The control of groundwater abstraction from coastal aquifers is typically aimed at minimizing the risk of seawater intrusion, excessive storage depletion and adverse impacts on groundwater-dependent ecosystems. Published approaches to the operational management of groundwater abstraction from regulated coastal aquifers comprise elements of "trigger-level management" and "flux-based management". 1832 A.D. Werner et al.Trigger-level management relies on measured groundwater levels, groundwater salinities and/or ecosystem health indicators, which are compared to objective values (trigger levels), thereby invoking management responses (e.g. pumping cutbacks). Flux-based management apportions groundwater abstraction rates based on estimates of aquifer recharge and discharge (including environmental water requirements). This paper offers a critical evaluation of coastal aquifer management paradigms using published coastal aquifer case studies combined with a simple evaluation of the Uley South coastal aquifer, South Australia. There is evidence that trigger-level management offers advantages over flux-based approaches through the evaluation of real-time resource conditions and trends, allowing for management responses aimed at protecting against water quality deterioration and excessive storage depletion. However, flux-based approaches are critical for planning purposes, and are required to predict aquifer responses to climatic and pumping stresses. A simplified modelling analysis of the Uley South basin responses to different management strategies demonstrates the advantages of considering a hybrid management approach that includes both trigger-level and flux-based controls. It is recommended that where possible, trigger-level and flux-based approaches be adopted conjunctively to minimize the risk of coastal groundwater degradation and to underpin strategies for future aquifer management and well-field operation.

To understand the possible impacts of changes in rainfall and potential evapotranspiration (PET) in a river catchment in which surface water and groundwater systems are connected, the dynamic interaction that exists between changes in surface runoff, groundwater recharge, and groundwater levels must be represented appropriately. While such a system can be modelled using fully coupled groundwater-surface water flow models, it is more common for separate specialised models to be developed independently by different teams for different purposes. The assumptions, parameters and outputs of the models are not compared. This paper develops a methodology for comparing specialist hydrological models commonly used in Australia to simulate catchment processes. Three models were developed, initially independently, of the Cox Creek sub-catchment in the Mount Lofty Ranges of South Australia: a LEACHM model of groundwater recharge, a SOURCE model of surface water runoff, and a MODFLOW model of groundwater flow. The models are reconciled by using multiple outputs of the LEACHM model as inputs to the MODFLOW model, and calibrating the MODFLOW model to SOURCE outputs. Reconciliation of the inputs and outputs of the three models with each other should improve the rigour in each model's simulation of catchment processes. The reconciled models will be run with stochastically-generated input data sets of rainfall and PET, representing a variety of possible future climate scenarios generated by one of the CMIP5 group of global climate models. Reconciled outputs of the three models are expected to reveal some of the complexities in the interrelated responses of groundwater and surface water flow systems to multi-decadal timescale changes in rainfall patterns.