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Warragamba Dam: Damned if you do, damned if you don’t 

With the NSW state election hanging in the balance, the proposed raising of the Warragamba Dam proposal is a dark horse election issue with the potential to swing voters in crucial electorates in western Sydney and the Blue Mountains. It’s also gaining increased attention thanks to leaks to the media last week that the government has secret plans to raise it 3 metres higher than publicly disclosed. But what exactly is this proposed project and what are the issues?


For many infrastructure projects, there’s conflict between conserving the natural environment and the economic benefits derived from infrastructure expansion to accommodate the needs of growing urban populations. 

This is dramatically the case for the Warragamba Dam, where increasing the height aims to reduce flood risk in towns and urban growth centres downstream of the dam in the western Sydney floodplain. 

But this proposal will also have negative impacts on areas upstream of the dam, including protected conservation areas and national parks of the Greater Blue Mountains Area. If the Warragamba Dam is raised, there will simultaneously be people and communities who stand to benefit, and those who will be at a loss.

Flood risk concerns have reached a tipping point in the region

Over the past fifty years there’s been numerous studies and reports on flood risk, management and mitigation in the western Sydney floodplain and Hawkesbury-Nepean river catchment. These studies and reports highlight how the natural characteristics, geography and topography of the Hawkesbury-Nepean river and the surrounding valley make it highly susceptible to major flooding with a wide area of impact. 

The likelihood of this flooding and its extent, combined with the potential economic consequences, means that the western Sydney floodplain has areas of high flood risk. The Insurance Council of Australia considers the Hawkesbury-Nepean river Valley to have the highest single flood exposure in New South Wales, if not Australia.

The threat of major flooding events has concerned governments for many years. Witnessing the impacts of the 2011 Brisbane floods, combined with the NSW government’s future planning in western Sydney and its urban growth centres, put flood risks back on the table at a state level. Following a number of reviews, studies and the establishment of the Hawkesbury-Nepean flood risk management committee, Infrastructure NSW prepared the Hawkesbury-Nepean Valley Flood Risk Management Strategy. The NSW government adopted this strategy in 2017 with its objectives of reducing risk to life, property and social amenity from floods in the Hawkesbury-Nepean Valley, now and into the future. 

Raising the dam wall considered most “cost effective and feasible” option

Increasing the height of the Warragamba Dam wall by around 14 metres is the primary structural measure identified by the strategy. Based on feasibility studies and cost-benefit analysis completed for a range of options to reduce flood risk, the NSW government concluded that it is currently the most cost effective and feasible flood mitigation option. 

Raising the dam to reduce flood risk in the western Sydney floodplain is not a novel idea. In 1995, a proposal to raise the Warragamba Dam by 23m was rejected by the then-Labor NSW government due to environmental concerns and by resolving the immediate issue of dam structural capacity at full water level with a significantly less expensive spillway option.

The current dam wall proposal will provide additional air space to temporarily store floodwaters upstream of the dam wall for flood mitigation purposes only. This would reduce flood risk downstream by temporarily holding back floodwaters from the Warragamba catchment upstream, and then releasing these floodwaters in a controlled manner down the Hawkesbury-Nepean river. This will reduce the depth and extent of potential flooding downstream following major rainfall (which are 1 in 100 to 1 in 500 year events).

Infrastructure NSW have reported that if the Warragamba Dam is raised by 14 metres it will reduce the number of properties potentially impacted by a 1 in 100-year flood event from around 5000 to 1000 in the Hawkesbury-Nepean river catchment. For a 1 in 500-year flood event, a raised dam wall could potentially reduce the number of impacted properties from 12,000 to 5000. 

This will reduce potential flood damage by up to around 75 per cent, and in monetary terms, for a 1 in 500 year flood the 14 metre dam wall raising would have an economic benefit (2015 present value) of $870 million from reduced flood damages for urban development. The reported cost of construction for raising the dam will be in the order of $670 million.

But it’s not just about money

This is all well and good for reducing the economic impacts of a major flooding event, but from an integrated water management perspective that considers the full range of social, environmental and economic outcomes, the project poses great risks. A few grey areas also exist in the decision making process undertaken so far. 

Firstly, flood risk in the Hawkesbury-Nepean Valley is reduced but not eliminated by raising the Warragamba Dam. This is because flood waters come from a range of other rivers and catchments in the region. 

Secondly, the variability and uncertain nature of natural disasters such as flooding presents considerable complexity in assessing the economic, social and environmental outcomes of such a project. And ultimately, the greatest concern – as touted by many that oppose the project – is the potential damage to the environment and indigenous heritage sites upstream of the dam.   

What are the negative impacts to the environment and indigenous heritage sites?

By raising the dam wall, water held back to prevent flooding downstream would inundate and flood extended areas upstream of the dam. This includes part of the Greater Blue Mountains World Heritage site and pristine wild rivers and bushland habitats home to native flora and fauna, including endangered species, as well as indigenous Aboriginal heritage sites.

The Gundungurra people are the traditional custodians of the Burragorang Valley located upstream of the dam. There are over 50 sites of Aboriginal indigenous heritage and significant cultural tradition in the area, including sites with archaeological artefacts such as stone tools and rock art and burial sites. If the dam is raised, these unique environmental and indigenous heritage features could be destroyed from by temporary inundation and flooding.

The dam raising proposal hasn’t taken these issues seriously enough 

These negative impacts have been addressed in a limited and insubstantial manner by the existing cost-benefit analysis for the dam raising project. It notes that there are a number of “intangible” costs associated with the proposed dam raising, such as increased risk of periodic, temporary inundation of 75 square kilometres of national parks and wilderness areas. But this is as far as it goes. 

The Environmental Impact Statement for the proposed project, which is currently being prepared and due for release in 2019, will identify and further quantify impacts of the project. But it will remain to be seen if the value of these environmental and indigenous heritage features is quantified and incorporated in the decision making process in an adequate and transparent way. 

The current cost-benefit analysis, which forms a core element of feasibility studies and the business case proposal for the dam raising project, is considerably limited by the fact that the value of these “intangible” costs of potential environmental and indigenous heritage loss have not been quantified for inclusion. 

Documented details of the cost-benefit analysis completed have not been released by the NSW government for review and critique, with only the final results of estimated project costs of $670 million for construction versus $870 million present value benefits from reduced flood risk. The positive net benefit which results from these numbers supports the proposed project, however, without including the cost to society of potential environmental and indigenous heritage losses, combined with the costs of environmental and biodiversity offset payments required by such a project, there remains a question of if the project would actually have an overall positive net benefit to society and the people of NSW. 

Is this all just to keep developers happy?

As well as these fundamental gaps in the cost-benefit analysis, there are other questions surrounding the Warragamba Dam proposal.  The most prominent is the unclear underlying motivations of the state government for pursuing the project, when a range of alternate flood mitigation and risk reduction measures are available, combined with the disproportionate distribution of benefits from the project, some of which would see immediate financial gains for private developers. 

It’s clear that the proposed dam raising will benefit private developers with investments in the western Sydney floodplain. Reports have already come out of a developer making almost $100 million profit after purchasing land in the western Sydney floodplain for $45 million and then following the announcement of the dam raising project, selling the undeveloped land for $138.8 million. 

Recent comments from the NSW Premier that raising the dam would provide future water security in Sydney casts more questions over the government’s motivations. This, in addition to leaked reports of secret plans for the dam to be raised a total

Joel Dalberger, McGregor Coxall

Joel Dalberger, McGregor Coxall

of 17 metres instead of the publicly disclosed 14 metres, is completely contradictory to the purpose of the project, as holding more water for storage purposes would negate any reduction in flood risk, combined with the direct and long lasting impacts upstream on the environment and indigenous heritage sites. 

The fact that the state government pushed through parliament the Water NSW Amendment (Warragamba Dam) Bill 2018, which makes allowances for flooding and inundation of protected conservation and national park areas, not only paves the way for the proposed dam raising, but clearly shows the preference and agenda of the party for development and urban growth in the western Sydney floodplain.

The current status of the project is in the balance. Preliminary designs and environmental impact assessments are being undertaken, while the possible guillotine of the NSW election looms with the NSW Labor and Greens parties opposing the project.

Joel is an environmental engineer with multi-disciplinary design firm McGregor Coxall and is currently completing a Masters thesis research project quantifying the value of environmental and indigenous heritage assets potentially impacted by the proposed Warragamba Dam raising. The research project will investigate and compare societal preferences for environmental and indigenous heritage conservation vs flood mitigation.

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