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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

51 time spent by a water parcel within a short river section is inversely proportional to the local cross-sectional area of the river channel. Accordingly, the average W and D for each river section were calculated using local cross-sectional area as a weighting function. Energy Fluxes in the Model The energy flux F in Eq. 1 has a number of components which are: RSW - The (downwards) shortwave radiation from the sun. RLWE - The (upwards) longwave emission from the water surface. RLWS - The (downwards) longwave emission from the sky. LE - The latent heat loss from the water surface by evaporation. H The rate of sensible heat exchange between the water surface and the air. These are evaluated as follows: RSW The shortwave radiation from the sun was estimated from the PAR measurements made at the meteorological station at Ruby Billabong adjacent to Douglas Daly Research Farm. Strictly speaking, PAR represents the photon flux at the wavelengths of photosynthesis which do not cover the whole of the visible wavelength band, whereas we require a measure of the energy flux from the sun which occurs mostly in the visible wavelength band. We assume that RSW is proportional to measured PAR. The proportionality constant was calculated using the assumption that the surface radiative flux under a pure, clear sky with the sun directly overhead is 1130 2Wm (Gaillard, 1981). In calculating the time series of RSW for input to the model, we account for possible shading of the river by the banks on either side at low sun elevations. The banks are assumed to have a height of 20m, and have an angle of 450 to the horizontal. The river channel is assumed to run in a uniform NW-SW direction which is approximately its mean orientation (see Fig. 29). We do not account for the actual meanders in the river through the study section. A proportion of the shortwave radiation incident at the water surface is reflected. To estimate the shortwave reflectance, we adopt the formula of Anderson (1954) which is: ASW = 0 0523 0 77. . (4) where ASW is the shortwave reflectance and is the solar altitude in radians. RLWE The longwave emission from the water surface is calculated using the Stefan-Boltzmann law: R TLWE w w= + ( . )27316 4 (5) where w is the emissivity of the water surface assumed to be 0.97 (Henderson-Sellers, 1986), is the Stefan-Boltzmann constant, and Tw is the water temperature in degrees Celsius.