Salinity - Impacts & Costs - Victoria

Dryland Salinity Impacts : Victoria overview
What, and how much, agricultural land occurs in areas at high risk from dryland salinity?
What biological resources occur in areas of high dryland salinity risk?
What water resources occur in areas of high dryland salinity risk?
What infrastructure occurs in areas of high dryland salinity risk?
Further information

Victoria

Dryland Salinity Impacts : Victoria overview

Impacts of shallow water tables and dryland salinity have been estimated using existing data relating to:

agricultural land use
gross margins for agricultural production
physical infrastructure
distribution of threatened flora and fauna
natural wetland habitat
water quality.

For all but water quality, impact assessments have been carried out by overlaying existing GIS themes on the depth to water table maps. Assessments are therefore based on current land use patterns, agricultural margins and habitat and species distributions. They also assume that best or worst case trends continue to apply and that there is no effective intervention to limit water table rises or increasing impact.

Table: Assets at high risk from salinity from shallow groundwater and under the worst-case scenario in Victoria:
Asset	Current	2020	2050
Agricultural land (ha)	555 000	1 170 000	2 800 000
Perennial vegetation (ha)	6 200	11 830	24 280
Railways (km)	131	303	952
Freeways and major roads (km)	808	1 541	3 597
Other roads (km)	3 088	6 513	17 326
Length of stream or perimeter of	10 121	18 146	34 599
Towns (number)	10	21	63
Ramsar wetlands* (number)	4	5	8

* Coastal wetlands have not been included in those at risk.

What, and how much, agricultural land occurs in areas at high risk from dryland salinity?

Area of agricultural land with shallow water tables

The area of agricultural land predicted to have shallow water tables increases from 0.55 Mha in 1998 to between 1.41 and 2.80 Mha in 2050 (for lower and upper limit trends, respectively). Land supporting pastures or grain crops (cereals, oilseeds, legumes) accounted for over 99% of these areas. The majority of the land on which shallow water tables are predicted to develop currently supports grazed pastures (0.55-1.80 Mha).

The area of grazing or pasture land affected by shallow water tables and salinity are greatest in the Glenelg-Hopkins, Goulburn-Broken, Corangamite and North Central regions with the upper limit trends (i.e. the worst case). Potential impacts on cropping land are greatest in the North Central and Goulburn regions.

Potential value of lost agricultural production

It is unlikely that the entire area of each DEM grid cell would be uniformly affected by shallow water tables and dryland salinity. Agricultural losses could be grossly overestimated if it was assumed that the entire grid cell was affected in this way. Therefore, two conservative assumptions have been made in estimating agricultural losses, namely:

plant growth and agricultural production is affected on only 25% of the area of grid cells with depth to water table of less than 2 m;
there is a 75% reduction in gross margin within these areas.

Spreadsheets used to calculate gross margins allow these assumptions to be varied.

Agricultural costs are predicted to increase from approximately $27 M/y to between $77 M/y and $166 M/y. Losses from pasture and cropping account for 95% of the current (predicted) loss in gross margin and between 80 and 82% of the loss in predicted gross margin in 2050. Although the area of horticultural land with shallow water tables is predicted to remain less than 1% of the State?s (dryland) agricultural land area, the high value of production means that there is predicted to be a large increase in the value of production lost due to shallow water tables.

Calculations suggest that nothing is done by horticulturalists to mitigate (the predicted) rising water tables. Given the value of production, this is considered to be most unlikely.

A breakdown of potential gross margin foregone for each CMA region and time period is given in presented in the Victorian Dryland Salinity Assessment 2000 Report. Agricultural losses are roughly in proportion to the areas of land in each CMA region with shallow water tables. They are predicted to be concentrated in the Glenelg-Hopkins, Goulburn-Broken, Corangamite and North Central CMA regions if trends follow the upper limit scenario or in the Glenelg-Hopkins, Goulburn-Broken and North Central CMA regions if they follow the lower limit scenario. Annual reductions in gross margins in each of the four potentially worst affected regions could amount to over $20M/y under the worst case trend scenario.

Agricultural losses are predicted to be concentrated in the Glenelg-Hopkins, Goulburn-Broken, Corangamite and North Central CMA regions if trends follow the worst case scenario or in the Glenelg-Hopkins, Goulburn-Broken and North Central CMA regions if they follow the best case scenario. Annual reductions in gross margins in each of the four potentially worst affected regions could amount to over $20M/y.

What biological resources occur in areas of high dryland salinity risk?

Wetland habitat

There is predicted to be a large expansion in the area of wetland habitat associated with land shallow water tables under the worst case trend scenario. The area of RAMSAR wetland in shallow water table areas is predicted to increase by over 30 000 ha during the next 20 years as lands surrounding the Western District lakes wetlands develop shallow water tables. The number of natural wetlands in landscapes with shallow water tables is predicted to increase to between 13 and 22% of all natural wetlands in the state by 2050. Wetlands in the Goulburn-Broken and Corangamite regions are expected to be the most affected, with over 40% of wetlands in each region predicted to be occupying landscapes with shallow water tables by 2050 under the worst case trend scenario.

Threatened flora and fauna

Estimates of the potential impacts of shallow water tables and dryland salinity have been made by identifying records of Victorian rare or threatened (VROT) classified species in areas predicted to have or develop shallow water tables. The number of Victorian rare or threatened classified plant species with records in shallow water tables areas is predicted to increase from 122 to between 196 and 346. The corresponding change for Victorian rare or threatened classified native fauna is from 269 to between 317 and 485 species. Up to 4-8% of all records of threatened flora in Victoria are predicted to be located in shallow water table areas by 2050 and 9-17% of all threatened fauna records.

More threatened species are currently associated with shallow water table areas in the Wimmera region than elsewhere in the state. The greatest long-term threat to such species appears to be in the Goulburn-Broken, Glenelg-Hopkins and Corangamite regions. Over 20% of these regions' threatened flora records and over 30% of their threatened fauna records are predicted to be located in areas of shallow water table by 2050 under the worst case trend scenario.

Changes in association between Victorian rare or threatened classified species and land predicted to develop under best and worst case trend scenarios.

The percentage of records of individual threatened species that are predicted to be located in areas of shallow water table in 2050 (worst case scenario) was determined to provide a further assessment of potential biodiversity impacts. Across the state, all records for 13 species of plant will be located in areas predicted to have shallow water tables. For 25 species of threatened fauna and 59 species of threatened flora, all records in at least one CMA region are predicted to fall within the shallow water table area by 2050. Under the worst case trend scenario, there are predicted to be five CMA regions (Corangamite, Glenelg-Hopkins, Goulburn-Broken, North Central and Wimmera) where at least 10 species of threatened plant or animal are predicted to have all of their records within the shallow water table area.

What water resources occur in areas of high dryland salinity risk?

Water resources

A two-three fold increase in the length of stream or perimeter of reservoir, lake or wetland located in areas of shallow water table is predicted over the coming 50 years. Under the worst case trend scenario, most of this increase is predicted to occur in the Corangamite, Glenelg-Hopkins, Goulburn-Broken and North Central regions. The proportional increase under this trend scenario was greater for the Port Phillip region (worst case trend scenario) than all other regions. If realised, this change would be expected to result in increased groundwater discharge to streams, greater salt wash off and increased stream salinity and salt load.

Current and future flow weighted stream salinities were estimated as part of the Victorian component of the MDBC Salinity Audit and has recently been supplemented by information for the Wimmera region. Data for the end of the major river systems are presented in the table below. The Goulburn, Campaspe and Wimmera Rivers are predicted to remain relatively fresh over the coming 50 years. This is considered to be at least in part due to dilution flows from major storages collecting water from higher rainfall, upper catchment areas. Stream salinity increases westwards across northern Victoria (to the Avoca River). Flow weighted salinity in the lower Loddon and Avoca Rivers either already or are predicted to exceed Murray-Darling Basin Commission benchmarks for water quality (800 and 1500 m S/cm).

Table: Current and predicted future flow weighted stream salinity at the end of the major Murray Basin river systems in Victoria.
Location	Current	2020	2050
	Flow weighted salinity (m S/cm)
Goulburn R upstream of Murray R	134	136	231
Broken R upstream of Murray R	114	231	968
Campaspe R upstream of Murray R	595	600	606
Loddon R downstream of Kerang Weir	871	883	903
Avoca R downstream of Marshes	1444	1468	2216
Wimmera R upstream of Lake Hindmarsh	680	684	691

Water quality is more variable across south-western Victoria and does not have a consistent pattern of increasing salinity either westwards or downstream. Flow weighted salinities in several of the major rivers (e.g. Barwon, Leigh, Woady Yalloak, Hopkins and Wannon) already exceed MDBC benchmarks and are generally greater than for streams in northern Victoria.

What infrastructure occurs in areas of high dryland salinity risk?

Asset	Current	2020	2050
Railways (km)	131	303	952
Freeways and major roads (km)	808	1 541	3 597
Other roads (km)	3 088	6 513	17 326
Towns (number)	10	21	63
Ramsar wetlands* (number)	4	5	8

Potential impacts of shallow water tables and dryland salinity on physical infrastructure in Victoria have been expressed in relation to transportation networks and rural towns. The figure below shows the change in the length of road and rail networks and number and area of rural towns predicted to be located in areas with shallow water tables. The length of road traversing shallow water table areas could increase from almost 4000 km currently to between 11 000 and 21 000 km in 2050. Up to 200 km of freeway and almost 3400 km of major road could be constructed on land that has or may develop shallow water tables. The length of railway could increase between four and seven-fold, from 131 km currently to 500-952 km in 2050. These changes, particularly for the road network, would be expected to greatly increase the maintenance costs incurred by local government and VicRoads.

The number of rural towns (not including provincial centres with populations exceeding 10 000) in Victoria located in areas predicted to have or develop shallow water tables could increase from 5 to between 28 and 63 in 2050.

Table: Victorian Towns with a dryland salinity risk

Towns with 500-1000 people

APOLLO BAY
AVENEL
BANNOCKBURN
EILDON
INDENTED HEAD
TIMBOON
VIOLET TOWN
WINCHELSEA
WYCHEPROOF
YEA

Towns with 1000-5000 people

ANGLESEA
BALLAN
BEAUFORT
BROADFORD
CASTERTON
CHARLTON
COBRAM
DROMANA
DRYSDALE
EUROA
GISBORNE
HEATHCOTE
KOO-WEE-RUP
LANCEFIELD
LORNE
MYRTLEFORD
NAGAMBIE
NUMURKAH
PAYNESVILLE
PORT FAIRY
ROMSEY
RUSHWORTH
TERANG
TORQUAY
YARRAWONGA