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ECOLOGICAL EFFECTS OF REDUCING STREAM
BASEFLOWS
FINAL REPORT
August 2005
Amara Barlow, Richard Norris and Sue Nichols
Report to Environment ACT
Prepared by Institute for Applied Ecology
University of Canberra
Ecological effects of reducing stream baseflows
TABLE OF CONTENTS
1
Project Details ............................................................................................................... 3
Project Title
Project Staff
Project Duration
Project Objectives
3
3
3
3
2
Background information .............................................................................................. 4
3
Introduction................................................................................................................... 5
4
Methods ......................................................................................................................... 5
4.1
5
The 8-step MLLE framework ................................................................................ 5
Results .......................................................................................................................... 6
Step 1. Describe the characteristics of the human activity
Step 2. Describe the characteristics of the investigation location
Step 3. Develop a conceptual model
Step 4. Relevant lines of evidence
Step 5. Conduct the literature review
Step 6. Refine conceptual model
Step 7. Catalogue and weight the evidence
Step 8. What is the verdict?
6
7
6
7
9
13
13
14
14
17
Issues – Baseflow reduction ...................................................................................... 18
6.1
Severity ............................................................................................................. 18
6.2
Extent ................................................................................................................ 19
6.3
Frequency and duration ..................................................................................... 19
6.4
Timing................................................................................................................ 20
Issues – Stream characteristics ................................................................................ 21
7.1
River enrichment ............................................................................................... 21
7.2
Position in the stream channel network.............................................................. 21
7.3
Proximity of boreholes ....................................................................................... 22
Conclusions ....................................................................................................................... 23
7.4
Overall conclusions............................................................................................ 23
7.5
Information gaps ................................................................................................ 23
7.6
Managing in the presence of knowledge gaps ................................................... 24
8
References .................................................................................................................. 24
9
Acknowledgements .................................................................................................... 25
10
Glossary ........................................................................................................... 25
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Ecological effects of reducing stream baseflows
Table of Figures
Figure 1. Steps in applying MLLE (Norris et al. 2005) ............................................................ 6
Figure 2a. Wet period .......................................................................................................... 10
Figure 2b. Dry period ........................................................................................................... 11
Figure 2c. Dry period with bores .......................................................................................... 12
Figure 2d. Dry period with lots of bores ................................................................................ 13
List of Tables
Table 1. ACT controlled water resources as at July 2004 (Environment ACT 2004)............... 7
Table 2. Weights applied to study types and control/reference and impact sites .................. 15
Table 3. Scheme for categorizing the importance of studies ................................................ 16
Table 4. Example of biological response and dose response weighting by study quality
(Norris et al. 2005). ....................................................................................................... 16
Table 5. Effects catalog for a reduction of baseflow on lines of evidence from aquatic
ecosystems. .................................................................................................................. 16
Table 6. Levels of evidence catalogue for a reduction of baseflow on lines of evidence from
aquatic ecosystems. ..................................................................................................... 17
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Ecological effects of reducing stream baseflows
Executive Summary
The Groundwater Study (Ecological Effects of Reducing Stream Baseflows) was undertaken by
the Institute for Applied Ecology, University of Canberra. The aim of the study was to establish
whether there is an impact on aquatic ecosystems by reducing baseflow in the manner caused
by groundwater abstraction. The study also considers how much could baseflow be reduced
without compromising stream aquatic ecosystems; and whether the effects of baseflow
reduction would be stream dependent.
The Multiple Lines and Levels of Evidence (MLLE) literature analysis shows expected effects of
reductions in baseflow on macroinvertebrates but not on other lines of evidence. Therefore, it is
clear from the literature that reductions in baseflows will have a negative ecological effect. This
will be most easily demonstrated by studying macroinvertebrates but we would need very well
designed local studies to demonstrate an effect on fish, algae, macrophytes or riparian
vegetation.
Issues that are likely to influence the ecological effects of baseflow reduction include:
 Severity of abstraction and low flows (e.g. cease to flow);
 Extent of low flows (e.g. how much of the catchment is affected?);
 Frequency and duration of low flow events; and
 Timing of low flow events.
10% groundwater abstractions are likely to have little effect on aquatic ecosystems, because
groundwater modeling by Evans et al. (2005) indicates little change to the frequency of no flow
events; and small changes have been shown in the literature to be of little concern. Whereas,
pumping at 20% of annual recharge results in quite marked changes in the flow duration (Evan
et al. 2005) and is likely to have a negative ecological effect.
Ecological effects will be most severe during dry periods when baseflow is controlled by
groundwater for up to >80% of the time (e.g. Sullivans Ck), but this may be catchment
dependent (Evans et al. 2005). Abstractions in wet or dry years will have the same effect in dry
years because of the lag time for groundwater to get to the stream. Therefore, it is not possible
to manage dry and wet years independently, and so abstraction should be controlled for all
years at a level that will be sustainable during dry years.
The effects of abstractions will, in part, be determined by:
 River enrichment;
 Position in the stream channel network (upland vs lowland reaches); and
 Proximity of boreholes (distance from stream edge).
Abstractions will have more effect on highly nutrient enriched rivers and rivers in the upper parts
of catchments. If the bores are located close to the stream, the faster the impact of abstractions
and the quicker the time to full impact, but also the quicker recovery time. At a distance of 500
metres from the stream the full impact of one year of pumping is effectively detected within
about 5 years, whereas, the full impact of extraction for one year at 2 km is ongoing for
considerable time (Evans et al. 2005).
The quality and quantity of groundwater resources may be constantly changing, and there are
many gaps in the knowledge of groundwater resources and the effects of groundwater use.
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Ecological effects of reducing stream baseflows
Therefore, an adaptive management approach is recommended based on studies designed to
assess the outcomes of management decisions and inform new decisions.
2
Ecological effects of reducing stream baseflows
1
Project Details
Project Title
Ecological effects of reducing stream baseflows in the ACT
Project Staff
Leader: Prof. Richard Norris
Project officers: Amara Barlow, Sue Nichols
Project Duration
May 2005 to 22 August 2005
Project Objectives
The project objectives were to determine:
1. Is there an impact on aquatic ecosystems by reducing baseflow in the manner caused by
groundwater abstraction?
2. How much could baseflow be reduced without compromising stream aquatic
ecosystems?
3. Would the answer to the question above be stream dependent or is it possible to draw
some general conclusions?
This report has been divided into three parts to address each of the project objectives
individually.
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Ecological effects of reducing stream baseflows
2
Background information
ACT Government is interested in refining the current environmental flow guideline for
abstraction from groundwater. Groundwater abstraction limits of 10% of recharge were adopted
in the 1999 Environmental Flow Guidelines and have followed through as being an educated
but precautionary abstraction approach to take. This guideline value is based on advice from
Ray Evans et al. (2004) regarding the shallow fractured rock aquifers in the ACT and the
recharge that eventually discharges from the aquifer in the sub-catchment. This discharge is
believed to comprise a major proportion of the baseflow in our rivers and streams. In
consequence of the above points, abstraction from an aquifer will result in reduction of baseflow
in streams downstream of the abstraction site (such as groundwater bores). The Guidelines
recognize that periods of low flow (e.g. baseflow) are periods when aquatic ecosystems are
under some stress, and reducing the baseflow further should not exacerbate this. Therefore, to
protect the aquatic ecosystems groundwater abstraction should be limited to provide protection
of stream baseflows. Currently, abstraction is limited to 10% of recharge as a conservative
measure. The purpose of this study is to answers questions regarding the ecological response
of streams to groundwater abstraction.
It is well appreciated that many streams from the Great Dividing Range in South-Eastern
Australia are baseflow streams and are highly dependent on groundwater discharge (Hatton
and Evans 1998). However, groundwater movement is unseen and poorly understood.
Exploitation of groundwater resources for irrigation, public water supply and many other uses,
has the potential to significantly alter groundwater levels and groundwater behaviour. In
addition, many land use practices also change groundwater behaviour. These groundwater
processes, may influence the health of aquatic ecosystems (Hatton and Evans 1998).
In aquatic ecosystems highly dependent on groundwater, moderate changes to groundwater
discharge or water tables would lead to substantial decreases in the extent, severity and
frequency of drying, or ceasing to flow. Such changes may markedly affect the health of these
aquatic ecosystems. There are some baseflow systems of the South-Eastern uplands that are
highly dependent on groundwater (Hatton and Evans 1998).
For a number of aquatic systems (streams and wetlands), it is likely that a unit change in the
amount of groundwater will result in a proportional change in the health of those ecosystems. In
other words, were groundwater discharge cut by half, one might expect some equivalent
diminution of the ecosystem. Some base-flow systems of the South-Eastern uplands are
proportionally dependent on groundwater (Hatton and Evans 1998).
Aquatic ecosystem dependence is not solely related to the amount of baseflow, but variability
and predictability of flow are likely to be important. Generally, if there is baseflow, then
ecosystems will tend to be more dependent and vulnerable in lower rainfall zones, and where
this baseflow arises from porous media aquifer systems (Hatton and Evans 1998).
There is limited groundwater data for the Canberra region and also limited information on the
relationships between baseflow conditions and the aquatic ecosystem responses. For the
purposes of this report we have used the available local information on groundwater aquatic
ecosystems and combined this with a rigorous assessment of the scientific literature. The
scientific literature has been incorporated into a quantitative framework known as Multiple
Levels and Lines of Evidence (Norris et al. 2005).
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Ecological effects of reducing stream baseflows
Part 1 – Impacts of groundwater abstraction
3
Introduction
Groundwater abstraction reduces baseflows (Evans et al. 2005); and it could be reasonably
expected that the effects would be most apparent in dry years, when baseflow dominates
streamflow. Further, the effects of groundwater abstraction would be likely to be seen first in the
upper parts of catchments that would tend to dry out first and where abstraction is in close
proximity to rivers or wetlands. Therefore, the possible effects have been dealt with for upper
and lower catchments and considered the aquatic ecological effects of:
•
Extent of drying or cease to flow;
•
Severity and;
•
Frequency of events.
4
Methods
4.1
The 8-step MLLE framework
The eight step MLLE framework (Fig.1) adapted by Norris et al. (2005) from Downes et al.
(2002) was used to conduct the literature review of reduced stream baseflow. The review
included international literature, Australian literature and local unpublished data.
Several studies suggest that artificially-induced low flows and natural droughts can have similar
consequences on lotic ecosystems (McIntosh et al. 2002; Suren et al. 2003). However,
Smakhtin (2001) in a review of low flow hydrology suggests that natural factors, which influence
the low-flow regime of the river and human effects on these processes, should be considered
separately.
A comparison of the MLLE outputs was conducted to determine whether the inclusion of the
natural drought literature produced similar results to literature that considered human influence
on low flows. There was little difference in the MLLE outputs, with the exception of
macroinvertebrate taxa richness or diversity. Macroinvertebrates may be adapted to naturally
occurring low flows, therefore, the decision was made not to include the natural drought
literature.
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Ecological effects of reducing stream baseflows
1. Characteristics of the human activity
Question(s)
2. Characteristics of location
Question(s)
3. Conceptual model
6. Additional lines
of evidence
4. Relevant lines of evidence
5. Literature review
7. Catalogue & weight the evidence
(local data & literature)
Can be done using the MLLE software)
8. The verdict
Figure 1. Steps in applying MLLE (Norris et al. 2005)
5
Results
Step 1. Describe the characteristics of the human activity
The human activity of concern is groundwater abstraction. In many regions groundwater and
surface water resources are connected, and most surface water features (rivers, lakes, dams,
wetlands) generally interact with groundwater. The exploitation of, or quality of one resource,
can therefore affect the other (Ivkovic et al. 2004).
Rivers generally interact with groundwater in three basic ways: streams gain water from inflow
of ground water through the streambed (gaining stream), they lose water to ground water by
outflow through the streambed (losing stream), or they do both, gaining in some reaches and
losing in other reaches (Ivkovic et al. 2004). However, while this relationship is obviously linear,
the spatial and temporal effects may not be so because of features such as stream gradient,
upstream/downstream location and proximity to the aquatic systems, especially sensitive ones
such as wetlands. Surface water bodies within the ACT are classified as gaining streams,
determined from 8 groundwater desktop studies conducted by iCAM in 2004.
Abstraction from an aquifer (such as through groundwater bores) may result in reduction of
baseflow in streams downstream of the abstraction site. Whenever a megalitre of groundwater
is extracted via a pumped bore, a megalitre of groundwater is lost from some other part of the
aquifer system (Evans et al. 2004).
The ACT Environmental Flow Guidelines recognize that periods of low flow (e.g. baseflow) are
periods when aquatic ecosystems are under some stress, and reducing the baseflow further
would exacerbate this (Environment ACT 2004).
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Ecological effects of reducing stream baseflows
Evans et al. (2004) suggest that it is likely that the drawdown associated with groundwater
pumping in the Woden Sub-Catchment has reduced the baseflows in the nearby creeks.
The impact of groundwater extraction may result in an increase in groundwater salinity because
of increased hydraulic gradients drawing in more saline groundwater. Consideration should be
given to limiting groundwater withdrawals in areas where groundwater salinities have been
shown to be increasing over a time span of several years. This will require specific changes to
licence conditions (Evans et al. 2004).
The response time for groundwater pumping to impact river flows in a hydraulically connected
groundwater-river system is a function of the aquifer diffusivity (expressed as the ratio of aquifer
transmissivity to storativity) and the distance of the bore to the river. Commonly, the natural
hydraulic connection between river and aquifer is exploited by near-river installation of wells
designed to draw down groundwater levels below the river level and induce recharge by surface
water. Once a bore’s pumping is balanced by stream depletion, the water allocation arguably
becomes a surface water allocation (Ivkovic et al. 2004).
Step 2. Describe the characteristics of the investigation location
The investigation location is the Australian Capital Territory (ACT), which lies within the Upper
Murrumbidgee Catchment. For the most part groundwater in the ACT is in shallow aquifers in
the joints of the bedrock (a fractured rock aquifer). These aquifers tend to be shallow (generally
less than 100 m deep), and the water from them varies in quality from good to saline, and also
in yield. With this sort of shallow aquifer, rainfall percolates through the soil into the aquifer,
travels through the aquifer and discharges back to the surface, usually into streams at the
bottom of valleys. The low flow in smaller streams is largely made up of this discharge except
during rainfall events (ACT Government 2004). Any reduction in discharge from the aquifer
would result in a reduction in the low flows in the stream (ACT Government 2004).
Consequently, if there is over abstraction from groundwater in a sub-catchment, streams that
used to flow may cease to flow and dry up causing a significant impact on the health of the
stream. In the ACT Environmental Flow Guidelines groundwater abstraction is limited to 10 per
cent of recharge to ensure that there is no significant impact on streams during periods of low
flow (ACT Government 2004).
There are 32 separate management units or subcatchments in the ACT (Table 1). Subcatchments in which the ACT has an interest are those within the ACT, water supply
catchments upstream of Googong Dam, and those that flow into or through the ACT
(Environment ACT 2004).
Table 1. ACT controlled water resources as at July 2004 (Environment ACT 2004)
Catchment
Subcatchment
number
Sub-catchment
name
ACT
Environment
Allocation (ML)
ACT controlled
groundwater
Available for Use
(ML)
Murrumbidgee and
tributaries
1
Michelago
2314
100
2
Tharwa
8806
250
3
Kambah
6643
173
4
Uriarra
15580
180
5
Woodstock
1225
30
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Ecological effects of reducing stream baseflows
6
Guises
1935
76
7
Naas
35619
950
8
Gudgenby
46569
1300
9
Tennent
6884
150
10
Corin
19283
950
11
Bendora
9533
500
12
Lower Cotter
9342
600
13
Paddys
36571
1010
Tuggeranong Ck and
tributaries
14
Tuggeranong
7193
60
Molonglo and tributaries
15
Upper Molonglo
1160
34
16
Kowen
4896
160
17
Fyshwick
1712
68
18
Jerrabomberra
Headwaters
0
0
19
Jerrabomberra
4236
240
20
Lake Burley Griffin
5116
68
21
Coppins
4832
119
22
Woolshed
2173
64
23
Sullivans
5726
73
24
Woden
6191
56
25
Weston
3628
24
26
Tinderry
7571
0
27
Googong
784
0
28
Lower
Queanbeyan
20
0
29
Burra
1077
0
30
Gungahlin
4727
80
31
Lake Ginninderra
5456
50
32
Parkwood
5150
90
Gudgenby and
tributaries
Cotter and tributaries
Queanbeyan and
tributaries
Ginninderra Ck and
tributaries
Groundwater reserves in the ACT are not large and are contained within confined fractured rock
aquifers with yields generally less than 1.0 litre per second. In addition, salinity levels can be
-1
high (over 1,000 mg L of total dissolved salts). Hence only limited use of groundwater occurs
relative to Murray-Darling Basin use, but within the ACT there are several subcatchments in
which the volume of water available for groundwater use has been fully licenced. While there
have been a number of desktop studies undertaken on aquifers within various subcatchments,
limited field analysis has been undertaken into the actual performance of particular ACT
aquifers.
The amount of groundwater available for extraction from each sub-catchment is limited to 10
per cent of groundwater recharge until research on a specific sub-catchment determines that a
higher level of groundwater use is sustainable (Environment ACT 2004).
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Ecological effects of reducing stream baseflows
Groundwater recharge is the entry of water into the saturated zone or water table and the
associated flow away from the entry point within the saturated zone. Any assessment of
recharge must be based on long-term data because of the slow recharge rates of most aquifers
(Environment ACT 2004).
There are many other potential sources of impact on aquatic ecosystems in the ACT:
 Urban water may contribute to groundwater recharge, therefore, some subcatchments
may have higher than natural groundwater levels and baseflow.
 River regulation (for drinking water supply, and recreational use) may already be
causing unnatural low flows in some river systems.
Step 3. Develop a conceptual model
During a wet period, the contribution of groundwater flow to the river is not critical to the aquatic
ecosystem because surface water (overland) contributes much larger volumes to the flow
(Figure 2a). However, abstractions during wet times may still affect dry weather flow because
of the lag time for groundwater to reach the stream and contribute to baseflow.
During a dry period, the contribution of groundwater flow to the river is critical to the
maintenance of the aquatic ecosystem because of the loss of surface water (overland) flow
(Figure 2b).
During a dry period, groundwater abstraction may lower flow levels and result in drying of the
channel and longitudinal fragmentation of the stream into pools (isolated pools provide refugia
for aquatic organisms) (Figure 2c).
During a dry period, extensive groundwater abstraction may lower flow levels to the point where
the river ceases to flow and the hyporheos also becomes dry (Figure 2d).
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Ecological effects of reducing stream baseflows
Figure 2a. Wet period
10
Ecological effects of reducing stream baseflows
Figure 2b. Dry period
11
Ecological effects of reducing stream baseflows
Figure 2c. Dry period with bores
12
Ecological effects of reducing stream baseflows
Figure 2d. Dry period with lots of bores
Step 4. Relevant lines of evidence
The lines of evidence considered in this study were:
 Change in fish community;
 Change in algae;
 Change in riparian condition;
 Change in macrophytes;
 Decrease in macroinvertebrate taxa richness or diversity;
 Decrease in macroinvertebrate abundance or density; and
 Change in macroinvertebrate community composition.
Step 5. Conduct the literature review
The databases used to search for articles were Cambridge Scientific Abstracts, Firstsearch, and
Web of Knowledge. The following keywords were entered as search terms: Groundwater, river,
stream, abstraction, baseflow, low flow, reduced flow, drought, surface-groundwater relations,
Australia. A total of 63 articles were collected and reviewed in the initial literature scan, 20 of
which were considered comparable to the current study and included in the MLLE assessment
(Appendix A).
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Ecological effects of reducing stream baseflows
Step 6. Refine conceptual model
There was little information on stream baseflow reduction, therefore, the literature review looked
at flow reduction in general, rather than just baseflow reduction. The literature review revealed
many potential impacts of instream flow reduction, including:
 Increased sedimentation;
 Changes to the morphology of the stream channel and floodplain;
 Changes to the distribution and abundance of stream biota;
 Exacerbate the effects of water pollution;
 Increased water temperatures during low-flow periods;
 Reducing overbank flooding;
 Changes in the density, productivity, and species composition of wetland and riparian
vegetation;
 Changes in the relative abundance of algae, allochthonous material and organics;
 Changes in aquatic habitat;
 Adverse water quality effects;
 Decreased food availability, depending on the species and functional feeding group;
 Species that are immobile or slow may lack the ability to adjust to reduced water levels;
therefore, allowing more mobile organisms to become the established dominant
species;
 Changes to the inter- and intra-specific interactions within the disturbed ecosystem;
 Physical and chemical processes (e.g. temperature, dissolved oxygen) can deviate
from normal conditions (Smakhtin 2001; McIntosh et al. 2002).
Step 7. Catalogue and weight the evidence
The schema of Norris et al. (2005) was followed for weighting and cataloguing the evidence
from the literature review.
To catalogue each line of evidence (LOE), the number and the importance of studies was
recorded against the different levels of evidence. The levels of evidence that we recorded were
adapted from Downes et al. (2002) and include:
 ‘biological plausibility’ - absorbed into the conceptual models and noted above to
indicate ecologically relevant LOEs, rather than kept as a line of evidence itself;
 ‘presence of a biological response’ – a recasting of the ‘experimental evidence’ level
but including evidence from all types of study including experimental and observational
studies;
 ‘evidence of a dose response relationship with the stressor’
 ‘consistency of association’ – consistent spatial and temporal association of stressor
and biological response.
The formal procedure developed by Norris et al. (2005) for weighting the quality of papers
based on the type of study design and the number of control/reference sites and the number of
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Ecological effects of reducing stream baseflows
impact sites (Table 2) was adopted. These were then combined to weight the levels of
evidence; a step necessary for environmental studies.
Studies in which error terms are well controlled (e.g. BACI designs) should exert greater
influence than less rigorously controlled designs (e.g. only impact sites sampled). Having a
control or reference brings an improvement in inferential power. There is some increase in
inferential power from having more than one control. A larger number of control locations adds
weight because it better estimates the envelope of ‘normal’ location behaviour (Downes et al.,
2002) so that departure from ‘normal’ can be detected with more confidence. More impact
locations leads to a better estimate of the range of ecological outcomes and stronger
comparisons with control/reference conditions with which they are compared.
An overall study weight was derived by summing each of the three categories (Table 2, 3)
following a set of rules (Table 4). These weights were then converted into quality categories
(High or Low) with the advantage that they more immediately relay the importance of the study
than a numerical value.
An example of how the number of High and Low quality studies are combined is shown in Table
4. The overall study weight for a high quality study ranges between 5 and 10 (Table 3). The
overall study weight for a low quality study ranges between 1 and 4 (Table 3). The example
shows the sum of the median quantitative study weights (7.5 = High quality study weight; 2.5 =
Low quality study weight) (Table 4).
Combinations of high and low quality studies with a median study weight of 20 or more are
deemed to have a high level of support from the literature (and accompanying studies) causal
criteria. A line of evidence with a median study weight of less than 20 has a low level of
evidence for the ‘biological response’ and ‘dose response’ causal criteria (Tables 3, 4).
Table 2. Weights applied to study types and control/reference and impact sites
Study design type
Weight
After impact only
1
Reference/Control vs impact no before
2
Before vs after no reference/control
2
Gradient response model
3
BACI or BARI MBACI or Beyond MBACI
4
Number of reference/control sites
0
0
1
2
>2
3
Number of impact locations
1
0
2
2
>2
3
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Ecological effects of reducing stream baseflows
Table 3. Scheme for categorizing the importance of studies
Overall study weight
Study importance category
5-10
High
1-4
Low
Table 4. Example of biological response and dose response weighting by study quality
(Norris et al. 2005).
Number of
Low quality
studies
showing
support
Number of High
quality studies
showing support
Sum of the Median
Conclusion –
Quantitative study weights evidence for
causal
(7.5 = Median high quality study
criterion
weight; 2.5 = Median low quality
study weight)
Biological response and dose response
0
AND
3
(0 x 2.5) + (3 x 7.5) = 22.5
High
2
AND
2
(2 x 2.5) + (2 x 7.5) = 20
High
5
AND
1
(5 x 2.5) + (1 x 7.5) = 20
High
8
AND
0
(8 x 2.5) + (0 x 2.5) = 20
High
4
AND
1
(4 x 2.5) + (1 x 7.5) = 17.5
Low
1
AND
2
(1 x 2.5) + (2 x 7.5) = 17.5
Low
7
AND
0
(7 x 2.5) + (0 x 7.5) = 17.5
Low
<2
AND
2
High
<5
AND
1
High
<8
AND
0
High
>= 0
AND
>2
Low
>=2
AND
2
Low
>=5
AND
1
Low
>=8
AND
>= 0
Low
Consistency
Table 5. Effects catalog for a reduction of baseflow on lines of evidence from aquatic
ecosystems.
RespEvid = Evidence of a biological response (higher number is better), doseEvid = Evidence of a dose response
(higher number is better), conEvid = Consistency among studies (low number is better).
Line of evidence
respEvid
doseEvid
conEvid
Change in fish community
11
1
0
Change in algae
8
0
5
Change in riparian condition
2
0
0
Change in macrophytes
9
0
0
Decrease in macroinvertebrate taxa richness or diversity
32
8
8
Decrease in macroinvertebrate abundance or density
36
8
12
Change in macroinvertebrate community composition
43
0
24
16
Ecological effects of reducing stream baseflows
Step 8. What is the verdict?
Although there was insufficient evidence to confidently determine whether reduced stream
baseflow causes a change in fish, algae, riparian or macrophyte communities, the majority of
studies analysed found an adverse impact on the aquatic ecosystem represented by these lines
of evidence (Table 4).
There was support for the hypothesis that reduced stream flows cause a decrease in
macroinvertebrate taxa richness or diversity; and a decrease in macroinvertebrate abundance
or density (Tables 4 and 5). However, the results were inconsistent in regard to whether
reduced flow changes macroinvertebrate community composition (Tables 4 and 5).
Table 6. Levels of evidence catalogue for a reduction of baseflow on lines of evidence
from aquatic ecosystems.
Line of evidence
Biological
response
Dose
response
Consistency
Conclusion
Change in fish community
Low
Low
High
Insufficient evidence
Change in algae
Low
Low
High
Insufficient evidence
Change in riparian condition
Low
Low
High
Insufficient evidence
Change in macrophytes
Low
Low
High
Insufficient evidence
Decrease in macroinvertebrate
taxa richness or diversity
High
Low
High
Support for
hypothesis
Decrease in macroinvertebrate
abundance or density
High
Low
High
Support for
hypothesis
Change in macroinvertebrate
community composition
High
Low
Low
Inconsistent results
In conclusion, reduction in baseflow may have effects on fish, algae, riparian condition,
macrophytes and invertebrate composition but the evidence from the literature is weak or
inconclusive. However, there is strong and consistent evidence that macroinvertebrate
abundance and richness are negatively affected.
These organisms are an important
component of aquatic ecosystems and used extensively as indicators throughout the world.
Therefore, we can conclude that reduction in baseflow will have an adverse effect on an
important indicator of the health of aquatic ecosystems.
17
Ecological effects of reducing stream baseflows
Part 2 – How much could baseflow be reduced?
6
Issues – Baseflow reduction
Issues that are likely to influence the ecological effects of baseflow reduction include:
 Severity of abstraction and low flows (e.g. cease to flow);
 Extent of low flows (e.g. how much of the catchment is affected?);
 Frequency and duration of low flow events; and
 Timing of low flow events.
6.1 Severity
The severity of groundwater abstraction may vary depending on the reliance of streams on
groundwater discharge and the other contributions to stream flow from surface water.
Thresholds that may cause stream degradation include: increased low flow levels; drying of the
channel; longitudinal fragmentation of the stream into pools; cease to flow; and drying of the
hyporheos (spaces in the stream bed that are often important refuges).
Rader and Belish (1999) found that macroinvertebrate communities were resilient to mild flow
alterations. However, in severely altered streams macroinvertebrate communities were
significantly impaired (reduced total invertebrate density, reduced taxa richness and
composition dominated by only a few taxa). Some change may have little effect but the degree
or severity of change will be an important determinant of ecological outcomes.
Streams that are highly dependent on groundwater discharge (based on the volume of baseflow
and its temporal variability, the type of aquifer systems and rainfall) will be particularly impacted
by a loss of baseflow. Groundwater dependent ecosystems are communities of plants, animals
and other organisms whose distribution and life processes are dependent on groundwater
(Hatton and Evans 1998). Many streams from the Great Dividing Range in South-Eastern
Australia are baseflow dependent. The Horse Park Wetland in North Gungahlin, Canberra, is
distinctive in that it is a groundwater-dependent one, whereas most others in the region are
basin type wetlands (Barlow et al. 2005). Further investigation is required to determine the
dependence of ACT stream systems on groundwater.
It is worth noting that at least one of Australia’s key fauna has a strong dependency on the
maintenance of river pools, if not flow, in the coastal rivers of South-Eastern Australia including
Kangaroo Island: the platypus. This species is completely dependent on the continuous
availability of river pools. In much of its current habitat, groundwater is likely to play a role in
this. It is apparently not a requirement for platypus to have flowing waters, but if changes in
groundwater availability induced a cessation of ponding in these systems at any time, then this
may to lead to local extinction. It is important to note that pools have dried up on occasion on
Kangaroo Island, but the platypus persisted by some as yet unknown strategy (Hatton and
Evans 1998).
Modelling of ACT groundwater resources done by Evans et al. (2005), suggests that the
severity of changes to baseflow by groundwater abstraction would be small if abstraction is
limited to the current cap of 10% of the resource in wet or dry years. However, an increase of
abstraction to 20% would reduce baseflows for up to >80% of the time in dry years. Therefore,
18
Ecological effects of reducing stream baseflows
based on groundwater modelling and the MLLE assessment, when conditions are extreme and
drying or cease-to-flow is already stressing aquatic biota, groundwater abstraction at levels
above 10% would be expected to have severe effects on aquatic biota.
6.2 Extent
2
If groundwater is abstracted on a large scale (greater than 10 km ) (particularly in the upper
parts of catchments, Evans et al. 2005), the effects could include the drying out of groundwaterfed systems, including rivers and wetlands. Aquatic biota restricted to groundwater-fed areas
may therefore, be particularly vulnerable to groundwater abstraction.
The rate of macroinvertebrate community recovery following a disturbance is influenced by the
distance of the stream to a source of potential colonists (Wallace 1990). The greater the extent
of baseflow reduction and stream disturbance in a catchment, the less likely that there will be a
source of colonists nearby.
Rapid colonization will occur of any newly available habitat that is within the dispersal range of
species living in nearby lotic or lentic habitats (Williams and Hynes 1976). Many insects are
capable of flight during their adult stages and have little difficulty in recolonizing stream habitats
(Williams and Hynes 1976), however, other macroinvertebrate taxa have low mobility and poor
dispersal abilities. Macroinvertebrates with poor dispersal abilities may take a long time to
recover if the extent of the disturbance is far reaching.
The extent of reduction in baseflow will be determined by the location of groundwater
abstraction as well as the volumes. Depending on the underlying geology, catchments
generally dry from their upper parts first. Therefore, abstraction in upper catchments will have
more effect on baseflow than in lower parts and larger volumes will also extend the effects.
Both are issues that will be likely to have significant ecological effects during dry years when
baseflows are maintained for extensive periods by groundwater.
6.3 Frequency and duration
Low-flow events and drying are natural phenomena (McMahon and Finlayson 2003) to which
aquatic ecosystem will be adapted. However, groundwater abstraction may increase the
frequency of low-flow events, and some aquatic communities or species may be unable to cope
with the change in flow patterns as demonstrated in the MLLE literature evaluation presented
above. An increased frequency of low flow events may affect ephemeral stream systems more
than perennial stream systems, because surface flow will provide more refugia for biota in the
perennial stream.
The ecological effect of a short-lived low-flow event is likely to be much less than one lasting for
many months (Suren et al. 2003). It has been demonstrated that the ACT streams and other
aquatic systems respond rapidly to rainfall and that most flows and most volume is directly
rainfall related (Evans et al. 2005). Therefore, little ecological effect of groundwater abstraction
at almost any level would be expected during wet periods when rainfall will contribute rapidly to
surface flow. During wet years, i.e. greater than average rainfall years, there will be continuous
periods of days and sometimes weeks when baseflow dominates the streamflow, and reduced
baseflow may have negative ecological effects during these periods. Groundwater extraction at
levels >10% of the resource is also likely to produce negative ecological effects in dryer years
(i.e. a year with below annual average rainfall) by extending both the frequency and duration of
drying or cessation of flow.
19
Ecological effects of reducing stream baseflows
6.4 Timing
Under extremely dry conditions, small decreases in surface water flows will cause relatively
large reductions in wetted channel area and thus habitat availability for aquatic organisms
(McMahon and Finlayson 2003). Whereas at higher flows, quite large recessions in base-flow
will have much less impact on habitat availability, because they mainly reduce water depth and
these differences are mitigated by channel shape (McMahon and Finlayson 2003). Therefore, if
a loss of baseflow eventuates during a dry period it will have a greater impact of the aquatic
ecosystem.
Groundwater modelling by Evans et al. (2005) found that for Sullivans Creek ACT, in the dry
years, baseflow dominates streamflow approximately 80% of the time. For Sullivans Creek, the
influence of baseflow (fraction-of-time-dominance) is stronger at the downstream gauge. For
Yarralumla Creek, the reverse appears to be the case. This may be because of the baseflow
2
filter underestimating the speed of the baseflow response in the smaller (5.6km ) upstream
catchment. Therefore, as noted above ecological effects groundwater abstraction may be
marked during dry years but they may be modified by location in the catchment and the type of
catchment.
Evans et al. (2005) also found that there is a time lag involved in the impacts of pumping on
stream flow that extends over many years. This results in a legacy of impact because of
previous years pumping. This finding has major ecological implications. An interpretation is
that the ecological impacts of groundwater pumping will be seen in dry years, even if the
abstractions occurred in previous wet years. Therefore, it is not possible to manage dry and wet
years independently, and so we should control abstraction for all years at a level that will be
sustainable during dry years.
20
Ecological effects of reducing stream baseflows
Part 3 - Are the effects of baseflow reduction
stream dependent?
7
Issues – Stream characteristics
The following issues may influence the effects of baseflow reduction, and are likely to be stream
(or location) dependent. These include:
 River nutrient enrichment;
 Position in the stream channel network (upland vs lowland reaches); and
 Proximity of boreholes (distance from stream edge).
7.1 River enrichment
Suren et al. (2003) suggest that the severity of low flows is influenced by a river’s degree of
enrichment, with greater impacts associated with high enrichment. The enrichment status of a
river may vary because of underlying geology and also because of human influences such as
land-use change. Drying will generally concentrate chemical constituents such as the major
ions and nutrients. Additionally, the exposure time to aquatic biota will be much greater when
flows are low. Under such conditions algal growth because of enhanced nutrients combined
with a lack of scouring flows can result in marked changes to primary productivity. Such
conditions also result in a degradation of other aquatic biota as noted in the MLLE evaluation.
7.2 Position in the stream channel network
The low flow behaviour of streams is further complicated by position in the stream channel
network (McMahon and Finlayson 2003). At the upper end of channel networks (the first order
streams of Strahler, 1952), channels may carry flow only immediately following rainfall. The
active channel network extends upstream during wet periods in all regime and climate types.
Thus, the length and severity of low flow periods, and frequency of cease-to-flow, typically
decrease with distance downstream in the channel network and, therefore, increasing
catchment area. Bedrock type also mitigates the nature of low-flow periods. Rivers draining
catchments containing major aquifers may continue to flow during long dry periods when
neighbouring streams on different bedrock have ceased to flow (McMahon and Finlayson 2003).
Armitage and Petts (1992) found that upland streams did not appear to suffer adverse effects as
a result of abstraction, whereas lowland streams appeared to be more degraded, but with the
exception of the Pang River, this could not necessarily be attributed to abstraction. The lack of
any consistent trends in taxon presence or absence may be a result of the very diverse nature
of the effects of abstraction, or to the natural diversity of the rivers chosen for study. In upland
streams within- and between-season flow variability is naturally high as is substratum
heterogeneity. The resident fauna is therefore well adapted to extreme conditions, which may
involve severe loss of wetted area (Armitage and Petts 1992).
In the ACT, there are many small upland streams that have naturally low flow during summer.
The aquatic fauna in these streams may be adapted to stream drying, however, if adverse
conditions are prolonged the availability of temporary refugia will be limited and benthic fauna
21
Ecological effects of reducing stream baseflows
losses are likely to occur. A more detailed examination is needed of the response of
invertebrates to the changing hydraulic conditions following reduced or altered flows.
7.3 Proximity of boreholes
Wood and Petts (1994) suggest that one of the management options for lessening the impact of
groundwater abstraction on rivers is the relocation of boreholes away from sensitive stream
reaches.
Groundwater modelling by Evans et al. (2005) shows that the closer the bore is to the stream
the faster the impact and the quicker the time to full impact but also the quicker recovery time.
At a distance of 500 metres from the stream the full impact of one year of pumping is effectively
detected within about 5 years, whereas, the full impact of extraction for one year at 2 km is
ongoing for considerable time. This shows that the impact of pumping is not confined to the year
in which it occurs. Rather, the impact is spread over many years and is proportional to the
distance from the stream. As noted above the ecological implications are marked and, while
ecological impacts may be seen in dry years, licensing of groundwater abstraction volumes and
locations should probably be set regardless of wet or dry years. It is unknown whether the
aquatic biota would be more affected by a high level of stream depletion observed over a short
period of time (borehole located close to the stream), or a lower level of stream depletion
observed for an ongoing period (borehole located away from the stream). However, this
difference is only observed for short-term pumping (one year of pumping followed by 125 years
of no pumping). The relocation of boreholes suggested by Wood and Petts (1994) is unlikely to
be an effective strategy if there is continuous groundwater pumping, because stream depletion
is similar for the different pumping distances (Evans et al. 2005).
The impact of groundwater extraction is a prolonged process, with the time to full impact varying
depending on the volume extracted and the distance of pumping from the stream (Evans et al.
2005). Thus, ecological impacts need to be considered in this context and effects somethwhat
remote in time and space will need consideration.
22
Ecological effects of reducing stream baseflows
Conclusions
7.4 Overall conclusions
 There is an impact on aquatic ecosystems by reducing baseflow in the manner caused
by groundwater abstraction. In particular, reduced stream baseflows causes a decrease
in macroinvertebrate taxa richness or diversity; and a decrease in macroinvertebrate
abundance or density. There may be effects on other ecosystem components such as
fish, macrophytes, algae and riparian vegetation, but support from the literature is weak
at this stage.
 Abstraction of 10% of the available resource is likely to have little ecological effect
because it causes only small changes in baseflow (Evans et al. 2005). Groundwater
abstractions of 20% or more of the available resource are likely to have significant
effects on baseflows, which in turn will produce negative ecological effects. However,
the effects may be stream dependent. Investigation of stream characteristics including
nutrient enrichment status, underlying geology, and natural flow variability may be
needed before a general rule for groundwater abstraction can be formulated.
 The ecological effects of groundwater abstractions will be most profoundly noticed in
dry years when stream flows are dependent on groundwater for >80% of the time.
 Groundwater abstractions in wet and dry years are likely to have the same effect in dry
years because of the time taken for re-charge and travel to the streams.
 There are unlikely to be any obvious ecological effects of groundwater abstractions
noticed within the wet years because most stream flow is generated by rainfall and
surface runoff in the ACT region.
7.5 Information gaps
There are several significant information gaps with respect to the impacts of groundwater
abstraction on rivers. These issues should be addressed in the form of observational studies to
gain a better understanding of the local riverine processes and the effects of abstractions. Such
studies would provide valuable information for both the future management of ACT groundwater
and surface water resources.
Further study of the ecological effects of low flows, groundwater abstraction and recovery is
required for individual rivers so that clear management plans can be made to protect both the
lotic and riparian ecosystems and the groundwater resource.
The main information gaps that may need addressing in conjunction with the review of
groundwater requirements are listed below:
 Species restricted to groundwater-fed areas;
 the effects of atypical low flows and bed drying on the aquatic ecosystem;
 the nature of ecosystems' dependency on groundwater;
 the minimum water requirements of the ecosystem and the degree to which baseflow
can be reduced without loss of habitat and refugia;
 the groundwater regime that will satisfy the water requirements of the ecosystem;
23
Ecological effects of reducing stream baseflows
 the impacts of change in groundwater regime on ecological processes and water
quality;
 the extent of impacts of groundwater abstraction on stream systems.
Future study of how water resources respond to groundwater abstractions could be
implemented to help develop management approaches and achieve desired outcomes. This
study could be designed in several ways to test the effects of abstraction. Suggested
approaches include:
1. Implement an experimental study, which diverts water from a stream during a period
when baseflow dominates;
2. Ongoing monitoring of a stream system influenced by groundwater abstractions,
preferably in a system where boreholes are located in close proximity to the stream, and
there are limited confounding influences;
3. Model the change in wetted channel area and habitat loss (e.g. riffles and pools)
associated with groundwater abstraction;
4. Evaluate the volume of baseflow and its temporal variability, the type of aquifer systems
and rainfall to determine stream dependence on groundwater.
7.6 Managing in the presence of knowledge gaps
The quality and quantity of groundwater resources may be constantly changing, and there are
many gaps in the knowledge of groundwater resources and the effects of groundwater use.
Therefore, an adaptive management approach is recommended.
8
References
ACT Government. (2004). Environmental Flow Guidelines: A Technical Background Paper. Australian
Capital
Territory,
Canberra.
Available
at
www.environment.act.gov.au/Files/
environmentalflowguidelines-atechnicalbackgroundpaper1204pdf.pdf.
ANZECC & ARMCANZ 2000, http://www.deh.gov.au/water/quality/nwqms/pubs/wqg-ch3.pdf.
Armitage, P. and Petts, G. (1992). Biotic score and prediction to assess the effects of water
abstractions on river macroinvertebrates for conservation purposes. Aquatic Conservation: Marine and
Freshwater Ecosystems, 2: 1-17.
Evans WR, BFW Croke, JL Ticehurst, B Schoettker and AJ Jakeman (2005). Sustainable
Groundwater Yield Assessment Sullivans Sub-Catchment, ACT. iCAM Client Report for Environment
ACT. Integrated Catchment Assessment and Management (iCAM) Centre, School of Resources,
Environment and Society, The Australian National University, Canberra, Australia.
Downes, B.J., Barmuta, L.A., Fairweather, P.G., Faith, D.P., Keough, M.J., Lake, P.S., Mapstone, B.D.
and Quinn, G.P. (2002). Monitoring Ecological Impacts: Concepts and Practice in Flowing Waters.
(Cambridge University Press.) 446 pp.
Evans W.R., B.F.W. Croke, J.L. Ticehurst and A.J. Jakeman (2004). Sustainable Groundwater Yield
Assessment Woden Sub-Catchment, ACT. iCAM Client Report 2004/7 for Environment ACT.
Integrated Catchment Assessment and Management (iCAM) Centre, School of Resources,
Environment and Society, The Australian National University, Canberra, Australia.
Environment ACT. (2004). Thinkwater, Act water Volume 3: State of the ACT’s water resources and
catchments,
April
2004.
Australian
Capital
Territory,
Canberra.
Available
at
http://www.thinkwater.act.gov.au/documents/Vol3screen_000.pdf.
24
Ecological effects of reducing stream baseflows
Hatton and Evans (1998). Dependence of Ecosystems on Groundwater and its Significance to
Australia’ by Tom Hatton and Richard Evans, LWRRDC Occasional Paper No 12/98. Land and Water
Resources Research and Development Corporation.
Ivkovic, K.M., Letcher, R.A. and Croke, B.F.W. (2004). Groundwater-River Interactions In The Namoi
Catchment, NSW and their Implications for Water Allocation. 9th Murray Darling Basin Groundwater
Workshop
"Balancing
the
Basin",
Bendigo,
2004.
Available
at
http://cres.anu.edu.au/people/ivkovic.pdf.
Norris, R., Liston, P. Mugodo, J., Nichols, S., Quinn, G., Cottingham, P. Metzeling, L. Perriss, S.,
Robinson, D., Tiller, D. and Wilson, G. (2005). Multiple lines and levels of evidence for detecting
ecological responses to management decisions. Proceedings of the 4th Australian Stream
Management Conference: Linking rivers to landscapes. 19-22 October, 2004, Launceston: Tasmania.
Rader, R.B. and Belish, T.A. (1999). Influence of Mild to Severe Flow Alterations on Invertebrates in
Three Mountain Streams. Regulated Rivers: Research & Management, 15: 353-363.
Wallace, J.B. (1990). Recovery of lotic macroinvertebrate communities from disturbance.
Environmental Management, 14 (5): 605-620.
Williams, D.D. and Hynes, H.B.N. (1976). Stream habitat selection by aerially colonizing invertebrates.
Canadian Journal of Zoology 54: 685-693.
Wood, P.J. and Petts, G.E. (1994). Low Flows and Recovery of Macroinvertebrates in a Small
Regulated Chalk Stream. Regulated Rivers: Research & Management, 9, 303-316.
9
Acknowledgements
This project built on prior work of the Cooperative Research Centre for Freshwater Ecology
(CRCFE). Several staff members were involved in the initial development of the MLLE
procedure and software.
Thank you to Barry Croke, Ray Evans, and Birte Schoettker (Salientsolutions/ICAM Team).
10 Glossary
Abstraction
Abstraction refers to the removal of water from a natural waterway,
impoundment or bore.
Allochthonous material
Exogenous food organisms, organic matter, and nutrients originating outside
and transported into an aquatic system (Armantrout, 1998).
Autochthonous
Endogenous materials such as nutrients organisms fixed or generated within
the aquatic system (Armantrout, 1998).
Aquifer
An aquifer is a layer of rock or soil that is permeable and has the capacity to
convey significant amounts of groundwater.
Baseflow
Baseflow describes the quantity of flow in a waterway that exists purely as a
result of seepage into the upstream channel from groundwater. Practically,
baseflow is determined from either field investigation after a prolonged period
without precipitation or one of several quantitative baseflow separation
models.
Ephemeral Streams
Ephemeral streams are waterways that are temporary in nature. That is,
waterways that exist for a relatively short period of time, usually a matter of
days, after a storm event.
25
Ecological effects of reducing stream baseflows
Flow Regime
Flow regime commonly describes the distribution of flow rate magnitudes over
time for a particular waterway. In this capacity it is similar to a unit hydrograph.
Fractured Rock Aquifer
A fractured rock aquifer is an aquifer that exists where the geological structure
is characteristically impervious rock with sediment filled fractures. These
fractures allow the conveyance of groundwater.
Hyporheos
Latticework of underground habitats through the alluvium of the channel and
floodplain associated with streamflows that extend as deep as the interstitial
water in the substrate.
Lotic
Aquatic system with rapidly flowing water, such as a creek, stream or river,
where the net flow of water is uni-directional from the headwaters to the
mouth.
Lentic
An aquatic system with standing or slow flowing water (e.g. lake, pond,
reservoir, swamp, marsh and wetland). Such systems have a non-directional
net flow of water.
Macroinvertebrate
Aquatic animals without backbones that can be seen with the naked eye, e.g.,
shrimps, worms, crayfish, aquatic snails, mussels, aquatic stage of some
insect larvae, such as dragonfly larvae, mayflies, caddisflies, etc.
Macrophytes
Macrophytes are large water plants. Emergent macrophytes are plants that
are rooted in the riverbeds or lakebeds, and protrude from the water surface.
Submerged macrophytes are plants that are rooted in the riverbeds or
lakebeds, but do not protrude from the water surface.
Refugia
Areas that have escaped ecological changes or stress occurring elsewhere
and so provide a suitable habitat for organisms to survive (Boulton and Brock,
1999).
Riparian Vegetation
Riparian vegetation is terrestrial vegetation that is influenced by its proximity to
a body of water.
Storativity
The volume of water an aquifer releases from or takes into storage per unit
surface area of the aquifer per unit change in head. It is equal to the product
of specific storage and aquifer thickness. In an unconfined aquifer, the
storativity is equivalent to the specific yield. Also called storage coefficient.
Transmissivity
Rate at which water is transmitted through a unit width of an aquifer under a
unit hydraulic gradient. Transmissivity values can be expressed as square
metres per day (m2/d) or square metres per second (m2/s).
26
Ecological effects of reducing stream baseflows
Appendix A – MLLE References
The following references were used in the MLLE assessment:
Armitage, P.D. and Petts, G.E. (1992). Biotic score and prediction to assess the effects of water
abstractions on river macroinvertebrates for conservation purposes. Aquatic Conservation:
Marine and Freshwater Ecosystems, 2: 1-17.
Armitage, P.D., Gunn, R., Furse, M., Wright, J. and Moss, D. (1987). The use of prediction to
assess macroinvertebrate response to river regulation. Hydrobiologia,144: 25-32.
Barlow, A., Lawrence, I., Williams, D., Osborne, W. and Norris, R. (2005). Horse Park Wetland
Environmental Assessment Report, August 2005. Water Research Centre, University of
Canberra, Australia.
Bickerton, M., Petts, G., Armitage, P., Castella, E. (1993). Assessing the ecological effects of
groundwater abstraction on chalk streams: Three examples from Eastern England. Regulated
Rivers: Research and Management, 8: 121-134.
Boulton, A.J. (2003). Parallels and contrasts in the effects of drought on stream
macroinvertebrate assemblages. Freshwater Biology, 48: 1173-1185
Bromley, J., Cruces, J., Acreman, M., Martinez, L., Llamas, M.R. (2001). Problems of
Sustainable Groundwater Management in an Area of Over-exploitation: The Upper Guadiana.
Water Resources Development, 17(3): 379-396.
Caruso, B.S. (2002). Temporal and spatial patterns of extreme low flows and effects on stream
ecosystems in Otago, New Zealand. Journal of Hydrology, 257: 115-133.
Castella, E., Bickerton, M., Armitage, P.D. and Petts, G.E. (1995). The effects of water
abstractions on invertebrate communities in U.K. streams. Hydrobiologia, 308:167-182.
Chester, H. and Norris, R. (2005). Dams and Flow in the Cotter River: Effects on instream
trophic structure and benthic metabolism. CRC Freshwater Ecology, University of Canberra,
Australia.
Choi, S.U., Yoon, B. and Woo, H. (2005). Effects of Dam-induced Flow Regime Change on
Downstream River Morphology and Vegetation Cover in the Hwang River, Korea. River
Research and Applications, 21: 315-325.
27
Ecological effects of reducing stream baseflows
Cortes, R., Ferreira, M., Oliveira, S., and Oliveira, D. (2002). Macroinvertebrate community
structure in a regulated river segment with different flow conditions. River Research and
Applications, 18: 367-382.
Englund, G., Malmqvist, B., and Zhang, Y. (1997). Using predictive models to estimate effects
of flow regulation on net-spinning caddis larvae in North Swedish rivers. Freshwater Biology, 37:
687-697.
Englund, G., and Malmqvist, B. (1996). Effects of flow regulation, habitat area and isolation on
the macroinvertebrate fauna of rapids in North Swedish rivers. Regulated Rivers: Research and
Management, 12: 433-445.
Holmes, N.T.H. (1999). Recovery of headwater stream flora following the 1989-1992
groundwater drought. Hydrological Processes, 13 (3): 341-354.
Johnson, I., Elliott, C., and Gustard, A. (1995). Modelling the Effect of Groundwater Abstraction
on Salmonid Habitat Availability in the River Allen, Dorset, England. Regulated Rivers:
Research and Management, 10: 229-238.
McIntosh, M., Benbow, M., and Burky, A. (2002). Effects of Stream Diversion on Riffle
Macroinvertebrate Communities in a Maui, Hawaii, Stream. River Research and Applications,
18: 569-581.
Norris, R., Chester, H. & Thoms, M. (2004). Ecological sustainability of modified environmental
flows in the Cotter River during drought conditions January 2003-April 2004: Final report. CRC
Freshwater Ecology, University of Canberra, Australia.
Peat, M. and Norris, R. (2005). The effect of low flow variation on periphyton downstream of
dams in the Cotter River. CRC Freshwater Ecology, University of Canberra, Australia.
Peat, M. and Norris, R. (2005). The biological condition of Cotter River during a drought flow
regime: December 2004. CRC Freshwater Ecology, University of Canberra, Australia.
Rader, R.B. and Belish, T.A. (1999). Influence of mild to severe flow alterations on invertebrates
in three mountain streams. Regulated Rivers: Research and Management, 15: 353-363.
Roberts, K. (2000). The effects of drought on community
macroinvertebrates: Honours thesis. University of Canberra.
structure
of
stream
28
Ecological effects of reducing stream baseflows
Strevens, A.P. (1999). Impacts of groundwater abstraction on the trout fishery of the River
Piddle, Dorset; and an approach to their alleviation. Hydrological Processes,13: 487-496.
Suren, A., Biggs, B., Duncan, M., Bergey, L., and Lambert, P. (2003). Benthic community
dynamics during summer low-flows in two rivers of contrasting enrichment 2. Invertebrates. NZ
Journal of Marine and Freshwater Research, 37: 71-83.
Wood, P.J., and Petts, G.E. (1994). Low flows and recovery of macroinvertebrates in a small
regulated chalk stream. Regulated Rivers: Research and Management, 9: 303-316.
Wood, P.J. and Petts, G.E. (1999). The influence
macroinvertebrates. Hydrological Processes, 13: 387-399.
of
drought
on
chalk
stream
Zektser, S., Loaiciga, H.A., Wolf, J.T. (2005). Environmental impacts of groundwater overdraft:
Selected case studies in the southwestern United States. Environmental Geology, 47: 396-404.
29