final year honour’s dissertation lauren marli miles€¦ · dryland salinity: “the movement of...

School of Environmental

Systems Engineering

School of

Engineering

Assessing the hydrologic connectivity and salinity of the

Darkin Swamp Management unit (Helena River Catchment);

Focusing on the study of macroinvertebrate communities and

investigating the use of a salinity and water balance model.

Final Year Honour’s Dissertation

Lauren Marli Miles

Supervisors:

Anas Ghadouani

(School of Environmental Systems Engineering)

Artemis Kitsios

(Department of Water)

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Assessing the hydrologic connectivity and salinity of the Darkin Swamp Management unit

ABSTRACT

The Darkin Swamp catchment management unit is one of the five Management units in the

Helena Catchment which is a water supply catchment for Perth. The management unit

contains several swamps, the largest of which is Darkin Swamp. During the completion of the

Department of Waters Salinity Situation Statement for the Helena River, it was revealed that

there was a lack of knowledge concerning how the overflow of these swamps could effect the

downstream salinity of the Helena River and hence the Mundaring Reservoir. One of the

reasons for this was because flow in this section for the catchment is ephemeral. The possible

saline input of the water into the Darkin Rivers is of importance because the salinity of the

Mundaring Reservoir is close to the desirable limit for drinking water.

The first aim of this study was to investigate the hydrologic connectivity between these

swamps and the Darkin River. This can allow a greater understanding of impact of the

swamps, particularly Darkin Swamp, would have on the salinity and flows of the Darkin - and

hence Helena - rivers. Lack of data specific to the Darkin Swamp Management Unit made this

difficult and so too did Perth’s record low rainfall in the year of the project, which created low

flows at the study site. However, the possible way in waterbodies in the section of the Helena

Catchment is discussed, using the results some salinity sampling in the Darkin Swamp area,

as well as analysis of data from a downstream gauging station. To achieve an indication of

connections between swamps, the possibility of using sampling and analysis of the

composition of macroinvertebrate communities was discussed. It was concluded that it could

be viable option to assess the hydrologic connectivity in a year of high flow. The

determination of this connectivity, plus further investigations into groundwater discharge

regimes, soil profiles and the bathymetry of Darkin Swamp could provide even greater

accuracy when modelling salt flows and salinity for the Darkin Swamp Management unit, via

the use of the ‘LUCICAT’ (Land Use Incorporated CATchment) model.

Results from sampling of the waters in the Darkin Swamp management unit revealed surface

waters were fresh, even for low flows. Data from a downstream gauging station which

provided relationships between rainfall, salinity and streamflow suggested that there is this

could be because there is little baseflow occurring, as suggested in previous research. The

distribution and magnitude of rainfall throughout the year was found to be a factor into

whether the Darkin Swamp overflowed and connected to the Darkin River. A trend towards

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less rainfall in the winter months could indicate that in the future Darkin Swamp will have a

lower probability of connecting to the Darkin River.

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ACKNOWLEDGEMENTS

There are many people who assisted me throughout the year in writing my Honour’s

dissertation, and I would like to extend my since thanks and gratitude to:

My supervisor at the School of Environmental Systems Engineering, Anas Ghadouani, for his

academic guidance as well as the friendly chats about anything.

Artemis Kitsios from the Department of Water for her help in all aspects of the project

including developing the scope, assistance with field work and also her amicable demeanour.

All staff from the Department of Water salinity branch especially Tim Sparks for his offer to

complete a project with support of the DoW, Melinda Burton, for help with field work,

making sure I had a desk to work at and helping consolidate ideas, Robin Smith for help with

field work and lending his knowledge in relation to the Helena Catchment, Mohammed Bari

for fielding questions about LUCICAT and also the Helena catchment, and also David

Rowlands, Renaè Dixon and Joanne Gregory with their help in data acquisition.

Karina Congdon from the Water Corporation for her role as contact in relation to the Helena

Catchment.

The staff at the School of Environmental Systems Engineering.

My fellow students at SESE for the comradery, friendship, laughs and the occasional

reminder to complete the task at hand.

And last, but not least, my friends and family who’ve supported me throughout the year.

So thankyou….I love you all!

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GLOSSARY OF TERMS

Baseflow: the entry of groundwater into lakes and rivers

Bathymetry: the shape and depth profile of a lake

Brackish water: water with total dissolved solids between 1000-2000 mg/L (Mayer, 2005)

Dryland salinity: “the movement of salt to the land surface with rising groundwater in non-

irrigated lands” (page 3, (Walker, 1999))

Dryland Rivers: rivers in low rainfall areas. Dryland rivers are usually do not flow in the summer months. Electrical conductivity: the relative ease at which electricity can pass through a solution, measured in EC units (mS/cm). Electrical conductivity can be used to measure salinity as an increased concentration of salts increases the electrical conductivity. Electro-conductivity meter: a sampling device to measure electrical conductivity, and hence salinity. Hydrology: the study of the movement of water through rocks, soil, lakes and rivers Interflow/Subsurface runoff: water which penetrates the top layers of soil and flows through

these soil layers to reach lakes and rivers

Saline water: Water with total dissolved solids between 10,000 and 30,000 mg/L (Mayer

2005)

Salinity: the concentration of salt in soil or water

Salt fall: The amount of salt which is deposited onto an area of land annually

Salt load: the total amount of salt in a waterbody

Surface flow: water which runs across the top layer of soil to flow into lakes and rivers

Topography: the relative elevation and features of a landscape, such as hills and valleys

Total Dissolved Solids: the concentration of solid material dissolved in a waterbody, usually

expressed in mg/L.

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TABLE OF CONTENTS

1. INTRODUCTION .......................................................................................................................................... 9 2. LITERATURE REVIEW.............................................................................................................................. 10

2.1. Dryland Salinity ................................................................................................................................. 10 2.2. Secondary Salinisation of Streams..................................................................................................... 10 2.3. Dryland Flows.................................................................................................................................... 11 2.4. Streamflow and Salinity: Surface Flow, Interflow and Baseflow...................................................... 11 2.5. Climate Change.................................................................................................................................. 12

Decline in Rainfall ........................................................................................................................................ 12 Potential Evaporation.................................................................................................................................... 12 Seasonality and Flood Events ....................................................................................................................... 12 Drying Catchment ......................................................................................................................................... 13

2.6. Water Quality..................................................................................................................................... 13 2.7. Biological Communities, Connectivity and Salinity.......................................................................... 14

Why are we concerned with macroinvertebrate populations?....................................................................... 14 How to sample for macroinvertebrates?........................................................................................................ 14 Tolerance - Testing of macroinvertebrate species and salinity thresholds .................................................... 15 Links between macroinvertebrate assemblages and flow variability ............................................................ 16 What causes surface water flows to change? ................................................................................................ 17

2.8. LUCICAT model ............................................................................................................................... 17 2.9. Similar Models................................................................................................................................... 19

LASCAM...................................................................................................................................................... 19 MAGIC ......................................................................................................................................................... 19

2.10. Darkin Swamp Background ............................................................................................................... 20 Upper Helena Catchment .............................................................................................................................. 20 Helena Salinity Situation Statement.............................................................................................................. 21 Darkin Swamp Management unit.................................................................................................................. 21 Catchment Characteristics............................................................................................................................. 22 Climate.......................................................................................................................................................... 24 Clearing of Darkin Swamp Subcatchment .................................................................................................... 24 Previous Modelling Darkin Swamp Management unit ................................................................................. 24 Surface Water Salinity Darkin Swamp Management unit............................................................................. 25 Groundwater.................................................................................................................................................. 25

3. METHODS ................................................................................................................................................... 26 3.1. Data Collection .................................................................................................................................. 26

Available rainfall, streamflow and salinity data............................................................................................ 26 3.2. Sampling ............................................................................................................................................ 27

Salinity .......................................................................................................................................................... 27 Macroinvertebrate sampling.......................................................................................................................... 28 LUCICAT MODELLING............................................................................................................................. 28 Climate change.............................................................................................................................................. 29 RELATIONSHIPS BETWEEN RAINFALL, STREAMFLOW AND SALINITY ..................................... 29

4. RESULTS ..................................................................................................................................................... 31 4.1. Sampling Results ............................................................................................................................... 31

June ............................................................................................................................................................... 31 Thursday 25th August, 2006. ......................................................................................................................... 33

4.2. Graphs Rainfall, Flow and Salinity.................................................................................................... 37 Rainfall for Darkin Swamp 2000-2003......................................................................................................... 37 Flow and Salinity 2000 and 2001.................................................................................................................. 38 Rainfall and Salinity 2000 and 2001 ............................................................................................................. 40 Flow and Rainfall 2000 and 2001 ................................................................................................................. 40

5. DISCUSSION ............................................................................................................................................... 43 5.1. Sampling of Darkin Swamp Management unit surface waters .......................................................... 43

Winter 2006: Driest on Record ..................................................................................................................... 43 5.2. Comparisons salinity, streamflow and rainfall................................................................................... 43

Streamflow and salinity................................................................................................................................. 43 Rainfall and salinity ...................................................................................................................................... 43 Rainfall and streamflow ................................................................................................................................ 44 Rainfall preceding swamp overflow compared to rainfall preceding record low flows................................ 44 Effect of climate change................................................................................................................................ 44

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5.3. How data from gauging stations is reflected in the field trip data...................................................... 45 5.4. LUCICAT .......................................................................................................................................... 46

Use of the model ........................................................................................................................................... 46 Likelihood of scenarios ................................................................................................................................. 46

6. CONCLUSIONS........................................................................................................................................... 47 7. FUTURE RECOMMENDATIONS.............................................................................................................. 48 8. APPENDIX 3 – GIS MAP OF PRIVATELY OWNED FARMLAND AND STREAMS IN THE UPPER HELENA CATCHMENT (Smith, 2006).............................................................................................................. 53 9. APPENDIX 4 – STREAMLINES AND 66 LUCICAT SUBCATCHMENTS USED FOR MODELLING IN HELENA SALINITY SITUATION STATEMENT (Smith, 2006) ................................................................ 54 10. ......................................................................................................................................................................... 54 APPENDIX 5 – DATA AND OBSERVATIONS OF THE HELENA CATCHMENT FIELD TRIP 13th FEBRUARY, 2006. .............................................................................................................................................. 55 REFERENCES ..................................................................................................................................................... 59 REFERENCES ..................................................................................................................................................... 60

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LIST OF FIGURES Figure 1. Mundaring Weir in June, 2006. ............................................................................................................. 20 Figure 2. Mundaring Reservoir in June, 2006....................................................................................................... 21 Figure 3. Diagram of flow-through, discharge and recharge regimes for baseflow into a lake (Bari, 2005a). ..... 29 Figure 4. June 29th, 2006. Left – area surrounding Darkin Swamp, right and bottom centre –Darkin River

gauging station. ............................................................................................................................................. 32 Figure 5. 25 August, 2006. Flow running off farm on eastern side Darkin Swamp Management unit................. 36 Figure 6. August 25, 2006. Flooding of Piggery Road in the vicinity of Darkin Swamp. .................................... 36 Figure 7. August 26, 2006. Picture of Little Darkin Swamp, north of Darkin Swamp. ........................................ 36 Figure 8. August 26, 2006. Southern fence-line of farm in Darkin Swamp Management unit after rain.............. 37 Figure 9. Graph of data for LUCICAT subcatchment including Darkin Swamp, 2000-2003............................... 37 Figure 10. Streamflow and salinity (total dissolved solids) for Darkin River gauging station in 2001. ............... 38 Figure 11. Salinity and streamflow measured at the Darkin River gauging station in 2000. ................................ 38 Figure 12. Salinity and streamflow for the Darkin River gauging station, 2000.................................................. 39 Figure 13. Salinity (TDS) and Rainfall for the Darkin River Gauging Station, 2001. .......................................... 39 Figure 14. Streamflow and salinity (total dissolved solids) for Darkin River gauging station in 2001. ............... 40 Figure 15. Daily rainfall and streamflow for the Darkin River Gauging station 2001.......................................... 40 Figure 16. Daily streamflow and rainfall, Darkin River Gauging Station, 2000................................................... 41 Figure 17. Interpolated rainfall from 1992-1996 at the 47 Mile Peg gauging station ........................................... 41 Figure 18. Rainfall for years 1976-1979 at the Darkin River gauging station ...................................................... 42

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LIST OF TABLES Table 1. Summary of catchment characteristics, including vegetation and topography. Information from (Smith,

2006), unless specified otherwise.................................................................................................................. 23 Table 2. Salinity sample results for Darkin Swamp Management unit 29th, June 2006........................................ 33 Table 3. Salinity sample results and flow observations for Darkin Swamp Management unit, August 25th, 2006.

...................................................................................................................................................................... 35

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1. INTRODUCTION

Dryland salinity is a battle facing a large proportion of catchments across Western Australia

and one of the consequences of this is salinisation of streams. This is of particular importance

in a water resource catchment, as world health organisation standards specify that the salinity

of drinking water be no greater than 800 EC units (approximately 500 mg/L). The Darkin

Swamp Catchment Management Unit is one of the five Management units in the Helena River

Catchment which discharge into the headwaters of the Mundaring Weir. Water enclosed by

the Weir is extracted for potable use and errs close to the guideline for drinking water. The

Department of Water is close to completing a Salinity Situation Statement for the Helena

River which suggests that although it currently has little impact, there still could be potential

for the swamps within the Darkin Swamp Catchment Management Unit to elevate the salinity

of the Darkin, and further downstream Helena, rivers.

The Darkin Swamp area is located on Eastern side of the catchment which receives less than

half the rainfall than the Western side and currently has a small percentage of clearing. It

comprises of a series of swamps, the largest of which is Darkin Swamp, which discharges

intermittently into the Darkin River. The soon to be published salinity study for the Helena

catchment states there is little sign of hydrologic connection between these swamps. This

project aims to explore ways to define the possible hydrologic connections in the Darkin

Swamp Management unit, how this contributes towards the salinities of the surface waters. It

also defines what measures could be taken in order to establish the water balance of Darkin

Swamp with greater accuracy so as to quantify salinity changes in the Darkin River after

potential land use and climate changes.

There have previously been several studies which link the composition of macroinvertebrate

assemblages and salinity in the south-west of Western Australia and similar regions. In order

to establish the connectivity between Swamps and the Darkin River, the possibility of using

macroinvertebrate sampling to indicate points which are hydrologically connected will be

explored, however implementation is outside the scope of this project. Connections between

points in a catchment are required in order to accurately model salinity and flow using the

computer model ‘LUCICAT’ (Land Use Change Incorporated CATchment model). This

model can be used to predict the impact that vegetation removal and climate change,

specifically changes in rainfall, will have on the salinity and flow of the water which enters

into the Darkin River and eventually discharges into the Mundaring Reservoir.

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2. LITERATURE REVIEW

2.1. Dryland Salinity Dryland salinity effects 1.8 million hectares of land in the south-west of Western Australia

alone (Nulsen, 2000);(Walker, 1999), and costs Australia as a whole approximately $3.5

billion annually (Warnick, 2006). Stream salinity is one of the important consequences of

dryland salinity (Walker, 1999). Like the rest of Australia, surface soils in the south-west of

Western Australia naturally contain salt due to rainfall depositing salt on the land over

thousands of years (Smith, 2006);(Walker, 1999); (Mayer, 2005), as well as from “dew and

dry fallout” (page 7, (Mayer, 2005)) . The relatively low rainfall over most of Australia

limited flushing of these salts out of the soil (Walker, 1999). As rainfall decreases with

distance inland, the amount of salt in the soil increases (Mayer, 2005). This was not

considered a problem when the dominant vegetation was deep rooted (Smith, 2006), as was

the case before European settlement (Walker, 1999), because the water level was kept well

below topsoil containing most of the salt (Smith, 2006);(Walker, 1999). When this deep

rooted vegetation was removed and replaced with shallow rooted cropping the water levels

were raised high enough – due to a decreased evapotranspiration and water storage by plants -

to dissolve the salt in the top 1-2m of soil (Smith, 2006). Capillary forces brought salts

upwards resulting in the accumulation of salt surface (Smith, 2006);(Mayer, 2005). Increased

salinity in soils can render formerly arable land unproductive (Smith, 2006).

The processes behind salinity are still occurring (Taylor, 2003) and millions of dollars are

spent every year by governments, farmers and other stakeholders trying to combat its effects.

In general the effects of dryland salinity are worse in low rainfall areas, such as Western

Australia’s wheatbelt region (Smith, 2006), as there is less flushing of salt from the soil

(Smith, 2006).

2.2. Secondary Salinisation of Streams The groundwater level rise which causes dryland salinity can also result in stream salinity

(Walker, 1999). A rising water table can lead to increased baseflow into lakes and rivers

(Smith, 2006); (Mayer, 2005) and saline runoff from soils (Smith, 2006), increasing the

salinity of lakes and rivers. In the south-west of Western Australia, 56% of lakes and rivers

are brackish or saline (Mayer, 2005), the majority of these having undergone secondary

salinity. Secondary salinity not only impacts the biota of a waterbody (Warnick, 2006), but

also the people who are reliant on a lake or river for drinking water and irrigation (Walker,

1999).

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2.3. Dryland Flows

The hydrology of dryland rivers differs from those in catchments with higher rainfalls. One of

the main differences is that dryland river systems are by nature discontinuous throughout

much of the year (Sheldon, 2000). This has an impact in shaping composition of the biota,

such as fish and waterbirds (Timms, 2001), as well as macroinvertebrates, discussed further in

Section 2.7. There is a deficit in research concerning dryland river systems in relation to

ecology, hydrology and chemistry, which can be attributed to sections of river being dry for

most part of the year and also “lack of accessibility” when obtaining data through field work

(page 2, (Timms, 2001)). Catchments in these low rainfall areas also tend to share the

characteristic of having a system of lakes, ranging in salinity from fresh to saline (Timms,

2001), which intermittently overflow (Sheldon, 2000). This is exemplified in the wheatbelt

region of Western Australia, where lake systems such as lakes Nunijup, Carabundup and

Poorrarecup have poor drainage due to their flat topography and although receive flow from

the surrounding catchment, do not discharge except after high rainfall events (Bari, 2005a).

This is thought to be the case for Lake Dumbleyung (Bari, 2003) and also Darkin Swamp ,

which is part of the focus for this study.

2.4. Streamflow and Salinity: Surface Flow, Interflow and Baseflow There are several components which contribute to the generation of streamflow. One of these

is surface runoff (Mayer, 2005). When precipitation falls runoff can be created either by the

intensity of the precipitation being greater than the infiltration capacity of the soil, known as

infiltration runoff, or the soil already containing so much water that it is saturated, so can not

hold anymore water, known as saturation excess runoff (George, 1990). If there is an

impermeable layer beneath the soil, or the sub-surface soil is saturated, rainfall can penetrate

through the soil and flow through to reach a watercourse (System, 2005). This is known as

interflow or subsurface runoff (Training). In terms of salinity interflow and surface runoff are

relatively fresh. The other important mechanism to note is baseflow. Baseflow is created by

the discharge of groundwater into a lake or river (George, 1990), (Smith, 2006). Baseflow can

often be saline, though it depends on the soil and position in the landscape (Taylor, 2003).

Water held in lakes can also seep through the lake bottom down to the water table, as

discussed in Section 3.1.

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2.5. Climate Change

Decline in Rainfall

Since the mid 1970s, the rainfall in the south-west of Western Australia has dramatically

declined. This decrease has been calculated as high as 20% (Berti, 2004). A more permanent

change is set to occur with the average rainfall predicted to reduce by 11% (Berti, 2004). In

dryland rivers, a slight reduction in rainfall can have a much greater effect on the flow of a

waterbody (Berti, 2004);(Smith, 2006). This is due to the low percentage of precipitation

which eventually becomes stream flow, sometimes only 1-2% for dry catchments (Smith,

2006). For example, the drop in rainfall since the 1970’s was approximately 10% for the half

of the catchment west of the study area, and this resulted in a 30-50% decline in the amount

of flow into the catchments rivers (Smith, 2006). In approximately the next 50 years, the

calculated drop in water yield for the south-west catchment regions is 31%, for a predicted

11% reduction in precipitation (Berti, 2004).

Potential Evaporation

A change in potential evaporation could be set to occur as well. Whether this change will be

an increase or decrease is a topic of contention. Berti, 2004 calculated that an increase of 10%

for potential evaporation would add another 9% reduction to the estimated 31% drop in total

water yield for the south-west (Berti, 2004). A decrease of 10% potential evaporation,

however, would create only a 9% deficit from current water yields (Berti, 2004). Potential

evaporation will not be taken into account in this study.

Seasonality and Flood Events

In addition to a reduction in precipitation for the south-west in the last 30 years, there has also

been a shift in the seasonality of rainfall events throughout the year and their respective

intensity. The long-term climate of the south-west region sees the most rain falling in winter

(Pinder, 2005) and typically dry summers (Hatton, 2003), (Pinder, 2005) with the exception

of infrequent storms or rain due to cyclones generally in the north of the state (Smith, 2006).

Rainfall patterns since the 1970’s suggests that there is a change in the timing of winter

rainfall, with less rainfall occurring in May and July and the average rainfall from August

through to October being higher than that of the long-term average (Smith, 2006). In

Beraking Brook, a Management unit within the Upper Helena Catchment, an overall decrease

in average precipitation has been recognised for winter, and an overall increase for summer

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has also become apparent (Smith, 2006). Overall streamflow has also decreased (Smith,

2006). This is decrease can be explained as dry catchments in summer produce less runoff

than a catchment receiving the same amount of rainfall in winter so a (Smith, 2006), so this

scenario would produce a smaller total streamflow for a whole year (Smith, 2006).

.

A change occurring in the intensity and frequency of high rainfall events for the Australia’s

coastal regions is predicted (CSIRO, 2002). There is a tendency for high intensity storm

events to become less common and more severe (CSIRO) even in regions like the south-west

of Western Australia, where total rainfall is likely to decline (CSIRO, 2002). This is could be

especially evident in summer, with an increase in intensity of cyclones likely to occur

(CSIRO, 2002).

Drying Catchment

It is suggested in Smith, 2006 that a continued decrease in rainfall in the Darkin Swamp area,

which is the focus of this study, will lead to this section of the catchment “drying out”. This is

referring to the decrease in water storage of the soil. There are changes in hydrology

associated with a catchment becoming dry. As mentioned above, decreased runoff from dry

soil decreases river flow (Smith, 2006).

2.6. Water Quality The water quality in a waterway is important, especially for those which are source of water

for public use. There are five parameters for water quality, being biological, physical,

chemical, aesthetic and radioactive (NSW EPA, 2001). The Australian and New Zealand

Guidelines for Fresh and Marine Water Quality are used as a reference to identify whether the

levels of water quality parameters in a water body are within acceptable limits (Department

for Natural Resource Management, Date Unknown). Salinity is a physical water quality

parameter (NSW EPA, 2001), and it is recommended that the salinity of water intended for

drinking is below 800 EC units (Department for Natural Resource Management, Date

Unknown) or 500 mg/L TDS (Smith, 2006). Water quality parameters are monitored by

Water Corporation throughout the Helena River Catchment, which includes the study site (K.

Congdon, personal communication, 13 February, 2006.).

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2.7. Biological Communities, Connectivity and Salinity

Why are we concerned with macroinvertebrate populations? A macroinvertebrate can broadly be described as a small animal without a backbone which

can be caught in a net of mesh with holes .25mm in diameter (Waters and Rivers

Commission, 2001). The use of the term macroinvertebrates in this case will be referring to

aquatic macroinvertebrates. Investigating macroinvertebrate populations is recognized as an

important way for investigating water quality (Whiles, 2002), and also as a method for

establishing the degree of impact pollution has had on a waterbody (Whiles, 2002).

How to sample for macroinvertebrates? The Waters and Rivers Commission began the “Ribbons of Blue” program, which aims

towards gaining an indication of the water quality in Western Australian waterbodies through

sampling of macroinvertebrate communities. The sampling methodology for this program

stipulates that macroinvertebrates must be identified immediately after collection and then

returned to the waterbody to minimise disruption to the macroinvertebrate populations

(Waters and Rivers Commission, 2001). The macroinvertebrate samples are collected in one

of two ways, being a “kick sample” for river beds covered mostly with stones or rocks and a

“sweep sample” which is used when the bottom of a waterbody is covered mainly in mud and

sediment (Waters and Rivers Commission, 2001). In order to dislodge macroinvertebrates at

the stony bottom of a waterbody, a sampler stands with their back to the flow direction of the

waterway, the floor of the waterway is kicked with the samplers feet (hence the term “kick

sample”) and a net is positioned to collect the disturbed macroinvertebrates as they move

downstream (Waters and Rivers Commission, 2001). For a “sweep sample” instead of

disturbing the bottom of a waterbody using feet, the back of a sample net is used to churn the

sediment and then the front of the net is swept through the cloudy water to retrieve the

dispersed macroinvertebrates (Waters and Rivers Commission, 2001). To identify the

macroinvertebrate species in each sample, similar macroinvertebrate species are grouped

together using ice block trays, identified using a chart of macroinvertebrate species, counted,

and then released into the same location from which they were taken. Another sampling tool

for collecting macroinvertebrates is the activity trap. Activity traps were used in conjunction

with sampling nets in the study by Boeholt (2001), which examined the macroinvertebrate

assemblages in a brackish lagoon on the Kitsap Peninsula, Washington, in comparison with

three similar lagoons, one fresh and two also brackish. Activity traps were used because they

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are presumably able to capture macroinvertebrate species which reside in thick vegetation,

especially that found on the edges of waterbodies, or those species which can move quickly

away from a hand held net (Boeholt, 2001).

Measurements of general water quality are also required when using statistical software to

determine a relationship between sets of macroinvertebrate samples. The data collection in a

study by (Strehlow, 2005), which included examining how macroinvertebrate communities

changed from season to season in both primary and secondary saline wetlands, required a

suite of water quality parameters for statistical analysis using the ANOVA and RM-ANOVA

statistical software packages. These water quality parameters were “water depth, temperature,

salinity, pH, turbidity, colour (gilvin), water column chlorophyll a, sediment chlorophyll a”

(page 19, (Strehlow, 2005)), and were taken at the same position and time as

macroinvertebrate sampling.

Tolerance - Testing of macroinvertebrate species and salinity thresholds

There have been testing in both field and laboratory studies which examine the thresholds of

individual macroinvertebrate species and their tolerance to rising levels of salinity. Kefford

(2003) completed a study where a range of macroinvertebrates species were removed from the

Barwon River under laboratory conditions placed in sets of water tanks with a range of

salinities. After 72 hours the salinity at which 50% the macroinvertebrates were killed was

recorded. The 72 hour and 50% threshold chosen was arbitrary, but served as a mechanism

for comparing the tolerance of salinity of common macroinvertebrate species to that of rare

macroinvertebrate species, as well as differences of tolerance between taxonomic groups. The

results of this study found that in general the macroinvertebrates with hard exoskeletons and

jointed limbs (arthropods) were able to survive in waters with much higher salinities than

those that this not (Kefford, 2003). The explanation given for this is that a hard exoskeleton

may be able to prevent salt ions dissolved in water from entering into the bodies of the

macroinvertebrates which possess one (Kefford, 2003). From this it can be extended that

when looking at macroinvertebrate species as an indicator of salinity, a significantly higher

abundance of arthropods in comparison to non-arthropods in a given location may mean that

the macroinvertebrate assemblage has shifted in order to be able to cope with highly saline

conditions (Kefford, 2003). Apart from two taxa, the common species of macroinvertebrates

had a notably lower salinity threshold than rare taxa (Kefford, 2003). These results indicate

that the composition of macroinvertebrate species found at a location can give a good

indication of the salinity of a waterbody.

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Distribution – Further links between macroinvertebrate assemblages and

salinity/water quality.

Even though macroinvertebrates are widely used as an indicator of water quality, the links

between macroinvertebrate assemblage and salinity are not as well researched. There has also

been less studies for this done in Australia in comparison to many other countries in the world

and additionally, information on the links between salinity and macroinvertebrate species is

lacking for Western Australia compared to the rest of Australia. Noting this gap in

knowledge, Pinder et al. collected data for macroinvertebrate populations and salinity from

230 wetlands, some of which had undergone secondary salinisation, in the wheatbelt region of

the south-west of Western Australia within a three year period. It was found that “there was

clearly a strong underlying relationship between salinity and species richness” (,

(Pinder, 2005)). This is even after accounting for factors which effect macroinvertebrate

assemblages between samples and waterbodies such as differing hydrology, topography,

vegetation and variation of habitat (Pinder, 2005). The threshold value for salinity was

established in these lakes above which salinity began to have a significant impact on the

species richness of macroinvertebrate populations.

Links between macroinvertebrate assemblages and flow variability

There have been several studies linking flow variability to macroinvertebrate assemblage. It

has already been recognized that in Australian dryland river systems the abundance and

diversity of species can be linked to the length of time, and extent to which, sections of river

are connected (Sheldon, 2000). The study by Sheldon (2000), showed that in four dryland

rivers - the lower Murray River, Darling River - both in the Murray-Darling Basin, and the

Diamantina River and Cooper Creek, both in the Lake Eyre Basin. The connectivity of these

rivers, along with the Darkin river and other dryland rivers, varies naturally. However, high

levels of modification to the natural flow variability have occurred in the lower river Murray

and Diamantina due to damming of river tributaries, and water extraction (Sheldon, 2000). To

study the macroinvertebrate assemblages, macroinvertebrate sampling was undertaken on

these four rivers (Sheldon, 2000). Variables for the macroinvertebrate populations were

calculated (Sheldon, 2000). The data for the temporal and spatial variability for these four

rivers was examined and then variables based on this were also calculated (Sheldon, 2000).

Several forms of statistical analysis were used to examine the relationships between the

- 17


variables (Sheldon, 2000). There was a link between connectivity and macroinvertebrate

community composition for complex, but not broad-scale, flow variability (Sheldon, 2000).

Hydrology, however, seemed to have the largest impact on macroinvertebrates assemblage

composition(Sheldon, 2000). The study was completed when rainfall was below average and

at differing times for differing sites, so there is a possibility there could have been an even

stronger relationship found between flow variability and macroinvertebrate assemblage than

found in these four rivers(Sheldon, 2000). Of the rivers in this study, Cooper Creek in

particular, can be seen to have similar characteristics to the Darkin river as the can have a

variable degree of connectivity, are in areas of variable rainfall and also have lake systems

which are sporadically connected by surface flows.

What causes surface water flows to change?

Surface water flows can change from their natural state due to anthropogenic activity and

climate change. In Australia, most dryland systems are not highly connected all year round

(Sheldon, 2000). Due to processes such as damming, tributaries are connected to river

systems on a continual basis, thus altering the hydrology and composition of biota. As

mentioned in section 2.5 a change in climate can also have an impact on surface water flows.

In a study relating to physical water quality parameters and aquatic invertebrates in a dryland

river in Victoria, it was noted that the strength of El Nino also had an impact on whether the

wetlands in the catchment filled (Timms, 2001).

2.8. LUCICAT model

The LUCICAT (Land Use Change Incorporated CATchment) model was developed to be

able to predict the flow and salinity of a waterbody after a change in landuse (Bari, 2004b). A

distinguishing feature it has compared to other catchment models developed for Western

Australia, is that it represents the mathematics involved with representing variations in

streamflow and discharge of salts with groundwater flow to a higher accuracy (Bari, 2005b).

Within the model, a series of ‘subcatchments’ are defined for the larger catchments and

streamflow and salinity is established for each of these (Bari, 2005a). The model has been

adapted to include a the water balance of lakes, as well as streams, in a catchment (Bari,

2005b). LUCICAT has been used in studies of lakes in catchments in the South-West

including three lakes in the Kent Catchment which have been subject to secondary salinity

(Bari, 2005a);(Bari, 2004a), Dumbleyung Lake in the Upper Blackwood catchment (Bari,

2003) and has also been tested for the Ernies and Lemon experimental catchments (Bari,

2004b);(Bari, 2005b) as well the Salmon and Wights experimental catchments (Bari, 2005c).

- 18


The LUCICAT model was also used in the recent salinity situation statement for the Helena

River (Smith, 2006).

The Nunijup, Poorrarecup and Carabundup Lakes in the Kent catchment, which were the

focus of study completed by Bari et al. 2005, have characteristics similar to that of the lake

system in the Darkin Swamp Management unit. They overflow infrequently, have become

saline due to clearing carried from the 1940’s to the 1970’s and they exist on a flat landscape

with poorly draining soil (Bari, 2005a). The groundwater level for Nunijup is close to the

surface, being measured as shallow as 30cm. This is also suspected to be the case for the

water table below Darkin Swamp (R. Smith, personal communication, 6 January, 2006).

LUCICAT was used in the Kent catchment study to be able to establish firstly which

mechanisms (surface runoff, flowthrough, baseflow) produced streamflow and hence which

were sources of salinity, and then to create knowledge of the water balance and thus salt

balance of lakes Nunijup, Poorrarecup and Carabundup (Bari, 2005a). The effect of planting

0%, 25% or 50% trees on currently cleared land was evaluated by LUCICAT (Bari, 2005a), in

order to determine a Management strategy for the area. The capability to first be able to

understand more about how streamflow and salinity mechanisms in the study site interact and

how landuse changes could influence these is an attractive idea, particularly as part of the

study area is currently cleared. The main problems associated with using this model on

swamps in the study sites in salinity situation statement for the Helena River were associated

with lack of data, so assumptions were made in order to be able to give a reasonable depiction

of the streamflow and salt loads which could be produced given a change in land use in the

region as discussed in 3.1. The inputs and outputs of the model are below.

The inputs for the model are:

(i) Rainfall (Bari, 2005a)

(ii) Vegetation (M. Bari, personal communication,19 October, 2006)

(iii) soil salt profile (Bari, 2005b)

(iv) stream length and width (M. Bari, personal communication,19 October, 2006)

(v) salt fall (Bari, 2005b)

(vi) groundwater discharge regime (Bari, 2005b)

(vii) bathymetry of lake (Bari, 2005a)

Due to the nature of the model, knowledge of the connections between subcatchments is also

required (M. Bari, personal communication, 19 October, 2006., Department of Water 2006).

- 19


The model outputs can be:

(i) Daily, monthly and annual salinity streams in a catchment (Bari, 2005a)

(ii) Daily, monthly and annual salinity salt load streams in a catchment (Bari, 2005a)

(iii) Streamflow for catchment

(iv) Water balance for lake

(v) Salt balance for lake

2.9. Similar Models There are two models other than LUCICAT - LASCAM and MAGIC - which also focus upon the need for greater understanding of the hydrology and salinity of catchments in Western Australia:

LASCAM

The Large Scale Catchment Model (LASCAM), LASCAM was developed to be able to model streamflow in large catchments and also elements of water quality such as sediment loads, nutrient levels and salinity (Sivapalan). It is of assistance when looking at the effects of predicted changes in landuse and climate (Sivapalan). Like LUCICAT it divides a catchment into a number of smaller subcatchments (Sivapalan).

MAGIC

The MAGIC model was used along with LUCICAT in the Helena Salinity Situation Statement. It can further divide subcatchments into smaller cells (25m by 25 m), so as to display catchment characteristics with further accuracy (Smith, 2006). Unlike LUCICAT, however, it is a “steady-state model” (page 44, (Smith, 2006)) so factors such as vegetation cover can not be changed from year to year (Smith, 2006).

- 20


2.10. Darkin Swamp Background

Upper Helena Catchment

The Mundaring Weir was built in the late 19th Century, damming the lower reaches of the

Helena River in order to create a water supply to pump to the dry, yet prosperous, goldfields

at Coolgardie and surrounding regions (Corporation, 2005). The Mundaring Weir can

currently hold 63.6 million m³ of water with a surface area of 76.1 km² (Corporation, 2005).

The area of the whole Upper Helena River catchment from which water flows to the Weir is

1470 km² (Department of Environment, 2006). In the Helena catchment there are two main

rivers, the Helena River and the Darkin River which joins the Helena downstream of where it

flows into Lake C.Y. O’Connor (also referred to as Mundaring Reservoir). The areas which

deliver water to these rivers are referred to as the Darkin subcatchment and Helena

subcatchment, respectively (Smith, 2006). In order to manage the whole catchment for the

Mundaring Reservoir it is viewed as five separate Management units, these being the Helena

West Management unit, which encompasses the Mundaring weir and Lake C.Y O’Connor,

the Poison Lease and Ngangaguringuring Management units which cover the Upper Helena

Catchment, as well as the Darkin Swamp and Beraking Brook Management units

(Department of Environment, 2006). Appendices 4 and 5 show the position of Mundaring

Weir, Lake C.Y. O’Connor, the five Management units, and the flow paths of the Helena and

Darkin rivers.

Figure 1. Mundaring Weir in June, 2006.

- 21


Figure 2. Mundaring Reservoir in June, 2006.

Helena Salinity Situation Statement

As Mundaring Reservoir is a source of drinking water, the quality of the water flowing into

Upper Helena River is of high importance. The Department of Water is currently in process of

completing the Helena Salinity Situation Statement. This document concerns the salinity of

stream flow and runoff of the whole Upper Helena Catchment (Smith, 2006). Effort has been

taken to examine the salinity of flow in the catchment in regards to historical and present

climate, clearing, loss of vegetation and reforestation (Smith, 2006). Modelling was also

undertaken using the MAGIC and LUCICAT models in order to be able to predict the effect

that possible future scenarios such as climate change, reforestation of privately owned land,

forest fire and dieback would have on the salinity of flows in the catchment (Smith, 2000).

The area surrounding Darkin Swamp, including the several swamps in the same Management

unit, was identified as lacking research and data (R. Smith, personal communication, 06

January 2006).

Darkin Swamp Management unit

The Darkin Swamp Management unit covers an area of 273.624 km² and a perimeter of 119.9

km (Department of Environment, 2006), and contains four main swamps: Darkin Swamp,

Little Darkin Swamp, Goonaping Swamp and Dobaderry Swamp. A map identifying the

location of these swamps is available in Appendix 4. It is not known whether these swamps

are hydrologically connected, or to what extent they contribute to the flow of the Darkin

River, which begins in the Darkin Swamp Management unit and flows towards the

- 22


Mundaring Weir (R. Smith, personal communication, 6 January, 2006.). It is known that on

rare occasions the Darkin Swamp overflows and discharges into Darkin River (Smith, 2006).

Catchment Characteristics

The eastern and western sides of the Helena Catchment differ in characteristics such as

vegetation and soil structure. A summary of these characteristics being, vegetation,

topography, and soil type is displayed in Table 1. The vegetation surrounding Darkin Swamp

and Little Darkin Swamp is dominated by paperbarks (personal observation). Away for the

swamps, wandoo dominates (Croton, 1999). Smith, 2006, found the topography in the area

surrounding Darkin Swamp is flat relative to the rest of the catchment, hence giving reason to

suggest that the groundwater drainage in this area is “poorly developed” ((page 28, Smith,

2006).

- 23


West of Catchment East of

Catchment

Darkin

Swamp

area

Average Annual rainfall

(mm)

(1990-2002)

1050 500

Average annual

Evapotranspiration (mm)

1900 (Croton, 1999) 2100

(Croton,

1999)

Vegetation: Canopy cover 70% (reference) 20%

Vegetation: Dominant

Species

Karri (reference)

Marri

Jarrah (Croton,

1999)

Wandoo

Flooded Gum

(Croton,

1999)

Paperbark

(personal

obs.)

Described

as

“Swamp

complex”

(Croton,

1999)

Vegetation: Other species Yarri (Croton, 1999)

Bullich (Croton,

1999)

Description topography Hills, valleys Flat,

“poorly

developed

drainage”

Description soil structure Sandy,

possibly

palaeocha-

nel

sediments

Soil porosity high

Table 1. Summary of catchment characteristics, including vegetation and topography. Information from (Smith, 2006), unless specified otherwise.

- 24


Climate

The Darkin Swamp region is in the low rainfall zone. The general climate fits the broader

description of the south-west in section 2.5. The long-term trend for rainfall in the Helena

Catchment is for the majority of rain to fall between May and October (Smith, 2006) and dry

hot, summers, which the exception of storm activity. As shown in Table 1, the average

rainfall for this part of the catchment is approximately 500mm (1990-2002) and the

evapotranspiration for the catchment is 1900 mm/yr (Smith, 2006).

Clearing of Darkin Swamp Subcatchment

Throughout the history of the Helena Catchment there has been a sequence of clearing,

followed by reforestation when it has become apparent that the salinity of the water in

Mundaring Reservoir has been elevated significantly (Smith, 2006). In the Darkin Swamp

Management unit there is currently a section of privately owned land occupying 15.2 km²

(Smith, 2006), which had begun to be cleared in the 1940’s. The other vegetation removal

events which may have influenced the salinity levels in the Darkin Swamp area, are logging

from 1950-1975 as well as more deforestation to provide land for agricultural purposes in the

1960’s (Smith, 2006).

Previous Modelling Darkin Swamp Management unit

The Helena Salinity Situation Statement established the links between the streams and

swamps for the modelling purposes using topography (M. Bari, personal communication, 19

October, 2006). The streamlines used can be found in Appendix 2. As aforementioned, there

is a lack of research concerning the hydrology and salinity of the Darkin Swamp area. Hence,

when the modelling was completed for the Darkin Swamp Management unit in the Helena

Salinity Situation Statement, assumptions were made based on available data and research,

field observations and sampling over several years and personal experience. An assumption

made for the LUCICAT modelling was that most of the Management unit including the

smaller lakes acted like an “overflowing bucket”, only flowing when the water level rises

high enough after subsequent rains. Data for Darkin Swamp modelling was taken from similar

lakes in south-west (in regards to rainfall range, bathymetry etc.) (M. Bari, personal

communication, 19 October, 2006).

- 25


Surface Water Salinity Darkin Swamp Management unit

All data available for the surface water, of the Darkin Swamp Management unit (before

sampling for this project) is displayed in Appendix 1 shows all TDS values well below 500

mg/L throughout the year. There is no data available to indicate the surface water salinity

during storm events. One area of concern is Darkin Swamp, as it has been established that it

could be “accumulating salt” (Smith, 2006). Overflow of Darkin Swamp could add a large

pulse of saline water into the Darkin River, having impacts downstream for the quality of

water resources.

Groundwater

The groundwater flow regime in this section of the catchment has been hypothesised via

observations (M. Bari, personal communication, 19 October, 2006). The relatively low

salinity of the surface waters suggests that the water level is not high enough to discharge into

streams and the swamps (M. Bari, personal communication, 19 October, 2006). There is the

possibility those years when the rainfall is high enough, that groundwater can discharge into

surface waters (Smith, 2006). The quality of the groundwater has not yet been established,

though the trees around the swamp look under stress, possibly due to saline groundwater close

to the surface (R. Smith, personal communication, 6 January,2006).

- 26


3. METHODS

3.1. Data Collection

Available rainfall, streamflow and salinity data

There is a lack of data concerning the Darkin Swamp area. There are no rainfall or gauging

stations for the Darkin Swamp Management unit, however downstream there is the Pine

Plantation gauging station which has records both the flow and salinity of the Darkin River,

upstream of where it joins with the Helena River (Smith, 2006). Rainfall for this area is

obtained from the nearby gauging station (509 256), for which data has been able to be

obtained for the years 1974-1989. There is records which indicate flow and salinity data

available for the Pine Plantation gauging station from 1968 and 1969, respectively (Smith,

2006), although salinity data was only found for this project from 2000, which was the year

the gauging station’s measurements became continuous (Smith, 2006). There is also select

data from the Department of Environment 2002-2005 covering measurements for a stream

near the Darkin River Qualen Road grazing property and also the Darkin River near reservoir

road, as shown in Appendix 1.

Data was also made available from this project from available for this project from the

Department of Water’s soon to be published Salinity Situation Statement for the Helena

River. Before rainfall data was used for the LUCICAT model in the Helena Salinity Situation

Statement, it was pre-processed in order to give each point in the catchment a value, using the

nearest three rainfall gauging stations (M. Bari, personal communication, 19 October, 2006).

To gain some further insight into the salinity levels of the area surrounding Darkin Swamp, in

June and August 2006, salinity measurements were taken as summarised in Tables 1 and 2.

Limitations were met in the sampling as there was below average rainfall during winter 2006

and below average rainfall in the several preceding years.

- 27


3.2. Sampling

Salinity

The purpose of two field trips, conducted on 29th June and 25th August in 2006 was to obtain

additional data for the salinity levels of the Darkin Swamp Management unit. A preliminary

visit was also made to the Helena Catchment on 13 February 2006. Data and observations are

available for this field trip in Appendix 6, though are not discussed in great length in this

document. The salinity was measured using a WTW Cond 330i electrical conductivity meter

in the June sampling and a “mili-mho” electrical conductivity meter in August. Different

instrumentation was used due to availability. Both conductivity meters were calibrated to

25°C (R. Smith, personal communication, 24 November, 2006). This is a standard

temperature to compare conductivities (Department for Natural Resource Management, Date

Unknown). The conductivity meter used in June allowed for salinity to be measured both near

the surface as well as deeper in the water column at each site. This was considered

advantageous as it was assumed the potential presence of groundwater flow into a stream

could be indicated by fresh water in the upper layers of the water column and salty water

closer to the bottom of the water column. The mili-moh salinity meter was only able to

measure the surface layer for salinity. It was planned for both occasions to sample at all points

A-G as shown in APPENDIX 8. However, due to the delay in the 2006 winter rainfall, most

sample points in June were dry. The results of the sampling for dates in June and August are

shown in Tables 1 and 2, respectively.

In order to obtain a results for salinity in total dissolved solids, the approximation “total

dissolved solids (mg/L) = .68×conductivity (µS/cm)” (page 2, (Department for Natural

Resource Management, Date Unknown)) was used. This is considered acceptable if the water

is relatively fresh. Ideally, analysis of soil samples in a catchment can be used reveal a more

accurate relationship between electrical conductivity and total dissolved solids for the surface

waters of a catchment (R. Smith, personal communication, 24 November 2006) though this

can be expensive. Otherwise, a salinity chart can be a means for estimation of total dissolved

solids.

- 28


Macroinvertebrate sampling Macroinvertebrate sampling and analysis of macroinvertebrate communities was planned as

part of the proposed thesis, but due to the low levels of water in the Darkin Swamp region and

time restrictions, this was unable to be completed. An outline of the processes used for the

sampling of macroinvertebrates has been discussed in Section 2.7. It is suggested that

conducting this research could be greater for the understanding of how the Darkin Swamp

management unit are connected; this could be achieved in a high flow year, when there is

more surface water present.

LUCICAT MODELLING

It seems logical that the accuracy of the output of a model is dependent upon the accuracy of

the data input to the model. The assumptions made for the original modelling of the Darkin

Swamp Management unit were done so with the using the best available data and knowledge

of similar situations. Although there was not the funding or time to complete a more in depth

study of the water balance of Darkin Swamp or the smaller swamps in the Darkin Swamp

Management unit, there are some characteristic of the area which, listed below, which would

give a greater understanding of the groundwater and subsurface hydrology of the Darkin

Swamp MU.

(i) Testing for groundwater quality

It is assumed that the salinity of the groundwater underneath Darkin Swamp is high (R.

Smith, personal communication, 06 January 2006). Testing this would verify this assumption.

(ii) Groundwater monitoring bores

To further establish the connections between the swamps in the Darkin Swamp Management

unit, and establish the water balance of Darkin Swamp to a greater degree of accuracy

groundwater bores can be used to establish the direction of groundwater flow and also the

groundwater discharge regime. There a three possible options for the groundwater regime of a

lake. The figure on the following page illustrates these: recharge, discharge and flow-through.

A good indication of the groundwater discharge regime is required for input into the

LUCICAT model.

- 29


Figure 3. Diagram of flow-through, discharge and recharge regimes for baseflow into a lake (Bari, 2005a).

(iii) Sub-surface soil structure of Darkin Swamp and its surrounding area:

Not currently known (M. Bari, personal communication, 19 October, 2006).).

In previous modelling, assumptions for its composition have been made ((M. Bari, personal

communication, 19 October 2006).).

The extraction of soil cores can be completed at same time as drilling for groundwater bores.

(iv) Bathymetry

Not currently known (M. Bari, personal communication, January 2006)

Can be put into the MAGIC (steady state) model before LUCICAT

In previous modelling, the bathymetry was used for a similar lake (M. Bari, personal

communication, 19 October, 2006).

Climate change The major climate change scenario for the LUCICAT model would be to assume 11%

reduction in rainfall by mid-century as in Berti, 2004.

The removal of vegetation due to wandoo crown death could also be explored, as in Smith,

2006, it is suggested as possible occurrence in the future for the East of the Catchment in

Smith, 2006 though is not as imminent.

RELATIONSHIPS BETWEEN RAINFALL, STREAMFLOW AND SALINITY

Previous to the initiation of the Salinity Situation Statement, a report was conducted by

(Croton, 1999) for the then Waters and Rivers Commission to establish the link between

stream salinity, clearing and subsequent reforestation in the Helena Catchment. As part of the

study, comparison of yearly streamflow, rainfall and salinity data for seven of the working

gauging stations was conducted with one of the aims to derive relationships between the

relative amounts of surface runoff, interflow and groundwater discharge contributing to

- 30


streamflow (Croton, 1999). Similar comparison looked to be advantageous for this study, to

verify whether surface flow and interflow dominate in the Darkin Swamp subcatchment, and

thus demonstrate how the swamps could possibly be connected if they overflowed into one

another. The previous work conducted in this way used data for 1980-1994, and used annual

time-steps. In order to incorporate seasonal variability, monthly data was used for these

comparisons. As salinity data was only available for 2000 onwards only the years 2000-2005

were included. This method proved to be inconclusive, so another approach was taken, as

below.

The rainfall of 2000-2005 was also graphed to be able to see visually the variation in rainfall

across these 6 years. There was a large peak in the rainfall in the Darkin Swamp area in 2001,

so the 2001 pre-modelled data for Darkin River Gauging Station was graphed along with

actual streamflow and salinity for the same gauging station example of the relationship

between these factors in a year with high rainfall in a relatively short time frame. The year

2000 proved to be more widely distributed throughout the year, so the same plots were drawn

in order to see any difference between the two different rainfall scenarios. Darkin River

gauging station also collects data from the uncleared Beraking Brook Management unit,

which has to be taken into account in analysis.

The year 1979 has been noted having as the lowest streamflow out of all of the Darkin

Swamp gauging station records (Smith, 2006). There is the possibility of swamps in low

rainfall areas with poor drainage, such as those described in section 2.3, to discharge after a

very high rainfall event. However, as the Darkin Swamp rarely overflows, it is suspected that

it could take several seasons of high rainfall for discharge into Darkin River to occur. The

pre-modelled rainfall data for the Darkin Swamp Management unit is graphed in Figure 17.

The year 1979 has been noted having as the lowest streamflow out of all of the Darkin

Swamp gauging station records (Smith, 2006). This, however, does not correspond to the

lowest rainfall year for the Perth metropolitan region. To understand why, the rainfall for the

years 1976-1979 were plotted, to see if several years with below average rainfalls could have

resulted in the catchment drying, so even a lower percentage of rainfall than the average

converted to runoff.

- 31


4. RESULTS

4.1. Sampling Results

June

The results for the June 29th sampling of surface water salinity in the Darkin Swamp area is

shown in Table 1 below. Measurements were only taken for several points, as the catchment

was dry, so there was little available water to sample. Photos illustrating the lack of flow in

the catchment are shown in Figure 4.

- 32


Figure 4. June 29th, 2006. Left – area surrounding Darkin Swamp, right and bottom centre –Darkin River gauging station.

- 33


Site Coordinates Salinity Temp. Salinity Flow/Comments

(µS/cm) (°C) (mg/L)

Gauging 428067E

6

No flow. S me water

Station

616010

456450 N

o

present

Corner

To d

Dry.

pher an

Darkin Rd

Intersection 454204 E No evidence of stream

Some pu es on

Pig

Piggery Rd.

near Darkin

Swamp.

6447143 N intersecting Darkin

Swamp.

ddl

gery Rd near area of

Swamp

330µS/cm 9.4°C ~224.4 Surface

Swamp

Q d

454208E

324 µS/cm 6.9°C ~ Bottom

Corner

ualen an

Darkin Road

–Pond (C)

6447166N

Table 2. Salinity sample results for Darkin Swamp Management unit 29th, June 2006.

Thursday 25th August, 2006.

displays the results for salinity sampling for the Darkin Swamp area undertaken on

ent

Table 3

August 26, 2006. This sampling trip followed a heavy period of rain two days earlier.

Although not all selected sample points had flow, there was still flow in some parts of the

Darkin Swamp Management unit. The below figures give a visual indication of the catchm

after heavy rain.

- 34


Site Coordinates Salinity

(µS/cm)

Temp.

(°C)

Salinity

(mg/L)

Flow/Commen

ts

100 15 ~ 68 Flowing

Shallow section

of river

Crossing

Yarra

Rd and

Darkin

River

80 14.4 ~ 54

Turning

left onto

Warrigal

Road

448906 E

64501720 N

110 17.5 ~ 74.8 Little flow

Heading

towards

Darkin

Swamp

area

Large Puddles

on side of road

Little

Darkin

Swamp

(H)

- Dam

454019E

6453031N

150 20.5 ~ 102

Little

Darkin

Swamp

- Swamp

Edges

454019E

6453031N

110 18.7 ~ 74.8

Little

Darkin

Swamp

– main

section

454019E

6453031N

190 20.8 ~ 129.2

Second

Channel

North

Little

Darkin

Swamp

(B)

453606E

6455229N

Dry.

- 35


Main

Crossing

Qualen

Road

and

Darkin

Swamp

454397 E

6447072 N

110 22.7 ~ 74.8 Visible flow.

Pond

near

farm (C)

454208E

6447166N

180 17.5 ~ 122.4 No/little flow

Point G

- pond

of recent

runoff

454461E

6443571N

50 21.5 ~ 34 Salinity close to

that of

rainwater

South

side of

Farm,

Darkin

River –

stagnant

puddles

70 24.3 ~ 47.6

Piggery

road –

large

puddle

in main

section

120 21.9 ~ 81.6 Other large

stagnant

puddles on road

Table 3. Salinity sample results and flow observations for Darkin Swamp Management unit, August 25th, 2006.

- 36


Figure 5. 25 August, 2006. Flow running off farm on eastern side Darkin Swamp Management unit.

Figure 6. August 25, 2006. Flooding of Piggery Road in the vicinity of Darkin Swamp.

Figure 7. August 26, 2006. Picture of Little Darkin Swamp, north of Darkin Swamp.

- 37


Figure 8. August 26, 2006. Southern fence-line of farm in Darkin Swamp Management unit after rain.

4.2. Graphs Rainfall, Flow and Salinity

Rainfall for Darkin Swamp 2000-2003

0

20

40

60

80

100

120

Janu

ary

May

Month

Rai

nfal

l (m

m)

2000 aggregate 2001 aggregate 2002 aggregate 2003 aggregate

Figure 9. Graph of data for LUCICAT subcatchment including Darkin Swamp, 2000-2003.

The graph above was used to establish 2001 as a year with a high peak in rainfall in winter, and 2000 as a year where the rainfall was distributed more evenly throughout the year.

- 38


Flow and Salinity 2000 and 2001

2001, Darkin River Gauging Station: Flow and Salinity

0

500

1000

1500

2000

2500

1/01/2

001

15/01

/2001

29/01

/2001

12/02

/2001

26/02

/2001

12/03

/2001

26/03

/2001

9/04/2

001

23/04

/2001

7/05/2

001

21/05

/2001

4/06/2

001

18/06

/2001

2/07/2

001

16/07

/2001

30/07

/2001

13/08

/2001

27/08

/2001

10/09

/2001

24/09

/2001

8/10/2

001

22/10

/2001

5/11/2

001

19/11

/2001

3/12/2

001

17/12

/2001

31/12

/2001

Date

0

100000000

200000000

300000000

400000000

500000000

600000000

Stream flow (M3)Total Dissolved Solids (mg)

Figure 10. Streamflow and salinity (total dissolved solids) for Darkin River gauging station in 2001. The figure above shows a close relationship between streamflow and salinity.

0

5000000000

10000000000

15000000000

20000000000

25000000000

30000000000

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Figure 11. Salinity and streamflow measured at the Darkin River gauging station in 2000.

The above figure shows that, like the year 2001, there is a strong connection between salinity and streamflow.

- 39 Total Dissolved Solids (mg) Discharge (M3)

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Figure 12. Salinity and streamflow for the Darkin River gauging station, 2000

The figure above shows a strong relationship between salinity and streamflow in the year 2000.

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Figure 13. Salinity (TDS) and Rainfall for the Darkin River Gauging Station, 2001.

There appears to be a lag between the peak in rainfall and the peak in salinity in the above

graph for the year 2001.


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Rainfall and Salinity 2000 and 2001

Darkin River Gauging Station, Rainfall and Salinity 2000

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Figure 14. Streamflow and salinity (total dissolved solids) for Darkin River gauging station in 2001.

There appears to be a loose correlation between rainfall and salinity for the year 2000 at the

Darkin River gauging station, and also a lag between peak rainfall and peak salinity.

Flow and Rainfall 2000 and 2001

Darkin River Gauging Station, Rainfall and Streamflow 2001

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Figure 15. Daily rainfall and streamflow for the Darkin River Gauging station 2001

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A lag between peak rainfall and peak discharge is apparent in the above figure.

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Figure 16. Daily streamflow and rainfall, Darkin River Gauging Station, 2000.

The above figure shows that rainfall in the summer months of 2000 did not produce a proportionate level of streamflow. In the winter months there appeared to be a greater association, though there was a lag time between peaks in winter rainfall and peaks in streamflow.

0

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Figure 17. Interpolated rainfall from 1992-1996 at the 47 Mile Peg gauging station

The years 1996, 1995 both had July rainfalls over 100mm more than 1994 and 1993.

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Figure 18. Rainfall for years 1976-1979 at the Darkin River gauging station

Figure 18 shows that there was high rainfall in winter 1978, which was the year preceding

low flows. 1979, however, had lower rainfall distributed throughout the year.

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5. DISCUSSION

5.1. Sampling of Darkin Swamp Management unit surface waters

Winter 2006: Driest on Record

Winter 2006 had the lowest rainfall ever recorded for Perth (Bureau of Meteorology, 2006)

and overall, Western Australia received its second lowest recorded winter of rainfall (Bureau

of Meteorology, 2006). With only a small percentage of rainfall contributing to streamflow in

dryland rivers (Taylor, 2003), this would explain the little streamflow experienced in the area

surrounding Darkin Swamp, as observed in late June. The dry state of the Darkin Swamp

Management unit in June could have also been increased as the year preceding it was also

dry. This is demonstrated in Appendix 2, where it shows a departure of 400mm from the long-

term mean rainfall in Perth and its surrounding regions, in the period November 2005-October

2006.

5.2. Comparisons salinity, streamflow and rainfall

Streamflow and salinity The graphs for 2001 and 2000 show close relationship between stream flow and salinity. It

also indicates that it is possible the saline waters are transported via streamflow.

Rainfall and salinity There appeared to be a weak relationship between rainfall and salinity. This could be due to

the sandy texture of the soil. Mayer (2005) explains this as more rainfall can able to flow

through sandy soil in a shorter amount of time (Mayer, 2005). In catchments further inland

than the Helena, there is a strong relationship between rainfall and salinity, explained by a

high concentration of salt in the soil (Mayer 2005). There also was low salinity in the summer

months for 2000 and 2001. This suggests there is no baseflow, as baseflow salinities tend to

be high (Taylor, 2003), (Croton, 1999) and so even low baseflows would still increase salinity

(Croton, 1999).

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Rainfall and streamflow

The rainfall and streamflow for winter years 2000 and 2001 showed a lag time in between

rainfall occurring and an increase in streamflow. This could be because of transport time or

also because in winter, the dominant process causing runoff is saturation excess (George,

1990) and so takes time for runoff to occur.

Rainfall preceding swamp overflow compared to rainfall preceding record low flows The graph of rainfall of 1992-1996, showed that in 1995 and 1996 there was heavy rainfall,

particularly in winter. This gives support to the hypothesis that it takes more than one season

of heavy rainfall for Darkin Swamp to overflow. For lake systems in the wheatbelt region, it

is suggested that a series of lakes can overflow after a winter with a higher than average

rainfall, including a major storm event (Hatton, 2003). It is conceded, however, that there can

be sections of these series of lakes which have a “low probability of connecting” (Hatton,

2003). This could be the case for the Dobaderry and Goonaping swamps, which are not

expressed in the literature as overflowing at the same times as Darkin swamp. Little Darkin

Swamp, which is also in the Darkin Swamp Management unit, has a much higher chance at

overflowing and connecting up with the Darkin River. It was observed that driving towards

Little Darkin Swamp, after rain in August 2006, which was a record low rainfall year (Bureau

of Meteorology, 2006), there was still evidence of large puddles appearing to have the

potential to connect with Darkin River given slightly higher rainfall (personal observation).

This scenario is verified in the observations by Smith, 2006. As measured in Table 3, the

overflow of Little Darkin swamp should not have a severe impact on the Darkin Rivers

salinity, as the salinity measurements showed it to be very fresh.

Effect of climate change

The concern of Darkin Swamp and the other swamps in the same Management unit

overflowing is the impact that this will have on the water quality in the Mundaring Weir.

Unfortunately no salinity data for 1996 was able to be attained for this year at the Darkin

Swamp gauging station. A large pulse in the salinity measured at the station, in relation to

streamflow, could have given an indication that the swamp could indeed discharge salty water

into Darkin River, and hence elevate the salinity upstream. It is accepted that in the nearby

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wheatbelt region, severe storms can trigger a significant change in both the source of flow,

and hence salt load, of a catchment and also the magnitude of flow (Hatton, 2003). This was

apparent after very heavy rainfall in the summer of 2000, where a large part of the catchment

area which contributed flow to the Swan River estuary (Hatton, 2003). This rainfall event

prompted the subcatchment feeding the Lockhart River to overflow (Hatton, 2003). Upstream

in the Swan River, this discharge elevated nutrient levels so highly that an algal bloom

occurred (Hatton, 2003). A decline in the water quality of the Blackwood River is a

possibility if Lake Dumbleyung overflows (Hatton, 2003). There is evidence of the discharge

of Darkin Swamp effecting a parameter of Mundaring Weir’s water quality, with water colour

having increased at Mundaring Weir when the swamp overflowed in 1996 (Smith, 2006).

The mid-1970s was the point at which a marked reduction (~20%) of rainfall in Western

Australia’s south-west occurred (Berti, 2004). The graph of rainfall for the years 1976-1979

showed that in 1979, a year recorded as having record low flows, there was low rainfall

distributed throughout the year, as compared to the year beforehand, which had a much higher

peak in rainfall most of which fell in the winter months. This could indicate that it only takes

one season of below average rainfall to create very low flows. Another perspective of this

could be, however, that a year of high rainfall may not have much impact on a catchment if it

has become dry due to several years of low flow, as there were in the second half of the

1970’s (Smith, 2006). Another subsequent low flow year would hence create record low

flows. This is worth noting for the Darkin Swamp Management unit. If the catchment

becomes drier due to a shift in climate producing low rainfalls, an anomalous year or two with

high flow may still not be able to create connections between the set of swamps or between

Darkin Swamp and the Darkin River. It is also of importance that very low flows occurred in

1979, where rainfall was distributed throughout the year, where as Darkin Swamp overflowed

in 1996, following two seasons of high rainfall, primarily in winter. If climate change is set to

create less rainfall in winter, and more in summer, this could also decrease the possibility of

connection between swamps occurring.

5.3. How data from gauging stations is reflected in the field trip data The salinity samples taken in all three field trips this year, as well as the data in Appendix 1,

all have total dissolved solids less than 250 mg/L –even during summer-which is considered

fresh. These results verify the findings in Smith, 2006, that there is no discharge of

groundwater occurring in the Darkin Swamp Management unit. This also fits well with the

analysis of streamflow, rainfall and salinity where surface flow and interflow were found to

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dominate flows. It must be noted that the Darkin River gauging station measures the salinity

and flows of the Darkin River after it has received a significant flow input from the Beraking

Brook Management unit. This Management unit is almost completely forested and according

to the Salinity Situation Statement for the Helena River, poses little salinity risk. It is hence

presumed in this project that elevated levels of salinity would be due to an increase of saline

discharge for the Darkin Swamp Management unit.

5.4. LUCICAT

Use of the model

In testing of catchments in the low rainfall category, which have little to no clearing, in which

the Darkin Swamp Management unit fits, the LUCICAT model has been shown replicate the

streamflows and salt loads to a reasonable degree (Bari, 2004). This, coupled with the fact it

has also been used in the study of streamflows and salt loads in the Helena Catchment, makes

it good choice any further modelling of the water balance of Darkin Swamp and the salt and

stream flows in its surrounds.

Likelihood of scenarios

LUCICAT is capable of predicting changes regarding stream salinity when there is a change

in climate and/or vegetation. Large scale clearing of vegetation is not likely, as most of the

Darkin Swamp Management unit resides in state forest and the small section of private land is

already cleared. A possible change in vegetation could become apparent, however, if the

wandoo in the East of the Helena catchment is thinned due to what the disease known as

crown death decline (Smith, 2006). Increasing the sparsity of vegetation could increase

groundwater levels, leading to the occurrence of baseflow into the Darkin River. Depending

on the risk of crown death decline advancing into the east of the Helena catchment there could

be scope to put this into a LUCICAT scenario in the future. A change of climate, primarily a

decrease in rainfall is a widely accepted prediction for Western Australia’s south-west. This

scenario would be of higher priority to model. The 20% reduction in rainfall predicted by

Berti, 2004, could be used.

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6. CONCLUSIONS

The results of field trips conducted and the analysis of the data from the Darkin River

Gauging station revealed that surface water flows in the Darkin Swamp Management unit are

fresh. This could imply that surface flow and interflow are the dominant processes through

which the streams and swamps in this area are connected. An increase in the salinity of the

surface waters could occur if Darkin Swamp overflows or if the groundwater table rises high

enough for baseflow to occur. It was discovered there were strong rainfalls in the winter

months in 1995 and then in 1996, which resulted in Darkin Swamp overflowing. A shift in

climate with an increase in rainfall in the summer months, as has been observed for the south-

west of Western Australia, could in even less frequent overflow of Darkin Swamp. A

predicted 11% decrease in rainfall over the next 50 years could also lead to less possibility of

overflow and connections between the swamps in the Darkin Swamp management unit and

also Darkin Swamp and Darkin River. ‘Drying out’ of the catchment could also decrease the

amount of runoff coming from the catchment if rainfall does increase.

The LUCICAT model has already been used to assess the flows and salinity coming from the

Darkin Swamp management unit in the Helena Salinity Situation Statement. In order to be

able to quantify the extent of flow and salinity coming from the Darkin Swamp management

unit to a higher degree of accuracy, testing in the fields of groundwater and soil analysis

should be undertaken, as well as surveying for the bathymetry of Darkin Swamp. Literature

suggests that there is a strong link between macroinvertebrate sampling, connectivity and

salinity. This established relationship can be used to identify connections between swamps in

a year of high flow.

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7. FUTURE RECOMMENDATIONS

To further establish the connections between the swamps in the Darkin Swamp Management

unit, and establish the water balance of Darkin Swamp to a greater degree of accuracy, the

following research would be advantageous. Not all options may be economically feasible:

• Survey to map the bathymetry of Darkin Swamp.

• Groundwater bores and soil core analysis in the area surrounding Darkin Swamp.

• The above two options could be used to create a more accurate output for the LUCICAT

modelling of the Darkin Swamp Management unit. The main scenario of concern would

be a decrease in rainfall in the next 25 years, with the possibility of increased summer

storm events.

• The above survey could be used to give a renewed estimate the total amount of salt which

is being held by Darkin Swamp.

• Macroinvertebrate analysis could yield a cheaper alternative to bores for proving

connections between swamps. This could be conducted in a high flow year.

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APPENDIX 1 – AVAILABLE DATA FROM DARKIN SWAMP SUBCATCHMENT

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APPENDIX 2 – MAP OF VARIATIONS FROM LONG_TERM AVERAGE ANNUAL RAINFALL FOR WESTERN AUSTRALIA, IN THE YEAR NOVEMBER 2005 – OCTOBER 2006

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APPENDIX 3 – GIS MAP OF PRIVATELY OWNED FARMLAND AND STREAMS IN THE UPPER HELENA CATCHMENT (Smith, 2006)

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APPENDIX 4 – STREAMLINES AND 66 LUCICAT SUBCATCHMENTS USED FOR MODELLING IN HELENA SALINITY SITUATION STATEMENT (Smith, 2006)

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APPENDIX 5 – DATA AND OBSERVATIONS OF THE HELENA CATCHMENT FIELD TRIP 13TH FEBRUARY, 2006.

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APPENDIX 6 – Rainfall Isohyets for the Helena Catchment (Croton 1999)

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APPENDIX 7 – SAMPLE POINTS A-G. MAP. COURTESY OF A. KITSIOS (2005)

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BARI, M. A., RUPRECHT, J.K. (2003) The Salt and Water Balance Modelling of Dumbleyung Lake. IN ENGINEERS, I. O. (Ed.) 28th International Hydrology and Water Resources Symposium. Wollongong, Australia.

BARI, M. A., SILVA, J., RUPRECHT, J.K. AND SMETTEM, K.R.J. (2004a) Water and Salinity Modelling of Catchment and Lake Systems in the Kent River, Western Australia. Geophysical Research Abstracts, 6, 07765.

BARI, M. A., SMETTEM, K. R.J. (2004b) Modelling Monthly Runoff Generating Processes Following Land Use Changes: Groundwater-Surface Runoff Interactions. Hydrology and Earth System Sciences, 8.

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STREHLOW, K., DAVIS, J., SIM, L., CHAMBERS, J., HALSE, S., HAMILTON, D., HORWITZ, P., MCCOMB, A., FROEND, R. (2005) Temporal changes between hydrological regimes in a range of primary and secondary salinised wetlands. Hydrobiologia, 552, 17-31.

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