Modelling the regional impacts of multiple MAR schemes on the Northern Adelaide Plains

R R Martin, B Barnett[1], C Pitman, C Kaufmann[2], and A Swiatnik, C Burgess[3]
[1] Sinclair Knight Merz, Level 5, 33 King William St, Adelaide SA 5000 (E-mail: rmatin@skm.com.au)
[2] City of Salisbury 12 James St, Salisbury, SA 5108.
[3] City of Playford, 12 Bishopstone Rd, Davoren Park SA 5113

Abstract Managed aquifer recharge (MAR) utilising both captured stormwater and treated reclaimed water is being increasingly adopted across Australia to supplement traditional water supplies. MAR has been adopted to control abstraction and restore the groundwater balance, prevent seawater intrusion and to take pressure off traditional water supplies. Some local government authorities in South Australia are implementing MAR as part of their integrated water management plans to meet irrigation water demand. Once all of these schemes are operational it is expected that they will capture an estimated 20 gigalitres of stormwater annually for summer reuse. Market gardens have been the principal land use on the Northern Adelaide Plains with irrigation water traditionally sourced from the deeper Tertiary aquifer systems. As a consequence of over 60 years of prolonged use groundwater taking across the Northern Adelaide Plains Prescribed Wells Area is managed under a set of rules outlined in the water allocation plan for the area.

MAR represents a new use juxtaposed with the traditional groundwater use. There is the potential for one activity to impact on the other if not effectively administered. For example, the new use results in greater summer drawdowns in the aquifer which may require existing users to deepen their wells. During winter, recharge pressures may create artesian conditions requiring existing users to enclose the well headworks to prevent flooding. Additionally, the existing management policies may, in the longer-term, exacerbate the potential problem associated with artesian impacts during the winter recharge period. A regional numerical groundwater model of the Northern Adelaide Plains aquifers was used to test these and other potential impacts the results of which are presented in this summary paper.