prepared for dpiw tasmania

Development of Models for Tasmanian

Groundwater Resources

Conceptual Model Report for

King Island

Prepared for DPIW Tasmania

GPO Box 44 Hobart TAS 7001

December 2008

Document Title

Conceptual Model Report For King Island

Document Author(s)

Glenn Harrington

Distribution List

Copies Distribution Contact Name 1 DPIW (electronic) Don Rockliff

Document Status

Doc. No. Approved for Issue

Rev No. Name Signature Date

Project Manager Stuart Richardson

Peer Reviewer Stuart Richardson, Jenny Deakin, Miladin Latinovic

Resource & Environmental Management Pty Ltd ABN 47 098 108 877 Suite 9, 15 Fullarton Road, KENT TOWN SA 5067 Telephone: (08) 8363 1777 Facsimile: (08) 8363 1477

Aquaterra Consulting Pty Ltd ABN 49 082 286 708

Ground Floor, 15 Bentham Street Adelaide, South Australia, 5000 Tel: (08) 8410 4000 Fax: (08) 8410 6321

Conceptual_Model_King Is ver3.1.doc


Table of Contents 1 INTRODUCTION ............................................................................................ 1

1.1 Scope 1

1.2 Catchment Water Balance 1

2 BACKGROUND ............................................................................................. 2

2.1 Study Area 2

2.2 Climate 2

2.3 Topography and Soils 2

2.4 Land Use 3

2.5 Geology 3

2.6 Hydrogeology 4

2.7 Surface Water – Groundwater Interaction 5

2.8 Water Use and Management Issues 5

2.9 Groundwater and Surface Water Monitoring 6

3 GROUNDWATER INFLOWS ......................................................................... 7

3.1 Diffuse Recharge 7

3.2 Point Source Recharge 9

3.3 Recharge from Losing Streams 9

4 GROUNDWATER FLOW ............................................................................. 10

4.1 Water Table Contours 10

4.2 Groundwater Flow Direction 10

4.3 Flow rates 10

5 GROUNDWATER OUTFLOWS ................................................................... 11

5.1 Lateral Discharge 11

5.2 Groundwater Extraction 11

5.3 Evapotranspiration from Shallow Water Tables 11

5.4 Groundwater Discharge to Streams 11

6 CONCEPTUAL MODEL ............................................................................... 12

6.1 Block Diagram 12

6.2 Preliminary Water Budget 12

6.3 Knowledge Gaps and Uncertainty 12

7 RECOMMENDATIONS FOR FIELD STUDIES ............................................ 14


8 REFERENCES ............................................................................................. 15


List of Tables, Figures and Appendices

TABLES

Table 1 Summary of King Island geology (largely derived from Gresham, 1972). Table 2 Calibration parameters for Australian catchments plotted on curves derived

by Zhang et al. (1999, 2001). Table 3 Diffuse recharge estimates for the Quaternary coastal sands aquifer in the

King Island catchment.

FIGURES

Figure 1 Schematic diagram showing the main components required to develop a catchment-scale groundwater balance.

Figure 2 Location, surface water features for the King Island model catchment. Figure 3 Total annual rainfall and cumulative deviation from mean annual rainfall for

King Island catchment. Figure 4 Topography, Land System and Primary Soil Classification for King Island. Figure 5 Land use and Groundwater Salinity (all wells) for King Island. Figure 6 Surface geology for King Island. Figure 7 Schematic geological cross section from workshop. Figure 8 Well yield and Salinity for Coastal Sands, Devonian Granite, Quaternary

Alluvium, Tertiary Basalt/Sediments and Precambrian aquifer wells in the King Island catchment area.

Figure 9 Empirical curves derived by Zhang et al. (1999, 2001), plotted for Australian catchments using parameters from Table 2.

Figure 10 Potentiometric Elevation contours and Inferred Groundwater Flowlines for King Island.

Figure 11 Conceptual Hydrogeological Model for the King Island catchment. Figure 12 Preliminary catchment water balance for King Island.

APPENDICES

Appendix A Geological descriptions for features shown in Figure 6. Appendix B Data Inventory for King Island

Conceptual Model Report for King Island

PAGE 1

1 INTRODUCTION

1.1 Scope Resource & Environmental Management Pty Ltd. (REM) in association with Aquaterra Pty Ltd has been engaged by the Tasmanian Department of Primary Industries and Water (DPIW) to undertake the project Development of Models for Tasmanian Groundwater Resources.

Stage 1 of the project required the compilation of available data and reports, confirmation of the proposed catchment prioritisation and categorisation, and agreement on preferred modelling approaches. Meetings and a two day workshop were held in June 2007 with local experts, including current and retired geologists from both private and Government sectors, to facilitate the data collection tasks. These forums provided background geological and hydrogeological information, enabling the assembly of schematic cross-sections, data inventory spreadsheets and a reference list.

Stage 2 of the project involves the development of preliminary conceptual models. This report is part of a series of nineteen reports that present the preliminary conceptual models for each of the study catchments, with this report representing the King Island catchment.

1.2 Catchment Water Balance In order to develop a conceptual model for a particular groundwater catchment1, it is important to identify and characterise all relevant components of the water balance. These components are illustrated in Figure 1, and may include any or all of the following: rainfall, surface water runoff, evaporation, transpiration, groundwater recharge, aquifer throughflow, groundwater discharge to springs or streams, groundwater abstraction and lateral discharge to either down-gradient catchments or (ultimately) the sea.

1 The term groundwater catchment is not as easy to define as surface water catchment. If a distinct region of groundwater was a catchment in the true sense of the word, then the boundaries of that region would represent locations across which there is no horizontal flow of groundwater. In reality, this rarely occurs and is very difficult to measure, so for the purpose of this project the basis for defining each catchment boundary will be reported.


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2 BACKGROUND

2.1 Study Area The study catchment covers the entire area of King Island, which is located approximately 85 km off the northwest tip of the main island of Tasmania (Figure 2). The island is about 65 km long and up to 25 km wide, providing a total area of 1,085 km2. The landscape is dominated by a very low relief (see section2.3) inclined plateau, with numerous small ephemeral streams, particularly on the eastern side of the island.

King Island is best known for its dairy products, despite there being relatively little irrigation activity on the island compared with other dairying regions of northwest Tasmania. Groundwater is currently only used for the town water supply at Currie (population about 1,500), industrial purposes associated with dairies, and stock wells (pers. comms. from workshops 2007).

2.2 Climate Historical rainfall data for the nearest Bureau of Meteorology station to the centroid of King Island at the Currie Post Office (Figure 3) provides a mean annual rainfall value of 699 mm/yr. The cumulative deviation from mean annual rainfall trend is also shown in Figure 3 and indicates a period of below-average annual rainfall for most years between 1910 and 1945, followed by a period when most years experienced above-average annual rainfall up to 1980. Annual rainfall was below average for all years between 1980 and 1990. Historical data for any years after 1991 is not available for this station, however rainfall records for other stations in northwest Tasmania (data not shown) reveal most of the 1990s were above average, and most years from 2000 to 2006 were below average.

Historical evaporation measurements are not available for King Island. However, Class A pan evaporation data adopted by the current project for the Smithton Syncline catchment (NW Tasmania) provides a mean annual evaporation rate (Epan) of 1039 mm/yr for the period 1900-2005 (HydroTas sourced from SILO2). In order to convert this value into an actual evapotranspiration rate (ET) (i.e., incorporating both evaporation from within and above the soil, and transpiration from plants), the following expression is used;

ET = fc . cp . Epan (1)

where fc is known as the crop coefficient, which varies from 0 to 1 depending on crop type and season; and cp is the pan coefficient, typically around 0.5. Assuming an average value of 0.8 for fc across the entire catchment, ET is estimated to be about 416 mm/yr.

2.3 Topography and Soils King Island exhibits very low topographic relief with the highest point being less than 150 mAHD. A large portion of the island is characterised by a gently-sloping alluvial plain rimmed with recent

2 SILO ET data is all “patched” prior to 1968


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coastal sand dunes. Topographic elevation rarely exceeds 50 mAHD in the northern half of the island.

Soil orders have been mapped using the Australian Soil Classification layer for Tasmania supplied by DPIW (Figure 4). This map reveals that most of the southern half of King Island is covered by undulating plains of Kurosols (strongly acidic B horizon). The western margins of the southern half of the island, and about two thirds of the northern half of the island, are classified as flat plains of Podosols (soils that typically form in coastal sedimentary environments with B horizons dominated by the accumulation of organic matter, aluminium and/or iron). Seasonally-inundated soils (Hydrosols) cover a considerable area in the northwest of the island around the town of Reekara. (Refer to the Key to Soil Orders3 for further information about soil characteristics).

It should be noted however, that the layer presented in Figure 4 was constructed from line work for Land Systems developed by the Tasmanian Department of Agriculture between 1978-1989 using geology, vegetation and climate data rather than soil surveys per se. Nevertheless, field observations in many areas have revealed that it is a reasonable representation of the actual conditions, particularly in the north and northwest of the State where many of this study’s catchments are situated (pers. comm. Simon Lynch, DPIW 2007). There has also been observed agreement between this layer and the more spatially confined Soils Reconnaissance map that was supplied originally by DPIW.

2.4 Land Use Figure 5 presents the current range of land uses in the King Island catchment. Approximately 84% of the area is classified as ‘environmental’, which is defined in BRS (2002) as “environmental and indirect production uses (eg prevention of land degradation, wind-breaks, shade and shelter)”. The remaining 16% of the island is primarily either remnant native vegetation (49 km2), some form of protected area, or forestry (7 km2). No land is classified as ‘grazing’ or ‘dairy’ despite this being a significant activity on the island, so it is assumed that ‘environmental’ includes such land uses. As revealed in Figure 5, no part of King Island is currently classified as being used for irrigation purposes.

2.5 Geology King Island has long been of interest to geologists, mainly due to the presence of large scheelite ore bodies (Gresham, 1972). The surface geology is essentially an eroded plateau of Precambrian sedimentary and metamorphic rocks with intrusions of granite and basic igneous rocks, overlain by a thin veneer of Quaternary alluvium and coastal sands (Figure 6, full lithology descriptions provided in Appendix A).

Schematic east-west geological cross sections through the southern and northern parts of the island are presented in Figure 7. The main difference along these sections is that the mudstones and siltstones of the Rocky Cape Group are close to surface in the south (rarely outcropping, except at the coast and in deeply-incised creek beds), whereas they are covered in part by Tertiary limestone and Quaternary fill in the north.

3 Key to Soil Orders can be found at http://www.clw.csiro.au/aclep/asc_re_on_line/soilkey.htm


PAGE 4

The sand dunes that overlie large areas of basement rocks on King Island are of two different lithologies; the ‘Old Dunes’ are almost entirely comprised of silica, while the ‘New Dunes’ are carbonate rich (Matthews and Cromer, 1973), which explains why they are referred to locally as lime sands’.

A detailed history of geological exploration and characterisation of the various lithologies is provided in Gresham (1972) and has been summarised in Table 1.

Table 1 Summary of King Island geology (largely derived from Gresham, 1972).

Formation Age Approx. Maximum Thickness (m)

Description

Quaternary sands Holocene >10 m New Dunes and shorelines, carbonate-rich sands

Quaternary alluvium and aeolian sands

Pleistocene 25 m Lacustrine and estuarine sediments, and aeolian sands in Old Dunes and shorelines

Tertiary Limestone

Miocene ~20m Fossiliferous (bryzoal) limestone, occurring locally as shore platforms (east coast)

Devonian Granite Late Devonian - early Carboniferous

1 km in SE and NE

Intrusion of predominantly granodiorite and adamellite, associated tin and tungsten mineralisation

Cambrian volcanics

Middle Cambrian

> 2500 m Spilites and picrite basalts

Cambrian sediments

Early Cambrian > 400 m Tillite, dolomitic siltstone, shale, slate and pelitic carbonates.

Neoproterozoic Togari Group, Arthur Meta-morphic Complex

Late Proterozoic - early Cambrian

> 6000 m Siltstones, mudstones, shales and minor sandstones. Metamorphosed at depth to form schists.

Mesoproterozoic Rocky Cape Group

Proterozoic > 5500 m Siltstones, sandstones and quartzite. Intense deformation and metamorphism in parts (West Coast Schists), with granite intrusion along the west coast.

2.6 Hydrogeology The following hydrogeological map sheets from Mineral Resources Tasmania cover the King Island catchment:

• Groundwater Prospectivity of Tasmania 1:500 000;

• Map 1 – Hydrogeological Inventory 1:100 000;

• Northwest Tasmania Groundwater Map 1:250 000; and


PAGE 5

• Northwest Tasmania Groundwater Quality Map 1:250 000.

These maps provide broad generalisations on the common aquifer types and groundwater characteristics for the regions they cover. However, whilst the maps indicate the aquifer type nearest to ground surface, they do not demonstrate the presence nor type of deeper aquifers. Furthermore, the maps present well yields and salinities for wells completed at any depths without differentiating between aquifers.

The main aquifer currently being developed on King Island is the Quaternary costal sands, particularly along the west coast near the town of Currie. Whilst this groundwater resource is not likely to be extensive, either laterally or vertically, it does provide reliable (albeit low) yields (Figure 8a) of very good quality water (Figure 8b and Figure 5). A map of all recorded well yields is shown in Figure 6, which indicates that yields are low throughout the catchment; although there is little data for the area near Currie.

There are also a number of high-yielding metamorphic fractured-rock aquifers in the southeast of the island, and fractured granites on the west coast. As pointed out by Matthews and Cromer (1973), the success of water wells drilled in these units will depend on there being close, interconnected and open joint systems.

The only reported hydraulic parameters for any of the aquifers on King Island are for the aeolian coastal dunes aquifer near Currie. A 14 day aquifer pumping test conducted on a circular array of spear points yielded an aquifer transmissivity of 124 m2/day and a specific yield of 0.26 (Cromer, 1978).

2.7 Surface Water – Groundwater Interaction The main river systems on King Island are the Sea Elephant River in the central-northeast region and the Ettrick River in the far southwest. It is not possible to compare likely groundwater and surface water levels along each of these river systems due to limited groundwater elevation data for this catchment (see section 4.1). Nevertheless, it is likely that both systems are losing steams in the upper reaches, and gaining streams in the lower reaches.

2.8 Water Use and Management Issues As discussed previously in section 2.1, the main groundwater use on King Island is for Currie town water supply (<100 ML/yr, pers. comm. King Island Council). This supply is sourced via a nest of shallow spear point wells completed in the sand dunes. The groundwater quality is generally very good (salinity in the range 700 - 800 mg/L) although it is high in bicarbonate. The long-term sustainability of this resource is likely to be one of the primary groundwater management issues for the island.

The only other known groundwater users are the local abattoir and King Island Dairy to the north of Currie. Annual rates of abstraction for either of these users is currently unknown. Irrigation is not as widespread on King Island as it is in other parts of northwest Tasmania (section 2.4), and any that does occur is likely to source water from streams or rivers. The current level of surface water allocation for the entire island is only 1,019 ML/yr (DPIW, 2007).

Acid mine drainage is a problem in parts of southwest and central northwest King Island (pers. comm. L. Matthews, 2007). Managing the impacts of this drainage on the local surface water


PAGE 6

ecology will present a future resource management issue. Dryland salinity is also known to occur on the island- typically in low lying areas with low topographic gradients.

2.9 Groundwater and Surface Water Monitoring The MRT statewide groundwater monitoring network currently has no observation wells located on King Island. The only groundwater monitoring known to have occurred in this catchment was historical, and mainly focussed on the coastal sand aquifer along the west coast (pers. comm. J. Sloane 2007).

DPIW have monitored seasonal river levels and daily stream flow at one station (ID 13200) on the Ettrick River between 1978 and 1994. Over this period, the range of measured stage and stream flows was 0 to 0.6 m (mean 0.29 m, relative to some local datum) and 0 to 1600 ML/day (mean 28 ML/day) respectively.


PAGE 7

3 GROUNDWATER INFLOWS

3.1 Diffuse Recharge Diffuse groundwater recharge is believed to occur throughout King Island, although it may be at a lower rate on the eastern side where there is greater surface runoff. Because the west coast has almost no surface water discharge, recharge to the coastal sands aquifer must be significant (Matthews and Cromer, 1973). For the fractured rock aquifers, the main recharge zone is in the elevated areas between Pegarah and Grassy, on the southeast end of the island (Miladin Latinovic, pers. comm., 2008).

Recharge rates can be estimated using a range of methods, from simple and crude water balance calculations, to sophisticated and expensive isotope and tracer dating techniques. The current project has used two methods to estimate recharge. The first is known as the steady state Chloride Mass Balance (CMB),which has been applied successfully to a range of climatic and hydrogeological settings around the world over the last 40 years. The method, which assumes the chloride ion behaves conservatively in the sub-surface environment4, is based upon conservation of mass between the chloride deposited at the land surface in rainfall and the chloride reaching the water table as groundwater recharge. This mass balance can be expressed as follows:

Recharge rate x [Cl] in recharge = Precipitation rate x [Cl] in precipitation (2)

Cromer (1978) reported the results of three chloride analyses for the Currie TWS (coastal sands aquifer); each returned a concentration of 310 mg/L. Matthews (1966) reports a range of 172-310 mg/L for the chloride concentration in this aquifer. Adopting this range as the Cl concentration in recharge water, and a mean annual precipitation rate of 699 mm/yr, the Cl concentration in precipitation is the only variable required to obtain an estimate of recharge rate. In the absence of chemical analyses for local rainfall samples, the Cl concentration in precipitation must be estimated. Numerous studies of near-coastal aquifers on mainland Australia have measured rainfall Cl at 5 - 10 mg/L. Using this range of values for Cl concentration in precipitation derives a range of recharge rates of 11 - 41 mm/yr for the coastal sands aquifer. This range is also plausible for other parts of the island, as any location is never more than about 12 km from the coast.

There is some uncertainty with regard to the recharge rates calculated using the chloride mass balance approach. Changes to land use (such as forestry) may affect the interpretation since the method relies on the assumption that the loading of chloride from rainfall is in steady-state with the chloride loading to groundwater.

The second method employed by this project to estimate recharge utilises an empirical relationship derived by Zhang et al. (1999, 2001) for estimating evapotranspiration under different

4 Conservative behavior of chloride is usually a valid assumption as the chloride ion rarely participates in water-rock interactions, except in situations when the water is approaching, at or above saturation with respect to halite.


PAGE 8

land use combinations and annual rainfall. The relationship, which has recently been calibrated for Australian catchments (Table 2), is:

(3)

where ET is actual evapotranspiration, P is annual rainfall, E0 is a rainfall scaling parameter, and ω is a parameter related to plant available water. This relationship is plotted in Figure 9 using the parameters provided in Table 2.

Table 2 Calibration parameters for Australian catchments plotted on curves derived by Zhang et al. (1999, 2001)

Factor Grass/Cleared Trees

E0 1400 1800

w 0.5 4

Figure 9 Empirical curves derived by Zhang et al. (1999, 2001), plotted for Australian catchments using parameters from Table 2.

“Excess water” can be defined as the difference between rainfall and evapotranspiration, or equally by assuming negligible change in groundwater storage, the sum of groundwater recharge and stream flow. Whilst only “grass/cleared” and “tree” curves are plotted in Figure 9, the excess water for any catchment containing a mix of these two extreme land uses can be estimated simply by linear scaling.

For the King Island catchment, the long-term average rainfall value of 699 mm/yr (section 2.2), together with a land use mix of 95 % grass/cleared and 5 % trees (comprising remnant native vegetation and plantation forestry, Figure 5) was used to estimate the annual excess water as being 134 mm/yr for the catchment. In the absence of monitored or modelled stream flows for any of the main rivers on the island, it was assumed runoff equals 15% of the mean annual

0

100

200

300

400

500

600

700

0 300 600 900 1200 1500

Annual Rainfall (mm)

Ann

ual E

xces

s W

ater

(mm

)

Grass/ClearedTrees

( )( )( ) ( )( )⎟

⎟⎠

⎞⎜⎜⎝

⎛++

+=

00

0

11

EPPEPEPET

ωω


PAGE 9

rainfall (i.e., 105 mm/yr). This runoff value was then subtracted from the excess water value to obtain a recharge estimate of 29 mm/yr.

A summary of the derived estimates for diffuse recharge at King Island is summarised in Table 3. The different methods calculated a similar recharge rate, and the average (27 mm/yr) will be used to define a preliminary water budget.

Table 3 Diffuse recharge estimates for the Quaternary coastal sands aquifer in the King Island catchment.

Method (Source) Recharge Rate (mm/yr)

Steady-state Chloride Mass Balance 11 – 41

Annual excess water less stream flow Zhang et al. 29

Assumed recharge for preliminary water budget 27

3.2 Point Source Recharge Localised recharge to any of the aquifers on King Island is considered to be negligible due to the absence of any surface karst features or areas of intensive irrigation.

3.3 Recharge from Losing Streams Groundwater recharge is likely to be important in the uppermost reaches of the surface water catchments on King Island. However, without detailed time-series groundwater level and/or surface water monitoring data, this process cannot be quantified.


PAGE 10

4 GROUNDWATER FLOW

4.1 Water Table Contours MRT’s drillhole database for water wells contains records of the latest depth to water level measured at each well, in addition to an attribute that states “geology of the main aquifer”. From this database, all wells that have ‘Precambrian’, ‘Devonian’, ‘Tertiary’ or ‘Quaternary’ listed as the geology of the main aquifer and a depth to water level measured within the last 20 years, were selected to construct a water table (potentiometric) contour map. As the majority of wells do not have surveyed elevations, the potentiometric contour map was produced by initially constructing a depth to water level surface, then subtracting it from a gridded topographic surface. (Earlier data related mainly to the Currie coastal sand aquifer where the watertable elevation is in a range of 5 to 40 mAHD).

Whilst the available data is sparse, the resultant water table contours are shown in Figure 10 and reveal a range in groundwater elevations from around 130 mAHD in the southeast to less than 20 mAHD in the coastal and northern regions of the island. A steep hydraulic gradient is evident in the southeast corner where the topography is most pronounced. Elsewhere the hydraulic gradient is very flat.

4.2 Groundwater Flow Direction Groundwater flow directions have been inferred on Figure 10, and can be summarised as follows:

• The general direction of flow is radially outwards towards the coast (i.e., westerly on the western side of the island and easterly on the eastern side); and

• The steep gradient zone in the southeast forms a defined groundwater flow divide, with water either flowing towards the southeast or northwest.

4.3 Flow rates Groundwater flow through the King Island catchment will occur via both inter-granular flow under laminar conditions and fracture flow under turbulent conditions. The coastal sands fringing the island are likely to support the first of these two groundwater flow mechanisms, and thus have an estimated average linear flow velocity of between 15 to 150 m/yr determined using Darcy’s Law5.

5 Darcy’s Law can be expressed as v = K.i/η, where v is the average linear flow velocity [LT-1], K is aquifer hydraulic conductivity [LT-1] (12.4 m/day assuming a thickness of 10 m, section 2.6), i is hydraulic gradient [-] (0.01-0.001 from Figure 10) and η is aquifer porosity [-] (assume 0.3 given specific yield is 0.26, section 2.6).


PAGE 11

5 GROUNDWATER OUTFLOWS

5.1 Lateral Discharge The shape and distribution of the interpreted groundwater elevation contours shown in Figure 10 suggest that groundwater discharges to the western and eastern coastlines of King Island. The rate of groundwater discharge has been estimated using conventional flow net analysis6 and is of the order of 13,600 ML/yr.

5.2 Groundwater Extraction Groundwater abstraction on King Island is predominantly sourced from the Quaternary coastal sand aquifer on the west coast. The annual rate of abstraction for Currie town water supply is known (<100 ML/yr, pers. comm. King Island Council 2007) but for the other main users, i.e. the abattoir and King Island Dairy, extraction is unknown. For the purpose of developing a water balance in the current project, total annual abstraction for all uses on King Island is estimated to be less than 1,000 ML/yr.

5.3 Evapotranspiration from Shallow Water Tables Where water tables are close to the ground surface, typically within 2 - 3 m, evapotranspiration can remove large volumes of groundwater. To estimate this flux for the King Island catchment would require a detailed knowledge of the rooting depths of local plant species and their annual rate of groundwater use. Whilst this information is not readily available to the current project, the areas of the catchment in which this process may be important are shown by way of yellow dots on Figure 10. These are well locations where the depth to water has been recorded and is less than 3 m below ground level. While the water levels may be affected by locally confining conditions, the map indicates a significant number of shallow water levels in the Quaternary aquifer in the vicinity of Currie, where losses to evapotranspiration may be significant. The shallow nature of the aquifer at this location suggests it plays an important role regarding dryland salinity processes, which may in turn affect water supply. Shallow water levels could exist in similar Quaternary aquifers elsewhere on the island.

5.4 Groundwater Discharge to Streams Groundwater discharge to streams may be an important component of the water balance for King Island, particularly in the lower reaches of each surface water catchment. However, as discussed previously for groundwater recharge (section 3.3), there is no time-series groundwater or surface water monitoring data to test this hypothesis or estimate its likely magnitude.

6 Flow net analysis is an application of Darcy’s Law: Q = T.i.w, where Q is the groundwater flux [L3T-1], T is aquifer transmissivity [L2T-1] (124 m2/day, section 2.6), i is hydraulic gradient [-] (average 0.002) and w is aquifer width [L] (150 km).


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6 CONCEPTUAL MODEL

6.1 Block Diagram A three-dimensional conceptual hydrogeological model of the King Island catchment has been built (Figure 11) using a Digital Elevation Model (DEM) for the topographic surface. The key features to the conceptual model are provided below:

• The primary aquifer is associated with aeolian coastal sands, extending some 20 - 30 km along the east and west coasts;

• Secondary aquifers include the fractured Proterozoic igneous and metamorphic rocks that underlie most of the island, and to a lesser degree, the Tertiary Limestone that occurs in limited horizontal extent beneath alluvium in the north; and

• The groundwater flow systems within each aquifer type are sub-catchment scale, with diffuse recharge to generally unconfined water tables and subsequent discharge at the coast.

6.2 Preliminary Water Budget Using the calculations derived in previous chapters, Figure 11 has annotations of preliminary estimates for the main components of the water balance, and an indication of where in the catchment they may occur. This data is also summarised as either groundwater inflows or outflows in Figure 12 to establish a catchment groundwater balance. This budget is considered to be very approximate and should not be used for any purpose other than to inform the project team of where efforts should be focussed for the upcoming field program. The water budget has indicated that:

• The groundwater system is recharged predominately through rainfall infiltration which is mainly discharged at the coast (and probably ET from shallow water tables, although this component remains unquantified);

• A surplus of water exists in the catchment, but this is most likely an artefact of not being able to estimate discharge to streams and ET losses; and

• The volume of extraction relative to rainfall recharge is considered to be very small, which places this region in a low category of threat.

6.3 Knowledge Gaps and Uncertainty This groundwater budget is considered to be very approximate and should not be used for any purpose other than to highlight existing knowledge gaps. In particular, it should not be used for defining existing levels of use or sustainable yield for management purposes.

A summary of all data sources made available for the preparation of this conceptual model report is provided in the Data Inventory in Appendix B.


PAGE 13

The preliminary conceptual model (Figure 11) and groundwater budget (Figure 12) highlight at least two key components of the water balance that need to be better defined for the King Island catchment. These are groundwater discharge to streams, and ET losses from shallow water tables.


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7 RECOMMENDATIONS FOR FIELD STUDIES

Based on the available data, the following fieldwork is recommended for the King Island catchment via future funding opportunities.

• Run-of-river sampling and flow gauging of major surface water features to enable the estimation of surface water discharge, and groundwater discharge rates and locations.

• Installation of new monitoring wells, or re-establishment of existing wells, to enable the collection of time-series groundwater level and quality data.


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8 REFERENCES

Bureau of Rural Sciences (2002). Land use mapping at catchment scale. Principles, procedures and definitions, Edition 2. 46 pp.

Cromer, W.C. (1978). Pump testing an unconfined coastal aquifer, Currie, King Island. Tasmanian Mines Department, unpublished report UR1978_29.

Matthews, W.L. (1966). Water supply at Currie, King Island. Tasmanian Department of Mines, report TR10_93_99.

Matthews, W.L., and Cromer, W.C. (1973). Groundwater investigations at Currie, King Island. Tasmanian Department of Mines, report TR18_106_121.

Gresham, J.J. (1972). The regional geology of King Island. Report by Geopeko Limited, ISG 70-0676.

Zhang, L., Dawes, W.R., and Walker, G.R. (1999). Predicting the effect of vegetation changes on catchment average water balance. Technical report 99/12, CRC for Catchment Hydrology.

Zhang, L., Dawes, W.R., and Walker, G.R. (2001). Response of mean annual evapotranspiration to vegetation changes at the catchment scale, Water Resources Research, 37: 701-708.

FIGURE

1

LateralGroundwaterInflow

R:\GIS\Dept PIW Tas\01_GW Models\Maps\3D Block Diagrams\figure1.cdr

Schematic diagram showing the main components ofa catchment-scale groundwater balance

Groundwater Dischargeto Streams

Inte

raquife

r leakage

Groundwater Rechargefrom Streams

Surface Evaporation

Diffuse GroundwaterRecharge

Rainfall

Transpiration

Lateral Groundwater Outflow

Surface Runoff

Evaporation fromShallow Water Tables

Dam Storage

Groundwater Abstractionfor Irrigation

Surface Water Usefor Irrigation

Water Use for Domesticand Other Purposes

CURRIE

GRASSY

CAPE WICKHAM

STOKES POINT

Ettrick River Upstream South Rd

SEA ELEPHANT RIV

ER

SEA

L R

IVER

E

TTRICK RIVER

YELLOW ROCK RIVER

POR

KY C

REEK

FRASER RIVER

EGG LAGOON CREEK

YAR RA CREEK

SALT

WATE

R C

REEK

BARRIER C REEK

BADGER BOX CREEK

ELDORADO CREEK

BLOWHOLE CREEK

PASS RIVER

LYMWOOD

PEGARAH

LOORANA

REEKARA

PARENNA

NARACOOPA

PEARSHAPE

YAMBACOONA

EGG LAGOON

YARRA CREEK

SEA ELEPHANT

COOPER BLUFF

FRASER BLUFF

HUXLEY HILL WIND FARM

210000 220000 230000 240000 25000055

5000

055

6000

055

7000

055

8000

055

9000

056

0000

056

1000

0

Figure

2KING ISLANDSurface Water

R://GIS/Dept PIW Tas/01_GW Models/ Maps/King Island/King Island_Map1.mxd

Project: FQ-01-1

BASS STRAIT ¯King Island

Tasmania

0 5 10 km

Catchment Boundary

Surface Water

Water Gauging Station

Coastline

Dams

Towns

Dcurrie

Stamp

Dcurrie

Stamp

FIGURE

Document AZ-01-D017

PROJECT AZ-01 July-02

Total annual rainfall and cumulative deviation from mean annual rainfall for

King Island catchment 3

0

200

400

600

800

1000

1200

1400

1908

1918

1928

1938

1948

1958

1968

1978

1988

Date

Tota

l Ann

ual R

ainf

all (

mm

)

-2000

-1500

-1000

-500

0

500

1000

1500

2000

Cum

ulat

ive

Dev

iatio

n fr

om M

ean

(mm

)

Total Annual Rainfall (mm)

Deviation from the Mean (mm)

699 mm Mean Annual Rainfall

dcurrie

Text Box

BOM site: Currie Post Office (ID 98001)

CURRIE

GRASSY

CAPE WICKHAM

STOKES POINT

210000 220000 230000 240000 250000 26000055

5000

055

6000

055

7000

055

8000

055

9000

056

0000

056

1000

056

2000

0

Figure

4KING ISLANDTopography, Land System and Primary Soil Classification

R://GIS/Dept DWI Tas/01_GW Models/Maps/King Island/King Island_Map2.mxd

Project: FQ-01-1

¯

Tasmania

King Island

BASS STRAIT

Catchment Boundary

CoastlineLand System and Primary Soil Type (%)

coastal dunes & beach, Rudosol, (100%)

coastal dunes & beach, Rudosol, (55%)

flat plains, Hydrosol, (100%)

flat plains, Organosol, (100%)

flat plains, Podosol, (100%)

undulating plains, Kurosol, (70%)

undulating plains, Tenosol, (100%)

0 5 10 km

Dcurrie

Stamp

Dcurrie

Stamp

CURRIE

GRASSY

CAPE WICKHAM

STOKES POINT

210000 220000 230000 240000 25000055

5000

055

6000

055

7000

055

8000

055

9000

056

0000

056

1000

0

Figure

5KING ISLANDLand Use and Groundwater Salinity

R://GIS/Dept PIW Tas/Maps/King Island/King Island_Map3.mxd

Project: FQ-01-1

¯

Tasmania

King Island

BASS STRAIT

Catchment BoundaryCoastline

Groundwater Salinity (mg/L)0-100100-250250-500500-10001000-2500

Land UseBuilt EnvironsEnvironmentalForestry/PlantationNational Park/Reserve/WildernessOtherRemnant VegetationWater

0 5 10 km

Lsv

Tm

Tm

Q

Lr

Ltp

Lg

Lg

Qh

Qh

Qh

Lg

Qh

Qh

Qps

Dgn

Qh

Qh

Q

Qh

Qps

Qps

Qh

Qps

Qps

Qps

Qps

Qps

Qps

Qh

Ltp

Laa

Lg

Qps

Qps

Lg

Qh

Lg

Ltp

Dgn

Qps

Laa

Qh

Lg

Lg

Dgn

Qh

Laa

Qh

Laa

Lsb

Lg

Dgn

Ltp

Dgn

Qps

Lsv

Ltp

Tb

Laa

Tm

Lss

TbTb

Tb

Tm

Laa

Lsv

Dgn

CURRIE

GRASSY

CAPE WICKHAM

STOKES POINT

210000 220000 230000 240000 250000 26000055

5000

055

6000

055

7000

055

8000

055

9000

056

0000

056

1000

056

2000

0

Figure

6SORELL TERTIARY BASALT

Surface Geology and Well Yields

I:\VESA\Projects\VE30047\DPIW Tas (FQ)\01_GW Models\GIS\Maps\King Island\King Island_Map7.mxd

Project: FQ-01-1

BASS STRAIT ¯King Island

Tasmania

0 5 10 km

Catchment Boundary

Coastline

Nominal Well Yields (L/s)

not recorded

dry

< 0.05

0.05 - 0.5

0.5 - 1.5

1.5 - 5.0

5.0 - 10.0

> 10.0

Geology 1:250k

Quaternary

Q

Qh

Qps

Tertiary

Tb

Tm

Early Carboniferous-Early Devonian

Dgn

Neoproterozoic

Laa

Lg

Lsb

Lss

Lsv

Ltp

Mesoproterozoic

Lr

All wells as listed in the MRT database are shown on this map.Nominal yields are mostly the result of short term airlift or pump testsof variable accuracy. Different well depths and aquifers arerepresented, which affects spatial relationships of yield; althoughmost wells in this catchment are installed in Quaternary costalsands. The well locations have variable accuracy and were mainly defined by drillers and MRT staff using maps, rather than GPS units.

Dcurrie

Stamp

Dcurrie

Stamp

WEST EAST

R:\GIS\Dept PIW Tas\01_GW Models\Maps\cross sections\king island.cdr

FIGURE

7KING ISLAND

Schematic geological cross-section from workshop

NeoproterozoicTogari Group

MesoproterozoicRocky Cape Group

Older Proterozoicphyllite


ProterozoicGranite

DevonianGranite

MesoproterozoicRocky Cape Group

Tertiary LimestoneTertiary Limestone



quaternary cover

Lagoons

southern part of island

northern region

beach ridgescoastal dunes

ProterozoicGranite

FIGURE

Document AZ-01-D014PROJECT AZ-01 June-02

Well yield and Salinity for Coastal Sands, Devonian Granite, Quaternary Alluvium,

Tertiary Basalt/Sediments and Precambrian aquifer wells in the

King Island catchment area 8

0

10

20

30

40

0 to 1 1 to 5 5 to 10 10 to 15 15 to 20 >20 UnknownYield (L/sec)

Freq

uenc

y (%

)

Coastal Sands Aquifer Wells

Devonian Granite, Quaternary Alluvium and TertiaryBasalt/Sediment Aquifer WellsPrecambrian Aquifer Wells

88

2423

1 02

0 0

23. Number of wells in catchment area

0 000000004

66

22

12

Well yield for aquifer wells in the King Island catchment area

0

10

20

30

40

<500 >500 >1000 UnknownSalinity (TDS mg/L)

Freq

uenc

y (%

)

Coastal Sands Aquifer Wells

Devonian Granite, Quaternary Alluvium and TertiaryBasalt/Sediment Aquifer WellsPrecambrian Aquifer Wells

26

74

1

45

91

7. Number of wells in catchment area

68

18

1 1

34

Salinity for aquifer wells in the King Island catchment area

!

!

!

!

!!

!!!

!

!! !

!!!

!! !

!

!! !

!

!!

!

!!

!

!!!!! !!!

!!!!!!

! !!

!!!

!!

!! !

!!!!

!!!

!!!!!!

!

!

!!

!

!

Lg

CURRIE

GRASSY

CAPE WICKHAM

STOKES POINT

90

40

10080

2

96

9290

98

84

787975

867981

2826

32

3444

29

21

15

-6

135115

134120

106106

103108

220000 230000 240000 25000055

5000

055

6000

055

7000

055

8000

055

9000

056

0000

056

1000

0

Figure

10KING ISLANDPotentiometric Elevation Contours and Inferred Groundwater Flowlines

Project: FQ-01-1

R://GIS/Dept PIW Tas/Maps/King Island/King Island_Map5.mxd

TownsCatchment BoundarySurface Water

! Groundwater Wells - Depth to Water <3 m

!

Groundwater Wells - Devonian,Precambrian, Tertiary, QuaternaryInferred Groundwater Elevation Contour (mAHD)Interpreted Groundwater Elevation Contour (mAHD)Inferred Groundwater Flow Direction

Geology Description: See Figure 6

0 5 10 km

BASS STRAIT

King Island

Tasmania

Dcurrie

Stamp

Dcurrie

Stamp

R:\GIS\Dept PIW Tas\01_GW Models\Maps\3D Block Diagrams\king island.cdr

FIGURE

11KING ISLAND

Conceptual Hydrogeological Model

0

-100

(m A

HD

)

North

Neoproterozoic(Togari Group)

Coastal Sand Aquifer

Prote

rozo

ic B

asem

ent

Rock

s –

Prote

rozo

ic B

asem

ent

Rock

s –

Fractured

Rock

Aquifer

Fractured

Rock

Aquifer

TertiaryLimestone

Aquifer

Lateral groundwaterdischarge

(entire coastline13,600 ML/yr)

Diffuse rechargeto coastal sands11-41 mm/yr

Lateralgroundwater

discharge

Groundwater abstractionCurrie town water supply

and other local users<1,000 ML/yr

2CATCHMENT AREA 1085 km

MEAN ANNUAL RAINFALL 699 mm/yr

QuaternarySediments

Surface waterdischarge

Sea Elephant River(flow unknown)

Diffuse recharge11-41 mm/yr

Proterozoic

Granite

CATCHMENT NAME: King Island

Area: 1085 km2

Mean Annual Rainfall: 699 mm/yr

Annual Average Surface Water Discharge: unknown ML/yr

comprising of

Annual Average Surface Runoff: unknown ML/yr

Annual Average Baseflow: unknown ML/yr

CONFIDENCE IN ESTIMATEGROUNDWATER INFLOWS (1 = Very Low, 5 = Very High)

Lateral Inflow: 0 ML/yr 5

Recharge by:

Diffuse Rainfall Recharge: 29,295 ML/yr (11-41 mm/yr) 3

Point Source Infiltration: negligible ML/yr 5

Stream Losses: not quantified ML/yr 2

29,295 ML/yr

GROUNDWATER OUTFLOWS

Lateral Discharge: 13,600 ML/yr 3

Groundwater Abstraction: 1,000 ML/yr 4

Evapotranspiration: not quantified ML/yr 1

Discharge to Streams: not quantified ML/yr 1

14,600 ML/yr

GROUNDWATER BALANCE

CHANGE IN AQUIFER STORAGE:14,695 ML/yr

FIGURE

PROJECT FQ-01 July-08

King Island

Low ThreatModerate ThreatHigh Threat

> 10 GL/yr

Extraction 0 - 25% 25 - 75% >75%

5-10 GL/yr

< 5 GL/yr

ΣINFLOWS - ΣOUTFLOWS =

TOTAL INFLOWS =

TOTAL OUTFLOWS =

Groundwater Threat Index

Extraction/Recharge

PRELIMINARYCATCHMENT WATER BALANCE

FOR KING ISLAND 12

Dcurrie

Stamp

Appendix A

Geological descriptions for Figure 6

Symbol DescriptionQ Undifferentiated Quaternary sediments.Qh Sand gravel and mud of alluvial, lacustrine and littoral origin.Qps Coastal sand and gravel.Tb Basalt (tholeiitic to alkalic) and related pyroclastic rocks.Tm Marine limestone.Dgn Dominantly granodiorite / adamellite (I-type).Laa Amphibolite ( Arthur Metamorphic Complex).Lg Granitic rocks.Lr Undifferentiated the Rocky Cape Group rocks.

Lsb Tholeiitic basalt (Spinks Creek Volcanics, Bernafai Volcanics and correlates).Lss Shallow marine dolomite, chert, shale and diamictite (Black River Dolomite, Savage Dolomite and correlates).Lsv Turbiditic mudstone, siltsone, lithicwacke and diamictite with dominantly mafic detritusLtp Dominantly pelitic sequences, mainly phyllite, with greenschist facies metamorphism.

Appendix B

Data Inventory for King Island

King Island

Data Available Source / Publications CommentsOverview of Geology

Age and depositional enviroments

post-depositional history (tectonics, metamorphism)

Topography / Physiographic Setting

DEM ***Y DPIW - electronic

- contoursY DPIW - electronic

- point heightsraster DPIW - electronic

soil typeY DPIW - electronic Simon Lynch

land use (i.e., native vegetation vs. dry land farming vs. irrigation vs. plantation forestry) Y DPIW - electronic Simon Lynch

Basic Hydrogeology

stratigraphy - no. aquifers/aquitardsT limestone, Q fill

thicknesses (reliable geological logs)

porosity/specific yield

hydraulic conductivity

Groundwater Monitoring

multilevel piezometers

time series gw levels ***John Sloane historical monioting wells

time series gw chem

Water table contoursPhil Dyson?

Groundwater flow – direction, rates?

Surface water monitoring

time series sw flows

time series sw chem

Surface water-groundwater interaction ***

baseflow separation from sw monitoring

gw monitoring responses

Groundwater Recharge

Rainfall seasonality/history

Diffuse recharge

- relationship with soil/land use

- rainfall-gw chemistry/salinity

Localised recharge (e.g. flood or preferential)

- flood extent and duration

- bore hydrograph responses

- gw quality maps

Groundwater pumping (extraction) ***

Irrigation type/efficiency

Crop types/volumes applied

History of useabbattoir, dairy, TWS

Bore density

Drawdown/recovery responses

Evapotranspiration

depth to water table

vegetation types/health

evidence of salinisation

Artificial Drainage

network

drain elevation cf. groundwater levels

Groundwater Model - type, purpose and necessary features

Data Inventory - Class ABC

prepared for dpiw tasmania

Documents