Assessing GW and SW interaction

An Overview of Tools for Assessing Groundwater-Surface Water ConnectivityRoss Brodie, Baskaran Sundaram, Robyn Tottenham, Stephen Hostetler and Tim Ransley

Commonwealth of Australia 2007This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the Commonwealth. Requests and inquiries concerning reproduction and rights should be addressed to the Commonwealth Copyright Administration, Attorney Generals Department, Robert Garran Offices, National Circuit, Barton ACT 2600 or posted at http://www.ag.gov.au/cca. The Australian Government acting through the Bureau of Rural Sciences has exercised due care and skill in the preparation and compilation of the information and data set out in this publication. Notwithstanding, the Bureau of Rural Sciences, its employees and advisers disclaim all liability, including liability for negligence, for any loss, damage, injury, expense or cost incurred by any person as a result of accessing, using or relying upon any of the information or data set out in this publication to the maximum extent permitted by law. Postal address: Bureau of Rural Sciences GPO Box 858 Canberra, ACT 2601 Internet: http://www.brs.gov.au

Preferred way to cite this publication: Brodie, R, Sundaram, B, Tottenham, R, Hostetler, S, and Ransley, T. (2007) An overview of tools for assessing groundwater-surface water connectivity. Bureau of Rural Sciences, Canberra.

ForewordIntegrated management of surface water and groundwater is critical in ensuring sustainability of the water resource and for meeting the objectives of the National Water Initiative. Water issues such as over-allocation, environmental flows and river salinity are all influenced by the connectivity between streams and aquifers. This means that groundwater-surface water interactions need to be assessed and incorporated into the management response to a range of water quantity and quality issues. The assessment of stream-aquifer connectivity can be difficult and complex and there is a wide variety of approaches that can be taken. This includes conventional approaches such as interpreting water chemistry or stream hydrographs, as well as other methods which are not routinely used in Australia such as temperature monitoring and seepage meters. Each of these methods have their strengths and weaknesses and measure stream-aquifer connectivity at different scales in time and space. This report outlines the different approaches available for assessing groundwatersurface water interactions and encourages combining different methods in an overall strategy. Field work has been undertaken in two trial catchments by Bureau of Rural Sciences (BRS) to evaluate some of these assessment methods and to help develop a conceptual understanding of water flow in and between streams, wetlands and aquifers. This report is part of the Managing Connected Water Resources project, a collaboration between BRS, Australian Bureau of Agricultural and Resource Economics (ABARE), the Australian National University and State agencies. The project objective is to progress a more coordinated approach to the management of surface water and groundwater resources. The project has developed a comprehensive information package on connectivity issues, including assessment methods, at www.connectedwater.gov.au.

Colin Grant Executive Director Bureau of Rural Sciences April 2007

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Tools for Assessing Groundwater-Surface Water Connectivity


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Executive SummaryGroundwater and surface water resources are hydraulically connected in many regions of Australia and better understanding of this connectivity is critical for effective water resource management. Assessing groundwater-surface water interactions is often complex and difficult. However, there are a range of methods available as documented in this report, including:(i.) (ii.) (iii.) (iv.)

(v.)

(vi.) (vii.)

(viii.)

(ix.) (x.) (xi.) (xii.)

Seepage Measurement, the direct measurement of water flow at the surface water-groundwater interface using seepage meters or similar devices; Field Observations, where an initial reconnaissance can highlight hotspots where groundwater is interacting with surface water features; Ecological Indicators, mapping of specific vegetation communities or biota that indicate groundwater discharge to surface water features; Hydrogeological Mapping, to define the hydrogeology surrounding a surface water feature including specific geological features such as faults, facies changes or river morphology that can control groundwater flow; Geophysics and Remote Sensing, the use of geophysical and remote sensing technologies such as airborne electromagnetics (AEM), radiometrics, seismic waves, electrical charge, or satellite imagery; Hydrographic Analysis, the use of techniques such as recession analysis or baseflow separation to analyse the monitoring record of water levels or flows; Hydrometric Analysis, investigating the hydraulic gradient between groundwater and surface water systems and the hydraulic conductivity of the intervening aquifer and bed material; Hydrochemistry and Environmental Tracers, the interpretation of the chemical constituents of water such as major ions, isotopes, radon and chlorofluorocarbon (CFC); Artificial Tracers, the monitoring of the movement of an introduced tracer such as a fluorescent dye; Temperature Studies, the use of time series monitoring of temperature in both the surface water and groundwater systems; Water Budgets, approaches such as river reach water balances; Modelling, the use of analytical or numerical modelling techniques based on governing mathematical equations to predict water movement.

Simple methods such as field observations, field chemistry surveys or stream flow measurements can give valuable information in terms of providing a catchment-scale perspective on connectivity as well as targeting areas for more detailed investigation. Site specific investigations using simple tools such as seepage meters, minipiezometers, temperature loggers or environmental tracers provide more detail in terms of understanding and quantifying key processes. There is a need to use a combination of assessment methods rather than relying on any particular one. This is necessary to not only confirm any interpretation but also to extrapolate any findings in time and space.

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ContentsExecutive Summary.......................................................................................................................... 3 Contents ............................................................................................................................................ 5 Figures............................................................................................................................................... 9 Table ................................................................................................................................................ 11 1. Introduction................................................................................................................................. 13 2. Assessment of Connectivity ..................................................................................................... 15 2.1 Available Assessment Methods for Connectivity .................................................................. 16 2.2 Comparison of Methods ........................................................................................................ 18 2.3 Assessment Strategy............................................................................................................. 23 2.4 Data Collation ........................................................................................................................ 24 2.5 Desktop Analysis ................................................................................................................... 26 2.6 Field Survey........................................................................................................................... 27 2.7 Site Investigations ................................................................................................................. 28 3. Seepage Measurement............................................................................................................... 29 3.1 Seepage Meter Design.......................................................................................................... 30 3.2 Seepage Meter Operation ..................................................................................................... 33 3.3 Automated Seepage Meters.................................................................................................. 35 3.4 Advantages and Disadvantages............................................................................................ 36 3.5 Data Availability ..................................................................................................................... 37 3.6 Relevant Links ....................................................................................................................... 37 4. Field Observations ..................................................................................................................... 39 4.1 Advantages and Disadvantages............................................................................................ 39 4.2 Data Availability ..................................................................................................................... 39 5. Ecological Indicators ................................................................................................................. 43 5.1 Advantages and Disadvantages............................................................................................ 43 5.2 Data Availability ..................................................................................................................... 43 6. Hydrogeological Mapping.......................................................................................................... 45 6.1 Advantages and Disadvantages............................................................................................ 49 6.2 Data Availability ..................................................................................................................... 49 7. Geophysics and Remote Sensing............................................................................................. 51 7.1 Advantages and Disadvantages............................................................................................ 53 7.2 Data Availability ..................................................................................................................... 53 8. Hydrographic Analysis .............................................................................................................. 57

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8.1 Baseflow Separation.............................................................................................................. 59 8.2 Graphical Separation Methods.............................................................................................. 59 8.3 Filtering Separation Methods ................................................................................................ 60 8.4 Frequency Analysis Methods ................................................................................................ 62 8.5 Recession Analysis Methods ................................................................................................ 64 8.6 Advantages and Disadvantages............................................................................................ 68 8.7 Data Availability ..................................................................................................................... 70 8.8 Relevant Links ....................................................................................................................... 70 9. Hydrometric Investigations ....................................................................................................... 73 9.1 Piezometers........................................................................................................................... 73 9.2 Head Difference Measurement ............................................................................................. 77 9.3 Hydraulic Conductivity Measurement.................................................................................... 78 9.4 Flow Net Analysis .................................................................................................................. 80 9.5 Advantages and Disadvantages............................................................................................ 81 9.6 Data Availability ..................................................................................................................... 82 9.7 Relevant Links ....................................................................................................................... 82 10. Hydrochemistry ........................................................................................................................ 85 10.1 Field Water Quality Parameters .......................................................................................... 85 10.2 Major Ion Chemistry ............................................................................................................ 86 10.3 Stable Isotopes.................................................................................................................... 87 10.4 Radioactive Isotopes ........................................................................................................... 89 10.5 Industrial Chemicals ............................................................................................................ 90 10.6 Advantages and Disadvantages.......................................................................................... 90 10.7 Data Availability ................................................................................................................... 91 10.8 Relevant Links ..................................................................................................................... 91 11. Artificial Tracers ....................................................................................................................... 95 11.1 Advantages and Disadvantages.......................................................................................... 97 11.2 Relevant Links ..................................................................................................................... 98 12. Temperature Studies................................................................................................................ 99 12.1 Advantage and Disadvantages ......................................................................................... 101 12.2 Data Availability ................................................................................................................. 102 12.3 Relevant Links ................................................................................................................... 102 13. Water Budgets ........................................................................................................................ 105 13.1 Stream Flow Measurement ............................................................................................... 105 13.2 Volumetric Analysis ........................................................................................................... 106 13.3 Velocity-Area method ........................................................................................................ 106 13.4 Slope-Area Method............................................................................................................ 108


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13.5 Dilution Gauging ................................................................................................................ 111 13.6 Thin Plate Weirs ................................................................................................................ 111 13.7 Advantages and Disadvantages........................................................................................ 112 13.8 Data Availability ................................................................................................................. 112 13.9 Relevant Links ................................................................................................................... 112 14. Acknowledgements................................................................................................................ 115 15. References .............................................................................................................................. 117 16. Appendix 1 .............................................................................................................................. 128

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FiguresFigure 2.1: Examples of different methods of assessing stream-aquifer connectivity ..................... 19 Figure 2.2: Components of a strategy for investigation and assessment of connectivity ................ 24 Figure 2.3: A framework for conjunctive water management ........................................................... 25 Figure 3.1: Basic design of a seepage meter with inverted open chamber ..................................... 32 Figure 3.2: Basic components of the seepage meter including seepage chamber and collection bag.................................................................................................................................... 32 Figure 4.1: Field indicators of discharge of shallow acid groundwater into a coastal drainage network ............................................................................................................................................. 40 Figure 4.2: Lawn Hill Creek at Lawn Hill........................................................................................... 41 Figure 6.1: Different scale groundwater flow systems within a catchment....................................... 45 Figure 6.2: Groundwater flow systems operating within an alluvial riverine valley .......................... 46 Figure 6.3: Schematic cross section of the hydrogeology of the Alstonville Plateau ....................... 47 Figure 6.4: Extent of traditional published hydrogeological maps at 1:250,000 scale or more detailed ............................................................................................................................................. 48 Figure 7.1: A seismic gun used to fire a shotgun charge into the ground to generate a shockwave. ....................................................................................................................................... 53 Figure 7.2: A 144m long floating electric .......................................................................................... 54 Figure 7.3: EC ribbon images........................................................................................................... 54 Figure 7.4: EC ribbon images from geo-electric surveys ................................................................. 54 Figure 7.5: Airborne electromagnetics image showing groundwater recharge zone. ...................... 55 Figure 7.6: Paleochannels detected from airborne magnetics survey in Honeysuckle Creek subcatchment ................................................................................................................................... 55 Figure 8.1: Components of a typical flood hydrograph..................................................................... 58 Figure 8.2: Graphical baseflow separation techniques .................................................................... 60 Figure 8.3: Flow distribution curves for examples of (2a) high baseflow and (2b) low baseflow streams ............................................................................................................................................. 63 Figure 8.4: Procedure for recession curve displacement method.................................................... 68 Figure 8.5: Annual baseflow indices for unregulated streams in the Murray-Darling Basin............. 71 Figure 8.6: Annual volume of Q90 percentile for available stream gauges in the Richmond River catchment................................................................................................................................ 72

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Figure 9.1: Configuration of minipiezometer and stilling well for hydrometric measurement of seepage flux. .................................................................................................................................... 74 Figure 9.2: Example of monitoring bore construction....................................................................... 75 Figure 9.3: Stages in the installation of minipiezometer and stilling well for hydrometric investigations of seepage flux .......................................................................................................... 76 Figure 9.4: Watertable contour patterns around streams................................................................. 81 Figure 9.5: Plan view of example groundwater flow net towards a gaining surface water feature............................................................................................................................................... 81 Figure 9.6: Groundwater and surface water level measurements for Yellow Creek site during March, 2005...................................................................................................................................... 83 Figure 9.7: River levels versus nearby bore water levels in key sites in the Border rivers catchment ......................................................................................................................................... 84 Figure 10.1(a) Field electrical conductivity (uS/cm) and (b) pH of Gum Creek and nearby springs, July 2004............................................................................................................................. 92 Figure 10.2. Deuterium versus oxygen-18 concentrations for river water and groundwater in the Border Rivers Catchment ........................................................................................................... 93 Figure 10.3 Chloride versus deuterium concentrations for river water and groundwater in the Border Rivers Catchment ................................................................................................................. 93 Figure 11.1: Dye tracer technique for assessing groundwater and surface water interaction in the field ............................................................................................................................................. 96 Figure 12.1: Common temperature sensors used to measure sediment and stream temperatures..................................................................................................................................... 99 Figure 12.2: Temperature variation of groundwater and stream under gaining (a) and losing stream (b) conditions ...................................................................................................................... 100 Figure 12.3 Observed stream and sediment temperatures downstream of Goondiwindi Weirs.... 103 Figure 13.1: Stream flow measurements taken in November 2004 on the Alstonville Plateau ..... 114


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TablesTable 2.1: Summary of tools to assess stream-aquifer connectivity ................................................ 20 Table 2.2: Spatial scales in stream-aquifer connectivity .................................................................. 23 Table 2.3: Time scales in Stream-Aquifer Connectivity.................................................................... 23 Table 2.4: Typical catchment hydrology datasets and sources ....................................................... 26 Table 3.1: Comparison of automated seepage meters .................................................................... 36 Table 3.2: Results of seepage meter trials in Meershaum Drain, Tuckean Swamp ........................ 38 Table 7.1: Different Ground-based electromagnetic techniques...................................................... 53 Table 7.2: Common geophysical tools used in borehole logging..................................................... 51 Table 8.1: Recursive digital filters used in base flow analysis.......................................................... 62 Table 8.2: Different storage-outflow models used in recession analysis ......................................... 69 Table 9.1: Commonly used units for hydraulic conductivity (K) ....................................................... 78 Table 9.2: Indicative hydraulic conductivities of some rock types.................................................... 79 Table 10.1: Australian Standards related to water sampling............................................................ 87 Table 10.2 Relative abundances of the oxygen and hydrogen isotopes.......................................... 88 Table 10.3: Decay constants and half-lives of selected radioactive isotopes with application to hydrology .................................................................................................................................. 90 Table 13.1: Different procedures for determining mean velocity at a vertical ................................ 107 Table 13.2: Mannings n values for small natural streams .............................................................. 109 Table 13.3: Calculation of Mannings n from Field Observations.................................................... 110 Table 16.1: Inventory of published hydrogeological maps in Australia .......................................... 128

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1. IntroductionGroundwater and surface water have been historically managed as isolated components of the hydrologic cycle, even though they interact in a variety of physiographic settings (Sophocleous, 2002). In many catchments, groundwater and surface water are hydraulically connected. For example, surface water features such as rivers, lakes, dams and wetlands can receive groundwater from underlying aquifers (Winter et al, 1998). These interactions can have significant implications for both water quantity and quality. Seepage of fresh groundwater into a river can be important in maintaining flows during extended dry periods. This can be critical for supplying the needs of surface water users such as irrigators as well as for aquatic ecosystems. Pumping from an aquifer near a river can dramatically change the amount of this baseflow to the river. In contrast, if the groundwater is salty or contaminated, increased groundwater discharge can have a negative effect on river water quality. Hence, effective management of water quantity and quality issues requires an understanding of these surface water-groundwater interactions. Assessing groundwater-surface water interactions is often complex and difficult. Commonly, groundwater level measurements are used to define the hydraulic gradient and the direction of groundwater flow. Flow measurements at various points along the stream are used to estimate the magnitude of gains or losses with the underlying aquifer. Other tools used to investigate groundwater-surface water interaction include seepage meters (Lee and Hynes, 1978; Cherkauer and McBride, 1988; Brodie et al, 2005), river bed piezometers (Baxter et al, 2003), time-series temperature measurements (Stonestrom and Constanz, 2003) and environmental tracers (Crandall et al, 1999; McCarthy et al, 1992; Herczeg et al, 2001; Baskaran et al, 2004). In most cases the limited number of data collection points results in a lack of detailed understanding of groundwater-surface water interactions in the field. Numerical modelling approaches on the other hand can provide a valuable tool for developing a framework by combining information obtained from the other field methods. This report documents the tools available to assess connectivity between surface water and groundwater systems in a catchment. This report also gives examples of trials of some of these assessment tools to better understand the nature of connectivity in the two catchments, the Border Rivers in the Murray-Darling Basin and Lower Richmond on the north coast of New South Wales.

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2. Assessment of ConnectivityTraditionally, surface water and groundwater resources have been independently assessed. An important addition in taking an integrated approach is that connectivity is also assessed. The nature and level of this assessment will depend on the:(i.) (ii.) (iii.) (iv.)

(v.) (vi.)

Key water management issues within the catchment; Significance of the water resource in terms of social, economic and environmental values; Relative development of the water resource in terms of the ratio between use (and allocation) and sustainable limits; Risk assessment of the likely magnitude of impacts associated with the management issue, such as loss of economic productivity, land and water degradation or poor ecosystem health; Availability of resources such as data, budget and expertise, and; Management and policy timeframes.

Hence, water resource assessment includes investigation of:(i.)

(ii.)

(iii.)

Surface water features including streams, reservoirs, wetlands and estuaries. This includes such aspects as flow duration and dynamics, water storage capacity, water quality, aquatic ecosystems, land use impacts, climate variability and water extraction regimes; Groundwater systems, covering aspects such as aquifer geometry, geological and stratigraphic configurations, hydraulic properties such as transmissivity and storativity, water sources and sinks such as recharge, abstractions and discharge mechanisms, environmental dependencies and the impacts of land use, and; Surface water-groundwater interactions, involving the analysis of the dynamics of water flow between aquifers and surface water features, and the impacts of this interaction in terms of water quantity, quality and ecology.

Hence, the focus is to acquire the baseline information to describe the characteristics of surface water and groundwater systems of the catchment, and their interactions, both spatially and temporally.

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2.1 Available Assessment Methods for ConnectivityA wide range of tools are available to assess the nature and degree of the connectivity (Figure 2.1). A summary of these methods is outlined below, with more detailed information provided in the following chapters of this report.Seepage Measurement

The direct measurement of seepage flux at the stream-aquifer interface can be undertaken using seepage meters or similar devices. The basic concept is to cover and isolate the stream bed with an inverted open chamber and measure the change in volume of water contained in a bag attached to the chamber over a measured time interval. Additional water in the bag over the time of operation indicates gaining stream conditions. Several modifications have been made to the design and operation of the seepage meter to address potential sources of measurement error and to handle logistical issues. Automated versions using different technologies to enable real-time monitoring of seepage flux have been developed.Field Observations

Visual evidence of seepage flux can be observed in certain catchments and settings. An initial reconnaissance can highlight hotspots where groundwater is discharging to streams; provide guidance to useful parameters to measure and to identify management issues that are impacted by connectivity. Examples of field indicators include direct observation of water flow from springs at the margins or within the stream bed, water vapour or ice-free conditions around springs during winter, mineral precipitates or iron-bacteria accumulations, or changes in water colour or odour.Ecological Indicators

Specific vegetation communities or biota can indicate groundwater discharge to surface water features. Changes in the composition and accumulated biomass of submerged aquatic plants can relate to groundwater seepage. The near-stream presence of phreatophytic plants, which are deep-rooted and can access groundwater, can indicate a shallow watertable. The extent and composition of biota that inhabit the hyphoreic zone can also indicate the processes of near-stream groundwater and surface water mixing.Hydrogeological Mapping

Knowledge of the hydrogeology surrounding a surface water feature is critical in understanding connectivity. This involves mapping the configuration and characteristics of the groundwater flow systems within the catchment. This covers aspects such as aquifer geometry, host geology and stratigraphy and hydraulic properties (such as transmissivity and storativity). Also included are specific geological features such as faults, facies changes or river geomorphology that can locally control groundwater flow.


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Geophysics and Remote Sensing

Geophysical and remote sensing technologies such as airborne electromagnetics (AEM), radiometrics, seismic waves, electrical charge, or satellite imagery can be used to interpret connectivity. These surveys can map the variation in parameters such as groundwater salinity, vegetation types or soil moisture that can be secondary indicators of groundwater discharge. They can also be used to identify geological features that control seepage flux. Mapping of landscape parameters (such as soil type, land use and vegetation cover) that can have an impact on seepage flux can also be supported by geophysical or remote sensing technologies.Hydrographic Analysis

The stream hydrograph can be processed and analysed to characterise the magnitude and timing of groundwater discharge to streams. Baseflow separation techniques use the time-series record of stream flow to derive a baseflow hydrograph. Of these techniques, recursive filters are the most commonly applied. Frequency analysis takes a different approach by deriving the relationship between the magnitude and frequency of stream flows. Recession analysis focuses on recession curves which follow stream flow peaks. These curves are fitted using storage-outflow models to characterise the natural storages that feed the stream.Hydrometric Analysis

Hydrometric methods are based on Darcys Law so focus on the hydraulic gradient between groundwater and surface water systems and the hydraulic conductivity of the intervening aquifer and bed material. Piezometers are used to measure groundwater levels which are compared with the elevation of the stream stage. Pump (or slug) tests can be undertaken on these piezometers to estimate the transmissivity of the aquifer material.Hydrochemistry Studies

Interpretation of the chemical constituents of water can provide insights into streamaquifer connectivity. Dissolved constituents can be used as environmental tracers to track the movement of water. For example, a particular characteristic of the groundwater chemistry (such as high radon levels) can be used as an indicator of groundwater discharge when measured in the surface water. Environmental tracers can occur naturally or have been released into the general landscape by human activities. Some of the commonly used environmental tracers include field parameters such as: EC or pH; the major anions and cations such as calcium, magnesium, sodium, chloride and bicarbonate; stable isotopes in the water molecule of oxygen-18 (18O) and deuterium (2H); radioactive isotopes such as tritium (3H) and radon (222Rn); and industrial chemicals such as chlorofluorocarbons (CFC) and sulphur hexafluoride (SF6).Artificial Tracers

Artificial tracer tests are used to evaluate the extent to which aquifers interact with streams, providing information on groundwater flow paths, travel times, velocities, dispersion, flow rates and the degree of hydraulic connection. These tests involve the

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introduction of a tracer material or chemical and subsequent monitoring of its movement. This differs from environmental tracer methods which rely on the measurement and interpretation of background concentrations. Fluorescent dyes (such as Rhodamine WT), conservative major ions (such as chloride or bromide), organic compounds (such as ethanol or fluorinated benzoates), isotopes (such as selenate or deuterium) and non-pathogenic micro-organisms or colloidal material (such as clubmoss spores) have been used in tracer studies.Temperature Studies

Heat can also be used as a tracer to characterise seepage flux. Time series monitoring of temperature in both the surface water and groundwater systems is used. Stream temperatures have a characteristic diurnal pattern overprinting seasonal trends, whilst regional groundwater temperatures tend to be relatively constant at the daily scale. Temperature monitoring at varying depths in the stream bed can indicate the relative influence of groundwater and surface water processes. Numerical models of heat flow (such as VS2DH and SUTRA) can be used to quantify seepage flux.Water Budgets

A common approach to investigating seepage flux between a stream and underlying aquifer is to measure stream flow at specific points. These measurement sites subdivide the stream into reaches and a water budget is estimated for each reach, accounting for inputs such as tributary flows and outputs such as evaporative losses and diversions. The difference between inflows and outflows is then attributed to the seepage flux. The method relies on accurate measurement of stream flow and appropriate accounting of the other gains and losses.

2.2 Comparison of MethodsTable 2.1 presents a summary comparing these different assessment methods. These tools are described in the context of:(i.)

(ii.)

(iii.) (iv.) (v.) (vi.) (vii.)

Spatial Scale, classified in terms of local (ie at a point or site), intermediate (at the scale of a feature such as a stream reach) and regional (at the catchment scale), refer Table 2.2; Temporal Scale, classified in terms of short-term (over the timeframe of days to months such as tidal, evapotranspiration or discrete episodic processes), medium-term (at the seasonal to yearly scale) and long-term (exceeding the decadal timeframe such as influences of climate change), refer Table 2.3; Cost, associated with collection, analysis and interpretation of data; Ease of Use, focusing on the accessibility of technology and the extent of prior expertise required; Advantages, the inherent benefits of applying the methodology; Limitations, the potential constraints and limiting assumptions; Application, outlining the extent that the method has been used in Australia.


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a b

c

Field Assessment Tools for Stream-Aquifer Connectivityd f

e

Figure 2.1: Examples of different methods of assessing stream-aquifer connectivity (a) direct measurement of flux using seepage meters (b) hydrometric studies using minipiezometers in the stream bed (c) monitoring of groundwater levels and stream levels/flows (d) temperature monitoring in the stream and shallow bed sediments (e) run-of-river geophysical survey (f) water sampling for hydrochemistry

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Table 2.1: Summary of tools to assess stream-aquifer connectivityMethod Spatial Scale Temporal Scale Cost Ease of Use Advantages Limitations Application

Desktop ToolsHydrographic Analysis Processing of time-series stream flow monitoring to define baseflow (groundwater discharge) component Intermediate to regional Hydrograph represents water balance for subcatchment above gauge Medium to long-term Depends on length of monitoring record Low High Many analysis techniques and software tools available. Stream flow data routinely collected Uses existing flow monitoring data. Can be undertaken as a desktop study prior to detailed field investigations. Provides information of seepage changes through time Applicable to gaining stream conditions only. Assumption that baseflow is groundwater discharge may not be valid. Baseflow effected by water use and management activities (eg regulation) does not provide spatial distribution of groundwater input along stream Compiling and interpreting hydrogeological data can be time consuming and complex. Limited borehole data can lead to misinterpretation. Commonly applied method for unregulated Australian catchments

Hydrogeological Mapping Mapping of groundwater systems including flowpaths, groundwater quality, aquifer structure and properties and geomorphology.

Intermediate to Regional Typical mapping scales of 1:100,000 to 1:250,000

Short to Mediumterm Usually average conditions at time of mapping Some parameters such as aquifer transmissivity or structural contours are time-insensitive

Medium to High Depends on data availability. Expensive if drilling required to supplement existing data

Low to Medium Knowledge of hydrogeological principles required

Provides conceptual understanding of groundwater systems around stream and hydrogeological controls on connectivity

Groundwater flow system, surface geological and hydrogeological mapping available at a coarse scale for many groundwater management areas across Australia.

Modelling Simulate water flow regime around stream using mathematical equations

Intermediate to Regional Typical models are 2D profiles or 3D grids

Medium to Longterm Used to predict future events

Low to High Depends on data availability and model complexity

Low to Medium Requires good conceptual understanding of hydrological processes and modelling expertise

Useful predictive tool for management and policy. Helps define information gaps. Transient 3-D models can estimate changes in seepage through time and space.

Oversimplified models may not be adequately robust. Overcomplex models can be data hungry, costly and timeconsuming

Commonly, surface water models for a catchment are developed in isolation to groundwater models.


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Method

Spatial Scale

Temporal Scale

Cost

Ease of Use

Advantages

Limitations

Application

Field ToolsField Indicators Visual indications of seepage such as water clarity, springs, aquatic plant species, chemical precipitates etc Local Site specific observation of seepage indicators Short-term Current at time of observation Low Medium to High Easily incorporated into field work. Depends on familiarity with indicators. Medium Need to establish monitoring network Medium Conceptually simple but needs expertise in field measurement and data interpretation Low Needs technical expertise in field equipment operation and data interpretation Can identify seepage hotspots quickly. Return visits can provide information on seasonal changes in seepage flux. Field indicators can form basis for mapping (eg airphoto interpretation) Limited in quantifying seepage flux. Effectiveness varies with observers knowledge of field indicators (eg plant or aquatic biota). Used in specific settings such as acid groundwater (eg iron precipitates, lilies) and karstic streams (eg travertine deposits). Assessment of groundwaterdependent ecosystems not routine

Artificial Tracers Monitoring movement of introduced tracers such as fluorescent dye to track water flow

Local to Intermediate

Short to Medium term Typical tracer studies over days to weeks

Can provide direct evidence of water movement between stream and aquifer. Aquifer parameters and fluid transport properties can be quantified.

Tracer studies require careful planning including meeting environmental regulatory controls. Processes such as degradation, precipitation or sorption can affect tracer performance.

Not routinely applied in connectivity studies in Australia. Overseas focus on karstic aquifers or investigations of contaminated sites.

Geophysics and Remote Sensing Use of geophysics (eg resistivity, EM, radiometrics) or remote sensing (eg Landsat) to map landscape features that indicate or control connectivity Hydrochemistry and Environmental Tracers Use of chemical constituents of water (such as major ions, stable isotopes, radon) to track water flow

Local to Regional Range from site specific (eg downhole surveys) to intermediate (eg runof-river EC imaging), to catchment scale (eg satellite imagery).

Short-term Measures conditions at the time of survey. Multiple surveys can provide trends through time.

Medium Per hectare cost depends on technology and platform (eg ground, airborne)

Allows rapid, non-invasive mapping of landscape parameters with good spatial resolution. Some techniques provide information at depth.

Requires specific equipment, technical expertise and logistical support. Can require complex data processing and calibration with other datasets. Ground surveys can encounter obstacles such as rough terrain, vegetation cover etc.

Opportunities exist to use geophysical data collected for other purposes eg. mineral exploration. Satellite imagery commercially available, some free in public domain.

Local to Regional Depends on scope of water sampling survey.

Short to Mediumterm Defines chemistry at time of sampling. Time-series monitoring (eg EC, pH) possible.

Medium to High Can be expensive due to sampling logistics and cost of analyses

Low Requires expertise in appropriate sampling and data interpretation

Useful in quantifying seepage flux and defining key hydrological processes (such as groundwater recharge and discharge).

Can have long lead times between sample collection and final analytical results.

Commonly used in Australia to identify hydrogeological processes including groundwater seepage to streams.

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MethodHydrometrics Measurement of hydraulic gradient between aquifer and stream and the hydraulic conductivity of intervening aquifer material. Based on Darcys Law. Seepage Measurement Direct measurement of water flow between stream and aquifer using seepage meters

Spatial ScaleLocal to Regional Can range from instream studies, to borehole transects to regional flow net analysis

Temporal ScaleShort to Mediumterm Possible to compare hydrographs of stream and groundwater levels

CostLow to Medium Can use existing data but costly if drilling of bores is required

Ease of UseMedium to High Comparison of groundwater and stream levels simple. Estimation of hydraulic conductivity more difficult. Low Simple concept with meters easy to use and no prior technical knowledge required. Medium to High Temperature simple to measure. Heat transfer modelling to quantify seepage more difficult. Medium to High Conceptually simple using existing monitoring data. Water balance components such as extraction or diversions can be difficult to quantify

AdvantagesComparison of stream and groundwater levels a simple guide to seepage direction. Installation of minipiezometers in stream bed allows direct local measurement of potential seepage direction.

LimitationsRelies on reasonable estimate of hydraulic conductivity to quantify seepage flux. Assumption of simple groundwater flow conditions may not be valid. Point measurement. Need to correct for density effects.

ApplicationComparison of stream levels with nearby groundwater levels commonly used to define direction of potential seepage.

Local Point measurement of seepage. Many measurements required to map spatial variations.

Short-term Meters typically installed over days/weeks. Measures aggregate seepage over time of operation. Short-Medium term Temperature can be included in timeseries monitoring.

Low to Medium Can be time consuming if measuring at multiple sites.

Direct measurement of seepage flux. Meters are simple and inexpensive to construct and provide a semiquantitative measurement.

Potentially significant measurement errors due to meter design and operation. Unsuitable for high stream flow, gravel and heavy clay sediment beds

Main application to date in Australia has been investigating leakage from irrigation channels or studying aquatic ecosystems

Temperature Monitoring Monitor variations in stream and sediment temperatures to trace seepage.

Local Multiple measurements required to map spatial variability in seepage Intermediate to Regional Does not provide spatial variability of seepage along reach being investigated

Low Temperature loggers are cheap and widely available.

Temperature loggers are simple, robust and cheap. Heat transfer models that can compliment flow models to quantify seepage are available.

Only measures at a point. Interpretation of monitoring requires confirmation using other assessment methods.

Not specifically applied to study stream-aquifer connectivity in Australia to date. Opportunities to incorporate real-time temperature monitoring into existing hydrographic network

Water Budgets Quantification of stream reach water balance to define seepage component

Short to Medium Term Possible to use timeseries monitoring of stream flow at multiple stations

Low to Medium Can be expensive if data collection required for estimating water balance components

Simple water balances estimated rapidly using existing stream flow monitoring. Provides estimate of aggregate seepage along reach.

Measurement errors in stream flow data can be significant, hence more suited to long reaches. Can be misleading if water balance component (eg extraction) is not adequately accounted for.

Routinely applied, particularly for regulated rivers or irrigation channels.


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Table 2.2: Spatial scales in stream-aquifer connectivityScale Typical Units Relevance

Catchment-scale Regional

>100 km2

Hydrogeological setting Water management areas Catchment management targets Catchment monitoring and reporting Water management decisions Environmental Planning Process studies Ecosystem dependencies Water quality protection

Feature-scale Intermediate Site-Scale Local

1-100 km

200 mm rain Local Meteoric Water Line (Barakula) Evaporation trend slope = 4.7

River water GW-upstream of Keetah (far stream) GW-upstream of Keetah (near stream) GW-downstream of Keetah

o

-50 -60 -10 -8

Global Meteoric Water Line

-6

-4o

-2

0

2

4

Oxygen-18 ( /oo , SMOW)

Figure 10.2. Deuterium versus oxygen-18 concentrations for river water and groundwater in the Border Rivers Catchment The chloride-deuterium plot (Figure 10.3) suggests that three types of groundwater occur in the study area namely: (i) some groundwaters upstream of Keetah, characterised by low chloride and relatively enriched D, that is most frequently recharged by river water (ii) some groundwaters upstream of Keetah and a few groundwaters that are close to the MacIntyre River reach near Goondiwindi Weir, with low chloride and depleted D, representing areas that are recharged less frequently by the river and more frequently by high rainfall and (iii) highly saline groundwaters further downstream of Goondiwindi, with very high chloride and lower D, that never or rarely receive recharge from surface water.100000 10000Chloride (mg/L)

infrequently or never recharged by river most frequently recharged by river

1000 100 10 less frequently 1recharged by river

-50

-40

-30

-20

-10

0

10

Deuterium ( o/oo, SMOW)

GW-upstream of Keetah

River water

GW-downstream of Keetah

Figure 10.3 Chloride versus deuterium concentrations for river water and groundwater in the Border Rivers Catchment The results of hydrochemical and environmental isotope sampling from the Border Rivers catchment indicate that the river and the shallow alluvial aquifers close to the river in the area upstream of Keetah have a close hydraulic relationship. In this upper catchment area, the streams are dominantly losing and recharge the shallow aquifers. The environmental isotope data demonstrated that recharge of the alluvial aquifers by surface water occurs by bank infiltration as well as diffuse recharge during high rainfall events.

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11. Artificial TracersArtificial tracer tests can be used to evaluate the extent to which aquifers interact with streams, providing information on groundwater flow paths, travel times, velocities, dispersion, flow rates and the degree of hydraulic connection (Flury and Wai, 2003;Otz et al, 2003). These tests involve the introduction of a tracer material or chemical and subsequent monitoring of its movement. This differs from environmental tracer methods which rely on the measurement and interpretation of background concentrations of the chemical constituents of water (such as major ions, stable or radioactive isotopes, refer Chapter 10). In artificial tracer tests, a substance is introduced and monitored to track the movement of water. Hence, the movement of the tracer should match that of the water flow regime, so it should not be effected by sorption onto geological material, changes in chemistry (such as pH or salinity), or degradation by physical or biological processes. The tracer should not affect the water flow regime, by changing fluid density or viscosity. The tracer should have low background levels and be able to be measured simply and cheaply to low detection levels. As tracer tests involve an introduction of a substance into the environment, the tracer should have low toxicological or pathogenic impacts. The tracer should be stable for the duration of the test but not be retained as residual material in the longer term. Dyes have had a long tradition of use as tracers, commencing with tracing the source of typhus epidemics in Europe (des Carrieres, 1883). Sulforhodamine B, Rhodamine B, Sodium Fluorescein and Rhodamine WT are popular due to low cost, easy detection to low limits with a fluorometer, and the potential for visualisation (Flury and Wai, 2003). Major ions such as chloride and bromide have been used as they behave conservatively and rarely sorb onto geological material. A lithium chloride solute tracer was used to estimate seepage fluxes in a headwater stream (Harvey et al, 1996). Organic compounds such as ethanol, benzoate and fluorinated benzoates have been proposed as tracers (Malcolm et al, 1980; Bowman and Gibbens, 1992). However, retardation and degradation is an issue in low pH conditions and with the presence of abundant clay, iron oxides or organic material (McCarthy et al, 2000; Jaynes, 1994). Flourescent polyaromatic sulfonates have been trialled in geothermal groundwater studies due to their resistance to thermal decay (Rose et al, 1998). The use of isotopes as artificial tracers tends to be limited due to radiation risks and the complexity of chemical analysis. Short lived isotopes such as selenate (75S) as well as deuterium (2H) are considered the most useful (Flury and Wai, 2003). In some studies, a particular pollutant of water is investigated, requiring the tracer to follow the fate of the pollutant rather than water flow. This is the case when non-pathogenic microorganisms are used to trace the transport of human pathogens. Solid and colloidal particles such as clubmoss spores have been used in studies in karstic aquifers, but analysis requires filtering and microscopic examination (Drew, 1968). The use of nanotechnology in hydrogeochemical studies, especially the application of chemical-specific nano-scale tracers developed by the biomedical industry has been suggested (Divine and McDonnell, 2005).

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Various strategies can be used to undertake an artificial tracer test. The constant injection rate technique is commonly employed in the field to assure complete mixing of the injected tracer. A dye such as Rhodamine WT is released upstream of the study reach (see Figure 11.1). Using medical devices for controlling intravenous fluid injection, the dye injection can be started several hours before the beginning of the investigation. Water samples are collected regularly at different locations and the dye concentration analysed with a fluorometer. In this way, very low concentrations can then be measured far downstream. The samples are taken from the centre of the channel at each location. By analysing the dye concentration in the sample, the amount of water required to dilute the injected dye solution to the sample concentration can be determined. The amount of water includes the amount of stream flow passing the injection site, plus any groundwater contributions the stream has received between the injection and sample sites.

Figure 11.1: Dye tracer technique for assessing groundwater and surface water interaction in the field (Otz et al, 2003)

A tracer injection trial can provide valuable insights into the rate and direction of groundwater movement near a surface water feature (Dahm and Valett, 1996). This involves establishing monitoring sites both within the aquifer and along the stream. This network can include:(i.) (ii.) (iii.) (iv.) (v.)

Existing boreholes or piezometers in the vicinity of the stream; Sampling pits dug near the stream and accessing the shallow watertable (these should be refilled after the experiment); Any springs or seepage areas evident in the area; Specific sites to monitor the stream itself; Constructing minipiezometers both within and adjacent to the stream bed.

A tracer is then injected into a centrally located pit or piezometer and the time recorded. Each of the groundwater and stream monitoring sites is subsequently sampled to measure if the tracer is detected, and the time when this occurs. This is used with the distance between the injection site and the monitoring site to calculate groundwater velocity and direction.


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An even simpler approach is to inject a small bolus of dye about 5-15 cm within the stream sediment using a syringe with a long cannula, or via a minipiezometer (Grimm and Fisher, 1984). The time of injection and also the time and position that the dye first appears at the sediment surface is recorded. The distance between the injection point and emergence point is used to calculate groundwater velocity and direction. If the dye does not emerge, dig up the injection site or check the minipiezometer for the status of the dye bolus. If the dye has disappeared this suggests that lateral or downward seepage conditions prevail, rather than upward. In a point dilution test, the tracer is added to a piezometer and the subsequent rate of dilution of the tracer within the piezometer is monitored. This data is used to estimate the groundwater velocity at the piezometer (Halevy et al, 1967; Gaspar, 1987). Electrical conductivity measurements were used to record the dilution of a KCl tracer added to piezometers at three contrasting Australian riparian and estuarine sites (Lamontagne et al, 2002). Displacement of the tracer by its improper release into the piezometer or due to the subsequent recirculation process was found to be the main technical difficulty.

11.1 Advantages and DisadvantagesArtificial tracers are a useful investigation tool as the application and monitoring of the tracer can be designed and implemented in a controlled way. The amount of tracer introduced is known, allowing quantification of aquifer parameters and fluid transport properties. Specific processes in particular hydrogeological settings can be investigated by using appropriate tracers. The method is particularly useful in characterising groundwater flow in highly variable aquifers (such as fractured rock or karsts, refer Box 11.1) and in solute transport studies (such as contaminants and nutrients). Specific tracers can be used to track pollutants such as human pathogens, where the movement and fate of these pollutants may not match water flow. Tracers can be used to assess the significance of local geological features (such as faults, clay layers or cave systems) on stream-aquifer connectivity. Seepage can be assessed either qualitatively (such as visual inspection of the presence of dye or the use of charcoal-based detectors) or quantitatively (such as modelling of time-concentration breakthrough curves to derive travel time characteristics). Tracers can provide direct evidence for the movement of water between one point to another, which is easily understood by the public, regulatory agencies or the courts (Mull et al, 1988). Appropriate application of tracers requires careful planning and design with some pretest knowledge of hydrogeology. Unanticipated short travel times can lead to high tracer concentrations being released to watercourses and potentially into public water supplies. This was the case when a borefield tracer test in 2003 unintentionally dyed red the water supply for about a million people (SS Papadopulos and Associates, 2004). Part of this planning is meeting any regulatory controls on the release of chemicals in the environment for public health or ecosystem protection. The performance of the tracer in matching water movement can vary with the hydrogeological setting. Dyes can have complex chemical interactions which tend to be pH-dependent or can be selectively sorbed with geological material. Sometimes, the dye mixture viscosity can be dramatically affected by variations in the ambient temperature, complicating the determination of flow rates. Tracer tests can have

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overheads in terms of cost and time, particularly when investigating longer or slower groundwater flow paths.

11.2 Relevant LinksUSGS Rhodamine WT Reader http://smig.usgs.gov/SMIG/rhodamine_reader.html Joint International Isotopes in Hydrology Program (JIIHP) http://www.iaea.or.at/programmes/ripc/ih/jiihp_home.htm

Box 11.1: Dye tracing tests of the Piora aquifer, Switzerland (Otz et al, 2003)In Switzerland, the Piora Valley is bounded on the north by the Cadimo Valley, to the southwest by the Leventina Valley, to the northwest by the Canaria Valley, and to the east by the St. Maria Valley. The Piora Valley is noted for losing streams and leaking lakes. Since construction of the hydroelectric power plant and dam at Lake Ritom over 80 years ago, dye tracing tests have been used to evaluate the hydrologic flow paths in aquifers of the Piora Valley. These dye tracing tests provided local information on the hydrogeology of the Piora Zone, but not a comprehensive understanding of the overall hydrodynamics of the Piora aquifer. The objective of the study by Otz et al, (2003) was to clarify and quantify water loss from major streams and lakes using additional dye tracing tests and to determine whether flow paths are regional in scale. A variety of organic fluorescent dyes were used to evaluate the hydrogeologic flow system in the Piora Valley and the adjacent valleys in Switzerland. The nature and chemical characteristics of the dyes and standard tracing procedures are described in Kass (1988). Briefly, multiple dyes were placed in different parts of the Pioral flow system and the dye breakthrough curves were monitored at possible discharge points. From the breakthrough curves, maximal flow velocities for the dyes to move from places of introduction to reemergence were calculated. Results of seven dye tracing tests done from 1993-1997 showed that the direction of groundwater flow in the Piora aquifer is from the Pioral Valley to the Ri di Lareccio springs in the Santa Maria Valley, and even further east to the di Campo Valley. Dye tracing tests show that a major sinkhole in the Piora Valley, Calderoni sinkhole, is located precisely on the water divide where subsurface flow in the Piora Valley and surface water diverge and move in the opposite direction. The dye tracing results also showed no hydraulic connection between surface water in the Piora Valley and the famous Pertusio spring, located in the upper Santa Maria Valley. Only a small amount of dye from the two dye tracing tests done in 1993 and 1997 entered an exploratory gallery built to test the variability of the AlpTransit tunnel, being built in competent rock under the Triassic Piora aquifer, effectively perched above.


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12. Temperature StudiesIn a connected system, the exchange of water between the stream and shallow aquifer plays a key role in influencing temperature not only in streams, but also in their underlying sediments. As a result, analysis of subsurface temperature patterns can provide information about seepage flux. Studies, notably in North America, have used temperature monitoring in the stream and underlying sediments as a screening tool for identifying gaining and losing reaches (Silliman and Booth, 1993; Stonestrom and Constanz, 2003). Recently, heat as a tracer has been demonstrated to be a robust method for quantifying surface water-groundwater exchanges in a range of environments, from perennial streams in humid regions (Lapham, 1989; Silliman and Booth, 1993) to ephemeral channels in arid locations (Stonestrom and Constanz, 2003). Logging devices that measure temperature at specific time intervals and store the information in memory can be installed both within the stream and at different depths in the sediments below the stream bed. The sensors most often employed are thermocouples, thermistors, resistance temperature devices and integrated circuit sensors (Figure 12.1). The characteristics of each type of temperature logging equipment along with their advantages and disadvantages and installation methods are

presented in Stonestrom and Constantz (2003).Figure 12.1: Common temperature sensors used to measure sediment and stream temperatures (Stonestrom and Constanz, 2003)

The hydraulic transport of heat enables its use as a tracer with temperature monitoring especially suited for delineating fine-scale flow paths. The heat tracer method has been used to estimate groundwater velocity and aquifer hydraulic properties, and to identify areas of recharge and discharge (e.g. Bouyoucos, 1915; Suzuki, 1960; Lee, 1985; Lapham, 1989; Silliman and Booth, 1993; Brewster Conant Jr, 2004). One way of using heat tracing in stream-aquifer studies is to compare the temporal patterns evident in stream and shallow sediment temperature. Stream temperatures have a characteristic diurnal pattern overprinting seasonal trends, being influenced by changes in solar radiation, air and ground temperature, rainfall and stream inflows that include groundwater discharge (Sinokrat and Stefan, 1993). These diurnal variations in temperature in the near-stream environment are often large and rapid, providing a clear thermal signal that is easy to measure. In contrast, the temperature of regional groundwater tends to be relatively constant at the daily scale. The movement of heat between surface water and groundwater systems is both advective (associated with

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fluid movement) and conductive (through the static solid/liquid phase). Ignoring the effect of insitu sources of thermal energy (such as from biological activity), the temperature pattern in the shallow stream sediment profile can be used to evaluate seepage flux. The temperature signatures for three potential forms of stream-aquifer connectivity (gaining, losing and neutral) have been hypothesised (Silliman and Booth, 1993). In gaining stream reaches, the hydraulic gradient is upward as indicated by a groundwater level in piezometers that is higher than the stream stage (Figure 12.2a). Although the stream has a large diurnal temperature variation, the shallow sediment has only a slight or no diurnal variation. The downward propagation of any surface temperature effects is moderated by water that is flowing up from depths where temperatures are constant at the daily time scale. At any given depth beneath the streambed, higher flows of groundwater to the stream lead to smaller variations in sediment temperature while smaller flow leads to larger variations. Consequently, shallow installation of temperature equipment is necessary to characterise gaining stream reaches, in order to detect significant temperature variations. In losing stream reaches, the stream stage is higher than the groundwater level so that the potential hydraulic gradient is downward. This downward flow of water transports heat by advection from the stream, resulting in deeper propagation of diurnal temperature fluctuations into the sediment profile (Figure 12.2b). As a consequence, deeper installation of temperature equipment (inside the piezometer or beneath the stream bed) is necessary for losing streams to be characterised. Losing streams also tend to have larger daily temperature fluctuations than gaining reaches, due to the absence of any moderating effect from groundwater inflow (Constanz, 1998).

Figure 12.2: Temperature variation of groundwater and stream under gaining (a) and losing stream (b) conditions (adopted from Stonestrom and Constanz, 2003)

In neutral reaches of the stream, thermal conduction will control stream sediment temperatures. This means that sediment temperature can vary due to changes in surface water temperatures, and will have an average that is between that of the surface water and groundwater. The distinct temperature signal of episodic infiltration associated with ephemeral streams has also been characterised (Ronan et al, 1998; Constanz et al, 2002).


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Estimating the water exchange between the stream and shallow aquifer requires knowledge of the hydraulic and thermal conductivity of the material and the hydraulic gradient as defined by the stream stage and groundwater level. Numerical models of heat flow, such as VS2DH (Healy and Ronan, 1996) and SUTRA (Voss, 1984) can be used to quantify seepage fluxes. These can supplement and help calibrate more traditional groundwater flow models. In particular, temperature modelling can help constrain estimates of hydraulic conductivity which can vary over several orders of magnitude, as the thermal conductivity of sediments has a much smaller range of potential values. Stream sediments composed of sand and gravel can have a hydraulic conductivity six orders of magnitude higher than clay. In contrast, the thermal conductivity of porous materials depends upon the composition and arrangement of the solid phase with the potential range in thermal conductivity between coarse grained sand (2.2 W/m oC) and clay (1.4 W/m oC) being much smaller than that for hydraulic conductivity (Stonestrom and Constantz, 2003). The work of Bravo et al (2002) is a recent example of using temperature data to constrain estimates of boundary fluxes and hydraulic conductivity in a groundwater flow model for a wetland system. Fluctuations in temperature can also directly influence seepage rates due to its influence on water density. The hydraulic conductivity of the stream bed is both a function of the porous medium and the water itself, the latter in terms of density and dynamic viscosity. Hence, transmission rates through the sediment bed can increase with increased water temperature. This process was used to explain diurnal variations in seepage flux in losing reaches of a small alpine stream (Constanz, 1998).

12.1 Advantage and DisadvantagesThe use of temperature as a hydrologic tracer has several advantages over other field methods. Temperature logging devices are robust, simple and relatively inexpensive and available for various scales of measurement. The temperature signal arrives naturally and the temperature data are immediately available for inspection and interpretation. Temperature monitoring can be used as a screening tool for identifying gaining and losing stream reaches. Such a screening method can be valuable both as a rapid investigative tool for small studies and as a precursor to more detailed studies such as the design/installation of a groundwater monitoring network. Once installed, loggers can also provide useful time-series data that can provide information on seasonal changes in seepage flux. Temperature studies are particularly useful in defining small-scale flow paths, such as associated with stream banks or sand bars (Stonestrom and Constanz, 2003). Despite these advantages, this method has some potential limitations. Interpretation of the temperature data can be ambiguous when viewed in isolation. It is recommended that temperature monitoring be used in conjunction with other methods such as minipiezometers, seepage meters or hydrographic analysis when interpreting streamaquifer connectivity. Also, the temperature measurement is at a point in space and many measurements may be required to obtain information on spatial variability. It can be difficult to separate localised effects (such as associated with weirs or shallow throughflow) from the broader seepage domain.

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It is suggested that temperature loggers can be readily and cheaply incorporated into existing hydrographic networks to provide a supplementary dataset for understanding stream-aquifer connectivity. This is because the water level data can indicate the potential seepage direction and the temperature data can help estimate the magnitude of the seepage. It is also recommended that the existing temperature logging used to calibrate pressure transducers for monitoring water levels be upgraded to sufficient accuracy for heat transfer studies. Temperature monitoring would be particularly useful in estimating infiltration rates in Australian ephemeral streams, where conventional water level recording and hydrographic analysis is problematic. Routine recording of temperature data also has relevance to the investigation and management of aquatic ecosystems, notably within the hyporheic zone.

12.2 Data AvailabilityStream temperature data can be routinely collected as part of the stream gauging network, as pressure transducers that measure stream level require such data for calibration. Brodie et al (2007) outlines the key hydrographic databases across Australia, mostly maintained by State and Territory water management agencies. However, this temperature data is not commonly made available and may not be of adequate resolution for heat transfer studies. Groundwater temperature can also be recorded in the same way, as pressure transducers are a common logging device for groundwater levels. It would be rare for both groundwater and surface water temperatures to be monitored in close enough vicinity at a site for application in heat transfer studies. For instance, temperature monitoring in the shallow stream bed sediments at stream gauging stations is not routinely done.

12.3 Relevant LinksUS Geological Survey Circular 1260 Heat as a tool for studying the movement of groundwater near streams http://pubs.water.usgs.gov/circ1260


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Box 12.1 Trialling of temperature monitoring in the Border RiversMonitoring of temperature in the stream sediment (0.25 1.2 m depth) as well as the stream itself was used to investigate groundwater-surface water interactions in the Border Rivers catchment in the Murray-Darling Basin (Baskaran et al, 2005). When interpreted with hydrographic and hydraulic conductivity data, the temperature monitoring provided useful insights into the spatial and temporal variability of stream-aquifer connectivity. At one site, sediment temperatures fluctuated with the diurnal temperature variation of the stream, reflecting river leakage (Figure 12.3). No diurnal signal was detected in the sediment temperatures at other sites, which is a typical indicator of gaining conditions. However, with water level measurements indicating negative gradients and the stream sediments dominated by clay at these sites, this lack of sediment temperature variability is interpreted to reflect very low rates of downward seepage. At one site, a transition from gaining to losing conditions was observed through time. In the field trials, operational issues such as timing the monitoring to coincide with reasonable diurnal variations of stream temperature, the requirement of understanding the shallow stratigraphy of the stream bed, and separating out localised effects (such as from weirs) were highlighted. The trials also highlighted that interpretation of the temperature data can be ambiguous when viewed in isolation.32

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(B) low flow (Winter)

(A) high flow (Summer)Temperature ( oC)30 Temperature ( oC) 28 26 24 22 2013 /1 1/ 20 04 10 /1 1/ 20 04 11 /1 1/ 20 04 12 /1 1/ 20 04 14 /1 1/ 20 04 15 /1 1/ 20 04 16 /1 1/ 20 04 9/ 11 /2 00 4

15

14

Stream 0.25 m below streambed 0.5 m below streambed

13

Stream 0.5 m below streambed13 /0 7/ 20 05 14 /0 7/ 20 05 15 /0 7/ 20 05 16 /0 7/ 20 05 17 /0 7/ 20 05 18 /0 7/ 20 05 19 /0 7/ 20 05 20 /0 7/ 20 05

1212 /0 7/ 20 05

12.3a

12.3b

Figure 12.3 Observed stream and sediment temperatures downstream of Goondiwindi Weir during (a) high flow and (b) low flow seasons (Baskaran et al, 2005) Stream and sediment temperatures recorded at the Goondiwindi site during high flow (summer) and low flow (winter) seasons are depicted in Figure 12.3. The sediment temperature shows regular fluctuations that relate to the diurnal stream signal. Such fluctuations were evident at different depths in the sediment during the November 2004 high flow conditions (Figure 12.3a). The sediment temperature measured at shallow depth (0.25 m) recorded a diurnal signal varying between 24.325.8oC, with the peaks lagging by 4 hours from the corresponding maxima in daily stream temperature. The dramatic change in shallow sediment temperatures after 13 November 2005 was due to premature removal of the logger from the stream bed, thereafter effectively measuring the stream temperature. The diurnal pattern deeper in the profile (0.5m) is more subtle in amplitude with a time lag of about 6 hours. This reflects the time taken to transfer heat by both conduction and advection downwards through the sediments. It should be noted that the diurnal variation in sediment temperature (0.5 m depth) is significantly greater during high flow than in the low flow season. This is most likely due to the fact that the stream temperature diurnal fluctuation was high (6-7oC) during the high flow summer but very low (0.5-2oC) during the low flow winter. Temperature fluctuations evident in the sediment profile indicate that the stream is losing water to the groundwater system, confirmed by measurement of the head gradient between the river stage and shallow groundwater level.

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13. Water BudgetsA common approach to investigating seepage flux between a stream and underlying aquifer is to measure stream flow at specific points. These measurement sites subdivide the stream into reaches and a water budget is estimated for each reach, accounting for inputs such as tributary flows and outputs such as evaporative losses and diversions. The difference between inflows and outflows is then attributed to the interaction between the stream and the underlying aquifer. When applied to a defined reach, the groundwater flux (Qgw) is estimated from:Qgw = Qdn Qup + Qout QinEquation 13.1

where Qdn is the flow at the downstream end of the reach, Qup is the flow at the upstream end, Qout are outputs from the reach (such as distributaries, evaporation and extraction) and Qin are inputs to the reach (such as direct rainfall, runoff, tributaries, irrigation drainage and sewage outfall). This follows the convention that a positive Qgw indicates a net input of groundwater to the reach. A negative Qgw indicates a net loss of surface water to the groundwater system and is commonly termed a transmission loss. Although the method is simple, involving the quantification of all fluxes to, or from, the river, it is difficult to apply in many cases. The method relies on the accurate measurement of surface water flow, as well as appropriately accounting for all the other gains and losses evident for the reach. The uncertainties associated with the flow measurements and estimates for water balance components such as unmetered extraction, evaporation, ungauged tributary flows, overbank flooding losses and flood return flows can often exceed the magnitude of the seepage flux being estimated. Stream flow measurement errors can be +25% during high flow conditions, and from 50 to +100% for flash floods in semiarid catchments (Lerner et al, 1990). This means that the reach must be relatively long so that the cumulative volume of seepage exceeds the errors in the water balance. A specific type of water balance technique called a pondage test is commonly used for man-made structures such as irrigation supply channels. A reach of the channel is isolated by placing embankments at each end, and filled with water to (or higher than) the operating level. After correcting for rainfall and evaporation, the subsequent decline in water level is attributed to seepage losses in the underlying aquifer. Alternatively, water is added to maintain a constant water level, and the added volume used in the seepage calculations.

13.1 Stream Flow MeasurementThe water budget method relies on accurate measurement of stream flow at the end points of the reach being considered. Stream flow or discharge is the rate at which a volume of water passes through the cross section of the stream per unit time, and as such has SI units of cubic metres per second (m3/s) or cumecs. Other common units used in Australia include megalitres per day (ML/d) or litres per second (L/s). Waterbudgets are commonly estimated for a specified river reach defined between two gauging

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stations where stream flow is routinely measured. This typically involves the monitoring stream level and defining a relationship between level and flow. The stage or the height of

the water surface from a benchmark is monitored as a time-series whilst stream discharge (Q) is measured at a less regular basis, particularly at various flow regimes. The relationship between stream stage and flow is called the flow rating curve and typically takes the form: Q = a(h Z ) bEquation 13.2

where h is the measured gauge height, Z is the gauge height at zero-flow conditions, and a and b are best-fit coefficients using non-linear regression. In this way, a timeseries of stream flow called a hydrograph can be generated from any continuous monitoring of stream level at the site. There are also a range of methods for the direct measurement of stream flow. These can be used in detailed surveys along the extent of the stream reach being considered. The common methods for measuring stream flow are volumetric analysis, the velocity-area method, the slope-area method, dilution gauging and thin-plate weirs.

13.2 Volumetric AnalysisVolumetric analysis or the bucket and stopwatch method involves the measurement of the time taken for a container of known capacity to be filled. This is a simple method for measuring small streams where all of the flow can be concentrated (such as naturally within a rock cascade or by constructing a temporary dam with a pipe). The method can also be used in larger streams which have flow concentrated or partitioned by culverts, pipes or weirs. A short, wide container is more suitable to fit under the falling water, than a tall, narrow one. The container volume should be such that it takes at least 3 seconds to fill. It is important that the bucket is held upright and that multiple (>3) readings are taken to reduce measurement error. An alternative approach is to hold down and open a heavy-gauge plastic garbage bag on the stream bed, time its filling and empty the bag contents into a measuring container (Hauer and Lamberti, 1996). The bag can also be weighed and the volume calculated if the density of the water is known. Stream discharge (Q) in L/s is calculated asQ = V/t Equation 13.3

where V is the contained volume (L) during time t (s).

13.3 Velocity-Area MethodIn the velocity-area method, stream velocity and water depth measurements are taken along a transect perpendicular to the stream. Total discharge (Q) is calculated by integrating the stream velocities with the cross sectional area of the stream profile defined by the transect. Different types of current meters are available to measure stream velocity. Propellertype meters have a horizontally aligned vane that rotates in proportion to the stream velocity. The number of rotations can be recorded visually, audibly or digitally. Cuptype meters work on the same principle, but the vane is oriented vertically.


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Electromagnetic meters measure the voltage induced when a conducting fluid flows through a magnetic field. These tend to be used in coastal and marine studies due to the high conductivity of saline water. Ultrasonic meters use sound wave propagation in water to measure water velocity. Some versions use the impedance on the time for an ultrasonic wave emitted from one side of the river to reach a receiver on the other side. Other versions use the Doppler Effect by measuring the wavelength of ultrasonic waves reflected off suspended particles in the stream flow. The procedure is to:(i.)

(ii.)

(iii.)

(iv.)

Choose a suitable site along the stream with a straight reach, uniform laminar flow conditions and relatively constant depth and width. Sites with extreme turbulence, protruding obstructions, eddies, stagnant zones or divided channels should be avoided; Set up a tagline consisting of a tape measure perpendicular across the stream to be used for locating the velocity/depth measurements. Measurements are taken along 10-20 verticals across the stream transect. Each vertical should partition stream flow equally, so that verticals should be closer together where water is faster or deeper; At each site, use a current meter to measure stream velocity and a graduated pole to measure stream depth. Typically, flow is measured at a depth considered to reflect average velocity conditions (0.6 of the stream depth measured downward from the surface). Other approaches include two measurements being taken and averaged for each vertical, at 0.2 and 0.8 of the water depth (refer Table 13.1); The stream flow can be calculated using the mid-section method: Q = ( X i +1 X i )(U iYi + U i +1Y1+1 ) / 2i =1 n

Equation 13.4

where the Xi are the distances to successive measurement points along the transect, where stream velocity (Ui) and water depth (Yi) are measured, starting with X1 being the initial point on one bank and Xn being the final measuring point on the opposite bank.Table 13.1: Different procedures for determining mean velocity at a vertical (after Gordon et al, 2004)Number of Points in Vertical1 2 3 1 Many

Depth of Measure

Assessing GW and SW interaction

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