Territory Stories

Modelling dry season flows and predicting the impact of water extraction of flagship species



Modelling dry season flows and predicting the impact of water extraction of flagship species


Georges, Aurthur; Webster, Ian; Guarino, Fiorenzo; Jolly, Peter; Thoms, Martin; Doody, Sean; CRC for Freshwater Ecology (Australia); University of Canberra. Applied Ecology Research Group


E-Publications; E-Books; PublicationNT; 57/2002; National River health program




Daly River


The aim of this project is to contribute to recommendations on environmental flows to ensure that they are consistent with maintaining the biota of the Daly River, given competing demands of agriculture, recreation and tourism, conservation and Aboriginal culture. Our focus is on flow, connectivity and water temperatures.


Made available by via Publications (Legal Deposit) Act 2004 (NT); Submitted to the Northern Territory. Department of Infrastructure Planning and Environment

Table of contents

1. Project Details -- 2. Executive Summary -- 3. Interpretation of the Brief -- 4. Variation of the Brief -- 5. Background -- 6. The Daly Drainage -- 7. The Pig-nosed turtle -- 8. Analysis of Historical Flow Data -- 9. Analysis of Contemporary Flow Data -- 10. Modelling Flow Reduction -- 11. Water Temperature Versus Flow -- 12. Impact on Flagship Species -- 13. References




Environmental Flows; Modelling; Biota

Publisher name

Northern Territory Government

Place of publication



Final Report


57/2002; National River health program


75 pages ; 30 cm

File type



Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government



Parent handle


Citation address


Page content

12 The digital terrain modelling described in the project scope was replaced by an analysis using the standard river analysis program HECRAS. Maps showing the degree of fragmentation under different flow regimes have been replaced by a single reference map and tabulated data on the location of break points under different flow regimes. Water conductivity was to be used to determine the relative contribution of surface flow and spring feed, but it became apparent very early in the study that spring feed made up 100% of the dry season flow after the transitional wet-dry months. Conductivity did not vary appreciably, and so this element of the study was abandoned. We achieved the objective of sourcing spring inputs in other ways. Background Alteration of hydrological regime is often claimed as the most serious and continuing threat to the sustainability of healthy riverine ecosystems (Naiman et al. 1995; Sparks 1995; Lundqvist 1998; Ward et al. 1999; Bunn and Arthington 2002). While the obvious irreversible impacts of large impoundments are now well recognised, there is also growing awareness of the pivotal influence of hydrological regime on the relationship between aquatic dependent organisms and their environment (Bunn and Arthington 2002). Movement of water across the landscape influences the ecology of rivers at a broad range of spatial and temporal scales (Vannote et al. 1980; Sparks 1995). Flow regime directly influences the morphology of river macro-channels, the distribution of riffle and pool habitats, and the stability of the bed sediments (Newbury and Gaboury 1993). This complex interaction between flows and physical habitat is a major determinant of the distribution, abundance and diversity of stream and river biota (Poff and Allan 1995; Ward et al. 1999). This is evident also at the smallest spatial scales, where variations in flow and velocity along the water column can dictate the distribution and abundance of many species of plants and animals (Wetmore et al. 1990). Close associations with physical habitat can be found in many stream organisms ranging from algae and aquatic plants to invertebrates, and large vertebrates such as turtles and fish. Perhaps more important than the influence of hydrological regime on the physical environment is its influence on animal life history strategies. Many aquatic species have life histories that have evolved in direct response to natural flow regimes (Bunn and Arthington 2002) and draw cues from flow attributes in order to time reproduction, movement and behavioural attributes. In some cases, critical life history events of aquatic vertebrates are tied to flow regime (e.g., phenology of reproduction, spawning or courtship behaviour, larval survival, growth patterns and recruitment) (Welcomme 1985; Junk et al. 1989; Sparks 1995; Humphries et al. 1999). These life events are synchronised with river temperature and daylength such that any change in the timing and or magnitude of flow can have severe repercussions for aquatic flora and fauna. Modified thermal patterns and day-length cues have been shown not only to disrupt insect emergence patterns but also to reduce population success (Ward and Stanford 1982). The maintenance of natural patterns of river connectivity is also essential to the viability of many riverine species (Bunn & Arthington 2002). Populations of many species of aquatic organisms depend on their ability to move freely through their lotic environment. The disappearance or decline of migratory fish species often follows river fragmentation (Harris 1984a, b, Joy and Death 2001). In southern Australia, reduced longitudinal connectivity in