2008 – A new approach to yield estimation for South East Queensland

Matthew Pollard, John Vitkovsky, Richard Priman

Abstract: South East Queensland (SEQ) currently has severe (Target 140) restrictions imposed to help secure supplies during the current drought which is the worst on record. Additionally, a $9 billion water infrastructure program is being fast-tracked to increase the climate resilience of the region and provide for long term sustainable growth.
The Draft South East Queensland Water Strategy (SEQWS) released in March 2008 was prepared by the Queensland Water Commission to reduce the likelihood of ever experiencing such severe restrictions again and to ensure water security into the future. The Strategy includes a Water Supply Guarantee underpinned by advanced analytical techniques for estimating the system yield from surface water, groundwater and manufactured water supplies connected by the SEQ Water Grid. This approach builds on the Level of Service (LOS) Objectives methodology, originally promulgated by the Water Services Association of Australia in their June 2005 paper entitled “Framework for Urban Water Resource Planning”. The approach has led to a significant improvement in our understanding of water supply risks and the associated planning implications for assessed yields/water availability.
To assess yield using the LOS objective methodology and to determine the benefits of the new water infrastructure, a regional water balance model for the connected SEQ Water Grid simulating the water sharing arrangements of all of the SEQ water sources was established. The model uses a logic tree to allocate water using a “proportional storage rule” from multiple sources to meet competing demands. This approach enabled quantification of the increase in system yield resulting from the construction of the SEQ water grid which allows demands from previously disconnected areas to be met by more efficient allocation of water from supply sources. Stochastically generated dam inflow data was used to facilitate a more comprehensive assessment of climate variability and water supply risk than is possible with historic data alone.
The paper discusses the managed hydrologic risk approach adopted in developing the regional water balance model which implements the LOS Objectives approach and improves the understanding of the relationship between the level of service, supply yield and risks associated with climate variability. The result is a far more thorough approach to planning for future water service delivery and water infrastructure.

Keywords: level of service objectives, South East Queensland Water Strategy, SEQ Water Grid, yield, water security, regional water balance model, stochastic modelling, climate variability.

Buy this resource