Sourcing Contributing Areas to River Flow in Ellen Brook, Western Australia, using Environmental Indicators and Mixing Models
Alice Micenko
Supervisor: A/Prof. Keith Smettem
Dissertation submitted in partial fulfilment of the requirements for Bachelor of Engineering (Environmental), University of Western Australia
Acknowledgements i
Acknowledgements
There are a number of people whose input and support was essential to this project. At the top of the list is my supervisor, Associate Professor Keith Smettem. Thank you Keith for imparting a small portion of your very extensive knowledge about rivers and catchment behaviour to me. I have learnt a lot from working with you this year.
I must thank Robin Smith, Wayne Tyson and Christian Zammit from the Department of Environment who provided data and maps for the project. I would also like to express my gratitude to Dianne Krikke and Elizabeth Halladin for their help with locating and understanding the laboratory equipment that I needed.
To my parents, family and friends: thanks for putting up with my somewhat erratic behaviour this year, and for listening to me complain about the Ellen Brook. You have been amazing. I promise I will return to normal next year!
I also strongly appreciate all the help and encouragement I received from the staff and students at the Centre for Water Research. Individual thanks go to Michael Evans, Jacinta Hewett and Ross Perrigo for their input into the project and dissertation.
Finally, a special thank you and congratulations go to all the final year students who worked through this year with me. I couldn’t have done it alone.
The mark of a successful man is one that has spent an entire day on the bank of a river without feeling guilty about it. – Now we can!
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Abstract ii
Abstract
The total flow in a stream is variable in both space and time, and is derived from a number of different sources. In ungauged catchments, environmental indicators, also known as environmental tracers, can be used to separate the contribution to total flow made by each of these sources. In order for environmental indicators to be used for this purpose, they must display conservative or predictable behaviour and significant spatial variation throughout the study area.
Australia has a large number of ungauged rural catchments and there is a need for a simple and inexpensive method of determining contributing areas in these catchments. The study site for this project, the Ellen Brook catchment, located 20km north-east of Perth, Western Australia, was chosen for the benefits that may be derived from a better understanding of streamflow generation processes in the catchment, and because it can easily be divided into discrete regions that display substantially different soil and water properties. The two catchment regions used for the purpose of this study are the Swan Coastal Plain area in the west and the Darling and Dandaragan Plateau area to the east.
Examination of a range of water parameters, including pH, temperature, colour intensity, dissolved oxygen, phosphorous and electrical conductivity, was undertaken at 9 sites throughout the catchment with the aim of identifying those parameters most suitable for use as environmental indicators of water source and flow contribution. Electrical conductivity and colour intensity measured through spectrophotometry were found to be the most strongly applicable tracers within the Ellen Brook catchment.
Significant water signature differences between the two regions of the catchment were observed, with high colour and low salinity on the Swan Coastal Plain and little or no colour but high salinity in streams emanating from the Darling and Dandaragan Plateaus. Electrical conductivity and colour levels in the main Ellen Brook channel immediately downstream from these two source areas indicated that between 60% and 80% of the flow at the catchment is contributed by the Swan Coastal Plain region, with the remainder being derived from the Darling and Dandaragan Plateaus. The proportional contribution by the Swan Coastal Plain region was found to increase towards the end of the winter season. This is thought to be due to a rapid response time and subsequent soil drying on the Plateaus.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Glossary iii
Glossary
Baseflow See “Old” water
Conservative substance A substance that does not undergo reactions or decay in a water body, and is transported at the velocity of the water body.
Contributing Areas The geographic regions of a catchment that contribute runoff to a stream. Contributing areas can vary with time (see Variable Source Area Runoff Generation).
Environmental tracer Any naturally occurring substance that can be used to follow the progression of water through a catchment. Generally conservative and additive in nature.
Ephemeral stream A stream that flows only after periods of significant rainfall. In south-west Western Australia, ephemeral streams flow mainly in Winter and Spring.
Hortonian Runoff Generation Runoff generation that occurs when the rate of rainfall exceeds the infiltration capacity of the soil. Also known as Infiltration Excess Runoff Generation.
Humus Substances derived from the decomposition of plant and animal material. Contains organic carbon.
Hydrograph A graph illustrating the changes in flow at one point in a stream over time. Hydrographs can depict discharge, stream height or stream velocity.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Glossary iv
Infiltration capacity The maximum rate at which precipitation water can enter a given soil under a given set of conditions.
Interflow Rapidly moving subsurface water with a travel time between those of baseflow and surface flow, derived from rainfall that infiltrates the soil but does not become part of the main groundwater body. Also known as throughflow or shallow groundwater flow.
Lateritic Derived from the weathering of aluminium and iron oxides and hydroxides. Lateritic soils are typically red, yellow or brown in colour due to the presence of iron.
‘New’ Water Water that is added to a catchment during a precipitation event.
‘Old’ Water Water that exists in a catchment prior to a precipitation event. The term ‘old’ water usually refers to that part of streamflow that is derived from groundwater. Also known as pre-event water or baseflow.
Overland flow Runoff generated by rainfall travelling along the surface of the ground to a stream channel or other collection point. Also known as surface runoff.
Palusplains Plains or flats that experience seasonal waterlogging.
Runoff In a steady-state catchment, the portion of rainfall that does not undergo evapotranspiration. For the purpose of this report runoff is defined as the portion of rainfall that enters a stream through baseflow, interflow or overland flow.
Saturation Excess Runoff Generation Runoff that occurs via overland flow when the soil becomes saturated so that no more rainfall can enter. Also known as the Dunne Saturation Excess Runoff Generation.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Glossary v
Source area The physical area in which the water comprising streamflow originates.
Spectrophotometry Technique whereby the light absorbance of a sample at different points on the electromagnetic spectrum is measured.
Surface runoff See “Overland Flow”
Variable Source Area Runoff Generation Theory The runoff generation theory that states that the areas of a catchment contributing to flow expand and contract as the extent of soil saturation changes.
Water signature The distinct combination of physical and chemical properties that allow a particular water body or source to be identified.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Table of Contents vi
Table of Contents
Acknowledgements...... i Abstract...... ii Glossary...... iii
1 Introduction to the Project...... 1 2 Literature Review...... 3 2.1 Introduction to Runoff Pathways ...... 3 2.2 Traditional hydrograph separation...... 5 2.3 Use of Environmental Tracers for Hydrograph Separation...... 6 2.4 Principles of tracer hydrology ...... 7 2.5 Previous use of tracers...... 9 2.5.1 Typical characteristics of previous tracer studies ...... 9 2.5.2 Success of previous tracer studies...... 10 2.5.3 Use of tracers to identify changes in flow pathways...... 11 2.5.4 Use of tracers for spatial separation of runoff sources ...... 11 2.5.5 Application to Ungauged Catchments: Use of Tracers as an alternative to complete flow data...... 12 2.6 Simple Tracers suitable for Australian Catchments...... 13 2.6.1 Electrical Conductivity ...... 13 2.6.2 Temperature ...... 14 2.6.3 Nutrient Concentrations...... 16 2.6.4 Turbidity...... 18 2.6.5 pH...... 19 2.6.6 Colour and tannin concentrations...... 19 2.7 Implications for catchment management...... 20 2.8 Applicability to the Ellen Brook Catchment...... 22 2.8.1 Site Characterisation ...... 22 2.8.2 Application of Tracer Hydrology ...... 27 2.8.3 Geomorphological Regions of the Ellen Brook Catchment ...... 28 3 Summary of Aims and Objectives...... 34 4 Methods...... 35 4.1 Research Plan...... 35 4.2 Sampling Considerations ...... 36 4.2.1 Timing...... 36 4.2.2 Rainfall Effects...... 36 4.2.3 Site Selection...... 37
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Table of Contents vii
4.2.4 Sample Collection...... 39 4.3 Calculation of Flow Volumes ...... 39 4.4 Sampling Dates ...... 40 4.4.1 Sampling Round 1: 29 June 2005 ...... 40 4.4.2 Sampling Round 2: 11 August 2005...... 41 4.4.3 Sampling Round 3: 15 September 2005 ...... 41 4.4.4 Sampling Round 4: 10 October 2005 ...... 41 4.5 Analysis ...... 42 4.5.1 Phosphorous ...... 42 4.5.2 Dissolved Oxygen...... 43 4.5.3 pH...... 43 4.5.4 Temperature ...... 43 4.5.5 Electrical Conductivity ...... 44 4.5.6 Colour ...... 44 4.5.7 Total Organic Carbon ...... 45 4.6 Selection of Appropriate Environmental Indicators ...... 45 4.7 Mixing Ratio Calculations ...... 45 4.7.1 Flow weightings ...... 47 5 Results and Site Observations...... 48 5.1 Water Levels ...... 48 5.2 Field Results...... 48 5.2.1 Absorbance method validity checks ...... 53 6 Calculations ...... 57 6.1 Cross-sections and Flow Volume Calculations ...... 57 6.1.1 Darling and Dandaragan Plateau Sites ...... 58 6.1.2 Swan Coastal Plain Sites ...... 60 6.1.3 Summary of Flow volumes ...... 62 6.2 Proportion of Total Flow Calculations...... 63 6.2.1 Flow ratios ...... 63 6.2.2 Application of mass balance mixing model...... 63 7 Discussion ...... 67 7.1 General Trends in the Data ...... 67 7.2 The effect of site location ...... 68 7.3 Validity of the colour absorbance method ...... 69 7.4 Selection of Appropriate Indicators from Preliminary Sampling ...... 70 7.4.1 Electrical Conductivity ...... 70 7.4.2 Colour ...... 71
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Table of Contents viii
7.4.3 pH...... 71 7.4.4 Phosphorous ...... 72 7.4.5 Stream Temperature ...... 72 7.5 Characterisation of Regional Hydrologic Units...... 73 7.5.1 Darling and Dandaragan Scarps ...... 74 7.5.2 Swan Coastal Plain ...... 74 7.6 Computation of Flow Contribution Proportions...... 75 7.6.1 Seasonal trends in flow contribution ratios ...... 75 7.6.2 Justification for exclusion of Site 7 from data ...... 76 7.6.3 Differences between indicators ...... 77 7.6.4 The Influence of the River Flood Plain Area...... 78 7.7 Cross-sections and Weightings...... 80 8 Conclusion...... 81 9 Recommendations for Further Work...... 83 9.1 Further Work within the Ellen Brook catchment ...... 83 9.2 Application of theory and findings to other catchments...... 84 References ...... 85
List of Appendices
Appendix A: Site Photos ...... 91 Appendix B: Validity of the mass balance model for absorbance ...... 93 Appendix C: Rainfall and Other Climatic Data For Day Prior to Sampling .....94 Appendix D: Culvert Cross-sectional Area calculations ...... 97 Appendix E: Channel Slope Calculations...... 99 Appendix F: Contribution ratio calculations and associated error ...... 100
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
List of Figures ix
List of Figures Figure 1: The Saturation Excess method of runoff generation...... 4 Figure 2: Different methods for the classification of storm runoff sources ...... 6 Figure 3: A coloured stream in the Ellen Brook catchment, Western Australia...... 20 Figure 4: Ellen Brook Catchment Location...... 23 Figure 5: Ellen Brook Annual Runoff for the years 1996-2003...... 24 Figure 6: Runoff:Rainfall Relations for Swan River Tributaries 1994 - 1999...... 24 Figure 7: Ellen Brook Yearly Hydrographs 1996-2003...... 25 Figure 8: Nutrient Concentrations in Ellen Brook and the Avon River 1987-2001 .... 26 Figure 9: Geomorphology of the Ellen Brook Catchment...... 29 Figure 10: Areas Prone to inundation ...... 32 Figure 11: Areas of Ellen Brook catchment prone to salinisation...... 33 Figure 12: Locations of the nine primary sampling sites...... 38 Figure 13: Representative diagram of a cross-section for a circular culvert ...... 40 Figure 14: Water levels on August 11 2005...... 48 Figure 15: pH values at Sites 1 to 8 over the first two sampling rounds ...... 51 Figure 16: Stream temperature at Sites 1 to 8 over the first two sampling rounds ... 51 Figure 17: Electrical Conductivity at Sites 1 to 9...... 51 Figure 18: Photometric absorbance at Sites 1 to 9...... 52 Figure 19: Phosphorous levels in unfiltered samples from Sites 1 to 9 ...... 52 Figure 20: Phosphate levels in filtered samples from Sites 1 - 9 ...... 53 Figure 22: Absorbance of Sampling Round 2 water samples at 304nm and 440nm 55 Figure 23: Relationship between ultraviolet absorbance and water dilution ...... 56 Figure 24: Cross-section of Rocky Creek culverts on Old Gin Gin Road...... 58 Figure 25: Cross-section of Nambah Brook culverts at Site 7 ...... 59 Figure 26: Cross section of Ki-it Monger Brook at Site 8 ...... 59 Figure 27: Cross-section of Chandala Brook channels at Site 3...... 60 Figure 28: Cross-section of culverts upstream of Site 5 ...... 61 Figure 29: Cross-section of culverts at Site 6 ...... 61 Figure 30: Cross-section of culverts at Site 9 ...... 62 Figure 31: Estimated Flow Contribution by the Swan Coastal Plain Region...... 66 Figure 32: pH and phosphate changes between Sampling Rounds 1 and 2 ...... 68 Figure 33: Conceptual Diagram of the Ellen Brook catchment ...... 74 Figure 34: Waterlogged area of the Ellen Brook catchment near Site 1 ...... 79
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
List of Tables x
List of Tables
Table 1: Cadmium concentrations in the Ellen Brook, Avon River and Swan River. Adapted from Gerritse (1995)...... 28 Table 2: Observed relative water levels in the Ellen Brook catchment streams ...... 48 Table 3: Measured values for pH, Stream Temperature and Dissolved Oxygen...... 49 Table 4: Measured values for Electrical Conductivity, Absorbance and TOC...... 49 Table 5: Measured values for phosphorous...... 50 Table 6: Dominant sample wavelength and corresponding absorbance for Sampling Round 2 ...... 54 Table 7: Absorbance values in photometric absorbance units of water samples from Sampling Round 2 at 304nm and 440nm ...... 54 Table 8: Correlation between TOC and photometric absorbance...... 55 Table 9: Absorbance of water sample with progressive dilution ...... 56 Table 10: Stream Dimensions and Flow Times ...... 57 Table 11: Flow volume calculation for Rocky Creek downstream of Site 2 ...... 58 Table 12: Flow volume calculation for Nambah Brook at Site 7...... 59 Table 13: Flow volume calculation for Ki-it Monger Brook at Site 8...... 60 Table 14: Flow volume calculation for Chandala Brook at Site 3...... 60 Table 15: Flow volume calculation at culverts upstream of Site 5 ...... 61 Table 16: Flow velocity and Flow volume calculations for Site 6 ...... 62 Table 17: Flow volume calculations at Site 9...... 62 Table 18: Summary of flow volumes at the seven contributing sites ...... 63 Table 19: Flow volumes relative to the lowest flowing sites...... 63 Table 20 Estimates of contribution to total flow for the two-region system calculated from non-weighted mean parameter levels...... 64 Table 21 Estimates of contribution to total flow for the two-region system, calculated by excluding Site 7 from the non-weighted mean parameter levels ...... 64 Table 22 Estimates of contribution to total flow for the two-region system, calculated from flow-weighted mean parameter levels ...... 65 Table 23 Estimates of contribution to total flow for the two-region system, calculated by excluding Site 7 from the flow-weighted mean parameter levels ...... 65
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Introduction to the Project 1
1 Introduction to the Project
Water in a stream originates from many different sources including subsurface flow, direct overland runoff, and precipitation on the stream channel itself. Each of these sources may have distinct chemical and physical properties that distinguish them from other water sources in the catchment. The combination of these properties is known as the water signature. Water signatures can also vary amongst flow components generated by the same mechanism in different geographic regions of a catchment, referred to as contributing areas.
Recently, scientists have made several attempts to use the water signature as a tool for hydrograph separation. The technique is based on the fact that different water bodies can be identified by their unique chemical and physical characteristics. Movement of the water body through the catchment can then be tracked through measurement of these characteristics, known as environmental tracers. An environmental tracer or environmental indicator is defined as any naturally occurring water property that can be followed as it progresses through a catchment. If the characteristics of a water source are assumed to be conservative and additive, they can be compared to the characteristics of stream outlet water with the aim of determining where the water originated. That is, environmental indicators can be used to separate the contribution to total streamflow made by a particular flow generation process in a particular location from that made by other water sources in the region.
Environmental tracers offer scientists the opportunity to examine runoff generation processes occurring in catchments where gauge data is limited or non-existent. As such, they may be particularly relevant to rural and agricultural catchments in Australia, which are often ungauged due to their large size and low population density. The majority of Australian agricultural catchments are characterised by low gradients, sandy or clayey soils and low to medium annual precipitation (Bureau of Meteorology 1995; McKenzie et al. 2004). Thus, the application of tracer hydrology to Australian catchments requires somewhat different techniques to those used in northern hemisphere studies.
This project attempts to apply simple environmental tracer techniques to determine the sources of streamflow in the Ellen Brook, Western Australia. The aim is to
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Introduction to the Project 2 ascertain whether or not different water sources in the catchment have distinct signatures, and if so, which signature properties can be most accurately traced through the catchment. The dissertation also examines the way in which source areas change throughout the winter season. Importantly, in order to allow wider applicability, the focus of the project will be on environmental tracers that require only simple techniques and are inexpensive to analyse.
The Ellen Brook catchment is ideal for use as a case study for tracer hydrology for two reasons. Firstly, the geomorphology and land use in the catchment is such that the different geomorphic regions should yield very different water signatures. Secondly, the Ellen Brook is one of the largest contributors of the high nutrient load to the Swan River Estuary, which has resulted in several nutrient blooms in the Swan in recent years. The catchment is also situated on the edge of the Gnangara Mound groundwater area, which supplies a large proportion of the drinking water for the city of Perth. Despite the high significance of hydrological processes in this area, specific water generation processes within the catchment are still not fully understood.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 3
2 Literature Review
This section provides an overview of the history of tracer hydrology and examines the relevance of the technique to Western Australian catchments. Background information relating to stream runoff generation and hydrograph separation is also included. In addition to this, the processes affecting the distribution of several different potential natural tracers are examined. Finally, a review of the Ellen Brook catchment is presented, with particular emphasis on characteristics of the catchment that make it ideal as a case study for the application of tracers to determination of contributing areas in low gradient, Australian agricultural catchments.
2.1 Introduction to Runoff Pathways
Water enters a stream through a variety of different mechanisms. These different mechanisms are often referred to as routes or pathways. Most commonly, runoff is divided into four categories: direct precipitation on the stream channel, overland flow along the surface of the ground, interflow or rapidly moving below-ground flow, and baseflow derived from groundwater (Hewlett and Hibbert 1967). Studies that attempt to quantify the amount of water derived from each of these different pathways are common. They can either use plotting and recession constants (e.g. Meyboom 1961) or be automated using computer models (e.g. Rutledge and Daniel 1994). The usefulness of these studies lies in the understanding of catchment processes that they provide, which can lead to more efficient land management practices.
Theories surrounding runoff generation mechanisms experienced significant evolution in the 20th century. In 1933 the overland flow theory, under which runoff is thought to result when the precipitation rate exceeds the infiltration capacity of the soil, was proposed (Horton 1933). The infiltration capacity of a soil is defined as the maximum rate at which precipitation water can enter the soil, and can decrease during a storm down to some constant minimum value (Horton 1933). This type of runoff generation is known as either the infiltration excess mechanism or Hortonian runoff generation, after Robert E. Horton who was the first to postulate the theory.
Horton’s runoff generation theory had a large influence on hydrological understanding. However, the concept did not accurately represent observed runoff generation patterns in the majority of climates. In particular, further studies failed to
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 4 observe the overland sheet flow on hill slopes predicted by the infiltration excess concept (Dunne and Black 1970a). Experimental evidence has shown that in reality, soil infiltration capacity is very rarely exceeded. As a result, overland storm runoff only occurs in small parts of the catchment (Betson 1964; Dunne and Black 1970b).
The variable source area runoff generation theory was proposed by Hewlett and Hibbert in the 1960s, and refined with the Dunne saturation excess concept in 1970 (Dunne and Black 1970b; Dunne and Black 1970a). Under the saturation excess concept, the majority of precipitation falling on a catchment infiltrates into the subsurface. The low-lying areas of the catchment then become fully saturated due to throughflow and water table rise (Hewlett and Hibbert 1967). Once this occurs, water can no longer infiltrate the soil pores, and must either pond at the surface or run off (Figure 1). Thus, discrete areas of the catchment act as sources for overland flow. The distribution of these regions can change as the precipitation event proceeds, leading to the term variable source areas. In the saturation excess model, the infiltration capacity of the soil is not as important as the level of soil saturation or moisture storage. When the soil becomes fully saturated, overland flow will occur as further infiltration is not possible. The variable source area mechanism is now widely accepted as the primary mechanism for runoff generation in most catchments (Obradovic and Sklash 1986).
Surface runoff occurs where the water Precipitation table reaches the surface, meaning that infiltrates non- the soil is fully saturated saturated areas Precipitation
Throughflow Runoff
Stream channel Figure 1: The Saturation Excess method of runoff generation The figure is based on theories developed by Hewlett and Hibbert (Hewlett and Hibbert 1967) and Thomas Dunne (Dunne and Black 1970b; Dunne and Black 1970a). Precipitation becomes direct overland runoff only when the underlying soil is fully saturated.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 5
2.2 Traditional hydrograph separation
The variable source area concept of streamflow generation implies that the distribution of runoff generation throughout a catchment is not uniform. The parts of a catchment that are contributing flow to a stream at any point in time are known as the contributing areas, and these can vary throughout the year. Flow contribution can occur via overland or subsurface flow. The term runoff is sometimes used only for overland flow, but will be defined as the total flow being generated in any particular catchment region via all pathways for the purpose of this report.
In traditional hydrograph separation, flow is divided into baseflow, or deep sub- surface flow, and surface runoff, which enters a stream primarily via overland flow. Calculation of flow volumes from each of these sources using baseflow separation utilises detailed knowledge of catchment properties and processes. In particular, data from rainfall and streamflow gauges throughout the catchment are usually required.
Many different equations relating the runoff hydrograph to catchment precipitation have been developed. The most universally applicable of these equations is a simple water balance. Although water balance equations appear in many different forms, the basic structure is as follows:
Equation 1: P = E + R + ΔS
where P is the rain falling directly on to the catchment; E is evaporation and transpiration; R is the runoff, which can be split into overland and groundwater components; and ΔS is the change in storage in the catchment. This is zero when the catchment is in equilibrium. (Edmunds et al. 1987; Sinha 1987)
The separation of streamflow into groundwater flow and overland flow implies that water is being differentiated based on its source locality. In reality, however, the classification of flows is commonly determined using the time taken for water to reach the stream, rather than by examining the actual flow pathways (Institution of Engineers Australia 1997). Water that arrives at the stream soon after a storm is assumed to be overland flow, whereas water that displays a longer travel time is
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 6 taken as baseflow. Shallow groundwater flow, also known as interflow or throughflow, is sometimes included as a third flow pathway. This term refers to water that displays a medium travel time, and thus cannot be easily defined as either subsurface or overland flow.
Some confusion exists due to different nomenclature used for streamflow components. This was clarified somewhat by Sklash et al. (1975) who produced a diagrammatic representation of the three methods for separating runoff following a storm. Under this model, streamflow following a given storm can be separated based on whether it was generated before or after the storm (Time Source classification); the physical mechanism by which it was generated (Mechanism Source classification); or by the geographic area in which it originated (Geographic Source classification) (Figure 2).
Source by Generation Geographic Source by Time Mechanism Source of Generation -Hortonian Overland Flow -Storm -Subsurface Storm Flow -Direct Runoff -Direct Rainfall -Prestorm -Partial Area Overland Flow -Direct Rainfall -Groundwater -Groundwater
Figure 2: Different methods for the classification of storm runoff sources (after Sklash et al. 1975)
2.3 Use of Environmental Tracers for Hydrograph Separation
Techniques for estimating the contribution of different sources to streamflow can be grouped into three categories: physical techniques, tracer techniques and numerical modelling (Scalan 2002). The type of technique most suitable for a particular catchment depends on many factors, including climate, geomorphology and geology as well as the amount of gauge data available for the catchment.
Peters and van Lanen (2005) highlight the associated difficulties of several different methods of hydrograph separation. Traditional tools, including recession constants, graphical methods and digital filters, require oversimplification of the problem and do not accurately portray reality, while the use of observed groundwater levels requires Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 7 complex analysis (Peters and van Lanen 2005). Stream gauging is usually the preferred option, but is expensive and can be difficult in ephemeral streams and streams that are subject to erosion (Scalan 2002).
Environmental indicators or tracers are now commonly used for separating the components of a hydrograph. The advantage of using tracers is that they display variations in abundance which directly depend on the physical area in which streamflow originates. Thus, they are an accurate Geographical Source Area method under the classification scheme used by Sklash et al. (1975) (Figure 2). Tracer studies are also commonly used in order to determine the relative contributions of “old water” derived from subsurface sources and “new water” in the form of direct runoff after rainfall events. This is a Time Aspect classification using the Sklash et al. terminology (1975), but is possible because pre-storm and storm runoff originate from different source areas, namely below and above the ground respectively, and thus have different physical and chemical properties which depend on the characteristics of these areas.
An environmental tracer can be either a naturally occurring signature characteristic of a water source, or an artificially introduced substance such as bromide (eg Gooseff and McGlynn 2005). Tracer studies can thus be divided into two categories: those that use naturally occurring indicators and those that require the injection of an indicator or dye, known as an artificial tracer, into the system. Tracers that occur naturally in the environment allow the characteristics of a large area to be examined and do not require the addition of any external substances which could potentially cause changes to the ecosystem in the study area. Thus, as well as being cost effective, they are generally “more useful and more environmentally accepted than artificially introduced tracers” (Gibson et al. 2005). This project therefore focuses on the first of the two categories, and in particular examines natural tracers that can be easily sampled and analysed.
2.4 Principles of tracer hydrology
Environmental tracers can be used as an alternative method of determining sources of streamflow in a catchment, thus eliminating the need for computationally expensive catchment modelling. The science behind the use of environmental tracers
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 8 for baseflow separation contains several assumptions that simplify the modelling process. These include: i) the concentration of the tracer in groundwater remains constant or varies predictably over the course of the storm event; ii) the groundwater and surface runoff tracer concentrations are significantly different from each other; iii) while moving through the watercourse, the tracer does not undergo change or changes predictably; and iv) watershed conditions can be adequately represented by a steady-state model. (Gremillion et al. 2000)
As the above requirements relate to the separation of groundwater flow from surface runoff they are not directly applicable to the separation of flow components originating in different parts of a catchment. The major requirement of substances that are to be used as environmental indicators is that they must exhibit spatial variability (Gibson et al. 2005). Therefore, in order to make the criteria outlined above more universally applicable, requirement (ii) can be replaced with the more general assumption that water generated from any given flow pathway contains a significantly different indicator concentration to water generated from other flow pathways. This allows the indicator to be used as a signature property of water originating in one particular location within the catchment.
Sklash et al. (1975) developed a set of mass balance equations for hydrograph separation using the conservative tracer oxygen-18. These equations were generalised for use with any conservative tracer by Gremillion et al. (2000) and others. In this method, the total discharge in the river, discharge of old water, and discharge of new water are defined as Qr, Qo and Qn, respectively. Similarly the tracer concentrations in old water, new water and river water are defined as Co, Cn and Cr, respectively. The following equations can then be used:
Equation 2: Conservation of flow mass: Qr = Qo + Qn
Equation 3: Conservation of contaminant mass: QrCr = QoCo + QnCn
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 9
Equation 3 can then be rearranged to give the discharge resulting from baseflow, as follows:
(Cn - Cr) Equation 4: Old water hydrograph contribution: Qo = Qr (Cn - Co) (Sklash et al. 1975; Gremillion et al. 2000)
This method makes the major assumption that Co and Cn are constant in both time and space (Obradovic and Sklash 1986). The assumption is usually valid because the substances used, such as stable isotopes, generally display only long-term changes. If parameters that experience rapidly changing concentrations were to be used as environmental indicators the above set of mass balance equations would only be valid if simultaneous measurement of Co, Cn and Cr could be undertaken, and if the travel time between runoff source and catchment outlet was short.
2.5 Previous use of tracers
Tracers have been used to separate baseflow from direct runoff since the 1970s. A well known early study was that conducted by Sklash et al. (1975), which used oxygen-18 to divide streamflow into three categories: direct runoff, direct rainfall on the channel, and flow from groundwater. Unlike the limited number of earlier studies, this study was able to show that groundwater contributed a significant proportion of the generated streamflow following a storm. Many further studies using oxygen-18 and other environmental tracers have now been undertaken. This section provides an overview of the findings of these studies, and their contribution to the scientific understanding of catchment hydrology.
2.5.1 Typical characteristics of previous tracer studies
A range of parameters has been used as tracers to attempt to describe runoff pathways. These tracers include Gran alkalinity (Soulsby et al. 2003), dissolved silica (Hoeg et al. 2000; Rodgers et al. 2004), specific conductance (Kunkle 1965), temperature (Kobayashi et al. 1999) and stable isotopes such as 18O (Sklash et al. 1975; Hoeg et al. 2000; James et al. 2000). Most studies have used a combination of two or more tracers to accurately determine runoff sources.
Previous tracer studies have generally focused on high gradient catchments with high rainfall. One common application of tracer hydrology is the study of snowmelt, Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 10 which often has distinctly different characteristics from nearby groundwater bodies (Hooper and Shoemaker 1986; Kobayashi et al. 1999; Rodgers et al. 2004; Soulsby et al. 2004).
There are fewer examples of tracer studies conducted in low-gradient catchments, although some do exist. One example is the study undertaken on the Econlockhatchee River in central Florida (Gremillion et al. 2000). This catchment is characterised by mild topographic gradients and sandy soils. In this study, stable isotopes of water were deemed to be the most appropriate indicator of streamflow origin due to their highly conservative nature. The study applied a series of mass balance models based on conservative tracers to upper parts of the catchment. The models gave similar predictions of the amount of water being provided by storm- event runoff (Gremillion et al. 2000). The success of this investigation suggests that environmental indicator studies can be applied to all types of catchments if valid tracers are identified.
2.5.2 Success of previous tracer studies
Studies of naturally occurring tracers have proven so successful that they are now widely applied when attempting to analyse flow pathways and stream source areas. Tracer studies have shown that subsurface flow is in fact a highly significant component of stormflow, and in many cases its contribution is at least as important as that of overland flow (Sklash et al. 1975; Kobayashi et al. 1999; Gremillion et al. 2000; Rodgers et al. 2004; Gibson et al. 2005; Peters and van Lanen 2005). This contrasts with early runoff generation concepts, including saturation excess studies by Dunne which concluded that storm hydrographs in the study site in Vermont, USA, were mainly dependent on overland flow generated on hill slopes (Dunne and Black 1970b). Thus, environmental tracers have made a major contribution to the progression in understanding of the stormflow generation process.
Stable heavy isotopes have been found to be particularly useful tracers (Gibson et al. 2005). Stable isotopes of water, including deuterium, are widespread and exist in different water bodies in different proportions. Groundwater bodies tend to display heavy isotope concentrations similar to those of precipitation, while preferential evaporation of lighter isotopes from surface waters causes heavy isotope enrichment in these bodies (Gibson et al. 2005). Because stable isotopes are incorporated into
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Literature Review 11 the water molecule, they do not undergo reactions and are thus more conservative than substances which are simply dissolved in the water (Sklash et al. 1975).
2.5.3 Use of tracers to identify changes in flow pathways
Although the use of environmental tracers has been applied to catchments undergoing urban development, the number of such studies is limited. The use of tracers in these circumstances has the potential to reduce the need for intensive use of catchment stream gauges during development in order to detect changes in catchment hydrology following urbanisation.
Gremillion et al. (2000) used oxygen-18, represented as δ18O, as a tracer to separate the contributions of pre-storm and storm-event water to runoff in subcatchments of the Old Econlockhatchee River. The study found that in an uncleared portion of the catchment, pre-storm or “old” water made up approximately 76% of river flow. However, in a partially cleared and urbanised adjoining subcatchment, pre-storm water was only about 47% of river flow. The researchers attributed this difference to a change in runoff flow paths following urban and agricultural development (Gremillion et al. 2000). This study shows that environmental tracers are sensitive enough to catchment changes to provide a useful tool for urban developers.
2.5.4 Use of tracers for spatial separation of runoff sources
The most common use of environmental tracers is to separate the contributions of groundwater and overland flow. However, environmental tracers may also be used to determine the geographical area in which groundwater flow originates if different regions throughout the catchment display different groundwater properties. This application of tracer theory uses the same principles that are used when separating baseflow from overland flow.
Kunkle (1965) used specific conductance of water in a reach in east-central Iowa, USA to determine the streamflow contributions of groundwater from alluvium and bedrock areas. Samples were collected from wells within an area of bedrock and from the stream itself. It was found that the conductivity of water in the bedrock wells was much higher than that of water flowing in the alluvium part of the catchment upstream. Consequently, stream conductivity was found to increase as water passed
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Literature Review 12 through the bedrock reach (Kunkle 1965). This verified the hypothesis that the reach discharges groundwater to the creek that flows through it.
The theory used by Kunkle (1965) could potentially be extended to separate surface runoff derived from different parts of a catchment. This would require rain falling in different parts of the catchment to acquire distinct chemical properties of the region in which it fell before reaching the stream.
2.5.5 Application to Ungauged Catchments: Use of Tracers as an alternative to complete flow data
Traditional hydrograph separation techniques often require time-consuming catchment modelling and extensive data analysis. In some cases, the benefits derived from hydrograph separation may not justify the cost and time involved with these methods. There is a need for an alternative method of hydrograph separation that can be performed with less intense catchment monitoring.
Although the installation of catchment gauges for modelling is an expensive process, analysis of isotopic tracer concentrations for hydrograph separation can be equally expensive (Obradovic and Sklash 1986). Therefore, tracer separation techniques are not highly beneficial unless less costly tracers can be found. However, there are many water characteristics that could potentially be used as tracers that are much simpler and more cost effective to analyse than isotopic signatures. The major problem with the majority of these simple tracers, which include ion concentrations, pH and conductivity, is that they are not conservative and instead display strong variations depending on factors such as the time of contact with soil (Obradovic and Sklash 1986).
If a straightforward and inexpensive set of environmental indicators is found, there is potential for the environmental tracer method to be used on its own as an accessible method of hydrograph separation. The method could then also be used as an aid when attempting to predict the effects of source areas changing throughout the year. When simple and easy to analyse tracers are chosen, environmental indicators are significantly more time effective and readily accessible than traditional catchment characterisation and modelling.
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2.6 Simple Tracers suitable for Australian Catchments
Catchments around the world vary significantly in terms of both geomorphology and climate. The majority of hydrological research occurs in northern hemisphere catchments that contain substantially different soil types and climates to those found in Australia. For this reason, studies specific to the various Australian catchment types need to be performed before runoff generation processes in these areas can be fully understood.
Catchments in south-western Australia are typically low gradient and often contain sandy soils (McKenzie et al. 2004). The exception to this is the old deep clay found on plateaus such as the Darling Plateau (Peters and Donohue 2001). Lateritic content is common in the clayey plateau soils (Peters and Donohue 2001). The climate in south-west Western Australia is temperate with warm to hot summers and cool to cold winters (Bureau of Meteorology 1995). Although snowfall is an occasional occurrence, it is not experienced in significant quantities anywhere in the region (Bureau of Meteorology 1995).
There are very few examples of tracer studies that have been undertaken in catchments similar to those found in Western Australia. This section presents a review of water properties that may be appropriate for use as tracers in Western Australian catchments. Particular focus will be given to characteristics relevant to the Swan-Canning Estuary region. Previous use of these tracers is covered where applicable. It must be noted that the aim of this study is to use simple indicators of streamflow origin. For this reason, several potential tracers, such as stable isotopes, have been ruled out due to the complexity and high cost involved in analysing samples.
2.6.1 Electrical Conductivity
Dryland salinity is an increasingly widespread problem in south-western Australia, with one million hectares of land already affected (Department of Environment 2003). The problem arises in areas of land where the groundwater table rises to the surface, bringing salt with it (Muirden et al. 2003). Thus, it is confined to spatially discrete, often low-lying areas. This makes salinity ideal for use as an indicator of streamflow source. Its widespread nature means that techniques will be widely applicable, while the patchiness of its distribution allows identification of streamflow source areas.
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Salinity levels are commonly determined through measurement of the electrical conductivity of a water sample (Department of Agriculture 2003). Measurement of electrical conductivity is non-specific with regards to the particular dissolved mineral substances affecting the reading (Fresenius et al. 1988). However, although measurement of electrical conductivity is more indirect than analysis of dissolved salt content, it is a much simpler technique and can be performed on site without the need for laboratory work. This makes it suitable for studies that require straightforward and cost-effective analysis.
In most cases, salinisation of surface water bodies in specific areas due to land degradation will cause water flowing from these areas to display higher electrical conductivity readings, while runoff formed directly from precipitation will be fresh and display low electrical conductivity (Degens 2002). Conductivity has been successfully used as a tracer in the United States of America by Kunkle (1965). Although it was not found to be the most accurate of the potential tracers that were considered in the study, it did show distinct variations with location, and also varied predictably with storm event progression (Kunkle 1965).
2.6.2 Temperature
Temperature has frequently been used as a tracer in mountainous catchments. In these studies, large temperature differences between different water sources have been observed. For example, Kobayashi et al. (1999) found that groundwater on Hokkaido Island in Japan was typically around 3-4°C while water generated from melting snow was assumed to be significantly colder at 0°C. Before snowmelt began, streamflow occurred below an insulating snow layer and was approximately 3°C despite air temperatures below 0°C. Once snowmelt commenced, the stream temperature dropped by around half a degree. In addition to this, the study also found that rainwater, which has a higher temperature than the groundwater in the study area, increased water temperature during the rising limb of the storm hydrograph (Kobayashi et al. 1999). This indicates that rainwater was discharged quickly following a storm event.
The difference in temperature between groundwater and precipitation in Western Australia would not be expected to be as large as the temperature differences seen in mountainous catchments. However, despite the fact that snowmelt is not a major Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 15 factor in non-mountainous Australian catchments, it may still be possible to ascertain the source of streamflow using water temperature. Several previous studies have used streamflow temperature to analyse groundwater behaviour, even where snowmelt was not involved (e.g. James et al. 2000; Conant 2004; Salem et al. 2004). These studies have generally been successful at quantifying the importance of subsurface discharge. In Ontario, Canada, Conant (2004) found that during the summer, areas of a stream in which high rates of groundwater discharge were occurring were cooler than other parts of the stream, whereas in winter high groundwater discharge sections were warmer than other parts.
Water temperature can be affected by any processes that influence heat load to the stream or the rate of discharge from the stream (Poole and Berman 2001). Therefore, it is not conserved within a stream. Despite this, temperature does vary in a predictable manner and thus fits the tracer criteria defined by Gremillion et al. (2000). Poole and Berman (2001) list the main factors influencing stream temperature as climatic drivers, stream morphology, groundwater influences and riparian canopy conditions.
The heat balance in a stream has been described by Sinokrot and Stefan (1993; 1994) (Equation 5).
∂T ∂(QT) ∂ ⎛ ∂T ⎞ BS Equation 5: A + = ⎜ADL ⎟ + ∂t ∂x ∂x ⎝ ∂x ⎠ ρcp where A is the channel cross-sectional area; T is the water temperature; t is time; Q is the stream flow rate x is distance in the downstream direction;
DL is a longitudinal dispersion coefficient in the x-direction; B is the width of the channel at the surface; S is a source or sink term. Heat transfer with the surrounding environment is included in this term; Ρ is the water density; and
Cp is the heat capacity of water.
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The baseline stream temperature is generally taken as the temperature of water in the surficial groundwater aquifer (Poole and Berman 2001). Any differences between stream and groundwater temperatures are due to climatic drivers and geomorphological influences. As water progresses through a stream channel, its temperature approaches that of the atmosphere, unless some insulating protection such as dense vegetation exists (Poole and Berman 2001). In some cases, heating and cooling effects can be neglected if the stream distance is short enough. This has been done in several previous studies that employed temperature as an environmental tracer (e.g. Kobayashi et al. 1999; Conant 2004).
2.6.3 Nutrient Concentrations
Nutrient concentrations are one of the most important characteristics of a water body and have a highly significant impact on ecosystems that rely on that water body. Pollution due to the two key nutrients, nitrogen and phosphorous, is now widespread, and is linked to a range of urban and agricultural activities (Fresenius et al. 1988; Peters and Donohue 2001; Turner et al. 2003). Nutrient sources include fertilizers, animal manure, industry discharge, urban runoff, and atmospheric deposition (Carpenter et al. 1998; Department of Environment and Heritage 2005). In Western Australian agricultural areas, the major sources of nutrient pollution of streams and waterways are phosphorous and nitrogen added to the soil through fertilizer (Carpenter et al. 1998; Peters and Donohue 2001; Viney and Sivapalan 2001).
The use of fertilizer in Australia and worldwide has increased in recent decades with the rise in global demand for agricultural products and simultaneous decrease in fertilizer costs (Peters and Donohue 2001). Fertiliser application can be spatially heterogenous throughout a catchment, with land used for different purposes receiving different levels of application. Gerritse et al. (1992) found that on Western Australia’s Darling Plateau, located to the north-east Perth, land used for orchards had higher rates of input of both nitrogen and phosphorous than land used for all other purposes.
Entry of nutrients into surface waters depends not only on availability, but also on the transport processes of erosion and leaching. Hydrological controls affect the routes taken by nutrients to streams, as well as the timing of peak nutrient export (Petry et al. 2002).
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The dependence of water nutrient levels on both land use and soil type means that catchments that display spatial gradients in these features should also display gradients in nutrient concentrations in waterways, making nutrient levels a feasible environmental tracer. The individual suitability of both nitrogen and phosphorous for tracer studies is discussed below.
Phosphorous Applied phosphorous is not immediately leached through a soil. Instead, some portion of it is adsorbed to soil particles until the soil reaches saturation. The amount of phosphorous that enters surface waters then increases as the phosphorous application to the soil increases (Carpenter et al. 1998). In particular, the amount of phosphorous found in runoff has been found to be linked to the phosphorous concentration in the upper 5cm of soil (Sharpley et al. 1996). In Western Australia’s Swan-Canning Estuary area, the concentration of phosphorous discharging in groundwater is expected to increase in the near future as the level of phosphorous saturation in soils increases (Gerritse et al. 1998).
Soil type has a strong influence on the level of phosphorous needed for soil saturation. For example, phosphorous has a high sorption affinity for lateritic soils due to their high levels of sesquioxides including alumina (Al2O3) and ferric oxide
(Fe2O3) (Litaor et al. 2004). Lateritic soils therefore have a high maximum phosphorous saturation (Gerritse et al. 1995). In contrast, sandy soils have a lower saturation capacity and hence a shorter phosphorous breakthrough time (Gerritse 1995). Thus, the presence of both lateritic and non-lateritic soils in a catchment should lead to distinct phosphate signatures in surface waters originating in different areas of the catchment. Many south-west Western Australian catchments contain these two soil types, making them highly suitable for environmental tracer investigations.
Nitrogen
Like phosphorous, nitrogen is applied to a soil through fertilizer and animal manure. However, nitrogen can also be transported into a catchment via atmospheric deposition resulting from airborne pollutants (Peters and Donohue 2001). Nitrogen is leached through soils much more quickly than phosphorous, predominantly as nitrate ions which do not adhere to lateritic or other particles (Turner et al. 2003). It is
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Literature Review 18 therefore not valid to assume that nitrogen and phosphorous are transported via similar pathways.
Gerritse et al. (1995) found that on the Darling Plateau nitrate concentrations were higher in streams draining agricultural areas than they were in streams draining residential areas, even when these residential areas were serviced by septic tanks rather than mains sewerage. Thus, surface water nitrogen concentrations can exhibit heterogeneity throughout a catchment, which could allow the nutrient to be used as an indicator of streamflow origin.
As nitrogen and phosphorous exhibit different spatial and temporal characteristics, environmental tracer studies should ideally consider both nutrients. However, where analysis is restricted by budget constraints, phosphorous appears to be the most suitable parameter for measurement. It is not only more spatially variable due to its differing affinity for different soils, but also requires only simple measurement techniques. Nitrogen is typically more expensive to analyse than phosphorous.
2.6.4 Turbidity
Turbidity is a measure of the abundance of suspended substances including clay particles and organic matter (Rodier 1975). Turbidity can be measured easily using light attenuation. No examples of previous studies in which turbidity was used as a tracer for the purpose of hydrograph separation could be found, but turbidity has been used to monitor changes in streams. One example of this was a study by Clifford et al. (1995) which used turbidity to analyse periodical changes in meltwater of a glacial stream. This study showed that turbidity changes can be sensitive enough to accurately indicate periodical variation in stream characteristics, which implies that it could also be used as a water signature property in environmental tracer studies.
The persistence of turbidity can be affected by particle settling and by scouring of the channel bottom (Rodier 1975). Therefore, turbidity is not a conservative substance. In order to use it as such, it must be assumed that stream length is short enough to prevent these changes from having a significant effect on turbidity levels.
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2.6.5 pH
The pH of a water body can display significant variations due to factors such as soil type, rainfall acidity and land use in the area. Despite this, no evidence of pH being successfully used as an environmental tracer was located. Obradovic and Sklash (1986) examined the behaviour of a large number of chemical properties, including pH, in the arctic Apex River catchment in Canada. Unlike the majority of metal ions considered in the study, it was found that pH did not vary predictably with length of time following a storm (Obradovic and Sklash 1986). Thus, it was concluded that pH was not suitable for use as an environmental tracer in this particular study, as it did not satisfy the necessary tracer characteristics.
The difficulty in applying tracer theory to pH possibly arises because a wide range of mechanisms can cause pH variations, which means that water body pH does not behave in a predictable manner. However, measurement of pH is sufficiently simple that it may be a valuable environmental indicator in some cases.
2.6.6 Colour and tannin concentrations
In forested areas, water bodies can appear yellow-brown in colour due to the presence of dissolved humic substances from surrounding vegetation (Gippel 1987; Bennett and Drikas 1993). These humic compounds enter water bodies following decomposition of plant matter and can affect ecosystem function by altering factors such as light penetration and nutrient availability (Cuthbert and del Giorgio 1992).
The effect of dissolved organic compounds on water colour was investigated by Gippel (1987) in a small catchment in southern New South Wales. The study examined the causes of stream colour following storm events, and found that fulvic acids from vegetation and leaf litter were the major sources. In particular, it was found that colour in stream water originated from rough-barked eucalypt species and other native sclerophyllous vegetation. It was noted that colour variation is likely to be more responsive to individual storm events than to seasonal changes in flow. During storm events, accumulated “colour” from wet areas was flushed into the stream channel, thus providing a “concentrated source of readily available coloured substances” (Gippel 1987). This effect was amplified during peak periods of litterfall. Although humic substances are also found in groundwater, the study showed that
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Literature Review 20 humic substances from groundwater contained less colour producing functional groups per weight of carbon, resulting in less strongly coloured water.
The difference in colour between water sources means that colour is suitable for use as a tracer in Australian catchments. Strongly stained water may indicate that the streamflow originated from surface or near-surface runoff in a region abundant in colour producing vegetation. An example of such vegetation is the Melaleuca genus of trees, which are often referred to as teatrees, bottlebrushes and paperbarks, and are commonly found growing along stream banks (Holliday 1989). Melaleucas are common in Western Australian catchments, including the Ellen Brook catchment. The Melaleuca genus is similar to the Eucalyptus found to be responsible for stream water colouration in the Gippel (1988) study in that they are both scleromorphic genera of the Myrtaceae family (Barlow 1994).
Figure 3: A coloured stream in the Ellen Brook catchment, Western Australia The strong brown stain is thought to be due to the presence of native vegetation along the stream banks.
2.7 Implications for catchment management
Anthropogenic activity, including catchment clearing, construction of impermeable surfaces and dams, and extraction of water from streams and groundwater bodies, will increase as the world population grows. Dealing with land-use changes and the resultant alterations to streamflow patterns is likely to be one of the major challenges of the future (De Fries and Eshleman 2004). It is therefore essential to understand streamflow generation processes and the source areas contributing to streamflow. A
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Literature Review 21 better awareness of flow generation processes may allow the relevant authorities to predict the effects of changes to one or more of the regions within a catchment. For example, the impact on outlet stream water quality due to an alteration in the water balance in the catchment could be predicted.
Recently, high nutrient levels in Western Australia’s Swan River Estuary have resulted in algal blooms which are associated with scums on the river surface, foul odours and fish kills (PPK Environment and Infrastructure 2000). This issue is of high importance due to the potential toxicity of the algal blooms and the aesthetic and recreational value of the Swan system to the general public. Each year, the Swan’s contributing catchments, including the Ellen Brook catchment, export large amounts of both phosphorous and nitrogen, which contribute to these algal blooms.
It has been recognised that restoration of eutrophic waters requires non-point sources of nutrients to be reduced (Sharpley et al. 1996; Carpenter et al. 1998; Scanlon et al. 2005). A better understanding of the spatial extent of nutrient origin may allow planners to better identify those areas most likely to contribute to problems such as algal blooms. This will allow the creation of more efficient and refined nutrient management strategies that target the regions of concern (Peters and Donohue 2001).
Political constraints dictate that the budgets allocated to research into catchment processes by environmental authorities are generally very limited. The identification of an inexpensive mechanism for catchment characterisation is therefore very important for future catchment management and protection. The ability to characterise a catchment’s source area hydrology without the use of extensive stream gauging would be an important step in this process. Simple environmental tracers, particularly those that can be measured on-site such as salinity and temperature, are therefore potentially of very high value to environmental management authorities.
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2.8 Applicability to the Ellen Brook Catchment
The case study for this dissertation is the Ellen Brook catchment in Western Australia. This catchment has several characteristics that make it highly suitable for testing the applicability of tracer hydrology in Western Australia. In particular, it contains three distinct regions that would be expected to produce very different water signatures. In addition to this, the Ellen Brook contributes large quantities of nutrients to the Swan River system, and yet streamflow generation processes within the catchment are poorly understood. This is in part due to the fact that the stream is only gauged at the catchment outlet. Thus, the use of environmental tracers may provide insight into catchment processes that could benefit Western Australian water and catchment management.
2.8.1 Site Characterisation
Location and Climate The Ellen Brook catchment is situated approximately 20km north-east of Perth, Western Australia, within the Shires of Chittering, Gingin and Swan (PPK Environment and Infrastructure 2000) (Figure 4). The catchment has a total area of 715km2 and is approximately 65km long from north to south (Swan River Trust 2005b). Catchment width is around 20km (Smith and Shams 2002). The confluence of the Ellen Brook and the Avon River marks the beginning of Perth’s major waterway, the Swan River. Ellen Brook contributes approximately 8.3% of the total flow in the Swan River (Swan River Trust 2005b).
Climate in the region is Mediterranean, with hot, dry summers and cool, wet winters. Average annual rainfall for the Ellen Brook catchment is approximately 800mm (Swan River Trust 2005b). This figure varies over the catchment, with averages of 820mm annually in the south and 660mm annually in the north (PPK Environment and Infrastructure 2000). Between 1987 and 1992, approximately six percent of this rainfall, or 56mm annually, became runoff, resulting in an average annual discharge of 37 million cubic metres into the Swan River (PPK Environment and Infrastructure 2000). Rainfall varies considerably between years, and observed runoff was significantly below average in the eight years to 2003 (Figure 5). Catchment investigation has shown a strong linear relationship between annual precipitation and corresponding runoff volumes (Figure 6).
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Figure 4: Ellen Brook Catchment Location (Smith and Shams 2002)
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60000
50000
40000
30000
20000 Annual Runoff (ML) 10000
0 1996 1997 1998 1999 2000 2001 2002 2003 Year
Figure 5: Ellen Brook Annual Runoff for the years 1996-2003 Calculated from daily flow data obtained from the Department of Environment (Zammit 2005 pers. comm.). The gauge is located near the Ellen Brook outflow. Dotted line represents 37,000 ML, the mean reported Ellen Brook discharge for 1987 to 1992 (PPK Environment and Infrastructure 2000).
Figure 6: Runoff:Rainfall Relations for Swan River Tributaries 1994 - 1999 (Smettem 2005 pers. comm.) The Ellen Brook closely fits a linear runoff:rainfall relationship. Runoff is a relatively low proportion of rainfall compared to the Perth metropolitan drains that were examined.
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The Ellen Brook is an ephemeral stream, with the majority of annual rainfall in the catchment occurring between May and October (PPK Environment and Infrastructure 2000). This results in flow for the Ellen Brook usually peaking in July or August (Figure 7). Over the summer months, the Brook usually ceases to flow and becomes dry except for a few persistent pools. In addition to the pools, the catchment contains several mound springs that support vegetation throughout the year (Smith and Shams 2002). These mound springs are the result of groundwater discharge.
18000 1996 1997 16000 1998 1999 14000 2000 2001 12000 2002 2003 10000 Mean
8000
6000
Total Monthly Flow (ML) 4000
2000
0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month
Figure 7: Ellen Brook Yearly Hydrographs 1996-2003 Calculated from daily flow data obtained from the Department of Environment (Zammit 2005). The gauge is located near the Ellen Brook outflow.
Vegetation and Land use
Extensive areas of the Ellen Brook catchment have been cleared for agriculture and urban use (PPK Environment and Infrastructure 2000). The cleared areas are now mainly used for stock grazing, although intense horticulture, light industry and residential use are all becoming more common (Smith and Shams 2002). Other land uses within the catchment include the Vines golf course and the RAAF Pearce auxiliary airfield.
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Some native vegetation remains in the catchment despite the extensive clearing. The catchment still contains areas of high conservation value where rare endangered flora and fauna species are present (PPK Environment and Infrastructure 2000). Tree plantations and remnant vegetation including melaleuca stands are found in the west of the catchment, in discrete areas in the north-east, and along surface water flow lines (PPK Environment and Infrastructure 2000).
Environmental Concerns/Issues The catchment experiences several land degradation problems due to past and current anthropogenic activities. These problems include salinisation, wind erosion, stream erosion, waterlogging, nutrient export, and inundation (Smith et al. 2002).
The Ellen Brook has been identified as a major contributor of nitrogen to the Swan River Estuary system. Research by the Swan River Trust has noted that nitrogen levels in the Ellen Brook are consistently higher than those in other coastal waterways contributing to the Swan, with organic nitrogen concentrations repeatedly exceeding 2mg/L (Jakowyna 2002) (Figure 8). This is well above the management targets that have been set for nitrogen export from the catchment. Export displays a seasonal pattern, with peak organic-N concentrations being observed in late winter (Jakowyna 2002).
2.5
2
1.5 TN Ellen Brook
TP Ellen Brook 1 TN Avon River
TP Avon River Concentration mg/L 0.5
0 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 Year
Figure 8: Nutrient Concentrations in Ellen Brook and the Avon River 1987-2001 Ellen Brook exports nutrients at concentrations significantly higher than those in the nearby Avon River. Concentrations are based on monitoring sites located near the catchment outlets Data collected by the Swan River Trust (Swan River Trust 2005b; Swan River Trust 2005a).
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Phosphorous export from the Ellen Brook catchment is an even bigger concern, with Ellen Brook exporting more phosphorous than any of the other Swan River tributaries. This has been highlighted by nutrient reduction programs such as the Swan-Canning Cleanup Program (Swan River Trust 2004). On average, Ellen Brook contributes 42% of the total phosphorous entering the Swan River Estuary each year, even though it makes up only 7% of the total annual flow (Peters and Donohue 2001). This equates to an average of 26 tonnes of exported phosphorous per year (PPK Environment and Infrastructure 2000). Phytoplankton growth in the middle and upper basins of the Swan River Estuary has been found to be strongly affected by phosphorous import from the Ellen Brook (Swan River Trust 2004). The health, ecological and recreational implications of this increase in primary production make nutrient reduction a priority for planners.
Like nitrogen, phosphorous concentrations in the Ellen Brook show a seasonal pattern with peak export occurring in July at the same time as peak rainfall (Donohue et al. 2001). This suggests that nitrogen and phosphorous are transported through similar pathways (Jakowyna 2002).
2.8.2 Application of Tracer Hydrology
The Ellen Brook catchment is ideal for this study as it can be easily divided into discrete regions. Each of these regions has unique characteristics, which should result in distinct and separable water signatures. The two major regions that are considered are the Swan Coastal Plain including the Gnangara Mound groundwater area in the west, and the Darling and Dandaragan Plateaus to the east (Figure 9). A third region, the River Flood Plain and Flats, is also examined but in less detail. Physical characteristics, historic and current land uses and water quality of these three regions are described in Section 2.8.3.
Previous work by Gerritse (1995) in the Ellen Brook catchment has found that export of phosphate varies significantly amongst regions with different soils. The application of phosphate fertilisers to soils also results in the addition of cadmium, a component of some fertilisers. If the same type of fertiliser is applied throughout a catchment, the ratio of cadmium to phosphate at application is constant. However, Gerritse (1995) found that surface water originating in regions of the Ellen Brook catchment with sandy soil had much lower Cd/P ratios than water originating in other areas. It was also found that water discharging from the Ellen Brook had a distinct water signature, Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 28 with a much higher concentration of cadmium than was observed in the Avon River or downstream of the confluence in the Swan River (Table 1).
Table 1: Cadmium concentrations in the Ellen Brook, Avon River and Swan River. Adapted from Gerritse (1995). All three samples were taken near the confluence of the Avon River and Ellen Brook at monthly intervals from June 1991 to December 1992. Water discharging from the Ellen Brook showed a significantly higher Cadmium concentration than water from the Avon catchment. Annual Average Concentration of Location Cadmium in Solution (μg/L) Avon River 0.02
Ellen Brook 0.07
Swan River 0.04
2.8.3 Geomorphological Regions of the Ellen Brook Catchment
A characteristic physiographic feature of the Ellen Brook catchment is the boundary between the Swan Coastal Plain and the Darling and Dandaragan Plateaus (Figure 9). Because of these distinct geological areas, soils in the Ellen Brook catchment can be divided into three main types. Bassendean sands comprise the western areas, the central valley consists of Guildford clays, and red earth soils dominate the eastern portion (Swan River Trust 2005b).
The northern reaches of the catchment are located within the Dandaragan Plateau, and can be described as sand and clay with a lateritic cap (Smith and Shams 2002). Lateritic soils are typically red, yellow or brown in colour; a result of their high levels of iron and aluminium oxides (Geoscience Australia 2005). The Dandaragan Plateau area contains several seasonally flowing streams (PPK Environment and Infrastructure 2000). Its western margin is the Gingin scarp. The Darling Plateau covers the south-western portion of the catchment. It is mainly composed of a lateritic cap over crystalline rocks (Smith and Shams 2002). Both ephemeral and permanent streams are present in this portion of the catchment (PPK Environment and Infrastructure 2000).
The Swan Coastal Plain, located in the west of the catchment, consists of two elements: aeolian deposits in western regions and fluviatile deposits along the flat valley track of the Ellen Brook (PPK Environment and Infrastructure 2000). The Gnangara Mound groundwater formation is located within the Swan Coastal Plain in the south-west of the catchment. Several round sumplands are found in this part of Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 29 the catchment (PPK Environment and Infrastructure 2000). The river bed and Gnangara mound elements would be expected to display different properties and will be considered as separate regions for the purposes of this study.
Specific characteristics of each of the three regions are discussed below. The focus is placed on characteristics that will affect the chemical and physical properties of water originating in the region, and thus make the regions suitable for source area hydrology studies.
RIVER FLOOD PLAIN AND FLATS
Figure 9: Geomorphology of the Ellen Brook Catchment (Smith and Shams 2002) The Darling and Gingin Scarps on the eastern side of the catchment mark the edge of the Swan Coastal Plain Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 30
The Swan Coastal Plain and the Gnangara mound The Swan Coastal Plain area to the west of the Ellen Brook catchment has been largely cleared for agricultural use as pastures (Smith and Shams 2002). High levels of phosphorous and nitrogen export from animal manure and fertiliser application in this region would therefore be expected. Gerritse (1995) found that sandy soils in the farmed regions of the Ellen Brook catchment were already almost saturated with phosphate. This means that if phosphate continues to be applied to the soil as fertilizer or in other forms, it will be exported in large quantities. PPK Environment and Infrastructure (2000) also identified the low-lying soils with low phosphorous binding capacity located on the south and east of the catchment as the most at risk of phosphorous export. The majority of these at risk regions lie within the Swan Coastal Plain area.
Despite the likelihood of high nutrient availability in this part of the catchment, water seeping out of the Gnangara mound would originally be fairly pristine. Therefore, the water signature for the Swan Coastal Plain region will depend on where the flow originates. High spatial variability in nutrient levels may result. The Swan Coastal Plain is not a high risk area for salinity (PPK Environment and Infrastructure 2000).
Water draining soils from the Swan Coastal Plain is expected to be highly coloured due to the relatively abundant level of vegetation. Large areas of the Swan Coastal Plain have been left uncleared due to low productivity, and pine plantations also exist in the area (Smith and Shams 2002).
The Darling and Dandaragan Plateaus Both the Dandaragan Plateau and the uplands of the Darling Plateau contain lateritic soils (PPK Environment and Infrastructure 2000). As a result, they have the ability to support high phosphorous levels without leaching occurring. This contrasts with the soils in the Swan Coastal Plain region, which have low phosphorous binding ability, suggesting that phosphorous has the potential to be an ideal tracer for distinguishing between water originating on the east and west of the catchment.
Groundwater in bores on the Darling and Dandaragan Plateaus has been found to be fresh to brackish (Smith and Shams 2002). The Plateau areas contain isolated salinity occurrences due to waterlogging along stream channels (PPK Environment and Infrastructure 2000). These isolated occurrences may restrict the use of salinity Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 31 as an environmental tracer, although it may still be possible to identify water originating on the Swan Coastal Plain, as this is the area with the lowest salinity.
The majority of the Darling Plateau and nearly half of the Dandaragan Plateau have been cleared (PPK Environment and Infrastructure 2000). Thus, water emanating in this part of the catchment would be expected to contain only low levels of organic carbon.
The River Flood Plain and Flats The areas of the Ellen Brook catchment located along the main north-south drainage line have been identified as prone to inundation (Figure 10). Inundation can arise where the water table rises to the surface or where low permeability surfaces, such as clays, cause waterlogging and result in mobilisation of nutrients and seasonal salinity (Smith et al. 2002). The seasonally waterlogged plains or flats known as palusplains are common in this part of the Ellen Brook catchment (PPK Environment and Infrastructure 2000).
Nutrients are drained from the central portion of the catchment following waterlogging between July and September (PPK Environment and Infrastructure 2000). Thus, water originating in the region of the main north-south drainage line would be expected to display high nutrient levels in the early winter months while this flushing occurs. High salinity levels are also expected due to the soil saturation (Figure 11).
Interestingly, the rainfall-runoff curve for the catchment does not display an upward curve as would be expected for a catchment where significant areas become saturated (Figure 6). The linearity of the curve, even at very high runoffs, instead implies that the runoff mechanisms responsible for runoff generation are independent of rainfall amount. If a large area of the catchment was experiencing saturation, it would be expected that at some point this area would begin to produce large volumes of runoff due to saturation excess and the rainfall-runoff curve would tend upwards. If this was the case, it is unclear what the signature of such a water source would be. Runoff may either display a signature similar to that of precipitation, or one similar to water that rises to the surface through the ground, which would be high in salinity and nutrients, as suggested above.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Literature Review 32
Figure 10: Areas Prone to inundation (Smith and Shams 2002) The area along the main channel of the Ellen Brook is subject to seasonal inundation and waterlogging.
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Literature Review 33
Figure 11: Areas of Ellen Brook catchment prone to salinisation (Smith and Shams 2002) Shaded areas are likely to have a high conductivity signature. This differs from mapping of areas that have the potential to be affected by waterlogging and salinity carried out by PPK Environment and Infrastructure (2000), which identifies the region along the valley track as the most susceptible.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Aims and Objectives 34
3 Summary of Aims and Objectives
Through the examination of a range of water body characteristics, this study aims to determine whether or not analytically simple water quality parameters can be used for hydrograph separation in Australian catchments. The Ellen Brook catchment is an ideal study site for this purpose because it displays land use and climatic patterns typical of many catchments in south-west Western Australia, as well as distinct geomorphological regions.
Identification of water quality parameters suitable for use as environmental indicators requires an understanding of whether streams originating from the three regions of the study site, namely the eastern Plateaus, western Swan Coastal Plain Area and central River Flood Plain, have significantly different water signatures to each other. Emphasis will be placed on water signature parameters that behave predictably and thus satisfy the requirements for use as an environmental tracer.
The secondary objective of the study is to contribute to the hydrologic characterisation of the Ellen Brook catchment by gaining an insight into the runoff generation processes occurring in the catchment. It is hoped to achieve this through the development of a conceptual model of the catchment that employs the use of suitable environmental indicators for hydrograph separation. This dissertation examines both the amount of flow derived from each of the regions under consideration, and also how this ratio changes as the winter season progresses. Understanding the hydrology of the Ellen Brook catchment is important for Western Australian water management, as the catchment is a significant contributor of nutrients to the Swan River Estuary, and at the same time is partly situated above the Gnangara Mound, one of Perth’s major drinking water supply areas.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
Methods 35
4 Methods
4.1 Research Plan
Three separate phases of work were carried out in order to satisfy the aims of the project. The first involved the identification of parameters that met the requirements outlined by Gremillion et al. (2000) and Gibson et al. (2005) for environmental indicators. Secondly, suitable indicators were used to estimate the flow volumes derived from each of Ellen Brook’s contributing areas using mixing models. Finally, flow volume data were collected in order to weight the contribution of the various streams and also to check the validity of the environmental indicator assessments.
The initial step in the identification of indicators was to thoroughly examine catchment land use, soil type and historical rainfall and flow data, as well as research previous tracer use, in order to gain an understanding of which water properties were likely to prove useful as tracers. Following this, pH, temperature, electrical conductivity, phosphorous, dissolved oxygen and colour were selected as the candidate parameters that could be suitable indicators in the Ellen Brook catchment. These are all common water quality measures and can all be analysed quickly and at little cost. They therefore satisfy the requirement that selected indicators be simple water properties. The second stage of indicator assessment involved analysis of these six parameters at various locations in the catchment through field and laboratory work, as described in the following sections. For each parameter, sampling and analysis aimed to determine: i) whether the parameter exhibited enough spatial variation between regions to act as a distinctive signature of water sourced from a particular region; and ii) whether the parameter behaved in an additive and predictable fashion.
Substances or properties that met these two criteria were deemed to be acceptable environmental indicators and were then employed in sourcing contributing areas within the catchment. It was decided initially to divide the catchment into two areas: the Swan Coastal Plain region in the west and the Plateau region in the east. Calculation of the flow contribution made by these two areas was achieved through application of the indicators to appropriate mathematical mixing models employing mass balance equations. The collection of environmental indicator data on several
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Methods 36 occasions throughout the flow season allowed changes in contributing areas to be assessed.
During the final stage of the project, the results of the mixing models were refined using streamflow volumes. Flow volume data was obtained at each of the sampling sites using the velocity-area method. This flow data was used to weight the contribution of the various streams to flow in the Ellen Brook, and then recalculate the contribution of the various regions based on these weightings.
4.2 Sampling Considerations
4.2.1 Timing
The timing of sampling was aimed at capturing the recessional limb of the Ellen Brook flow hydrograph so as to avoid the large water quality fluctuations commonly observed during the rising limb (George et al. 1996). In 2005, streamflow in Ellen Brook commenced around May. However, in the early weeks of flow the stream was expected to be mainly composed of direct precipitation, as Western Australian catchments generally require extensive amounts of rainfall before major baseflow runoff occurs (Loh 1974). Hence, sampling was not undertaken until a significant period of time had passed since flow commencement.
A discrete manual sampling regime was chosen due to time and budgets constraints. Sampling was undertaken four times during the year at intervals of three to six weeks, beginning in late June. For consistency, sampling was always performed in the morning and early afternoon.
4.2.2 Rainfall Effects
It is assumed that the majority of flow occurring during the sampling period was subsurface flow or near-surface interflow. In order to minimise the effects of direct rainfall it was aimed to sample only after a period of at least 48 hours without significant rain. This meant that sampling was not undertaken during channel flooding, which could mask the presence of environmental indicators. The disadvantage of this approach was that it restricted the times when sampling could be performed and resulted in unequal intervals between sampling rounds.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Methods 37
4.2.3 Site Selection
Sampling sites were chosen based on their accessibility and the benefits they would provide to the project. Each sampling round incorporated at least one sample site from each of the following categories: i) the Ellen Brook main channel; ii) streams originating on the Swan Coastal Plain; and iii) streams draining the Darling or Dandaragan Plateaus. The central River Flood Plain and Flats region could not be included as a separate region for analysis due to limited access to that part of the catchment. The fact that the boundary between the River Flood Plain and other regions is not well defined also necessitated exclusion of this region.
In total, 9 different sites were used (Figure 12). Photos of the sites are included as Appendix A. Site 1, near the catchment outlet and Site 4, just downstream of the confluence of Chandala Brook and Rocky Creek, lie on the main Ellen Brook channel. These two sites were sampled in order to examine the effects of mixing between streams from the two sides of the catchment.
Sites 3, 5, 6 and 9 are located on streams draining the western portion of the catchment, which is part of the Swan Coastal Plain. Site 3 is located on Brand Highway in the north-west of the catchment, and samples Chandala Brook, one of the largest tributaries. Sites 5, 6 and 9 are seeps originating in south-western agricultural pastures and are thought to be mainly composed of Gnangara Mound groundwater. Site 5 was sampled on Almeria Parade whilst sites 6 and 9 were both sampled where the seep intersected with Railway Parade. These three sites are all located within close proximity of each other with approximately 4.5km separating the northern-most and southern-most sites (Figure 12).
Finally, Sites 2, 7 and 8 are located on the eastern side of the catchment, and thus originate on the Darling and Dandaragan Plateaus (Figure 9). Site 2 is the most northern of these sites and thus represents the Dandaragan Plateau region. It samples Rocky Creek where the creek crosses Reserve Road. Site 7 was taken from Nambah Brook which originates on the Darling Plateau. This Brook was sampled in the inner parts of the catchment at Warren Road. Site 8, Ki-it Monger Brook, was sampled on Great Northern Highway just south of Bullsbrook (Figure 12). Two
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 38
further locations, downstream of Sites 2 and 8, were included in the final sampling round.
9
Figure 12: Locations of the nine primary sampling sites Land use map provided by the Department of Environment (Smith and Shams 2002)
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4.2.4 Sample Collection
Samples to be analysed in the laboratory were collected in clean 500mL glass jars, which were rinsed in water from the site before sample collection. Attempts were made to obtain water from clear, free-flowing parts of the channel rather than from the edge, but poor streambed access meant that this was not always possible.
4.3 Calculation of Flow Volumes
Flow volumes were calculated using the velocity-area method, in which discharge is obtained by multiplying the cross-sectional area of a stream at any point by the stream velocity at that point. This is one of the most common and easiest ways of determining the flow volume in small streams (Gordon et al. 1992). Where possible, culverts passing under roads were used in place of open-channel sections. This allows easier and more accurate calculation of cross-sectional area due to the simple geometric shapes of the culverts. At sites where more than one culvert was present, each was examined separately and the results summed to obtain a total flow for the site.
Flow velocities were calculated by measurement of the time taken for a float to travel the length of the culvert. Several runs were performed where flow appeared to be variable with time or across the culvert’s width. The length of the culvert was also recorded. Mean stream velocity for each site was then obtained from the distance and time measurements.
Sites 1 and 4, both located on the main Ellen Brook channel, were not evaluated. The flow volume at Site 1 is large and the stream channel is several metres wide. Measurement at a single point in this channel would not provide a reasonable estimate of discharge as velocity would vary significantly across the stream cross- section. Site 4 could not be included because saturation of the stream banks meant that the stream could not be accessed. At Site 8, access to culverts was restricted and a representative length of free-flowing stream was measured instead.
For all included sites, the width and height of the flow were measured at each of the culverts in order to determine the stream’s cross-sectional area at that point. For circular culverts, measurements of the culvert diameter were also taken. The equations used to calculate the cross-sectional flow area for circular culverts are
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 40 shown below (Equation 6 and Equation 7). These equations are applicable to culverts flowing at less than half full. It should be noted that flow width is easier to obtain and a more accurate measurement than flow height, as the latter is affected by measurement techniques. Flow width is therefore preferentially used in calculations of cross-sectional area, with flow height being used only to confirm the validity of the calculation.
θ r r
L Figure 13: Representative diagram of a cross-section for a circular culvert
r 2 Equation 6 Area of Segment = (θ − sinθ ) 2 L Equation 7 θ = 2*sin −1 ( ) 2r where r is the culvert radius; θ is the angle formed at the centre of the circle between the radii meeting the flow edges; and L is the width of the flow.
4.4 Sampling Dates
The four sampling rounds were in June, August, September and October. The wide distribution of sampling dates allowed identification of any changes in the catchment’s contributing areas that occurred with the progression of the winter season. Parameters and site locations were sometimes altered between rounds based on the results of previous rounds, in order to allow more thorough examination of interesting findings.
4.4.1 Sampling Round 1: 29 June 2005
The first round of sampling was undertaken on June 29th, following a period of approximately four days without rain. In this preliminary sampling round, samples were collected from Sites 1 to 6 only (Figure 12). Electrical conductivity and
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 41 temperature were measured at each of the sites, while pH and dissolved oxygen were analysed immediately upon return to the laboratory. Water samples were then stored in dark containers and refrigerated for analysis of phosphorous content and photometric absorbance at a later date.
4.4.2 Sampling Round 2: 11 August 2005
Light rainfall occurred in Perth in the second week of August, but no rain was recorded at either Pearce airbase, located within the catchment, or Perth airport, just south of the catchment, on August 10th (Appendix C). It was therefore decided that sampling should be undertaken despite the rain as it had been six weeks since the previous sampling round.
For this second sampling round, a further two sites, Sites 7 and 8, were added in order to better characterise the water signature of the Darling and Dandaragan Plateau region in the east (Figure 12).
Sampling Round 2 involved examination of the same parameters as were analysed in Sampling Round 1. However, in this sampling round air temperature was also measured in order to determine whether it was having a significant impact on the temperature of the stream.
4.4.3 Sampling Round 3: 15 September 2005
The final two rounds of sampling were intended as refinement rounds in which those substances that showed potential as suitable indicators could be examined in more detail. The final site, Site 9, was added to the sampling regime for this sampling round in order to characterise the water signature of the southern part of the Swan Coastal Plain region. For this round of sampling, electrical conductivity was measured both in the field and in the laboratory, whilst absorbance and phosphorous levels were measured from stored samples at a later date.
4.4.4 Sampling Round 4: 10 October 2005
During Sampling Round 4, flow volumes were calculated at each of the sites using the method outlined in Section 4.3 above. No water quality measurements were performed on-site for this sampling round due to the time required for cross-section
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 42 and velocity measurements. Absorbance, phosphorous and electrical conductivity were measured in the laboratory over the following days.
Two further sites, sites 2b and 8b, were added during this final sampling round. These sites were located downstream of the previous sampling locations on streams that were already included in the sampling. Rocky Creek was sampled on Old Gin Gin Road, approximately 2km downstream of the Reserve Road site where flow volumes could not be measured. Ki-it Monger Brook was sampled on Warren Road, 250m west of the Nambah Brook sampling site. The second Ki-it Monger Brook site, which was again approximately 2km downstream of the first, was sampled for the purpose of determining how the water quality changed as the stream entered the inner portions of the catchment.
4.5 Analysis
Measurements were undertaken both on site and in the laboratory. Initial laboratory work was performed in the Environmental Engineering Water Quality Lab at the University of Western Australia (UWA). Samples were then stored in dark bottles and refrigerated for further analysis in UWA’s Soil Sciences Teaching Laboratory. Details of analysis methods for each of the six water parameters are provided below.
4.5.1 Phosphorous
Phosphorous was analysed in the laboratory using the malachite green spectrophotometry method. Sample bottles were agitated to mix, and 3mL of the sample were transferred to a 10mL vial using a glass pipette. Another pipette was then used to add 1mL of the reagent: an equal volume mixture of malachite green and polyvinyl alcohol (PVA). The vial was mixed thoroughly by shaking and left for 10 minutes, during which time orthophosphate in the sample reacts with the reagent and forms green molybdenum complexes (Motomizu et al. (1983). A Shimadzu Corporation UV mini-1240 spectrophotometer was then used to measure the absorbance of the solution at 625nm, the dominant wavelength of the molybdenum complexes. The absorbance at this wavelength was converted to a phosphate concentration using the formula developed by Motomizu et al. (1983) (Equation 8).
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 43
Equation 8 A = 0.0018P + 0.0424 where A is the absorbance of the solution at 625nm; and P is the phosphate concentration in μg/L.
The method described above was initially applied to unfiltered water samples. Samples were also filtered using a 0.45µm Supor Membrane filter and re-analysed in order to determine the concentration of dissolved phosphate. This method occasionally resulted in reported phosphate levels being higher for filtered than for unfiltered samples. Where this occurred, samples were re-analysed to ensure that laboratory error was not responsible.
4.5.2 Dissolved Oxygen
Dissolved oxygen was measured immediately upon return to the laboratory using a TPS AQUA-D dissolved oxygen meter. This parameter was later discarded as the probe reading was found to be highly variable. It was also decided that laboratory measurements would not accurately correlate with on-site values, as disturbances during transport were likely to cause variation from the true on-site values.
4.5.3 pH
To ensure accuracy, pH was measured in the field as well as in the laboratory. Field measurements were taken in-stream using a calibrated TPS Model WP-81 Conductivity-Salinity-pH-Temperature meter. Laboratory measurements were taken with a similar probe, which was first calibrated using standard solutions of pH 7.0 and 4.0.
4.5.4 Temperature
Stream water temperature at each of the sites was also measured using the TPS Model WP-81 Conductivity-Salinity-pH-Temperature meter. In order for temperatures to be comparable across sites, the times of measurement were as close together as was practically possible. During the second sampling round air temperature was also measured using the same probe and a mercury thermometer.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 44
4.5.5 Electrical Conductivity Electrical conductivity was measured in-stream using the TPS Model WP-81 Conductivity-Salinity-pH-Temperature meter or a Hach Model 44600 Conductivity/TDS meter, both of which automatically compensate for temperature. The meter was calibrated prior to sampling using a solution with a known conductivity of 2.76mS/cm. To ensure accuracy, these measurements were repeated in the laboratory.
4.5.6 Colour
Several methods for colour analysis were considered, including colorimetry, visual assessment, ultraviolet absorbance at the dominant wavelength of the samples, and ultraviolet absorbance at 254nm, a standard wavelength used in the water treatment industry (CRC for Water Quality and Treatment 2005). Absorbance measured through spectrophotometry, a surrogate for true colour measurement, was deemed to be the most appropriate method of comparing colour intensity between sites. The photometric absorbance method is less costly and easier to perform than full spectral analysis, and is more scientifically accurate and reproducible than methods that rely on visual observation and comparison (Bennett and Drikas 1993). Ultraviolet and visible light spectrophotometry are both sufficient methods as humic acids absorb both ultraviolet light and low wavelengths of visible light.
The absorbance of the samples from Sampling Round 2 was measured at both the dominant wavelength of Ellen Brook catchment water, found to be approximately 304nm, and the dominant wavelength of blue light, namely 440nm, using a Shimadzu Corporation UV mini-1240 spectrophotometer. This was performed for both filtered and unfiltered samples. When used to analyse tannin levels in the water samples, this method contains an inherent assumption that all colour at the selected wavelength of a sample is a result of fulvic and humic acids. However, when used for environmental tracer studies the nature of the chemical substances causing light absorbance is not as important as spatial variation in absorbance levels throughout the catchment. Nevertheless, absorbance levels were plotted against Total Organic Carbon (TOC) concentrations in order to determine whether any of the four measurement methods showed a strong correlation with TOC.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 45
The dominant wavelength of colour in the samples was obtained by scanning a single sample for absorbance of light across the ultraviolet and low visible range of the electromagnetic spectrum. The wavelength attenuated most strongly was taken to be the dominant colour wavelength. The absorbance of all samples at this wavelength was then measured and recorded. Every sample from Sampling Round 2 was later scanned in the same way to assess the validity of applying the results of a single sample to all water from the catchment. The scan was performed across wavelengths ranging from 250 to 400nm.
In order to determine whether absorbance at 304nm was an additive property of water in the Ellen Brook catchment, progressive dilution of a representative sample with high colour intensity was performed. This allowed the correlation between sample concentration and absorbance to be examined and the mixing model to be applied appropriately.
4.5.7 Total Organic Carbon
Total Organic Carbon (TOC) was measured against standard carbon solutions using a Shimadzu TOC 5000A machine. Due to the time involved with the process, only a limited number of samples could be examined. Five samples displaying a range of colour intensities were therefore selected for analysis. These five samples were taken from Sites 1, 2, 4, 5 and 6 during Sampling Round 2.
4.6 Selection of Appropriate Environmental Indicators
The results from the first two sampling rounds were used to identify those parameters that would be most suitable for use as environmental tracers. Suitable parameters were chosen based on the level of variation between samples obtained from the eastern and western halves of the catchment. The third and fourth sampling rounds were then used to refine the level of detail provided by these indicators about the catchment.
4.7 Mixing Ratio Calculations
The flow volumes derived from each of the catchment regions were estimated by applying the environmental indicator concentrations or values to a mathematical mixing model (Equation 9 to Equation 12). The model assumes conservative mixing
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 46 and equal flow contribution by all tributaries originating in the same geographic region.
The methodology developed by Sklash et al. (1975) was adapted to apply to two catchment regions rather than old and new water. This requires the major assumption that the Swan Coastal Plain and the Darling and Dandaragan Plateau regions are the only sources of flow in the Ellen Brook. The implications of this assumption are discussed in Section 7.6.
If there are only two sources of water in the catchment, then conservation of mass requires that these sources sum to the total flow (Equation 9).
Equation 9 Qt = Q1 + Q2 where Q is flow volume; t is the total or resultant at the stream outlet (as measured at Site 1); 1 represents the Swan Coastal Plain; and 2 represents the Darling and Dandaragan Plateaus.
By assuming indicator concentrations are conservative and additive, we also have:
Equation 10 QtCt = Q1C1 + Q2C2 where C is the mean concentration or value of the environmental indicator.
Setting Qt to 1 and rearranging the above mass balance equations results in an equation that can be used to estimate the proportion of flow being contributed by the Swan Coastal Plain.
Ct - C2 Equation 11 Q1 = C1 - C2 The contribution made by the second region, the Darling and Dandaragan Plateaus, is then simply calculated as follows:
Equation 12 Q2 =1− Q1 The above calculation were repeated for each suitable indicator, and the flow contribution estimates compared to each other. The model was found to remain valid for photometric absorbance, which behaves in a predictable linear fashion. This is outlined further in Appendix B.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 47
4.7.1 Flow weightings
The above calculations use the arithmetic mean concentration of samples from the sites within each region. Due to high variation in some parameters between different sampling sites located in the same region, it was decided to repeat the calculations with the mean being weighted according to the flow volume at each site.
The results of the streamflow volume measurements were used to obtain a ratio of the size of each stream compared to each of the other streams. This ratio was then used to weight the flow within each region, and recalculate the predicted proportion of flow being derived from each of the catchment regions. These calculations were performed using Equation 9 through Equation 12 as above, but replacing the arithmetic mean with a weighted mean.
It was assumed that the flow volume ratios calculated for Sampling Round 4 could be applied to all of the sampling rounds for the purposes of the weighted flow region contribution calculations. Although it was considered likely that the relative flow volumes derived from each of the contributing areas would change as the winter season progressed, the stream size ratio within a particular region should show only minimal variation, as similar processes will be responsible for generating each of the streams in any one area. In reality, some variation in the stream size ratios would occur, but a varying ratio could not be obtained in this study as stream cross-sections were not measured for Sampling Rounds 1 through 3. It has been assumed that this variation would have little effect on the ratios obtained.
In order to allow simple calculation of streamflow volume in the future, an approximate value of the catchment slope in the region of each stream was obtained using Manning’s formula (Equation 13). Once the slope is known, all that is required for the determination of flow volume at any point in time is the depth of the stream at that time. 1 2 1 Equation 13 Manning’s Equation U = R 3 S 2 n where U is the stream velocity; R is the hydraulic radius of the channel; S is the channel slope, assumed to be constant; and n is Manning’s n, a roughness coefficient.
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5 Results and Site Observations
5.1 Water Levels
The height of the streams in the Ellen Brook catchment was observed to vary significantly between sampling rounds (Figure 14). Periods of high and low water were generally common to all streams in the catchment. The water level was observed to be highest during Sampling Round 1 and lowest during Sampling Rounds 2 and 4 (Table 2).
Water level on June 3029th Water level on June 3029th
(a) (b) Figure 14: Water levels on August 11 2005 a) Site 2 – Rocky Creek b) Site 1 – West Swan Road Bridge Markers identify the water level from the previous sampling round on June 29th. Both sites experienced significant water level drops between June 29th and August 11th.
Table 2: Observed relative water levels in the Ellen Brook catchment streams Sampling Observed Water Date Round Levels 1 June 29 Very High 2 August 11 Medium Low 3 September 15 High 4 October 10 Low
5.2 Field Results
The results of field and lab analysis are provided in Table 2 to Table 4. Neither pH nor temperature displayed strong trends between the two regions of the catchment (Table 3, Figure 15, Figure 16). pH ranged from 6.5 to 7.6 with a slight increase observed at all sites between Sampling Rounds 1 and 2. Stream temperature was highest in the small, shallow streams on the Swan Coastal Plain, and lowest in the partially shaded Rocky Creek (Table 3). The Dissolved Oxygen (DO) measurement technique resulted in highly variable readings.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 49
Table 3: Measured values for pH, Stream Temperature and Dissolved Oxygen pH, temperature and DO were excluded from monitoring for the final sampling rounds as they were found to be inadequate indicators of streamflow contributing areas. Reported pH values are the mean of field and lab measurements where both were taken. Temperature DO pH (ºCelsius) (% saturation)
Jun 29 Jun 29 Aug 11 Jun 29 Aug 11 Jun 29 Darling and Dandaragan Plateaus 2 Rocky Creek-Reserve Road 6.5 6.8 11.9 12.1 44.7 Rocky Creek- 2b - - - - - Old Gin Gin Road 7 Nambah Brook - 7.6 - 13.3 - 8 Ki-it Monger Brook - 7.6 - 13 - 8b Ki-it Monger Brook- Warren Rd - - - - - Swan Coastal Plain 3 Chandala Brook 6.8 6.9 12.4 12.8 40.6 5 Almiria Parade 7.0 7.3 13 15 47.7 6 Railway Parade 6.7 6.9 13.3 15.2 46.3 9 Near Warbrook Road - - Ellen Brook main channel 1 West Swan Road Bridge 6.9 7.2 12.6 13.75 46.3 4 Ellen Brook Brand Highway 6.9 7.1 12.3 13.3 43.4
Table 4: Measured values for Electrical Conductivity, Absorbance and TOC Reported Electrical Conductivity values are the mean of field and lab measurements where both were taken. Absorbance at 304nm Electrical Conductivity TOC (photometric absorbance (µS/cm) (mg/L) units)
Jun 29 Jun 29 Aug 11 Sep 15 Oct 08 Jun 29 Aug 11 Sep 15 Oct 08 Aug 11 Darling and
Dandaragan Plateaus Rocky Creek- 2 2350 3040 2170 2440 0.34 0.34 0.62 0.569 22.9 Reserve Road Rocky Creek- 2b - - - 1670 - - - 1.298 - Old Gin Gin Road 7 Nambah Brook - 800 570 710 NA 0.07 0.26 0.127 - 8 Ki-it Monger Brook - 2190 1440 1690 NA 0.00 0.18 0.19 - Ki-it Monger Brook- 8b - - - 1460 - - - 0.201 - Warren Rd Swan Coastal Plain 3 Chandala Brook 1147 1379 1310 1370 1.33 1.27 1.62 1.517 - 5 Almiria Parade 585 516 310 430 2.00 1.84 2.33 2.022 77.2 6 Railway Parade 605 519 420 490 2.40 2.56 2.67 2.415 90.6 9 Near Warbrook Road - - 520 540 - - 2.44 2.356 - Ellen Brook main channel West Swan Road 1 1276 1507 1140 1250 1.35 1.40 1.70 1.771 61.1 Bridge Ellen Brook Brand 4 1419 1650 1350 1450 1.14 0.95 1.47 1.31 42.7 Highway
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 50
The electrical conductivity of streams draining the Plateau Region was significantly higher than that of Swan Coastal Plain tributaries (Table 4, Figure 17). High values of electrical conductivity corresponded to periods of low streamflow, with a peak being observed in August, whilst low conductivity was recorded when streamflow was at its highest during Sampling Rounds 1 and 3.
Absorbance displayed an equally strong trend, with sites on the Swan Coastal Plain showing high absorbance, and sites representing the Darling and Dandaragan Plateaus showing low or negligible absorbance at the analysis wavelength of 304nm (Table 4, Figure 18).
Table 5: Measured values for phosphorous Suspended or Particulate Phosphorous is taken as the difference between Total and Dissolved Phosphorous. Unfiltered Suspended Phosphate Phosphorous Phosphorous (µg/L) (µg/L) (µg/L)
Jun 29 Jun 29 Aug 11 29-Jun 11-Aug Sep 15 Oct 08 Sep 15 Oct 08 Sep 15 Oct 08 Sep 15 Oct 08 Darling and
Dandaragan Plateaus Rocky Creek- 2 21 26 20 15 1 4 13 5 20 22 7 10 Reserve Road Rocky Creek- 2b - - - 108 - - - 98 - - - 10 Old Gin Gin Rd 7 Nambah Brook NA 299 5 0 - 211 0 0 - 88 5 0 Ki-it Monger 8 NA 70 11 2 - 36 0 0 - 34 11 2 Brook Ki-it Monger 8b Brook- Warren - - - 0 - - - 0 - - - 0 Rd Gnangara Mound and West 3 Chandala Brook 476 338 243 211 225 181 208 161 251 157 35 50 5 Almeria Parade 432 254 228 195 189 214 216 159 243 40 12 36 6 Railway Parade 532 289 234 186 245 210 236 167 287 79 0* 19 Near Warbrook 9 - - 264 218 - - 289 228 - - 0* 0* Road Ellen Brook main channel West Swan 1 432 376 231 199 191 191 185 206 241 185 46 0* Road Bridge Ellen Brook 4 365 254 207 219 164 151 193 139 201 103 14 80 Brand Highway * Calculation resulted in a negative concentration. Sample analysis was repeated but similar results were obtained. The reported values for unfiltered and filtered samples in these cases are a mean of the two analyses.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 51
pH Plateau Region Swan Coastal Ellen Brook Plain main channel 8 7 29-Jun 6 5 11-Aug 4 pH 3 2 1 0 '2 7 8 3 5 6 1 4 Site
Figure 15: pH values at Sites 1 to 8 over the first two sampling rounds
Temperature Swan Coastal Plain Ellen Brook 16 Plateau Region main channel 14 29-Jun 12 10 11-Aug 8 6 4 2 0 Stream Temperature (ºC) Temperature Stream '2 7 8 3 5 6 1 4 Site
Figure 16: Stream temperature at Sites 1 to 8 over the first two sampling rounds
Electrical Conductivity
3500 Plateau Region 3000 2500 Ellen Brook 2000 Swan Coastal Plain main channel 1500 1000 500 0 Conductivity (uS/cm) 278 3569 14 Site 29-Jun 11-Aug 16-Sep 10-Oct Figure 17: Electrical Conductivity at Sites 1 to 9
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 52
Absorbance at 304nm
3.0 Swan Coastal Plain Ellen Brook 2.5 main channel 2.0 1.5 Plateau Region 1.0 Absorbance (Photometric 0.5 absorbance units) absorbance 0.0 278 3569 14 Site 29-Jun 11-Aug 16-Sep 10-Oct Figure 18: Photometric absorbance at Sites 1 to 9 The chosen absorbance analysis method is examination of unfiltered sample water at the 304nm wavelength
High levels of phosphorous were measured in both filtered and unfiltered samples (Table 5, Figure 19, Figure 20). In some cases, measured orthophosphate was higher in the filtered sample than it was in the corresponding unfiltered sample. This is an analytical error but the magnitude of the difference in all cases is small. In these cases it has been assumed that all orthophosphate in the sample was present in dissolved form. In unfiltered samples, phosphorous levels showed a substantial decreasing trend as the winter season progressed.
Unfiltered Phosphorous
Swan Coastal Plain 600 Ellen Brook main channel
g/L) 500 μ 400 Plateau Region 300 200 100
Phosphorous ( Phosphorous 0 278 3569 14 Site 29-Jun 11-Aug 15-Sep 10-Oct
Figure 19: Phosphorous levels in unfiltered samples from Sites 1 to 9
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 53
Phosphate
600 500 g/L) Ellen Brook μ 400 Swan Coastal Plain main channel 300 Plateau Region 200 100 Phosphate ( Phosphate 0 278 3569 14 Site 29-Jun 11-Aug 15-Sep 10-Oct Figure 20: Phosphate levels in filtered samples from Sites 1 - 9
5.2.1 Absorbance method validity checks
High variation in colour intensity was seen throughout the catchment, with colour intensity appearing to be much higher in streams draining the Swan Coastal Plain than in streams draining the Dandaragan and Darling Plateaus (Figure 21). Colour intensity as seen by the naked eye correlated with the measured absorbance.
The dominant wavelength of a Swan Coastal Ellen Brook Plateau representative sample from the first Plain Main Channel Region sampling round was found to be 304nm. Analysis of the dominant wavelengths from samples taken in Sampling Round 2 showed some variation in maxima, with the location of the peak ranging from 297 to 339.5nm (Table 6). Peak wavelength was found to decrease as the 6 5 3 1 2 8 maximum absorbance increased Figure 21: Water samples of varying (Table 6). The absorbance value at colour taken from 6 catchment sites on the peak also related to apparent August 11 colour intensity as seen by the naked eye.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 54
Table 6: Dominant sample wavelength and corresponding absorbance for Sampling Round 2 The dominant wavelength is that of maximum absorbance between 250nm and 400nm. The sample from Site 6 had a minor peak at approximately 320nm, but continued to increase in the UV range at wavelengths beyond 250nm. Wavelength of Absorbance at peak Site number peak absorbance (photometric (nm) absorbance units) 1 298.0 1.53 2 307.0 0.39 3 298.5 1.28 4 298.5 1.03 5 297.0 1.98 6 No peak in range - 7 339.5 0.183 8 314.0 0.17
Table 7: Absorbance values in photometric absorbance units of water samples from Sampling Round 2 at 304nm and 440nm 304nm 304nm 440nm 440nm TOC Unfiltered Filtered Unfiltered Filtered
Scarp (East) 2 Reserve Road 0.34 0.36 0.059 0.022 22.9 7 Nambah Brook 0.07 0.07 0.033 0.017 8 Ki-it Monger Brook 0.00 0.05 0.062 0.022 Gnangara Mound and West 3 Chandala Brook 1.27 1.08 0.222 0.171 5 Almiria Parade 1.84 1.87 0.293 0.271 77.2 6 Railway Parade 2.56 2.37 0.397 0.361 90.6 Ellen Brook main channel 1 West Swan Rd Bridge 1.40 1.43 0.208 0.216 61.1 4 Ellen Brook Brand Hwy 0.95 0.90 0.164 0.135 42.7
Absorbance at 304nm displayed a significantly larger range of values than absorbance in the blue light wavelengths (Table 7 and Figure 22a). Total Organic Carbon levels in the water samples were found to be strongly correlated with absorbance for all analysis methods considered (Table 8 and Figure 22b). Additionally, filtered and unfiltered samples displayed similar absorbance values at both 304nm and 440nm wavelengths, with neither having a significantly stronger correlation to Total Organic Carbon than the other (Table 8 and Figure 22b).
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 55
304 unfiltered 304 filtered 440 unfiltered 440 filtered TOC TOC (mg/L) 3.0 120 3.0
2.5 100 2.5
2.0 80 2.0
1.5 60 1.5 Absorbance 1.0 40 Absorbance 1.0
0.5 20 0.5 (Photometric Absorbance Units) (Photometric (Photometric Absorbance(Photometric Units)
0.0 0 0.0 278 356 14 0 20406080100 a) b) Site number TOC (mg/L)
Figure 22: Absorbance of Sampling Round 2 water samples at 304nm and 440nm
Table 8: Correlation between TOC and photometric absorbance
Data set r²
304nm - filtered 0.9969 304nm - unfiltered 0.9803 440 nm - filtered 0.9914 440nm - unfiltered 0.9721
A strong linear correlation was observed between percentage dilution of the Site 5 sample and the level of absorbance (Table 9 and Figure 23). The equation for this correlation was:
Equation 14 y = 1.98x – 0.14 where y is the photometric absorbance of the unfiltered sample at 304nm; and x is the sample’s percentage dilution.
The near perfect linear correlation meant that the mass balance model was valid for this parameter, as the extra terms in the linear equation cancel out when the transformation from absorbance to dilution is applied (Appendix B).
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Results and Site Observations 56
Table 9: Absorbance of water sample with progressive dilution The sample was taken during Sampling Round 2 from Site 5, which displayed typical colour levels for the Swan Coastal Plain region Percentage original sample Photometric Absorbance at 304nm 100% 1.84 75% 1.34 50% 0.86 25% 0.35
2 1.8 1.6 1.4 1.2 1 y = 1.98x - 0.14 0.8 R2 = 0.9999
wavelength 0.6 0.4 Absorbance at 304nm 0.2 0 0% 25% 50% 75% 100% Percentage of pure sample water
Figure 23: Relationship between ultraviolet absorbance and water dilution The sample was taken during Sampling Round 2 from Site 5, which displayed typical colour levels for the Swan Coastal Plain region
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Calculations 57
6 Calculations
6.1 Cross-sections and Flow Volume Calculations
Table 10: Stream Dimensions and Flow Times Measured October 10th 2005. Multiple values indicate that more than one run was performed. Width Height Site Culvert Shape and Length of Float Travel Time of flow of flow No. No. Dimensions Culvert (m) Time (s) (cm) (cm) Circular 2 12:05 2-1 26 9 8.7 21, 22, 23 35cm diameter Circular 2-2 22 3.5 8.7 22* 35cm diameter Rectangular 3 12:50 3-1 115 38 17 95, 95 1.15m wide Rectangular 3-2 115 38 17 320 1.15m wide Rectangular 3-3 115 38 17 360 1.15m wide Rectangular 3-4 115 38 17 No flow 1.15m wide Rectangular 3-5 115 38 17 180 1.15m wide Rectangular 3-6 115 38 17 320, 280 1.15m wide Rectangular 3-7 115 38 17 400 1.15m wide Rectangular 3-8 115 38 17 460 1.15m wide Rectangular 3-9 115 38 17 No flow 1.15m wide Circular 5 13:30 5-1 50 15 12.4 13,13 85cm diameter Circular 5-2 41 12 12.4 10,11 85cm diameter
Arch 6 2:00 6-1 65 32 14.8 65 65cm base width Arch 6-2 60 32 14.8 80 60cm base width Circular 7 11:30 7-1 44 5 9.8 18, 21, 19, 18 90cm diameter Circular 7-2 36 4 9.8 19* 90cm diameter
8 11:40 8-1 Streambed used 100 13 5.6 14, 16, 14, 14
Circular 9 2:15 9-1 19 N/A 12.8 58 45cm diameter Circular 9-2 18 N/A 12.8 245 45cm diameter * Estimated value
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The measurements taken in order to perform velocity-area calculations are provided in Table 10. Flow volumes obtained from these measurements and site observations at the time of sampling are provided below. Appendix D contains further detail on the calculations performed in order to obtain cross-sectional areas from the height and width measurements. Estimates of channel slope obtained from the area-velocity measurements, which can be used in the future to obtain flow volumes, are included as Appendix E.
6.1.1 Darling and Dandaragan Plateau Sites
Site 2: Rocky Creek (Old Gingin Road) Flow velocity could not be measured at the normal Rocky Creek sampling location off Reserve Road due to blockages in the culvert and restricted stream access due to heavy vegetation. Flow was instead examined further downstream where Rocky Creek crosses Old Gingin Road. Visual observation suggests that the flow volume increases dramatically between these two sites. The culverts measured at Site 2 were 35cm circular concrete pipes partially obstructed by vegetation (Figure 24).
Width of flow 0.26m
Width of 0.75m flow 0.22m Diameter Diameter 0.35m 0.35m
0.09m 0.035m
2-1 2-2 Figure 24: Cross-section of Rocky Creek culverts on Old Gin Gin Road
Table 11: Flow volume calculation for Rocky Creek downstream of Site 2 Time taken to travel 8.7m Flow cross- Culvert Velocity Flow volume (s) sectional area Number (m/s) (m³/s) Run 1 Run 2 Run 3 Mean (m²) 2-1 21 22 23 22 0.395 0.0104 0.0041 2-2 N/A* 0.395* 0.0058 0.0023 Total flow at site: 0.0064 m³/s * Travel time for the second culvert could not be obtained due to a small pipehead dam partially blocking flow inside the culvert, and preventing the movement of floats. It has been assumed that water was travelling at the same speed through the two culverts
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Calculations 59
Site 7: Nambah Brook Flow in Nambah Brook passes under Warren Road via two 90cm diameter rough walled circular concrete culverts, which are not obstructed by vegetation. At the time of observation flow was unequally distributed between the two culverts (Figure 25).
Width of Width of flow 0.36m flow 0.44m Diameter Diameter 0.90m 0.90m
0.05m 0.04m 7-1 7-2 Figure 25: Cross-section of Nambah Brook culverts at Site 7
Table 12: Flow volume calculation for Nambah Brook at Site 7
Time taken to travel 9.8m Flow cross- Culvert Velocity Flow volume sectio area Number Mean time in (m/s) (m³/s) Run 1 Run 2 Run 3 Run 4 (m²) seconds 7-1 18 21 19 18 19 0.516 0.017 0.0088 7-2 N/A N/A N/A N/A 19* 0.516 0.009 0.0047 Total flow at site: 0.014 m³/s * Travel time for the second culvert could not be obtained due to an invisible obstruction preventing the movement of floats. It has been assumed that water was travelling at the same speed through the two culverts.
Site 8: Ki-it Monger Brook At this location, the stream channel can be approximated by one rectangular section and one triangular section (Figure 26). The streambed was made up of smooth gravel pebbles up to 10cm in diameter, with no vegetation obstructing flow.
8-2 0.13m
0.25m 0.75m
Figure 26: Cross section of Ki-it Monger Brook at Site 8
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Table 13: Flow volume calculation for Ki-it Monger Brook at Site 8
Time taken to travel 9.8m Flow cross- Culvert Velocity Flow volume sectional area Number Mean time (m/s) (m³/s) Run 1 Run 2 Run 3 Run 4 (m²) in seconds 0.25*0.13/2 8-1 0.063 14 16 14 14 14.5 0.39 =0.01625 0.75 * 0.13 8-2 0.038 =0.0975 Total flow at site: 0.101 m³/s
6.1.2 Swan Coastal Plain Sites
Site 3: Chandala Brook Chandala Brook passes under Brand Highway via a set of 9 rectangular concrete channels 17m in length. Each channel is 1.15m wide (Figure 27). The stream bends almost 90° as it enters the culverts. Two of the channels were stagnant at the time of observation, possibly due to blockages, with the other seven displaying differing flow velocities (Table 14). The total flow at this site was 0.22m³/s at the time of sampling (Table 14).
1.15m
0.38m
3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 Figure 27: Cross-section of Chandala Brook channels at Site 3
Table 14: Flow volume calculation for Chandala Brook at Site 3 Time taken to travel length of Stream Culvert Flow volume Culvert stream (17m) Velocity Depth Width (=velocity* Number (m/s) (m) (m) depth*width) Run 1 Run 2 Mean time (s) (m³/s) 3-1 1:35 1:35 95 0.179 .38 1.15 0.078 3-2 5:20 - 320 0.053 .38 1.15 0.023 3-3 6:00 - 360 0.047 .38 1.15 0.021 3-4 No flow - - 0 .38 1.15 0.000 3-5 3:00 - 180 0.094 .38 1.15 0.041 3-6 5:20 4:40 300 0.057 .38 1.15 0.025 3-7 6:40 - 400 0.043 .38 1.15 0.019 3-8 7:40 - 460 0.037 .38 1.15 0.016 3-9 No flow - - 0 .38 1.15 0.000 Total flow at site: 0.223 m³/s
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Site 5: Railway Parade Streamflow at the Site 5 sampling location on Almeria Parade could not be measured due to restricted access and a tortuous channel. Instead, the stream velocity and cross-section were measured approximately 50m upstream where the stream passes under Railway Parade. Flow under Railway Parade occurs through two 85cm diameter rough-walled concrete culverts (Figure 28).
0.85m 0.85m Width of flow 0.50m Width of flow 0.41m
0.15m 0.12m
5-1 5-2 Figure 28: Cross-section of culverts upstream of Site 5
Table 15: Flow volume calculation at culverts upstream of Site 5 Culvert Culvert Length Time Taken Velocity Flow Area Flow volume Number (m) (s) (m/s) (m²) (m³/s) 5-1 12.4 13 0.954 0.0277 0.0264 5-2 12.4 10.5 1.181 0.0146 0.0172 Total flow at site: 0.0436 m³/s
Site 6: Railway Parade between Stock and Savy Roads Flow at Site 6 passes under Railway Parade via three arch-shaped concrete culverts of unequal width (Figure 29). At the time of observation, two of the culverts were freely flowing and the other stagnant due to blockage by vegetation and debris at the culvert entrance.
6-1 6-2 6-3
Stagnant, no 0.32m 0.32 flow
0.65 0.60
Figure 29: Cross-section of culverts at Site 6 Flow occurred in the rectangular portion of the culvert only
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Table 16: Flow velocity and Flow volume calculations for Site 6 Culvert Time Flow Culvert Flow Culvert Velocity Flow volume Length Taken Depth Width Area Number (m/s) (m³/s) (m) (s) (m) (m) (m²) 6-1 14.8 65 0.228 0.32 0.65 0.208 0.0474 6-2 14.8 90 0.164 0.32 0.60 0.192 0.0315 6-3 14.8 No flow - - - - Total flow at site: 0.079 m³/s
Site 9: North of Warbrook Road Flow at Site 9 passed through two 45cm diameter circular concrete culverts (Figure 30). The height of the flow could not be measured at this site due to low accessibility, but flow width measurements were taken. This site experienced very low flow, possibly due to a small dam 50m upstream of the sampling location, and low water levels on the day of sampling.
0.45m 0.45m
Width of flow 0.19m Width of flow 0.18m
9-1 9-2
Figure 30: Cross-section of culverts at Site 9
Table 17: Flow volume calculations at Site 9 Flow volume Culvert Culvert Length Time Taken Velocity Flow Area (=velocity* area) Number (m) (s) (m/s) (m²) (m³/s) 9-1 12.8 245 0.0522 0.0027 0.00014 9-2 12.8 58 0.2207 0.0023 0.0051 Total flow at site: 0.00065 m³/s
6.1.3 Summary of Flow volumes
There was a large range of flow volumes, with the smallest stream, Site 9, having a flow velocity approximately three orders of magnitude lower than Chandala Brook, the largest of the tributaries (Table 18). The mean flow volume in the Ellen Brook in October between 1996 and 2003 was approximately 76 400 m³/day (Zammit 2005 pers. comm.). Thus, the sampled streams, which were flowing at 40 500 m³/day at
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Calculations 63 the time of sampling, can be estimated to be providing around half of the total catchment discharge.
Table 18: Summary of flow volumes at the seven contributing sites Calculated flow Site number Calculated flow (m³/s) (m³/d) 2 0.0064 553.0 3 0.223 19267.2 5 0.0436 3767.0 6 0.079 6825.6 7 0.014 1209.6 8 0.101 8726.4 9 0.00065 56.2 Total 0.468 40 500 m³/d
6.2 Proportion of Total Flow Calculations
6.2.1 Flow ratios
Site 8, Ki-it Monger Brook, dominates the flow for the Darling and Dandaragan Plateau Region, with the ratio for Sites 2, 7 and 8 being 1:2:16 (Table 19). The ratio for Swan Coastal Plain Sites 3, 5 and 6 is 5:1:2 (Table 19). As Site 9 displayed a flow volume far lower than any of the other sites in the region, and over 300 times lower than the flow at Chandala Brook, it was taken to be providing negligible contribution to the mean water signature of the region and excluded from the flow ratios and weighting calculations.
Table 19: Flow volumes relative to the lowest flowing sites Site 9 has been excluded due to disproportionately low flow volumes Darling and Dandaragan Plateau Swan Coastal Plain Flow volume Calculated Calculated Flow volume Site relative to Site Site flow volume Flow volume relative to Site 5 2 2 553.0 1 3 19267.2 5 7 1209.6 2 5 3767.0 1 8 8726.4 16 6 6825.6 2 Total for Total for 10489 19 29916 8 region region
6.2.2 Application of mass balance mixing model
The predicted proportion of flow being contributed to the Ellen Brook by each of the regions for several of the sampling parameters is shown below (Table 20 to Table 23). Predictions could not be obtained by pH for either Sampling Round 1 or
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Sampling Round 2 due to low variation and the lack of an intermediate value for the Ellen Brook main channel region (Table 3). Dissolved oxygen was not included as the data accuracy was poor. Further detail on the contribution ratio calculations and associated error is provided as Appendix F.
Equal contribution
Table 20 Estimates of contribution to total flow for the two-region system calculated from non-weighted mean parameter levels Note that the TOC prediction differs from that given by colour absorbance due to the difference in the number of sites used. Sampling Unfiltered Mean for Colour Region Colour EC Temp. TOC Mean Round P and EC only SCP 0.90 0.64 0.68 0.70 N/A 0.73 0.66 1 DDP 0.10 0.36 0.32 0.30 N/A 0.27 0.34
SCP 0.72 0.42 0.62 0.63 0.60 0.57 2 Error DDP 0.28 0.58 0.38 0.37 0.40 0.43 SCP 0.95 0.71 0.34 N/A N/A 0.67 0.53 3 DDP 0.05 0.29 0.66 N/A N/A 0.33 0.47 SCP 0.98 0.83 0.40 N/A N/A 0.74 0.62 4 DDP 0.02 0.17 0.60 N/A N/A 0.26 0.38 SCP – Swan Coastal Plain region DDP – Darling and Dandaragan Plateau region Error – mass balance model failed due to non-intermediary values in the main stream channel N/A – predicted flow volume could not be obtained due to lack of data
Equal contribution, exclusion of Site 7
Table 21 Estimates of contribution to total flow for the two-region system, calculated by excluding Site 7 from the non-weighted mean parameter levels Note that the predictions for Sampling Round 1 are the same as presented in Table 20 Sampling Unfiltered Mean for Colour Region Colour EC Temp. TOC Mean Round P and EC SCP 0.90 0.64 0.68 0.70 N/A 0.73 0.66 1 DDP 0.10 0.36 0.32 0.30 N/A 0.27 0.34 SCP 0.72 0.61 0.67 0.63 0.66 0.67 2 Error DDP 0.28 0.39 0.33 0.37 0.34 0.33 SCP 0.95 0.70 0.57 N/A N/A 0.74 0.64 3 DDP 0.05 0.30 0.43 N/A N/A 0.26 0.36 SCP 0.98 0.82 0.60 N/A N/A 0.80 0.71 4 DDP 0.02 0.18 0.40 N/A N/A 0.20 0.29 SCP – Swan Coastal Plain region DDP – Darling and Dandaragan Plateau region Error – mass balance model failed due to non-intermediary values in the main stream channel N/A – predicted flow volume could not be obtained due to lack of data
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Weighted contribution
Table 22 Estimates of contribution to total flow for the two-region system, calculated from flow-weighted mean parameter levels Sampling Unfiltered Mean for Colour Region Colour EC Temp. TOC Mean Round P and EC only SCP 0.89 0.75 0.76 0.99 N/A 0.85 0.76 1 DDP 0.11 0.25 0.24 0.01 N/A 0.15 0.24 SCP 0.84 0.56 0.71 0.56 0.70 2 Error Error DDP 0.16 0.44 0.29 0.30 0.30 SCP 0.97 0.85 0.58 N/A N/A 0.80 0.72 3 DDP 0.03 0.15 0.42 N/A N/A 0.20 0.28 SCP 0.98 0.98 0.63 N/A N/A 0.86 0.81 4 DDP 0.02 0.02 0.37 N/A N/A 0.14 0.19 SCP – Swan Coastal Plain region DDP – Darling and Dandaragan Plateau region Error – mass balance model failed due to non-intermediary values in the main stream channel N/A – predicted flow volume could not be obtained due to lack of data
Weighted contribution, exclusion of Site 7
Table 23 Estimates of contribution to total flow for the two-region system, calculated by excluding Site 7 from the flow-weighted mean parameter levels Note that the predictions for Sampling Round 1 are the same as presented in Table 20 Mean for Sampling Unfiltered Region Colour EC Temp. TOC Mean Colour and Round P EC SCP 0.89 0.75 0.76 0.99 N/A 0.85 0.76 1 DDP 0.11 0.25 0.24 0.01 N/A 0.15 0.24 SCP 0.84 0.62 0.71 0.72 0.73 2 Error Error DDP 0.16 0.38 0.29 0.28 0.27 SCP 0.97 0.85 0.66 N/A N/A 0.82 0.75 3 DDP 0.03 0.15 0.34 N/A N/A 0.18 0.25 SCP 0.98 0.98 0.69 N/A N/A 0.88 0.83 4 DDP 0.02 0.02 0.31 N/A N/A 0.12 0.17 SCP – Swan Coastal Plain region DDP – Darling and Dandaragan Plateau region Error – mass balance model failed due to non-intermediary values in the main stream channel N/A – predicted flow volume could not be obtained due to lack of data
The Swan Coastal Plain is estimated to contribute approximately 60% to 80% of the flow at Site 1. The highest estimate of the Swan Coastal Plain region’s contribution was given by the weighted mean calculations that excluded Site 7 from the data (Figure 31).
The calculated trend in catchment contribution ratios is an initial high contribution by the Swan Coastal Plain, followed by a period around August when the Plateau contribution increases. Later in the season, the system moves back towards high contribution from the Swan Coastal Plain (Figure 31).
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Calculations 66
0.90
0.80
0.70 Region 0.60
Proportion of flow at Site 1 0.50
contributed by Swan Coastal Plain Jun-05 Jul-05 Aug-05 Sep-05 Oct-05 Sampling Date Non-weighted all sites Non-weighted, no Site 7 Weighted, all sites Weighted, no Site 7
Figure 31: Estimated Flow Contribution by the Swan Coastal Plain Region Plotted values are the mean estimates made by Electrical Conductivity and Photometric Absorbance for each of the four weighting methods.
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7 Discussion
7.1 General Trends in the Data
Some clear trends in water quality emerged from the sampling regime. These are discussed where they influence either identification of suitable environmental indicators or determination of catchment contributing areas. It should be noted however that the main aim of this study was not to analyse water quality trends, but rather to use water quality parameters to examine the contribution to Ellen Brook flow made by different areas at discrete points in time.
Electrical conductivity was observed to peak in August at all sampling locations (Figure 17). Low water levels at this time suggest that the peak may be directly linked to individual rainfall events rather than seasonal patterns. It is possible that a constant catchment salt load was more concentrated in the smaller volume of water available at this time. Clear differentiation between the Darling and Dandaragan Plateau and Swan Coastal Plain hydrological units was still observed despite high electrical conductivity results throughout the catchment on this date.
The majority of waters sampled in the catchment displayed phosphorous enrichment, with filtered phosphate at the majority of sites well above 65μg/L, the ANZECC guideline limit for total phosphorous in south-western Australian slightly disturbed lowland rivers (ANZECC and ARMCANZ 2000). The phosphorous data also shows evidence of nutrient flushing or uptake. At most sites there is a clear decrease in phosphorous concentrations of the unfiltered samples as the season progresses (Figure 19). This is consistent with the findings of the Swan River Trust nutrient monitoring program, which has identified a winter peak in total phosphorous levels in the catchment (Swan River Trust 2000). The trend suggests that as the season progresses the influence of soil properties on the water signature decreases, and the signature becomes closer to that of unpolluted rain or groundwater.
One explanation for the decreasing phosphorous levels is that nutrient sources in the soil are subject to vegetation uptake and therefore are diminished. This, combined with the dissolution of the previously applied phosphorous in the first winter rain, means that phosphorous levels display a significant decrease to less than half their June values by October. The decreasing concentration trend was not seen to the same extent in the filtered phosphate samples, with Swan Coastal Plain and Ellen
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 68
Brook main channel phosphate levels remaining high at all times. This implies that a reasonably constant, diffuse source is present, or that dissolved phosphate has infiltrated the groundwater body and is continuously leached.
As phosphorous decreases there is a concurrent increase in pH. pH increased at every site between June 29 and August 11, with the overall mean moving from 6.8 to 7.2. Unpolluted rainwater has a pH of between 5 and 6 (Holper 1996). There is no clear correlation between the magnitude of pH increase and phosphorous decrease (Figure 32). pH and phosphorous levels therefore do not appear to be controlled by the same catchment property. The main conclusion that can be drawn from combined examination of pH and phosphorous trends is that the groundwater signature in the Ellen Brook becomes stronger as the season progresses. This implies that late in the season a greater proportion of streamflow originates from groundwater aquifers, probably including the Gnangara mound.
250
200 g/L) μ 150 y = -574.26x + 243.63 100 R2 = 0.3599
50 phosphorous ( Decrease in unfiltered 0 0.0 0.1 0.2 0.3 0.4 0.5 Increase in pH (pH units) Figure 32: pH and phosphate changes between Sampling Rounds 1 and 2 The changes in pH and phosphorous at each site show only a weak negative correlation
7.2 The effect of site location
Site selection had a major influence on the results of the project. A limited number of sampling locations could be included, and stream access was one of the major contributing factors to site selection. This method is not ideal as it meant that the sites were all located at different distances from the main Ellen Brook channel. This affects the streamflow weighting calculations, as discharge volume increases downstream.
In addition to streamflow volume calculations, site location also impacts the reported water signature for each stream. This is highlighted by the values of the
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 69 environmental indicators reported for sites 2b and 8b. It is thought that as the sampled streams move towards their confluence with the Ellen Brook itself, they pick up the characteristics of the River Flood Plain region and their signature moves away from the true characteristics of the Darling and Dandaragan Plateaus. Both phosphorous and absorbance increased by an order of magnitude in Rocky Creek, but not in Ki-it Monger Brook, whilst electrical conductivity decreased in both streams. The fact that in both cases the sites were located only 2km from the original stream sampling location emphasises the major influence that sampling location plays on stream properties.
The introduction of new sampling locations between sampling rounds introduces error to the calculations. Each new site was found to have a significant effect on the mean water signature of a region. Ideally, all potential sampling locations would have been identified before sampling commenced and thus included in all sampling rounds.
A large number of the Ellen Brook tributaries flow partly or wholly through private land, including the Vines Golf Course, RAAF Pearce training base and privately owned pastures and farmland. Access to these parts of the catchment could greatly improve the accuracy of the technique. It would allow more systematic calculation of the discharge of tributaries, as each stream could be examined where it enters the Brook. It would also allow streams that originate in the central portion of the catchment to be analysed, meaning that a three-system model of the catchment could be implemented.
7.3 Validity of the colour absorbance method
The dilution testing that was performed on the Site 5 sample confirmed that absorbance increases linearly with the concentration of Total Organic Carbon, which contains colour producing functional groups (Figure 23). This relationship holds down to a 25% dilution, but may not be valid at lower levels. The linear correlation means that mixing models can be applied to this tracer in the same way as for other, additive indicators (Appendix B).
The strong correlation between the photometric absorbance and Total Organic Carbon levels of the samples indicates that organic carbon is the major contributor of stream colour at the 304nm wavelength. It also suggests that the chemical makeup
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 70 of TOC is similar throughout the catchment. Transformations of organic material with time are known to occur (Choudry 1984; Lydersen 1998). These need to be examined in more detail in order to determine whether use of the 304nm wavelength as a surrogate for TOC is valid at all times throughout the winter season. However, spectrophotometry at any wavelength is valid for the purpose of hydrograph separation as long as there is a clear difference between the measured absorbance of two regions.
Although absorbance at both wavelengths and for both filtered and unfiltered sample types showed high correlation with Total Organic Carbon, use of the 304nm wavelength is more reliable for application to the set of mass balance equations as the much larger range of results means that percentage error in the final predictions will be smaller. This wavelength was therefore chosen as the preferred measurement option. Unfiltered samples were used because the added time required for filtering samples was not justified by the very minor increase in correlation (Table 8).
7.4 Selection of Appropriate Indicators from Preliminary Sampling
The first two sampling rounds were used to identify the substances that could most easily be applied to tracer hydrology. Observations from the preliminary sampling rounds and the validity of using each of the analysed parameters as an indicator of streamflow origin are discussed below.
7.4.1 Electrical Conductivity
Electrical conductivity showed strong spatial distribution gradients, with Swan Coastal Plain sites generally displaying significantly higher conductivity than Darling and Dandaragan Plateau sites. The exception to this was Nambah Brook, which was sampled at Site 7. Although not the least saline of all the sites in the catchment, Nambah Brook displayed conductivity readings an order of magnitude lower than the other sampled streams emanating from the Plateaus, and closely resembled the conductivity signature of the Swan Coastal Plain. The implication of this is that Site 7 significantly lowers the mean electrical conductivity reported for the Plateau region, and may bias contributing area calculations to report larger flow volumes from the
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 71 region than actually exist. This is discussed further in Section 7.6 (Computation of Flow Contribution Proportions).
The Ellen Brook main channel displayed a mean conductivity reading between those of the Plateau and Swan Coastal Plain hydrological units. Initial, non-quantitative examination suggested an approximate 1:1 mixing ratio over Sampling Rounds 1 and 2. That is, the use of electrical conductivity predicted that the Plateaus and the Swan Coastal Plain contribute equally to flow in the main channel of the Brook. This initial analysis excludes the effect of other sources of water to the main stream and considers all streams within a region to have equal weight.
7.4.2 Colour
Like electrical conductivity, colour intensity measured through photometric absorbance met the requirement for strong spatial distribution gradients. Over the first two sampling rounds, the sites draining the Plateau region displayed a mean absorbance of 0.19, equivalent to a 16% solution of water from the Swan Coastal Plain, which had a mean measured absorbance of 1.90 (Equation 14). The Ellen Brook main channel displayed absorbances intermediate to those of the two peripheral regions. Use of colour absorbance suggested a similar mixing ratio to that predicted by electrical conductivity, but with a slightly higher proportion of flow being calculated to come from the Swan Coastal Plain region.
Low colour and TOC levels on the Plateaus are thought to be due to the large proportion of cleared the land in this region. This is supported by the fact that Rocky Creek, which flows through a region of the Dandaragan Plateau that still contains some native vegetation, displayed slightly higher colour levels than the other two sites.
7.4.3 pH pH was found to be slightly higher in waters draining the Dandaragan and Darling Plateaus than in those draining the Swan Coastal Plain, with mean readings of 7.1 and 6.9 respectively during the first two rounds of sampling. However, this difference is minimal compared to the accuracy of the equipment used. Additionally, individual examination of each of the sampling rounds does not suggest predictable mixing patterns. On the second sampling date, Plateau waters were slightly more acidic than
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 72 those of the Swan Coastal Plain, but the pH observed in the main channel was higher than in either contributing region. It was concluded that pH does not adequately fulfil the spatial discrimination requirements of environmental indicators.
7.4.4 Phosphorous
In addition to the decreasing seasonal trend mentioned previously, phosphorous appeared to show some spatial distribution gradients over the first two sampling rounds, with mean concentrations for both filtered and unfiltered samples being lower for the Plateau region than for the Swan Coastal Plain. This substantiates the hypothesis that the lateritic soils of the Darling and Dandaragan Plateaus bind excess phosphorous that is applied to the soil and thus prevent it from entering the stream.
Mixing between streams from the Plateaus and Swan Coastal Plain was not evident in the Ellen Brook main channel phosphorous data. The mean phosphorous level for the Brook itself was higher than for either of the two inputting regions. This implies that phosphorous enters the stream from another source. Possible sources include: i) sampled streams downstream of sampling locations; ii) unsampled stream channels; and iii) direct groundwater inputs to the main channel rather than its tributaries.
Based on the above information, it was decided that the first two sampling rounds were insufficient to determine whether phosphorous can be used as an environmental indicator in the Ellen Brook catchment for the purpose of determining contributing areas. Therefore, measurement of phosphorous concentrations in both filtered and unfiltered samples was continued into the final sampling rounds.
7.4.5 Stream Temperature
As would be expected, the highest temperatures were recorded in small, unshaded streams, particularly Sites 5 and 6. The shallow nature of these streams makes them more susceptible to warming from solar radiation and less likely to retain the cool water signatures of precipitation or groundwater. The Ellen Brook main channel at Site 1, however, exhibits the largest flow volume but was not the coolest of the sampling sites. This is evidence that factors other than solar radiation are influencing
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 73 stream temperature. These other factors could include different base temperatures in water sources from different regions of the catchment, influences such as shading and stream friction, or systematic sampling bias that is independent of the natural stream conditions.
On initial inspection, streams on the eastern side of the catchment appeared to be somewhat cooler than those on the west. Intermediate temperatures in the Ellen Brook main channel indicate that water temperature could possibly be used to spatially discriminate water sources in this catchment. One explanation of differences in stream temperature is that water is originating from groundwater bodies with different temperatures from each other. However, as the temperature difference is small (less than 2°C) it is difficult to eliminate the influence of sampling strategy. Streams on the Swan Coastal Plain were always sampled later in the day than those on the plateaus. The time difference of two to three hours between first and last sampling may have been sufficient to allow warming of streams.
With use of continuous temperature gauges, it is possible that stream temperature could be a useful environmental tracer. Such monitoring was beyond the budget of this study and temperature was therefore excluded from contributing area calculations and eliminated as a potential environmental tracer.
7.5 Characterisation of Regional Hydrologic Units
Clear water signature differences were seen between the Darling and Dandaragan Plateau and the Swan Coastal Plain regions. Streams emanating from the Swan Coastal Plain are characterised by low salinity, high colour and phosphorous enriched waters, whilst those draining the Darling and Dandaragan Plateaus display low phosphorous levels and low colour intensity, but high salinity (Figure 33).
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 74
Dandaragan Plateau Chandala Brook Rocky Creek 3
• High conductivity 2 • Low colour intensity Swan Coastal Plain • Low phosphorous • Low conductivity • High Colour intensity 4 Ki-it Monger Brook • Phosphorous enriched 8 Unsampled 5 Streams Unsampled Nambah Brook Streams
6 Ellen Brook 7 Darling Plateau 9 Swan River 1 Figure 33: Conceptual Diagram of the Ellen Brook catchment Boxes represent approximate location of the sampling sites
7.5.1 Darling and Dandaragan Scarps
Darling and Dandaragan Plateau sites 2, 7 and 8, located on Nambah Brook, Ki-it Monger Brook and Rocky Creek, respectively, displayed similar levels of Total Organic Carbon and colour to each other, but electrical conductivity and phosphorous levels varied significantly. The values of these two parameters were similar at Sites 2 and 8, but very different at Site 7. Site 7 is believed to be a misrepresentation of the region. This is discussed in Section 7.6.2 below.
7.5.2 Swan Coastal Plain
With the exception of the strong colour signature, the water in streams draining the Swan Coastal Plain was found to be characteristic of Gnangara Mound groundwater or fresh rainwater. The Gnangara mound is characterised by fresh water with a saline layer at the watertable due to evapoconcentration (Smith and Shams 2002). It has also been found to have high orthophosphate concentrations resulting from leaching and throughflow in the sandy soil (Smith and Shams 2002). This dissolved orthophosphate explains the fact that filtered samples from Swan Coastal Plain sites did not show the same decreasing phosphorous trend as the unfiltered samples
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 75
(Figure 19 and Figure 20). It appears that phosphorous applied in particulate form is converted or flushed from the system, but dissolved phosphate levels are buffered by the high concentrations in the groundwater body.
Sites 5, 6 and 9 are located in close proximity to each other. This is reflected in the very similar results obtained for these three sites (Table 3 to Table 5). Although still on the Swan Coastal Plain, Site 3, on Chandala Brook, is located to the north of the other three sites (Figure 12). This site displayed a slightly different water signature, with less intense colour and higher salinity across the four sampling rounds. It is possible that Chandala Brook originates from a part of the Gnangara Mound area that displays different groundwater properties to the southern regions, and that this is influencing the stream chemistry. It may therefore be more useful to exclude Chandala Brook from the Swan Coastal Plain region and consider it as a separate area for analysis. This has been included as a recommendation in Chapter 9, Recommendations for Further Work. Interestingly, phosphorous levels were similar for all four sites, suggesting similar land use practices and soil types throughout the four subcatchments.
7.6 Computation of Flow Contribution Proportions
7.6.1 Seasonal trends in flow contribution ratios
The environmental tracers employed indicate that the contribution of the Darling and Dandaragan Plateau region peaks in August. The Swan Coastal Plain dominates at all other times. Ideally, sampling would have also taken place in late October and November, to analyse how the catchment behaves when the water table and soil saturation begins to return to its dry season levels.
One explanation of the observed trends is that the Plateau region is initially dry before the winter season commences, and that water is rapidly transmitted through it so that it returns to its initial state quickly. That is, its response to rainfall is much faster than that of the Swan Coastal Plain, which is kept at relatively constant saturation levels throughout the season due to the presence of the Gnangara Mound. Under this theory the hydrograph peak for the Darling and Dandaragan Plateaus would be short and sharp, while the Swan Coastal Plain’s would display a wider base time. However, the limited number of sampling dates means that it is difficult to be
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 76 certain that this is occurring. It is also possible that the contribution by each region is more strongly affected by recent rainfall events than by overall seasonal patterns.
7.6.2 Justification for exclusion of Site 7 from data
Site 7 exhibited results that were anomalous from those of the rest of the Plateau region. With the exception of one outlying phosphorous result, the major difference was that it displayed significantly lower electrical conductivity readings than the other two sites from the region. Although the upper reaches of Nambah Brook could not be accessed, examination of regional maps suggests that this stream does not extend east into the high elevation portion of the catchment. It may therefore originate from a groundwater seep or spring rather than from shallow groundwater throughflow off the Scarps. Streams generated from groundwater throughflow have the most contact with the soil, and are therefore more likely to pick up properties of this soil than streams generated via other mechanisms.
The exclusion of Site 7 from the mean used in the mixing models is only valid if it is assumed that the mechanism by which it is generated is unique or unusual for this part of the catchment. If many streams are generated in the same way it would be necessary to include the site, as its water quality would be representative of a subset of watercourses in the region. However, no examples of other streams that appeared to originate from the eastern parts of the catchment in a similar way to Nambah Brook were observed. On the other hand, it is likely that the inner streams of the catchment will be generated from baseflow or saturation excess rather than rapid interflow, and therefore have similar properties to Site 7. The water signature at this site may therefore represent that of the central River Flood Plain and Flats region.
The exclusion of Site 7 data only makes a significant difference to proportional flow predictions for the non-weighted analysis during Sampling Rounds 2, 3 and 4. The decrease in the predicted proportion of Ellen Brook flow that originates from the Plateau region is almost entirely caused by the difference in electrical conductivity readings between Site 7 and Sites 2 and 8. As the flow volume at Site 7 is very small, its effect is almost eliminated in the weighted mean calculations.
The phosphorous level at Site 7 was anomalously high in both filtered and unfiltered samples from the August sampling round (Figure 19 and Figure 20). This could have been due to a recent fertiliser application, spill or other similar occurrence. It
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 77 may also be a result of contamination of the sample jar, but is not likely to be a laboratory error as different water was used in the filtered and unfiltered samples analysis, yielding similar results. Ideally, further sampling would have been undertaken upon discovery of the high reading to determine whether or not the site was a true anomaly for that part of the catchment at that time. This was not possible as remaining unsampled streams in the area all appeared to be located wholly within private land. The results of the mixing ratio calculations were not affected because phosphorous could not be successfully applied to flow separation in the two-system model of the catchment.
7.6.3 Differences between indicators
As the main Ellen Brook channel continued to display the highest phosphorous concentrations of the catchment, it was concluded that phosphorous cannot be used as a tracer for the purpose of two-region hydrograph separation in this catchment. This left electrical conductivity and colour absorbance as the only remaining applicable indicators.
Electrical conductivity indicated a much lower proportion of flow emanating from the Swan Coastal Plain than was predicted by photometric absorbance. In addition to this, the two parameters did not show the same trends, with electrical conductivity suggesting an increase in the input from the Plateau region as the season progresses, and absorbance suggesting a decrease. The most logical explanation for these differences is that another water source is influencing the final water signature. The third water source is thought to be the River Flood Plain region of the catchment. The fact that the discrepancy is not apparent for the first sampling round suggests that it is only when the central region of the catchment is saturated that it begins to contribute significant amounts of flow to the Brook, and thus affects the two-region environmental indicator model.
If it is assumed that the two-region system is in fact accurate and there is not a third region, then one of the following must be true: i) The mean absorbance of water from Rocky Creek, Nambah Brook and Ki-it Monger Brook is higher than the true average for the Scarps ii) Absorbance at Sites 3, 5, 6 and 9 is higher than the true average for the Western catchment area
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 78
iii) Electrical conductivity of water from Rocky Creek, Nambah Brook and Ki-it Monger Brook is higher than the true average for the Scarps iv) EC Colour concentration at Sites 3, 5, 6 and 9 is higher than the true average for the Western catchment area Thus, if the mean value of either absorbance or electrical conductivity was lowered for one of the regions by the inclusion of more sites, the predictions given by each of the parameters would move closer to each other.
7.6.4 The Influence of the River Flood Plain Area
The limited spatial distribution of sampling locations meant that the water signature of the central valley area of the catchment could not be determined. As the sampled streams contained only around half of the expected total flow for the catchment (see Section 6.1.3), it is likely that the River Flood Plain region makes a significant contribution to total flow.
It is unclear whether runoff generation in this area is mainly via subsurface flow or by overland flow due to excess saturation. Saturation excess runoff generation was thought to be unlikely as no upward curve has been reported in the rainfall-runoff curve for the catchment (Smettem 2005 pers. comm.). However, visual observation of saturated areas in this study, and the envisaged water signature of the central parts of the catchment, suggest that saturation excess is a possibility (Figure 34). As well as this, the depth to groundwater in the central part of the catchment is normally very shallow (Smith et al. 2002). This means that only small rainfall and throughflow volumes would be necessary for saturation to occur.
As mentioned above, the average pH reading during the first sampling round for the main Ellen Brook channel was higher than the average reading from either the east or west sides of the catchment. Similar results were seen for phosphorous in the second sampling round. This suggests that the Central River Plain area is inputting water with high pH and high phosphorous levels. The significant electrical conductivity difference between Nambah Brook and the other Plateau sampling locations further emphasises the need for a third study area. However, further research is needed to fully elucidate the behaviour of the River Flood Plain region of the catchment before its water signature can be defined and a three-system model applied.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 79
Waterlogging was apparent in the central part of the catchment in the later months of the project (Figure 34). This is consistent with the mapping of areas susceptible to inundation (Figure 10) (PPK Environment and Infrastructure 2000; Smith and Shams 2002). The area was also identified by PPK Environment and Infrastructure (2000) as susceptible to salinity. However, the results discussed above indicate that the region did not contribute a high salt load to the Ellen Brook in the study year.
Ellen Brook stream channel
Waterlogged area
Figure 34: Waterlogged area of the Ellen Brook catchment near Site 1
The August peak in calculated contribution by the Plateau region coincides with the peak in catchment electrical conductivity readings. At this stage it appears that these two trends are related and that both contribution ratio and electrical conductivity depend on the water level in the catchment. Although there was still strong differentiation between regions, it can be assumed that when the water level in the catchment is low, the River Flood Plain and Flats region makes a less significant contribution to the total flow exiting the catchment. The central region of the catchment would be expected to mirror the water signature of the Swan Coastal Plain region more closely than that of the Plateaus, with high phosphorous due to agricultural land use and low salinity as explained above. Therefore, a large proportion of flow that is attributed to the Swan Coastal Plain may in fact be originating from the central River Flood Plain region. As this central region dries out following periods of low rainfall, the contribution of the Swan Coastal Plain region calculated by the two-region model, appears to increase.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Discussion 80
7.7 Cross-sections and Weightings
The predicted depth of streamflow as calculated from width measurements was very close to actual stream depth measured at the same location (Appendix D). This implies that the calculated cross-sectional areas are accurate. Any errors in streamflow volumes must therefore stem from the velocity calculations rather than the cross-sectional area.
There are several potential sources of error that may arise from the technique that was used to determine stream velocity. The largest of these is that the technique assumes constant velocity both vertically and horizontally across the culvert or stream cross-section. In reality, velocity gradients would exist in both directions. Floats were introduced at the centre of the flow and remained near the surface at all times. Thus, the velocity reported is in fact the maximum velocity of the stream. It is assumed that because the streams are small, the maximum velocity will not differ greatly from mean velocity, and the calculate streamflow volume is therefore a valid estimate.
The channel slope calculations performed using Manning’s formula resulted in a wide variation in predicted channel slopes (Appendix E). The discrepancies in slopes calculated for the same stream section using different culverts are most likely to be due to inaccurate estimates of Manning’s n. Estimates of Manning’s n did not consider blockages inside the culverts or bends in the stream as it entered pipework.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Conclusion 81
8 Conclusion
If environmental indicators can be applied to hydrograph separation in Australian catchments such as the Ellen Brook, the need for expensive stream gauging at many points throughout a catchment will be reduced. This first attempt at applying environmental indicators for such a purpose has shown that they do have the potential to act as useful estimates of streamflow origin. However, if applied incorrectly these indicators can be misleading and may oversimplify the complex hydrological processes occurring within the catchment.
The study confirmed that distinct water signatures do exist within the Ellen Brook catchment. The Darling and Dandaragan Plateau region was found to be characterised by low colour intensity as measured by photometric absorbance, low phosphorous levels and relatively high salinity, while the Swan Coastal Plain region exhibited high colour intensity, elevated phosphorous and low salinity. At all sites, the water signature moved closer to that of unpolluted rainwater or groundwater as the winter season progressed, but the differentiation between regions was apparent at all times.
In the two-region analysis of the catchment, electrical conductivity and photometric absorbance were shown to be the most strongly applicable environmental indicators. Phosphorous, temperature, pH and dissolved oxygen were found to be unsuitable. However, the results also suggested that the two-region system may be insufficient for this catchment. It was shown that the inner portions of the catchment, in the vicinity of the main stream channel, do not contribute high salt loads to the Ellen Brook, although they do become waterlogged late in the season. This makes it difficult to separate the contribution of the central river flood plain region from that of the true Swan Coastal Plain region to the west. The chosen environmental indicators were not applicable for the purpose of separating waters emanating from the Swan Coastal Plain and the Gnangara Mound from those emanating from the River Flood Plain region.
The dominant factor controlling predicted contribution volumes appeared to be the level of saturation of the catchment. The predicted contribution made by the Darling and Dandaragan Plateau region was shown to vary inversely with catchment saturation. The results suggest that the contribution of the Plateau region decreases
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Conclusion 82 as the season progresses. This is thought to be due to a rapid response to major rainfall events by this part of the catchment, and quick transmittance of rainfall to the main stream as interflow or throughflow runoff.
Significant differences were observed between the calculated streamflow contribution ratios obtained from weighted and unweighted data. This implies that stream weighting is an important step in the application of environmental indicators. The velocity-area method is a straightforward way of doing this and provides a reasonable estimate of streamflow volume. Use of a current meter would be preferable to employing floats, as more accurate velocity estimates could be obtained.
The final conclusion of this study that relates particularly to the Ellen Brook catchment is that the colour producing functional groups on organic carbon molecules in the water samples absorb light at similar dominant wavelengths. This suggests that the material causing water colour throughout the catchment is similar, and may therefore be linked to one particular plant species or a group of species.
A significant finding that may have implications for future hydro-chemical studies is that water colour, as analysed through the surrogate ultraviolet spectrophotometry method, does mix predictably and therefore can be used as an environmental indicator of contributing areas. Variation in the colour of water originating from different regions of a catchment is common throughout south-western Australia and Australia in general, meaning that this indicator may be widely applicable.
Further study must be undertaken before the true usefulness of environmental indicators in Australia can be determined. This will be a worthwhile endeavour as the preliminary investigation undertaken in this study has already identified several parameters that have the potential to be useful environmental tracers.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Recommendations for Further Work 83
9 Recommendations for Further Work
Refinement of the study is necessary to further investigate the applicability of environmental indicators in Australian catchments. The following recommendations for future work that will progress the study of tracers as hydrograph separation tools have been divided into those that should be carried out in the Ellen Brook catchment, and those that have wider applicability.
9.1 Further Work within the Ellen Brook catchment
This study could not record changes in contributing areas over the entire winter season due to time restraints which prevented sampling in late October and November. • It is recommended that spring and early summer sampling be undertaken in the Ellen Brook catchment.
The channel slope calculations performed in this study gave highly variable results. Knowledge of the channel slope is useful because it means that discharge can be calculated from a single flow height reading, thus eliminating the need for multiple stream dimension measurements and calculations. • It is recommended that channel slope estimates be improved with more accurate estimates of Manning’s n or through the use of stream surveying.
Chemical transformations of organic carbon may occur over the course of the season and change the dominant sample wavelength, affecting the validity of the absorbance measurement method used. • The correlation of photometric absorbance at 304nm with Total Organic Carbon should be assessed several times over one winter season. • Dissolved Organic Carbon (DOC) should be assessed in addition to TOC as this is the organic component that causes true water colour.
In order to fully assess the applicability of the environmental indicator technique the calculated contribution ratios must be compared to ratios obtained through accurate stream gauging. • It is recommended simultaneous measurement of the flow volumes of the major tributaries of the Ellen Brook, and the Brook itself, be undertaken.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Recommendations for Further Work 84
Stream access was identified as one of the major limitations of this project. The accuracy of the results could be greatly improved by further sampling. • Permission to take water samples from streams located on privately owned land should be sought prior to the commencement of any further studies in the Ellen Brook catchment. • The water signature of the central River Flood Plain region of the catchment should be investigated and described in more detail. • The water signature of the northern part of the Gnangara Mound in the area of Chandala Brook should be analysed in more detail to determine whether it should be considered as a separate region.
9.2 Application of theory and findings to other catchments
Mass balance mixing models are simple to apply when there are only two sources of streamflow in a catchment. When three or more sources are present, concurrent examination of more than one indicator is required, which significantly increases the complexity of the flow contribution calculations. It is likely that a computer based matrix solution will be required. • It is recommended that a three-system set of mass balance mixing equations be developed, and the benefits of such calculations over traditional catchment modelling assessed.
The linearity of photometric absorbance as a surrogate for colour measurement may have been a result of the particular organic carbon groups that are present in the Ellen Brook catchment. • It is recommended that the colour measurement investigation process be repeated in other catchments, in order to determine whether the technique is universally applicable.
Finally, the success of the environmental indicator technique in this project may be due to the Ellen Brook catchment’s unusual geomorphology. • The use of environmental indicators for sourcing contributing areas should be examined in other Australian catchments, in order to determine whether tracer hydrology theories have widespread applicability in this country.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models References 85
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Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Appendices 91
Appendix A: Site Photos
Ellen Brook Main Channel
Site 1: West Swan Road Bridge (15/09/05) Site 4: Upper parts of catchment (15/09/05)
Darling and Dandaragan Plateaus
Site 3: Rocky Creek (15/09/05) Site 7: Nambah Brook (11/08/05)
Site 8: Ki-it Monger Brook (11/08/05)
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Appendices 92
Swan Coastal Plain
Site 3: Chandala Brook (11/08/05) Site 5: Almeria Parade (11/08/05)
Site 6: Railway Parade Between Stock and Savy Roads (11/08/05)
Site 9: Railway Parade near Warbrook Road (15/09/05)
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models Appendices 93
Appendix B: Validity of the mass balance model for absorbance
A strong linear correlation was observed between percentage dilution of the Site 5 sample and the level of absorbance. The equation for this correlation was y = 1.98x – 0.14 Thus, the value of the environmental indicator, designated C as for all other indicators, is C = AX + B i.e. the absorbance measurement is a linear transformation of percentage dilution, which is an additive property.
Rearranging gives, X = (C – B)/A
The conservation of flow mass equation (Equation 10) remains the same. X is substituted into this equation, with X effectively acting as the concentration of the pure sample. Thus QtXt = Q1X1 + Q2X2
Xt - X2 Q1 = X1 - X2 C − B C − B t - 2 A A Q1 = C − B C − B 1 - 2 A A
(Ct − B) − (C2 − B) Q1 = (C1 − B) − (C2 − B)
Ct − B − C2 + B Q1 = C1 − B − C2 + B
Ct - C2 Q1 = as before C1 - C2 Therefore the same formula can be applied to absorbance as is used for the other parameters, which are assumed to be additive.
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models
) knots ( ) 35 19 26 14 8:51 8:51 km/h 14:50 14:50 ( ) C ( Min Min Temp ) ---- C 18 10.518 20 6.7 11 28 15 ( 18.5 8.3 30 16 17.4 1319.218.5 7 41 7.3 22 30 31 16 17 Max Max (Bureau of Meteorology 2005b) 13:10 6:04 13:36 13:36 14:32 6:0915:51 7:5513:46 9:25 6:3214:16 9:25 22:4413:33 7:48 23:31 14:32 7:48 14:26 14:32 14:26 13:36 13:36 Temp ) mm 9am ( since ) hPa ( Press Rain ) knots ( ) km/h ( in Ellen Brook, Westernin EllenUsing Australia, ) knots ( ) Wind Speed WindGust Max WindGust km/h ( ic Data For Day Prior to Sampling Dir Current Observations Extremes Wind ) % Rel Rel ( Hum Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental ) C g Point de ( s for the Perth Region Perth for the s ) C g Temp Dew de ( ) Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing Date Date Time AWST ( 10 22:01 8.810 22:0110 22:01 - 8.2 12.310 21:00 96 - 10.4 8.510 22:01 SSW 88 1510 22:01 0 - 7 ENE 7.110 22:00 10.4 ENE 0 11 90 7.810 22:01 75 6.4 15 SSW 9.3 610 22:00 SW 0 7.2 13 95 8 12.810 22:00 20 SW 96 8 13 0 7 10.210 22:00 15 NNE - 6 11 91 12.7 1021 7 84 13 6 8 24 N 0.4 3 - 10.4 S - 7 3 86 - 13 9 9 - 7 CALM 1020.4 2 - 7 NE 5 - 12.2 5 4 0 4 4 1020.8 SSW 9 - 11 4.8 1021 - 2 5 - 6 - 0 SE 1021.1 - 4 1020.8 SSW W 0.2 - 0 - 2 1020.5 - WSW 0.6 - - - SW - - - WSW - - - - S -
Station Name Station Current Weather Detail Current These current observations have not been quality controlled. quality been not have observations current These AWST 22:01 updated: Last 2005 Wednesday August 10 OCEAN REEF SWANBOURNE BICKLEY ISLAND ROTTNEST JANDAKOT AIRPORT AIRPORT PERTH RAAF PEARCE GARDEN ISLAND WATERMELVILLE MANDURAH PERTH METRO
Appendices Appendix C: Rainfall and Other Climat 94 ) knots ( ) 20 11 31 17 0:02 0:02 0:12 0:12 km/h ( ) C ( Min Min Temp ) ---- C 16 11.218 52 5.6 28 18 10 ( 17.6 7.917.3 2818.5 2.8 15 5.5 13 18 7 10 17.4 5.1 20 11 Max Max 11:22 5:2414:24 5:4514:03 0:00 6:2514:32 0:00 6:1915:06 0:06 5:05 0:06 0:00 0:00 0:18 0:18 7:40 7:40 12:58 6:08 0:50 0:50 Temp (Bureau of Meteorology 2005c) ) mm 9am ( since ) hPa 028.1 0 SSE 027.4 0.2 - ( Press Rain ) knots ( ) km/h ( in Ellen Brook, Westernin EllenUsing Australia, ) knots ( ) Wind Speed WindGust Max Wind Gust km/h ( Current Observations Extremes Dir Wind Wind Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental ) % ( Rel Hum ) C g Point de ( for the Perth Region ) C g Temp Dew de ( Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing ) Date Date Time AWST ( 50:0.74S79120SSW 07:509.97.484SE00631 15 15 07:50 07:509.5784ESE749510280 15 07:51 - 10.915 07:00 5.615 07:51 - 6.3 13.215 73 4 -15 07:50 5.9 07:0095.981SE74951 ESE 10.415 07:50 89 E 61 11 11.315 07:00 ESE 6.4 17 SE 10.315 07:50 13 5.2 6 76 2615 - 5.9 9 66 S 7 15 ESE 14 74 18 - 11 SE 18 13 8 37 10 - 6 13 10 7 - 20 ESE - 17 7 1027.3 - 13 18 0 0 - 9 15 0 10 7 1028.1 - 1028 8 - 15 0.2 0 1027.5 - - SSE 8 0.2 SSE SSE - - - - SW - - ESE ------SSE
Appendices 95 Station Name Current Weather Details PERTH METRO OCEAN REEF OCEAN DW60034 These currentobservations controlled. havebeen quality not 07:51 AWSTLast updated: 15 September Thursday 2005 SWANBOURNE BICKLEY ISLAND ROTTNEST JANDAKOT AIRPORT PERTH AIRPORT PEARCE RAAF ISLAND GARDEN WATERMELVILLE MANDURAH 61 33 43 23 13:40 13:40 12:48 12:48 Extremes Min Temp the last ten minutes. g ---- Max 15.8 12.7 50 27 16.2 13.615.7 13.116.1 59 11.916.7 32 10.916.7 68 10.3 56 37 57 30 54 31 29 15:03 2:08 14:37 14:37 14:08 6:4412:45 16:45 5:4614:26 16:45 21:1615:18 22:20 15:3710:15 14:23 15:37 23:58 14:23 11:35 11:35 13:30 13:30 Temp (Bureau of Meteorology 2005a) 9am since since Press Rain hest wind speed recorded durin recorded speed wind hest g ion ust is the hi is the ust g in Ellen Brook, Westernin EllenUsing Australia, g 7 20 11 1025.4 0.2 SW Wind SpeedWind Gust Wind Gust Wind Max 43 Dir Current Observations Wind es and the reported wind wind reported the and es g Rel Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental Hum ed one minute data. minute ed one ils for the Perth Re ils g Point unavera g Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing (AWST) C) (deg C) (deg (%) (km/h) (knots) (km/h) (knots) (hPa) (mm) (C) (C) (km/h) (knots) 09 22:41 9.409 22:4009 22:40 2.6 - 9.509 22:00 62 - 5.909 22:40 3.1 S 11.8 -09 22:40 64 2 13 3.8 7.3 SSE SSE09 22:40 76 7.8 59 20 2409 22:41 3.8 S SSE 7.109 22:00 3.8 78 11 13 15 11.609 22:41 3.2 76 S 33 28 4.8 -09 22:00 77 8 S 23 9 10.9 63 18 SSE 15 13 30 - SSE 57 3.9 5 7 - - 33 7 16 62 - 31 13 0 - 4 SSE 1024.3 18 SE - 17 0 20 7 - 9 20 0.4 39 9 1025.4 11 0.4 - 1025.5 - 11 5 21 0.4 SSW 30 SSW 1025.2 1025.2 24 - 0.2 0 SSW 16 - 13 1025.2 - 0.2 SW - - - SW - SSW ------S - Date TimeDate Temp Dew Section of the table, the maximum temperature is measured between 9am and 6pm, the minimum temperature is measured from measured is temperature minimum the 6pm, and 9am between measured is temperature maximum the table, the of Section
Extremes Station Name Station Current Weather Deta IDW60034 quality been controlled. not have observations current These 2005Lastupdated: 22:41AWST Sunday 9 October NOTE: ***Wind speeds and directions are ten minute avera minute ten are directions and speeds ***Wind In theIn Ocean Reef is the exception, usin exception, the is Reef Ocean 6pm the previous day until 9am on the current day. The maximum wind gust is reset at midnight. gust is reset wind maximum The day. 9am on the current until day 6pm the previous PERTH METRO OCEAN REEF OCEAN SWANBOURNE BICKLEY ROTTNEST ISLAND JANDAKOT AIRPORT AIRPORT PERTH RAAF PEARCE GARDEN ISLAND WATERMELVILLE MANDURAH
Appendices 96
0.0023
0.0027
47.2 49.95 0.87 0.82 47.16 0.00909
0.44 0.36 0.19 0.18 0.36 0.44 0.2250.45 0.45 0.225 0.05m 0.04m0.09m 0.035m 0.3926 0.41240.05740.204 0.03760.021 0.2062 0.1034 0.0432 0.0833 0.0188 0.0221 0.0371 0.0171 0.0097 0.0208 0.0093
in Ellen Brook, Westernin EllenUsing Australia, 0.015 0658.541.02 1.01 57.68 0.82
0.028
Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental 0.0058
0.26 0.5 0.41 0.22 1.67 95.95 1.36 77.972. 1.26 0.175 0.425 0.175 0.425 0.09m 0.035m0.09m 0.035m 0.0104 0.1172 0.344 0.1361 0.0578 0.081 0.0389 0.372 0.053 0.0256 0.114 0.0208 0.0076 0.043 0.0075 0.091 0.038 Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing
Appendices Area calculations Appendix D: Culvert Cross-sectional 97 Culvert Number width of flow(L) radius of circular culvert (R) centre Theta - angle of flow at of circle (radians, degrees) =2ASIN(L/(2R)) 2-1 flowdistance between top of and centre of circle (H) height of flow (m) Measured height (from field) 2-2 Area of sector (m²) Area of 1/2 triangle (m²) 5-1 Area of segment (m²) 5-2 7-1 7-2 9-1 9-2
Appendices 99
Appendix E: Channel Slope Calculations
Manning’s Equation: 1 2 1 U = R 3 S 2 n S = U 2 n 2 R 3 where n is Manning’s n (Gerhart et al. 1992; Streeter et al. 1998) R is the hydraulic radius; S is the slope of the channel, assumed to be uniform; and U is the stream velocity.
Table E1: Calculation of catchment slope Values for Manning’s n were obtained from Frazini et al. (1997) and Munson et al. (1990)
Area of Wetted Hydraulic Calculated Velocity Manning’s Site flow Perimeter Radius Slope U (m/s) n A (m²) P (m) A/P (m) (m/m)
2-1 0.010 0.29 0.035 0.395 0.014 1.37E-09 2-2 0.006 0.24 0.024 0.395 0.014 4.43E-10 3-1 0.437 1.91 0.229 0.179 0.014 7.52E-08 3-2 0.437 1.91 0.229 0.053 0.014 6.59E-09 3-3 0.437 1.91 0.229 0.047 0.014 5.19E-09 3-5 0.437 1.91 0.229 0.094 0.014 2.07E-08 3-6 0.437 1.91 0.229 0.057 0.014 7.63E-09 3-7 0.437 1.91 0.229 0.043 0.014 4.34E-09 3-8 0.437 1.91 0.229 0.037 0.014 3.21E-09 5-1 0.028 0.53 0.052 0.954 0.014 2.47E-08 5-2 0.015 0.43 0.034 0.028 0.014 5.95E-12 6-1 0.208 1.29 0.161 0.228 0.014 4.27E-08 6-2 0.192 1.24 0.155 0.164 0.014 1.96E-08 7-1 0.017 0.46 0.037 0.516 0.014 2.64E-09 7-2 0.009 0.37 0.024 0.516 0.014 7.47E-10 8 0.11 0.90 0.126 0.390 0.045 6.22E-07 9-1 0.0027 0.20 0.014 0.052 0.014 1.38E-12 9-2 0.0023 0.19 0.012 0.221 0.014 1.77E-11
Sourcing Contributing Areas To River Flow in Ellen Brook, Western Australia, Using Environmental Indicators and Mixing Models flow in Ellen Brook, Westernin EllenUsing Australia, of the prediction compared to the mean excluding phosphorous. compared to the mean excluding phosphorous. of the prediction trical Conductivity and Photometric Absorbance trical Conductivity Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing
proportion from the meangiven by Elecproportion from prediction at West Swan Road Bridge (Site 1). to flow of contribution are estimates All calculations error Deviation from mean haspercentage been calculated as a of the predicted volume data was not available. Reported error is the deviation obtained as real flow True error could not be • • • 100
Appendices Appendix F: Contribution ratio calculations and associated error Notes: TOC TOC -0.71 N/A (celcius) (celcius) Temperature Temperature Electrical (uS/cm) Conductivity his value his value ns Colour Absorbance Electrical (uS/cm) Conductivity in Ellen Brook, Westernin EllenUsing Australia, Phosphate (mg/L) Phosphate Phosphate (mg/L)Phosphate Absorbance Colour Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental 0.10 -0.51 0.05 0.02 0.36 0.28 0.29 0.170.24 0.32 0.27 0.58 0.16 0.66 -0.04 0.60 0.19 0.30 0.34 0.38 0.15 0.37 0.22 0.23 0.16 0.05 0.07 0.20 pH pH % Error :% Error Error % Mean 22.9 68.9 6.0 6.0 10.9 11.1 Mean % Error % Mean 75.0 Mean % Error % Mean 9.3 Mean % Error % Mean 57.8 Mean % Error % Mean 114.8 Mean % Error % Mean 6942.8 Mean % Error % Mean 73.4 Mean % Error % Mean 75.1 Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing June August June August Sept Oct June August Sept Oct June August Sept Oct June August August 0.43 % Error: 217.9 35.2 35.2 11.7 0.21: % Error 16.7 8.2 8.2 4.3 0.44 % Error: 89.3 32.8 51.2 0.25 % Error: 6.2 35.7 35.7 381.6 0.38 % Error: 95.1 54.4 58.7 0.10 % Error: 64.8 65.9 89.4 0.15 % Error: 127.2 49.0 49.0
Predicted proportion site 2' proportion Predicted Predicted proportion sites 2, 7 and 8 proportion Predicted At Site 1 At Site 4 At Site Mean 6.5 7.4 21.0 131.7 12.0 5.8 0.34 0.14 0.35 0.30 2350.0 2010.0 1393.3 1613.3 11.9 12.8 22.9 Mean 6.8 7.0 480.0 293.7 242.2 202.3 1.91 1.89 2.26 2.08 779.0 804.7 640.0 707.5 12.9 14.3 83.9 2 Reserve Road78 6.5 6.8 NA NA 21 7.6 26 7.6 NA 20 NA 299 15 70 0.34 5 11 0.34 0 2 0.62 NA 0.57 NA 0.07 2350 0.00 0.26 3040 0.18 2170 0.13 0.19 2440 11.9 800 12.1 2190 570 1440 22.9 710 1690 13.3 13 3 Chandala Brook5 Almiria Parade6 Parade Railway 9 Warbrook Near Road 6.8 7.0 6.7 6.9 7.3 6.9 476 432 532 338 254 289 243 228 234 211 195 1.33 186 264 2.00 1.27 2.40 1.84 218 2.56 1.62 2.33 2.67 1.52 2.02 1147 2.42 585 1379 605 516 1310 2.44 519 1370 310 2.36 420 12.4 430 490 12.8 13 13.3 15.2 15 520 90.6 77.2 540 1 West Swan Rd Bridge4 Ellen Brook Brand Hwy 6.9 6.9 7.2 7.1 432 365 376 254 231 207 199 219 1.35 1.14 1.40 0.95 1.70 1.47 1.77 1.31 1276 1419 1507 1650 1140 1350 1250 1450 12.6 12.3 13.75 13.3 61.1 42.7 Mean Sampling 1*Round Sampling Mean 0.34 2* Round Sampling Mean Mean Sampling 1" Round Sampling Mean Mean Sampling 3* Round Sampling Mean Mean Sampling 2" Round Sampling Mean Mean Sampling 4* Round Sampling Mean Mean Sampling 3" Round Sampling Mean Mean Sampling 4" Round Sampling Mean ^ Predicted proportion^ at Site of flow 1 that originates from Plateau sites 2, 7 and 8 as calculated using mass balance equatio ' Predicted proportion at Site of 4 that flow is originates from Plateau Site 2 as calculated using mass balance equations is the" Mean mean predicted proportion absorbance by given and Error is EC only. calculated as the percentage deviation from t * Mean is the Mean mean* predicted proportion by absorbance given and EC only. isError calculated as the percentage deviation from t Scarps (East) Swan Coastal Plain Ellen Brook main channel 101
Appendices Non-weighted, all sites TOC TOC (celcius) (celcius) Temperature Temperature Electrical Conductivity (uS/cm) Conductivity Electrical his value his ns Colour AbsorbanceColour (uS/cm) Conductivity Electrical in Ellen Brook, Westernin EllenUsing Australia, Phosphate (mg/L) Phosphate Phosphate (mg/L) Colour Absorbance Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental 0.10 -0.34 0.05 0.02 0.36 0.28 0.30 0.18 0.32 0.39 0.43 0.40 0.30 0.33 0.37 pH pH % Error : % Error Mean %Error 22.9 Mean %Error 68.9 58.3 Mean %Error 41.0 Mean %Error 56.9 6.0 6.0 10.9 11.1 Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing June August June August Sept Oct June August Sept Oct June August Sept Oct June August August 0.34 % Error:0.35 % Error:0.28 % Error: 199.6 86.2 93.5 15.3 12.4 36.5 15.3 24.3 40.6 2.8
Predicted proportion sites 2, 7 and 8 7 and 2, sites proportion Predicted Non-weighted, excluding Site 7 At Site 1 At Site Mean 6.5 7.2 21.0 48.0 15.4 8.7 0.34 0.17 0.40 0.38 2350.0 2615.0 1805.0 2065.0 11.9 12.6 22.9 Mean 6.8 7.0 480.0 293.7 242.2 202.3 1.91 1.89 2.26 2.08 779.0 804.7 640.0 707.5 12.9 14.3 83.9 102
Appendices 2 Reserve Road8 6.5 6.8 NA 21 26 7.6 20 NA 15 70 0.34 11 0.34 2 0.62 0.57 NA 2350 0.00 3040 0.18 2170 0.19 2440 11.9 12.1 2190 22.9 1440 1690 13 3 Chandala Brook5 Almiria Parade6 Parade Railway 9 Warbrook Near Road 6.8 7.0 6.7 6.9 7.3 6.9 476 432 532 338 254 289 243 228 234 211 195 1.33 186 264 2.00 1.27 2.40 1.84 218 2.56 1.62 2.33 2.67 1.52 2.02 1147 2.42 585 1379 605 516 1310 2.44 519 1370 310 2.36 420 12.4 430 490 12.8 13 13.3 15.2 15 520 90.6 77.2 540 1 West Swan Rd Bridge4 Ellen Brook Brand Hwy 6.9 6.9 7.2 7.1 432 365 376 254 231 207 199 219 1.35 1.14 1.40 0.95 1.70 1.47 1.77 1.31 1276 1419 1507 1650 1140 1350 1250 1450 12.6 12.3 13.75 13.3 61.1 42.7 NB Estimates of flow contribution at Site 4 were not repeated as Site 7 does not influence the Site 4 water signature water 4 Site the influence not does 7 as Site repeated not 4 were Site at Estimates contribution ofNB flow Mean SamplingRound 1* 0.34 Mean SamplingRound 2* Mean SamplingRound 3* Mean SamplingRound 4* ^ Predicted proportion of flow at Site 1 that originates from Plateau sites 2, 7 and 8 as calculated using mass balance equatio balance mass using 8 as calculated 7 and 2, sites Plateau from originates 1 that Site at of flow proportion Predicted ^ * Mean is the mean predicted proportion given by absorbance and EC only. Error is calculated as the percentage deviation from t Scarps (East) Swan Coastal Plain Ellen Brook channel main Brook Ellen TOC TOC (celcius) (celcius) Temperature Temperature Electrical Conductivity (uS/cm) Electrical Conductivity (uS/cm) his value ns in Ellen Brook, Westernin EllenUsing Australia, lculated using mass balance equatio 264 218 2.44 2.36 520 540 Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental Phosphate (mg/L)Phosphate Colour Absorbance Phosphate (mg/L)Phosphate Colour Absorbance EC only. Error is Error calculated as the EC only. percentagefrom t deviation 0.11 -0.27 0.03 0.02 0.25 0.16 0.15 0.02 0.24 0.44 0.42 0.37 0.01 -0.11 0.29 om Plateau sites 2, 7 and 8 as ca7 and 8 as 2, om Plateau sites pH pH Mean % Error 8075.2 Mean % Error 59.5 Mean % Error 104.9 % Error :Mean % Error 38.4 53.3 1.9 1.9 96.6 21.7 Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing 6.7 6.9 532 289 234 186 2.40 2.56 2.67 2.42 605 519 420 490 13.3 15.2 90.6 7.0 7.3 432 254 228 195 2.00 1.84 2.33 2.02 585 516 310 430 13 15 77.2 NANA 7.66.8 7.6 NA 6.9 NA 299 70 476 5 338 11 0 243 2 NA 211 NA 0.07 1.33 0.00 1.27 0.26 0.18 1.62 0.13 0.19 1.52 1147 800 1379 2190 570 1310 1440 1370 710 1690 12.4 12.8 13.3 13 6.5 6.8 21 26 20 15 0.34 0.34 0.62 0.57 2350 3040 2170 2440 11.9 12.1 22.9 June August June August Sept Oct June August Sept Oct June August Sept Oct June August August 0.23 % Error: 91.4 90.8 60.0 0.30 % Error: 88.9 47.9 41.6 0.30 % Error: 191.0 46.1 46.1 136.3 0 2 1 2 5 1 16
Predicted proportion sites 2, 7 and 8 103
Appendices Weighted, all sites At Site 1 Weighted Mean 6.8 6.9 484.5 315.3 238.9 202.6 1.7 1.7 2.0 1.8 941.3 1056.1 962.5 1032.5 12.7 13.7 86.1 Weighted Mean 6.5 7.6 21.0 91.8 10.8 2.5 0.3 0.0 0.2 0.2 2350.0 2088.4 1386.8 1626.3 0.6 13.0 1.2 Site Weighting 1 West Swan Rd Bridge4 Ellen Brook Brand Hwy 6.9 6.9 7.2 7.1 432 365 376 254 231 207 199 219 1.35 1.14 1.40 0.95 1.70 1.47 1.77 1.31 1276 1419 1507 1650 1140 1350 1250 1450 12.6 12.3 13.75 13.3 61.1 42.7 9 6 8 5 7 3 2 Mean Sampling Round 4* Sampling Mean Mean Sampling Round 3* Sampling Mean Mean Sampling Round 1* Sampling Mean 0.24 Round 2* Sampling Mean * Mean is the mean * Mean absorbancepredicted by andproportion given ^ Predicted proportion of flow at Site 1 that originatesfr 1 that Site at of flow proportion Predicted ^ Ellen Brook main channel main Brook Ellen Swan Coastal Plain Scarps (East) TOC TOC (celcius) (celcius) Temperature Temperature Electrical Conductivity (uS/cm)Electrical Conductivity Electrical Conductivity (uS/cm)Electrical Conductivity his value ns in Ellen Brook, Westernin EllenUsing Australia, 264 218 2.44 2.36 520 540 Phosphate (mg/L) ColourAbsorbance Phosphate (mg/L) ColourAbsorbance Environmental Indicators and Mixing Models Models and Mixing Indicators Environmental 0.11-0.250.030.020.250.160.150.020.240.380.340.310.01-0.100.29 pH pH % Error % Error :Mean % Error 38.4 53.3 1.9 1.9 96.6 21.7 Mean % Error 102.5 Mean % Error 52.6 Mean % Error 7797.7 Sourcing Contributing Areas To River Flow To River Flow Contributing Areas Sourcing NA 7.6 NA 70 11 2 NA 0.00 0.18 0.19 2190 1440 1690 13 6.5 6.8 21 26 20 15 0.34 0.34 0.62 0.57 2350 3040 2170 2440 11.9 12.1 22.9 7.06.7 7.3 6.9 432 532 254 289 228 234 195 186 2.00 2.40 1.84 2.56 2.33 2.67 2.02 2.42 585 605 516 519 310 420 430 490 13 13.3 15 15.2 90.6 77.2 6.8 6.9 476 338 243 211 1.33 1.27 1.62 1.52 1147 1379 1310 1370 12.4 12.8 June August June August Sept Oct June August Sept Oct June August Sept Oct June August August 0.27 % Error:0.27 % Error:0.20 % Error: 190.6 87.7 90.2 40.7 42.5 89.5 40.7 27.6 138.1 54.2 1 1 2 0 5 16
Predicted proportion sites 2, 7 and 8 Weighted Mean 6.5 7.5 21.0 67.4 11.4 2.8 0.3 0.0 0.2 0.2 2350.0 2240.0 1482.9 1734.1 0.6 12.9 1.2 Weighted Mean 6.8 6.9 484.5 315.3 238.9 202.6 1.7 1.7 2.0 1.8 941.3 1056.1 962.5 1032.5 12.7 13.7 86.1 104
Appendices Weighted, excluding Site 7 Site Weighting Site 8 2 6 9 5 3 1 West SwanBridge Rd 4 EllenHwy Brand Brook 6.9 6.9 7.2 7.1 432 365 376 254 231 207 199 219 1.35 1.14 1.40 0.95 1.70 1.47 1.77 1.31 1276 1419 1507 1650 1140 1350 1250 1450 12.6 12.3 13.75 13.3 61.1 42.7 Mean Sampling RoundMean 1* 0.24 Sampling RoundMean 2* Mean Sampling RoundMean 3* Sampling RoundMean 4* ^ Predicted proportion at^ Site 1 of flow that originates from Plateau sites 2, 7 and 8 as calculated using mass balance equatio * Mean is the mean* Mean predicted proportion absorbance given by and Error EC only. is calculated as the percentage deviation from t Scarps (East) Scarps Swan Coastal Plain Ellen Brook main channel main Brook Ellen