5 Management and Habitat Implications
5.2 Mid- and lower Finke River
antecedent moisture and widespread rainfall. If the study was for an open-cut mine along the axis of Arckaringa Creek, the model to run would be for a flash flood (because that will generate sufficiently great water and sediment discharge at the flood peak to risk
overwhelming site retention structures). This would probably call for input conditions of high-intensity local rainfall, and high hillslope runoff values.
A hydraulic (hydrodynamic) model is specific to a reach area. It might have flood height and water velocity for the modelled reach as outputs; measurable components would frame the model as inputs (e.g. rainfall, evapotranspiration) or parameters (e.g. roughness,
infiltration) (Justin Costelloe, pers. comm. 2014). Some other factors which affect a river’s behaviour are water slope, water density (which varies with sediment load), hillslope runoff coefficient, distribution and intensity of rainfall, floodplain roughness (and how it varies with increasing flood height), in-channel roughness (including boundary shape, bedforms, and vegetation), and valley cross-section. Hydraulic models can be challenging in the Australian drylands, where it is difficult to obtain some of these data. For example, the empirically-derived roughness value which is most used in such calculations (Mannings n) has not been estimated for some very common occurrences in Australian drylands rivers, such as in-channel large trees (see Graeme and Dunkerley 1993). Some inputs are based on relatively few data points, for example daily rainfall patterns are interpolated from information collected from meteorological stations, and these are sparse in drylands Australia.
If the numerical values for the relevant components can be obtained, then it would be possible to model the flow in the reach for which the measurements had been taken. (It would be a complex task: for example, the roughness values and therefore flow velocity would vary across different landforms, according to the distribution of trees.) The model outputs would yield valuable information for that reach, but would not necessarily be applicable to adjoining reaches, as they would be different. The distribution of different channel types down the Finke River, or anastomosing versus anabranching reaches in Arckaringa Creek, are a reflection of different flow behaviours in different reaches. Other factors change between reaches, for example transmission loss reduces discharge.
Groundwater and Salinity
The Finke River's groundwater context is complex. Some parts of the river receive
groundwater inputs, some of which are more prolific or more saline than others. The Finke River recharges GAB aquifers along the edge of the Pedirka basin. The palaeo-Finke River's sediments are likely to play a role in that recharge.
Artificial addition of water into the alluvial aquifer (for example, from mine waste) has the potential to create a salinity problem if alluvial aquifer waters are flushed to the surface.
Habitats: Rivers
The Finke River's main aquatic habitats are likely to be the permanent and semipermanent waterholes; the small waterholes, channels, and floodplains are unlikely to support the life cycles of aquatic invertebrates or fish (c.f. Cooper Creek and the Neales River). The Finke River's main terrestrial habitats are the more regularly inundated parts of the floodplains, which host water-retaining landforms and are supported by hyporheic water.
During high-flow and very large flood conditions, the Finke River's channel will host a dense cloud of rapidly-moving sand at depth, and the water column over channel and floodplain will hold moving fine sand and silt. This is likely to be a hostile environment for migrating fish, and is very different to the situation in the Neales River or the Channel Country rivers.
Habitats: Waterholes
Mid-Finke River waterhole locations can be permanent on a scale of many centuries (Duguid 2013), especially if their location is forced by boundary conditions. This is a similar degree of permanence to other important LEB refuge waterholes. It is a slightly lesser degree of permanence than upper-Finke River waterholes in the rocky ranges, but the difference is irrelevant on a human management timescale.
Occasional large floods are necessary to maintain waterhole depth. A long-term run of small flows would promote waterhole shallowing, which would be detrimental to refuge values.
Scouring and bedload transport during flood conditions may mean that waterhole substrate is frequently renewed: waterholes in permanent locations may be recurrent rather than
permanent, in the sense that the substrate could be renewed with every large flow event.
This is likely to have implications for invertebrate habitat.
Some waterholes benefit from groundwater input. If proximity to certain aquifers affects waterhole habitat qualities (e.g. salinity), and if some aquifers have tight constraints on their locations, then even small shifts in waterhole location may affect habitat persistence.
Banks and Habitat Description
The Finke River's channel mobility and diversity results in diverse bank types, from unambiguous long-term banks to obviously transient forms. This can be a challenge in description of physical habitat or vegetation communities, as the standard terminology may be a poor fit.
Management and Resource Industry Considerations
When making impact assessments on the effects of water extraction or discharge, it is important to have a sound understanding of the local geology, including the (sometimes poorly documented) Cainozoic geology, and the sedimentary composition of nearby landforms.
Artificial addition of water into the Finke River’s channel, floodplains, or terraces has the potential to create a salinity problem if alluvial aquifer waters are flushed to the surface.
Infrastructure such as pipeline crossings, compressor stations, pipeline access points etc.
should be designed and sited to minimise risk of damage and unplanned gas releases. In particular, gas pipelines across the Finke channel should be buried deep enough to avoid being vulnerable during bedload movement or channel relocation, and other infrastructure should not be placed on floodplains or lower terraces.
Overseas experience and theoretical modelling has indicated that feral trees can contribute to a complete change in river processes by immobilising bedload, with concomitant
destruction of habitat. Thickets of athol pine in areas of greatest channel mobility (such as the lower Finke River) are likely to be detrimental; they should be controlled.
Changes to the Finke River's flow regime, especially flood peak attenuation or flood volume reduction, would be detrimental to the Finke Floodout.