INFLUENCE OF DEEP AQUIFER

SPRINGS ON DRY SEASON STREAM

WATER QUALITY IN DARWIN RURAL

AREAS, NORTHERN TERRITORY,

AUSTRALIA

Anh Tho Tien

Water Monitoring Branch Natural Resource Management Division

Report 6/2006D

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Abstract

Typical of the wet/dry tropical environment in northern Australia, stream discharge increases in proportion with rainfall in the wet season and decreases with the recession of rainfall. Stream flow and groundwater level decrease as the dry season progresses. Towards the end of the dry season, some streams dry up whilst some retain a substantial flow, mainly due to groundwater discharge.

This study aims to determine:

* the sources of the spring-fed streams;

* the influence of deep aquifer spring on dry season stream water quality; and

* the change in water quality with distance from the groundwater input.

Historical data extracted from HYDSTRA and AUSRIVAS, and field investigation conducted in September 2005 at selected spring sites showed an electrical conductivity of ± 360 µScm-1 and a Ca,Mg-HCO3 water type, characteristic of dolomite water. Historical data of groundwater sampled at extraction level in bores drilled in dolomite also recorded electrical conductivity of ± 300 µScm-1 and a Ca,Mg-HCO3 water type, characteristic of dolomite water.

Palm Creek and Hudson Creek flow from Palmerston Dolomite aquifer which probably extends to the Elizabeth River catchment. Howard Springs, Melacca Spring, Banka Spring, Black Jungle Spring and probably the spring at Humpty Doo Station tap the Koolpinyah Dolomite formation. Berry Springs and Parson Spring exploit the Berry Springs Dolomite whilst Manton River flow from Coomalie Dolomite. A dolomite aquifer also exists at Acacia Gap downstream of Manton Dam.

In the dry season, baseflow originating from the dolomite aquifer gradually replaces surface runoff and dolomite groundwater characteristics gradually changes water quality in the streams with increasing electrical conductivity, pH and ionic concentrations of bicarbonate, calcium and magnesium.

Stream water quality also changes with distance from the input of groundwater. The further the stream flows away from the dolomite aquifer influence, the more the electrical conductivity, pH and ionic concentrations of bicarbonate, calcium and magnesium decreases.

Stream water quality is influenced by the regional lithology and deep aquifer spring in the dry season.

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Table of Contents Background ....................................................................................................................1 Scope..............................................................................................................................1 Physical setting ..............................................................................................................4

Location .....................................................................................................................4 Climate.......................................................................................................................4 Geomorphology and regional geology.......................................................................6 Hydrogeology ............................................................................................................6 Vegetation cover ........................................................................................................6 Land and water use ....................................................................................................6

Existing data...................................................................................................................6 Field investigation........................................................................................................11 Springs from Dolomite Aquifer ...................................................................................15

Palm Creek at Holmes Jungle ..................................................................................15 Hudson Creek Spring...............................................................................................16 Howard Springs .......................................................................................................18 Koolpinyah: Melacca Swamp and Banka Spring ....................................................27 Black Jungle Springs................................................................................................31 Springs in Elizabeth River Catchment.....................................................................31 Litchfield Creek .......................................................................................................31 Berry Springs ...........................................................................................................34 Parsons Spring .........................................................................................................38 Acacia Springs .........................................................................................................38

Changes in surface water quality with distance...........................................................42 Darwin River............................................................................................................42 Manton River ...........................................................................................................42 Howard River...........................................................................................................42

Changes in surface water quality with time.................................................................44 Springs in Cox Peninsula .............................................................................................44 Discussion and recommendations................................................................................45

Sources of the springs ..............................................................................................45 Difference in water quality in different dolomite aquifers ......................................45 Influence of deep aquifer springs on stream water quality in the dry season ..........46 Change in stream water quality with distance .........................................................46 Recommendations....................................................................................................47

Acknowledgement .......................................................................................................47 References....................................................................................................................48

List of Tables

Table 1. Reported springs with historical range of electrical conductivity and pH......8 Table 2. Reported stream water quality .........................................................................9 Table 3. Reported groundwater quality at depth of water extraction of bores drilled in dolomite aquifer. ............................................................................................................9 Table 4. Selected physicochemical parameters of springs visited in September 2005.......................................................................................................................................14 Table 5. Discharge and field measurements in 1999 and 2005. ..................................27 Table 6. Electrical conductivity and ionic composition at different sampling points downstream of Darwin River, Manton River and Howard River................................42 Table 7. Eigenvalues extracted from principal component analysis............................46 Table 8. Summary of factor analysis. ..........................................................................46

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List of Figures Figure 1. Location of the study area. ............................................................................2 Figure 2. Origin of springs as described by Van den Broek..........................................3 Figure 3. Monthly distribution of rainfall and evaporation in Darwin . ........................5 Figure 4. Annual distribution of rainfall and evaporation in Darwin ............................5 Figure 5. Springs coming from dolomite aquifers and sandstone .................................7 Figure 7. Piper diagram of the springs in the study area. ...........................................10 Figure 8. Piper diagram of the dolomite bores in the study area .................................11 Figure 9. Location of springs visited in September 2005. ...........................................13 Figure 10. Location of Palm Creek and Hudson Creek sampling point. .....................16 Figure 11. Location of Howard Springs ......................................................................19 Figure 12. Local geology at Howard Springs ..............................................................19 Figure 13. Geologic history of Howard Springs..........................................................20 Figure 14. Predicted spring flow at Howard Springs from 1870 to 2000....................21 Figure 15. Dry season flow recession at Howard Springs spring in 2000...................22 Figure 16. Increase in flow with distance in the wet season and no significant

difference in flow with distance in the dry season.....................................22 Figure 17. Increase in pH with time and distance........................................................23 Figure 18. Change of electrical conductivity in the wet and the dry season ..............23 Figure 19. Increase in dissolved oxygen with distance downstream of the spring.....24 Figure 20. Location of Melacca Swamp and Banka Spring, Hollands Creek at Black

Jungle and Litchfield Creek at Humpty Doo Station.................................28 Figure 21. Location of identified springs in creeks flowing into Elizabeth River.......32 Figure 22. Location and source of springs in Berry Springs Nature Park ..................35 Figure 23. Location of Berry Springs and Parsons Springs.........................................36 Figure 24. Location of Acacia Spring and Manton River............................................40 Figure 25. Changes in conductivity with distance from groundwater input...............43 Figure 26. Electrical conductivity in Howard River and Elizabeth River in 2005 dry

season.........................................................................................................44

List of Plates Plate 1. Upstream and downstream of a dirt road crossing of Palm Creek at Holmes

Jungle in September 2005.............................................................................15 Plate 2. Hudson Creek, September 2005. ....................................................................17 Plate 3. The spring at Howard Springs Nature Park, 2000. .........................................21 Plate 4. Howard Spring in September 2005................................................................25 Plate 5. Dry channel downstream of Howard Springs swimming pool, September

2005...............................................................................................................26 Plate 6. Flowing creek downstream Howard Springs swimming pool, September

2005...............................................................................................................26 Plate 7. Melacca Swamp, September 2005. .................................................................29 Plate 8. Banka Spring, September 2005.......................................................................30 Plate 9. Hollands Creek in Black Jungle Swamp, September 2005............................31 Plate 10. Litchfield Creek at Humpty Doo Station, September 2005. .........................33 Plate 11. Berry Springs in September 2005. ................................................................37 Plate 12. Parsons Spring confluence with Darwin River. ...........................................38 Plate 13. Parsons Spring. ............................................................................................39 Plate 14. Acacia Spring in September 2005.................................................................41

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Background Stream and river water quality are influenced by catchment characteristics such as geology, vegetation and land use, as well as aquifer springs inflows. In the catchment’s of Darwin and Bynoe Harbours, and Lichfield Shire (Fig. 1), development and the use of groundwater for consumptive purposes, could have a marked effect on stream water quality during the dry season by altering the relative contribution of water from aquifers with differing quality.

Typical of the wet/dry tropical environment, most of the rain falls in the wet season, increasing river discharge and eventually recharging the aquifers. River flow and groundwater level decrease as the dry season progresses. In the Darwin region, some streams dry up in the dry season whilst some rivers retain their flow. The perennial flow in rivers is sustained by groundwater discharge.

Scope Groundwater discharge includes stream baseflow, springs, seepage areas and evapotranspiration (Driscoll 1986). A spring is a large discharge from fissures or caverns in the rocks (Linsley & Franzini 1972; Freeze & Cherry 1979; Driscoll 1986).

For the purpose of this study, springs are defined as discharge from deep aquifers, not subsurface laterite flow which is common in the Darwin region. Springs are determined as streams still flowing after August, when flow from laterite sources has typically ceased. The flow of springs is maintained by groundwater emerging from the mottled zone or the upper fractured surface of the weathered Lower Proterozoic rocks (Figure 2).

The approach is to determine the location of the deep aquifer springs study area (Fig. 1), and collate the existing water chemistry and discharge data of the springs. The source of information is HYDSTRA, a hydrological database maintained by the Department of Natural Resources, Environment and The Arts, and other data sources such as Government reports and the AUSRIVAS program. The dry season behaviour of water quantity and water quality was investigated, and the influence of deep aquifer spring on stream water quality in the dry season was determined.

1

Figure 1. Location of the study area.

2

Figure 2. Origin of springs as described by Van den Broek (1975).

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Physical setting

Location The study area extends from the divide between the Finniss River Catchment and the Charlotte River Catchment in the west to Adelaide River in the east, comprising Bynoe Harbour, Darwin Harbour, the Litchfield Shire and the northern part of the Coomalie Shire (Figure 1).

Bynoe Harbour includes Port Patterson, Bynoe Harbour and the catchments of Milne Inlet, Annie River and Charlotte River.

Darwin Harbour is a shallow estuary defined as the water area south of a line from Charles Point in the west to Gunn Point in the east, including Port Darwin, Shoal Bay and the catchments of East Arm, Middle Arm and West Arm (Darwin Harbour Advisory Committee 2003). Freshwater inputs to the harbour are mainly sourced from Elizabeth River, flowing into East Arm, Blackmore River and Berry Creek, flowing into Middle Arm, and Howard River (Wilson et al. 2004).

The Litchfield Shire is bound by the Adelaide River on the east, and the northern part of Coomalie is bound by a straight line between the Adelaide River and the divide of the Finniss River Catchment just north of Batchelor on the south.

Climate The climate is monsoonal, the wet season usually spreads from October to April, with most rainfalls between December and March. The mean annual rainfall is 1690 mm, measured over 62 years (1941 – 2003) at the Darwin Airport DR014015 rain station. The distribution throughout the year shows a peak rainfall up to 430 mm in January, and negligible rainfall in the dry months (Figure 3). The rainfall varies between years, with a total annual rainfall up to 2500 mm in exceptionally wet years (Figure 4).

Evaporation usually exceeds rainfall throughout the year, except in the wet months (Figure 3). The monthly evaporation ranges from 170 mm in February to 270 mm in October. The mean annual evaporation is 2650 mm, measured over 27 years (1967 – 1994) at the Darwin Airport DE014015 meteorological station (Figure 4).

The hottest months are usually November and December, the temperature ranges from 27 oC to 34 oC, and the coolest month is July from 19 oC to 30 oC (Pietsch 1983). Relative humidity usually exceeds 70% in the wet season, and the mean relative humidity is over 60% (Van den Broek 1975).

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0

50

100

150

200

250

300

350

400

450

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Time (month)

Rai

nfal

l and

eva

pora

tion

(mm

)

rainfallevaporation

Figure 3. Monthly distribution of rainfall and evaporation in Darwin (averaged 1941

– 2003).

0

500

1000

1500

2000

2500

3000

3500

1940/41 1945/46 1950/51 1955/56 1960/61 1965/66 1970/71 1975/76 1980/81 1985/86 1990/91 1995/96 2000/ 1

Time (water years)

Ann

ual r

ainf

all a

nd e

vapo

ratio

n (m

m)

rainfallevaporationaverage rainfallaverage evaporation

Figure 4. Annual distribution of rainfall and evaporation in Darwin (averaged 1941 –

2003).

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Geomorphology and regional geology Geological surveys of Darwin region have been conducted as early as the start of the century (Brown 1895; Brown 1906). Numerous studies include surveys by Noakes (1949), Christian & Stewart (1953), Malone (1962), Walpole et al. (1968), van den Broek (1975), Pietsch (1983) and Verma (2002).

Geologically, the area is very complex in the Pine Creek Geosyncline, in which rocks are uplifted, subsided, folded, faulted and eroded (Verma 2002). The oldest rocks are Archaean rocks, limited to small areas and occurring mostly as domes. The Lower Proterozoic rocks cover most of the area. These rocks were repeatedly subsided and uplifted within the geosyncline, resulting in tight folding and faulting. Due to a long non-deposition period from 1800 to 225 Ma, surface weathering produced karst topography on carbonate surfaces, producing new layers from eroded carbonate rocks. Lower Cretaceous rocks are flat lying, light coloured stratified sedimentary rocks covering most of the areas except hills. Most of the lower elevation surface area is then covered by Cainozoic sediments of about 3 m thickness (Verma 2002).

Hydrogeology Major aquifers in the study area are within carbonate (mostly dolomite), fractured and weathered rocks. The aquifers in the fractured and weathered non-carbonate rocks or non-carbonate stratified rocks are not reported in this study, with the exception of listed in Table 1. The extent of dolomite in the study area has been determined using bore data (Figure 5).

Vegetation cover Vegetation in coastal and estuarine plains is mainly Melaleuca leucodendron, whilst open grasslands and scattered trees cover the alluvial plains. Open forests with Pandanus, Melaleuca, Grevillea, Acacia, Eucalypts, Calytrix and clumps of rainforests cover the northern plains north of Darwin. In the southern part of Darwin, stunted woodland, mixed scrub and palm forests cover the dissected foothills whilst Eucalyptus and mixed woodlands cover the dissected uplands (Verma 2002).

Land and water use The most intensive land use in the region includes the urban development of Darwin and Palmerston, and their rural hinterland. Groundwater is used for domestic supply in populated areas such as Darwin, Palmerston and rural areas, and horticultural industry such as mango, banana, tropical vegetables, orchids, etc. Other uses include pastoral industry, aquaculture, mining, recreation and tourism (Verma 2002).

Existing data A list of springs reported in previous studies including AUSRIVAS and recorded in HYDSTRA was collated (Figure 5; Table 1). The water chemistry and discharge data were compiled in Appendix A but is only available in electronic form on request.

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Electrical conductivity ~300µScm-1 was used as an indicator of the dolomite source of springs. The dolomite extent was determined using bore data (Tickell unpublished data).

Figure 5. Springs coming from dolomite aquifers (blue) and sandstone (green), and bores (brown) as reported in HYDSTRA.

Table 1. Reported springs with historical range of electrical conductivity and pH (HYDSTRA).

G Name *EASTING *NORTHING EC µScm-1 pH

Springs flowing from dolomite aquifer G8150012 Palm Creek At Holmes Jungle 710312 8628608 260 - 360 6.9 - 7.5

G8155311 Hudson Creek, Wishart Rd & Tivendale Rd 711624 8621421 112 7.7

G8155087 Howard Springs Reserve At Spring 723030 8621960 340 - 360 7.1 - 7.9 G8155309 Inflow Howard River: 4 Springs 726676 8618932 - - G8150179 Howard River At Koolpinyah Stn 726430 8621410 280 - 380 7.0 - 7.8 G8175079 Melacca Creek Spring, Koolpinyah 740836 8630898 - - G8175088 Banka Spring Creek 741542 8625877 - - G8175014 Black Jungle Creek At Spring 740530 8612860 360 7.5

G8175015 Black Jungle Spring At Near G8170083 741030 8612360 420 7.5

G8170064 Hollands Creek At Black Jungle 740130 8611560 337 - 370 7.2 - 7.5 G8155031 Burdens Creek At Spring 721730 8609660 260 7.9 G8155196 Spring At Strangways 724874 8608360 340 7.4 G8155032 Horns Creek At Spring 726030 8605660 414 7.3 G8155622 Horns Ck U/S Confluence Elizabeth R 725457 8605477 206 7.1 G8155625 Amys Ck U/S Rd Xing 723647 8604752 257 7.0 G8155025 Hympty Doo Stn At Spring 745430 8602660 340 7.7 G8170023 Litchfield Creek At Track Xing 744534 8602517 337 - 531 7.0 - 7.5 G8150171 Berry Springs At Pumping Stn 717311 8595361 300 - 420 6.9 - 8.1 G8155288 Berry Creek - Spring At Weir 716970 8594840 346 6.8 G8150028 Berry Creek U/S Cox Peninsula Road 717576 8594437 - - G8155088 Berry Creek @ Cox Peninsula Rd 717530 8593960 299 - 360 6.7 - 7.5 G8155033 Parsons Spring No.1 712330 8593460 370 - 425 7.4 - 8.5 G8150153 Darwin River At Old Army Rd Xing 713648 8589856 240 - 471 7.2 - 8.2 G8170075 Manton R @ Upstream Manton Dam 731230 8575360 424 - 543 7.6 - 7.9 G8155606 Acacia Ck @ Old Road Xing, Spring 738098 8584488 - - G8170033 Manton River At Acacia Gap 738944 8584120 180 - 340 7.0 - 7.7 G8170035 Manton River D/S Acacia Gap 740730 8584060 - - G8155613 Bamboo Ck @ Marrakai Rd 734961 8572140 238 7.1

Springs flowing from sandstone aquifer

G8150095 Imaluk Creek at <100m north of east spring, Cox Peninsula 684302 8626157 30 – 35 4.7 - 4.9

G8155001 Imuluk Springs (East) 688450 8624940 30 - 35 4.6 - 5.3

G8155002 Radio Australia Spring At Cox Peninsula 676630 8626860 46 - 135 5.2 - 5.7

G8155026 Belyuen (Delissaville) At Spring Near Lagoon No.1 681530 8613960 19 - 58 5.0 - 5.1

G8155027 Belyuen (Delissaville) At Spring Near Settlement 684830 8612860 20 - 21 5.6 - 5.7

G8155028 Belyuen (Delissaville) At Lagoon No.1 681630 8613860 21 - 65 5.8 - 6.0

G8155029 Belyuen (Delissaville) At Lagoon No.2 680230 8615660 180 6.1

G8155620 Point Stuart Spring (15m d/s of Spring outlet) 680054 8622776 21 4.65

G8155655 Diamond Creek @ road Xing to point Margaret 680050 8615802 12 4.77

G8150127 Rapid Creek @ d/s McMillans Road 703401 8629208 12 - 290 4.7 – 7.5

- data not available * all locations are GDA94, Zone 52

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The springs flowing from dolomite aquifer show a Ca,Mg-HCO3 water type (Figure 6), with an averaged electrical conductivity of 360 µScm-1, bicarbonate of 210 mgL-1, calcium of 30 mgL-1 and magnesium 27 mgL-1 (Table 2). The springs were then described separately, with respective geological setting, water quality and water quantity, and the potential source of the springs.

Bores with a geological log describing dolomite in their strata (Figure 5) and data of groundwater ionic chemistry sampled from bores drilled in the dolomite aquifer at the depth of water extraction were extracted from HYDSTRA (Appendix B, available in electronic form on request). Groundwater from dolomite aquifer is also of Ca,Mg-HCO3 water type (Figure 7), with an averaged electrical conductivity of 310 µScm-1, bicarbonate of 200 mgL-1, calcium of 30 mgL-1 and magnesium 20 mgL-1 (Table 3).

Table 2. Reported stream water quality (HYDSTRA), dry season conditions (April to

December). n = 104 EC

µScm-1 pH AlkalinitymgL-1

HCO3

mgL-1

SO4

mgL-1

Cl mgL-1

Ca mgL-1

Mg mgL-1

Na mgL-1

K mgL-1

Max 543 8.5 250 296 13 38 93 45 17 2.6Min 102 6.7 58 100 0.2 1.8 9 0.4 1 0.1Mean 348 7.5 177 202 5 10 31 27 4 0.9standard deviation 71 0.4 34 49 3 7 14 8 2 0.4percentile 10 258 7.0 131 121 2 4 18 16 2 0.3percentile 20 320 7.2 162 160 2 5 24 21 2 1.0Median 360 7.5 183 215 5 8 30 28 3 1.0percentile 80 390 7.8 197 234 7 11 32 31 4 1.0percentile 90 420 7.9 207 244 9 18 36 37 6 1.0

Table 3. Reported groundwater quality at depth of water extraction of bores drilled in

dolomite aquifer (HYDSTRA), April to December.

n = 683 EC µScm-1 pH Alkalinity

mgL-1HCO3

mgL-1

SO4

mgL-1

Cl mgL-1

Ca mgL-1

Mg mgL-1

Na mgL-1

K mgL-1

max 398 9.1 260 297 52 45 48 48 25 6min 195 5.4 102 102 1 1 2 11 1 0.3mean 307 7.7 162 196 7 5 28 22 3 1standard deviation 47 0.5 28 34 4 4 7 5 3 0.5percentile 10 240 6.9 124 149 3 2 20 16 2 1percentile 20 261 7.2 135 165 4 3 23 18 2 1median 310 7.7 164 198 6 4 29 22 2 1percentile 80 350 8.1 188 228 9 6 34 26 3 1percentile 90 370 8.3 197 238 10 8 37 29 5 1

9

80 60 40 20 20 40 60 80

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80 80

60

40

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80

Ca Na HCO3 Cl

Mg SO4

Figure 6. Piper diagram of the springs in the study area, n = 97.

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80 60 40 20 20 40 60 80

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80

Ca Na HCO3 Cl

Mg SO4

Figure 7. Piper diagram of the dolomite bores in the study area, n = 683.

Field investigation Field trips were organised from 13 to 23 September 2005 to investigate the location of the springs, the accessibility, flow and water quality (Figure 8). Field measurements included pH, electrical conductivity, dissolved oxygen and temperature using the Hydrolab serial number 7238/7278, whilst turbidity was measured using a Hach turbidity meter. Samples were collected for analyses of nutrients (total Kjeldahl nitrogen, total phosphorus, filterable reactive phosphorus, nitrate, nitrite, ammonia),

11

chlorophyll a, pheophytin, gilvin, soluble reactive silica, major cations (sodium, potassium, calcium, magnesium, iron) and anions (bicarbonate, sulfate, chloride, fluoride), and other parameters such as total dissolved solids, total hardness, total alkalinity. The results of these nutrient and ion samples are not documented within this report.

Following a wet season with low rainfall, most of the springs had already dried up, except Hudson Creek, Berry Springs, Parsons Spring, Melacca Creek and Banka Spring (Table 4). Water electrical conductivity indicated a dolomite source for all these springs (Table 4).

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Figure 8. Location of springs visited in September 2005.

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Table 4. Physico-chemical parameters of springs visited in September 2005 (field data in bold).

# G Name EASTING NORTHING EC µScm-1 pH flow

m3s-1

1 G8150012 Palm Creek at Holmes Jungle 710312 8628608 260 - 360 6.9 - 7.5 dry

2 G8155311 Hudson Creek Tivendale & Wishart Rd 711679 8621654 331 6.43 flowing

3 G8155087 Howard Springs Reserve at Spring 723030 8621960 340 - 360 7.1 - 7.9 dry

3 Howard Springs d/s swimming pool 723102 8622492 364 7.07 ~ 0.001

4 G8175079 Melacca Creek Spring, Koolpinyah 740814 8630932 310 7.14 0.085

5 G8175088 Banka Spring, Koolpinyah 741267 8625906 349 6.80 ~ 0.0005 6 G8175014 Black Jungle Creek At Spring 740530 8612860 360 7.5 - 6 G8170064 Hollands Creek, Black Jungle 739726 8611136 - - dry

6 G8175015 Black Jungle Spring At Near G8170083 741030 8612360 420 7.5 -

7 G8155031 Burdens Creek at Spring 721730 8609660 260 7.9 7 G8155196 Spring at Strangways 724874 8608360 340 7.4 7 G8155032 Horns Creek at Spring 726030 8605660 414 7.3

7 G8155622 Horns Ck u/s confluence Elizabeth R 725457 8605477 206 7.1

7 G8155625 Amys Ck u/s Rd Xing 723647 8604752 257 7.0 8 G8155025 Humpty Doo Stn at Spring 745430 8602660 340 7.7 - 8 G8155025 Humpty Doo Stn at Spring 745279 8602564 - - dry 9 G8150171 Berry Springs at pumping stn 717311 8595361 300 - 420 6.9 - 8.1 - 9 G8155288 Berry Creek – spring at weir 716970 8594840 346 6.8 - 9 G8155288 Berry Creek – spring at weir 716974 8594823 386 6.97 flowing

9 G8150028 Berry Creek U/S Cox Peninsula Road 717576 8594437 - - dry

9 G8155088 Berry Creek at Cox Peninsula Road 717530 8593960 299 - 360 6.7 - 7.5 -

10 G8155033 PARSONS SPRING NO.1 712330 8593460 370 - 425 7.4 - 8.5 - 10 G8155033 PARSONS SPRING NO.1 713063 8591974 373 6.67 flowing

10 G8150153 Darwin River at Old Army Rd Xing 713648 8589856 240 - 471 7.2 - 8.2 -

10 G8150153 Darwin River at Old Army Rd Crossing 714195 8590189 359 7.02 flowing

11 G8155606 Acacia Ck @ Old Road Xing 738098 8584488 - - - 11 G8155606 Acacia Ck @ Old Road Xing 735333 8583543 - - dry

11 G8170075 Manton River @ Upstream Manton Dam 731230 8575360 424 - 543 7.6 - 7.9 -

11 G8170075 Manton River @ Upstream Manton Dam 731154 8575136 464 6.92 flowing

11 G8170033 Manton River at Acacia Gap 738944 8584120 180 - 340 7.0 - 7.7 - 11 G8170035 Manton River d/s Acacia Gap 740730 8584060 - - -

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Springs from Dolomite Aquifer

Palm Creek at Holmes Jungle Palm Creek is situated in Holmes Jungle Nature Park, about 10 km south of Darwin (Figure 9; G8150012). In September 2005, the creek was dry (Plate 1). Little has been reported on this site, except that the creek is flowing from a dolomite aquifer (Figure 5). Dry season data recorded from 1974 to 1980 in HYDSTRA showed a range of electrical conductivity from 260 – 360 µScm-1 and pH from 6.9 – 7.5 (Table 1). Ion composition showed a Ca,Mg-HCO3 water type, typical of dolomite water (Figure 6).

Plate 1. Upstream and downstream of a dirt road crossing of Palm Creek at Holmes

Jungle in September 2005.

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Hudson Creek Spring Hudson Creek is situated west of Palmerston (Figure 9; G8155311). Investigation in September 2005 showed an electrical conductivity of 331 µScm-1 (Table 4). The stream was still flowing in the late dry season (Plate 2). Electrical conductivity and stream flow were determined in July 2000 (Brozek 2000). Relatively higher electrical conductivity of 112 and 181 µScm-1 compared to rainwater (generally approximately 50 µScm-1) indicated that the streams partially source from the same dolomite bed that feeds Palm Creek (Figure 5).

Figure 9. Location of Palm Creek (G8150012) and Hudson Creek (G8155311)

sampling point.

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Plate 2. Hudson Creek, September 2005.

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Howard Springs Howard Springs is situated in the Howard Springs Nature Park, approximately 35 km by road southeast of Darwin (Figure 10). The springs discharge from the Lower Proterozoic Koolpinyah Dolomite which is 2000 million years old (Figure 11). The Dolomite is usually overlain by up to 50 m of clayey sandstone of the Cretaceous Darwin Member (135 million years old) of the Bathurst Island Formation (Figure 12). The springs discharge to the surface directly from an opening in the Koolpinyah Dolomite (Plate 3) (CCNT, 1981; 1982; Pietsch, 1985).

In September 2005 the spring at Howard Springs Nature Park had dried up (Plate 4). Downstream of the swimming pool all the creeks had also dried up (Plate 5), except one channel where less than 1 Ls-1 was flowing (Plate 6). The pH and electrical conductivity of 7.07 and 364 µScm-1 respectively showed a dolomite source of the water (Table 4).

Previous studies The hydrology and geology of the region have been intensively studied. In 1975, the effects of geology, geomorphology and soil distribution, groundwater and natural drainage, and seismic activity on Darwin East urban development were reported (Van den Broek 1975). A potentiometric surface contour map has been drawn up and a large number of known springs have been located. However, it has not been stated whether the springs originate from shallow or deep aquifers.

In 2000, the relationship between spring flow and water quality in the recreational swimming pool was studied at Howard Springs (Tien 2002). Historical dry season spring flows over approximately 100 years have been synthesised and the calculated flow correlated well with actual gauging flow (Figure 13). In 2000, the Dolomite aquifer was fully recharged in the wet season and incoming rainfalls influenced favourably the spring discharge (0.310 m3s-1 in April). As the dry season progressed, the spring discharge declined rapidly following the cessation of rains and was only 0.031 m3s-1 at the end of the Dry season (Figure 14). In the wet season, the flow increased with distance downstream of the spring whilst in the dry season, there was not a significant difference between the flow at the spring, inflow to and outflow of the swimming pool (Figure 15).

In 2000, pH increased with distance downstream of the spring and increased with time as the dry season progressed (Figure 16). In the wet season, the electrical conductivity in the pool was lower than the electrical conductivity in the spring due to rainwater dilution, whilst the water in the pool was gradually the groundwater discharge from the spring with the progress of the dry season (Figure 17). Dissolved oxygen was low at the spring and increased with distance at the inflow to and outflow of the pool (Figure 18). The ion composition also followed the same pattern as electrical conductivity (Appendix C, but is only available in electronic form on request).

Historical surface water chemistry and gauging data at Howard Springs spring (G8155087) have been recorded in HYDSTRA, as well as groundwater chemistry and water level measurements in the adjacent bore RN009421 (Appendix C).

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Figure 10. Location of Howard Springs

Dolomite

Sand

SpringP

umping bore

Observation bore

Claystone

Mudstone

Dolomite

Sand

SpringP

umping bore

Observation bore

Claystone

Mudstone

Figure 11. Local geology at Howard Springs (Tickell unpublished)

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Figure 12. Geologic history of Howard Springs (Tickell unpublished)

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Plate 3. The spring at Howard Springs Nature Park, 2000.

0.0001

0.0010

0.0100

0.1000

1.00001900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Time (years)

Pred

icte

d sp

ringf

low

(m3 /s

)

synthesised baseflow actual gauging G8150005 actual gauging G8150031

18701860 18901880

Figure 13. Predicted spring flow at Howard Springs from 1870 to 2000 (Tien 2002). Minimum baseflows were calculated for the day prior to the first annual recharge event.

21

y = 1E+178e-0.0112x

R2 = 0.9758

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

03/2000 04/2000 05/2000 06/2000 07/2000 08/2000 09/2000 10/2000 11/2000 12/2000

Time (days)

Dis

char

ge (m

3 s-1)

Figure 14. Dry season flow recession at Howard Springs spring in 2000 (Tien 2002).

springinflow

outflow

10/10/2000

22/08/2000

27/06/2000

30/05/2000

03/05/200007/04/2000

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.500

Flow (m3s-1)

Location

Time (day)

10/10/200022/08/200027/06/200030/05/200003/05/200007/04/2000

Figure 15. Increase in flow with distance in the wet season and no significant difference in flow with distance in the dry season (Tien 2002).

22

springinflow

outflow

07/04/2000

03/05/2000

30/05/200027/06/2000

22/08/200010/10/2000

30/11/2000

6.50

7.00

7.50

8.00

pH

Location

Time (day)

07/04/200003/05/200030/05/200027/06/200022/08/200010/10/200030/11/2000

Figure 16. Increase in pH with time and distance (Tien 2002).

springinflow

outflow

07/04/2000

03/05/2000

30/05/200027/06/2000

22/08/200010/10/2000

30/11/2000

0

50

100

150

200

250

300

350

400

EC (µScm-1)

Location

Time (day)

07/04/200003/05/200030/05/200027/06/200022/08/200010/10/200030/11/2000

Figure 17. Rainwater dilution of spring water in the pool in the wet season and

groundwater discharge in the pool in the dry season as illustrated in change of electrical conductivity (Tien 2002).

23

outflowinflow

spring

07/04/2000

03/05/2000

30/05/200027/06/2000

22/08/200010/10/2000

30/11/2000

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Dissolved Oxygen (mgL-

1)

Location

Time (day)

07/04/200003/05/200030/05/200027/06/200022/08/200010/10/200030/11/2000

Figure 18. Increase in dissolved oxygen with distance downstream of the spring

(Tien 2002). A numerical model representing the McMinns / Howard East groundwater system has been developed to confirm the hydrogeological concepts presented in previous studies as well as to analyse flow regimes in detail and enable the components of the highly dynamic water balance to be quantified in ‘bulk’ estimate terms (Yin Foo 2004). The groundwater system is represented as a two-layer finite difference model. The upper layer’s (Layer 1) hydraulic characteristics combine the shallow laterite aquifer with the Cretaceous sediments whilst the lower layer (Layer 2) represents the aquifer developed in the Koolpinyah Dolomite and the highly weathered zone immediately above it. Different scenarios from natural conditions to different levels of development have been investigated. Groundwater discharges have been described as discharge to streams and springs in Layer 1, shallow surficial discharge from Layer 1, groundwater discharge to streams and springs in Layer 2, evapotranspiration from Black Jungle Swamp and all other evapotranspiration.

The significant spring discharges in the study area, Howard Springs and springs in Melacca Creek, are direct windows to the dolomite aquifer, and baseflows would be adversely affected by intensive drawdown (Yin Foo 2004).

24

Plate 4. Howard Spring in September 2005.

25

Plate 5. Dry channel downstream of Howard Springs swimming pool, September

2005.

Plate 6. Flowing creek downstream Howard Springs swimming pool, September

2005.

26

Koolpinyah: Melacca Swamp and Banka Spring In September 2005, whilst Howard Springs and the creeks in Holmes Jungle and Black Jungle dried up, there was still a substantial flow (Table 5) in Melacca Swamp (Plate 7) and Banka Spring (Plate 8).

Discharge and electrical conductivity have been measured in Melacca Swamp and Banka Spring (Figure 19) to determine the amount of groundwater discharge from the dolomite formation into the Koolpinyah station waterways (Van der Bersselaar 1999). It was found that through the dry season, the influence of runoff decreases and electrical conductivity increases, corresponding to the increasing discharge from dolomite water (Table 5).

Melacca Creek and Banka Spring together with Howard Springs are windows to the dolomite in the area (Yinfoo 2004). As the dry season progresses, the dolomite aquifer contribution to baseflow in these creeks increases and may be attributed to a reversal in gradient (i.e. upward leakage) through the shallow laterite aquifer.

Table 5. Discharge and field measurements in 1999 (Van der Bersselaar) and 2005.

Date Discharge

m3s-1

EC

µScm-1 pH

Melacca Swamp (G8175079)

08/6/1999 0.768 237 8.0

01/7/1999 0.564 261 7.5

10/8/2005 0.158 318 7.27

15/9/2005 0.085 310 7.14

Banka Spring (G8175088)

08/6/1999 0.079 233 8.0

01/7/1999 0.043 292 7.7

10/8/2005 0.003 335 7.5

15/9/2005 0.0005 349 6.80

27

Figure 19. Location of Melacca Swamp (G8175079) and Banka Spring (G8175088) sampling points, and Hollands Creek at Black Jungle (G8170064) and Litchfield Creek at Humpty Doo Station (G8155025).

28

Plate 7. Melacca Swamp, September 2005.

29

Plate 8. Banka Spring, September 2005.

30

Black Jungle Springs In September 2005, all the creeks had dried up (Plate 9). Not much has been reported, with the exception of data recorded in HYDSTRA in 1979 (Table 1). Discharge and electrical conductivity measurements were also undertaken in 1999 (Van der Bersselaar). Springs in Black Jungle Swamp (Figure 19) also tap the dolomite aquifer determined using bore data (Figure 5).

Plate 9. Hollands Creek in Black Jungle Swamp, September 2005.

Springs in Elizabeth River Catchment The springs and creeks identified in Elizabeth River Catchment (Figure 20) had all dried up at the end of September 2005. Data recorded in HYDSTRA showed a high electrical conductivity in the range of 206 to 414 µScm-1 (Table 1), indicating a probable source from dolomite aquifer or shale containing dolomite (Figure 5).

Litchfield Creek Data recorded in HYDSTRA showed a high electrical conductivity of 340 µScm-1 at Humpty Doo Station, an Aboriginal community (Figure 19), and 337 – 531 µScm-1 in Litchfield Creek downstream the station (Table 1). Measurements in Litchfield Creek in May 2005 (Fukuda in prep.) also showed an electrical conductivity of 335 µScm-1, indicating a probable source from dolomite aquifer. More investigation using bore drilling data (Figure 5) would be required. The creek had dried up in September 2005 (Plate 10).

31

Figure 20. Location of identified springs in creeks flowing into Elizabeth River.

32

Plate 10. Litchfield Creek at Humpty Doo Station, September 2005.

33

Berry Springs Water quality data recorded in HYDSTRA shows a typical Ca,Mg-HCO3 dolomite water type (Figure 6) with electrical conductivity ranging from 300 – 420 µScm-1 (Table 1). Data collected in September 2005 reported an electrical conductivity of 386 µScm-1 (Table 4). The spring maintained a substantial flow for the end of the dry season (Plate 11).

Geology in the Berry Springs – Noonamah region is strongly controlled by a major fault (The Giant Reef Fault) striking NE-SW in the southern part of the area where it cut across the Archaean rocks and created very tight folding, resulting in ridges of the Lower Proterozoic rocks. The silicified dolomite in the Berry Springs area has been named Berry Springs Dolomite, and likely to be deposited in the Middle Proterozoic age (Verma 1994). Berry Springs in the Berry Springs Nature Reserve is the main outlet for the small dolomite basin structure that is truncated at its northern end by a fault (Figure 21). The spring occurs at a low point in the landscape along the fault where the aquifer is in contact with impermeable shale and combines to form a tributary of Berry Creek (Figure 22). Berry Springs actually consists of numerous individual springs that spread along both the main fault and smaller ones, all of which are interconnected (Tickell unpublished).

Springflows from 1870 to 1999 have been synthesised from rainfall records and calculated recharge events (Jolly et al. 2000). For most of the period, the flow from the springs has been in excess of 100 Ls-1 at the end of the dry season, except in only 2 years (1906 and 1970), springflows of approximately 10 Ls-1 are likely to have occurred at the end of the dry season.

34

Figure 21. Location and source of springs in Berry Springs Nature Park (Tickell

unpublished)

35

Figure 22. Location of Berry Springs (G8155288) and Parsons Springs (G8155033).

36

Plate 11. Berry Springs in September 2005.

37

Parsons Spring The spring taps the same dolomite aquifer as Berry Springs (Figure 22) and flows into Darwin River (Plate 12). HYDSTRA records showed an electrical conductivity of 370 – 425 µScm-1 (Table 1), typical of a dolomite aquifer origin. At high tide, the spring is covered, but not influenced by the tide. Data collected in September 2005 showed an electrical conductivity of 373 µScm-1 (Table 4). The spring water is pumped for domestic and stockwater supplies (Plate 13).

Acacia Springs No data are recorded in HYDSTRA although Acacia Springs has been described as a high yielding dolomite aquifer with 1450 MLyear-1 (Tickell 2000). The Manton River and Acacia Creek cut through both the east and west side of the surrounding quartzite hills (Figure 23). Spring flows from the Coomalie Dolomite aquifer contribute to Manton River, Acacia Creek and their main tributaries up until mid way through the dry season. Groundwater discharges from the aquifers at low points in the landscape via seepage into streambeds and springs, therefore, many low lying areas are waterlogged and show active seepage throughout the wet season and for several months into the dry season. The springs naturally dry up well before the end of the dry season. Springs usually cease to flow by September at the latest (Tickell 2000), indicating that all of the previous wet season’s recharge drains out of the aquifer prior to the following wet season (Plate 14).

Plate 12. Parsons Spring confluence with Darwin River.

38

Plate 13. Parsons Spring.

39

Figure 23. Location of Acacia Spring (G8155606) and Manton River (G8155604).

40

Plate 14. Acacia Spring in September 2005.

41

Changes in surface water quality with distance

Darwin River The electrical conductivity downstream of the Darwin River Dam was in the range of 50 to 60 µScm-1 (Figure 24) and exceeded 300 µScm-1 when the river flows over the dolomite aquifer. The ionic composition of bicarbonate, calcium and magnesium followed the same pattern (Table 6).

Manton River The electrical conductivity at the gauging station G8170075 upstream of Manton Dam ranges from 424 to 543 µScm-1 (Table 1), reflecting the influence of dolomite water (Figure 24). Downstream of Manton Dam, fresher electrical conductivity of 120 µScm-1 was recorded in May 2005 (Table 6). Further downstream of Acacia Gap, Manton River electrical conductivity ranges from 180 to 340 µScm-1 (Table 1), probably due to the input of the dolomite spring at Acacia Gap (Tickell 2000).

Howard River The electrical conductivity at the sampling points upstream of Howard Springs showed a fresh water quality from 20 to 50 µScm-1 (Table 6) whilst at the surroundings of Howard Springs electrical conductivity ranges from 280 - 380 µScm-1 (Table 1), reflecting the dolomite influence of groundwater (Figure 24).

Table 6. Electrical conductivity and ionic composition at different sampling points downstream of Darwin River, Manton River and Howard River (HYDSTRA and AUSRIVAS).

G code Date pH E.C. µScm-1

HCO3mgL-1

Cl mgL-1

Ca mgL-1

Mg mgL-1

Na mgL-1

K mgL-1

Darwin River G8155479 29/04/2005 6.23 60 29 2.3 3.3 4.0 3.3 0.4G8155635 07/06/2005 6.18 51 26 2.2 3.0 3.0 3.4 0.5G8155636 08/06/2005 6.13 51 26 2.0 2.9 2.9 3.5 0.5G8155638 08/06/2005 6.17 50 27 2.0 3.2 3.1 3.5 0.4G8155639 09/06/2005 6.25 51 27 2.1 2.7 3.0 3.7 0.4G8155640 09/06/2005 6.29 51 27 2.0 2.7 3.2 3.7 0.4G8155641 09/06/2005 7.11 333 182 1.9 28 27 2.0 0.2G8155092 10/05/2005 7.20 317 170 1.8 26 26 2.3 0.4

Howard River G8150179 13/05/2005 7.01 280 141 5.0 18 25 3.0 0.3G8155477 19/05/2005 5.93 41 G8155475 19/05/2005 5.51 24

Manton River G8155604 06/05/2005 7.20 444.0 234 2.4 48 29 3.8 1.3G8155627 10/05/2005 6.75 120.0 65 1.6 11 7.1 3.1 0.5

42

Figure 24. Changes in conductivity with distance from groundwater input.

43

Changes in surface water quality with time In 2005, electrical conductivity was measured weekly in Howard River, Elizabeth River, Bennetts Creek and Rapid Creek (Butler 2005). Whilst Bennetts Creek and Rapid Creek were fresh with electrical conductivity less than 50 µScm-1 during the dry season (Appendix C), the electrical conductivity in Elizabeth River and Howard River increased as the dry season progressed (Figure 25). The contribution from dolomite aquifer to the Howard River was noticeable in May 2005 and since then groundwater has been the main component of river flow as shown by the range of electrical conductivity from 313 – 383 µScm-1. The increase in electrical conductivity in Elizabeth River was more likely related to ionic concentration due to evaporation when the river stopped flowing rather than the influence of dolomitic rocks (Figure 25).

0

100

200

300

400

500

02/2005 03/2005 04/2005 05/2005 06/2005 07/2005 08/2005

Time (month)

EC ( µ

Scm

-1)

G8150179Howard River

G8150018Elizabeth River

Figure 25. Electrical conductivity in Howard River and Elizabeth River in 2005 dry

season.

Springs in Cox Peninsula Groundwater flows from shallow aquifers at the unconformity between the Lower Proterozoic and the Lower Cretaceous rocks and in the weathered zone comprising the upper layer of the Lower Proterozoic rocks, and from deep aquifers associated with NS faulting (Doherty 1981; Verma 1982). Cretaceous sediments consist mainly of sandstone with siltstone and silicified claystone (Verma 1981). Groundwater discharges to a number of small springs (Verma 1981). The springs at Imuluk Creek and Diamond Creek have a low electrical conductivity ranging from 12 to 180 µScm-1 and low pH from 4.6 to 6.1 (Table 1).

44

Discussion and recommendations

Sources of the springs In September 2005, most of the springs had dried up (Table 4), except Hudson Creek, Melacca Creek, Banka Spring, Berry Springs and Parsons Spring (Figure 8). Palm Creek at Holmes Jungle, Hollands Creek at Black Jungle, Litchfield Creek and Acacia Spring are reported to naturally dry up at the end of the dry season (Tickell 2000).

Palm Creek and Hudson Creek flow from Palmerston Dolomite (Tickell unpublished). The typical high conductivity of approximately 300 µScm-1 recorded in the tributaries to the Elizabeth River (Table 1; Figure 20), and the location of the bores drilled in dolomite along the Elizabeth River (Figure 5) imply a possible dolomite origin of the stream water. The extent of the dolomite aquifer probably exists further south in the Elizabeth River catchment.

Howard Springs, Melacca Spring and Banka Spring flow from Koolpinyah Dolomite (Pietsch 1985). Modelling of different development scenarios concluded that land use has minimal impact on Melacca Spring and Banka Spring (Yinfoo 2004). However, rural development and extreme seasonal conditions such as low rainfall are reported to adversely impact Howard Springs dry season flows, the springs actually ceased to flow more often (Yinfoo 2004).

The springs at Black Jungle Swamp also originate from Koolpinyah Dolomite. The typical high conductivity of approximately 300 µScm-1 recorded in Litchfield Creek at Humpty Doo Station (Table 1; Figure 19) and the presence of bores drilled in dolomite in the vicinity of the spring imply a possible dolomite origin of the stream water. The extent of the dolomite aquifer could include Humpty Doo Station.

Berry Springs and Parson Spring flow from Berry Springs Dolomite (Verma 1994) and retain a substantial discharge throughout the dry season. However, the aquifers have been highly exploited mainly for horticulture and measures to protect the groundwater are currently under investigation.

Upstream of Manton Dam, Manton River flows from Coomalie Dolomite (Pietsch 1985) and has typical dolomite water quality (Table 4). Downstream of Manton Dam, Manton River flows along the quartzite Daly Range and the electrical conductivity becomes fresher (Figure 24). Downstream of the confluence with Acacia Creek at Acacia Gap, Manton River’s electrical conductivity reflects the dolomite origin of Acacia Springs (Table 4). Acacia Springs sources from Coomalie Dolomite aquifer at Larrakia Community (Tickell 2000).

Springs in Cox Peninsula flow from Cretaceous Sandstone and electrical conductivity reflects the fresh origin of stream water quality (Table 1).

Difference in water quality in different dolomite aquifers Water quality of bores from Koolpinyah Dolomite, Palmerston dolomite, and Berry Springs Dolomite have been listed (Appendix B). Principal component analysis was performed (StatSoft 1984-2005) to evaluate relationships among the chemical components and the dolomite aquifer. Two eigenvalues were greater than 1 and explained 50% of the total variance (Table 7). Factor 1 explained 36% of the variance among the elements and represented electrical conductivity, alkalinity, bicarbonate, hardness, total dissolved solids and magnesium. Factor 2 explained 15% of the variance and accounted for chloride, nitrate and sodium (Table 8).

45

Table 7. Eigenvalues extracted from principal component analysis

Eigenvalues % total variance Cumulative eigenvalues Cumulative %

1 6.05 35.6 6.05 35.6

2 2.48 14.6 8.53 50.2

Table 8. Summary of factor analysis. The factor loadings represent the correlation

coefficients between the original variables and the newly derived factor. Factor names and the high-loading variables Factor loadings

Factor1

Electrical conductivity 0.97

Alkalinity 0.95

Bicarbonate 0.94

Hardness 0.98

Total dissolved solids 0.92

Magnesium 0.77

Factor 2

Chloride -0.87

Nitrate -0.90

Sodium -0.90

Influence of deep aquifer springs on stream water quality in the dry season Data recorded in HYDSTRA reflect three different behaviours of surface and groundwater quality in the wet season. According to geological location, the streams and bores at the proximity of the coastline show a significant increase in electrical conductivity in the order of several thousand µScm-1 and significantly high chloride concentration of several hundred mgL-1. The streams receiving substantial runoff show a significant decrease in electrical conductivity (less than 50 µScm-1) due to rainwater dilution. Some bores and streams water quality (for example Berry Springs, Howard Springs, Manton River) remains the same with electrical conductivity of approximately 300 µScm-1.

In the dry season, due to the absence of rainfall, the effects of saltwater intrusion and rainwater dilution disappear. As the dry season progresses, static water level and stream flow decrease. During this period baseflow is maintained by groundwater discharge, with electrical conductivity and ionic composition of streams reflecting the dolomite origin of the deep aquifer (Table 3).

Change in stream water quality with distance Data collected in Darwin River, Manton River and Howard River at different distances upstream and downstream of the groundwater input show a significant difference in electrical conductivity (Figure 24). This reflects the influence of the

46

regional lithology on the stream water quality. The dolomite aquifer influences the high electrical conductivity and amounts of bicarbonate, calcium and magnesium in the rivers. Sandstone and quartzite aquifers bring fresher electrical conductivity to the streams.

Recommendations * Monitoring bore water levels as well as surface water gauging is needed to

better understand the groundwater – surface water interaction and the recharge – discharge process.

* Additional water sampling, and modelling is required to evaluate the impact of dolomite springs on stream water quality downstream of the discharge point.

* The extent of dolomite aquifer has been determined using bore data (Figure 5). More investigation is needed to determine the extent of the dolomite aquifer in the Elizabeth River catchment and Litchfield Creek at Humpty Doo Station.

Acknowledgement This project is funded by the NAP project number 2004/34. Many invaluable comments from Simon Townsend, Julia Fortune, Armando Padovan, Trevor Haig, Peter Jolly, Steven Tickell and Desmond Yin Foo are sincerely appreciated. Yusuke Fukuda is thanked for assisting in drawing the maps. Rodney Metcalfe, Roger Farrow, Yusuke Fukuda and Gisela Lamche helped so much in the field work. Judy and Rocky Bartolo kindly let us investigate Parson Springs in their domain.

47

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