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Australian Natural Resources Atlas

Australia

The material below is an extract from the Australian Agriculture Assessment 2001 report. For ease of cross reference, figure, table and section references pertain to the chapter structure of this report. The Further Information section provides links to the full graphics version of the material below and the Australian Agriculture Assessment 2001 report.

Rivers - nutrient loads and transport

SUMMARY

Nutrient sources*

• Relative importance of different sources of nitrogen and phosphorus varies between river basins.
• The dominant sources of phosphorus (over 50%) are: hillslope erosion in Queensland and New South Wales; gully and river bank erosion, and dissolved phosphorus in run-off in coastal Victoria, South Australia, Western Australia and Tasmania; and in some basins urban point source discharges (e.g. 30% of the total load for Moreton Bay).
• Dissolved nitrogen in run-off makes up a greater proportion of the total load than dissolved phosphorus. Total nitrogen loads come mainly from hillslope erosion in Queensland and coastal New South Wales; contributions from hillslope erosion and dissolved nitrogen loads in run-off in the Murray-Darling Basin are comparable in magnitude; and over 60% of the total load occurs as dissolved run-off in coastal Victoria, South Australia, Tasmania and much of Western Australia.
• Management of nutrient exports will vary according to the relative dominance of nutrient sources.

Nutrient exports to receiving waters

• Total nutrient loads discharged from river basins are partly dictated by basin size-large basins export larger loads. Smaller basins can export large loads if they have high natural or induced export rates (e.g. due to steep slopes and intense rainfall;increases in population (sewage discharges) and changes in land use and management, such as intensive cropping on river flood plains).
• Efficiency of phosphorus delivery from rivers to the coast varies from as low as 3% in the Murray-Darling Basin to over 90% in Tasmania. Nitrogen deliveries vary from 14% for the Murray-Darling Basin to over 90% for Tasmania.
• The major sink for phosphorus and nitrogen is floodplain sedimentation, but reservoir sedimentation (for both nitrogen and phosphorus) and riverine denitrification (for nitrogen only) can account for significant proportions.
• Nearly 19,000 tonnes of total phosphorus and 141,000 tonnes of total nitrogen are predicted to be exported down rivers to the coast each year from areas of intensive agriculture: highest exports occur in the Far North, northern Queensland, Moreton Bay and coastal New South Wales.

Changes in river nutrient loads

• Changes in nutrient load can indicate where important changes in water quality may have taken place. However, as nutrient loads in many rivers are dominated by storm events, changes in nutrient loads do not give a complete picture of the nutrient aspects of water quality.
• Annual total phosphorus loads in river networks averaged nearly 3 times higher than estimates for pre-European settlement levels. Average annual total nitrogen loads were estimated to be more than double pre-European settlement levels.
• In over 100,000 km of river (60% of river length assessed), total phosphorus loads had increased by more than 3.5 times, possibly resulting in substantial ecological changes. Total nitrogen loads increased by this amount in about 30% of the assessed river length.
• The greatest nutrient load impacts arising from catchment disturbances were predicted to be in the Burdekin, Murray-Darling, Murchison and Greenough basins.

* Due to a lack of data, intensive rural industries (e.g. feedlots and piggeries) were not included. However it should be noted that these industries are subject to certification, specific industry guidelines, and are regulated and monitored through State government activities.

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INTRODUCTION

Increases in river nutrient loads generally lead to increases in the production of algae and aquatic plants, with follow-on effects up the aquatic food chain. Large nutrient increases typically favour a small number of species at the expense of others, and so while overall system productivity is increased, biodiversity is reduced. The reduced diversity of species is often associated with reduced system resilience, and catastrophic collapses are common. Such collapses may include the death and decay of large algal blooms, thereby increasing biological oxygen demand, lowering dissolved oxygen levels and leading to massive fish kills and high mortality amongst other river fauna (see Australian Catchment, River and Estuary Assessment 2001 for the Audit river and estuary assessments).

River nutrient budgets for phosphorus and nitrogen allow determination of:

• major sources of nutrients to rivers;
• major loss pathways for nutrients transported through river systems; and
• magnitude of nutrient exported to estuaries and the coast.

They are linked to landscape nutrient budgets, because erosion and surface run-off are important pathways for nutrient loss from the landscape. An understanding of the fate of nutrients lost from landscapes and ecological responses to nutrient loads in the receiving waters, can help guide land and water planning and management.

A modelling approach was developed to combine outputs from erosion and river sediment transport modelling, with landscape-plant-soil-atmosphere-nutrient flux modelling and point source discharge data. River nutrient transport modelling considers dissolved nutrients that are associated with those bound to suspended sediments. Exchanges between these forms are modelled for phosphorus. Losses from transport include:

• fine sediment deposited in reservoirs and on floodplains; and
• denitrification of dissolved nitrogen to nitrogen gas.

Modelling river nutrient transport

Agricultural and urban disturbance within a catchment leads to increases in nutrients exported to the river systems. These increased nutrient loads affect river ecosystems, usually in undesirable ways. Assessing changes in nutrient loadings is therefore an important aspect for assessing river condition, and one that highlights the linkages between a river and its catchment.

Assessing river nutrient load is complex-either using measured data or by modelling-because of complex processes involved in nutrient sourcing and transport, and the highly time dependent variability of river flow. Process modelling is usually carried out in conjunction with detailed daily hydrology modelling. However, this is not required for broad-scale assessments of changes, and in any case sufficient data are often not available.

A model of river nutrient transport (Annual Network Nutrient Export-see box) was developed to predict current and pre-European nutrient loads in Australian rivers.

Losses of sediment-bound nutrients occur due to fine sediment deposition and long-term storage on floodplains and in reservoirs. These terms were estimated using the Sediment river Network (SedNet) model (Prosser et al. 2001) and assumed that:

• floodplain deposition accords to settling velocity theory; and
• reservoir deposition uses a modified 'Brune rule' (Brune 1953) that estimates the trap efficiency of a reservoir as a function of the storage capacity and the annual flow volume.

Nutrients not lost from transport by fine sediment deposition or denitrification are exported from the river network. As the Annual Network Nutrient Export model does not represent estuarine nutrient transport and transformations, 'exports' from the river network combines nutrient delivery to estuarine and near-shore marine environments.

Relative sizes of sources and sinks

Phosphorus sources

• Most phosphorus comes from hillslope erosion (65%) with loads as high as 85% in those regions contributing the largest loads.
• Gully erosion contributes a high proportion of total phosphorus load in some regions (e.g. gully erosion represents 59% of the load in the Indian Ocean region).
• Urban point source discharges represent 31% of the total phosphorus load in the Moreton Bay region. A large proportion of this enters the lower Brisbane River and can be expected to have significant ecological consequences for the lower river and Moreton Bay.

Phosphorus sinks

• 60% of the phosphorus load that reaches river networks is deposited on floodplains with fine sediment.
• 27% of the phosphorus load that reaches river networks is exported to the coast.
• 13% of the phosphorus load that reaches river networks is deposited in reservoirs with fine sediment. This particulate phosphorus should be considered in the long term as being bio-available for phytoplankton growth. The largest load of particulate phosphorus deposited in reservoirs occurs in the Murray-Darling, a region with a large number of reservoirs and a recent history of reservoir cyanobacteria bloom problems.

The efficiency of phosphorus delivery varies greatly between the regions.

• Small coastal catchments in Tasmania export over 90% of the phosphorus that reaches the drainage network.
• In the Murray-Darling only 3% of phosphorus is exported, but this applies only to the connected drainage network. This delivery ratio would be lower, if large areas of unconnected drainage had been assessed.

Nitrogen sources

The sources of sediment for particulate nitrogen were assumed to be the same as those for particulate phosphorus.

• Most nitrogen comes from hillslope erosion (65%) with loads as high as 85% in those regions contributing the largest loads.
• Gully erosion contributes a high proportion of total nitrogen load in some regions.

Dissolved nitrogen contributes a greater proportion of the total nitrogen source than does dissolved phosphorus of the total phosphorus source.

• On average, from 30% to 69% of total nitrogen load exists as dissolved nitrogen in the Western Australia's southern region.

Nitrogen sinks

Information on the sinks for nitrogen provides valuable guidance for land and stream management. With less of the total nitrogen load transported in particulate forms, the percentage losses to floodplain and reservoir sedimentation are lower.

• Overall, export is 39% on average because of extra losses (11% on average) of nitrogen from the river system through denitrification. The percentage denitrification losses vary between regions from as high as 22% in Western Australia South and Indian Ocean regions, to as low as 1% in North and Far North Queensland. Denitrification losses are highest where the water residence times are longest in the lower gradient rivers with extended periods of low or very low flows.
• Percentage exports range from 93% in Tasmania where the dissolved nitrogen fraction is high and denitrification losses are low (down to 14% in the Murray-Darling where both sedimentation and denitrification losses are high).

Area-based nutrient export rates

Mapping total nutrient loads across drainage network links (Figures 6.6, 6.7) shows that the largest rivers generally carry the largest nutrient loads. Dividing these loads by the upstream catchment or basin area provides area-based nutrient export rates. Export rates indicate the differences in nutrient source intensity from:

• natural differences in topography and rainfall that give rise to natural differences in erosion rates; and
• differences due to intensity of resource use-more intensive resource use increases export rates by increasing soil erosion, loss of fertiliser nutrients, run-off of animal wastes and point source discharges.

The highest export rates are generally a result of high erosion rates driven by topography, rainfall and land use.

• Averaged across river basins, the total phosphorus export rate was predicted to be 0.11 kg/ha/yr and the total nitrogen export rate was estimated at 0.85 kg/ha/yr.
• Export rates ranged from zero to as high as of 2.4 kg/ha/yr for total phosphorus and to 10.5 kg/ha/yr for total nitrogen from the Mulgrave - Russell rivers in Far North Queensland (Figures 6.4, 6.5).

Changes in total nutrient loads

Increases in nutrient load

Across the assesed basins, the average total annual phosphorus load increased 2.8 times relative to pre-European levels.

• At the region scale, the river link-averged increases ranged from a seven times increase in the Fitzroy basin to a 30% increase in Tasmania (Table 6.2).
• At the river basin scale (Appendix 1, Figure 6.9), total phosporus loads have increased by more than 10 times in the river networks of the Proserpine, O'Connell and Styx basins in Queensland, all of which drain to the Great Barrier Reef lagoon.

Significant increases in total phosphorus of between 5 and 10 times have ocurred in the rivers of the large Burdekin, Fitzroy, Burnett, and Brisbane basins in Queensland; nine other smaller basins along the Queensland coast; the Border Rivers, Gwydir and Namoi basins in upper Murray-Darling Basin; and the Greenough and Murchison basins in Western Australia.

Across the assessed basins the average total annual nitrogen loads increased 2.1 times.

• At the region scale, the river link-averaged increase ranges from a 3.6 times increase in the Burdekin to a 20% increase in Tasmania (Table 6.4).
• At the river basin scale (Appendix 1, Figure 6.10), total nitrogen loads have increased by more than 4 times in the river networks of the Don, O'Connell, Styx and Proserpine basins in Queensland; and in the Wakefield basin in South Australia.
• Significant increases in total nitrogen loads of between 3 and 4 times have occurred in the rivers of the large Burdekin, Fitzroy, Burnett, and Brisbane basins in Queensland; five other smaller basins along the Queensland coast; the Gwydir and Namoi basins in upper Murray-Darling Basin; the Macleay River in coastal New South Wales; the Broughton and Lake Torrens basins in South Australia; and the Murchison, Blackwood, Frankland and Avon basins in Western Australia.

Spatial patterns

Basin averages must be interpreted with care, since increases in nutrient loads are not evenly distributed (Figures 6.11, 6.12). For example, several basins in the New South Wales section of Murray-Darling Basin showed much larger increases in total phosphorus in the upper reaches compared to the lower reaches, because of intense gully erosion along the western slopes of the Great Dividing Range.

Where nutrient loads have increased by over 3.5 times, it is likely that aspects of the rivers will be substantially degraded:

• In many basins (particularly in Queensland and Western Australia) over 75% of the stream length has been degraded by increases in total phosphorus loads (Figure 6.13).
• In a few basins (including the Avon, the Gwydir, the Broughton, the Wakefield and several coastal Queensland basins) over 75% of the stream length has been degraded by increases in total nitrogen loads (Figure 6.14).

Not all basins with large increases in river nutrient loading also export large loads. Comparison of river link-averaged values indicates potential impacts on river condition, but does not necessarily translate to equivalent increases in basin export (e.g. the Paroo basin shows a moderate increase in link-averaged phosphorus loading, but does not export phosphorus under the natural or the currently modelled scenario).

Nutrient exports need to be linked back to catchment land uses, because nutrient loss pathways for dissolved and sediment-bound nutrients differ and may require different control practices.

Phosphorus

In the case of phosphorus, exchanges between dissolved (in water) and sediment-bound phosphorus pools occur during transport. The percentage increase in the load that is caused by each of four major source types has been determined (Appendix 1).

• phosphorus load increases are dominated by increases in channel (gully and stream bank) erosion in 61% of basins (or 45% by basin area); by increases in hillslope erosion in 36% of basins (or 55% by basin area), and by point sources in just four basins (Maroochy, the Queensland South Coast, the Onkaparinga and the Swan Coast-less than 1% by basin area).

Nitrogen

• Nitrogen load increases are dominated by increases in channel erosion in 40% of basins (or 39% by basin area); by increases in hillslope erosion in 40% of basins (or 49% by basin area); by increases in surface run-off loads in 17% of basins (or 10% by basin area); and by point sources in four basins (Queensland South Coast, the Maribyrnong, the Onkaparinga and the Swan Coast-less than 1% by basin area).
• Nitrogen load increases in several basins are dominated by dissolved nitrogen in surface run-off. These increases reflect both increased nutrient inputs via fertiliser and dissolved organic losses associated with changes in vegetation type. Particular care with fertiliser management is required in those regions where increases in dissolved nutrient loads are a high percentage of the total increase.

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NUTRIENT FORMS AND LIKELY ECOLOGICAL IMPACTS

Nutrient forms

Phosphorus

Particulate phosphorus occurs in organic and inorganic forms (inorganic particulate phosphorus mainly occurs as phosphate ions chemically adsorbed to eroded clay mineral particles)

Dissolved phosphorus is immediately available to aquatic plants and algae, but particulate phosphorus can change into the dissolved form as local water quality conditions change.

Most or all of the phosphorus in transport has the potential to be bio-available in the long term. In the short term, the ability of the suspended sediment in a river to provide phosphorus for algal growth beyond that in the dissolved fraction is described by the relative buffering capacity (Froelich 1988), which is proportional to the inverse of the ratio of dissolved phosphorus to total phosphorus. That is, for low values of this ratio the buffering capacity is high, and for high values of this ratio the buffering capacity is low.

Variation in the ratio of dissolved to total phosphorus (Figures 6.15,6.16) shows a spatial pattern in relative buffering capacity, and hence differences between rivers in their short-term ability to provide phosphorus from suspended sediments for algal growth.

• At the river basin scale, this ratio ranges from 0.01 in the Lake Torrens basin in South Australia to 0.97 in the Pieman River basin in Tasmania; with a basin average of 0.28. Generally, the highest values are for the rivers of Tasmania, east Victoria and parts of the south west of Western Australia. The low values for the major inland basins and the rivers of the Indian Ocean region, indicate the high relative buffering capacity of these rivers. In these basins, suspended sediments can be expected to act as a reasonably available source of phosphorus for algal growth should dissolved phosphorus become depleted.

Nitrogen

Most of the particulate nitrogen is organic, although some exists as ammonium chemically bound to sediments.

Dissolved nitrogen is more available to most aquatic plants and algae than other forms, although ammonium is relatively easily stripped from sediments for biological uptake. However, ammonium is only a small fraction of total load and the ratio of the dissolved load to the total nitrogen load is a reasonable indicator of the proportion of the nitrogen load that is readily available to aquatic plants and algae (Figures 6.17, 6.18).

• At the river basin scale, the nitrogen ratio ranges from 0.08 in the Don River in Queensland to 0.98 in the Shannon River in the south-west of Western Australia. The Australian basin average was 0.61. Generally, the highest values are for the rivers of south-west Western Australia, north-west Tasmania and parts of Victoria. In these basins, a high proportion of the total nitrogen load will be readily available for algal growth.

Nitrogen:phosphorus ratios

The ratio of nitrogen to phosphorus in water indicates their relative availability to aquatic organisms. This ratio in algae approximates to the relative amounts of these two nutrients actually used by the algae.

An expression of the nitrogen to phosphorus ratio is known as the 'Redfield ratio' (Redfield 1958). The 'Redfield ratio'defines a threshold value (approximately 6.8, by weight) which can be used to evaluate the nutrient status of a water body.

Total nitrogen to total phosphorus ratios vary for pre-European conditions from slightly less than 6.8 to nearly 20 (Table 6.6). Where turbidity is not extreme and these ratios are high (e.g. south-west of Western Australia) growth of phytoplankton is likely to be phosphorus limited.

Redfield ratio

When the Redfield ratio is greater than 6.8 the water body is regarded as phosphorus deficient, and when it is less than 6.8 it is regarded as nitrogen deficient. Nitrogen deficient conditions favour those species of algae (including many blue-green algal species) that fix atmospheric nitrogen.

The Redfield ratio must be interpreted with caution because of the differing bio-availability of different nutrient forms under different river conditions. They are only a strong determinant of phytoplankton community structure in situations where population growth is primarily limited by nutrient supply. The ratio is less relevant in very turbid rivers, where phytoplankton growth is mainly limited by light.

Region	Current TN/TP	Natural TN/TP	Current/natural TN/TP
Far North Queensland	6.3	8.8	0.77
North Queensland	5.9	9.1	0.70
Burdekin	3.5	6.5	0.59
Fitzroy	4.6	10.3	0.46
Moreton Bay	7.6	15.7	0.49
Queensland South	6.9	14.4	0.49
Murray-Darling Basin	13.2	18.8	0.72
New South Wales North	9.9	17.6	0.57
New South Wales South	10.0	16.3	0.61
Victoria East	16.4	19.8	0.82
Victoria West	17.2	21.0	0.84
South Australia Gulf	21.5	18.2	1.23
Western Australia South	24.7	22.4	1.11
Indian	8.7	21.7	0.52
Tasmania	12.8	15.9	0.86

• Averaged across the entire river network, the pre-disturbance total nitrogen to total phosphorus ratio was close to 17, and is now currently 12.5. This reduction is generally caused by increased sediment loads, that in relative terms, increase total phosphorus loads more than total nitrogen.
• The ratio has increased in some areas (e.g. in parts of south Western Australia, South Australia, Victoria, Tasmania and the lowland rivers of the Murray-Darling Basin [Figures 6.19, 6.20]). However, in these areas the ratios were naturally high, and the change is unlikely to be ecologically important.

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IMPLICATIONS FOR LAND AND WATER MANAGEMENT

• As a consequence of long residence times of fine sediment stores in parts of river systems, the long-term availability of nutrients to river ecosystems has increased in many areas. Dealing with nutrient sources is necessary, but management of these riverine nutrient stores is also required in the future, if adverse ecological responses are to be minimised.
• Priority areas for reducing river and estuarine nutrient loads are likely to differ. Large relative increases in river nutrient loads do not always coincide with large total exports, and estuaries differ in their sensitivity to increases in nutrient loading, particularly because of differences in residence times and tidal flushing.
• Erosion control and management will provide a significant benefit to managing supply of nutrients from increased sediment loads to most rivers.
• In areas where a large part of the increase is caused by surface run-off loads or point source discharges, close attention needs to be given to fertiliser applications, ensuring appropriate amounts are applied at appropriate times, and with application methods that minimise run-off losses.
• Point sources from intensive rural industries may be dominant nutrient sources in some catchments. They deserve close attention to ensure adequate retention of nutrients occur on-site.
• The dominant impact of storm events in determining total nutrient loads may mask spatial patterns in the changes in nutrient concentrations at low flows. This is important in determining ecological responses (e.g. the substantial increases in nutrient loads that are predicted to have occurred in some Far North Queensland basins do not match local knowledge of their ecological impact). Further work is required to improve the modelling of regional-scale water quality changes in rivers and land use mapping to include intensity and practice attributes.

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REFERENCES

Brune G.M. 1953, 'Trap efficiency of reservoirs',Transactions, American Geophysical Union vol. 34, pp. 407 - 418.

Cole R.A. 1973, 'Stream community response to nutrient enrichment', Journal of Water Pollution Control Federation vol. 45, pp. 1875 - 1888.

Edmonson W.T. & Lehman J.R. 1981, 'The effect of changes in nutrient income on the conditions of Lake Washington', Limnology and Oceanography vol. 26, pp. 1 - 28.

Froelich P.N. 1988, 'Kinetic control of dissolved phosphate in natural rivers: a primer on the phosphate buffer mechanism', Limnology and Oceanography vol. 33, pp. 649 - 668.

Prosser I.P., Hughes A.O., Rustomji P., Young W. & Moran C.J. 2001, Assessment of River Sediment Budgets for the National Land and Water Resources Audit, CSIRO Land and Water Technical Report xx/01 (in press), Canberra.

Redfield A.C. 1958, 'The biological control of chemical factors in the environment', American Scientist vol. 46, pp. 205 - 222.

Schindler D.W., Armstrong F.A.J., Holmgren S.K. & Brunskill G.J. 1971, 'Eutrophication of Lake 227, Experimental Lakes area, Northwest Ontario, by addition of phosphorus and nitrate', Journal of the Fisheries Research Board Canada vol. 28, pp. 1763 - 1782.

Vollenweider R.A. 1992, 'Coastal marine eutrophication: principles and control', in R.A. Vollenweider, R. Marchetti & R. Viniani (eds), Marine Coastal Eutrophication, Science of the Total Environment Supplement, Elsevier, Amsterdam.

Further information

View the Australian Agriculture Assessment 2001 report.

View the river nutrient loads and transport chapter of the Australian Agriculture Assessment 2001 (theme) report.

A range of technical reports have been prepared by CSIRO Land and Water in the development of this work on river nutrient loads and transport: nutrient loads in river networks;regionalisation of flows

Nutrient loads in river networks

As a part of the National Land and Water Resources Audit (NLWRA), sediment and nutrient transport were modelled in large-scale networks across Australia. This report describes the nutrient transport model and its validation at the national scale. The model - ANNEX (Annual Network Nutrient Export) is a static model that predicts the average annual loads of phosphorus and nitrogen in each link in a river network under given catchment conditions. ANNEX is based on a node-link representation of a river network and because of its dependence on the suspended sediment budget, it is run in conjunction with the SedNet model (Prosser et al., 2001) For each link ANNEX requires values for the sediment-bound and dissolved nutrient inputs from the immediate catchment of the link. ANNEX then routes nutrient loads through the river network estimating the losses associated with floodplain and reservoir sedimentation and instream denitrification. While the sediment-bound and dissolved nitrogen budgets are calculated separately, for phosphorus, the exchanges between the sediment-bound and dissolved phases during transport are modelled.

ANNEX has been calibrated for "current conditions" at a national scale using nutrient load estimates from flow and water quality measurements at 93 stations. Improved predictions of nutrient loads at a regional or catchment scale are probably attainable by calibrating to local load estimates, and by using better local input data.

View or download a technical report on " Modelling nutrient loads in large-scale river networks " by W.J. Young, I.P. Prosser, and A.O. Hughes (PDF 0.6 MB)

Regionalisation of flows

As a part of the National Land and Water Resources Audit, sediment and nutrient transport were modelled in large-scale river networks across Australia. These models required estimates of a number of hydrologic variables for each link in the river network. To provide these estimates, simple hydrologic regionalisation models were developed. These models predict the required hydrologic variables as functions of drainage area to the network link and the mean annual rainfall spatially-averaged across this drainage area. The hydrologic data used to build the models were a mixture of modelled daily flows and observed daily flows. The primary model that was developed is used to estimate the mean annual flow in a network link. Mean annual flow models were developed for three different regions of Australia defined by similarity of mean annual runoff coefficients. The models vary in robustness between regions, partly as a result of different size data sets. The mean annual flow models are for drainage areas between 50 km² and 2000 km². Values for links with larger drainage areas were estimated by linear interpolation between the regionalised values and AWRC basin outflow estimates. Secondary models were developed to predict the median daily flow, the bankfull flow, the median over-bank flow, and a parameterised function of daily flows used to estimate sediment transport capacity. These secondary models were all functions of the mean annual flow. While most of these variables are reasonably predicted by mean annual flow, the median daily flow (which for the highly skewed flow distributions of most Australian rivers is an indicator of typical low flow conditions) is poorly predicted by mean annual flow. Predictors other than drainage area and mean annual rainfall are required to build more robust regionalisation models for median daily flow.

Further Information

• a technical report on the " Regionalisations of flow variables used in modelling riverine material transport " by W.J. Young, P. Rustomji, A. O. Hughes, D. Wilkins (PDF 896 KB)
• Link to the Australian Natural Resources Data Library