Assessing the feasibility of managed aquifer recharge under uncertainty
Date
2015
Authors
Arshad, Muhammad
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This thesis presents a new approach, with application, for assessing the feasibility of Managed Aquifer Recharge (MAR) under uncertain conditions. MAR is the intentional storage and treatment of water in aquifers for future use or storage conservation. A few studies indicate that MAR can be more profitable than surface storage and other alternatives. But the studies have substantial weaknesses. Firstly, they do not take consideration of uncertainty into account. Various types of uncertainties often exist such as whether MAR systems will remain operationally effective and profitable in the future, because long term feasibility of MAR depends on many uncertain hydrogeologic and financial variables. A second weakness has been the lack of a quantitative, integrated approach. The two gaps have been identified as the two major methodological needs for assessing the feasibility of MAR. These methodological gaps are conjointly addressed in the thesis by using an integrated and quantitative approach that considers a range of values for influencing variables from the distinct but complementing disciplines of hydrology, hydrogeology and financial economics. Hydrologic and hydrogeologic feasibility is assessed by examining source water availability from the frequency of large flood events and by considering hydrogeologic opportunities and constraints of storing water underground. Financial feasibility is assessed through cost-benefit analysis. Uncertainties are assessed by identification of cross-over points of many hydrogeologic and economic variables using break-even analysis. Cross-over points describe combinations of values where cost-benefit analysis shows two alternatives to be of equal value. These points are the thresholds where MAR and surface storage yield equal financial returns. The uncertainty approach systematically searches for conditions under which the requirements for MAR may not be met and failure might occur. The application of the suggested feasibility approach is demonstrated through a case study in the lower Namoi Catchment, NSW. Under existing water allocation and capture rules, on average 85 GL per annum of floodwater is available that can be potentially stored in the aquifers of the lower Namoi Catchment. Results of the financial cost-benefit analysis indicate that, under a wide range of plausible conditions, the basin infiltration method is more profitable than surface storage and that Aquifer Storage and Recovery (ASR) is less profitable than surface storage of irrigation water. The thesis presents a framework of sequential steps that constitute a transferable approach for assessing the feasibility of MAR. The core of the approach, which is a method of identifying cross-over points from multidisciplinary perspective, is beneficial in three ways: firstly, it can determine minimum hydrogeologic and cost requirements under which MAR can be worthwhile; secondly, it can substantially lower the cost of geophysical and hydrogeologic investigations by assessing only areas that satisfy minimum requirements of MAR; and thirdly, it can improve confidence in decision making for adopting MAR systems. It is found that the method is of more general utility to a range of cost-benefit applications where there is uncertainty in the values of influencing variables.
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