Modelling aquifer recharge and water use in the Koo-Wee-Rup basin

Abstract

Overpumping for irrigation has caused a general lowering of the piezometric surface in a multilayered aquifer in the Westernport Bay area of Victoria. This lowering effectively increases costs for agricultural production because of the higher pumping lifts now needed, and sets a limit to further development for irrigation in this vegetable-growing locality. In addition, there is now some seawater intrusion into the aquifer. A finite-difference model had been developed by the Department of Minerals and Energy of Victoria for the prediction of piezometric surfaces associated with steady-state pumping rates. This model was altered so that the influence of various possible recharge sources on the piezometric surface could be predicted. The recharge sources were infiltration from rainfall in localities where there are outcrops of the aquifer formation, beds of rivers passing over the general area, and rainfall infiltration in the surrounding hill country. Correspondence between the results of the model and the field behaviour as recorded in a dense grid of bores, was adequate in that it confirmed the existence and relative importance of the postulated recharge sources. Recommendations are made as to the limited advisability of artificial recharge of the aquifer from surface sources.