About River Ecology

Stream Ecosystems


Ecosystem Ecology

Ecology has been defined in a variety of ways.  One “school” of ecologists follow Andrewartha and Birch (1954) in regarding ecology as the study of the distribution and abundance of organisms (e.g. Begon, Harper and Townsend 1990, Krebs 1994) and see ecology as a subset of biology. This school emphasises the ecology of populations and communities, and is an approach commonly adopted in ecology courses taught in biology departments.  Another “school” of ecologists views ecology as the interaction between organisms and their environment, with the environment including both other organisms and the physical environment.  This approach is closer to Haeckel’s (1866) original definition, and has been typified in the works of Odum (1971), and Likens (1992).  It typically arranges ecology along a continuum from ecology of individuals, to populations, to communities to ecosystems to landscapes and biospheres.  Ecosystem ecology, under this classification typically encompasses the interactions of the physical environment and biotic communities (which overlaps with community ecology), as well as the study of ecosystem level processes such as the flows of energy (e.g. studies of production) and materials (e.g. nutrient cycles).


The organism-environment approach has been widely adopted in freshwater ecology (e.g. Hutchinson 1957, 1967, 1975, 1993) partly because lakes, in particular, have always appeared to be excellent examples of discrete ecosystems.  Lakes have, at human scales, a discrete physical boundary, and their physico-chemical properties such as shape, depth, salinity and seasonal pattern of water temperature clearly have a marked influence on the biota which is present.  The same approach has been extended to streams (e.g. Hynes 1970) which appeared to be similarly physically discrete and where the physical environment also clearly has a powerful influence over the biota.


Environmental managers with responsibilities for streams are often interested in the interactions between the physical environment and the stream biota – the interface between ecosystem ecology and community ecology.  They want to know, for example, how the stream biota responds to changes in water chemistry? How do we restore the physical habitat in degraded streams? How much water must we allow to flow in a river to maintain a “healthy” stream biota?


Fisher (pers. comm.) has distinguished two approaches to stream ecology as “the ecology of streams” vs “ecology in streams”.  One approach tries to understand specifically how streams work as ecological systems.  The other approach uses streams as a good place to conduct ecological experiments (usually at the community or population level) which are intended to be of general applicability in other types of ecological systems.  Note that these two general approaches are not  necessarily mutually exclusive.  But the emphasis in my lectures is on the ecology of streams.


Secondly, the emphasis in these notes is on upland streams, which are typically small, steep and stony.  These are the streams which have been most studied by stream ecologists.  They are not necessarily the most important, although the downstream flow of water ensures that changes in upland streams will influence, to some extent, lowland streams.  Nor are upland streams necessarily the most interesting, they are just the streams I know most about.  Thirdly, I will emphasise Australian streams, particularly southeastern Australian mainland streams, and their similarities and differences with streams elsewhere.


The ecosystem approach emphasises the interactions between the biota and the physical environment.  These notes firstly review the biota of streams, secondly discuss some important features of the physical environment of, and within streams, and thirdly look at materials and energy flows within streams.




The Biota of Streams


Major Components


In upland streams most organisms are benthic or nektonic – plankton is not abundant.  In lowland streams plankton is abundant, and the benthos much less diverse.  Hynes (1970) (Chapters IV, V, VI, VII and XV) provides the best overview of the biota of streams, although it is far more detailed than you need to know.




Bacteria, fungi, protists & algae.  Apart from the algae not well known. All mainly benthic (Epilithic, epipelic, epixylic).  Have great ecological importance as a food source & transducers of organic materials and nutrients.  The epilithon utilises light (through its algal component), dissolved organic material (through its bacterial and fungal component) and inorganic nutrients such as phosphorus and nitrogen to grow.  It in turn provides food for many stream invertebrates.




Not  very abundant in upland streams, much more significant in lowland streams.  Mosses and liverworts most common in headwater (light limited) situations. May be important as habitat, appear to be not much grazed.




Insects predominate in temperate streams, crustacea (amphipods and decapods) also common, increasingly so in tropical streams.  Most invertebrate groups with aquatic representatives are also represented in streams.


Notable absentees are : echinoderms, cephalopods, polychaets (restricted to a few rare species).


Among the insects several orders are predominantly stream dwellers :

Plecoptera (stoneflies)

Ephemeroptera (mayflies)

Trichoptera (caddisflies)

Megaloptera (alderflies)


In the Diptera (two-winged flies) the families Simuliidae (blackflies) and Blephariceridae (net-winged midges) are restricted to streams while the Chironomidae (non-biting midges) are very abundant in streams.




Fish, amphibians, reptiles, birds and mammals all common in streams.


Some notable features of Australian stream biotas


For biogeographical reasons the fauna is taxonomically distinctive, with groups which are uncommon or absent in the Northern Hemisphere being dominant here, while groups which are dominant or common in the Northern Hemisphere are absent or rare here.  Our stream fauna is most similar phylogenetically to that in southern South America and New Zealand.  This reflects the Gondwanaland origin of many of our stream invertebrates, although we also have cosmopolitan and a tropical elements to out fauna.  Bayly and Williams (1973, pp 151-155) discuss some aspects of the unique composition of Australian stream biotas.



The Australian freshwater fish fauna is not diverse. (~ 200 spp).

Present : Galaxiidae – native trout (~20 species) (May be a Gondwana group)

Absent : Salmonidae – salmons and trouts, Cyprinidae – carps, Percidae – perches, Ciclidae – cichlids




Ephemeroptera (mayflies)

Present – Leptophlebiidae (Atalophlebiinae) (dominant)

Absent or almost absent – Ephemeridae, Heptageniidae, Ephemerellidae (1 species)

Biogeographic relationships : Leptophlebiidae (Atalophlebiinae) G; Baetidae C;                                         Prosopistomatidae T.


Plecoptera (stoneflies)

Present – Eustheniidae, Gripopterygidae

Absent – Perlidae, Capniidae, Leuctridae

Biogeographic relationships : Eustheniidae, Gripopterygidae G.



Species from diverse phylogenetic origins often show striking morphological convergence in their adaptations to particular stream habitats.  Between North America and Europe the fauna is often distinct  at the genus level whereas between Australia and the Northern Hemisphere differences are often at the family level (Table 1). Campbell (1990) discussed this convergence in relation to Australian mayflies.  Hynes (1970) discusses these convergences for a range of stream insects from North America, Europe and Africa, but without Australian examples.









Table 1. Some convergent patterns of adaptation between mayflies from Australia, North America and Europe.


Adaptation Australia North America Europe
Burrowing – anterior projections, hairy gills etc Jappa (Leptophlebiidae) Potamanthus (Potamanthidae) Ephemera (Ephemeridae)
Adhesion – enlarged  leg bases or gills to form suckers Kirrara (Leptophlebiidae) Epeorus (Heptageniidae) Rhithrogena semicolorata (Heptageniidae)


Flattened form Austrophlebioides (Leptophlebiidae) Stenonema (Heptageniidae) Rhithrogena (Heptageniidae)


Filterfeeding mouthparts Coloburiscoides (Coloburiscidae) Lachlania (Oligoneuriidae) Oligoneuria





Sampling the Biota


Streams are extremely physically heterogeneous places so sampling is a significant problem.  Most techniques are substrate specific, or, in some other way, sample a selective component of the stream biota.  Sampling techniques for invertebrates are discussed comprehensively in Merritt and Cummins (1996) (Chapter 3).


Kick sampling – semi quantitative.

Quadrat style samples – surber, airlift, suction.

Artificial substrata – tiles, bricks, microscope slides



Streams And Their Catchments


The catchment of a stream contributes water, dissolved substances (ions, organic material), and organic material.  The amount and pattern of water discharge in the stream together with geology of the catchment influences the stream channel form. Hynes (1975) provides a good introduction to the relations between streams and catchments.


Catchment landuse/vegetation influences the amount and timing of stream runoff. In American literature the term “watershed” is used in place of “catchment”.  Stream size depends on the rainfall and the catchment area and may be expressed in terms of discharge, catchment area or stream order.


The plot of discharge through time is referred to as a hydrograph.


Runoff from a natural catchment is rarely ever via overland flow, so flood hydrographs tend to rise and fall slowly.  Stream discharge variability increases as rainfall decreases (i.e. the variability of discharge of streams in arid areas is greater than for streams in higher rainfall areas).  But flow variability in Australian streams is greater than for streams elsewhere.


Water quality varies with discharge – but not in a simple manner.  Suspended solids and materials transported on them (e.g. many pesticides, trace metals and nutrients) give a hysteresis curve when plotted as a time series against discharge.


Flow in upland streams is mostly turbulent (vs laminar).  So these streams are well mixed and well aerated.


The flow patterns in upland streams are complex and animals key in on particular types of flow.  E.G. Simuliidae are filter feeders and aggregate in areas of critical velocity where flow is fast and laminar.  Fish key in on noise generated by hydraulic jumps, and return eddies.


Invertebrates react to hydraulics at scales different to those at which hydrologists traditionally measure.  There has been a lot of recent work attempting to relate various hydraulic parameters to the distribution of stream invertebrates (e.g Davis 1986, Davis and Barmuta 1989, Statzner, Gore and Resh 1988, Statzner and Müller 1989).


Terms you should be able to define :

stream order, discharge, catchment, hydrograph, turbulence, turbidity, dissolved solids, hysteresis curve.

Carbon Dynamics in Streams


Carbon is important because it is the main energy currency in streams. Sources of carbon are : primary production, terrestrial plant litter, and dissolved material in groundwater.  Carbon can be lost from a stream section through downstream transport (as coarse particulate organic matter [CPOM] fine particulate organic matter [FPOM] or dissolved organic matter [DOM]) or as losses to the atmosphere as respired CO2.


Primary Production

Primary production provides the best measure of the importance of in-stream plants (macrophytes and micro-algae) to the stream ecosystem.  Where macrophytes are absent (which is mostly the case in stony upland streams) most primary producers are microalgae attached to stones – in the epilithon.  The standing crop of algae may be measured in various ways, of which the most common is by extracting chlorophyll directly off the stones.  There are two potential problems with this approach: the level of chlorophyll in algal cells may vary with time and environmental conditions so that the level of chlorophyll may not reflect the number of algal cells present, and, more importantly, if there is significant grazing there may be a low level of algal biomass and therefore chlorophyll, but a high level of production.  An analogous situation to a grazed pasture where the grass grows rapidly but is just as rapidly eaten.  Thus even though there may be a low level of chlorophyll the epilithic algae may be contributing a large amount of energy to the system.


Primary production is usually measured by measuring the amount of oxygen produced by photosynthesis


Gross primary production (GPP) is a measure of the total amount of  energy fixed through photosynthesis.  Some of that energy is used for production of new tissue, and some for plant self-maintenance (respiration).  The fraction used for tissue production is termed “nett primary production” (NPP).




where R = respiration.  In lowland streams streams primary production mainly occurs in the water column and because water flow is laminar (smooth) the rate of exchange of oxygen between the water and the atmosphere can be estimated.  So if oxygen concentration is measured over a 24 hour period, nett production can be determined using the dark period to estimate respiration and the light period to estimate primary production + respiration.


In upland streams most primary production occurs in the epilithon, and because the stream is turbulent the rate of exchange of oxygen between the water and the atmosphere cannot be estimated.  As a result the most common methods used to measure primary production in these systems are chamber methods, in which a sample of streambed material is enclosed

in a sealed chamber within which the water is moved by a pump.  The change in O2 over time can then be measured, with transparent chambers used to measure photosynthesis + respiration and blacked out chambers used to measure respiration alone.  Strictly speaking, because these studies usually include invertebrates, bacteria and fungi etc in the chamber (because these are present in the sample of stream bed included) what is measured in the chambers is nett metabolism of the stream community, rather than primary production alone.


Terrestrial Plant Litter

The measurement of terrestrial plant litter entering streams can be carried out by placing interception traps above the stream and lateral traps to intercept material blowing in across the forest floor.    Plant litter includes leaves, wood, bark, flowers and fruits.  In Australia most of the plant litter enters the stream in summer (Campbell & Fuchshuber 1994) but litter input is less seasonal here than in Northern Hemisphere deciduous forest streams, with about 15% of the litter entering in winter – the season of least litter fall, compared with about 5% entering NH deciduous forest streams in winter (their season of least litter fall).  Southeast Australian eucalypt forest streams receive about the same weight of leaves, but more bark than NH deciduous forest streams.


Groundwater DOC

Dissolved organic carbon entering streams through groundwater can be estimated from measurements of DOC levels in groundwater and estimates of total groundwater inflow (= stream discharge where the stream is entirely groundwater fed.).


Carbon Losses

Respired carbon is measured using the same technique as (and as part of the process of) measuring primary production.  Transport losses are measured by sampling the stream using nets to sample particulate material and water samples to measure dissolved material.


Carbon Budgets

Using the methods outlined above we have constructed a carbon budget for Keppel Creek near Marysville.  The data in Table 1 are expressed in terms of gm organic matter per m2 of stream bed.


Note that the major source of carbon is DOC in groundwater.  What we don’t yet know is to what extent that carbon is used by the instream biota.  This is material which has passed through the forest soil where a huge variety of fungi and bacteria etc have has first use of it.  Does that mean that all that is left by the time it enters the stream are materials that the organisms in the stream are unable to use?  Fiebig and Lock (1991) found that when groundwater was passed upwards through stream sediments that the concentration of DOC in the water dropped – but it is not known whether that was due to physical adsorption or to some biological process.


Most of the standing crop of organic carbon within the stream is in the form of wood.


Only 26% of the organic matter lost from the stream section is lost as respiration, the rest is exported, but note that, although 5,500 g m-2 enters as DOC only 1,690 (i.e. 31%) of that amount is exported as DOC, indicating that some transformation has taken place.


The stream gained 2.4 kg m-2  during the nominal year of this study.  During years with significant flood streams may export more organic matter than they gain, while in other years they may gain more than they export.


Table 1. An organic carbon budget for Keppel Creek, near Marysville. (Data from Treadwell, Campbell and Edwards in prep.)




     Gross Primary Production


     Allochthonous Accession



          Lateral litter movement




   Total Accession



Standing Crop

     Wood (>10 mm)


     CBOM (> 1 mm, not including wood)


     FBOM (< 1 mm)


   Total Standing Crop














   Total Export



Nett Change




Life Histories of Aquatic Insects


Aquatic insects may be hemimetabolous (e.g. Plecoptera, Odonata, Ephemeroptera) of holometabolous (Coleoptera, Trichoptera, Megaloptera).


Growth of an insect = and increase in size.  Development = physiological and morphological progression towards reproductive maturity.  Size at maturity may vary within a species so size is not necessarily a good indication of degree of development. Instar number is a better indicator if it can be determined and is fixed (see Butler 1984)


Some insects have a small number of instars (e.g. Trichoptera 5-7, Diptera 4-7) while others have many (Ephemeroptera 15-25, Odonata 10-12).  Life histories may be determined by sampling a population at a series of time intervals and examining size frequency changes through time (e.g. see Campbell 1986).  Some species have clear “cohorts” – groups of individuals which hatch at about the same time and grow synchronously to emerge at about the same time.  But often species have less synchronous life cycles and cohorts cannot be determined from size frequency analyses. In such cases insects may be grown in the laboratory or in field cages to determine growth rates and thus the length of the life cycle.


The time taken for a life cycle is influenced by the size of the adult (ie how much the insect must grow) the temperature (development time is frequently measured in “degree days”) the diet (in terms of nutritional value detritus < plants < animals).  Some insects switch diets to more nutritional (lipid rich) foods shortly before emergence to produce the large energy reserves needed to produce eggs and support their adult life.


Many northern hemisphere insects are univoltine (ie have a single generation per year).  Those with 2 year life cycles are described as semivoltine while those with several generations per year are described as multivoltine.  Diapause as an egg or a nymph is common, especially in summer.


A number of Northern Hemisphere examples are known of related (e.g. congeneric) species which co-exist and have their life cycles out of phase.  Thus the larvae of the different species are of different sizes at any one time, which may lead to a reduction in competition.  Few Australian examples of this are known.


Life cycles of Australian aquatic insects are typified by a low level of synchrony, extended adult emergence (usually over several months) a wide size range of larvae present throughout the year.  Synchrony becomes greater in populations at higher altitudes, and higher latitudes.


These Australian patterns may be a product of a climate with less extreme seasonal variation

than occurs in many Northern Hemisphere regions where life cycles have been studied, the year-round availability of food in Australian streams due to evergreen forest, or the greater hydrological variability of Australian streams (see discussion in Lake et al 1985).




Invertebrate Production


Production of stream invertebrates means nett production – ie the amount of animal tissue produced per unit area per unit time.


Production is one measure (probably the best measure) of the ecological importance of a species.  Other measures are numbers (e.g. 57 m-2 ) and biomass (e.g. 5 gm m-2).  Production may be measured in energy units (kcal m-2 yr-1) or carbon or organic material units (gm m-2 yr-1).  As measures of importance numbers, biomass and production may not be consistent estimators. For example see table 1


Table 1. Mean annual biomass (B), production (P) and production to biomass ratios (P/B ratios) for 3 mayfly taxa from snag habitats in the Ogeechee River.  Data expressed as mg dry mass of organic material (From Benke 1993).




mg . m-2


mg. m-2. yr-1



Ephemerella argo




Tricorythodes sp.




Baetis intercalaris






The ecological importance of production is that it indicates both the impact of a species on lower trophic levels (i.e. the amount of food a species consumed during a period) and the potential contribution of the species to higher trophic levels (how much tissue is available to be eaten by predators or used by decomposers).



Three methods may be used – the actual cohort method, the size frequency method and the instantaneous growth method.  Which is more appropriate depends on the life history characteristics of the species. The chart below (from Benke 1993) summarises method selection:


Actual Cohort Methods

These mostly measure the number of animals present at a series of time intervals and the mean mass, and add up the change in mass (  ) times the mean number (N) over the number of time intervals.  These can only be used where cohorts are obvious, and if there are several cohorts or generations per year the cohort production (which is what has been calculated above) must be adjusted to estimate annual production (e.g. if there are 2 cohorts per year multiply cohort production by 2).


Size Frequency Methods

Uses arbitrary size classes, and avergae annual data.  So, for example, data on the number of insects in a  series of arbitrary size classes (say for example 0.2 mm head width intervals) collected from a series of samples over a year (say monthly) are averaged.  Then the sum of mean mass of insects in each size class times the average number present in the size class can be used to estimate annual production of a univoltine insect.  Some other, independent, data is needed to demonstrate that the species is univoltine.  If it is not then the estimate must again be adjusted to determine annual production.


Instantaneous Growth Methods

For this technique the growth rate of the insect species is estimated by growing animals in the lab or in cages in the field.  Growth is determined as mg. mg-1. day-1. Using that data plus data about biomass present the production per unit time can be estimated.  The sum of these estimates over the life cycle of the insect will give a production estimate.


Functional Feeding Groups


Functional Feeding Groups (FFG’s) were first proposed by Cummins (1973) as a means of simplifying descriptions of the biota of stream ecosystems. The best outline of the system is given by Cummins and Klug (1979).  Essentially the proposal is that to simplify our understanding of the function of stream ecosystems we can lump species, of which there may be  several hundred in a few metres of stream length, by their mechanisms of obtaining food. Note that the mechanism of feeding is not the same as what you eat.  You can eat rice with a spoon, chopsticks a fork or your fingers – but it is still rice.  Those proposing (and using) the system have not always maintained this distinction (see the discussion in Hawkins and MacMahon 1989). One of the groups however, is predators, which is based on food consumed rather than feeding method.


The categories proposed are


Shredders – which shred coarse particulate organic material (CPOM) – leaves, wood etc.

e.g. limnephilid caddisflies such as Archaeophylax spp.


Collectors – collect fine particulate organic matter (FPOM) – which may be produced by the activities of shredders and other groups.  Two sub-groups are often recognised:


collector gatherers – sediment feeders such as oligochaets


filter feeders – suspension feeders such as net spinning caddisflies

(e.g. Hydropsychidae) and filtering mayflies (e.g. Coloburiscidae)


Scrapers – scrape material adhering to solid surfaces such as epilithon from the surfaces of stones.  e.g. Austrophlebioides (Ephemeroptera).


Piercers – suck the contents of plant cells.

e.g. Hydroptilidae (Trichoptera)


Predators – capture live prey

e.g. Odonata, Eustheniidae (Plecoptera).



The classification can be viewed as analogous to “trophic levels” in other ecological studies.  It has proven to be extremely useful – but very imprecise.  Some workers have found it  difficult to allocate species to a particular FFG, but often this is because they have tried to use food consumed (based on gut contents) rather than feeding method.  Species sometimes change feeding group – most commonly this occurs where late instar larvae change from some other group and become predators. Cummins, and others have at times referred to them as “Fictional Feeding Groups”.  They have won more widespread acceptance in the US where major texts on aquatic invertebrates tabulate functional feeding groups at the generic level (and thus perhaps they are accepted less critically?) they are less accepted in Australia where workers have to determine FFG’s themselves and are thus more aware of the limitations.






River Continuum Concept


There is a long history of attempts to classify and explain downstream changes in stream biological structure and function.  Early attempts were made, amongst others, by Thorup and Illies the latter recognising major upstream (rhithron) and downstream (potamon) zones with a variety of sub-zones within them. The RCC combines functional feeding groups, organic matter sources and stream geomorphology in a schema of river function (Vannote et al 1980).  It has been widely used and widely debated.  Two major issues of discussion have been whether the concept is correct, and if so whether it is applicable outside North America (e.g. see Winterbourn et al. 1981, Barmuta and Lake 1982).



Invertebrate Drift


Drift is the downstream transport of invertebrates entrained in the water column.  Extensive reviews of drift in streams are to be found in  Brittain and Eikeland (1988), and Waters 1972. Several different types of drift have been recognised by various workers :

Catastrophic drift – drift resulting from floods or spates


Behavioural drift – drift resulting from the behaviour of the invertebrate


passive – when the animal is dislodged while foraging – displays a temporal                                                          pattern


active – animal actively enters the water column


Distributional drift – method of dispersal of young stages (a subset of behavioural                                                drift?)


Constant or background drift – accidental dslodgement in low numbers irrespective of                             temporal periodicity


Drift is sampled by placing nets passively in the stream, and measured interms of either the total number of organisms passing through a cross-section of stream per unit time (drift rate as number per day) or numbers per unit volume of stream (drift density as numbers m-3).


Some groups of invertebrates appear to be more abundant in drift than in benthos (e.g. Ephemeroptera (especially baetids), Plecoptera, Trichoptera, Simuliidae & Chironomidae (Diptera), and Amphipoda.  Other groups are rare (e.g. Oligochaeta, Mollusca) – possible because of their habitats and/or habits.


Drift density varies temporally being higher at night than during the day, often with peaks just after dusk and just before dawn.  Individual animals may drift distances up to several hundred metres.


There is no simple explanation for drift.  Some possible causes which have been advanced are:


1. To avoid adverse condition such as pollution, turbidity etc.


2. To avoid predators


3. As a means of dispersal to find food patches or better habitat or avoid competitors


4.  Accidental – animals are washed away during their normal activities (many are normally more active at night thus explaining the diurnal rhythm).


5. Because they are sick or dying.



Invertebrate drift may be important because :


1. It may be an important pathway for recolonisation of stream patches after disturbance


2.   It may be an important pathway between “patches” (i.e. from stone to stone).


3.  It forms an important food resource for many fish (e.g. trout sit at the top of pools, just below the riffle).


4.  It may play an important role in population dynamics


a) may be excess production


b) may require replacement through upstream migration




Environmental Flows


With increasing competition for water there is increasing pressure on ecologists to tell engineers  how much water is necessary to maintain a river in an “ecologically healthy” state.


This raises a number of questions – beginning with “what does an “ecologically healthy state” mean?” and can it be quantified?  Nevertheless river ecologists must be prepared to argue for environmental flows – since no-one else can.


Many of the methods that have been proposed to determine environmental flows are summarised in Kinhill (1988) and by Tharme (2003), and they tend to fall into four groups :



Rule of Thumb

These methods select some proportion of the existing stream flow.  The amount selected may be based on annual, seasonal or monthly flows, and incorporate other criteria (e.g. “the first flood of each year or wet season must be unimpeded”, or “at least one event of 200% of the mean daily flow for 3 days must be allowed as a flushing flow during September”).  Some of the methods have been derived from the work of Tennant in Montana.  Arguments against these types of methods include their arbitrariness and the difficulty in defending them (why 60% of monthly flow in May – why not only 55%?).  Fixed proportions of flow recommended for streams in one geographical locality (e.g. Montana) are not likely to apply in other places (e.g. Victoria), and the original recommendations were based on providing sufficient flows for trout streams – which may not be appropriate for Australia.


Arguments for these methods are their low cost and rapidity, and the feeling that many ecologists have that reducing discharge by a fixed proportion while keeping all else constant will “mimic” natural flows including a range of high and low flow events which are thought, but cannot be unequivocally demonstrated to be important.


Habitat Area Methods

These methods measure the area of stream bed which is wetted (usually as wetted perimeter) at a range of discharges and produce a plot of area vs discharge.  The assumption is that the area of stream bed relates directly to the area of habitat available for fish and/or invertebrates.  This technique was one of those used by Victorian fisheries biologists.


Weighted Useable Area Methods

These methods define fish habitat for various stages of a species life cycle (e.g. adult, spawning, larval development) in terms of preferences for depth, current velocity and substrate.  Field measurements of stream conditions are then used with hydraulic models to predict the weighted useable area (WUA) available at any given discharge.  The models assume that the factors measured and modeled (depth, current and substrate) are the critical factors, and there is often an assumption that available habitat is the factor that limits fish populations.  The model does not account for long-term temporal variability (e.g. large scale droughts and floods) which may be necessary to maintain channels and native fish populations.


Holistic Methods

These are techniques which attempt to consider the whole spectrum of the ways in which flows influence the stream ecosystem, including impacts on the channel morphology, the riparian vegetation and the instream biota – including plants, invertebrates and fish.  The early approcaches included the Building Block Method (BBM) (King et al. 2000), which was adapted in Victoria as the FLOWS method (DNRE 2002), and more recently the DRIFT method (



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