Darwin region level of service objectives analysis

The Power and Water Corporation (PWC) in the Northern Territory are currently in the process of reviewing the water supply strategy for Darwin. As part of the review, the role of water restrictions in meeting PWC's Level of Service (LoS) objectives was modelled in detail. PWC and SMEC in collaboration developed a model to gain an understanding of the impact that various management actions would have on Darwin's water supply security. Recommended LoS objectives required compromises to be made between minimising risk of restrictions and maximising overall yield. The study has incorporated consideration of an interesting combination of factors including, intense wet season inflows, low dry season inflows with high evaporation, small storage size and a community with no experience of water restrictions and relatively high water usage. The study comprised three components. Firstly, a review of the level of service objectives of other Australian water agencies; secondly, facilitation of development of a set of LoS objectives for the Darwin region water supply that considered unrestricted demand reliability, restricted demand reliability, contingency storage and the development of drought or emergency response plans. Thirdly, the study facilitated a review of Power and Water's existing water restrictions policy and setting of restriction rules and triggers for the Darwin region water supply system. A Fortran code model was used to simulate up to four levels of restrictions. The modelling process simulated runoff using an 8,000 year stochastically generated set of inflows. The elements to which yield was assessed to be most sensitive were low inflow assumptions, groundwater availability, climate change and lowering trigger levels.