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Hydrology of Lake Eyre, Australia: El Niño link
Palaeogeography, Palaeoclimatology, Palaeoecology, 84 (1991): 87-98 Elsevier Science Publishers B.V., Amsterdam
87
Hydrology of Lake Eyre, Australia: E1 Nifio link Vincent Kotwicki a and Peter Isdale b
aWater Resources Branch, Engineering and Wa'ter Supply Department, Box 1751, Adelaide, S.A. 5001, Australia bAustralian Institute of Marine Science, PMB No. 3, Townsville M.C., Qld. 4810, Australia (Received 4 November, 1988; revised and accepted 13 July, 1990)
ABSTRACT Kotwicki, V. and Isdale, P., 1991. Hydrology of Lake Eyre, Australia: El Nifio link. Palaeogeogr., Palaeoclimatol., Palaeoecol., 84: 87-98. All major ephemeral rivers of Australia lie in the Lake Eyre basin. Dry for years, on occasions they carry enormous floods, with annual volumes of 40 km 3 and instantaneous discharges of the order of 30,000 m 3 s - 1. Mean annual runoff of the basin is 4 km 3 or 3.5 mm, significantly less than the 57 mm for the whole of Australia. This paper examines Lake Eyre and its drainage basin, describing the historical hydrology of the catchment, both in terms of instrument records and inflows hindcast using a model based on the technique of coral fluorescence palaeohydrological reconstruction. Coral fluorescence is a function of nearby-river discharge, and can be used to reconstruct annual river outputs beyond the instrument period. The Burdekin River catchment runoff history is strongly paralleled by the volumes of Lake Eyre inflows during the period of common reliable instrument gaugings. The Burdekin runoff data have been extended back to 1735 A.D. using the correlation between river discharge and annual growth-band fluorescence in an old coral from Pandora Reef, off the North Queensland coast. For the instrument period 1952 to 1980, 73% of the variance between coral fluorescence and Burdekin discharge is common. During the period 1949-1980, 41% of the variance between coral fluorescence and Lake Eyre inflow data is common. Modelled inflows to Lake Eyre for the period 1885-1948 are based on the latter data set.
Introduction A u s t r a l i a has the d u b i o u s d i s t i n c t i o n o f being p r e s e n t l y the m o s t lakeless a n d waterless continent. Salt lakes ( " d r y l a k e s " w o u l d be p r o b a b l y a m o r e a c c u r a t e d e s i g n a t i o n ) are, however, plentiful a n d in recent years they have received c o n s i d e r a b l e a t t e n t i o n ( J o h n s o n , 1980; Bowler, 1981, 1986; D e D e c k k e r , 1983, 1988). T h e largest o f them, L a k e Eyre - - in fact the largest e p h e m e r a l lake in the w o r l d - - w h i c h as Bowler (1981) observes " h a s its o w n e n i g m a t i c f a s c i n a t i o n to l i m n o l o g i s t s the w o r l d o v e r " , was c o n s i d e r e d p e r m a n e n t l y d r y since its d i s c o v e r y in 1840 until its first r e c o r d e d filling in 1949. In the d e c a d e s t h a t followed, fillings o f L a k e Eyre were still c o n s i d e r e d as isolated, u n i q u e a n d i n d e p e n d e n t events. O n l y recently have they 0031-0182/91/$03.50
been l o o k e d at as a p r e d i c t a b l e m a n i f e s t a t i o n o f the w o r l d - w i d e a t m o s p h e r i c a n d oceanic circulation, o f which the E1 N i f i o - S o u t h e r n Oscillation ( E N S O ) is one o f the m o s t significant p h e n o m e n a . A l l a n (1985) suggested t h a t L a k e Eyre floods are a physical m a n i f e s t a t i o n o f s t r o n g a n d positive S o u t h e r n Oscillation phases a n d are usually o u t o f p h a s e with the Pacific D r y Z o n e rainfall a n d El Nifio events. R o p e l e w s k i a n d H a l p e r t (1987) investigated the links between E N S O a n d large-scale p r e c i p i t a t i o n p a t t e r n s a n d identified 17 global core regions t h a t ~tppear to have a clear E N S O - p r e c i p i t a t i o n relationship. Five o f those are located in A u s t r a l i a a n d two o f them, eastern A u s t r a l i a a n d central A u s t r a l i a , c o v e r the entire L a k e Eyre basin. M a s s i v e corals f r o m the G r e a t Barrier R e e f c o n t a i n sequences o f skeletal fluorescence which
© 1991 - - Elsevier Science Publishers B.V.
88
V. KOTWlCKI AND P. ISDALE
can be measured as proxy records of adjacent river discharge (Isdale, 1984). These records, for the past several centuries, are capable of resolving hydrological events a few months apart. We consider, the Burdekin River (Fig.l), whose western basin boundary is contiguous with the eastern
~ ~
_
boundary of the Lake Eyre basin. Coral cores from Pandora reef, lying in the path of the river plume, can be used to reconstruct the palaeohydrology of the river system. Land-derived organic compounds trapped by the growing coral skeleton fluoresce strongly under ultra-violet light. The
BURCHEKIN VER Camooweal
QUEENSLAND •
km 0 , 800 km
MT. ISA
NORTHERN TERRITORY ~-,=~---'~~ALICE SPRINGS/~o ~ Hermannsbur(
Glengyle
~ ....
lackall
~onkira
'~ H o r s e s h o e ~"' 8end • .~..~p S I M P S O N • DALHOUSIE ~o SPRINGS , Country
I
AUSTRALIA~ Innamincka
COOBER PEDY ake
Lake
Frome
NEW SOUTH WALES
BRISBANE SYDNEY URNE
km0 t,
100 200 I = ( SCALE
300 km I
Fig.l. Topographic features of the Lake Eyre Basin. Inset maps show the regional extent of the modern Lake Eyre Basin and the underlying Great Artesian Basin.
HYDROLOGY OF LAKE EYRE, AUSTRALIA: EL NII~O LINK
fluorescence intensity is correlated with discharge of the adjacent river (Isdale, 1984; Boto and Isdale, 1985). The core used in this study was measured on a custom-built machine at the Australian Institute of Marine Science. This instrument illuminates the core with long-wave ultraviolet light and records fluorescence intensity within the core as the optical sensors scan its length. Using the annual density bands in the" coral core as a temporal reference, a "yearly" time-series of fluorescence intensity was constructed for the period 17351980.
Lake Eyre basin Lake Eyre is the terminal point of the great continental drainage system which spreads over 1.14 × 106 km 2 of arid central Australia. The Lake Eyre basin is mostly flat with extensive areas of sandy and stony deserts. There are regions with some relief near its boundaries, but only 30% of the area is elevated more than 250 m a.s.1. Catchment area to lake surface area ratio AC/AL = 118, significantly more than for most major closeddrainage systems in the world, and virtually identical to that of Lake Chad ( A C / A L = 1 2 0 ) in Africa. Some hydrological parallels could be drawn between both lakes: Lake Chad has a basin of 2.5 × 106 km 2, about double the size of the Lake Eyre basin, its surface area is 20,830 km 2 and its volume 72 km 3, about twice the size of Lake Eyre in 1974. Both lakes are subject to similar evaporation rates (2000 mm y r - 1) but the Lake Chad basin receives some 500 mm y r - 1 of rainfall, about twice that of the Lake Eyre basin. In effect, the Chari River, Lake Chad's main tributary, carries on average 40 (19-54) km 3 yr 1, compared to 2.4 (0-25) km 3 yr -~ of the Diamantina River, the main tributary of Lake Eyre. As a result, Lake Eyre dries up after periodic floods and Lake Chad remains permanent, despite significant water-level fluctuations.
Climate The Lake Eyre basin lies in the arid zone which covers some 60% of Australia. However, Gentilli (1972) demonstrates that the aridity of this region
89
does not equal that of the Sahara or Namib and that even a slight increase in rainfall would transform it into a semi-arid environment. It may be helpful to visualize here what a deficiency o f water is. The Lake Eyre basin, which covers 0.8% of the Earth's land area or 4.3% of the areas without outflow to the sea, receives some three times less rainfall than the world average and is subject to some three times more intense evaporation. Although these figures may appear at the first glance not very significant, they entail far-reaching consequences. If the amount of the fresh liquid water on Earth were distributed uniformly by areal proportions, the Lake Eyre basin would contain some 50 times more water flowing in rivers and 200 times more water stored in lakes than it currently does (Kotwicki, 1991). The average annual temperature varies from 21°C in the south of the basin to 24°C in the north, and the average maximum temperatures are 18°C and 24°C respectively in July, and 36°C and 39°C in January. The annual hours of sunshine vary from 3250 to over 3500, and the average global radiation is 600 mWh cm-2 day-1 Large parts of the Lake Eyre basin are poorly instrumented, but it is estimated that an area of some 5 x 105 km 2 receives less than 150mm of rainfall per year on average. The highest rainfalls, with annual averages of about 400 ram, occur in the northern and eastern margins, where rainfall is received from the southern edges of the summer monsoon. However, this region lies barely on the periphery of the planetary monsoon system, and the Australian monsoon is erratic both in space and time (Allan, 1985). The mean annual evaporation as measured by Class A evaporation pans ranges from 3600 mm for the central and southwestern part of the basin to 2400 mm for its eastern edge. The pan coefficient which converts pan data into evaporation from large water surfaces is of the order of 0.6 in the Lake Eyre area. The annual evaporation rate for the filled Lake Eyre ranges from 1800 to 2000 mm (Tetzlaff and Bye, 1978). Some indication of the evaporation rate from the dry lake floor (excluding the salt crust) has been given by Allison and Barnes (1985), who found a mean value of 1 7 0 m m y r -1 for
90
nearby Lake Frome. Ullman (1985) calculated the net evaporation rate from the salt-covered surface of Lake Eyre at between 9 and 28 mm yr- ~. Woods et al. (1988) estimate that evaporation from shallow water tables fed by vertical leakage from the Great Artesian Basin near Lake Eyre is of the order of 0.5-10 mm yr-~ in unfractured areas. Groundwater Most of the Lake Eyre basin overlies the Great Artesian Basin which covers an area of 1.7 x 1 0 6 km 2 and is one of the largest in the world. Aquifers are formed from porous sandstones of the Triassic, Jurassic and Cretaceous, which crop out along the Great Dividing Range and are up to 3000 m deep in its central part. From the mountainous recharge zone, water percolates very slowly towards the terminal base level of Lake Eyre, reaching this area after a calculated travel time of up to three million years (Thompson and Barnett, 1985). Intakes along the arid western rim make only a minor contribution. Apart from natural vertical leakage through the confining beds over the entire basin, natural discharge occurs from some 600 springs located in 11 groups along the western and southern boundaries of the basin, many of which appear to be fault controlled. Flows from the mound springs amount to 0.03 km 3 yr-~ and are thought to be only a minor discharge component. Artificial withdrawal from the basin is around 0.5 km 3 yr -~, diminishing steadily from around 0.7 km 3 in 1915. Measured flows from springs range from 0.0001 to 0.23 m 3 s- 1 totalling around 1 m 3 s- 1. Salinities range from 700 to 1400 g m -3, pH from 7.1 to 8.0 and water temperature from 30 to 40°C (Kotwicki, 1988). Williams and Holmes (1978) and Holmes et al. (1981) correlated measured spring discharges with the area of swamp vegetation which they support. The first study found that in the Dalhousie region the spring water is dissipated by a mean evaporative flux of 6.5 mm day-~, and the second, concerned with springs west of Lake Eyre found the measured swamp areas anomalously small, requiring a presumed evaportranspiration rate of more than 10 mm day-1. It was concluded that signifi-
V. KOTWICKI AND P. ISDALE
cant evaporation must occur from bare ground, beneath which the water table is sufficiently shallow to supply water by upward capillary rise.
Tributaries of Lake Eyre Mabbutt (1977) notes that the drainage system of Lake Eyre is exceptional for the persistence of an extensive network, despite its inclusion in the driest parts of the continent. This is a result of the favourable structural disposition of more effectively watered peripheral uplands combined with centripetal lowland slopes on weak and generally impervious rocks, leading to the downfaulted terminal basin. Much of this drainage is disconnected as a relict from linked river systems which developed under higher rainfall conditions and which became disorganised, under the present arid climate. The lake is fed mainly by its eastern tributaries, the Cooper Creek and the Diamantina and Georgina rivers system, whose flow data are shown in Table 1. Significant runoff originates in the desert west of the basin, which is drained by the Neales and the Macumba. Under the current climatic conditions only some 68% of the basin contributes water to the lake - - although in pre-Quaternary time, under more moderate and wetter conditions, drainage from the Simpson Desert and Finke River catchments would have contributed also. All streams are characterised by extreme variation in discharge and flow duration. Mean annual runoff of the basin is 4 km 3 or 3.5 mm in depth, the lowest of any major drainage system in the world. This is significantly less than the 57 mm for the whole of Australia and only 1.5% of the mean annual runoff of all the land areas of the world, estimated as 247 mm. The aridity of the basin is more graphically demonstrated by its specific yield of only 10 m 3 km -2 day-~ in comparison to the Nile or the Amazon which have specific yields of 115 and 2200 m 3 kin- 2 day- 1, respectively. In arid central Australia 15-20 mm of rain of moderate intensity can cause a flow in minor streams that lasts only for an hour or two. Such a flow may occur as often as five times each year. However, about 50 mm is needed for a full channel flow and such falls can be expected less frequently
91
HYDROLOGY OF LAKE EYRE, AUSTRALIA: EL Nl/'qO LINK
TABLE 1 Tributaries of Lake Eyre River and location of gauging station Cooper at Currareva Cooper at Innamincka Cooper at its mouth Georgina at Roxborough Downs Diamantina at Birdsville Diamantina at its mouth Western tributaries
Maximumflow Annual flow Mean annual flow Catchmentarea (m3 s - 1) (kin3) (kin~) (kin2)
Annual runoff (mm)
Timeriver dry (%)
5400 3700 1000"
15.0 11.5 4.0
3.4 2.1 0.6
150,000 237,000 306,000
22 9 2
46 62 >95
3800
6.3
1.2
82,000
14
55
4700
10.6
1.4
115,000
12
38
2000* 30,000*
24.0 10.0
2.4 0.7
365,000 206,000
6 3
90 >95
*estimate.
than once a year. Major floods in the Lake Eyre basin result from annual rainfalls which exceed 500 ram: the runoff coefficient in such years approaches 0.05. Eastern tributaries Eastern tributaries of Lake Eyre originate in more humid areas and flow quite frequently, however, only a small proportion of these flows reach Lake Eyre, due to very high transmission losses. The Cooper Creek for example can lose up to 10 v m 3 k i n - 1 in its central reach, filling innumerable salt lakes and interdune corridors of the Tirari Desert. Usually the Cooper Creek terminates at the Coongie Lakes (Lloyd and Balla, 1986, Kotwicki, 1988; Hacker, 1988; Reid and Gillan, 1988), the only permanent wetlands within the 5 × 1 0 6 km 2 area that comprises arid central Australia. The Cooper Creek only reaches Lake Eyre on average, once in six years. The transmission losses of the Diamantina River are usually much lower. The mean velocity of floods is 12.5 km day - 1 for the Diamantina and 3.1 km d a y - 1 for the Cooper. Water quality analyses in the central reaches of the main tributaries (Glatz, 1984) show that the mean annual inflow of 4 k m 3 transfers some 2.5x 105 t of salt into the lake, some 0 . 2 t k m - 2 y r -1 in comparison to the world average of 2 6 t km -2 yr -~. On this basis, the
period of accumulation represented by existing salt crust appears to be as short as 1600 yr. Mabbutt (1977) details the possible causes of evident salt losses, discussed also in Duffy and A1-Hassan (1988). The load of suspended solids is of the order of 1.5x 1 0 6 t y r -1, the equivalent of a 0.15ram layer over the lake. The specific suspended sediment load is 1.5 t km -2 yr -1, very low in comparison to the world average, of 9 0 t km - 2 y r -1 (Walling and Webb, 1987). Western tributaries The hydrology of the western tributaries is largely unknown. Several major rivers carry water infrequently, possibly only once in ten years. Flood volumes can be, however, enormous: for example in 1984 and in 1989 Lake Eyre received some 8 km 3 from western tributaries in three days, which implies discharges of the order of 30,000 m3s - t, or one-sixth that of the Amazon.
L a k e Eyre
Lake Eyre, whose lowest parts lie 15.2 m below sea level, consists of two sections: Lake Eyre North and Lake Eyre South,joined by the narrow Goyder Channel. The morphometric parameters of both lakes are shown in Table 2. Lake Eyre North was a permanent saline lake from 5000 to 10,000 years
92
V. KOTWlCKI AND P. ISDALE
TABLE 2 Morphometric parameters of Lake Eyre at -9.5 m AHD Parameters
Lake Eyre North
Lake Eyre South
Maximumlength, Im, (km) Maximumeffectivelength, Ira,, (km) Maximum width, Wm~x,(km) Direction of main axes Area, A, (km2) Mean width, Wm=A Lm- 1 (kin) Maximum depth, dm~x,(m) Volume, V, (km3) Mean depth, din,(m) Development of volume, Dv= 3dindma~-1 Shoreline, L, (km) Development of shoreline, DL= L (2~/nA)- 1
144 144 77 NNW 8430 59 5.7 27.7 3.3
64 64 24 NE 1260 20 3.7 2.4 1.9 1.5 328 2.6
ago and entered a playa phase between 5000 and 3000 years ago (Gillespie et al., 1991). A salt crust up to 460 mm thick covers the southern part of Lake Eyre North. The 4 x 10a t of salt deposited in the lake (Bonython, 1955) dissolve completely at times of major inflows (Dulhunty, 1974, 1978). The origin of this salt is a matter of considerable discussion, as the possible sources are very diverse ranging from marine aerosol transport ("cyclic salt") to rock weathering and groundwater discharge from aquifers deposited during the Cretaceous marine transgression that inundated central Australia. These and related issues are discussed in Bonython (1955), Dulhunty (1974, 1978, 1987), De Deckker (1983), Gunn and Fleming (1984), Allan et al. (1986), Chivas et al. (1991) and Herczeg and Lyons (1991). The presence of several old beach lines, 0.7, 1.6 and 2.8 m above the 1974 water level, indicate the occurrence of previous unrecorded major inflows (Dulhunty, 1975). The term "full" should therefore be used cautiously in relation to Lake Eyre. The above levels would represent approximate storages of 35 km 3, 48 km 3 and 67 km 3 respectively and the potential available storage to sea-level is more than 200 km 3, i.e. almost seven times greater than the 1974 storage. Fillings of Lake Eyre
L a k e Eyre lies in a remote and desolate area. Despite the current level of interest in the lake and
1.7
1390 4.3
its hydrology, very little data on its fillings have been collected, and many minor floodings escape attention.
Palaeohydrology Bowler (1981) notes that a longer period of constant filling of Lake Eyre occurred probably in the late Pleistocene, during a wetter climate in southern Australia, between about 45,000 and 25,000 yr B.P. This was followed by a phase of lake contraction, dune building and desiccation. Since European occupation, the climate has been almost equivalent to that of the driest phases of the last 10,000 years.
Recorded fillings The existence of water in Lake Eyre was first reported by Ross in 1869 and then by Halligan in 1922, however, their reports were dismissed as observation errors. Madigan who explored the area after a long drought in 1929 was convinced that the lake is permanently dry. The first reliable record of filling was in 1949-1950, when Lake Eyre North reached a peak storage of 21 km 3 (Lake Eyre Committee, 1955). This was followed by a series of minor floodings in 1953, 1955, 1956, 1957, 1958, 1959, 1963, 1967 and 1971, leading to a most significant flood event which began in 1973, reached its peak in 1974 and persisted until 1977. Lake Eyre North reached its highest recorded level
HYDROLOGY
OF
LAKE
EYRE,
AUSTRALIA:
EL
NI/~O
93
LINK
of - 9 . 0 9 m A H D in June 1974, and the equilibrium level of - 9 . 5 m A H D between both lakes was achieved in October 1974. The peak combined storage was 32.5 km 3. The last decade brought two unexpected events. The filling of 1984 with a total volume of 10 km 3 was a relatively minor one, but it proved that the western tributaries can fill Lake Eyre in a matter of days. Lake Eyre South this time filled first - an event never previously recorded and considered to be extremely unlikely - - and overflowed to Lake Eyre North (Allan et al., 1986). In 1989 this event was repeated, coinciding with the filling of the second largest Australian playa, Lake Torrens, which filled for the first time since 1878. The wet spell continued into 1990 when, after some of the most devastating floods in Australian history, water from the CoQper Creek reached Lake Eyre for the first time since 1974.
who calibrated a rainfall-runoff model on the short streamflow records available, and then extended modelling for the period in which only rainfall data were available. Problems associated with this technique are well summarized in Pilgrim et al. (1988). The modelling clearly showed that the inflows to Lake Eyre North were relatively frequent and occurred on average every alternate years in the period investigated. The mean annual inflow was 3.8 km 3, with a standard deviation of 6.2 km 3. Annual inflows shown on Fig.2 have a slight downward trend of 0.005 km 3 y r - 1 coinciding with the decrease in lake water levels in the Northern Hemisphere which Kalinin and Klinge (1973) estimate as 30 km 3 yr -1 since 1940. Global warming need not necessarily be the cause, as in the period 1910-1940 the said decrease was of the order of 50 km 3 yr-1. For more illustration, the Caspian Sea dropped its level by 3 m in 1860-1970, the Dead Sea by 4.5 m in 1885-1960 and the Great Salt Lake by 3.5 m in 1850-1960, but the Great Lakes in turn, are at their highest in decades. The overall mechanism causing lake level variations
Modelled fillings The inflows to Lake Eyre in the period 18851984 were reconstructed by Kotwicki (1986, 1987),
Annual inflows to Lake Eyre 1885- 1989 40
E
0
........................................................................................................................................
i
JuJ,,t,J, tl
.................................................................................................................
O
i
1111 i l l H T H i t i i l i i N i l
1885
I1,
ill t lit ii INI litiNii
1905
ii illl lilll Nit i1111|lt1111||lltlt
1925
1945
I,
i l i l i i i iI i i i l i 1 1 1 1 1 i 1 1 | TIIF
1965
198~
Fig.2. Estimated annual inflows (km 3) to Lake Eyre North for the period 1885-1989 based on a calibrated rainfall-runoff model (Kotwicki, 1986, 1987).
94
throughout the world is clearly not recognizable at this stage. The Diamantina and Georgina rivers system, which covers only 32% of the Lake Eyre basin, contributed 65% of the total water entering the lake. The mean annual inflow from this source was 2.4 km 3, with a standard deviation of 3.8 km ~. The input from Cooper Creek and from other tributaries was 0.63 and 0.72 km 3 yr -1 respectively, both with a standard deviation of 1.9 km 3. Rainfall-runoff modelling undertaken and a series of recent fillings show (Fig.2) that Lake Eyre North fills much more frequently than was previously thought. In fact a return period of a 10 km 3 inflow is 8 years. Such a volume of water covers almost the entire surface area of Lake Eyre North and evaporates during the following year.
"The Greenhouse" effect The behaviour of such a delicate system under the influence of enhanced "greenhouse" processes is a subject of justifiable curiosity. Although future fillings of Lake Eyre cannot be presently predicted with any degree of confidence, the effects of the possible climatic changes can be evaluated. The most frequently quoted forecasts today (Pearman, 1988) suggest that in Australia by the year 2030, the temperature will have increased by 2-4°C, summer rainfall will increase by 50%, winter rainfall will decrease by 20% and overall wind speed will decrease by 10-20%. As more than 95% of total inflows to Lake Eyre are generated during the Australian summer (December to March), the change in winter rainfalls will have relatively little effect on the frequency of filling of the lake. The effect of other factors on runoff tend to cancel each other. The 50% increase in the summer rainfall would have by itself a substantial effect on streamflow, increasing it possibly two- or threefold. This is demonstrated by Nemec (1986) who states that an increase of 25% in precipitation and a decrease of I°C in temperature can increase the simulated runoff by 250%. The central reaches of all tributaries would be inundated more frequently which would significantly intensify the evaporation transmission losses, where according to Budyko (1980),
V. KOTWICKI AND P. ISDALE
a change of I°C corresponds to a 4% change in evapotranspiration. The larger areal extent of evaporating water surface and ground would, however, be partially compensated by the lower wind speed which would reduce evaporation. Although it appears that major tributaries will probably be flooded more often in their upper and central reaches, it is unclear whether their waters will be reaching Lake Eyre more often due to the increased transmission losses.
Coral fluorescence hydrology Rainfall over terrestrial catchments dissolves humic compounds from soils and leaches them into river systems (Susic and Isdale, 1989). These compounds are transported to the ocean and mixed in the inshore waters of the reef lagoon. Massive corals extract these humic compounds from seawater along with the calcium carbonate with which they build their aragonitic skeletons. The humic compounds, trapped in a solid crystal matrix, fluoresce under ultra-violet light, providing a measurable index of their concentration in the skeleton, and hence, their concentration in seawater at the time of deposition. The skeletal fluorescence can be quantified by custom-built instrumentation (Isdale, 1984), and the data aggregated into an annual index, representing annual river discharge. The great ages of these massive living corals means that cores taken from them (Isdale and Daniel, 1989) provide centuries of proxy palaeohydrological data for adjacent coastal rivers. The relationship between the annual skeletal fluorescence index in the coral core which recorded Burdekin outflow and the hydrograph record for the river during the period of most reliable instrumentation (1952-1980) is such that the index can be used to approximate historical river discharge (Isdale, 1984; Isdale and Kotwicki, 1987). We have used this reconstructed Burdekin discharge from 1735 to 1980 as a predictor of Lake Eyre inflows for the period, on the basis of a simple linear regression model of the form: Lake Eyre annual inflow = (annual coral fluorescence index - 169)/6.98
95
HYDROLOGY OF LAKE EYRE, AUSTRALIA: EL NllqO LINK
We have constructed the model using the period for which reliable inflow data exist (1948-1980) as the calibration period (Fig.3). Figure 4 shows the modelled inflow to Lake Eyre from 1735 to 1980. Some 41% of the variance in Lake Eyre inflows in the period can be explained by reference to coral fluorescence proxies of Burdekin discharge. This model, while perhaps not as robust as more complex constructions, does provide a good first approximation of the range and size/frequency distributions to Lake Eyre before human records began. It is worth noting the lack of correlation between Burdekin runoff and Lake Eyre inflow in years in which substantial rainfall resulted from cyclonic or rain depression activity in the Burdekin catchment, but which did not affect catchments to the west of the Divide. Addition of this factor alone (which is beyond the scope of this study) to the hindcasting model would no doubt improve the common variance by a reasonable measure.
8 years. Rainfall-runoff modelling undertaken and existing observational data suggest that Lake Eyre North fills on average to: - 12.5 m A H D level once in 5 years - 11.7 m A H D level once in 10 years - 11.0 m A H D level once in 20 years - 10.4 m A H D level once in 50 years - 9 . 5 m A H D level once in 100 years - 7 . 5 m A H D level once in 500 years - 6 . 3 m A H D level once in 1000 years. Old shorelines found at 0.7, 1.6 and 2.8 m above the 1974 level ( - 8 . 8 m , - 7 . 9 m and - 6 . 7 m AHD) represent approximately 1:200, 1:500 and 1:1000 years return periods respectively.
El Ni~o link The Lake Eyre drainage system and the Burdekin River catchment (in Queensland) show historical consistencies in their hydrological histories, as evidenced by both modelled streamflow data and coral fluorescence proxy records (Fig.5). Noise within the system (trend anomalies in the respective residual mass curves) within the period 1885-1985
Discussion Lake Eyre holds some quantities of water and almost all its area is covered on average once in
Lake Eyre inflow reconstruction 1948-1980 (calibration pedod)
+ lO-; ................
.
1948
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1958
[~
Lake Eyre I
.
.
.
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.
.
.
.
.
.
.
.
.
.
.
.
::
.
1968 I Coral
1978 I
Fig.3. Lake Eyre inflow reconstruction 1948-1980 (calibration period). Actual (dark bars) and modelled inflows (blank bars); the latter based on the coral fluorescence signal from near the Burdekin River.
96
V. KOTWICKI
AND
P.
ISDALE
Reconstructed inflows to Lake Eyre 1735- 1980
50 45 t ...........................................................................................................................................................................................................................
{~-
~
25
0
~ 20-
1 0 : .........................................................................................: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
, i tiiJllli[lll]ltllIliilill .
O
n IllUlIIII
lll
1735
fl I l U ~ l l
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m~H~mm~U~£~H~HRu~u~[~n~n~W~M~n~n~H~n~u~nmR
1835
1885
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1935
Fig.4, Lake Eyre inflow reconstruction (1735-1980 A.D.) from a coral fluorescence proxy record from near the Burdekin River.
ENSO-Lake Eyre-coral proxy relationship 1935-1980 _
54-
=
z: ............................../-~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ ............................................................................................................:. L~
/
~ o~
•.....
~
...............
i
k
~," ~,
................
'
~
/"
/",
i
-2 ~
-4
1935
1945 - -
SOl
1955
1965
Lake Eyre . . . . . . .
pO8
1975 coral
Fig.5. Comparison of variations (standard residuals from the means) in recorded ENSO intensities (labelled SOl=Southern Oscillation Index), fluorescence intensity in coral core (p08) from near the Burdekin River, and calculated Lake Eyre inflows for the period 1935-1980.
HYDROLOGYOF LAKE EYRE. AUSTRALIA:EL NIIqO LINK
can be explained in terms of synoptic scale climatologies, whereas coincident trends during the period for which data are available indicate the broad spatial extent of major low-frequency climatic influences on Australian continental river basin hydrology, such as the Southern Oscillation. We believe that the simple model we have used and which is based on this link between the two basin hydrologies explains the low-frequency (decadal level?) variability, and regard the sub- to annual frequencies as the residual. Given the strong relationship between the Burdekin River proxy, Lake Eyre inflow records, and the Southern Oscillation Index (Fig.5), we propose that the nature of the links (the lower frequencies referred to above) are to be found in those which are ENSO (or E1 Nifio) related. Figure 5 shows the sensitivity of the Lake Eyre and Burdekin basins to ENSO-driven climatic variability. The main catchment areas lie under the "fluctuation zone" of the seasonal migration of the monsoonal trough, a major determinant of wet-season intensity. In addition, the main belt of cyclogenesis moves to the west, nearer the east coast of the continent in years when the Southern Oscillation Index is high. A major proportion of the annual runoff from these coastal catchments, and the adjacent ones such as the Burdekin, is derived from such extreme events. References Allan, R., 1985. The Australian summer monsoon, teleconnections and flooding in the Lake Eyre Basin. R. Geogr. Soc. Aust., S. Aust. Br., 47 pp. Allan, R. J., Bye, J. A. T. and Hutton, P., 1986. The 1984 filling of Lake Eyre South. Trans. R. Soc. S. Aust., 110: 81-87. Allison, G. B. and Barnes, C. J., 1985. Estimation of evaporation from the normally "dry" Lake Frome in South Australia. J. Hydrol., 77: 229-242. Bonython, C. W., 1955. The salt of Lake Eyre - - Its occurrence in Madigan Gulf and its possible origin. Trans. R. Soc. S. Aust., 79: 66-92. Boto, K. and Isdale, P. J., 1985. Fluorescent bands in massive corals result from terrestrial fulvic acid inputs to the nearshore zone. Nature, 315: 396-397. Bowler, J. M., 1981. Australian salt lakes. A palaeohydrological approach. Hydrobiologia, 82: 431-444. Bowler, J. M., 1986. Spatial variability and hydrologic evolution of Australian lake basins: analogue for Pleistocene
97 hydrologic change and evaporite formation. Palaeogeogr., Palaeoclimatol., Palaeoecol., 54: 21-41. Budyko, M., 1980. Climate in the Past and in the Future. Gidrometeoizdat, Leningrad, 374 pp (in Russian). Chivas, A. R., Andrew, A. S., Lyons, W. B., Bird, M. I. and Donnelly, T. H., 1991. Isotopic constraints on the origin of salts in Australian playas. 1. Sulphur. Palaeogeogr., Palaeoclimatol., Palaeoecol., 84: 309-332. De Deckker, P., 1983. Australian salt lakes: their history, chemistry and biota - - a review. Hydrobiologia, 105: 231-244. De Deckker, P., 1988. Biological and sedimentary facies of Australian salt lakes. Palaeogeogr., Palaeoclimatol., Palaeoecol., 62: 237-270. Duffy, C. J. and AI-Hassan, S., 1988. Groundwater circulation in a closed desert basin: topographic scaling and climatic forcing. Water Resour. Res., 24: 1675-1688. Dulhunty, J. A., 1974. Salt crust distribution and lake bed conditions in southern areas of Lake Eyre North. Trans. R. Soc. S. Aust., 98: 125-134. Dulhunty, J. A., 1975. Shoreline shingle terraces and prehistoric fillings of Lake Eyre. Trans. R,. Soc. S. Aust., 99: 183-188. Dulhunty, J. A., 1978. Salt transfer between North and South Lake Eyre. Trans. R. Soc. S. Aust., 102: 107-112. Dulhunty, J. A., 1987. Salina bed instability and geodetic studies at Lake Eyre, South Australia. Trans. R. Soc. S. Aust., 111: 183-188. Gentilli, J., 1972. Australian Climate Patterns. Griffin Press, Adelaide, 285 pp. Gillespie, R., Magee, J. W., Luly, J. G., Dlugokencky, E., Sparks, R. J. and Wallace, G., 1991. AMS radiocarbon dating in the study of arid environments: Examples from Lake Eyre, South Australia. Palaeogeogr., Palaeoclimatol., Palaeocol., 84: 333-338. Glatz, A., 1984. Surface water quality data in South Australia, July 1978-June 1983. S. Aust. Eng. Water Supply Dep. Rep., Lib. Ref. 84/34. Gunn, R. H. and Fleming, P. M., 1984. The estimated store of soluble salts in the Lake Eyre catchment in Queensland and their possible transport in streamflow to Lake Eyre. Aust. J. Soil Res., 22: 119-134. Hacker, J. M., 1988. The spatial distribution of the vertical energy fluxes over a desert lake area. Aust. Meteorol. Mag., 36: 235-243. Herczeg, A. L. and Lyons, W. B., 1991. A chemical model for the evolution of Australian sodium chloride lake brines. Palaeogeogr., Palaeoclimatol., Palaeoecol., 84: 43-53. Holmes, J. W., Williams, A. F., and Henschke, C. J., 1981. Measurements of discharges from some of the mound springs in the desert of northern South Australia. J. Hydrol., 49: 329-339. Isdale, P., 1984. Fluorescent bands in massive corals record centuries of coastal rainfall. Nature, 310: 578-579. Isdale, P. and Daniel, E., 1989. The design and deployment of lightweight submarine fixed drilling system for the acquisition of coral cores. Mar. Technol. Soc. J., 23: 3-10. Isdale, P. and Kotwicki, V., 1987. Lake Eyre and the Great Barrier Reef: A paleohydrological ENSO connection. J. R. Geogr. Soc. S. Aust., 87: 44-55.
98 Johnson, M., 1980. The origin of Australia's salt lakes. Rec. Geol. Surv. N.S.W., 19: 221-266. Kalinin, G. P. and Klinge, R. K., 1973. Level of closed bodies of water as one of the criteria of global water exchange. Soy. Hydrol., 11(6): 47-57. Kotwicki, V., 1986. Floods of Lake Eyre. Eng. Water Supply Dep., Adelaide, 99 pp. Kotwicki, V., 1987. On the future of rainfall-runoff modelling in arid areas - - Lake Eyre case study. In: Water for the Future: Hydrology in Perspective, Proc. Rome Symp., April 1987. IAHS Publ., 164: 341-351. Kotwicki, V., 1988. Hydrology of wetlands in arid central Australia. Proc. Int. Symp. on Hydrology of Wetlands in Semiarid and Arid Regions. Seville, Spain, May 1988, pp. 95-98. Kotwicki, V., 1991. Water in the Universe. J. Hydrol. Sci. 36, 179-156. Lake Eyre Committee, 1955. Lake Eyre, South Australia: The Great Flood~ag of 1949-1950. R. Soc. S. Aust., Adelaide, 75 pp. Lloyd, L. and Balla, S., 1986. Wetlands and water resources in South Australia. S. Aust. Dep. Environm. Planning, Adelaide. Mabbutt, J. A., 1977. Desert Landforms. Aust. Nat. Univ. Press, Canberra, 340 pp. Nemec, J., 1985. Water resources system and climatic change. In: J. C. Rodda (Editor), Facets of Hydrology II. Wiley, New York, NY. Pearman, G. I. (Editor), 1988. Greenhouse: planning for climate change. Brill, Leiden, 752 pp. Pilgrim, D. H., Chapman, T. G. and Doran, D. G., 1988. Problems of rainfall runoff modelling in arid and semiarid regions. J. Hydrol. Sci., 33: 379-400. Reid, J. and Gillan, J., 1988. The Coongie Lakes study. S. Aust. Dep. Environm. Planning, Adelaide, 312 pp.
v. KOTWICKIANDP. ISDALE Ropelewski, C. F. and Halpert, M. S., 1987. Global and regional scale precipitation patterns associated with the E1 Nifio/Southern Oscillation. Mon. Weather Rev., 115: 1606-26. Susic, M. and Isdale, P. J., 1989. A model for humic acid carbon export from a tropical river system using coral skeletal fluorescence data. In R. A,, Falconer, P. Goodwin and R, G. S. Matthews (Editors), Hydraulic and Environmental Modelling of Coastal, Estuarine and River Waters. Gower, Aldershot, pp. 588-597. Tetzlaff, G. and Bye, J. A. T., 1978. The water balance of Lake Eyre for the flooded period between January 1974 and June 1976. Trans. R. Soc. S. Aust., 102: 91-96. Thompson, R. and Barnett, S., 1985. Geology, geomorphology and hydrogeology. In: J. Greenslade, L. Joseph, and A. Reeves (Editors), South Australia's Mound Springs. Nat. Conserv. Soc. South Aust., Adelaide, pp. 3-27. Ullman, W. J., 1985. Evaporation rate from a salt pan: Estimates from chemical profiles in near-surface groundwaters. J. Hydrol., 79: 365-373. Walling, D. E. and Webb, B. W., 1987. Material transport by the world rivers: evolving perspectives. In: Water for the Future: Hydrology in Perspective, Proc. Rome Symp., April 1987. IAHS Publ., 164: 313-329. Williams, A. F. and Holmes, J. W., 1978. A novel method of estimating the discharge of water from mound springs of the Great Artesian Basin, Central Australia. J. Hydrol., 38: 263-272. Woods, P. H., Walker, G. R. and Allison, G. B., 1988. Evaporation from shallow water-tables fed by leakage from the Great Artesian Basin near Lake Eyre. In: A. R. Chivas (Editor), SLEADS (Salt Lakes, Evaporites and Aeolian DepositS) Conference. Aust. Natl. Univ., Canberra, pp. 81-84.
87
Hydrology of Lake Eyre, Australia: E1 Nifio link Vincent Kotwicki a and Peter Isdale b
aWater Resources Branch, Engineering and Wa'ter Supply Department, Box 1751, Adelaide, S.A. 5001, Australia bAustralian Institute of Marine Science, PMB No. 3, Townsville M.C., Qld. 4810, Australia (Received 4 November, 1988; revised and accepted 13 July, 1990)
ABSTRACT Kotwicki, V. and Isdale, P., 1991. Hydrology of Lake Eyre, Australia: El Nifio link. Palaeogeogr., Palaeoclimatol., Palaeoecol., 84: 87-98. All major ephemeral rivers of Australia lie in the Lake Eyre basin. Dry for years, on occasions they carry enormous floods, with annual volumes of 40 km 3 and instantaneous discharges of the order of 30,000 m 3 s - 1. Mean annual runoff of the basin is 4 km 3 or 3.5 mm, significantly less than the 57 mm for the whole of Australia. This paper examines Lake Eyre and its drainage basin, describing the historical hydrology of the catchment, both in terms of instrument records and inflows hindcast using a model based on the technique of coral fluorescence palaeohydrological reconstruction. Coral fluorescence is a function of nearby-river discharge, and can be used to reconstruct annual river outputs beyond the instrument period. The Burdekin River catchment runoff history is strongly paralleled by the volumes of Lake Eyre inflows during the period of common reliable instrument gaugings. The Burdekin runoff data have been extended back to 1735 A.D. using the correlation between river discharge and annual growth-band fluorescence in an old coral from Pandora Reef, off the North Queensland coast. For the instrument period 1952 to 1980, 73% of the variance between coral fluorescence and Burdekin discharge is common. During the period 1949-1980, 41% of the variance between coral fluorescence and Lake Eyre inflow data is common. Modelled inflows to Lake Eyre for the period 1885-1948 are based on the latter data set.
Introduction A u s t r a l i a has the d u b i o u s d i s t i n c t i o n o f being p r e s e n t l y the m o s t lakeless a n d waterless continent. Salt lakes ( " d r y l a k e s " w o u l d be p r o b a b l y a m o r e a c c u r a t e d e s i g n a t i o n ) are, however, plentiful a n d in recent years they have received c o n s i d e r a b l e a t t e n t i o n ( J o h n s o n , 1980; Bowler, 1981, 1986; D e D e c k k e r , 1983, 1988). T h e largest o f them, L a k e Eyre - - in fact the largest e p h e m e r a l lake in the w o r l d - - w h i c h as Bowler (1981) observes " h a s its o w n e n i g m a t i c f a s c i n a t i o n to l i m n o l o g i s t s the w o r l d o v e r " , was c o n s i d e r e d p e r m a n e n t l y d r y since its d i s c o v e r y in 1840 until its first r e c o r d e d filling in 1949. In the d e c a d e s t h a t followed, fillings o f L a k e Eyre were still c o n s i d e r e d as isolated, u n i q u e a n d i n d e p e n d e n t events. O n l y recently have they 0031-0182/91/$03.50
been l o o k e d at as a p r e d i c t a b l e m a n i f e s t a t i o n o f the w o r l d - w i d e a t m o s p h e r i c a n d oceanic circulation, o f which the E1 N i f i o - S o u t h e r n Oscillation ( E N S O ) is one o f the m o s t significant p h e n o m e n a . A l l a n (1985) suggested t h a t L a k e Eyre floods are a physical m a n i f e s t a t i o n o f s t r o n g a n d positive S o u t h e r n Oscillation phases a n d are usually o u t o f p h a s e with the Pacific D r y Z o n e rainfall a n d El Nifio events. R o p e l e w s k i a n d H a l p e r t (1987) investigated the links between E N S O a n d large-scale p r e c i p i t a t i o n p a t t e r n s a n d identified 17 global core regions t h a t ~tppear to have a clear E N S O - p r e c i p i t a t i o n relationship. Five o f those are located in A u s t r a l i a a n d two o f them, eastern A u s t r a l i a a n d central A u s t r a l i a , c o v e r the entire L a k e Eyre basin. M a s s i v e corals f r o m the G r e a t Barrier R e e f c o n t a i n sequences o f skeletal fluorescence which
© 1991 - - Elsevier Science Publishers B.V.
88
V. KOTWlCKI AND P. ISDALE
can be measured as proxy records of adjacent river discharge (Isdale, 1984). These records, for the past several centuries, are capable of resolving hydrological events a few months apart. We consider, the Burdekin River (Fig.l), whose western basin boundary is contiguous with the eastern
~ ~
_
boundary of the Lake Eyre basin. Coral cores from Pandora reef, lying in the path of the river plume, can be used to reconstruct the palaeohydrology of the river system. Land-derived organic compounds trapped by the growing coral skeleton fluoresce strongly under ultra-violet light. The
BURCHEKIN VER Camooweal
QUEENSLAND •
km 0 , 800 km
MT. ISA
NORTHERN TERRITORY ~-,=~---'~~ALICE SPRINGS/~o ~ Hermannsbur(
Glengyle
~ ....
lackall
~onkira
'~ H o r s e s h o e ~"' 8end • .~..~p S I M P S O N • DALHOUSIE ~o SPRINGS , Country
I
AUSTRALIA~ Innamincka
COOBER PEDY ake
Lake
Frome
NEW SOUTH WALES
BRISBANE SYDNEY URNE
km0 t,
100 200 I = ( SCALE
300 km I
Fig.l. Topographic features of the Lake Eyre Basin. Inset maps show the regional extent of the modern Lake Eyre Basin and the underlying Great Artesian Basin.
HYDROLOGY OF LAKE EYRE, AUSTRALIA: EL NII~O LINK
fluorescence intensity is correlated with discharge of the adjacent river (Isdale, 1984; Boto and Isdale, 1985). The core used in this study was measured on a custom-built machine at the Australian Institute of Marine Science. This instrument illuminates the core with long-wave ultraviolet light and records fluorescence intensity within the core as the optical sensors scan its length. Using the annual density bands in the" coral core as a temporal reference, a "yearly" time-series of fluorescence intensity was constructed for the period 17351980.
Lake Eyre basin Lake Eyre is the terminal point of the great continental drainage system which spreads over 1.14 × 106 km 2 of arid central Australia. The Lake Eyre basin is mostly flat with extensive areas of sandy and stony deserts. There are regions with some relief near its boundaries, but only 30% of the area is elevated more than 250 m a.s.1. Catchment area to lake surface area ratio AC/AL = 118, significantly more than for most major closeddrainage systems in the world, and virtually identical to that of Lake Chad ( A C / A L = 1 2 0 ) in Africa. Some hydrological parallels could be drawn between both lakes: Lake Chad has a basin of 2.5 × 106 km 2, about double the size of the Lake Eyre basin, its surface area is 20,830 km 2 and its volume 72 km 3, about twice the size of Lake Eyre in 1974. Both lakes are subject to similar evaporation rates (2000 mm y r - 1) but the Lake Chad basin receives some 500 mm y r - 1 of rainfall, about twice that of the Lake Eyre basin. In effect, the Chari River, Lake Chad's main tributary, carries on average 40 (19-54) km 3 yr 1, compared to 2.4 (0-25) km 3 yr -~ of the Diamantina River, the main tributary of Lake Eyre. As a result, Lake Eyre dries up after periodic floods and Lake Chad remains permanent, despite significant water-level fluctuations.
Climate The Lake Eyre basin lies in the arid zone which covers some 60% of Australia. However, Gentilli (1972) demonstrates that the aridity of this region
89
does not equal that of the Sahara or Namib and that even a slight increase in rainfall would transform it into a semi-arid environment. It may be helpful to visualize here what a deficiency o f water is. The Lake Eyre basin, which covers 0.8% of the Earth's land area or 4.3% of the areas without outflow to the sea, receives some three times less rainfall than the world average and is subject to some three times more intense evaporation. Although these figures may appear at the first glance not very significant, they entail far-reaching consequences. If the amount of the fresh liquid water on Earth were distributed uniformly by areal proportions, the Lake Eyre basin would contain some 50 times more water flowing in rivers and 200 times more water stored in lakes than it currently does (Kotwicki, 1991). The average annual temperature varies from 21°C in the south of the basin to 24°C in the north, and the average maximum temperatures are 18°C and 24°C respectively in July, and 36°C and 39°C in January. The annual hours of sunshine vary from 3250 to over 3500, and the average global radiation is 600 mWh cm-2 day-1 Large parts of the Lake Eyre basin are poorly instrumented, but it is estimated that an area of some 5 x 105 km 2 receives less than 150mm of rainfall per year on average. The highest rainfalls, with annual averages of about 400 ram, occur in the northern and eastern margins, where rainfall is received from the southern edges of the summer monsoon. However, this region lies barely on the periphery of the planetary monsoon system, and the Australian monsoon is erratic both in space and time (Allan, 1985). The mean annual evaporation as measured by Class A evaporation pans ranges from 3600 mm for the central and southwestern part of the basin to 2400 mm for its eastern edge. The pan coefficient which converts pan data into evaporation from large water surfaces is of the order of 0.6 in the Lake Eyre area. The annual evaporation rate for the filled Lake Eyre ranges from 1800 to 2000 mm (Tetzlaff and Bye, 1978). Some indication of the evaporation rate from the dry lake floor (excluding the salt crust) has been given by Allison and Barnes (1985), who found a mean value of 1 7 0 m m y r -1 for
90
nearby Lake Frome. Ullman (1985) calculated the net evaporation rate from the salt-covered surface of Lake Eyre at between 9 and 28 mm yr- ~. Woods et al. (1988) estimate that evaporation from shallow water tables fed by vertical leakage from the Great Artesian Basin near Lake Eyre is of the order of 0.5-10 mm yr-~ in unfractured areas. Groundwater Most of the Lake Eyre basin overlies the Great Artesian Basin which covers an area of 1.7 x 1 0 6 km 2 and is one of the largest in the world. Aquifers are formed from porous sandstones of the Triassic, Jurassic and Cretaceous, which crop out along the Great Dividing Range and are up to 3000 m deep in its central part. From the mountainous recharge zone, water percolates very slowly towards the terminal base level of Lake Eyre, reaching this area after a calculated travel time of up to three million years (Thompson and Barnett, 1985). Intakes along the arid western rim make only a minor contribution. Apart from natural vertical leakage through the confining beds over the entire basin, natural discharge occurs from some 600 springs located in 11 groups along the western and southern boundaries of the basin, many of which appear to be fault controlled. Flows from the mound springs amount to 0.03 km 3 yr-~ and are thought to be only a minor discharge component. Artificial withdrawal from the basin is around 0.5 km 3 yr -~, diminishing steadily from around 0.7 km 3 in 1915. Measured flows from springs range from 0.0001 to 0.23 m 3 s- 1 totalling around 1 m 3 s- 1. Salinities range from 700 to 1400 g m -3, pH from 7.1 to 8.0 and water temperature from 30 to 40°C (Kotwicki, 1988). Williams and Holmes (1978) and Holmes et al. (1981) correlated measured spring discharges with the area of swamp vegetation which they support. The first study found that in the Dalhousie region the spring water is dissipated by a mean evaporative flux of 6.5 mm day-~, and the second, concerned with springs west of Lake Eyre found the measured swamp areas anomalously small, requiring a presumed evaportranspiration rate of more than 10 mm day-1. It was concluded that signifi-
V. KOTWICKI AND P. ISDALE
cant evaporation must occur from bare ground, beneath which the water table is sufficiently shallow to supply water by upward capillary rise.
Tributaries of Lake Eyre Mabbutt (1977) notes that the drainage system of Lake Eyre is exceptional for the persistence of an extensive network, despite its inclusion in the driest parts of the continent. This is a result of the favourable structural disposition of more effectively watered peripheral uplands combined with centripetal lowland slopes on weak and generally impervious rocks, leading to the downfaulted terminal basin. Much of this drainage is disconnected as a relict from linked river systems which developed under higher rainfall conditions and which became disorganised, under the present arid climate. The lake is fed mainly by its eastern tributaries, the Cooper Creek and the Diamantina and Georgina rivers system, whose flow data are shown in Table 1. Significant runoff originates in the desert west of the basin, which is drained by the Neales and the Macumba. Under the current climatic conditions only some 68% of the basin contributes water to the lake - - although in pre-Quaternary time, under more moderate and wetter conditions, drainage from the Simpson Desert and Finke River catchments would have contributed also. All streams are characterised by extreme variation in discharge and flow duration. Mean annual runoff of the basin is 4 km 3 or 3.5 mm in depth, the lowest of any major drainage system in the world. This is significantly less than the 57 mm for the whole of Australia and only 1.5% of the mean annual runoff of all the land areas of the world, estimated as 247 mm. The aridity of the basin is more graphically demonstrated by its specific yield of only 10 m 3 km -2 day-~ in comparison to the Nile or the Amazon which have specific yields of 115 and 2200 m 3 kin- 2 day- 1, respectively. In arid central Australia 15-20 mm of rain of moderate intensity can cause a flow in minor streams that lasts only for an hour or two. Such a flow may occur as often as five times each year. However, about 50 mm is needed for a full channel flow and such falls can be expected less frequently
91
HYDROLOGY OF LAKE EYRE, AUSTRALIA: EL Nl/'qO LINK
TABLE 1 Tributaries of Lake Eyre River and location of gauging station Cooper at Currareva Cooper at Innamincka Cooper at its mouth Georgina at Roxborough Downs Diamantina at Birdsville Diamantina at its mouth Western tributaries
Maximumflow Annual flow Mean annual flow Catchmentarea (m3 s - 1) (kin3) (kin~) (kin2)
Annual runoff (mm)
Timeriver dry (%)
5400 3700 1000"
15.0 11.5 4.0
3.4 2.1 0.6
150,000 237,000 306,000
22 9 2
46 62 >95
3800
6.3
1.2
82,000
14
55
4700
10.6
1.4
115,000
12
38
2000* 30,000*
24.0 10.0
2.4 0.7
365,000 206,000
6 3
90 >95
*estimate.
than once a year. Major floods in the Lake Eyre basin result from annual rainfalls which exceed 500 ram: the runoff coefficient in such years approaches 0.05. Eastern tributaries Eastern tributaries of Lake Eyre originate in more humid areas and flow quite frequently, however, only a small proportion of these flows reach Lake Eyre, due to very high transmission losses. The Cooper Creek for example can lose up to 10 v m 3 k i n - 1 in its central reach, filling innumerable salt lakes and interdune corridors of the Tirari Desert. Usually the Cooper Creek terminates at the Coongie Lakes (Lloyd and Balla, 1986, Kotwicki, 1988; Hacker, 1988; Reid and Gillan, 1988), the only permanent wetlands within the 5 × 1 0 6 km 2 area that comprises arid central Australia. The Cooper Creek only reaches Lake Eyre on average, once in six years. The transmission losses of the Diamantina River are usually much lower. The mean velocity of floods is 12.5 km day - 1 for the Diamantina and 3.1 km d a y - 1 for the Cooper. Water quality analyses in the central reaches of the main tributaries (Glatz, 1984) show that the mean annual inflow of 4 k m 3 transfers some 2.5x 105 t of salt into the lake, some 0 . 2 t k m - 2 y r -1 in comparison to the world average of 2 6 t km -2 yr -~. On this basis, the
period of accumulation represented by existing salt crust appears to be as short as 1600 yr. Mabbutt (1977) details the possible causes of evident salt losses, discussed also in Duffy and A1-Hassan (1988). The load of suspended solids is of the order of 1.5x 1 0 6 t y r -1, the equivalent of a 0.15ram layer over the lake. The specific suspended sediment load is 1.5 t km -2 yr -1, very low in comparison to the world average, of 9 0 t km - 2 y r -1 (Walling and Webb, 1987). Western tributaries The hydrology of the western tributaries is largely unknown. Several major rivers carry water infrequently, possibly only once in ten years. Flood volumes can be, however, enormous: for example in 1984 and in 1989 Lake Eyre received some 8 km 3 from western tributaries in three days, which implies discharges of the order of 30,000 m3s - t, or one-sixth that of the Amazon.
L a k e Eyre
Lake Eyre, whose lowest parts lie 15.2 m below sea level, consists of two sections: Lake Eyre North and Lake Eyre South,joined by the narrow Goyder Channel. The morphometric parameters of both lakes are shown in Table 2. Lake Eyre North was a permanent saline lake from 5000 to 10,000 years
92
V. KOTWlCKI AND P. ISDALE
TABLE 2 Morphometric parameters of Lake Eyre at -9.5 m AHD Parameters
Lake Eyre North
Lake Eyre South
Maximumlength, Im, (km) Maximumeffectivelength, Ira,, (km) Maximum width, Wm~x,(km) Direction of main axes Area, A, (km2) Mean width, Wm=A Lm- 1 (kin) Maximum depth, dm~x,(m) Volume, V, (km3) Mean depth, din,(m) Development of volume, Dv= 3dindma~-1 Shoreline, L, (km) Development of shoreline, DL= L (2~/nA)- 1
144 144 77 NNW 8430 59 5.7 27.7 3.3
64 64 24 NE 1260 20 3.7 2.4 1.9 1.5 328 2.6
ago and entered a playa phase between 5000 and 3000 years ago (Gillespie et al., 1991). A salt crust up to 460 mm thick covers the southern part of Lake Eyre North. The 4 x 10a t of salt deposited in the lake (Bonython, 1955) dissolve completely at times of major inflows (Dulhunty, 1974, 1978). The origin of this salt is a matter of considerable discussion, as the possible sources are very diverse ranging from marine aerosol transport ("cyclic salt") to rock weathering and groundwater discharge from aquifers deposited during the Cretaceous marine transgression that inundated central Australia. These and related issues are discussed in Bonython (1955), Dulhunty (1974, 1978, 1987), De Deckker (1983), Gunn and Fleming (1984), Allan et al. (1986), Chivas et al. (1991) and Herczeg and Lyons (1991). The presence of several old beach lines, 0.7, 1.6 and 2.8 m above the 1974 water level, indicate the occurrence of previous unrecorded major inflows (Dulhunty, 1975). The term "full" should therefore be used cautiously in relation to Lake Eyre. The above levels would represent approximate storages of 35 km 3, 48 km 3 and 67 km 3 respectively and the potential available storage to sea-level is more than 200 km 3, i.e. almost seven times greater than the 1974 storage. Fillings of Lake Eyre
L a k e Eyre lies in a remote and desolate area. Despite the current level of interest in the lake and
1.7
1390 4.3
its hydrology, very little data on its fillings have been collected, and many minor floodings escape attention.
Palaeohydrology Bowler (1981) notes that a longer period of constant filling of Lake Eyre occurred probably in the late Pleistocene, during a wetter climate in southern Australia, between about 45,000 and 25,000 yr B.P. This was followed by a phase of lake contraction, dune building and desiccation. Since European occupation, the climate has been almost equivalent to that of the driest phases of the last 10,000 years.
Recorded fillings The existence of water in Lake Eyre was first reported by Ross in 1869 and then by Halligan in 1922, however, their reports were dismissed as observation errors. Madigan who explored the area after a long drought in 1929 was convinced that the lake is permanently dry. The first reliable record of filling was in 1949-1950, when Lake Eyre North reached a peak storage of 21 km 3 (Lake Eyre Committee, 1955). This was followed by a series of minor floodings in 1953, 1955, 1956, 1957, 1958, 1959, 1963, 1967 and 1971, leading to a most significant flood event which began in 1973, reached its peak in 1974 and persisted until 1977. Lake Eyre North reached its highest recorded level
HYDROLOGY
OF
LAKE
EYRE,
AUSTRALIA:
EL
NI/~O
93
LINK
of - 9 . 0 9 m A H D in June 1974, and the equilibrium level of - 9 . 5 m A H D between both lakes was achieved in October 1974. The peak combined storage was 32.5 km 3. The last decade brought two unexpected events. The filling of 1984 with a total volume of 10 km 3 was a relatively minor one, but it proved that the western tributaries can fill Lake Eyre in a matter of days. Lake Eyre South this time filled first - an event never previously recorded and considered to be extremely unlikely - - and overflowed to Lake Eyre North (Allan et al., 1986). In 1989 this event was repeated, coinciding with the filling of the second largest Australian playa, Lake Torrens, which filled for the first time since 1878. The wet spell continued into 1990 when, after some of the most devastating floods in Australian history, water from the CoQper Creek reached Lake Eyre for the first time since 1974.
who calibrated a rainfall-runoff model on the short streamflow records available, and then extended modelling for the period in which only rainfall data were available. Problems associated with this technique are well summarized in Pilgrim et al. (1988). The modelling clearly showed that the inflows to Lake Eyre North were relatively frequent and occurred on average every alternate years in the period investigated. The mean annual inflow was 3.8 km 3, with a standard deviation of 6.2 km 3. Annual inflows shown on Fig.2 have a slight downward trend of 0.005 km 3 y r - 1 coinciding with the decrease in lake water levels in the Northern Hemisphere which Kalinin and Klinge (1973) estimate as 30 km 3 yr -1 since 1940. Global warming need not necessarily be the cause, as in the period 1910-1940 the said decrease was of the order of 50 km 3 yr-1. For more illustration, the Caspian Sea dropped its level by 3 m in 1860-1970, the Dead Sea by 4.5 m in 1885-1960 and the Great Salt Lake by 3.5 m in 1850-1960, but the Great Lakes in turn, are at their highest in decades. The overall mechanism causing lake level variations
Modelled fillings The inflows to Lake Eyre in the period 18851984 were reconstructed by Kotwicki (1986, 1987),
Annual inflows to Lake Eyre 1885- 1989 40
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Fig.2. Estimated annual inflows (km 3) to Lake Eyre North for the period 1885-1989 based on a calibrated rainfall-runoff model (Kotwicki, 1986, 1987).
94
throughout the world is clearly not recognizable at this stage. The Diamantina and Georgina rivers system, which covers only 32% of the Lake Eyre basin, contributed 65% of the total water entering the lake. The mean annual inflow from this source was 2.4 km 3, with a standard deviation of 3.8 km ~. The input from Cooper Creek and from other tributaries was 0.63 and 0.72 km 3 yr -1 respectively, both with a standard deviation of 1.9 km 3. Rainfall-runoff modelling undertaken and a series of recent fillings show (Fig.2) that Lake Eyre North fills much more frequently than was previously thought. In fact a return period of a 10 km 3 inflow is 8 years. Such a volume of water covers almost the entire surface area of Lake Eyre North and evaporates during the following year.
"The Greenhouse" effect The behaviour of such a delicate system under the influence of enhanced "greenhouse" processes is a subject of justifiable curiosity. Although future fillings of Lake Eyre cannot be presently predicted with any degree of confidence, the effects of the possible climatic changes can be evaluated. The most frequently quoted forecasts today (Pearman, 1988) suggest that in Australia by the year 2030, the temperature will have increased by 2-4°C, summer rainfall will increase by 50%, winter rainfall will decrease by 20% and overall wind speed will decrease by 10-20%. As more than 95% of total inflows to Lake Eyre are generated during the Australian summer (December to March), the change in winter rainfalls will have relatively little effect on the frequency of filling of the lake. The effect of other factors on runoff tend to cancel each other. The 50% increase in the summer rainfall would have by itself a substantial effect on streamflow, increasing it possibly two- or threefold. This is demonstrated by Nemec (1986) who states that an increase of 25% in precipitation and a decrease of I°C in temperature can increase the simulated runoff by 250%. The central reaches of all tributaries would be inundated more frequently which would significantly intensify the evaporation transmission losses, where according to Budyko (1980),
V. KOTWICKI AND P. ISDALE
a change of I°C corresponds to a 4% change in evapotranspiration. The larger areal extent of evaporating water surface and ground would, however, be partially compensated by the lower wind speed which would reduce evaporation. Although it appears that major tributaries will probably be flooded more often in their upper and central reaches, it is unclear whether their waters will be reaching Lake Eyre more often due to the increased transmission losses.
Coral fluorescence hydrology Rainfall over terrestrial catchments dissolves humic compounds from soils and leaches them into river systems (Susic and Isdale, 1989). These compounds are transported to the ocean and mixed in the inshore waters of the reef lagoon. Massive corals extract these humic compounds from seawater along with the calcium carbonate with which they build their aragonitic skeletons. The humic compounds, trapped in a solid crystal matrix, fluoresce under ultra-violet light, providing a measurable index of their concentration in the skeleton, and hence, their concentration in seawater at the time of deposition. The skeletal fluorescence can be quantified by custom-built instrumentation (Isdale, 1984), and the data aggregated into an annual index, representing annual river discharge. The great ages of these massive living corals means that cores taken from them (Isdale and Daniel, 1989) provide centuries of proxy palaeohydrological data for adjacent coastal rivers. The relationship between the annual skeletal fluorescence index in the coral core which recorded Burdekin outflow and the hydrograph record for the river during the period of most reliable instrumentation (1952-1980) is such that the index can be used to approximate historical river discharge (Isdale, 1984; Isdale and Kotwicki, 1987). We have used this reconstructed Burdekin discharge from 1735 to 1980 as a predictor of Lake Eyre inflows for the period, on the basis of a simple linear regression model of the form: Lake Eyre annual inflow = (annual coral fluorescence index - 169)/6.98
95
HYDROLOGY OF LAKE EYRE, AUSTRALIA: EL NllqO LINK
We have constructed the model using the period for which reliable inflow data exist (1948-1980) as the calibration period (Fig.3). Figure 4 shows the modelled inflow to Lake Eyre from 1735 to 1980. Some 41% of the variance in Lake Eyre inflows in the period can be explained by reference to coral fluorescence proxies of Burdekin discharge. This model, while perhaps not as robust as more complex constructions, does provide a good first approximation of the range and size/frequency distributions to Lake Eyre before human records began. It is worth noting the lack of correlation between Burdekin runoff and Lake Eyre inflow in years in which substantial rainfall resulted from cyclonic or rain depression activity in the Burdekin catchment, but which did not affect catchments to the west of the Divide. Addition of this factor alone (which is beyond the scope of this study) to the hindcasting model would no doubt improve the common variance by a reasonable measure.
8 years. Rainfall-runoff modelling undertaken and existing observational data suggest that Lake Eyre North fills on average to: - 12.5 m A H D level once in 5 years - 11.7 m A H D level once in 10 years - 11.0 m A H D level once in 20 years - 10.4 m A H D level once in 50 years - 9 . 5 m A H D level once in 100 years - 7 . 5 m A H D level once in 500 years - 6 . 3 m A H D level once in 1000 years. Old shorelines found at 0.7, 1.6 and 2.8 m above the 1974 level ( - 8 . 8 m , - 7 . 9 m and - 6 . 7 m AHD) represent approximately 1:200, 1:500 and 1:1000 years return periods respectively.
El Ni~o link The Lake Eyre drainage system and the Burdekin River catchment (in Queensland) show historical consistencies in their hydrological histories, as evidenced by both modelled streamflow data and coral fluorescence proxy records (Fig.5). Noise within the system (trend anomalies in the respective residual mass curves) within the period 1885-1985
Discussion Lake Eyre holds some quantities of water and almost all its area is covered on average once in
Lake Eyre inflow reconstruction 1948-1980 (calibration pedod)
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Fig.3. Lake Eyre inflow reconstruction 1948-1980 (calibration period). Actual (dark bars) and modelled inflows (blank bars); the latter based on the coral fluorescence signal from near the Burdekin River.
96
V. KOTWICKI
AND
P.
ISDALE
Reconstructed inflows to Lake Eyre 1735- 1980
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Fig.4, Lake Eyre inflow reconstruction (1735-1980 A.D.) from a coral fluorescence proxy record from near the Burdekin River.
ENSO-Lake Eyre-coral proxy relationship 1935-1980 _
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HYDROLOGYOF LAKE EYRE. AUSTRALIA:EL NIIqO LINK
can be explained in terms of synoptic scale climatologies, whereas coincident trends during the period for which data are available indicate the broad spatial extent of major low-frequency climatic influences on Australian continental river basin hydrology, such as the Southern Oscillation. We believe that the simple model we have used and which is based on this link between the two basin hydrologies explains the low-frequency (decadal level?) variability, and regard the sub- to annual frequencies as the residual. Given the strong relationship between the Burdekin River proxy, Lake Eyre inflow records, and the Southern Oscillation Index (Fig.5), we propose that the nature of the links (the lower frequencies referred to above) are to be found in those which are ENSO (or E1 Nifio) related. Figure 5 shows the sensitivity of the Lake Eyre and Burdekin basins to ENSO-driven climatic variability. The main catchment areas lie under the "fluctuation zone" of the seasonal migration of the monsoonal trough, a major determinant of wet-season intensity. In addition, the main belt of cyclogenesis moves to the west, nearer the east coast of the continent in years when the Southern Oscillation Index is high. A major proportion of the annual runoff from these coastal catchments, and the adjacent ones such as the Burdekin, is derived from such extreme events. References Allan, R., 1985. The Australian summer monsoon, teleconnections and flooding in the Lake Eyre Basin. R. Geogr. Soc. Aust., S. Aust. Br., 47 pp. Allan, R. J., Bye, J. A. T. and Hutton, P., 1986. The 1984 filling of Lake Eyre South. Trans. R. Soc. S. Aust., 110: 81-87. Allison, G. B. and Barnes, C. J., 1985. Estimation of evaporation from the normally "dry" Lake Frome in South Australia. J. Hydrol., 77: 229-242. Bonython, C. W., 1955. The salt of Lake Eyre - - Its occurrence in Madigan Gulf and its possible origin. Trans. R. Soc. S. Aust., 79: 66-92. Boto, K. and Isdale, P. J., 1985. Fluorescent bands in massive corals result from terrestrial fulvic acid inputs to the nearshore zone. Nature, 315: 396-397. Bowler, J. M., 1981. Australian salt lakes. A palaeohydrological approach. Hydrobiologia, 82: 431-444. Bowler, J. M., 1986. Spatial variability and hydrologic evolution of Australian lake basins: analogue for Pleistocene
97 hydrologic change and evaporite formation. Palaeogeogr., Palaeoclimatol., Palaeoecol., 54: 21-41. Budyko, M., 1980. Climate in the Past and in the Future. Gidrometeoizdat, Leningrad, 374 pp (in Russian). Chivas, A. R., Andrew, A. S., Lyons, W. B., Bird, M. I. and Donnelly, T. H., 1991. Isotopic constraints on the origin of salts in Australian playas. 1. Sulphur. Palaeogeogr., Palaeoclimatol., Palaeoecol., 84: 309-332. De Deckker, P., 1983. Australian salt lakes: their history, chemistry and biota - - a review. Hydrobiologia, 105: 231-244. De Deckker, P., 1988. Biological and sedimentary facies of Australian salt lakes. Palaeogeogr., Palaeoclimatol., Palaeoecol., 62: 237-270. Duffy, C. J. and AI-Hassan, S., 1988. Groundwater circulation in a closed desert basin: topographic scaling and climatic forcing. Water Resour. Res., 24: 1675-1688. Dulhunty, J. A., 1974. Salt crust distribution and lake bed conditions in southern areas of Lake Eyre North. Trans. R. Soc. S. Aust., 98: 125-134. Dulhunty, J. A., 1975. Shoreline shingle terraces and prehistoric fillings of Lake Eyre. Trans. R,. Soc. S. Aust., 99: 183-188. Dulhunty, J. A., 1978. Salt transfer between North and South Lake Eyre. Trans. R. Soc. S. Aust., 102: 107-112. Dulhunty, J. A., 1987. Salina bed instability and geodetic studies at Lake Eyre, South Australia. Trans. R. Soc. S. Aust., 111: 183-188. Gentilli, J., 1972. Australian Climate Patterns. Griffin Press, Adelaide, 285 pp. Gillespie, R., Magee, J. W., Luly, J. G., Dlugokencky, E., Sparks, R. J. and Wallace, G., 1991. AMS radiocarbon dating in the study of arid environments: Examples from Lake Eyre, South Australia. Palaeogeogr., Palaeoclimatol., Palaeocol., 84: 333-338. Glatz, A., 1984. Surface water quality data in South Australia, July 1978-June 1983. S. Aust. Eng. Water Supply Dep. Rep., Lib. Ref. 84/34. Gunn, R. H. and Fleming, P. M., 1984. The estimated store of soluble salts in the Lake Eyre catchment in Queensland and their possible transport in streamflow to Lake Eyre. Aust. J. Soil Res., 22: 119-134. Hacker, J. M., 1988. The spatial distribution of the vertical energy fluxes over a desert lake area. Aust. Meteorol. Mag., 36: 235-243. Herczeg, A. L. and Lyons, W. B., 1991. A chemical model for the evolution of Australian sodium chloride lake brines. Palaeogeogr., Palaeoclimatol., Palaeoecol., 84: 43-53. Holmes, J. W., Williams, A. F., and Henschke, C. J., 1981. Measurements of discharges from some of the mound springs in the desert of northern South Australia. J. Hydrol., 49: 329-339. Isdale, P., 1984. Fluorescent bands in massive corals record centuries of coastal rainfall. Nature, 310: 578-579. Isdale, P. and Daniel, E., 1989. The design and deployment of lightweight submarine fixed drilling system for the acquisition of coral cores. Mar. Technol. Soc. J., 23: 3-10. Isdale, P. and Kotwicki, V., 1987. Lake Eyre and the Great Barrier Reef: A paleohydrological ENSO connection. J. R. Geogr. Soc. S. Aust., 87: 44-55.
98 Johnson, M., 1980. The origin of Australia's salt lakes. Rec. Geol. Surv. N.S.W., 19: 221-266. Kalinin, G. P. and Klinge, R. K., 1973. Level of closed bodies of water as one of the criteria of global water exchange. Soy. Hydrol., 11(6): 47-57. Kotwicki, V., 1986. Floods of Lake Eyre. Eng. Water Supply Dep., Adelaide, 99 pp. Kotwicki, V., 1987. On the future of rainfall-runoff modelling in arid areas - - Lake Eyre case study. In: Water for the Future: Hydrology in Perspective, Proc. Rome Symp., April 1987. IAHS Publ., 164: 341-351. Kotwicki, V., 1988. Hydrology of wetlands in arid central Australia. Proc. Int. Symp. on Hydrology of Wetlands in Semiarid and Arid Regions. Seville, Spain, May 1988, pp. 95-98. Kotwicki, V., 1991. Water in the Universe. J. Hydrol. Sci. 36, 179-156. Lake Eyre Committee, 1955. Lake Eyre, South Australia: The Great Flood~ag of 1949-1950. R. Soc. S. Aust., Adelaide, 75 pp. Lloyd, L. and Balla, S., 1986. Wetlands and water resources in South Australia. S. Aust. Dep. Environm. Planning, Adelaide. Mabbutt, J. A., 1977. Desert Landforms. Aust. Nat. Univ. Press, Canberra, 340 pp. Nemec, J., 1985. Water resources system and climatic change. In: J. C. Rodda (Editor), Facets of Hydrology II. Wiley, New York, NY. Pearman, G. I. (Editor), 1988. Greenhouse: planning for climate change. Brill, Leiden, 752 pp. Pilgrim, D. H., Chapman, T. G. and Doran, D. G., 1988. Problems of rainfall runoff modelling in arid and semiarid regions. J. Hydrol. Sci., 33: 379-400. Reid, J. and Gillan, J., 1988. The Coongie Lakes study. S. Aust. Dep. Environm. Planning, Adelaide, 312 pp.
v. KOTWICKIANDP. ISDALE Ropelewski, C. F. and Halpert, M. S., 1987. Global and regional scale precipitation patterns associated with the E1 Nifio/Southern Oscillation. Mon. Weather Rev., 115: 1606-26. Susic, M. and Isdale, P. J., 1989. A model for humic acid carbon export from a tropical river system using coral skeletal fluorescence data. In R. A,, Falconer, P. Goodwin and R, G. S. Matthews (Editors), Hydraulic and Environmental Modelling of Coastal, Estuarine and River Waters. Gower, Aldershot, pp. 588-597. Tetzlaff, G. and Bye, J. A. T., 1978. The water balance of Lake Eyre for the flooded period between January 1974 and June 1976. Trans. R. Soc. S. Aust., 102: 91-96. Thompson, R. and Barnett, S., 1985. Geology, geomorphology and hydrogeology. In: J. Greenslade, L. Joseph, and A. Reeves (Editors), South Australia's Mound Springs. Nat. Conserv. Soc. South Aust., Adelaide, pp. 3-27. Ullman, W. J., 1985. Evaporation rate from a salt pan: Estimates from chemical profiles in near-surface groundwaters. J. Hydrol., 79: 365-373. Walling, D. E. and Webb, B. W., 1987. Material transport by the world rivers: evolving perspectives. In: Water for the Future: Hydrology in Perspective, Proc. Rome Symp., April 1987. IAHS Publ., 164: 313-329. Williams, A. F. and Holmes, J. W., 1978. A novel method of estimating the discharge of water from mound springs of the Great Artesian Basin, Central Australia. J. Hydrol., 38: 263-272. Woods, P. H., Walker, G. R. and Allison, G. B., 1988. Evaporation from shallow water-tables fed by leakage from the Great Artesian Basin near Lake Eyre. In: A. R. Chivas (Editor), SLEADS (Salt Lakes, Evaporites and Aeolian DepositS) Conference. Aust. Natl. Univ., Canberra, pp. 81-84.