Anlysing Drought Planning Measures with Wathnet Model: Urban Experience

Water New South Wales of Australia (WaterNSW) is a state-owned Corporation (i) supplies water from dams, pipelines, and rivers in New South Wales state in Australia (ii) with more than 40 dams across the state, supply two-thirds of water used in NSW to regional towns, irrigators, Sydney Water Corporation and local utilities. The WaterNSW uses Wathnet, a generic water balance model for planning of the Greater Sydney water supply system. The model is mainly used for (i) system yield estimation of urban area, (ii) drought planning, (iii) short- to long term planning, (iv) rural water supply, (v) system augmentation and (vi) optimisation. The model is run for a series of synthetic replicates containing stochastic climate and streamflow data similar to historic data.

The WaterNSW’s water supply system yield for Greater Sydney is the maximum annual average demand that can be supplied by the system whilst conforming to the design criteria. Sydney’s raw water supply system is designed to meet service standards to ensure (i) supply continuity and to (ii) minimise the frequency and duration of water restrictions. The supply system’s performance is assessed against a three pronged criteria such as reliability, robustness and security.

The Wathnet model was used to develop Greater Sydney’s Metropolitan Water Plan in 2004, 2006, 2010 and 2016. After the Metropolitan Water Plan scenario modelling, all the scenarios were costed for further assessment (2010). This was done outside the Wathnet system model. The WaterNSW saw benefits in being able to perform the economic assessment of the system’s performance for each of the synthetic inflow replicates through the system model and has progressed work in this area. The new version of Wathnet modeling software incorporated an economic functionality along with the water supply system simulation capabilities.

The purpose of this paper is to demonstrate the new Wathnet model’s capability in analysing the drought planning measures and its imaapct on the system reliability. Drought is a common and recurring part of the Australian climate that must be taken into account in the management of water supply systems. With the current drought already the worst on record, the WaterNSW as part of its responsibility for water supply has analysed the severity of the current drought. This paper showed various measures availble to deal with the drought. The model shows how to use different measures (both short- and long term measures) and how it impacting drought to maintain supply continuity.