Melbourne, Australia, Water Security

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--Nichole Hoskin 12:24, 10 February 2009 (EST)

 Related Links:
 Sydney, Australia, Water Security
 Sydney Catchment Rainfall graphs with trend lines
 Melbourne Catchment Rainfall graphs with trend lines
 BoM graphs with trend lines
 Perth, Australia, Water Security
 Perth Catchment Rainfall graphs with trend lines

--Nichole Hoskin 14:33, 28 January 2009 (EST)

1 Melbourne Water data
2 Melbourne Catchment Rainfall graphs with trend lines
3 Australian Bureau of Meteorology (BoM) rainfall data for Melbourne's catchment areas
4 BoM graphs with trend lines
5 Bushfires in Melbourne’s Catchment Areas
6 References

Melbourne Water data

 Melbourne Catchment is defined as Maroondah, O’Shannassy, Upper Yarra and Thomson, which are the four largest catchment 
 areas.

Graphs by Nichole Hoskin, derived from Melbourne Water's 'Weekly Water Updates' archives.

Melbourne Water 'Water Supply Map'

Melbourne Catchment Rainfall graphs with trend lines

To view the above graphs with linear regression and 5-year moving average trend line, Click here: Melbourne Catchment Rainfall graphs with trend lines

Australian Bureau of Meteorology (BoM) rainfall data for Melbourne's catchment areas

 Graphs by Nichole Hoskin, derived from Australian Bureau of Meteorology data for stations closest to Melbourne’s main 
 catchment areas. The time frame was determined by when records begin and end. Annual rainfall is the sum of the monthly  
 readings, excluding years when records were incomplete.

In correspondence with Dr David Jones, the head of the National Climate Centre at the Australian Bureau of Meteorology, on the issue of which BoM station records are representative of Melbourne catchment rainfall, he said that the BoM “gauges network clusters around the catchments rather than within the catchments. The best catchments records are from Marysville and O'Shannassy which sit just to the east and west of the catchments.”

Australian Bureau of Meteorology data for Marysville (Victoria, Australia)

Marysville is north-west and approximately 34 kms (by road) from O’Shannassy Reservoir

Australian Bureau of Meteorology data for O'Shannassy Reservoir (Victoria, Australia)

Australian Bureau of Meteorology data for Maroondah Weir (Victoria, Australia)

Australian Bureau of Meteorology data for Upper Yarra Dam (Reefton) (Victoria, Australia)

Australian Bureau of Meteorology data for Walhalla

Walhalla is south-east and approximately 34kms (by road) from Melbourne’s largest reservoir, Thomson.

Dr Jones described the climate of Melbourne Water’s four main catchment areas as “generally very similar - the Maroondah, Upper Yarra, O'Shannassy and Thompson reservoirs are along-side each other.”

“These are pristine protected wet forest with some small stands of rainforests. There is no active land management and fire has been excluded for close to 70 years (last major fire was in 1939) in Maroondah and longer in the case of O'Shannassy - in other words these forests are mature. The forests are experiencing very widespread die back with many old trees dying or dead - Melbourne water are actually observing runoff which is in excess of what they expect for the rainfall temperature combination which they put down to the loss of much of the leaf canopy due to water stress. The current drought is very far outside of historical experience in terms of rainfall and temperature and affects all areas which rely on westerly rainfall, and particularly those which previously had an autumn rainfall peak - the area around Melbourne had a unique climate historically in that it once had two separate rainfall peaks - one in autumn and one in spring.”

“The autumn drying which is a large part of the drought story now dates back 20-30 years across southern Australia and is getting worse (even earlier in the case of SW WA), while the recent spring drying has seen the 1st, 3rd and 4th driest starts to spring on record occur in three consecutive years across parts of central Victoria is far outside of historical experience. Broadly speaking these changes are exactly what we expect as the Hadley circulation expands pole ward in a warmer world pushing the mid latitude weather systems south. We see this expansion very clearly with rising pressures in the subtropics across the southern hemisphere.”

For the sake of clarity, Dr David Jones' comments are in italics

BoM graphs with trend lines

To view the above graphs with linear regression and 5-year moving average trend line, Click here: BoM graphs with trend lines

Bushfires in Melbourne’s Catchment Areas

--Nichole Hoskin 15:18, 17 February 2009 (EST)

On February 17, 2009, fire had burnt O'Shannassy, Maroondah and other smaller catchments, including Armstrong, Tarago and Wallaby, with only about 18% of Melbourne Water's catchments areas having fire damage.^[1]

ABC News Online reported that fires had burnt 90% of the O’Shannassy catchment area and 40% of the Maroondah catchment area.^[2] (see table 1)

Melbourne's two largest catchment areas, Upper Yarra and Thomson, are mostly unaffected by fire at this stage, with the Upper Yarra catchment area estimated to have less than 2% burnt, while fire has not affected the Thomson catchment area.^[3] (see tables 1 and 2 below)

In order to prevent contamination of Melbourne's drinking water by ash and debris, Melbourne Water has moved water out of fire-affected catchment areas to other catchments.^[4]

On the issue of whether fire damage at some catchment areas threatened Melbourne’s water supplies, Melbourne Water's manager of water supply operations, John Woodland, said that in the short-term, supply is protected because there are nine reservoirs and, "At this stage we're not too concerned because we do have the flexibility to shunt water around and take water out of those reservoirs that are out of harm's way."^[5]

According to Melbourne Water, "We continue to transfer water away from reservoirs in the bushfire areas as a precaution. So far, we've moved more than 10 billion litres of drinking water from Upper Yarra Reservoir to other storages that won’t be impacted. These type of reservoirs (including Cardinia) currently hold around 200 billion litres. Over 100 of our fire fighters and planners are working closely with the Department of Sustainability and Environment to minimise damage to the catchments."^[6]

--Nichole Hoskin 21:52, 25 February 2009 (EST)

By February 25, 2009, Melbourne Water estimated that about 93% of the O'Shannassy catchment area and 75% of the Maroondah catchment area has been burnt.^[7] (see table 2 below) However, “around 30% of Melbourne's catchments have some degree of bushfire damage. Most of this is centred on the O’Shannassy and Maroondah catchments.”^[8]

Melbourne Water's two largest catchment areas remain largely unaffected by fire, with the Upper Yarra catchment area still estimated to have about 2% burnt. Melbourne Water and associated Victorian agencies have been working to minimise the risk of fire in the Upper Yarra catchment, with fires still burning in surrounding areas.^[9]

According to Melbourne Water, “With increased fire risk expected later this week, our fire crews are working around the clock with authorities to prevent fire fronts progressing into the Upper Yarra catchment. Even under a worst-case scenario, we can take affected reservoirs out of service until their water quality returns to normal. In this instance, we would use water from our reservoirs that are out of harm’s way. Over 200 billion litres is already sitting in reservoirs that can’t be compromised by bushfire contamination (Cardinia, Sugarloaf, Greenvale and Silvan reservoirs).”^[10]

"Water quality and supply to customers remains unaffected. We continue to transfer water away from reservoirs in the bushfire areas as a precaution. This will provide Melbourne with plenty of water reserves while we manage any short term impacts on reservoirs. We have an intensive monitoring program in place to ensure water quality is maintained."^[11]

--Nichole Hoskin 19:23, 20 February 2009 (EST)