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

52 RLWS The longwave emission from the sky adsorbed by the river is estimated using the following formula suggested by HEC (1978) and Zison et al. (1978) which is an extension of the Swinbank formula (Swinbank 1963) including the effects of cloud cover: R A C TLWS LW a= + + 5 3 10 1 1 017 2731613 2 6. ( )( . )( . ) (6) In this equation, the units of RLWS are Wm 2 , ALW is the longwave reflectance assumed to be 0.03, C is the fractional cloud cover, and Ta is the air temperature in degrees Celsius. Penman (1948) suggested the following relationship between the incident shortwave radiation above the atmosphere ( ), the radiation at ground level ( s ), and the ratio of the number of hours of sunshine to the number possible (n D/ ). s n D= + ( . . / )018 0 55 (7) Suppose that s 0 is the radiation at ground level with zero cloud then: s 0 0 73= . (8) If n D/ is a measure of the duration of the sunshine amount then 1 n D/ could be taken to be a measure of the amount of cloud so: n D C/ = 1 (9) Solving for C after substitution of Eqs. 8 and 9 into Eq. 7 gives: )1(33.1 0 s sc = (10) For the evaluation of Eq. 10, s is taken to be the measured short-wave radiation and s 0 is the short-wave radiation that would have been measured on a cloud-free day which is calculated from the height of the sun. LE The heat loss due to evaporation is just the product of the latent heat of vaporisation, (2 2 106 1. J Kg ), and the evaporation rate, E (Kg m s2 1 ). The evaporation rate is determined using the model of Webster and Sherman (1995) which is applicable to waterbodies of limited wind fetch. It includes evaporation due to forced convection associated with the wind blowing over the water surface as well as free convection which may occur during calm conditions such as at night. The model estimates evaporation rate from prescribed surface water temperature, air temperature, relative humidity, and wind speed. H The ratio of the sensible heat flux ,H, to the evaporative heat flux, LE, is assumed to be provided by Bowens ratio, R, (Bowen, 1926) where: R T T e e w a w a = 62 . (11)