The use of environmental tracers to determine focused recharge from a saline disposal basin and irrigation channels in a semiarid environment in Southeastern Australia

Lake Tutchewop in southeastern Australia is a former ephemeral wetland that has been used as a saline disposal basin since 1968, forming part of the salinity management of the Murray River. The extent of saline focused recharge from Lake Tutchewop and fresh recharge from nearby unlined irrigation channels was determined using pore water and groundwater stable isotope and major ion chemistry, which were able to separate the influence of lake water, irrigation water and regional groundwater. In ∼45 years, saline water from Lake Tutchewop has infiltrated only up to 165 m from the lake edge in most directions, due to the underlying relatively impermeable clay-rich sediments, and a maximum of 700 m due to preferential groundwater flow along a sandy palaeochannel. The saline leakage has had limited, if any, impact on surrounding agricultural land use. Fresh water leakage from unlined irrigation channels extends up to 10 m deep, validating the current program to replace these channels with pipelines. This study demonstrates that focused recharge from different sources can be positively identified where the recharge waters have distinctive compositions, and that underlying clay-rich sediments restrict the extent of seepage. Therefore, management of focused recharge sources, particularly those that could decrease groundwater quality, requires a detailed knowledge of both the groundwater composition around the site and the underlying geology.