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

58 Provided the water temperature just upstream of the spring is less than the spring temperature (which it is for the scenarios shown), spring inflow of spring water at x = 29km increases water temperatures by an amount that depends on the volume of the upstream flow and the difference in temperature between the spring and the upstream river water. These two factors affecting the size of the temperature jump tend to act opposite to one another as discharges change so the jump tends to be fairly constant in size for the scenarios shown. The scenario 3 -120m sdQ = has a jump of 0.7 0C and 3 -140m sdQ = has a jump of 0.5 0C despite these scenarios having almost a three-fold difference in the flow volumes upstream of the spring. Downstream from the spring, the river temperatures again tend to approach equilibrium that also tends to depend on flow volume and on the size of the departure of water temperature from equilibrium. For 3 -110m sdQ = , the spring caused the river temperature to exceed the equilibrium temperature so the river cooled as it flowed downstream, whereas the downstream river temperatures increased towards equilibrium. Impact on a Flagship Species Fragmentation and Home Range Home range of the pig-nosed turtle at the study site has been determined by radio-telemetry (Doody et al., 2002). Female Carettochelys insculpta were more active, moved farther, and occupied home ranges twice the size of that of males (Table 17). Linear home range size (95th percentile) for radio-telemetered females ranged from 2.5 to 13.9 km (8.3 + 2.88 km, n=13) and for males ranged from 1.5 to 4.5 km (3.2 + 1.32 km, n=5). These differences between the sexes are not likely attributable to food type, as dry season food types do not differ between the sexes (Heaphy, 1990; Welsh, 1999), and are more likely to be associated with the energetic and behavioural demands of reproduction. We modelled the restriction of home range size against habitat fragmentation caused by flow reduction (Table 18). This table is quite difficult to interpret. For example, under base flow conditions of 2 cumecs, 49.6% of the river is fragmented to a state at which all female turtles would have their observed home ranges restricted and 11 out of 13 turtles would be restricted everywhere. At 16.1 cumecs, there is effectively only one continuous system with no turtles restricted anywhere.