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Parliamentary Questions


Question On Notice No. 3167 asked in the Legislative Council on 9 September 2020 by Hon Robin Chapple

Question Directed to the: Minister for Regional Development representing the Minister for Water
Parliament: 40 Session: 1


Question

I refer to water levels in Lake Argyle, and I ask:
(a) what level is the water in Lake Argyle currently at;
(b) what is the long term average level of Lake Argyle at this time of year;
(c) what percentage of the long term average water level is Lake Argyle currently at;
(d) when was the last time Lake Argyle was this low at this time of year;
(e) why is Lake Argyle at this low level;
(f) what is the minimum operating level at Lake Argyle;
(g) what is the current allocation limit from Lake Argyle for the Ord irrigation area;
(h) what percentage of reliability is the current allocation limit at;
(i) how much water has been used in total from Lake Argyle for irrigation for each of the past five years;
(j) as a result of low water levels, are restrictions currently in place for any current water users drawing from Lake Argyle:
(i) if yes to (j), for which users and what are the restrictions; and
(ii) if no to (j), why not;
(k) are further or future restrictions planned for any current water users drawing from Lake Argyle:
(i) if yes to (k), for which users and what are the planned restrictions; and
(ii) if no to (k), why not;
(l) based on Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Bureau of Metereology (BoM) climate change, evaporation and rainfall modelling for the East Kimberley Region, does the Minister expect Lake Argyle water level scenario to worsen, stay the same or improve in coming years:
(i) if the Minister expects the water level to stay the same or improve, what scientific basis does the Minister base their conclusion;
(m) based on current water levels and future expected climate, evaporation and rainfall outcomes as modelled and reported by CSIRO and BoM for the East Kimberley Region is there sufficient water to maintain existing irrigated agricultural water usage levels;
(n) based on current water levels and future expected climate, evaporation and rainfall outcomes as modeled and reported by CSIRO and BoM for the East Kimberley Region, is there sufficient water to expand the agricultural area under irrigation from Lake Argyle:
(i) if yes to (n), by what area and volume and water
; and
(o) if the Ord irrigation area has reached or exceeded its likely long term water availability from Lake Argyle, will the Minister be advising existing and potential future investors:
(i) if no to (o), why not?

Answered on 4 November 2020

 

(a)      82.11 metres as at 7 October 2020.

 

(b)   90.06 metres between 1996 and 2019.  The longest record that can be compared to the current water level is from 1996 to present day.  Although the Ord River Dam was completed in 1971, the storage capacity of Lake Argyle increased when the spillway wall was raised during the 1995 dry season.

 

(c)   The volume of water currently in storage in Lake Argyle is 39 per cent of the average storage at this time of year since 1996.

 

(d)   1992 (82.48 metres, before the spillway was raised).

 

(e)   Three consecutive wet seasons have produced lower than the long-term average streamflow from the Ord River into Lake Argyle.  Evaporation and releases from the Ord River Dam have been relatively consistent over this same three year period.

 

(f)   The minimum operating level is 71.91 metres relative to the Australian Height Datum.  This level was determined in the original design of the Ord River Dam to protect the structural integrity of the asset.

 

(g)   Water for the Ord irrigation area is supplied from the Main Ord sub-area and the Carlton-Mantinea sub-area.  The allocation limit for the Main Ord sub-area is 750 gigalitres and the allocation limit for the Carlton-Mantinea sub-area is 115 gigalitres.

 

(h)   The Ord surface water allocation plan 2013 indicates the full allocation limits of 750 gigalitres for the Main Ord sub-area and 115 gigalitres for the Carlton-Mantinea sub-area  could be supplied in at least 19 out of 20 years. 

 

(i)    See table below:

 

Year

2015

2016

2017

2018

2019

Used for irrigation (gigalitres)

217

202

182

234

313

 

(j)    No.

 

(i)    Not applicable.

 

(ii)   Lake levels are currently below the hydropower risk assessment trigger, however, due to lower hydropower demands there has been no need to restrict hydropower operations this year.

 

(k)   Water use restrictions will be applied in a staged way if storage drops below identified trigger levels.  Releases for hydropower would be reduced initially and if storage is very low releases for environment and irrigation would be reduced.

 

(i)    As for answer (k)

 

(ii)     As for answer (k)

 

(l)    Future climate change projections for the Kimberley region, downscaled from general circulation models, do not show a consistent trend in either warmer wetter or warmer drier potential climates compared to the observed historical record.  More importantly for this location, the observed historical climate variability is greater than the future climate change projections.  

Based on the observed historical record, there is a higher probability that lake levels will be at similar levels to 2020 or higher, compared to the probability that levels will decline further.

 

(i)    Refer to answer (l)

 

(m)  Yes.

 

(n)   Yes.

 

(i)    368 gigalitres remains unallocated in the Ord Main sub-area and 114.90 gigalitres unallocated in the Carlton-Mantinea sub-area.  The extent to which agriculture can be expanded depends on the nature of the agricultural developments and crops grown.

 

(o)   The Ord River irrigation area has not reached or exceeded its likely long-term water availability from Lake Argyle.

 

(i) Not applicable.