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

63 Table 21. Impact of habitat fragmentation on the feeding grounds of pig-nosed turtles. Feeding grounds (patches of V. nana) were assessed visually from a Helicopter during 2001. Data in the table are the percentage of the river under study (73.7 km) that had V. nana beds. Number of pools with or without V. nana and the mean number of beds per pool are also included. At below 50% flow reduction there is effectively only one continuous system with no turtles restricted anywhere. Flow (cumecs ) No. of pools without Vallisineria * No. of pools with Vallisineria Length of reach without Vallisineria (km) No. of beds per pool (meansd) 2.0 19 (11) 15 38.8 (53%) 3.9 2.5 4.8 11 (6) 8 38.9 (53%) 7.4 5.9 7.6 8 (4) 4 37.5 (51%) 14.8 6.1 10.5 4 (2) 3 34.2 (46%) 19.7 15.8 13.3 2 (1) 3 32.2 (44%) 19.7 1 5.5 *Parentheses indicate the number of pools (in the first 32km downstream of Dorisvale Crossing) that did not have major V. nana beds. At base flow conditions, the average number of beds per pool was less than four and more than 53% of these pools had no V. nana beds. At the 80% flow increment the average number of beds per pool rose to 7.4, but the proportion of pools without V. nana remained similar to that of base flow conditions. This is largely due to the initial 32 km of river having a natural absence of V. nana beds and 3 major break points, which we regard as a condition that may be peculiar to our study year yet representative of the system. Consequently, we retained the 32 km data in our modeling. At flow reductions between 70% and 50% the density of V. nana beds per pool are high and appear to level off. Also, the number of pools having V. nana begins to outweigh those without, suggesting that little effect would be had on restricting turtle access to feeding grounds under these conditions. Impact of Thermal Modification Modelling Turtle Development We have used the most widely accepted non-linear model of poikilotherm development, that of Sharpe and DeMichele (1977), to model development in response to temperature in the pig-nosed turtle. This model extends the work of Eyring (1935), Johnson and Lewin (1946) and Hultin (1955) in the formulation of a biophysical model that describes the non-linear response of development rate to incubation temperature at both high and low temperatures, as well as a linear response at intermediate temperatures. Six fitted parameters must be estimated using non-linear regression. A computational form of the equation more suitable for this purpose was developed by Schoolfield et al. (1981), namely ++ = THTr HH TLTr LH Tr AHTRHO dt ds 11 exp 11 exp 1 1 15.298 1 exp 15.29825 ................................... [12]

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