Flow Guidelines

ID#sort descending Guide Comment Project Reference ELOHA Step Ref
A01 Stakeholders and Indigenous communities must be actively engaged throughout water management planning.

Successful water management planning depends on stakeholders being engaged throughout, which in turn depends on genuine inclusiveness, clarity, transparency and equity in decision-making processes. Early engagement is recommended to gather information, determine issues and help prioritise issues which need a participatory approach to problem-solving.

A03 Valuing and managing water primarily for irrigated agriculture is not a common view.

 

 Australians place a higher value on environmental, recreational and Aboriginal cultural values than production-based services (i.e. irrigated agriculture) provided by tropical rivers.

 

A04 The ability for Aboriginal people to use important waterholes for customary activities (e.g. wildlife harvest) must be taken into consideration in planning.

 The ecosystem services provided by tropical rivers and valued most highly by Australians is the ability for Aboriginal people to undertake their customary activities at important waterholes.

A05 The contribution of the Customary sector (e.g. wildlife harvest) to the Indigenous economy should be recognised in addition to the Market (e.g. employment) and State (e.g. welfare) sectors.

 Indigenous people in the Daly River (NT) and Fitzroy River (WA) catchments rely heavily on the harvest and consumption of aquatic species, and the use of these species makes a direct contribution to household income. Reductions in the Indigenous harvest is likely to result in increased expenditure for household budgets. We recommend using a "hybrid economy" approach which recognises the contribution of the Customary sector (e.g. wildlife harvest) in addition to the Market (e.g. employment) and State (e.g. welfare) sectors.

A06 The Indigenous economy is unlikely to benefit from growth in the non-Indigenous economy.

 Indigenous and non-Indigenous economic systems are asymmetrically divided: growth in the Indigenous economy will benefit the non-Indigenous economy, but growth in non-Indigenous sectors (e.g. agriculture) will generally not flow on through to Indigenous people. The exception is with structural change (i.e. employment, ownership of resources).

A07 Modest growth in water-intensive agricultural activities could rapidly deplete available water resources.

 Expansion of the agricultural sector by 5% per annum, particularly if water-intensive practices are employed, could double water use in a short period, e.g. by 2018 in the Mitchell River (QLD), by 2012 in the Daly River (NT).

A08 Cultural flows are important to Indigenous people.

 Cultural flows are important to Indigenous people and are distinct from consumptive uses of water

A09 The trade of environmental and cultural flows is not supported by stakeholders.

While just over half of the surveyed population viewed water as a tradeable commodity, people did not want to see trade in environmental or cultural flows, and a number of these people imposed a caveat that any trading framework must involve Indigenous people. Respondents believed that the ability to trade water would reduce wastage, but wanted unique cultural and ecological values present across the north to be protected. The preservation of certain aquifers and catchments, and that consumptive water use was constrained in these catchments, was also important to respondents.

A10 Land use change can alter sediment sources and loads to northern rivers.

In the Mitchell River, the riverbed sediments are predominantly sourced from alluvial gully erosion, probably initiated or accelerated as a consequence of the switch from Indigenous management to cattle grazing at European settlement. This erosion is occurring predominantly in the riparian zones, which is where the youngest and most productive soils are located, and so is degrading the productivity of alluvial soils for the pastoral industry and the downstream aquatic ecosystem.

A11 Remedial action to reduce sediment delivery in northern catchments should be targeted to riparian zones.

Subsoil erosion in riparian zones contributes a considerably larger proportion of sediments to northern rivers than hillslope erosion from soil surfaces.

A12 Flow regimes, riparian zones and catchment land use should be managed to retain aquatic habitat for benthic microalgae.""

 Benthic microalgae (i.e. biofilm) is a primary energy source supporting fish and food webs in tropical rivers and floodplains. Factors which alter the production of benthic microalgae, e.g. altered dry season flows, altered inundation regimes of floodplains, increased nutrient inputs, altered riparian canopy cover, and disturbance from feral animals or weeds, are likely to alter food web structure and the biomass of key fish species such as black bream and barramundi. While algae is consumed by fish and invertebrates, nutrients have stronger effects on the biomass of algae than grazing animals. These impacts can be disproportionately greater in disconnected pools of intermittent rivers during the dry season, and in all rivers when flows recommence with storm runoff events in the early wet season.

A13 Human impacts on Darwin Harbour are minor and localised, and depend on flushing.

Most of the nutrient load in Darwin Harbour comes from the ocean rather than from river or urban inputs. This is due to the large tidal exchange and the relatively low-nutrient inputs from unimpacted rivers. However, sewage inputs in tidal creeks with less flushing (e.g. Buffalo Creek) increase nutrient inputs, which promote algal growth, which in turn increase sediment and nutrient loads, reduce dissolved oxygen, and release nutrients which promote algal growth.

A14 Managing flows for selected widespread and common species will sustain the economic contribution of aquatic species to Indigenous livelihoods.

Some of the most economically valuable aquatic species harvested by Indigenous communities in the Daly River (NT) and Fitzroy River (WA) catchments are also among the most common and widespread species (rather than rare and threatened species) across these northern catchments. Furthermore, the top five species harvested in each catchment contribute the majority (up to 90%) of the economic value of the total aquatic harvest. However, this contribution is spread across the landscape, and is not necessarily from a subset of sites. In the Daly River catchment these species are long- and short-necked turtles, barramundi, black bream and magpie geese. In the Fitzroy River catchment these species are black bream, fork-tailed catfish, freshwater sawfish, barramundi and cherabin

A15 In the Fitzroy River catchment (WA), freshwater sawfish (a threatened species) comprise an economically valuable species for Indigenous harvesting.""

Freshwater sawfish are among the top five species harvested by local Indigenous communities in the Fitzroy River (WA). While this species has listed conservation status, only small numbers of sawfish are harvested, their relatively large body size provides a substantial and economically valuable food source. A long history of Indigenous harvest combined with the continuing health of sawfish populations suggests that the Indigenous harvest should not necessarily be the focal point of conservation concern.

B01 Before water quality monitoring is implemented, it should be preceded by a clear plan developed within a framework which incorporates all aspects.

 In developing plans for water quality (and ultimately river health) monitoring, there is considerable benefit in beginning with a framework to:

  1. explicitly link water and land use impacts with their effects on water quality (e.g. by using a pressure/threat “stressor“ ecological response model) and ensure the monitoring is integrated , collaborative and linked to management
  2. manage water quality for the multiple beneficial uses of water
  3. provide a basis for continual review and improvement (i.e. adaptive management)
  4. provide clear and accessible communication of the purposes and aims of monitoring
  5. acknowledge that water quality monitoring is more than data collection and includes understanding, design, data storage, management, assessment, reporting and communication.
B02 There are constraints on the capacity to successfully apply the Framework for the Assessment of River and Wetland Health (FARWH) in northern Australia.

The Framework for Assessment of River and Wetland Health (FARWH) relies on a sound knowledge of the "reference state" as a comparison against which the degree of impact can be measured, but these sites are often lacking in northern Australia. The FARWH relies on the random selection of sites with equitable spatial coverage and stream order; this is not possible due to the remote location of sites and lack of vehicular access, and occasional failure to secure landholder access to sites. Finally, the FARWH trial conducted in tropical NT and WA was applied to perennially-flowing streams and rivers and in the dry season only; its application to wet season conditions and wetlands has not been tested.

B03 Site selection for river health assessment should include small streams, and should approximate their contribution to the river network.""

 Small streams are more vulnerable to health degradation than large rivers. River health monitoring tools, which are based on model predictions from reference site data, need to include small streams and in a proportion that approximates their contribution to the river network under assessment.

B04 The Flows Stress Ranking (FSR) is a suitable monitoring tool to assess deviations in flow regimes

 The Flow Stress Ranking (FSR) procedure to assess deviations from the natural flow regime was successfully applied to the Ord River (WA) and Darwin River (NT) hydrographic data sets, and also to the Katherine River (NT) where the effect of groundwater extraction on river discharge could be modelled.

B05 The Tropical Rapid Assessment for Riparian Condition (TRARC) approach is not sensitive to the detection of cattle disturbance in riparian zones.

 The Tropical Rapid Assessment for Riparian Condition (TRARC) was applied to the physical form and fringing zones themes in trialling the FARWH (the Framework for Assessment of River and Wetland Health). The results were not strongly correlated to cattle disturbance possibly because there was no impact, the impact was only a small proportion of stream length, and/or the TRARC is not sensitive to small scale, localised disturbances when the scale in question is considerably less than the assessed area. Therefore, alternative methods for riparian zones should be considered such as using the raw data for a subset of TRARC indices rather than the use of categories, or a more focused effort on the most likely impact, e.g. plot seedling recruitment assessments.

B06 The Catchment Disturbance index in the FARWH includes a fire component to link fire management with river health assessment.

 The catchment disturbance index included a fire component, in recognition of the damage fire can do to fringing zone vegetation and canopy cover, and its contribution to increased catchment erosion.

B07 The Water Quality index in the FARWH may not be suitable for northern Australian rivers.

The application of the FARWH water quality theme is problematic because it requires a zero score for "polluted" waters and relies on subjective judgement. It also requires knowledge of the ecological impact of water pollution which, with the exception of mine pollution, is poorly understood.

B08 Open-system diurnal oxygen curves provide a good measure of total photosynthesis.

 Photosynthesis as measured by the diurnal oxygen curve method is responsive to light and the biomass of primary producers in clear, low-nutrient tropical rivers such as the Daly River (NT).

B09 Photosynthesis (as measured by diurnal oxygen curves) does not provide a good measure of the production rate of plant and algal biomass in clear, low-nutrient tropical rivers such as the Daly River

Photosynthesis (as measured by diurnal oxygen curves) substantially over-estimates primary production by algal and plant biomass in nutrient-limited tropical rivers. Photosynthesis is not inhibited at high light intensities in clear, low-nutrient rivers such as the Daly River (NT), and therefore diurnal oxygen curves are not an effective way to measure the gross rate of production of biomass in these types of rivers. (Most carbon fixed by photosynthesis is extruded to the water by algae and plants as dissolved organic material, rather than incorporated into plant biomass.

B10 Dry season nutrient concentrations should be routinely monitored, including both soluble and insoluble forms.

The growth and accumulation of primary producers is constrained, in part, by available nutrients. Nutrients in the water column may be monitored in their soluble form or as a total amount (which includes both soluble and insoluble forms). Both have advantages and disadvantages, but monitoring for both provides the best information. Both organic and inorganic soluble forms should be monitored.

B11 Nutrient loads (both organic and inorganic species) should be monitored in low-nutrient rivers such as the Daly River (NT) to allow early detection of changes to nutrient loads.

Increased nutrient loads are a common consequence of changes in land use. Nutrient addition to low-nutrient rivers such as the Daly River (NT) is likely to alter aquatic vegetation assemblages, particularly algae. The Daly River is adapted to low nutrient (nitrogen and phosphorus) concentrations in the dry season, and nitrogen and/or phosphorus limit the biomass of primary producers. Inorganic nutrients are rapidly taken up by aquatic algae, so increased nutrient loads may not immediately be reflected in increased nutrient concentrations. Any increase in dry-season nutrient stores in the river is likely to result in increased production of fast-growing algae such as Spirogyra, possibly at the expense of slower-growing aquatic plants.

B12 Nutrient loads should be monitored during the dry and at the end of the wet season as flows recede.

In perennial reaches of the Daly River (NT), and possibly other perennial rivers (although this remains to be tested), primary productivity increases over the dry season. During the early dry season, growth of plant biomass (e.g. fast-growing plants like periphyton and Spirogyra) is supported by the direct uptake of nutrients from the water column. Later in the dry season, plant biomass (e.g. slower-growing plants like Vallisneria) is supported by the recycling of nutrients within benthic communities (e.g. the trapping of nutrients by fast-growing Spirogyra), and possibly also by releases from sediment stores. Consequently, nutrient loads towards the end of the wet season are “driving” subsequent dry season production.

B14 Despite some consistent patterns in biotic assemblages, there appears to be little capacity for using "surrogates" to represent multiple assemblages.

Vegetation, fish and macroinvertebrate assemblages show concordant patterns of spatial variation across river landscapes, but are organised along different sets of environmental gradients and filters. While flows regime and ecosystem size are important in describing the distribution of each assemblage type, there are also other environmental variables which contribute to their distributions. This means one assemblage type cannot be used as a surrogate for either of the other assemblage types. Genetic analyses further indicate that across northern Australia, biodiversity is higher, and species distributions narrower, than previously thought, and that there are distinct areas of high genetic diversity and high endemism.

C01 Rivers of northern Australia can be characterised and grouped according to flow regime type. Flow components which distinguish individual rivers can be identified.

There are six distinct flow regime types in northern Australia, distinguished by perenniality/intermittency, predictability, and the timing of major floods. Most rivers are in one of two flow types: predictable summer highly intermittent (most common, e.g. Fitzroy (WA), Mitchell (QLD)), or stable summer baseflow (i.e. perennial, e.g. Daly (NT)).

C02 Flow-ecology relationships and insights relating to ecological function may be transferred between catchments within the same flow type.

The flow regime classification provides a spatial context for individual rivers and a valid foundation for extrapolating findings between catchments. The classification therefore promotes the identification of ecological patterns associated with particular flow regimes and particular flow components.

C03 River flows during the early dry season can be sustained by local groundwater stores in the riverbanks; flows can be sustained from deeper aquifers in the later dry season.

In the lower Fitzroy River (WA), river flow over the weeks and months of the early dry season are sourced from local groundwater sources in the river banks. As the dry season progresses, flows are sourced from regional and deeper aquifers. In the Daly River (NT), regional aquifers can sustain flow throughout the year.

C04 Altering catchment vegetation can alter hydrology: native savannah vegetation maintains relatively constant water use year-round.

In the Daly (NT), pastoral vegetation uses more water in the wet season and less in dry season, whereas native savannah vegetation uses water comparatively constantly year-round. In areas vegetated by native savannah, soils dry out more during the dry season, hence groundwater recharge is lower during the wet season.

C05 Long-term flow regime patterns can affect channel morphology.

The lower Daly River (NT) has experienced channel widening and extensive bank erosion since the 1970s, supporting the hypothesis that the channel is adjusting to a wetter hydrologic regime over this period. While there has been no net sediment accumulation during this period, the eroded bank sediments appear to have been exported from the reach (and potentially deposited in the estuary), and the riverbed sediments in the lower Daly River appear to have been sourced from upstream (but this remains to be investigated).

C06 Wet season flows are important in structuring channel morphology from year to year.

 In the Daly River (NT), greater magnitude wet season flows due to wetter conditions since 1966 have contributed to greater bank erosion and channel widening. In the Mitchell River (QLD), wet season flows can move large amounts of bed sediments, e.g. 50 million m3/yr between 1988-2007. The bed sediments of the Mitchell River are highly dynamic, e.g. about 40% of the suspended sediments consist of sands, which results in a highly dynamic distribution of permanent pools from year to year despite the total pool area being constant.

C07 Hydraulic and hydrodynamic models of perennial rivers should appropriately model the impact of hydraulic breaks.

 Dry season flows in perennial rivers such as the Daly River (NT) are controlled by hydraulic breaks, i.e. relatively sharp drops in water surface levels along the river channel. The choice of hydraulic or hydrodynamic models for the Daly River must be guided by the capacity of the model to include the impact of hydraulic breaks (not all models do so). Accurate modelling of river hydraulics and water surface levels under different flow conditions will require detailed bathymetry that is capable of properly defining the hydraulic breaks.

C08 Dry season baseflows in perennial rivers should be protected to maintain instream habitat diversity, particularly gravel runs and pools, for algal communities""

 In perennial rivers, the hydraulic environment during the dry season is dependent on river flow and bathymetry. Gravel runs and pools are maintained by dry season baseflows and are key habitats for benthic microalgae which contribute to most primary production in the Daly River (NT). A reduction in baseflow will alter the hydraulic environment, therefore will alter the distribution and abundance of velocity "patches", and will generally reduce the area of riverbed subject to relatively high velocities and shear stress. The ecological significance of this is poorly understood, although there is evidence that it will negatively affect primary production. Small reductions in dry season baseflows could have disproportionately large effects on productivity and habitat availability.

C09 Dry season baseflows in perennial rivers should be protected to maintain the movement of fine sediments over the dry season and prevent infilling of pools.

Sediments are highly dynamic during the dry season in perennial rivers such as the Daly River (NT). Continual reworking of the bed sediments moves fine sediments into pools and gravel beds, increasing the organic content of gravel beds over the course of the dry season. Water flows through sand ripples, penetrating 5-10 cm before being advected back into the water column. Sand ripples are potentially important zones for bacterial breakdown of organic material and nutrient recycling, but this remains a knowledge gap.

C10 Seasonal flow patterns should be preserved to maintain aquatic plant community structure.

 Plant biomass (including algal biomass) is strongly affected by seasonal changes in flows. Sloughing or scouring of benthic plant material occurs under higher flows, and nutrient transfer rates decrease under low flows, both of which play an important role in the seasonal distribution and relative abundance of different species.

C11 Dry season baseflows in perennial rivers should be protected to maintain instream habitat diversity, particularly gravel runs and riffles, for instream biota.""

 Rocky riffles and gravel runs in perennial rivers are key areas for the growth of benthic microalgae (i.e. biofilm), which is a primary food source supporting fish and food webs in tropical rivers. Riffles are key areas for the emergence of adult aquatic insects, which are an important link to terrestrial food webs by providing food for fauna such as spiders, birds and bats. Aquatic insect emergence peaks in the dry season. Riffles are also key areas for the juveniles of numerous fish species where they are safe from predation and can access food resources (e.g. black bream, Butler's grunter).

C12 Permanent waterholes in intermittent rivers and on floodplains are critical aquatic refugia and should be preserved.

 Waterholes remaining in intermittent river channels and on floodplains are critical habitats during the dry season, as well as for terrestrial biota which rely on aquatic resources (e.g. birds). Wet season flows inundate floodplains, influencing persistence of waterholes throughout the dry season (there is little evidence that groundwater sustains waterholes across most of the north). Waterholes are refugia for aquatic biota (algae, vascular plants, invertebrates and fish) during the dry season. and provide food resources (plants, invertebrates, adult insect emergence and fish) for terrestrial consumers that rely on aquatic food resources. Predation and competition may intensify over the course of the dry season as habitats retract. Physical conditions can also become harsh as dissolved oxygen decreases and turbidity increases. Refugia also provide the resources for recolonising newly inundated and connected habitats once flows resume. Local impacts such as nutrient inputs and disturbance from feral animals and weeds, can have disproportionately greater effects in these isolated waterholes

C13 Wet season flows should be preserved to maintain instream habitat supply.

Wet season flows are important for redistributing instream habitat, e.g. wood aggregations, sediment turnover, scouring rockbars, all of which provide habitat for benthic algae, invertebrates, fish, birds and crocodiles during the dry season. Wet season flows move large amounts of wood in the Daly River (NT), redistributing around 50% of aggregated wood and resulting in a high degree of habitat turnover and heterogeneity for instream biota from year to year. Modifications to wet season flows can reduce instream habitat and turnover.

C14 Wet season flows should preserve hydrological connectivity between rivers and floodplains.

 Wet season flows are needed to reconnect floodplains (and their waterholes) with the river, allowing nutrient and sediment exchange, providing opportunities for fish, invertebrate and plant growth (including algae), and critical food sources and nesting habitats for waterbirds. The growth of microalgae on floodplains during the wet season is consumed  by fish, even during relatively short inundation periods. Macroinvertebrates and small fish (e.g. bony bream, eel-tailed catfish) are then responsible, as prey, for transferring this energy to "higher-value" species such as barramundi. Fish grow rapidly during this time and carry this floodplain "signal" back to refugial areas such as rivers, waterholes and coastal areas during the dry season. It appears that the strength of this reliance is positively related to the period of floodplain inundation. Thus the provision of food resources and habitats during wet season inundation of floodplains can have far-reaching effects on biotic populations and communities, well into the following dry season. Reduced flows which reduce the extent of floodplain inundation are most likely to adversely affect small off-channel waterholes on the lower floodplain, and can exacerbate harsh physical conditions in waterholes at the end of the dry season.

C15 Riparian zones provide a critical link between aquatic and terrestrial food webs.

Terrestrial inputs from the riparian zone contribute to the diets of aquatic fauna. Terrestrial leaves can be utilised by microbial communities and benthic macroinvertebrates, particularly when canopy cover is heavy and reduces light inputs for algal growth. Terrestrial arthropods contribute to the diets of a range of aquatic fauna such as invertebrates, fish and crocodiles.

C16 Flow regime plays a key role in structuring biodiversity and species distributions.

 Vegetation (both riparian and aquatic), fish and invertebrate assemblages display spatial concordance in their distributions: each assemblage differs between the Daly (NT) and Fitzroy (WA) catchments, and between main channels, tributaries and waterholes within catchments, in the same way as the other two assemblage types. Vegetation, fish and invertebrate assemblages are structured along a particular set of environmental gradients (meaning one assemblage type cannot be used as a surrogate for overall biodiversity), but flow regime and ecosystem size are important for all three assemblage types. Species diversity is higher in hydrologically connected, perennial systems. In particular, there is distinct genetic diversity in some fish species of the Daly River, and the northern Kimberley has a high degree of endemism (i.e. species not found anywhere else).

C17 Flow regime influences the strength of consumer-resource coupling within food webs.

 Strength of coupling between fish consumers and their energy sources is related to hydrological connectivity: coupling is stronger in food webs which are more hydrologically isolated (e.g. the Fitzroy River (WA)), and weaker in food webs which are more hydrologically connected, or perennial (e.g. The Daly River (NT)). Hydrological connectivity promotes the movement of fish and higher-order consumers, so they can access and integrate energy sources across a range of locations across the riverine landscape and thus weaken coupling to site-specific resources. Local impacts on benthic algae can have disproportionately greater effects on food webs in hydrologically isolated systems because consumers, being unable to move between locations, are more strongly coupled to site-specific resources.

C18 Flow regime, and the consequent degree of hydrological connectivity, influences variability of some food web structure""

Overall food web structure, as described using community-wide metrics, is remarkably consistent and does not vary spatially across northern Australia. Facets of food web structure such as the diversity of basal resources, trophic diversity and food web niche width do not vary with hydrological connectivity, despite hydrological connectivity influencing species assemblage structure and consumer-resource coupling. However, the variability of niche width (the trophic space taken up by a food web) is significantly lower in more hydrologically connected (i.e. perennial) sites. Together, these findings suggest that food web structure is fairly stable and that perennial flows may confer extra stability to food webs, therefore factors which may upset hydrological connectivity (e.g. water abstraction) may increase the likelihood of destabilising food webs, potentially altering resource availability for  fisheries and Indigenous livelihoods.

C19 Water quality in disconnected waterholes can be naturally highly variable.

Seasonal effects on water quality and primary production in disconnected waterholes appear to be as strong as ecological effects. That is, waterholes in the late dry season have vastly different physical (e.g. turbidity) and chemical (e.g. nutrients, chlorophyll) properties compared to the same waterholes early in the dry season after floodwaters recede. This is true for sites with and without major disturbances from cattle and feral pigs, so any efforts to quantify the effects of these introduced animals or other pressures must take into account the large and natural seasonal variation. However, there exist few locations that are truly pristine that could allow determination of pre-European conditions.

C20 Floodplain residence times can be highly variable across northern Australia.

 Western Cape York (QLD) rivers are dominated by large distributary fan systems with low inundation frequency and are  only inundated for a short time (e.g. around two months in a wet year). In these systems the floods recede in a "wedge" manner such that waterbodies in the upper fan are inundated for a shorter period than the lower more coastal part of the distributary fan. The vast floodplains of the Southern Gulf (QLD) have extensive floods occurring across complex anabranching drainage networks but with short inundation periods. The Fitzroy (WA) floodplain is the most dominant floodplain in the western part of the TRaCK study area and has large but short duration floods (< n two months in a wet year); flood inundation is more confined to the areas adjacent to the main channel and the flood events occur as "pulse" such that most waterbodies on the floodplain are inundated for approximately the same period regardless of catchment position. The areas of highest inundation frequency and longest flood residence times in the TRaCK study area occur across the northernmost parts of the NT and include Alligator (Kakadu wetlands), Goyder (Arafura Swamp), and Daly-Douglas river systems. The Daly floodplain differs significantly from the Mitchell and the Fitzroy with long flood residence times (greater than 6 months), the majority of the floodplain being dominated by aquatic vegetation, and floods gradually recede to large perennial waterbodies. It appears that food webs in catchments with longer flood and flow periods have weaker coupling between fish consumers and their local, site-specific resources, but are more connected between locations due to the movements of fish across the river landscape.

C21 Wet season floods affect estuarine and coastal productivity

Experiments in the Norman River (QLD) estuary indicate that freshwater inundation of saltflats can release nutrients and increase chlorophyll a, thereby increasing coastal productivity. But sustained flooding in the Southern Gulf coincided with reduced salinity, reduced algae and meiofauna on the mudflats, and a migration of banana prawns out of the Norman River estuary. Post flooding, there is evidence that mudflat productivity is enhanced, but not water column productivity. Floodplumes from the Norman River result in large areas of freshwater in the coastal areas, with freshwater fish and crustacean species replacing estuarine species.

C22 Modifications to dry season flows in perennial rivers which narrow the range of, or alter, current velocities will impact benthic communities""

 Benthic algal biomass is highly variable over different current velocities, resulting in heterogeneous patchiness of growth over the riverbed, which has been shown to support high abundance and diversity of instream fauna. Macroinvertebrate assemblages differ between patches of low and high current velocity, with high velocity areas (about 0.8 m/s) supporting unique species which are not found in other areas. However, once velocities increase beyond 1 m/s, there appears to be a decline in macroinvertebrate abundance and diversity.

C23 Alterations to flow regimes which introduce, or increase, intermittency, will reduce fish habitat and diversity and alter fish assemblages. ""

 Fish assemblages are structured by the interaction of landscape, instream habitat and flow regime. Fish assemblages in intermittent rivers and reaches are a subset of assemblages found in perennial reaches; intermittent reaches have fewer species, fewer large-bodied species, fewer large individuals and fewer predators.

C24 Many tropical fish species require hydrological connectivity to be able to move between reaches.

 Many fish species need to move between riverine reaches for migration, spawning and dispersal: one third of species recorded in the Daly River (NT) need to move between estuarine and freshwater reaches for spawning (e.g. barramundi, freshwater sole), and one third need to move between different freshwater reaches for spawning (e.g. black bream, plotosid catfish). The distance of movement upstream appears to be limited only by flow intermittency, so flow alterations which introduce intermittency will affect fish movement. Instream barriers will also disconnect river reaches and impede fish movement.

C25 Seasonal hydrology and timing is important for fish migration and spawning.

 There are four migration "guilds" of fish:

  1. fish species whose juveniles migrate upstream from estuaries during the wet season (e.g. barramundi, freshwater sole)
  2. species who migrate between freshwater reaches to spawning sites in the wet season (e.g. black bream, plotosid catfish)
  3. species who migrate between freshwater reaches during the dry season (e.g. longtom, bony bream)
  4. species that move and spawn all year round (e.g. rainbowfish, hardyheads).

Modifications to either wet season or dry season flows can affect the movement and spawning of numerous fish species.

C26 The transition periods between the wet and the dry seasons (and vice versa) are key times for biotic production and movement.

 In perennial reaches of the Daly River (NT), flows go through a clearwater phase during the transition between the wet and dry seasons due to groundwater inputs. The timing of this phase depends on the ratio of surface water volume to groundwater volume. The clearwater phase promotes the growth of aquatic plants (e.g. benthic algae and vascular plants) providing food and habitat for macroinvertebrates, fish and turtles. In tributaries of the Daly River, these transition periods coincide with increases in algal biomass and the abundance of aquatic invertebrates. Transition between the wet and dry seasons are also key times for the movement of fish in Daly River tributaries: fish move upstream during the early wet season, and downstream in the late-wet/early-dry season. The abundance of fish moving downstream during the late-wet season is greater in intermittent tributaries without permanent water, suggesting the movement is related to finding refuge. Flow modifications which disrupt the timing of these transition periods, or alter their duration, can negatively affect benthic production and fish movement.

C27 Interannual variability in wet season flows influences variation in fish assemblages.

 Sampling over longer time periods (i.e. more years) provides a far more complete picture of interannual changes in fish assemblages: for example, the abundance of predators in the Daly River (NT) has been considerably greater in years 3 and 4 of sampling compared to the first two years. It is possible that fish assemblages are returning to pre-flood conditions after major flooding in 2006. Multiple years of sampling are required to properly understand variation in fish assemblage structure.

C28 Dry season water extraction in perennial rivers can increase the risk of habitat loss for numerous fish species.

 Qualitative modelling of fish habitat under future water use scenarios indicates that dry season water extraction in the Daly River catchment (NT) will increase the risk of habitat loss for 40 species, although some species are at considerably higher risk than others, e.g. black bream, barramundi, both of which are species of socioeconomic importance.

C29 Dry season water extraction in perennial rivers can reduce the abundance of key fish species.

 Modelling of future water use scenarios indicates that flow reduction in the Daly River (NT) during the dry season will double the risk of "extremely low" abundances of black bream and barramundi. Both species are among the most economically important species harvested by local Indigenous communities, and barramundi are also an important recreational fishery in the Daly River.

C30 Commercial and recreational fisheries catch is linked with the scale of freshwater flows.

Freshwater flows flush estuarine species of commercial interest into deep waters, making them accessible to commercial and recreational fisheries. Freshwater species, or species tolerant of freshwater, replace estuarine species in the estuaries during the wet season, increasing food availability and hence recreational fisheries stocks.

C31 Altered wet season flows, both magnitude and timing, are likely to reduce the recruitment and catch of coastal fisheries.""

 Coastal finfish production (i.e. catch) is positively correlated with wet season flows, with increased catchability within the year of the flow. Recruitment of barramundi is positively correlated with early wet season flows (i.e. in December). This appears to be fairly consistent between tropical estuaries.

C32 Flow modifications which reduce the abundance and diversity of aquatic species can negatively affect household incomes of local communities.

 Indigenous people in the Daly River (NT) and Fitzroy River (WA) catchments rely heavily on the harvest and consumption of aquatic species, and the use of these species makes a direct contribution to household income. Reductions in the Indigenous harvest is likely to result in increased expenditure for household budgets. However, a lack of information on customary fisheries (e.g. harvest impact versus harvest success) makes it difficult to specify exactly how the Indigenous harvest may be affected by flow alterations.

C33 Both wet season and dry season flows sustain the few species that are of most economic value to Indigenous households.

 The top five species harvested by local Indigenous communities in the Daly River (NT) and Fitzroy River (WA) catchments, which contribute up to 90% of the total aquatic harvest, span the entire flow regime. Barramundi and black bream require dry season flows to be maintained, especially over shallow riffle areas, cherubin require late wet season flows for upstream migration, and turtles and magpie geese have nesting requirements met by wet season flows.

C34 Indigenous harvest of aquatic resources is strongly seasonal and can vary between catchments due to the strong dependence on accessibility to aquatic habitats.

Patterns of Indigenous use of aquatic resources can be spatially and seasonally variable. For example, in the Fitzroy River (WA) catchment the frequency of harvesting trips is at its highest during the wet season, whereas in the Daly River (NT) it is at its lowest during the wet season. In the Fitzroy catchment, harvesting activities are concentrated on the main river channel; more than 70% of harvesting trips are to the main channel regardless of season. In the Daly catchment, the main channel is the focus for harvesting activities during the wet season, but during the dry season harvesting activities are focussed on floodplain waterholes; up to 70% of trips during the late dry season are to billabongs. This switch does not occur in the Fitzroy River catchment.

D01 Land use change can alter sediment sources and loads to northern rivers.

In the Mitchell River, the riverbed sediments are predominantly sourced from alluvial gully erosion, probably initiated or accelerated as a consequence of the switch from Indigenous management to cattle grazing at European settlement. This erosion is occurring predominantly in the riparian zones, which is where the youngest and most productive soils are located, and so is degrading the productivity of alluvial soils for the pastoral industry and the downstream aquatic ecosystem.

D02 Remedial action to reduce sediment delivery in northern catchments should be targeted to riparian zones.

Subsoil erosion in riparian zones contributes a considerably larger proportion of sediments to northern rivers than hillslope erosion from soil surfaces.

D03 Flow regimes, riparian zones and catchment land use should be managed to retain aquatic habitat for benthic microalgae.

 Benthic microalgae (i.e. biofilm) is a primary energy source supporting fish and food webs in tropical rivers and floodplains. Factors which alter the production of benthic microalgae, e.g. altered dry season flows, altered inundation regimes of floodplains, increased nutrient inputs, altered riparian canopy cover, and disturbance from feral animals or weeds, are likely to alter food web structure and the biomass of key fish species such as black bream and barramundi. While algae is consumed by fish and invertebrates, nutrients have stronger effects on the biomass of algae than grazing animals. These impacts can be disproportionately greater in disconnected pools of intermittent rivers during the dry season, and in all rivers when flows recommence with storm runoff events in the early wet season.

D04 Human impacts on Darwin Harbour are minor and localised, and depend on flushing.

Most of the nutrient load in Darwin Harbour comes from the ocean rather than from river or urban inputs. This is due to the large tidal exchange and the relatively low-nutrient inputs from unimpacted rivers. However, sewage inputs in tidal creeks with less flushing (e.g. Buffalo Creek) increase nutrient inputs, which promote algal growth, which in turn increase sediment and nutrient loads, reduce dissolved oxygen, and release nutrients which promote algal growth.

E01 Interactive GIS system for classifying tropical rivers according to individual requirements.

 Users can develop classifications of tropical rivers according to user-defined input variables from a range of geophysical data, thus allowing tailor-made outputs for specific purposes.

E02 Classification of river flow regimes.

The classification can be used to describe a river's flow regime, and to promote and identify ecological patterns associated with particular flow regimes.

E03 Qualitative risk assessment of dry season water abstraction on fish assemblages of the Daly River (NT)

 Uses habitat and life history information to rank 40 fish species according to their relative risk from dry season water extraction in the Daly River (NT).

E04 Bayesian Belief Networks for dry season barramundi and black bream abundances in the Daly River (NT).

 Bayesian Belief Networks for barramundi and black bream abundances under future water use scenarios in the Daly River (NT).

E05 Map-based metadatabase comprising all TRaCK research.

A map-based database containing all the TRaCK research projects, where they occurred, their associated metadata (i.e. descriptions of data files), and contact details for further information.

E06 Management Strategy Evaluation (MSE) application.

Application which provides integration between TRaCK science domains and resource management knowledge domains. Delivers the capability to evaluate different water-use scenarios  to water resource managers and stakeholders.

E07 Conceptual models of northern riverine structure and function

 Conceptual models of how northern Australian river, estuary and floodplain ecosystems are structured and how they function, with an emphasis on seasonal differences.