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ABSTRACT
Farm dams are essential infrastructure for many farming operations, including livestock watering and crop irrigation. With demand for food increasing, many farmers are looking to capture, store and use more runoff to achieve higher yields under worsening climate extremes. The aim of this article is to advance understanding of farm dams in catchments and the current tools for accounting for them, providing an opportunity to consider a new runoff storage accounting framework to support integrated policy. The Australian dam management setting is provided for context. A longitudinal cohort survey of 254 South Australian farmers provides a snapshot of farmer perceptions of dams and dam management behaviours. Farmers express increasing concern about the future availability of water, how much is allocated to the environment and how this is accounted for. Whilst the field of IWRM and others have integrated disciplines for improved water decision-making, so far there has been limited attention to how to incentivise improved farm dam management through links to farm accounting and business. This study proposes a preliminary framework for assisting dam decision-making across scales to support the health and safety of environments and communities.
Acknowledgements
The paper was part of a detailed Australian Research Council Discovery Project (DP0987825) investigation of dam safety in addition to a Department of Human Services/SACOSS funded project investigating water security threats and challenges. The authors would like to acknowledge these bodies and the participants. Thank you also to Ms Kirsty Willis and her team at the Ehrenberg Bass Institute, Mr Arthur Spassis, Dr Mitali Panchal, Dr Elnaz Etihad and Square Holes for support with data collections. The discussants and participants at the 2020 Massachusetts Institute of Technology (MIT) J-WAFs Seminar Series (Boston) and 2022 International Conference on Irrigation and Drainage (Adelaide) are thanked for their helpful comments. Finally, we acknowledge the help of the anonymous reviewers whose comments greatly improved this manuscript.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Notes
1 The farm dams being referred to are typically embankment dams that largely take water from local overland flows and exist in an area of undulating topography.
2 The landscape drainage area that channels water to a particular point along a network based on its surface topography is called a catchment (Wagener, Wheater, and Gupta Citation2004). Every part of the land on earth forms part of a catchment and so farms necessarily all reside within catchments. However, the catchments referred to in this article are those with undulating topographies where additional water stored in dams poses a greater risk to downstream communities.
3 A particular on-farm water storage management practice that creates a dual-extreme problem is spillway blocking and/or under-designing. By blocking spillways (either by artificial blockage or purposeful neglect of natural vegetation growth) or by under-designing them, farmers are able to store significant additional amounts of potentially non-entitled water; significant because small increases in storage height (resulting from a shallower spillway) at the top end of the reservoir, which has a triangular prism-like geometry, results in large increases in storage volume (Pisaniello Citation2016; McMurray Citation2004). Hence, suitable policy is required to plan, coordinate and manage elements of rural water systems effectively integrated to address equity and safety threats.
4 Most farm dams (which comprise earthen banks) are designed/built with a spillway to prevent overtopping and eroding during flood events. Most dam owners/designers/builders recognise that any farm dam with any catchment area (even if just its own reservoir area) must have a spillway of some kind (e.g. weir, channel, conduit) otherwise it would be highly vulnerable to overtopping, eroding and being washed away as soon as it fills. This was clearly demonstrated by Pisaniello, Tingey-Holyoak, and Burritt (Citation2012, ) where 504 Australian farm dams were randomly surveyed and 91 per cent had spillways.
5 The Council of Australian Governments at its meeting in Hobart on 25 February 1994 agreed to the principles of competition policy with the intent to achieve and maintain consistent and complementary competition laws and policies which will apply to all businesses in Australia regardless of ownership.
6 Hazard in this context refers to a dam’s individual ‘hazard rating’ or ‘consequence category’ as defined by ANCOLD (Citation2012) Guidelines. These Guidelines assist engineers, consultants and departments working with dams to prepare consequence category assessments. Assessment of the hazard /consequence category has evolved since 2000 from a three-tier classification (Low, Significant and High) to a seven-tier system operating today (Very Low, Low, Significant, High C, B, A and Extreme) (ANCOLD Citation2012).
7 In terms of the dual safety-equity problem posed by farm dams, administration problems exist usually because qualified interdisciplinary personnel and funding are lacking. The sheer number of farm dams to be monitored poses a considerable challenge (Baillie Citation2008), and benefits are perceived to rarely outweigh the costs of monitoring most small farm dams, unless their failure would put a vulnerable population at risk (KPMG Citation2013).
8 For example, when numerous farm dams pose a cumulative threat within the catchment of a large hazardous public dam, such as South Australia’s Kangaroo Creek Dam. This is a large, high hazard public dam (65 m high, 19,000 ML capacity) in the River Torrens catchment of South Australia. A flood study found the dam’s peak inflow would increase four-fold assuming all small dams (>1000) in the catchment failed at the same time in a 1-in-200 years flood event: a reasonable assumption as supporting studies found most small dams cannot pass such an event. This additional flow to Kangaroo Creek dam would exceed its spillway capacity, which should otherwise be capable of passing at least a 1-in-10,000 years flood event, putting downstream communities and the environment at unacceptable risk (Pisaniello Citation2016).
9 From a more localised cascade perspective, the dam upstream of a more significant dam can certainly be of insignificant size in terms of its normal storage capacity posing any threat, but it may have a large catchment and associated large/deep spillway to safely pass the catchment flows, and so as soon as its spillway is blocked, its increased storage capacity that poses a threat to downstream equity and safety can become significant (Pisaniello Citation2010; Pisaniello and Tingey-Holyoak Citation2017). As such, original dam size and ‘stand-alone’ hazard are not necessarily the critical determining factors of the severity of dual-extreme cascade/cumulative risks within a catchment (de Lima et al. Citation2022). Severity depends more on physical catchment circumstances, such as relative locations of dams and downstream communities (ANCOLD Citation2012), as well as the jurisdictional circumstances that influence dam management practices (Pisaniello, Tingey-Holyoak, and Burritt Citation2012).
10 Extra water means the water that is stored above the amount the dam is designed to hold safely at full capacity.
11 These reports include volumetric information on both a physical flow basis (in the statement of water flows) and an accrual basis (in the statement of water assets and water liabilities, and the statement of changes in water assets and water liabilities). When these statements are analysed, captured natural inflows ratios and other ratios take consumption into account, but this is only a potential feature of GPWA and only extrapolatable/useful if more preparers conduct the analysis.
12 Recently in the Murray Darling Basin, Fowler et al. (Citation2015) advanced an equation across a larger dataset to get a better understanding of the water held in the region’s 650,000 farm dams which had an accuracy to within 16 per cent of on the ground methods.
13 A full description of the tool is available in Pisaniello, Tingey-Holyoak, and Burritt (Citation2012) and Pisaniello (Citation2016).
14 It is important to note that farm dam storage capacity, spillway flood capability, and in turn cumulative storage and flood capacity are inter-related, i.e. storage capacity depends on reservoir area and height at full supply level, which affects the ‘flood attenuation’ ability of the reservoir, and hence, its spillway flood capability and downstream ‘domino effect’. The extent to which each variable can be altered for a single dam to meet (1) current acceptable standards for both spillway capacity and yield, (2) a farmer's minimum storage needs and even (3) the surrounding landscape, can be determined using Pisaniello, Tingey-Holyoak, and Burritt (Citation2012).
15 The CATI system facilitates stratified probability sampling of the segmentation matrix, centralised data collection, standardised interviewer behaviour, and reduced survey costs (Vemuri et al. Citation2011).
16 Methane is a greenhouse gas that is 34 times more potent than carbon dioxide (Grinham et al. Citation2018). Ollivier et al. (Citation2019) measured the GHG emissions from farm dams in south-eastern Australia and found them 3.43 times higher than temperate reservoir emissions. By modelling these results to the entire state of Victoria, the researchers found a farm dam CO2-equivalent/day emission rate of 4853 tons, 3.1 times higher than state-wide reservoir emissions in spite of farm dams covering only 0.94 times the area comparatively.