Water-energy nexus in irrigation supply systems using a demand-based dynamic nodal network model

Scarcity, high price tag and environmental footprints of water and energy use are now well-recognized wicked problems in irrigated agriculture. Efficient irrigation technologies are an important means for boosting crop productivity; however, the benefits of improved yields may be at the cost of increased water and energy inputs and associated environmental impacts (Pimental et al., 2004). These issues have become more pressing for water-scarce and environmentally-aware countries like Australia. In response, the Australian government has initiated a 10-year $10 billion 'Water for Future' programme to improve irrigation infrastructure, efficiencies and to give the environment its fair share. This article is one of the outcomes of research that investigated water'energy nexus on a large irrigation area in southeast New South Wales, Australia. Three types of infrastructure are mainly in place in the study area to deliver irrigation water to the farms, namely: (1) Gravity-based open channel network that mainly delivers water to farms growing broad acre crops. High seepage and evaporation loss is associated with this system; (2) Gravity-based open channel network with on-farm storages where water is supplied to the on-farm reservoirs. Water is then pumped from the on-farm reservoir to mainly operate sprinkler/drip system(s) to irrigate crops when required. This involves additional evaporation loss from on-farm storages which would otherwise have been socialized if left in the original source storage; (3) an emerging technology, the integrated high pressure (IHP) system. It consists of a centralized pump(s) station and a number of farms connected to it. The system is designed to deliver water with certain pressure head to operate farm pressure irrigation equipments without need for on-farm pumping. The IHP system can be an On-demand supply system, where a constant pressure is maintained in the mains and the farmers start irrigation when needed by opening the control valve manually or wirelessly, or a restricted supply system where there is restriction on frequency of water orders. Lamaddalena & Sagardoy (2000) noted that when restricted frequency demand is applied, all farmers tend to over-irrigate because of uncertainty in water availability. In contrast, using the on-demand operation farmers irrigate when it is needed. Farmers are required to place a water order with the irrigation company in advance (order time varies with irrigation supply system).