- Email: [email protected]
Land and stream salinity in Western Australia
Agricultural Water Management, 4 (1981) 11--18
11
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
L A N D A N D STREAM S A L I N I T Y
IN WESTERN A U S T R A L I A
R.M. HILLMAN Director of Engineering, Public Works Department, Western A u s t r a l i a . West Perth, W.A. 6005. 1
INTRODUCTION Dryland s a l i n i t y has been a threat to the land and water resources of the
south-west of Western A u s t r a l i a since the commencement of a g r i c u l t u r e in this State.
However i t is only in recent years that the seriousness of the problem
has become widely known and accepted within the community.
The phenomenon is
not r e s t r i c t e d to Western A u s t r a l i a ; i t is found in countries throughout the world, but i t is believed that in few other parts of the world is i t so evident or so widespread, and nowhere else is i t a cause f o r such general community concern.
Because of this concern the phenomenon has a t t r a c t e d r e l a t i v e l y great res-
earch e f f o r t in this State, and those working on the problem here are in a good position to exchange ideas and information with other concerned people from throughout the world.
For this reason i t is believed that Western Aus t r a lia provides
a suitable venue f o r the Seminar.
The papers, which were presented by s c i e n t i s t s
from a number of d i f f e r e n t countries, were chosen f o r the authors' p a r t i c u l a r expertise in s a l i n i t y and the relevance of that expertise to dryland s a l i n i t y , Dryland s a l i n i t y is manifest in each of the other States of A u s t r a l i a . also a s i g n i f i c a n t problem in the Great Plains region of North America.
I t is In
Canada i t occurs extensively in the p r a i r i e provinces of Manitoba, Saskatchewan and Alberta, and in the United States in the states of Montana, North and South Dakota ( M i l l e r et a l . ,
1976).
In t o t a l , approximately. O.8 m i l l i o n hectares (2
m i l l i o n acres) of farmland in this region is severely affected by saline seeps. Dryland s a l i n i t y is also said to occur in South Africa and Thailand, and i t probably exists - recognised or unrecognised - in other countries. The serious effects of dryland s a l i n i t y on farmlands and water resources in a l l these areas has stimulated extensive research in an e f f o r t to f i n d practical solutions to this complex problem.
Many of the phenomena associated with s a l t and
water movement through the soil under dryland a g r i c u l t u r e are s i m i l a r to those associated with such movement under i r r i g a t i o n .
I t was f e l t that the bringing
together of the group of engineers and s c i e n t i s t s at the Seminar and Workshop would provide an opportunity f o r a l l aspects of the problem to be discussed. 0378-3774/81/0000--0000/$02.50 @ 1981 Elsevier Scientific Publishing Company
12 2
HISTORYOF SALINITY IN WESTERNAUSTRALIA By overseas standards a g r i c u l t u r e in Western A u s t r a l i a is young.
150th anniversary of the f i r s t
Last year the
settlement by Europeans was celebrated.
other hand the land mass is very old.
On the
Over thousands of years a degree of e q u i l i -
brium had been reached in the s a l t cycle w i t h i n the hydrological cycle. troduction of a g r i c u l t u r e has upset t h i s e q u i l i b r i u m .
The in-
The r e s u l t is a dryland
s a l i n i t y problem in the south-west of the State which is of very serious proportions. The area of Western A u s t r a l i a is about 2.5 x 106km2 and i t s present p o l u l a t i o n is some 1.25 x 106 people.
Most of the population is to be found in the south-
west corner of the State (Fig. i ) w i t h i n an area of less than about 200 x 103km2, and w i t h i n which most of the State's a g r i c u l t u r a l development has taken place. %
LEGEN STATE FOREST(eucolypts) RAINFALL ISOHYETS Fig. 1.
5,0 .... o,
~o
,o,o
Scale of Kilomelres
The south-west region of Western A u s t r a l i a .
,~o
13
Settlement came late to Western A u s t r a l i a and f o r many years the population increased very slowly.
People of European o r i g i n in the population numbered only
about 180 x 103 by 1900.
The growth of the a g r i c u l t u r a l industry, in p a r a l l e l
with the p o l u l a t i o n , was at f i r s t Farming in the wheatbelt f i r s t
slow. commenced in the 500 to 600 mm r a i n f a l l region
and has gradually developed eastwards into the lower r a i n f a l l tural practices improved. whole of the State. first
regions as a g r i c u l -
By 1900 there were only 300 km2 sown to wheat in the
At present there are approximately 41 x 103km2.
A f t e r the
seventy years of settlement, clearing in the susceptible areas of the
wheatbelt would, no doubt, have provided evidence of s a l t leaching, but i t cert a i n l y could not then have been considered a problem.
/ To KALGOORLIE& The Goldfields PERTI 'Mundaring Weir Catchment Area
~'-Wellington Oam Catchment Area
"
r
~
LEGEND ~I Moj°r pipelines
• CRANBROOK
50
10 Scale
Fig. 2.
Sl0 100l of Kilometres
150!
Great southern towns, g o l d f i e l d s and a g r i c u l t u r a l water supply systems.
In t h i s State s a l i n i t y f i r s t
came to be recognised as a problem in connection
with the supply of b o i l e r feed water f o r railway steam locomotives. engineer, W.E. Wood was the f i r s t
to publish data on the phenomenon.
A railway In a paper
14
in the Journal of the Royal Society of Western Australia in 1924 he hypothesised as to the cause and cited examples he had found, or of which he had heard during the course of his work. Early examples were from Yorke Peninsula in South Austr a l i a in 1894; Northam and Toodyay in 1897 (Fig. 2); Goomalling in 1904 and Cranbrook in 1905. Manyothers followed. In the early years of the century concern was f e l t for the apparent increase in s a l i n i t y in the water stored in the reservoir behind the recently completed Mundaring Weir, some 40 km from Perth (Fig. 2).
The water from this reservoir
was to be pumped 584 km inland to supply the Kalgoorlie and eastern goldfields. A sequence of below average r a i n f a l l years followed the completion of the weir in 1902.
In an e f f o r t to improve the runoff, trees on an area of the
catchment were ringbarked.
As a result of this action there was an apparent in-
crease in the s a l i n i t y of water in the streams from the ringbarked area.
In 1908 a
decision was taken to cease ringbarking on unalienated land, to resume the ~lienated land whenever possible and to reforest the resumed lands.
A recommendation
was also made to scour from the bottom offtake valve of Mundaring Weir, but this was not accepted. T h i s course of action and the scouring recommendedhave many parallels with the action now being taken on the Wellington Catchment. In the years 1900 to 1930 agriculture expandedrapidly; over this period an estimated 50 x 103km2 was brought into production.
With this expansion dryland
s a l i n i t y emerged as a significant problem to agriculture and started to receive more detailed attention.
Expandingupon Wood's hypothesis, valuable contributions
to the understanding of the process were made by L.J.H. Teakle, G.H. Burvill and others from the Department of Agriculture over the decade prior to the start of the second world war. By 1929 i t had been recognised that: (i)
dryland s a l i n i t y was at least partly due to cyclic salt in r a i n f a l l ,
(ii)
i t was most prevalent in low r a i n f a l l areas,
(iii)
its occurrence was influenced by topography and soil type, and
(iv)
i t s basic cause was the removal of the natural vegetation.
As more and more land was released for agriculture the l i k e l y impact of dryland s a l i n i t y was frequently raised.
However, the demandfor new land was so great
that the adverse effects were overlooked with the result that the release of large contiguous blocks of land was condoned and the complete clearing of a l l natural vegetation occurred over extensive areas. Agriculture in the State went through a period of decline from about 1930 to the late 1940's. During this time as new salt patches developed dryland s a l i n i t y
15 continued to be regarded e s s e n t i a l l y as an a g r i c u l t u r a l problem. Mundaring Weir had been resolved.
The problem of
Railway operations were f a i r l y f l e x i b l e and
adequate sources of b o i l e r water supply could always be found. A second major period of expansion of a g r i c u l t u r e in the State started in the early 1950's and continued up to the mid-1960's.
As a consequence soil s a l i n i s a -
tion increased and increased concern over the problem followed.
Salt land sur-
veys to gauge the f u l l extent of affected land were carried out in 1955 and again in 1962, and, also in 1962, a major study of the cause of dryland s a l i n i t y was undertaken w i t h i n the Department of A g r i c u l t u r e . In p a r a l l e l with the a g r i c u l t u r a l expansion of the 1950's there was a demand f o r the provision of r e t i c u l a t e d water supplies to the country towns and farms. These supplies are provided from the major surface storages of Wellington and Mundaring reservoirs or from local catchments.
During this period there was
growth in the south-west i r r i g a t i o n areas and also an expansion in mining and industry.
The increased water demand gave r i s e to an increased awareness of the
e f f e c t that increasing s a l i n i t y was having on the water resources of the region. For the general public dryland s a l i n i t y progressed from being regarded as a problem of importance only to farmers, to a matter of concern to a l l and of v i t a l concern to the future development and prosperity of the State.
The increased
general public awareness of the problem has had two important results. Firstly,
i t has brought about a widespread recognition of the i n t e r - r e l a t i o n -
ship between land uses and t h e i r e f f e c t on the quantity and q u a l i t y of runoff. This has led to the introduction of more careful and sophisticated land use planning. Secondly, the need f o r more research both fundamental and applied has become obvious and this has led to a substantial increase in a c t i v i t y in this area. EFFECTS OF SALINITY IN WESTERN AUSTRALIA The seriousness of the s a l i n i t y problem in this State can be i l l u s t r a t e d by quoting some figures of the effects on farming and of the effects on resources of water. 3,1
Effects on Farming
Dryland s a l i n i t y has resulted in the loss of considerable areas of productive farmland.
In the most recent 1979 s a l t land survey by the Department of A g r i c u l -
ture, (Henschke, 1981) i t was found that there are 264 x 103 ha of once productive land in the south-west that are no longer suitable f o r a g r i c u l t u r e . represents 1.75% of a l l cleared land in the region.
This figure
The average increase has
16
been 7.8 x 103 ha yr -1 since 1955.
In two shires the r a t i o o f salt land to
cleared land is greater than 6%, in five other shires between 4% and 5%. Many other shires are also seriously affected. In most instances where land has been lost i t was land with the best s o i l , the most productive land on the farm. The lost land capitalised as i t was by clearing, f e r t i l i s a t i o n , fencing and other factors represents a considerable economic loss to individual farmers, to the State and the nation.
3.2
Effects on Water Resources
The south-west of Western A u s t r a l i a is an area w i t h r e l a t i v e l y resources.
l i m i t e d water
I t has been assessed t h a t w i t h i n the area, the surface water nomina-
l l y a v a i l a b l e f o r d i v e r s i o n , was approximately 2.6 x 109m3 y r -1 (Fig. 3). ever, of t h i s t o t a l
How-
135 x 106m3yr -1 or 5% are now saline (over 3000 mg L - 1 T S S ) ,
780 x 106m3yr -1 or 30% are brackish (1000 - 3000 mg L -1TSS) and 425 x 106m3yr -1 or 16% are marginal (500 - 1000 mg L - I TSS). divertible
This leaves only some 50% of the
surface water resource l a r g e l y unaffected and s t i l l
fresh.
Total Divertible Surface Water Resources : 2600 xlO6 m3yr'1
35xi06 m3 \ \
~
x
(3 ÷'x''
Fig. 3. D i v e r t i b l e surface water resources of the south-west of Western Australia.
17 Thus i t can be seen that the leaching of the s a l t s stored in the landscape has had a most serious e f f e c t on the q u a l i t y of the water resources in the region. The imPortance of the remaining d i v e r t i b l e resources which contain less than 1000 mg L - I TSS is appreciated when i t is recognised that 400 x 106m3yr- I or about 25% of the t o t a l remaining fresh and marginal resources are already used. addition i t has been estimated that a f u r t h e r 660 x 106m3yr- I ,
In
i . e . about 40% of
the t o t a l s in those categories, could be adversely affected by s a l i n i t y i f not c a r e f u l l y managed. Furthermore, environmental considerations may preclude the diversion of much of the nominally d i v e r t i b l e resources. To arrest and reverse the d e t e r i o r a t i o n of the q u a l i t y of these water resources, clearing controls have been introduced on f i v e important r i v e r catchments. first
The
of these was on the Wellington Catchment on the C o l l i e River (Fig. 2),
where controls were introduced in 1976.
In 1978 controls were introduced on four
other catchments. Wellington Reservoir on the C o l l i e River is the water storage with the greatest y i e l d in the south-west.
The average y i e l d of t h i s reservoir is I00 x 106m3yr- I
I t provides a water supply f o r i r r i g a t i o n on the coastal p l a i n and f o r town supply in the wheatbelt.
I t has been calculated that i f clearing controls had not
been introduced the average water q u a l i t y in the reservoir would have reached 1700 mg L- I TSS and that during dry cycles of weather the f i g u r e would have been much higher.
Even with clearing controls s a l i n i t y is expected to increase f o r
some time because there is a considerable time lag between clearing and the f u l l manifestation of the r e s u l t i n g s a l i n i t y .
The s a l i n i t y of the water in the res-
e r v o i r may reach an average of 11~0 mg L - I TSS. Similar conclusions could be drawn from studies of each of the other catchments over which clearing controls have been imposed. 4
RESEARCH ACTIVITIES The r e a l i s a t i o n of the seriousness and complexity of the problem has generated
considerable research in Western A u s t r a l i a over the l a s t i0 years.
This research
is being undertaken at a l l l e v e l s , t h e o r e t i c a l , fundamental and applied.
Broadly,
theoretical and fundamental research is being undertaken by the U n i v e r s i t i e s and the Commonwealth S c i e n t i f i c and I n d u s t r i a l Research Organisation. ment Departments have concentrated on applied research.
State Govern-
The number of organisa-
tions involved is quite large but research has benefited from the informal coordination and co-operation which has developed amongst the researchers. The helpful co-operation which has developed has had a major influence on the enthusiasm and c a l i b r e of the research which is being undertaken in'Western A u s t r a l i a . The a v a i l a b i l i t y
of basic data is always a problem when such complex and wide-
18 spread problems are involved.
The careful i n s t a l l a t i o n of gauging weirs,
piezometers and other equipment is now beginning to bear f r u i t and w i l l be i n valuable to the research e f f o r t in the coming years. 5
CONCLUSION I t is hoped that in t h i s short introductory paper some i n d i c a t i o n has been
given of the magnitude of dryland s a l i n i t y in Western A u s t r a l i a .
The f o l l o w i n g
papers, which were presented at the Seminar and discussed in Workshop sessions, cover a range of research a c t i v i t i e s and management strategies which are being undertaken to combat stream s a l i n i t y .
I t is hoped the papers and discussion
presented in these proceedings w i l l benefit the many people who are working in the f i e l d of dryland s a l i n i t y . 6
REFERENCES
Henschke, C.J., 1981. The 1979 Saltland Survey. J. Agric. West. Aust. in press). M i l l e r , M.R., Van der Pluym, H., Holm, H.M., Vasey, E.H., Adams, E.P. and Bahls, L.R., 1976. An overview of saline-seep programs in the States and Provinces of the Great Plains. In: "Regional Saline Seep Control Symposium Proceedings". B u l l . No. 1132, pp. 4-17. (Montana State Univ., Bozeman, Montana). Wood, W.E., 1924. Increase of s a l t in soil and streams f o l l o w i n g the destruction of the native vegetation. J. Roy. Soc. West. Aust. I0: 35-47.
11
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
L A N D A N D STREAM S A L I N I T Y
IN WESTERN A U S T R A L I A
R.M. HILLMAN Director of Engineering, Public Works Department, Western A u s t r a l i a . West Perth, W.A. 6005. 1
INTRODUCTION Dryland s a l i n i t y has been a threat to the land and water resources of the
south-west of Western A u s t r a l i a since the commencement of a g r i c u l t u r e in this State.
However i t is only in recent years that the seriousness of the problem
has become widely known and accepted within the community.
The phenomenon is
not r e s t r i c t e d to Western A u s t r a l i a ; i t is found in countries throughout the world, but i t is believed that in few other parts of the world is i t so evident or so widespread, and nowhere else is i t a cause f o r such general community concern.
Because of this concern the phenomenon has a t t r a c t e d r e l a t i v e l y great res-
earch e f f o r t in this State, and those working on the problem here are in a good position to exchange ideas and information with other concerned people from throughout the world.
For this reason i t is believed that Western Aus t r a lia provides
a suitable venue f o r the Seminar.
The papers, which were presented by s c i e n t i s t s
from a number of d i f f e r e n t countries, were chosen f o r the authors' p a r t i c u l a r expertise in s a l i n i t y and the relevance of that expertise to dryland s a l i n i t y , Dryland s a l i n i t y is manifest in each of the other States of A u s t r a l i a . also a s i g n i f i c a n t problem in the Great Plains region of North America.
I t is In
Canada i t occurs extensively in the p r a i r i e provinces of Manitoba, Saskatchewan and Alberta, and in the United States in the states of Montana, North and South Dakota ( M i l l e r et a l . ,
1976).
In t o t a l , approximately. O.8 m i l l i o n hectares (2
m i l l i o n acres) of farmland in this region is severely affected by saline seeps. Dryland s a l i n i t y is also said to occur in South Africa and Thailand, and i t probably exists - recognised or unrecognised - in other countries. The serious effects of dryland s a l i n i t y on farmlands and water resources in a l l these areas has stimulated extensive research in an e f f o r t to f i n d practical solutions to this complex problem.
Many of the phenomena associated with s a l t and
water movement through the soil under dryland a g r i c u l t u r e are s i m i l a r to those associated with such movement under i r r i g a t i o n .
I t was f e l t that the bringing
together of the group of engineers and s c i e n t i s t s at the Seminar and Workshop would provide an opportunity f o r a l l aspects of the problem to be discussed. 0378-3774/81/0000--0000/$02.50 @ 1981 Elsevier Scientific Publishing Company
12 2
HISTORYOF SALINITY IN WESTERNAUSTRALIA By overseas standards a g r i c u l t u r e in Western A u s t r a l i a is young.
150th anniversary of the f i r s t
Last year the
settlement by Europeans was celebrated.
other hand the land mass is very old.
On the
Over thousands of years a degree of e q u i l i -
brium had been reached in the s a l t cycle w i t h i n the hydrological cycle. troduction of a g r i c u l t u r e has upset t h i s e q u i l i b r i u m .
The in-
The r e s u l t is a dryland
s a l i n i t y problem in the south-west of the State which is of very serious proportions. The area of Western A u s t r a l i a is about 2.5 x 106km2 and i t s present p o l u l a t i o n is some 1.25 x 106 people.
Most of the population is to be found in the south-
west corner of the State (Fig. i ) w i t h i n an area of less than about 200 x 103km2, and w i t h i n which most of the State's a g r i c u l t u r a l development has taken place. %
LEGEN STATE FOREST(eucolypts) RAINFALL ISOHYETS Fig. 1.
5,0 .... o,
~o
,o,o
Scale of Kilomelres
The south-west region of Western A u s t r a l i a .
,~o
13
Settlement came late to Western A u s t r a l i a and f o r many years the population increased very slowly.
People of European o r i g i n in the population numbered only
about 180 x 103 by 1900.
The growth of the a g r i c u l t u r a l industry, in p a r a l l e l
with the p o l u l a t i o n , was at f i r s t Farming in the wheatbelt f i r s t
slow. commenced in the 500 to 600 mm r a i n f a l l region
and has gradually developed eastwards into the lower r a i n f a l l tural practices improved. whole of the State. first
regions as a g r i c u l -
By 1900 there were only 300 km2 sown to wheat in the
At present there are approximately 41 x 103km2.
A f t e r the
seventy years of settlement, clearing in the susceptible areas of the
wheatbelt would, no doubt, have provided evidence of s a l t leaching, but i t cert a i n l y could not then have been considered a problem.
/ To KALGOORLIE& The Goldfields PERTI 'Mundaring Weir Catchment Area
~'-Wellington Oam Catchment Area
"
r
~
LEGEND ~I Moj°r pipelines
• CRANBROOK
50
10 Scale
Fig. 2.
Sl0 100l of Kilometres
150!
Great southern towns, g o l d f i e l d s and a g r i c u l t u r a l water supply systems.
In t h i s State s a l i n i t y f i r s t
came to be recognised as a problem in connection
with the supply of b o i l e r feed water f o r railway steam locomotives. engineer, W.E. Wood was the f i r s t
to publish data on the phenomenon.
A railway In a paper
14
in the Journal of the Royal Society of Western Australia in 1924 he hypothesised as to the cause and cited examples he had found, or of which he had heard during the course of his work. Early examples were from Yorke Peninsula in South Austr a l i a in 1894; Northam and Toodyay in 1897 (Fig. 2); Goomalling in 1904 and Cranbrook in 1905. Manyothers followed. In the early years of the century concern was f e l t for the apparent increase in s a l i n i t y in the water stored in the reservoir behind the recently completed Mundaring Weir, some 40 km from Perth (Fig. 2).
The water from this reservoir
was to be pumped 584 km inland to supply the Kalgoorlie and eastern goldfields. A sequence of below average r a i n f a l l years followed the completion of the weir in 1902.
In an e f f o r t to improve the runoff, trees on an area of the
catchment were ringbarked.
As a result of this action there was an apparent in-
crease in the s a l i n i t y of water in the streams from the ringbarked area.
In 1908 a
decision was taken to cease ringbarking on unalienated land, to resume the ~lienated land whenever possible and to reforest the resumed lands.
A recommendation
was also made to scour from the bottom offtake valve of Mundaring Weir, but this was not accepted. T h i s course of action and the scouring recommendedhave many parallels with the action now being taken on the Wellington Catchment. In the years 1900 to 1930 agriculture expandedrapidly; over this period an estimated 50 x 103km2 was brought into production.
With this expansion dryland
s a l i n i t y emerged as a significant problem to agriculture and started to receive more detailed attention.
Expandingupon Wood's hypothesis, valuable contributions
to the understanding of the process were made by L.J.H. Teakle, G.H. Burvill and others from the Department of Agriculture over the decade prior to the start of the second world war. By 1929 i t had been recognised that: (i)
dryland s a l i n i t y was at least partly due to cyclic salt in r a i n f a l l ,
(ii)
i t was most prevalent in low r a i n f a l l areas,
(iii)
its occurrence was influenced by topography and soil type, and
(iv)
i t s basic cause was the removal of the natural vegetation.
As more and more land was released for agriculture the l i k e l y impact of dryland s a l i n i t y was frequently raised.
However, the demandfor new land was so great
that the adverse effects were overlooked with the result that the release of large contiguous blocks of land was condoned and the complete clearing of a l l natural vegetation occurred over extensive areas. Agriculture in the State went through a period of decline from about 1930 to the late 1940's. During this time as new salt patches developed dryland s a l i n i t y
15 continued to be regarded e s s e n t i a l l y as an a g r i c u l t u r a l problem. Mundaring Weir had been resolved.
The problem of
Railway operations were f a i r l y f l e x i b l e and
adequate sources of b o i l e r water supply could always be found. A second major period of expansion of a g r i c u l t u r e in the State started in the early 1950's and continued up to the mid-1960's.
As a consequence soil s a l i n i s a -
tion increased and increased concern over the problem followed.
Salt land sur-
veys to gauge the f u l l extent of affected land were carried out in 1955 and again in 1962, and, also in 1962, a major study of the cause of dryland s a l i n i t y was undertaken w i t h i n the Department of A g r i c u l t u r e . In p a r a l l e l with the a g r i c u l t u r a l expansion of the 1950's there was a demand f o r the provision of r e t i c u l a t e d water supplies to the country towns and farms. These supplies are provided from the major surface storages of Wellington and Mundaring reservoirs or from local catchments.
During this period there was
growth in the south-west i r r i g a t i o n areas and also an expansion in mining and industry.
The increased water demand gave r i s e to an increased awareness of the
e f f e c t that increasing s a l i n i t y was having on the water resources of the region. For the general public dryland s a l i n i t y progressed from being regarded as a problem of importance only to farmers, to a matter of concern to a l l and of v i t a l concern to the future development and prosperity of the State.
The increased
general public awareness of the problem has had two important results. Firstly,
i t has brought about a widespread recognition of the i n t e r - r e l a t i o n -
ship between land uses and t h e i r e f f e c t on the quantity and q u a l i t y of runoff. This has led to the introduction of more careful and sophisticated land use planning. Secondly, the need f o r more research both fundamental and applied has become obvious and this has led to a substantial increase in a c t i v i t y in this area. EFFECTS OF SALINITY IN WESTERN AUSTRALIA The seriousness of the s a l i n i t y problem in this State can be i l l u s t r a t e d by quoting some figures of the effects on farming and of the effects on resources of water. 3,1
Effects on Farming
Dryland s a l i n i t y has resulted in the loss of considerable areas of productive farmland.
In the most recent 1979 s a l t land survey by the Department of A g r i c u l -
ture, (Henschke, 1981) i t was found that there are 264 x 103 ha of once productive land in the south-west that are no longer suitable f o r a g r i c u l t u r e . represents 1.75% of a l l cleared land in the region.
This figure
The average increase has
16
been 7.8 x 103 ha yr -1 since 1955.
In two shires the r a t i o o f salt land to
cleared land is greater than 6%, in five other shires between 4% and 5%. Many other shires are also seriously affected. In most instances where land has been lost i t was land with the best s o i l , the most productive land on the farm. The lost land capitalised as i t was by clearing, f e r t i l i s a t i o n , fencing and other factors represents a considerable economic loss to individual farmers, to the State and the nation.
3.2
Effects on Water Resources
The south-west of Western A u s t r a l i a is an area w i t h r e l a t i v e l y resources.
l i m i t e d water
I t has been assessed t h a t w i t h i n the area, the surface water nomina-
l l y a v a i l a b l e f o r d i v e r s i o n , was approximately 2.6 x 109m3 y r -1 (Fig. 3). ever, of t h i s t o t a l
How-
135 x 106m3yr -1 or 5% are now saline (over 3000 mg L - 1 T S S ) ,
780 x 106m3yr -1 or 30% are brackish (1000 - 3000 mg L -1TSS) and 425 x 106m3yr -1 or 16% are marginal (500 - 1000 mg L - I TSS). divertible
This leaves only some 50% of the
surface water resource l a r g e l y unaffected and s t i l l
fresh.
Total Divertible Surface Water Resources : 2600 xlO6 m3yr'1
35xi06 m3 \ \
~
x
(3 ÷'x''
Fig. 3. D i v e r t i b l e surface water resources of the south-west of Western Australia.
17 Thus i t can be seen that the leaching of the s a l t s stored in the landscape has had a most serious e f f e c t on the q u a l i t y of the water resources in the region. The imPortance of the remaining d i v e r t i b l e resources which contain less than 1000 mg L - I TSS is appreciated when i t is recognised that 400 x 106m3yr- I or about 25% of the t o t a l remaining fresh and marginal resources are already used. addition i t has been estimated that a f u r t h e r 660 x 106m3yr- I ,
In
i . e . about 40% of
the t o t a l s in those categories, could be adversely affected by s a l i n i t y i f not c a r e f u l l y managed. Furthermore, environmental considerations may preclude the diversion of much of the nominally d i v e r t i b l e resources. To arrest and reverse the d e t e r i o r a t i o n of the q u a l i t y of these water resources, clearing controls have been introduced on f i v e important r i v e r catchments. first
The
of these was on the Wellington Catchment on the C o l l i e River (Fig. 2),
where controls were introduced in 1976.
In 1978 controls were introduced on four
other catchments. Wellington Reservoir on the C o l l i e River is the water storage with the greatest y i e l d in the south-west.
The average y i e l d of t h i s reservoir is I00 x 106m3yr- I
I t provides a water supply f o r i r r i g a t i o n on the coastal p l a i n and f o r town supply in the wheatbelt.
I t has been calculated that i f clearing controls had not
been introduced the average water q u a l i t y in the reservoir would have reached 1700 mg L- I TSS and that during dry cycles of weather the f i g u r e would have been much higher.
Even with clearing controls s a l i n i t y is expected to increase f o r
some time because there is a considerable time lag between clearing and the f u l l manifestation of the r e s u l t i n g s a l i n i t y .
The s a l i n i t y of the water in the res-
e r v o i r may reach an average of 11~0 mg L - I TSS. Similar conclusions could be drawn from studies of each of the other catchments over which clearing controls have been imposed. 4
RESEARCH ACTIVITIES The r e a l i s a t i o n of the seriousness and complexity of the problem has generated
considerable research in Western A u s t r a l i a over the l a s t i0 years.
This research
is being undertaken at a l l l e v e l s , t h e o r e t i c a l , fundamental and applied.
Broadly,
theoretical and fundamental research is being undertaken by the U n i v e r s i t i e s and the Commonwealth S c i e n t i f i c and I n d u s t r i a l Research Organisation. ment Departments have concentrated on applied research.
State Govern-
The number of organisa-
tions involved is quite large but research has benefited from the informal coordination and co-operation which has developed amongst the researchers. The helpful co-operation which has developed has had a major influence on the enthusiasm and c a l i b r e of the research which is being undertaken in'Western A u s t r a l i a . The a v a i l a b i l i t y
of basic data is always a problem when such complex and wide-
18 spread problems are involved.
The careful i n s t a l l a t i o n of gauging weirs,
piezometers and other equipment is now beginning to bear f r u i t and w i l l be i n valuable to the research e f f o r t in the coming years. 5
CONCLUSION I t is hoped that in t h i s short introductory paper some i n d i c a t i o n has been
given of the magnitude of dryland s a l i n i t y in Western A u s t r a l i a .
The f o l l o w i n g
papers, which were presented at the Seminar and discussed in Workshop sessions, cover a range of research a c t i v i t i e s and management strategies which are being undertaken to combat stream s a l i n i t y .
I t is hoped the papers and discussion
presented in these proceedings w i l l benefit the many people who are working in the f i e l d of dryland s a l i n i t y . 6
REFERENCES
Henschke, C.J., 1981. The 1979 Saltland Survey. J. Agric. West. Aust. in press). M i l l e r , M.R., Van der Pluym, H., Holm, H.M., Vasey, E.H., Adams, E.P. and Bahls, L.R., 1976. An overview of saline-seep programs in the States and Provinces of the Great Plains. In: "Regional Saline Seep Control Symposium Proceedings". B u l l . No. 1132, pp. 4-17. (Montana State Univ., Bozeman, Montana). Wood, W.E., 1924. Increase of s a l t in soil and streams f o l l o w i n g the destruction of the native vegetation. J. Roy. Soc. West. Aust. I0: 35-47.