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

61 freshwater crocodiles, pig-nosed turtles do not nest on sand banks that are separated from open water by vegetation of any sort, terrestrial or aquatic. Sand banks chosen for nesting are principally those comprised of clean fine sand, though the turtles will occasionally nest in gravel or loam. Sand banks where the sand is falling into the water are preferred. Suitable sand banks occur where sand is trapped behind woody debris or rocky outcrops, where sand accumulates on bends in the river, and where sand is deposited by small tributaries that flow only as the wet season floods recede. Sand banks used for nesting vary in size from a few square metres to large accumulations up to 300 m in length. The size, number and location of these sand banks varies considerably from year to year, as the river bed and banks are remodeled extensively each wet season. The turtles cannot rely upon the continued existence of a sand bank from year to year, or on the extent and quality of the nesting habitat for those that do persist in some form from year to year. Each year, they must seek out suitable nesting areas, and this no doubt contributes to the extent of their movements up and down the river during the dry season. A survey between Dorisvale Crossing and Jinduckin Creek in 1998 revealed 54 sand banks suitable for nesting, of which 42 were subsequently used (Doody unpublished data). This yields an estimate of the density of nesting beaches as 1.04 beaches per km of river. Base Flow (90% reduction) (2.0 cumecs) Under base flow conditions the probability of a pig-nosed turtle being able to nest is determined by whether a nesting bank occurs in each of the 33 fragmented pools. Percentiles for the probability of a nesting bank occurring in a particular pool are shown in (Table 19). Under this regime, 50% of the pools have 83% or less chance of having a nesting bank and 25% of the pools have a 64% or less chance of having a nesting bank. The mean number of pools having a nesting bank under this flow regime was 77.817.2%; suggesting on average that 77% of the turtles would be successful in nesting. Table19. Percentiles for the probability of having the opportunity to nest under base flow conditions in Daly River, Northern Territory. P is the probability of a nesting bank occurring within a particular pool. Percentile P Max 99.75 95% 99.31 90% 98.27 Q3 92.65 Median 83.12 Q1 63.83 10% 49.53 5% 45.53 Min 45.29