Measuring Over Allocation of Water Resources

Dr Ian Prosser, Science Director Water for a Healthy Country Flagship

Premise

• Much of current water reform and associated investment ($10B)

is aimed at reducing over allocation of water resources.

• Over allocation is understood only in the broadest terms and

there are no accepted ways of measuring it.

• How can we have confidence in resolving over allocation if we

cannot measure it?

Semantics don’t matter

• Is it “over allocation”, “over entitlement”, “over use”, or

“unsustainable use”?

• What it is called is of secondary concern

• All terms reflect a primary concern that too much water is used

with an unacceptable impact on the environment

• It is more important to have acceptable measures of over

allocation than argue about the appropriate term

• How much extractive use is too much?

MDB Sustainable Yields - relative level of surface

water use

Where is use too high ?

Why can’t more water be used ?

0%

10%

20%

30%

40%

50%

60%

70%

Paroo

Ove

ns

Easte

rn M

t Lofty

Ran

ges

Barwon

-Dar

ling

Warre

go

Mac

quar

ie-C

astle

reag

h

Lach

lan

Lodd

on-A

voca

Borde

r River

s

Moo

nie

Cam

pasp

e

Mur

ray

Nam

oi

Gwyd

ir

Gou

lburn

-Bro

ken

Mur

rum

bidg

ee

Con

dam

ine-

Balon

ne

Wim

mer

a

MDB

Rela

tive level of surf

ace w

ate

r use (

%) Historical climate Median 2030 climate

Low

M oderate

M oderately high

High

Very high

Extremely high

No simple measure of acceptable use

Region State Relative level of

use

Fraction of

MDB SW

Resource

Environmental

Assets

Change in average

period between

env. beneficial

floods

Wimmera VIC 55% 1% International 786%

Condamine-Balonne QLD 53% 6% International 384%

Murrumbidgee NSW 53% 18% National 188%

Goulburn-Broken VIC 50% 14% Regional 328%

Gwydir NSW 41% 3% International 77%

Namoi NSW 37% 4% Regional 26%

Murray NSW/VIC/SA 36% 22% Multiple International 155%

Campaspe VIC 36% 1% Regional 58%

Moonie QLD 34% 0% Regional 15%

Border Rivers NSW/QLD 34% 5% Regional 22%

Loddon-Avoca-Avoca VIC 32% 1% Regional 82%

Lachlan NSW 28% 5% National 71%

Macquarie NSW 24% 7% International 114%

Warrego QLD 12% 2% National 0%

Barwon-Darling NSW 11% 0% National 82%

Eastern Mount Lofty Ranges SA 5% 1% National 0%

Ovens VIC 1% 8% National 2%

Paroo QLD 0% 2% Multiple International 0%

Flows required to sustain ecosystems

Arthington et al. 2006

What is over allocation?

• Demands for water cannot all be met

• Conflict between environmental water demand and demand for

extraction

• Need to introduce concept of environmental assets, and values

to recognise fundamental trade-off with reference conditions

• Need to represent environmental water as a demand in the

same terms as other use – volume, timing, reliability

• Over allocation is where environmental and extractive demands

cannot both be met to the required reliability

Why can’t more water be used (max 50%)?

Daily flow (ML)

0

50000

100000

150000

200000

250000

300000

1940

1940

1941

1942

1943

1943

1944

1945

1946

1947

1947

1948

1949

1950

1951

1951

1952

1953

1954

1955

1955

1956

1957

1958

1958

1959

99,864

Total flow in an

unregulated river in

southern Australia used

for summer irrigation,

without floodplain

harvesting

…for environmental use or consumptive use.

Where are the conflicts in resource use?

Manageable water resource 1 – remove floods

Daily flow (ML)

0

50000

100000

150000

200000

250000

3000001940

1940

1941

1942

1943

1943

1944

1945

1946

1947

1947

1948

1949

1950

1951

1951

1952

1953

1954

1955

1955

1956

1957

1958

1958

1959

93,685 Removes 6% of the flow

Manageable water resource 2 – irrigation season

Daily flow (ML)

0

50000

100000

150000

200000

250000

3000001940

1940

1941

1942

1943

1943

1944

1945

1946

1947

1947

1948

1949

1950

1951

1951

1952

1953

1954

1954

1955

1956

1957

1958

1958

1959

56,646 Removes 44% of flow

Manageable water resource 3 – remove low flows

Daily flow (ML)

0

50000

100000

150000

200000

250000

3000001940

1940

1941

1942

1943

1943

1944

1945

1946

1947

1947

1948

1949

1950

1951

1951

1952

1953

1954

1954

1955

1956

1957

1958

1958

1959

44,945 Removes 55% of total flow

Manageable water resource, which can be used, is 45% of total flow

High level of use in many drier years

• Level of use >70 percent of total flow in 25 percent of years

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 10,000 20,000 30,000 40,000 50,000

Annual flow (GL)

Re

lative

le

ve

l o

f u

se

Uneven risk sharing

Steps to measuring over allocation

• Identify environmental assets, values, condition required

• Define environmental water demands and reliability (timing etc)

• Define extractive water demands and reliability

• Analyse through a range of scenarios if both extractive and

environmental demands can be met at required level of

reliability

• Ensure exposure to risk of reduced supply is shared evenly

• Over allocation is the extent (volume) to which combined

demands cannot be met

Simple example

Year 1 2 3 4 5 6 7 8 9 10

Resource (Gl/y) 500 100 1000 300 400 700 600 800 200 500

Extractive

demand (Gl/y)

200 200 100 200 200 200 200 150 200 200

Environmental

demand (Gl/y)

250 50 900 200 100 600 300 600 50 250

Over allocation

(Gl/y)

0 150 0 100 0 100 0 0 50 0

Sustainable extraction limit at 90% reliability is 100 Gl/y

Over allocated by 100 Gl/y

Conclusions

• Over allocation is subjective

• Must define environmental assets and their condition

• Over allocation is degree of conflict between demands

• The conflicts are often restricted in time – summer, droughts,

low flows, regulation of floods

• Can only be evaluated with detailed analysis of demands

through times and rules for entitlements

• Some simplified proportions of use may be possible for rivers of

the same class

www.csiro.au/mdbsy

Murray-Darling Basin Sustainable Yields Project

funded under the

Raising National Water Standards Program

of the

National Water Commission