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

60 Table 18. Impact of habitat fragmentation on the home range size of pignosed turtles. Home range sizes are based on the 95th percentile of the linear extent of movement of 13 female and 5 male radio-tracked turtles (Doody et al., 2002). Data in the table are the percentage of the river under study (73.7 km) where all turtles would have their observed home ranges restricted by fragmentation, and the percentage of the river where none of the turtles would have their home ranges restricted. The p values in brackets are the number of pools that contribute to the stated percentage; the n values are the number of turtles that are restricted everywhere; the m values are the number of turtles that are not restricted anywhere. FLOW FEMALES MALES All restricted None restricted All restricted None restricted 2.0 cu 49.6 (p=25) 0% (n=11) 18.6 (p=14) 15.2 (p=2) 4.8 cu 23.5 (p=11) 0% (n=2) 6.1 (p=4) 65.2 (p=6) 7.6 cu 14.2 (p=6) 47.0 (p=2) 1.7 (p=1) 81.3 (p=5) 10.5 cu 7.5 (p=3) 69.5 (p=2) 0% (m=1) 92.5 (p=4) 13.3 cu 2.4 (p=1) 93.7 (p=3) 0% (m=1) 97.8 (p=4) 16.1 cu 0% (m=13) 100 (p=1) 0% (m=5) 100 (p=1) The above analysis is based on a linear home range calculated from the 95th percentile of fixes with respect to the centroid of the turtles distribution. The analysis is conservative for the following reasons: (a) It does not include occasional sorties outside the primary home range area (i.e. movements in the 95th to 100th percentile) which may serve an essential purpose in their life history. For example, seven gravid females were linked to their nesting locations. Most turtles (87.5 %) nested within 95 % of their linear home range. The exception was turtle F08, who to lay her second nest, made a deliberate movement of ca. 6 km, returning two days later to the area she occupied prior to the sortie. Of 12 nesting events by 10 turtles with sufficient movement data (N > 24), in seven cases females made upstream movements just before nesting, compared to one case of downstream movement, two cases of no movement, and two cases with movements in both directions just prior to nesting. These nesting movements were not included in the home range analysis, but rather were captured in the analysis of nest bank access. (b) We deliberately chose individuals with established home ranges within the study site, not a random selection of turtles. A number of turtles are transients, presumably seeking a permanent home range or simply behavioural variants. Their needs are not accommodated in this analysis. Fragmentation and Nest Bank Access Pig-nosed turtles nest on sand banks adjacent to the river (Doody unpublished data). The sand banks are largely free of vegetation and have a direct connection to the water. Unlike