Groundwater flow in the Campaspe and Loddon Valleys of Northern Victoria: an enhanced role for the Shepparton Formation

Abstract

Recent work on the fluvial aquifer systems of the Campaspe and Loddon Valleys in northern Victoria has shown that a two-aquifer conceptualisation and use of ‘typical’ hydraulic parameters for the Calivil Formation regional aquifer and its notional aquitard the Shepparton Formation, may mask the true nature of their interactions. In the highland tracts of the Loddon and Campaspe Valleys the regional aquifer system comprises the Calivil Formation and much of the Shepparton Formation. On the southern Loddon Plains, intensive groundwater development occurs from both the Calivil Formation and a Shepparton Formation ‘sand sheet’ aquifer, which follow separate paths across the plain, dictated by an evolving late Tertiary palaeogeography. Whatever the aquifer system invoked, the emphasis has been on horizontal down basin flow. At other times, upbasin flow of saline water under reversed hydraulic gradients into irrigation areas has been stressed, with the concerns for aquifer salinisation. Yet it is shown that in the Campaspe Valley, vertical flow from overlying or underlying aquifers poses a far more immediate salinity threat to the regional Calivil Formation aquifer than upbasin horizontal flow. Overall, the role of the Shepparton Formation as a significant aquifer system, and elsewhere as a conduit for salinisation via vertical flow, has been largely overlooked. More generally, the lithological variability of the Shepparton Formation across north central Victoria strongly influences the behaviour of the regional aquifer system, including groundwater throughflow and groundwater development. This is especially clear on the permeable Campaspe Fan, which is the principal recharge area in the Campaspe Valley, with recharge coming from direct precipitation, the Campaspe River, irrigation, and the Waranga-Western and Campaspe No 1 channels.