DEPARTMENT OF NATURAL RESOURCES THE ENVIRONMENT AND THE ARTS NATURAL RESOURCES DIVISION

GROUNDWATER RESOURCES

OF THE

TINDALL LIMESTONE

REPORT 34/2005 S.J.TICKELL DARWIN APRIL 2005

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Summary ........................................................................................................................... 1 Introduction ....................................................................................................................... 1

Aim ............................................................................................................................... 1 Previous Work ............................................................................................................... 1 Study area...................................................................................................................... 2 Methodology.................................................................................................................. 2 Climate .......................................................................................................................... 4 Geomorphology............................................................................................................. 4

Geology............................................................................................................................. 5 Pre-Daly River Group Rocks ......................................................................................... 5 Daly River Group .........................................................................................................10

Tindall Limestone .....................................................................................................10 Jinduckin Formation .................................................................................................12

Cretaceous Rocks..........................................................................................................12 Geological structure......................................................................................................13

Groundwater.....................................................................................................................23 Groundwater flow.........................................................................................................24 Recharge.......................................................................................................................25 Discharge......................................................................................................................26

Roper River ..............................................................................................................28 Flora River................................................................................................................29 Katherine River.........................................................................................................38 Edith and Ferguson Rivers ........................................................................................38

Aquifer Characteristics .................................................................................................38 Water quality ................................................................................................................40 Resource assessment .....................................................................................................41

References ........................................................................................................................43

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Figures Figure 1 Extent and thickness of the Tindall Limestone ..................................................... 3 Figure 2 Regional geology of the Palaeozoic basins ........................................................... 6 Figure 3 Bedrock geology beneath the Daly Basin ............................................................. 7 Figure 4 Gamma log showing a typical profile of the Tindall Limestone...........................15 Figure 5 Gamma log cross-section of the Tindall Limestone, Douglas River to Dunmarra.

.................................................................................................................................16Figure 6 Extent of Cretaceous rocks..................................................................................17 Figure 7 Section 1, Gamma log cross-section Daly Basin to Wiso Basin...........................18 Figure 8 Section 2, Gamma log cross-section Daly Basin to Georgina Basin.....................19 Figure 9 Elevation of the base of the Tindall Limestone....................................................20 Figure 10 Section 3, Gamma log cross-section, Venn area ................................................21 Figure 11 Section 4, Gamma log cross-section Wiso Basin to Georgina Basin ..................22 Figure 12 Springs on the Katherine River .........................................................................23 Figure 13 Confining beds on the Tindall Limestone..........................................................30 Figure 14 Potentiometric surface, Tindall aquifer..............................................................31 Figure 15 Bore hydrographs..............................................................................................32 Figure 16 Minimum annual flows at the Katherine River railway bridge. ..........................33 Figure 17 Cross-section through Fig Tree Spring ..............................................................34 Figure 18 TDS zones ........................................................................................................42 Plates Plate 1 Limestone towers, Katherine area........................................................................... 8 Plate 2 Aerial view of a recent sinkhole collapse, Katherine area ....................................... 8 Plate 3 Cutta Cutta caves ................................................................................................... 9 Plate 4 Potholes and solution grooves typical of karstic weathering of Tindall Limestone .. 9Plate 5 Source of Katherine Hot Springs ...........................................................................11 Plate 6 Groundwater fed lake, Zimmin Drive Katherine....................................................27 Plate 7 Source of Rainbow Spring near Mataranka............................................................35 Plate 8 Bitter Springs, swimming area...............................................................................35 Plate 9 Fig Tree Spring .....................................................................................................36 Plate 10 Stalactites at the tufa dam on Elsey Creek ...........................................................37 Plate 11 Kathleen Falls .....................................................................................................37

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Summary The Tindall Limestone is one of the two major fractured and cavernous aquifers in the Daly Basin. The regional groundwater flow paths are described with most flow occurring parallel to the basin edge and towards the streams that cut across the basin. In the central part of the basin where the aquifer is at considerable depth, only minor flow is considered to occur. The aquifer is unconfined in places around the basin margin. Elsewhere it is confined or partly confined by younger formations. Recharge is highest in the unconfined areas, negligible where the confining layer is the Jinduckin Formation and intermediate in value where Cretaceous rocks overlie the aquifer. Discharge zones are mainly located along the major rivers and comprise both karstic springs and more diffuse stream bed discharge. The geological and hydrogeological relationships between the Daly Basin and the Wiso and Georgina Basins to the south are delineated in this report. Groundwaters from the two southern basins flow north into the Daly Basin. Water quality of the Tindall aquifer groundwaters is typical of those from dolomite aquifers. They are slightly alkaline with calcium, magnesium and bicarbonate being the dominant ions. Most groundwaters have a high hardness but are suitable for stock and domestic purposes. The only major variation in water quality is found in the area between Mataranka and Daly Waters. That groundwater originates from the Georgina Basin, flows north into the Daly Basin and has relatively high values of sodium, chloride, sulphate and TDS. The source of these ions is thought to be evaporite minerals within the Anthony Lagoon Beds. There appears to be hydraulic connection between that formation and the underlying Gum Ridge Formation. The latter is continuous with the Tindall Limestone.

Introduction Aim

This study aims to describe the regional hydrogeology of the Tindall Limestone aquifer, including its extent, thickness, geology, hydraulic properties, recharge, regional flow pattern, discharge and water quality.

Previous Work

The Tindall Limestone was first described as a separate formation of the Daly Basin by Randal (1962) and Malone (1962). It was formally defined by Kruse and others (1990). The earliest hydrogeological assessment of the Daly Basin was done by Laws (1968). It was a preliminary study to evaluate the prospects for water supplies and to propose a regional drilling program. At that time there were only 44 bores known to tap the Tindall aquifer. Springs in the northern part of the basin were identified and sampled. Many of those springs issued from the Tindall aquifer. The general hydrology of the Katherine/Daly River system and the potential of the Tindall Limestone as an aquifer were described in a report by the Department of Northern Territory (unnamed 1976). Late Dry season surveys of the Katherine, Daly and Flora Rivers were

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carried out in the early 1980’s (unnamed, 1983, 1985 and 1988). Baseflows and water quality were measured during these surveys. Jolly (2002) identified the main groundwater discharge sites along the rivers. Tickell and others (2002) and Russ and others (2005) measured baseflows across the Daly Basin and refined the locations of discharge sites. The Water Resources Branch and the Geological Survey carried out a program of deep stratigraphic / water investigation drilling in the Daly Basin from the late 1960’s through to the 1980’s. Many of these holes including RN7838 (DB30a), RN6825 (DB10), RN33510 (NTGS 83/2), RN33512 (NTGS 83/4), RN32097 (NTGS 86/1) and RN8855 (KRVH1), intersected Tindall Limestone and are described in Lau (1981a and 1981b) and Kruse (1987). Jolly (1984) studied the regional hydrogeology of the northern Daly Basin, including the Tindall Limestone. He described the hydrogeology of the Tindall aquifer in the Douglas River area and estimated a safe yield. Estimates of recharge were revised and extended to the Katherine area by Jolly (2002) utilising base flow data from the Daly River. Groundwater availability of the Tindall aquifer in the area south or the Roper was estimated by Jolly and others (2004) Various geological mapping projects have covered the area and have defined the extent and geological properties of the Tindall Limestone (Malone 1962, Randal 1962, Randal 1963, Kruse et al 1990 and Kruse et al 1994). The Bureau of Mineral Resources completed the Katherine and Ferguson River 1:250 000 scale mapsheets in 1963 and 1962 respectively and the Katherine sheet was remapped by the Northern Territory Geological Survey in 1994. The northern section of the basin has been largely covered by 1:100,000 geological mapping done by the Geological Survey and in some instances in conjunction with the Bureau of Mineral Resources. Karp (2002) described the karstic terrain formed on the Tindall Limestone around Katherine. The influences of human activities on sinkhole collapses were emphasised.

Study area

The area under investigation is the full extent of the Daly Basin. The basin trends north-west / south-east and extends from Tipperary station in the north-west, to Larrimah in the south-east and from Katherine in the north-east to the Flora River Nature Park in the south-west (Figure 1). An outlier of Daly Basin rocks not described here occurs to the north west of the main part of the basin between the lower Daly and Reynolds Rivers.

Methodology

Borehole strata logs, down-hole gamma logs, geological mapping, satellite imagery, topography and airborne geophysical surveys were utilised to make an assessment of the Daly Basin’s stratigraphy, the distribution of the main formations and aquifers. Much of this information was compiled using ARCVIEW, a Geographic Information System. Information from existing reports has also been included here.

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Figure 1 Extent and thickness of the Tindall Limestone

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Climate

The area falls within the wet-dry tropics, having two distinct seasons. The wet season is from December to April and the dry season spans the remainder of the year. During the wet season the area comes under the sporadic influence of the monsoon as well as intense rain depressions resulting from decaying tropical cyclones. This results in a rainfall that is highly variable. Annual (October to September) rainfall totals at Katherine vary from a low of 364 mm (1951/52) to a high of 1990 mm (1897/98). The impact of the monsoon results in over 90% of Katherine’s mean annual rainfall of 970 mm occurring between the months of November and March. The mean annual rainfall progressively decreases inland. In the north it is about 1000 mm at the Douglas River but is only about 800mm at Larrimah in the south. Annual pan evaporation is high at around 3000mm. Evaporation rates are highest around October and lowest around March. Temperatures range from a mean annual maximum of 340C to a minimum of 200C. Temperatures are highest in October and November when daily maxima approach 380C.

Geomorphology

The study area falls within the catchment of the Katherine, Daly and Roper Rivers. On a broad scale, underlying geological structure influences the location of all of the major streams. Two dominant directions are apparent, a northeast – southwest orientation, perpendicular to the long axis of the Daly Basin and a northwest – southeast orientation parallel to the axis. The Daly and the lower section of the King River have the latter orientation. Streams with the former orientation include the upper section of the King, the Dry, the Katherine upstream of the King, the Flora, Douglas and the Ferguson Rivers, and Stray and Bradshaw Creeks. These cut across the general north-west to south-east strike of the Tindall Limestone along the margins of the basin. The structures, which guide the drainage pattern, are likely to be fractures rather than faults as few faults have been recognised within the Daly Basin sequence. The present day landscape is largely erosional and has resulted from the dissection of soft Cretaceous sedimentary rocks that formerly blanketed the whole area. The upper surface of those rocks forms a peneplain that has been broadly warped and lateritised (the Tennant Creek Surface of Hays 1967). Only remnants of the surface are preserved as mesas and plateaus capped with laterite or silcrete and they generally form the higher terrane with elevations varying between 120 and 300m. The Tindall limestone is mainly exposed in lower lying areas adjacent to the major rivers. In some locations the present day land surface closely approximates the contact between Cretaceous rocks and the underlying Tindall Limestone. It represents an exhumed pre-Cretaceous land surface. This can be seen around Katherine, for example in the Cutta Cutta Caves reserve. Such areas are flat to gently undulating with occasional low hills or mesas of Cretaceous sandstone or claystone. In some cases the contact between the two formations may not be the original land surface as some dissolution of the limestone has occurred since the Cretaceous. This is evidenced by outcrops of sandstone that consist of large jumbled blocks that have undergone differential movement as the limestone beneath has been dissolved away.

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Outcrops of Tindall Limestone commonly exhibit features typical of dissolution of limestone. These range from the large scale, such as towers, fissures, sinkholes, caves and pavements (Plates 1, 2 and 3), through to the smaller scale, such as grooves, pans, potholes and honeycomb like cavities (Karp 2002)(Plate 4). Cave systems are extensively developed in the Katherine area. Elsewhere few have been reported but it is possible that it is because those areas are relatively unexplored.

Geology The Daly River Group is a sedimentary sequence of Lower Palaeozoic age (approximately 500 million year old). It comprises the Daly Basin, a broad basin structure, elongated in a north west / south east direction. It is some 70 km wide by 350 km long and has a maximum recorded thickness of 708.5m (NT Geological Survey stratigraphic drill hole NTGS 86/1, RN32097). The Tindall Limestone is the basal formation of the Daly River Group and so is exposed around the margins of the basin. It is overlain by the Jinduckin Formation which is in turn overlain by the Oolloo Dolostone. The regional geology of the Daly Basin and adjoining Palaeozoic basins is shown in Figure 2.The Daly River Group sits unconformably on a variety of Pre-Cambrian and Early Cambrian rocks and is inturn overlain in places by Cretaceous clays and sandstone.

Pre-Daly River Group Rocks

A variety of different formations underlie the Tindall Limestone. The majority of these only host minor fractured rock aquifers. The youngest of these formations are Early Cambrian in age, only slightly older than the Tindall itself but not considered to be part of the Daly River Group. They comprise two formations, the Jindare Formation and the Antrim Plateau Volcanics. The Jindare Formation is sandstone which is exposed on the north eastern margin of the Basin between Douglas Station in the north to Maranboy in the south. It mostly overlies the Antrim Plateau Volcanics but is also interbedded with it in places. Conformity between the Jindare Formation and the Tindall Limestone has not been established (Kruse and others 1990). The Antrim Plateau Volcanics are more widespread (Figure 3). They underlie the Daly Basin south of the Edith River and extend westwards into the Victoria River District and into Western Australia. The formation is mainly basalt with minor sandstone interbeds. The thickest section of basalt that has been drilled is 222 metres on Nutwood Downs Station, 110km south of Mataranka. Few bores have penetrated the full thickness of the formation however. On its north eastern side, the Daly Basin is underlain by Proterozoic aged sedimentary and volcanic rocks and granites which intrude them. These are part of the Pine Creek Geosyncline and Tolmer Group. On the north west side similar rocks are part of the Victoria River Basin and Tolmer Group. Proterozoic rocks also directly underlie the basin along its margin between the King River and Mataranka and further to the southeast. These are also mainly sedimentary rocks but include minor volcanics.

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Figure 2 Regional geology of the Palaeozoic basins and cross-section locations, note that overlying Cretaceous rocks not shown

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Plate 1 Limestone towers, Katherine area (photo D. Karp)

Plate 2 Aerial view of a recent sinkhole collapse, Katherine area (photo D. Karp)

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Plate 3 Cutta Cutta caves, 20 km south east of Katherine (photo D. Karp)

Plate 4 Potholes and solution grooves typical of karstic weathering of Tindall Limestone (photo D. Karp)

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Daly River Group

The Daly River Group (Noakes 1949) comprises the sedimentary fill of the Daly Basin. It is made up of three formations. The lowermost unit is the Tindall Limestone overlain by the Jinduckin Formation and then the uppermost unit, the Oolloo Dolostone. The Tindall and Oolloo are dominantly limestone and dolostone, while the Jinduckin Formation is mainly siltstone with minor limestone and sandstone.

Tindall Limestone The Tindall Limestone is the basal formation of the Daly River Group. It was defined by Kruse and others (1990), with its type section in the cored drill hole RN32097 (NTGS 86/1) between the depths 579.3 and 760.0 metres. Thicknesses recorded in boreholes range from 133m (RN031108 in the Dry River area) to a maximum of 204m (RN6331 on Tipperary station). Thirteen bores fully penetrate the formation and there is no obvious trend in the thickness across the basin (Figure 1).Note that these thicknesses have not been corrected to true thicknesses as the beds generally have very low dips (less than 20). The formation is present throughout the Daly Basin. It is also laterally continuous with equivalent formations in the Georgina and Wiso Basins to the south. In the Georgina basin its equivalent is the Gum Ridge Formation and in the Wiso Basin it is the Montejinni Limestone. There is no sharp divide between the Tindall Limestone and its southern equivalents. The formation unconformably overlies various Pre-Cambrian and Early Cambrian rocks (Figure 2). South of about the Edith River, the Antrim Plateau Volcanics are widespread and directly underlie the Tindall Limestone with a low angled unconformity. North of about the Edith River, the Tindall Limestone mostly overlies Proterozoic rocks. The degree of deformation in these older rocks varies considerably across the area. Consequently the contact with the overlying Tindall Limestone varies from low angled unconformity to steep angular unconformity. The contact between the Tindall Limestone and the overlying Jinduckin Formation is conformable across the Daly Basin. It is exposed at the source of the Katherine Hot Springs (Plate 5). Kruse and others (1994) describe breccias and cave formations at the top of the Tindall Limestone, from which they inferred local exposure and thus a break in sedimentation prior to the deposition of the Jinduckin Formation. Chert nodules are also commonly seen in the uppermost beds of the Tindall Limestone both in outcrop (Kruse and others 1994) and in drill cuttings (D.Karp personal communication). These also suggest a period of exposure. Limestone and dolomitised limestone are the main rock types in the Tindall Limestone, with minor gray, maroon and green siltstone interbeds. The limestones are light gray to gray-brown in colour, hard and mostly medium to coarsely crystalline. Styolites are common and most fine-scale sedimentary structures and fossils have been obscured by recrystallisation. In outcrop the limestone is coarsely bedded to massive. The siltstone beds rarely outcrop. Their locations are marked by low-lying, soil covered areas between the rocky strike ridges of limestone.

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Plate 5 Source of Katherine Hot Springs, the contact between the Tindall Limestone and the Jinduckin Formation is exposed below the water line. The brown siltstone on the right belongs to the Jinduckin Formation (photo D. Karp)

In the Douglas / Daly area Kruse and others (1990) describe a distinctive “two tone” limestone found within the upper part of the sequence. It consists of centimetre-scale interbeds of limestone and dolomitic siltstone and is mainly restricted to the northern end of the basin. Down-hole natural gamma ray logs have been run on many water bores and these have proven useful for locating formation boundaries and for correlating lithological units within formations. Gamma logs reflect the clay content of rocks and so those with low clay contents such as limestone and sandstone can be distinguished from clay rich ones such as siltstone and shale. The Tindall Limestone contrasts strongly to the overlying Jinduckin Formation (Figure 4). The Tindall Limestone shows much less variation in gamma count and is generally low. A typical gamma log in this formation shows massive limestone units separated by occasional thinner intervals of alternating siltstone/shale and limestone. The massive limestones range in thickness from 10 metres to 75 metres but average about 30 metres. The intervening shales are typically less than 10 metres thick. Individual units within the Tindall Limestone are remarkably persistent across the Daly Basin (Figure 5). In many cases the same beds can be recognised over distances of the order of at least 300 km. Notable lateral changes include an increase in shale in the north of the basin. The “two toned” limestone described above from the Douglas / Daly area, represents a shaley sequence and this gradually passes southwards into massive limestone by Katherine. The lowermost section is predominantly shale and siltstone between Tipperary and the Flora River and again it passes into massive limestone south of there.

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Jolly (1984) and Jolly (unpublished data) subdivided the Tindall Limestone into sub-units based on gamma logs and drill cuttings in the Douglas / Daly and Katherine areas respectively. He recognised six sub-units in the Douglas /Daly area and five at Katherine. His subdivisions correspond approximately to the same limestone and siltstone dominant intervals depicted in Figure 5.

Jinduckin Formation The Jinduckin Formation is the middle formation of the Daly River Group and conformably overlies the Tindall Limestone right across the Daly Basin. It was defined by Kruse and others (1990), with its type section in the cored drillhole NTGS 86/1 between the depths 243.9 and 579.3 metres. Only four boreholes have fully penetrated the formation; RN33510, RN6825, RN32097 and RN7838. These encountered thicknesses of 356, 348, 335 and 303 metres respectively. It is dominantly a dolomitic siltstone with inter-beds of dolostone and sandstone. Outcrops are generally limited to thin beds of resistant dolostone which form low strike ridges. These dolostones are typically well bedded with fine algal laminations as opposed to the more massive limestones and dolostones of the Tindall Limestone and Oolloo Dolostone. The siltstones range in colour from maroon to green and gray. The formation generally has a higher gamma count than the Tindall Limestone and shows rapid changes reflecting alternating beds of siltstone and limestone. Individual beds are typically two metres or less in thickness and rarely exceed five metres. Formations equivalent to the Jinduckin Formation are found in both the Georgina and Wiso basins. These are the Anthony Lagoon Beds in the former and the Hooker Creek Beds and possibly the Port Wakefield Beds in the latter basin. These formations are not presently continuous between the basins but are lithologically similar and occupy the same stratigraphic positions above the basal limestone formations.

Cretaceous Rocks

Early Cretaceous rocks overlie much of the Tindall Limestone in the south-eastern half of the Daly Basin (Figure 6). To the north west of the Edith and Flora Rivers, they are only preserved on isolated mesas over the limestone. They unconformably overlie the Tindall Limestone as the strata transgresses the tilted sequence in the basin (Figure 7). The beds are sub-horizontal and consist predominantly of clay, claystone and sandy clay with lesser sandstone, sand and clayey sand. Outcrop is generally sparse due to the soft nature of the rock but in places silicification has altered them to porcellanite and sandstone which outcrop reasonably well. Thicknesses are generally less than 50 metres. The maximum recorded thickness directly overlying Tindall Limestone is 97 metres in the Venn subdivision, 30 km south east of Katherine. A twofold subdivision is apparent in outcrops; a basal quartz sandstone and an overlying sequence of claystone with minor sandstone. Kruse et al (1994) considered that the sandstone corresponds to unit A of Skwarko (1966) and the claystone to his units B and C. Borehole gamma ray logs indicate beds have poor lateral continuity between the relatively widely spaced test holes and that the two-fold subdivision is not as obvious as in outcrop.

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The basal sandstone is widespread across the Daly Basin. Good exposures occur in the vicinity of Katherine. It is generally less than 10 metres thick and is sometimes absent. Outcrops are typically silicified to a hard, medium to coarse-grained sandstone or quartzite, which tends to form rounded boulders. Secondary quartz associated with the silicification often fills most of the intergranular pores. The overlying claystone is often silicified in outcrop to porcellanite, a hard rock that outcrops in places. It is white to cream coloured with rust brown, pink, yellow or orange mottles and streaks. The sand content varies from traces up to clayey sandstone. Clean sandstones are rare. Bedding is moderately well developed into units typically half a metre thick.

Geological structure

The Daly Basin extends from Tipperary in the north to Larrimah in the south. At its southern end the basin passes into the Wiso and Georgina Basins. The divide is marked by a structural high at the base of the Tindall Limestone. This is illustrated in cross-sections (Figure 7 and 8) and on the map showing the elevation of the base of the Tindall Limestone (Figure 9). The basin is only broadly warped with its constituent formations dipping basin-wards at angles usually less than one degree. The axis of the basin trends north-west to south-east and lies immediately north-east of the Daly River. Near the King River the axis is offset slightly to the north-east where it continues towards Larrimah and meets the divide with the Georgina Basin. West of Larrimah on the Sturt Plateau the basin forms a shallow shelf. The Tindall Limestone being the basal formation is exposed around the basin margins. South of about the latitude of Mataranka the Jinduckin Formation is not present but exposures of Tindall Limestone are rare due to a thin but extensive cover of Cretaceous clay and sand. Breaks in continuity of the formation’s outcrop occur on both sides of the basin where the margins are faulted (Figure 9). In those cases Jinduckin Formation is faulted against the pre-Daly Basin rocks and the Tindall Limestone is only found at depth (Figure 10). South of the Daly Basin, a bedrock high, the Tennant Creek Inlier, separates the Wiso and Georgina Basins. This extends northwards beneath the Daly Basin. In the Sturt Plateau, Yin Foo and Matthews (2000) informally named the Birdum Creek Fault, a structure associated with the eastern side of the bedrock high. An unnamed fault was also mapped on the western side of the bedrock high. The Birdum Creek Fault trends north-south where it crosses into the Daly Basin and then curves around to the north -west by the time it reaches the Dry River. At Larrimah it has a displacement of about 200 metres, down thrown to the east (Figure 11). Further north between Western Creek and Dry River, bores drilled on either side of the fault show a displacement of about 300 metres, downthrown to the north-east. A possible extension of this fault has been identified by drilling at the Flora River. In the bore RN31928 the top of the Tindall Limestone was encountered at a depth of 164 metres but less than a kilometre to the south east in RN31387 it was struck at only 75 metres. That fault has a displacement of about 80 metres, downthrown to the north and is postulated to trend east-west. Drilling on either side of a section of the Dry River suggests that it may follow a fault which down-throws the Daly River Group to the north (Figure 7). Interestingly the overlying Cretaceous rocks show the reverse displacement. Aeromagnetics suggest that the trend of that fault is parallel to the Dry River.

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Minor folds are found within the basin at Katherine (Figure 12) and Douglas/Jindare stations (Figure 9) on the north eastern side of the basin and at Dorisvale station on the opposite side of the basin. Each consists of a paired anticline on the basinward side and a syncline on the outer side. The folds trend parallel to the axis of the basin and extend from 5 to 25 kilometres along strike. They are most likely associated with faulting. The fold at Katherine was first mapped by Schwabe and Haylen (1977) as part of a uranium exploration program. The Katherine River crosses the folds, so the Tindall Limestone / Jinduckin Formation contact is encountered in the river three times rather than the normal one. Evidence for an anticline on Douglas/Jindare stations is the presence on the Pine Creek 1:100,000 geological sheet of two inliers of Tindall Limestone surrounded by Jinduckin Formation. There is no direct evidence for a matching syncline to the north east. On Dorisvale station an outlier of Oolloo Dolostone is preserved in a syncline. A corresponding anticline is presumed to occur immediately to the north east.

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RN6825RN33511

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Figure 6 Extent of Cretaceous rocks

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Figure 7 Section 1, Gamma log cross-section Daly Basin to Wiso Basin, see Figure 2 for cross-section location

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Figure 8 Section 2, Gamma log cross-section Daly Basin to Georgina Basin, see Figure 2 for cross-section location

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100 to 2000 to 100-100 to 0-200 to -100-300 to -200-400 to -300-500 to -400-500 to -600-600 to -700

154 Thickness of the Tindall Limestone(metres AHD)

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Figure 9 Elevation of the base of the Tindall Limestone

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aves

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Figure 10 Section 3, Gamma log cross-section, Venn area, see Figure 2 for cross-section location

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Figure 11 Section 4, Gamma log cross-section Wiso Basin to Georgina Basin, see Figure 2 for cross-section location

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Katherine

Kath

erin

e

River

Katherine Hot Spring

Northbank Spring

Springvale Spring

Jinduckin Formation

Tindall Limestone

Anticline

Syncline

Figure 12 Springs on the Katherine River

Groundwater The Tindall Limestone forms an extensive fractured and cavernous rock aquifer. It is a major source of baseflow for the Katherine, Flora, Roper, Douglas and Daly Rivers. It is utilised as a water supply for the town of Katherine and the townships of Mataranka, Larrimah and Daly Waters. Katherine’s water supply is about 40% groundwater while the other places are solely dependant on groundwater. Minor irrigated horticulture takes place in the Katherine and Mataranka areas. In the Douglas River area the aquifer is tapped for stock supplies and for small scale irrigated cropping. Widespread use for stock watering takes place on the Sturt Plateau. In the aquifer, water can move through both the network of fine fractures and also through solution cavities. The latter can vary from sub-millimetre scale to large caves. The larger openings are generally more localised than pervasive fractures and the finer solution cavities. A feature that has a major influence on the hydrogeology of the aquifer is the presence or absence of overlying less permeable formations. The pattern of groundwater flow, recharge, the hydraulic characteristics of the aquifer and the water quality are all affected.

23

The aquifer is unconfined around the basin margin mainly to the northwest of the Victoria Highway (Figure 13). A significant unconfined area also occurs in the Mataranka area. In these areas the limestone either outcrops or only has a soil cover. In the central part of the basin, the aquifer is confined by the overlying Jinduckin Formation. That unit is considered to have low vertical permeability, so there is likely to be negligible movement of water between the two formations. South of Katherine, Cretaceous aged sands and clays are extensive and form a semi-confining cover over the aquifer.

Groundwater flow

Water levels are monitored in the Tindall aquifer at 60 locations across the basin (Figure 10). The majority of these are concentrated around the Katherine, Douglas River and Mataranka areas where agricultural development is centred. Elsewhere there is only sparse coverage, particularly so in the confined sections of the aquifer. The flow pattern has been derived from water levels in the observation bores (Figure 14). In areas between these bores, historic water levels obtained from drillers reports of water bores were used to interpolate the potentiometric surface. The minor shale beds that are interbedded with the limestone do not appear to restrict vertical groundwater flow, at least not on a regional scale. Solution cavities have probably resulted in abundant collapses through the shale beds, creating pathways for water to move between the adjoining limestones. On a more local scale they undoubtedly form barriers to flow but this has not been investigated. In the Katherine area several cave systems have been mapped and they dominantly trend north west to south east (Lauritzen and Karp 1993). They have developed on fractures parallel to the strike of the beds. As a consequence groundwater flow towards the river is enhanced. Such cave systems act as drainage collectors for the network of fractures and finer solution cavities. The major springs on the river are the discharge points for these systems. A dye tracing test conducted just north of the Katherine river showed that water movement through cave systems can be rapid (Karp 2005). Dye released into a sinkhole took two and seven days respectively to reach springs on the river, located at distances of 2.5 km and 4 km from the sinkhole. Groundwater moves relatively slowly through the regional fracture network but when it reaches a cave system it is rapidly transported to the river. Flow can be recognised on two scales in the Tindall aquifer; regional and basin-wide. The bulk of flow occurs in a series of regional flow cells (groundwater catchments) situated mainly along the north eastern basin margin where the aquifer is unconfined (Figure 14). Flow is dominantly parallel to the basin margins and towards the major rivers where discharges occurs. The divides between the groundwater catchments correspond approximately to the surface water divides. The Katherine, Edith, Ferguson, Douglas, Daly and Roper Rivers and the Stray Creek each support local groundwater catchments. The King River situated close to a groundwater divide is a notably exception. It is a relatively minor stream and in the vicinity of the Stuart Highway, its bed lies about 30 metres above the watertable. Flow also occurs on a basin-wide scale particularly in the south. Groundwater flows from south to north on either side of the “Western Creek” bedrock high. To the east, groundwater moves from the north western section of the Georgina Basin northwards

24

towards the Roper River, where it discharges. To the west it moves from the northern part of the Wiso Basin eventually discharging into the Flora River. In both cases the groundwater catchment extends beyond the geological divide between the basins. In the main part of the Daly Basin where the Tindall aquifer is confined beneath the Jinduckin Formation, basin-wide scale flow also occurs. The potentiometric gradient is generally lower than that in unconfined areas, suggesting that flow is slow. All water in this area must originate from the unconfined or semi-confined areas on the basin margins. Similarly all discharge must occur in the same zones that the local unconfined flow systems discharge to. The volume of water moving through the confined aquifer is considered to be minor in comparison to that in the unconfined aquifer.

Recharge

Recharge to the Tindall aquifer varies considerably across the basin depending on whether it is covered by younger formations and amount of rainfall an area receives. The limestone outcrops or is near surface around the basin margin, particularly in the northern half of the basin (Figure 13). Here the aquifer is unconfined and recharge rates are highest. There are two possible mechanisms for recharge there; by-pass flow and distributed recharge. The former consists of rapid recharge directly to the aquifer via sinkholes and other open channels such as soil macro-pores. Surface runoff pouring directly down sinkholes has been observed in the Katherine area (Karp 2004). Many local watercourses terminate in sinkholes. Heavy rainfall events capable of producing flash floods are the most likely to result in by-pass recharge. Large volumes of water can enter the aquifer in a short time. Distributed recharge on the other hand involves downward seepage through the finer soil pores. It is a much slower process than by-pass flow but takes place over a much wider area. Rainwater may take up to years or decades to reach to the aquifer via this process. Wilson and others (2006) estimated that the recharge in uncleared areas of the Oolloo aquifer (also in the Daly Basin) comprised 30% diffuse and 70% bypass mechanisms. Sinkholes are more prominent in the Tindall Limestone so a higher proportion of recharge via that route may be expected. Jolly (2002) estimated average recharge to areas of unconfined Tindall aquifer to be 100mm/year. In the central part of the basin where the aquifer is confined by the Jinduckin Formation, recharge is considered to be negligible in comparison to that in unconfined areas. The aquifer is also overlain by Cretaceous aged clay and sand over a large part of the basin, particularly in the south. This restricts recharge to varying degrees, depending on the composition and thickness of the overlying material. Jolly (2002) estimated average recharge in the Katherine area through Cretaceous sediments to be 50mm/year, half that in the unconfined areas. He noted that the annual groundwater level rises in the unconfined aquifer during average rainfall years is about 7 metres compared to 3 metres in areas with Cretaceous cover. Figure 15 compares groundwater level changes in unconfined and confined parts of the aquifer. Rises due to annual recharge are pronounced in the former but muted in the latter, reflecting the lower recharge. Longer term water level variations are related to long term rainfall changes. In the case of the confined aquifer these long term changes are more pronounced than the annual recharge events.

25

Discharge

Groundwater moves under the action of gravity from recharge areas high in the catchment to low-lying discharge points. In the Daly Basin these latter areas are mostly where the major streams cut the aquifers. Discharge occurs in two main ways; through discrete karstic springs and via diffuse seepage into stream beds. Karstic springs are usually prominent features with relatively large amounts of water flowing out of solution cavities in limestone. The spring waters are crystal clear and the springs are sometimes surrounded by rainforest. This makes them attractive for tourism and several have been developed as parks / reserves. The water temperatures are of the order of 330C, similar to the ambient temperature of the local groundwaters. On a cold Dry season morning when the air temperature may be 150C the spring water feels hot and steam can rise off the water. As a result of this some of the springs are locally referred to as “hot” or “thermal” springs. This is not strictly correct as a common definition of a thermal spring is one with a temperature greater than body temperature (370C). The only true thermal springs are Douglas Hot Spring and Sybil Spring located in the northern part of the Daly Basin. They however discharge water from aquifers in Proterozoic rocks beneath the basin and not from the Tindall aquifer. In those two cases the older rocks have been faulted up through the Daly Basin rocks. The other main form of groundwater discharge, stream bed seepage, is not readily seen and is normally detected by measuring the stream flow at progressive points along the stream. Despite this, it is the dominant form of discharge from the Tindall aquifer. For example flow from observed springs along the Katherine River constitutes only about 20% of the total discharge to that river. The remainder comes through stream bed seepage. There is a continuum between discharge via point springs and through diffuse stream bed discharge. For example on a small scale many small springs in a river bed could be considered to be point springs but on a larger scale, if there are a lot of them, they constitute a zone of diffuse stream bed seepage. Such springs are generally not visible individually. Discharge zones expand or contract in extent depending on the height of the watertable. This is particularly noticeable during above average rainfall periods when elevated watertables cause groundwater to discharge in places that are normally dry. A good example of this occurred in the Tindal area during the 2003/2004 wet season (Rajaratnam and others, 2004). Several localised, large rainfall events rapidly filled the aquifer to the extent that discharge occurred over a considerable area where it had never been recorded before. It occurred as general discharge through fractures and fine solution cavities and more localised discharge through sinkholes. At one locality a small groundwater fed lake formed in a shallow closed depression. These discharge zones quickly dried up during the following dry season and the lowest lying area, the Tindal Creek had ceased to flow by September. A similar but slightly more extensive ephemeral lake forms just north of Zimmin Drive near Katherine (Plate 6) but only during very wet years (Karp 2002). It is fed by groundwater that discharges from caves on the edge of the lake. When the watertable begins to fall, part of the water drains back down the same caves and it is usually dry by the early to mid-dry season. A drain was constructed several years ago to stop flooding of the road and this has reduced the time that the area is inundated.

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Plate 6 Groundwater fed lake, Zimmin Drive Katherine. (photo D. Karp)

As the Dry season begins, the river flow is dominated by surface runoff. This source becomes rapidly depleted and groundwater then becomes the main component. Typically by July nearly all of the river flow is sourced from groundwater. This is reflected in both the recession curves of the river flow and by the chemical composition of the water. In the early Dry season the flow is high and the electrical conductivity of the water is low. The flow decreases rapidly and the electrical conductivity increases as runoff water dissipates and the proportion of groundwater increases. An inflection in the recession curve often marks the time at which the runoff component ceases. At the same time the electrical conductivity approaches the average value of groundwater. The amount of groundwater discharge is at a maximum at the peak of the Wet season when groundwater levels are highest and at a minimum at the end of the Dry season when the levels are lowest. Apart from the seasonal variation in discharge, longer term changes also occur as a result of long term rainfall variations. Series of above average wet seasons can have dramatic effects on recharge and hence on dry season river flows (Figure 16). The reverse is also true. Note that groundwater discharge to the Katherine River is currently at a high level in comparison to the historic record. Jolly (2000) determined a relationship between rainfall and recharge to the Tindall aquifer and synthesised end of Dry season river flows at Katherine back to the 1880’s when rainfall was first recorded there. This indicated that groundwater discharge has been considerably less than the present day’s for significant periods during that time. Discharge zones of the Tindall aquifer have been identified on the Roper, Flora, Katherine, Douglas and Daly Rivers. They also occur on the Edith, Stray, Bamboo and Bradshaw Creeks. Tickell and others (2002) measured end of Dry season (September) flows from most of these zones. Each of the major discharge zones will now be described:

27

Roper River Near Mataranka the Roper River and its tributaries discharge between 0.8 and 4 cumecs during the late Dry season. During the 1950’s and 1960’s the discharge was lower and at times less than 1 cumec. There are several prominent kastic springs including Rainbow, Bitter and Fig Tree Springs and their flows account for about half of the observed river flow. Rainbow Spring is located on the floodplain of the Waterhouse River and consists of a vertical solution hole, about 1 metre in diameter and at least 4 metres deep.(Plate 7). Limestone is visible on the walls of the cavity. The water then follows a narrow channel through a palm forest to the river. A swimming area has been constructed on the channel and this is a major tourist attraction. Measured flows range from 0.2 to 0.4 cumecs. The water temperature is 320C and it has a total dissolved solids content of around 660mg/l. Bitter Springs is on a small tributary of the Little Roper River. It gains about 2 cumecs over a distance of one hundred metres. Water seeps through the river bed and through the adjacent palm swamp. No cavities have been observed but the large flow suggests that they are probably present, either covered or inaccessible. The river appears unnaturally straight on satellite images, suggesting that it follows a fault or fracture. Tufa deposits are exposed on the walls of the river channel. The water temperature ranges from 280C to 330C and it has a total dissolved solids content of around 900mg/l. This is also a tourist attraction (Plate 8). Fig Tree Spring is on the bank of the Roper River, several metres above the dry season river level. It consists of a small horizontal cave at the base of a cliff of tufa limestone (Plate 9). Although the Tindall Limestone is not present in the immediate area, it is probably the source of the groundwater (Figure 17). The tufa and the Tindall Limestone form a continuous aquifer in that area. The spring flow has only been visually estimated at 0.05 cumecs. The water temperature ranges from 220C to 300C and it has a total dissolved solids content ranging from 1700mg/l to 2370mg/l. An extensive swampy area occurs just south of a 10 kilometre stretch of the Roper River within the Elsey National Park. It is a groundwater discharge zone with numerous seepage areas. The watertable is at or close to ground level. This supports patches of melaleuca and palm forest. Spring waters in the swamp and in Salt Creek have salinities ranging between 1200 and 3100 mg/l, considerably higher than other springs in the area. The vegetation extracts sufficient groundwater to concentrate the salts in the aquifer beneath and so raise the salinity of the groundwater. Minor areas of bare salinised soil and dead trees have resulted from higher than normal watertables during recent above average wet seasons. Two similar but smaller swampy areas occur immediately east and south of Jilkminggan community. They are also maintained by groundwater discharge from the Tindall aquifer. The area is underlain by a thick section of limestone that is flanked by bedrock highs. Unnaturally straight edges on sections of the swamps suggest that the discharge is associated with faulting.

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A layer of tufa up to 4 metres thick directly underlies the swamp. It has abundant solution cavities as seen at Fig Tree Spring and forms an aquifer. The Tindall aquifer is thin or absent beneath the swamp, so groundwater flowing towards the Roper River passes into the overlying tufa aquifer and then discharges into the swamp. Groundwater discharge from the tufa is also likely to occur directly into the bed of the Roper River as well as from springs such as Fig Tree Spring. Tufa consists of calcium carbonate that is chemically precipitated when the water is oversaturated with that mineral. It tends to occur on pre-existing rock bars where the deposits build upwards, forming dams across the stream. A major component of tufa dams is encrusted vegetation such as pandanus. Calcium carbonate grows around both living plants and plant debris caught in the dams. Damming causes the stream to fill with sediment and it is eventually forced to find a new course. This has occurred over a long period of time and the result is a continuous limestone deposit composed of many individual tufa dams and associated sediments. The sediments include both clastic deposits and chemically precipitated carbonate mud. The mud forms in the waterholes upstream of the dams when evaporation increases the concentration of the calcium carbonate to its saturation point. Only two tufa dams are known to be active at present, Mataranka Falls on the Roper River and an unnamed set of falls a short distance away on Salt Creek. There are no active tufa dams in the swamp itself. A unique tufa dam occurs on Elsey Creek. It is no longer active and has been partially breached. The dam is a near vertical wall that is some 20 metres wide and 6 metres high. On the upstream side the tufa deposit extend along both banks for about 50 metres. Both the banks and the dam wall are covered in large bulbous stalactites that have a spiky coral like texture. The cores of broken stalactites are hollow and appear to be casts of pandanus roots. Unlike normal stalactites these ones are postulated to have grown underwater in the waterhole behind the dam. (Plate 10).

Flora River At the end of the dry season the Flora River gains some 2 to 5 cumecs where it crosses the Tindall Limestone. Karp (1997) identified one main spring and several minor ones. The main spring is located on the south bank of the river about a kilometre downstream of the Mathison Creek junction. It issues from several solution holes in Tindall Limestone. One cavity is two metres above river level and others are below river level. The discharge is difficult to estimate because the spring is partly submerged but it is of the order of 0.5 cumecs. The spring water has a temperature of 320C and a total dissolved solids content of 500 mg/l. The section of river where groundwater inflow occurs is deep because it has been dammed by a large tufa dam that forms Kathleen Falls (Plate 11). This is about 8 kilometres downstream of the main spring and has grown on an outcrop of limestone, belonging to the Jinduckin Formation. The waterfalls and the springs are within the Flora River Nature Park.

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Figure 13 Confining beds on the Tindall Limestone

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!

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RN029429 TINDAL R.A.A.F, UnconfinedRN022006 VENN, Confined by Cretaceous rocks

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KATHERINE RIVER @ RWY BRIDGE

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Figure 16 Minimum annual flows at the Katherine River railway bridge.

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Groundwater discharge area

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Figure 17 Cross-section through Fig Tree Spring

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Plate 7 Source of Rainbow Spring near Mataranka (photo D. Karp)

Plate 8 Bitter Springs, swimming area (photo S. Tickell)

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Plate 9 Fig Tree Spring emerging from a small cave at the base of the cliff (photo D. Karp)

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Plate 10 Stalactites at the tufa dam on Elsey Creek (photo D. Karp)

Plate 11 Kathleen Falls, tufa dam on the Flora River (photo D. Karp)

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Katherine River The Katherine River cuts through the Tindall Limestone at Katherine. It typically gains between 0.5 and 5.0 cumecs at the end of the dry season. Three main karstic springs are known, two on the north bank and one on the south bank. All are stratigraphically controlled, situated at the top of the Tindall Limestone, at or just below the contact with the Jinduckin Formation. The formations are folded by a minor syncline and anticline in that local area, so the river crosses the contact three times (Figure12). The springs are located where the contact dips to the west. North Bank and Springvale springs are on the north bank and Katherine Hot Spring (also known as CSIRO spring) is on the south bank (Plate 5). Discharges average 0.05, 0.15 and 0.4 cumecs respectively. Temperatures of the spring waters are around 320C and the total dissolved solids range from 350 to 440 mg/l.

Edith and Ferguson Rivers Up to 0.5 cumecs is discharged into these streams at the end of the dry season. Along the Edith River the edge of the basin is faulted against granite and the Tindall Limestone lies at a depth of 50 metres beneath Jinduckin Formation. Discharge from the Tindall aquifer must occur through the fault because a waterhole, several kilometres long is maintained immediately downstream. The aquifer is thought to be exposed along the Ferguson River so the bulk of the discharge probably comes from that stream. Groundwater inflow also occurs on the Douglas and Daly Rivers and Stray, Bamboo and Bradshaw Creeks where they cross the Tindall Limestone.

Aquifer Characteristics

Porosity and permeability of the aquifer has been enhanced by weathering of the limestone. Rainwater and surface waters in this region tend to be naturally acidic. For example Likens and others (1987) collected rainwater at Katherine between 1980 and 1984, and found that the average pH was 4.73. The acidic recharge water is corrosive to limestone and results in karstic weathering. Solution cavities and enlarged fractures are most abundant within about 60 metres from the surface but can extend much deeper. It is likely that there have been several intervals of karstic weathering over a long period of geological time. Kruse and others (1994) identified cavity fills at the top of the formation which were attributed to weathering prior to the deposition of the Jinduckin Formation. Another period of weathering occurred prior to the deposition of the Cretaceous rocks. The Daly Basin rocks were deformed and then eroded prior to the Cretaceous and have only undergone minor modification since then. There is no direct evidence for pre-Cretaceous weathering, such as palaeosoils or cave fillings dating from that period but there must be a possibility that they exist. Outcrops of the basal Cretaceous sandstone are often preserved in shallow circular depressions on the limestone and these are obviously related to karstic weathering. The sandstone is commonly broken into blocks with irregular orientation suggesting that the depressions formed after the sediment was deposited causing it to collapse. The surface that the Cretaceous rocks now sit on may not be the original one in all cases that they were deposited on. The limestone surface appears to be being deflated by solution, even beneath the Cretaceous sandstone. The timing of that process is unknown but is likely to be still occurring at the present.

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High yields can be obtained at any stratigraphic horizon within the formation. For example the Katherine town supply bores and irrigation bores in the Venn subdivision, located some 25 km to the south east, tap the same stratigraphic horizon, 20 to 50 metres above the base of the formation. On the other hand high yielding irrigation bores along Zimmin Drive and Florina Rd., north of the Katherine River tap an aquifer within the upper 80 metres of the formation. The main producing horizon at any location is dependant on the site’s location over the formation at right angles to the strike of the beds. Jolly (1984) noted that aquifer development has been concentrated around the watertable and so the type of rock at this level must have a big influence on the nature of the aquifer. In the Douglas/Daly area he mapped out a zone where lower yields could be expected. This corresponds to the distribution of the shaley sequence of the Tindall Limestone described previously. Over 150 domestic and irrigation bores that tap the Tindall aquifer have been pump tested. Only a handful of these include observation bore data. Transmissivities are generally high, up to several thousands or tens of thousands of m2/day. The sample is probably biased however as most tests are done on bores with high yields. In calibrating a groundwater model of the aquifer in the Katherine region Knapton (2006) found that the following aquifer parameters gave the most realistic results: transmissivity: 5,000 m2/day unconfined), 100 m2/day (confined); unconfined storage coefficient: 0.04 and confined storage coefficient: 0.0001. Bore yields of up to 100 Litres/sec. have be achieved in the Katherine and Mataranka areas in irrigation bores. Yields of 10 Litres/sec. or more are likely to be widely available in most areas where the aquifer is unconfined or confined by Cretaceous rocks. On a local scale however the frequency of cavities and fractures may vary considerably. In the Venn subdivision for example high yields have been encountered in most place but several bores drilled into the same stratigraphic horizon as nearby successful bores have only encountered small supplies. There is only sparse data about the potential of the aquifer in areas where it is confined by Jinduckin Formation. Several bores drilled immediatly south west of Katherine such have obtained yields of up to 50 Litres/sec. from beneath up to 90 metres of Jinduckin Formation. At the Rockhole and Binjaree communities further to the south west, the top of the Tindall Limestone is at depths of 129 metres and 202 metres respectively. Bores at both locations flowed at rates of 8 and 13 Litres/sec. respectively. The capabilities of the two bores are however limited by their relatively narrow casing diameters. A bore drilled more recently 17 kilometres south west of Katherine encountered the top of the Tindall Limestone at a depth of 319 metres and yielded 90 Litres/sec. The aquifer is cavernous and has a transmissivity of 17,000 m2/day. A fully cored deep stratigraphic hole CCVH1 (RN9058) (Lau, 1981a) struck Tindall Limestone at 228 metres and the cores contained abundant solution cavities, vughs and solution enlarged fractures in the upper and middle sections of the formation.

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Water quality

Groundwaters in the Tindall Limestone are slightly alkaline on average but pH can range from 6.4 to 8. Calcium, magnesium and bicarbonate are the dominant ions with the Total Dissolved Solids mostly ranging between 250 and 1500 mg/l. Calcium, magnesium and bicarbonate ions do not show much geographic variation. Their concentrations are largely a function of the carbonate equilibria within the aquifer. They dissolve relatively easily from the limestone and dolomite and once saturation is reached their concentrations do not increase any further. Sodium, chloride and sulphate ions (and therefore total dissolved solids) on the other hand show distinct geographic variations that enable the aquifer to be subdivided into three TDS zones (Figure 18). Those ions are sourced from rainfall and in some cases from dissolution of the rock. The main part of the basin in the north and the part which adjoins the Wiso Basin in the south west have low TDS, sodium, chloride and sulphate values. South of the Dry River, TDS tends to be slightly higher. This is probably related to the lower rainfall in that area and hence lower recharge in the south. Evaporative concentration of salts in the groundwater is thus greater. The two zones in the south east that adjoin the Georgina Basin show higher TDS than the main area to the north and west. One zone extends from Daly Waters to Mataranka and has groundwaters with the highest TDS. A smaller zone with slightly lower TDS is in the south east corner of the basin. The higher TDS in both these zones is mainly due to an increase in sodium, chloride and sulphate and reflects the influence of groundwaters sourced from the Anthony Lagoon Beds to the south. That formation like the Jinduckin Formation is known to contain the evaporite minerals halite (NaCl) and anhydrite (CaSO4). These were deposited at the time that the sediments were being laid down. Unlike the Daly Basin where there is negligible movement of groundwater between the Jinduckin and Tindall, in the Georgina Basin there seems to be good hydraulic connection between the two equivalent formations. The mechanism for such a connection is unknown. One possibility is that there is an aquifer developed in a palaeo-weathered zone immediately below the contact with the Cretaceous rocks and that it cuts across the boundary between the two Cambrian formations. Gamma logs of the lower part of the Anthony Lagoon Beds suggest that dolostones beds are thicker and more common than those in the equivalent position in the Jinduckin Formation. There is therefore more potential for aquifers to be present in the basal section of the Anthony Lagoon Beds. Note that the extent of the Anthony Lagoon Beds is not well defined at present. Northward groundwater movement from the Georgina Basin transfers these higher TDS waters all the way to discharge in the Roper River at Mataranka. The reason why TDS values are higher in the zone that extends from Daly Waters to Mataranka than in area to the east of there is unknown. Most groundwaters from the Tindall aquifer fall within acceptable limits (ADWG, 2004) for human consumption. Hardness is normally high and will cause scale build-up in plumbing. Total Dissolved Solids, sodium and chloride in the southern parts of the basin are often high enough to adversely affect the taste. Fluoride exceeds guideline values in a handful of bores out of thousands tested. Elevated levels of the naturally occurring radioactive isotope radium-226 (226Ra) have been measured in many water bores in the Katherine area (Qureshi and Martin, 1996). Some of

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these exceed the guidelines (ADWG 2004) for drinking water. High levels are restricted to areas where the Tindall aquifer is confined by the Jinduckin Formation and are found within 20 metres of the contact between the two formations. The source of the radium is unclear but was postulated to be the Jinduckin Formation.

Resource assessment

A broad scale water balance of the whole Daly River catchment was made by Jolly(2002). The study did not separate the contributions from the different aquifers but estimated total recharge and storage above and below the watertable. Groundwater modelling was first applied to the Tindall aquifer in the Katherine – Venn area (Water Studies 2001) in order to determine if there was sufficient groundwater to sustain further agricultural developments. Impacts from various development scenarios on the environment and on existing users were detailed in terms of water level declines and reductions in the flows of the Katherine River. A further model designed to improve on the above study was carried out by Puhalovich (2005). It included the Tindall aquifer between the Edith and Roper Rivers. It was designed to be used as a tool to test development proposals and to improve the conceptual model of how the aquifer works. Impacts on Dry season flows in the Katherine River were also a major output of the model. Knapton (2004) developed a broad scale model for the Tindall aquifer from Dunmarra north to the Roper River. It was done to assess the impacts of a proposed major groundwater development at Shenandoah Station on base flows of the Roper River, some 200 kilometres to the north. A further report by Jolly and others (2004) also included the modelling results but looked at wider implications of reduced flows to the Roper River, such as the effects on downstream users at Ngukurr. Knapton (2006) has expanded the previous modelling to cover the whole Daly Basin, including both the Tindall and Oolloo aquifers.

41

Flora R

iver

Katherine King River King R

iv er

Edith River

Ferguson River

Cu l

len

Riv

er

Stray Creek

Douglas River

Ferguson River

DalyRiver

Daly

Dry Rive

r

DalyRiver

River

River

Weste

rn Cre

ek

Roper

Rive

r

Elsey

Creek

Wat

erho

use

Riv

erBir dum

Creek

Bamboo Ck

Fish River

Victoria River

Mathison Ck

Bradsh

aw C

k

Katherine

Stuart Hwy

Vict

oria

Hwy.%

%Mataranka

Pine Creek%

Larrimah%

Roper Hwy.

Buntine Hw

y.

Dorisvale RdCentra

l Arnhem Rd

TDS: 200-500 mg/l

Cl: <25 mg/l

SO : <50 mg/l

TDS: 500-800 mg/l

Cl

SO : 100-250 mg/l: 50-300 mg/l

TDS: 500-1500 mg/l

Cl

SO : 100-250 mg/l: 100- 600 mg/lFlor

a Rive

r

Katherine King River King R

iv er

Edith River

Ferguson River

Cu l

len

Riv

er

Stray Creek

Douglas River

Ferguson River

DalyRiver

Daly

Dry Rive

r

DalyRiver

River

River

Weste

rn Cre

ek

Roper

Rive

r

Elsey

Creek

Wat

erho

use

Riv

erBir dum

Creek

Bamboo Ck

Fish River

Victoria River

Mathison Ck

Bradsh

aw C

k

Katherine

Stuart Hwy

Vict

oria

Hwy.%

%Mataranka

Pine Creek%

Larrimah%

Roper Hwy.

Buntine Hw

y.

Dorisvale RdCentra

l Arnhem Rd

TDS: 200-500 mg/l

Cl: <25 mg/l

SO : <50 mg/l

TDS: 200-500 mg/l

Cl: <25 mg/l

SO : <50 mg/l

TDS: 500-800 mg/l

Cl

SO : 100-250 mg/l: 50-300 mg/l

TDS: 500-800 mg/l

Cl

SO : 100-250 mg/l: 50-300 mg/l

TDS: 500-1500 mg/l

Cl

SO : 100-250 mg/l: 100- 600 mg/l

TDS: 500-1500 mg/l

Cl

SO : 100-250 mg/l: 100- 600 mg/l

Figure 18 TDS zones

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References ADWG. 2004. Australian drinking water guidelines. National Health and Medical Research Council. Jolly, P., 1984. Douglas/Daly groundwater resource investigations 1981 – 1983, Water Division, Northern Territory Department of Transport and Works, Report 8/84D. Jolly, P., 2002. Daly River catchment water balance, Report 10/2002, Natural Resources Division, Northern Territory Department of Lands, Planning and Environment. Jolly, P., Knapton, A. and Tickell, S. 2004. Water availability from the aquifer in the Tindall Limestone south of the Roper River. Northern Territory Department of Infrastructure, Planning and Environment. Report No.WRD04034D. Karp, D. (1997). Groundwater investigation Flora River Nature Park. . Report 22/1997D, Northern Territory Department of Lands, Planning and Environment. Karp, D. (2002). Land degradation associated with sinkhole development in the Katherine region. Report 11/2002D, Northern Territory Department of Lands, Planning and Environment. Karp, D. (2004). Sinkhole survey in the Katherine region. Report 16/2004D Northern Territory Department of Lands, Planning and Environment. Karp, D. (2005). Evaluation of groundwater flow by dye tracing, Katherine region. Report 22/2005D, Northern Territory Department of Natural Resources, Environment and the Arts Knapton, A. (2004). Modelling of water extraction at Shenandoah Station, Georgina Basin and effects on base flows in the Roper River. Northern Territory Department of Infrastructure, Planning and Environment. Report No.WRD04031D. Knapton, A. (2006). Regional groundwater modelling of the Cambrian limestone aquifer system of the Wiso Basin, Georgina and Daly Basin. Northern Territory Department of Infrastructure, Planning and Environment. Report No.WRD06029A. Kruse, P. D., Whitehead, B. R. and Mulder, C. A. 1990 Tipperary, Northern Territory 1:100 000 geological map series. Northern Territory Geological Survey Explanatory Notes SD 52-8 (5170) Kruse, P. D., Sweet, I. P., Stuart-Smith, P. G., Wygralak, A. S, Pieters, P. E. and Crick, I. H. 1994. Katherine, Northern Territory 1:250 000 geological map series Northern Territory Geological Survey Explanatory Notes SD 53-9. Kruse, P. D., 1987 Diamond drilling programme 1986, Daly Basin, Northern Territory Geological Survey, Technical Report GS 87/6 (unpublished).

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Lau, J. E., 1981a. Stratigraphic diamond drillholes KRVH1 and CCVH1, Daly River Basin, Northern Territory Geological Survey, Technical Report. GS 81/28. Lau, J. E., 1981b. Daly River basin, data record. Northern Territory Geological Survey, Technical Report. GS 81/29. Lauritzen, S. E. and Karp, D. (1993). Speleological assessment of karst aquifers developed within the Tindall Limestone, Katherine NT. Report 63/1993. Northern Territory Power and Water Authority. Laws, A. T., 1968. Preliminary appraisal of the geology and hydrogeology of the Daly Basin. Northern Territory Department of Mines and Energy, Water Resources Division, Report 36/68D. Likens, G.E., Keen, W.C., Miller, J.M. & Galloway, J.N. 1987. Chemistry of precipitation from a remote, terrestrial site in Australia. Journal of Geophysical Research, 92, 13299-13314. Malone, E. J., 1962 1:250000 geological series explanatory notes. Pine Creek, N.T. Bureau of Mineral Resources, Australia. Noakes, L.C., 1949 A geological reconnaissance of the Katherine – Darwin region, Northern Territory, with notes on the mineral deposits. Bureau of Mineral resources, Australia, Bulletin 16. Rajaratnam, L., Tickell S.J. and Farrow, R. 2004. Katherine Flooding, 2003 / 2004 Wet Season., Northern Territory Department of Infrastructure, Planning and Environment, Report WRD04011D Randal, M. A., 1962 1:250 000 geological series explanatory notes. Fergusson River, N.T. Bureau of Mineral Resources, Australia. Randal, M. A., 1963 1:250 000 geological series explanatory notes. Katherine, N.T. Bureau of Mineral Resources, Australia. Russ, A. J., Rance, D.K., Answer, S., Challinor, P., Cruickshank, S. and Willis, G. Stream flows and water quality parameters in the Daly Basin. Report 33/2005D, Northern Territory Department of Natural Resources, Environment and the Arts Schwabe, M. and Haylen, M., 1977 Exploration of MR 548, portion of the Daly River Basin near Katherine. 1976 field season. Northern Territory Department of Mines and Energy, Open File Company report 77/71 (unpublished). Skwarko, S.K., 1966. Cretaceous stratigraphy and palaeontology of the Northern Territory. Bureau of Mineral Resources, Australia, Bulletin 73.

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Tickell, S. J., Cruikshank, S., Kerle, E., and Willis, G., 2002. Stream baseflows in the Daly River. Report 36/2002, Natural Resources Division, Northern Territory Department of Infrastructure, Planning and Environment. Unnamed, 1976. Daly Region stage 1, resource inventory, Department of Northern Territory, Forward Planning and Major projects Co-ordination Branch. Unnamed, 1983. Baseflow water quality surveys in rivers in the Northern Territory, Volume 1. Katherine & East Alligator Rivers (Timor Sea drainage basin), Northern Territory Department of Transport and Works, Water Division, Report 16/83D. Unnamed, 1985. Baseflow water quality surveys in rivers in the Northern Territory, Volume 2. Finniss & Daly Rivers (Timor Sea drainage basin), Northern Territory Department of Mines and Energy, Water Resources Division, Report 28/85D. Unnamed, 1988. Baseflow water quality surveys in rivers in the Northern Territory Douglas, Flora and Reynolds Rivers, Volume 7, Northern Territory Power and Water Authority, Report 2/88D. Water Studies Pty. Ltd., 2001. Regional groundwater impact modelling, Venn agricultural area. Report for Northern Territory Land Corporation. Report No.WSDJ00188/DF1. 26 July 2001. Wilson, D., Cook, P., Hutley, L., Tickell, S. and Jolly, P. 2006 Effects of land use on evapotranspiration and recharge in the Daly River catchment. Report 17/2006D, Northern Territory Department of Natural Resources, Environment and the Arts. Yin Foo, D. and Matthews, I. 2000 Hydrology of the Sturt plateau 1:250 000 scale map explanatory notes. Report WRD00019D, Natural Resources Division, Northern Territory Department of Infrastructure, Planning and Environment.

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