfall as a major climate indicator and hydrology component plays an important role in regional hydrology and environment, as well as in water table change. This study attempts to quantify the impact of rainfall as a major climate indicator on shallow groundwater in the Wakool area based on the piezometric data in this area and the rainfall data in a wider area. GIS techniques have been extensively used in this study for data processing and analysis, especially for generating the spatial distributions of rainfall and groundwater table over the study period, for analyzing the spatial extent of groundwater table changes, and for calculating relevant volumes for various time intervals. This study has developed a method for isolating the impact of climate on shallow watertables. The method has been proven particularly effective in assessing the impact of rainfall for summer seasons which are the major irrigation periods in the study area. Statistical relationships were established to understand and quantify the impact of climate represented by rainfall on groundwater tables for different seasons in the year. The statistical relationships between rainfall and groundwater storage change derived from this study revealed some interesting bench mark rainfall figures: • For summer seasons, the bench mark rainfall is around 200mm, above which, it will likely to have an addition effect on groundwater storage; below which, it will likely to have a reduction effect on groundwater storage; • For the winter season, that bench mark rainfall is around 170mm The results of this study indicate that climate represented by rainfall, which is also a major source of flood, has a significant impact on the shallow groundwater tables in the Wakool area, as the correlations (R2) between rainfall and water table change are in the range of 0.7~0.9 for all the time intervals considered.