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

14 The study site was an 80 km stretch of the Daly River well above the tidal reaches between Dorisvale Gauging Station (131o 55'E, 14o37'S) and the inflow of Cattle Creek (131o13'E, 14o03'S) just downstream of Oolloo Crossing. The banks are of sand or sandy loam sloping steeply to a height of 20 m and covered in dense complex vegetation visually dominated by Melaleuca argentea, M. leucadendron, Barrintonia acutangula, Pandanus aquaticus, Cathormion umbellatum, Ficus racemosa, F. opposita, Nauclea orientalis, Casuarina cunninghamii, Eucalyptus spp. (trees), Diospyros cordifolia, Phyllanthus reticuloris, Tephnosia sp. (shrubs), Passiflora foetida, Flagellaria indica (vines), Sida sp., Lindsaea ensifolia, Pseudoraphis spinescens and Paspalum sp. (herbs, ferns and grasses). The riverbed is composed of sand, gravel and silt (sensu McIntyre and Loveday, 1974) interspersed with occasional limestone rock outcrops. Aquatic vegetation (principally Vallisineria nana) grows along the edges and in localized mid-stream patches, but for the most part the bed is clear of macrophytes. The river supports 28 species of fish, 3 species of crustacean and 3 species of mollusc (Midgley, 1980; pers. obs). Carettochelys may be found together with the northern long-necked turtle Chelodina rugosa, the northern snapping turtle Elseya dentata, the red-faced turtle Emydura victoriae and two yellow-faced species of chelid turtle (formerly Em. australis see Georges and Adams, 1992). The climate is typical of the wet-dry tropics of northern Australia (Taylor and Tulloch, 1985) with a mean monthly rainfall less than 7 mm from May to September, rising to a peak monthly average of 284 mm in February (Stn 014139/014941, Oolloo, 1962- 1985). Mean relative humidity (at 1500 hrs, Stn 014908, Daly River (Woolianna), 1966-1980) ranges from a low of 32% in august to a high of 73% in February. Mean monthly maximum air temperature ranges from 30.9C in June to a peak of 36.8C in October. Winds blow from the east-southeast during the dry-season. They are more variable in direction during the wetseason, but blow predominantly from the west-northwest. The Pig-Nosed Turtle The pig-nosed turtle, Carettochelys insculpta (Ramsay 1886) is a high profile species of considerable international concern as the sole remaining member of a once widespread Family. The species conservation status is uncertain, and they are classified by the IUCN as rare and insufficiently known. Pig-nosed turtles occupy the wet/dry tropics of northern Australia where they occur in four river systems; the most substantial Australian populations of the species reside in the Daly River. Pig-nosed turtles are adapted for a highly aquatic existence, having flippers superficially like a sea turtle making overland movement awkward and extensive overland migration virtually impossible). Their soft skin that overlies the bony shell makes them particularly vulnerable to desiccation. Pig-nosed turtles are long lived, slow growing and do not reach sexual maturity until about 20 years of age. In the Daly River, they feed principally upon rooted aquatic macrophytes, such as Vallisneria, and associated invertebrates (Welsh and Georges, in prep). Their principal food, Vallisneria, is flow and turbidity sensitive. During the dry season, females deposit clutches of 4 to 19 eggs in shallow chambers on sand banks adjacent to water (Georges and Kennett 1992). The eggs are white, hard-shelled and almost perfectly spherical. They incubate rapidly over 50-90 days to maturation depending on date laid and incubation temperature, which rises steadily as the season progresses. Temperatures within the nests are high and fluctuate widely each day (Georges 1992). On