Helen Keenan

Helen Keenan

Helen Keenan, Australia.

Helen Keenan is an aquatic ecologist from Sydney, Australia. She has worked in river management for almost two decades, and on the development of environmental flows in the Hawkesbury-Nepean River for the last seven.  Helen holds a PhD in palaeoecology from Macquarie University (Sydney), focussing on the changes in fossil diatom communities from lake sediments on subantarctic Macquarie Island. Her work has included management of cyanobacteria in freshwater, inland and coastal waters; water quality assessment and management in the Murrumbidgee and Hawkesbury-Nepean rivers; regulation activities for large water corporations; and, most recently, ecohydrological modelling to investigate the most appropriate variable environmental flow for Warragamba Dam.

Presentation Title:Developing a new environmental flow rule for Warragamba Dam: application of flow, ecological and economic modelling in the 2017 Metropolitan Water Plan.

In developing Sydney’s 2017 Metropolitan Water Plan, the NSW Government investigated the contribution that variable environmental flows (e-flows) from Warragamba Dam could make to improve the health of the Hawkesbury-Nepean River. As Warragamba Dam stores 80% of Sydney’s drinking water supply, it was important to determine the benefits to the environment and river users from the e-flows as well as the potential impact on urban water supply. This was undertaken through a staged modelling approach, commencing with a number of e-flow scenarios, through river flow and use modelling, to ecological models and finally economic valuation studies. Dam releases for each scenario were modelled by WaterNSW using Wathnet, the bulk water system model. Five e-flow scenarios were run through Wathnet to determine daily flow releases. These were then used as an input to the Hawkesbury-Nepean River IQQM model to determine changes in river flows downstream of the dam. River flows were input to ecological and water quality models to assess the relative change from the current condition.  Changes in fish migration opportunities, water quality and reduction in floating weed cover were estimated. These were translated into independent variables reflective of community values held for the river – which related to fishing, swimming and boating. These community values were estimated through a travel cost survey and a choice modelling study, and incorporated in a cost-benefit analysis of the options.  A portfolio analysis of alternative water supply augmentation options to replace urban water supplies that would be lost to increased e-flow releases was conducted, which included a separate choice modelling study of the willingness of Sydney households to incur water use restrictions. The preferred e-flow, with a benefit:cost ratio of 4 was included in the 2017 Metropolitan Water Plan.

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