Territory Stories

Modelling dry season flows and predicting the impact of water extraction of flagship species

Details:

Title

Modelling dry season flows and predicting the impact of water extraction of flagship species

Creator

Georges, Aurthur; Webster, Ian; Guarino, Fiorenzo; Jolly, Peter; Thoms, Martin; Doody, Sean; CRC for Freshwater Ecology (Australia); University of Canberra. Applied Ecology Research Group

Collection

E-Publications; E-Books; PublicationNT; 57/2002; National River health program

Date

2002-11-20

Location

Daly River

Abstract

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.

Notes

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

Language

English

Subject

Environmental Flows; Modelling; Biota

Publisher name

Northern Territory Government

Place of publication

Palmerston

Edition

Final Report

Series

57/2002; National River health program

Format

75 pages ; 30 cm

File type

application/pdf

Use

Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government

License

https://creativecommons.org/licenses/by/4.0/

Parent handle

https://hdl.handle.net/10070/885434

Citation address

https://hdl.handle.net/10070/885435

Page content

56 There are a number of sources of error in the modelling that could lead to the difference between model simulations and measurements. Disagreement between background modelled and measured temperatures could be partly to do with the model's failure to account properly for all the springs that flow into the Daly River between Dorisvale and Cattle Creek. The model has implicitly included the springs between x = 24 and 33km, but these are estimated to account for 63% of the inflow to the river from the June 3 gauging study. To model the effects of the springs properly we need to know their volumes as well as their temperatures. Errors in the estimation of the important meteorological parameters including radiation fluxes, wind speed and air temperatures will affect the degree of agreement between both the background and diurnal temperature variations. These errors could arise from the estimation of these parameters at the measurement site itself due to instrument inaccuracy or to the validity of the assumptions used to calculate parameters such as downwelling long-wave radiation for example. Other errors in model forcing could arise from the assumption that meteorological conditions over the river over its 64km length can be represented by measurements made at one site on the floodplain. Analysis of Water Extraction Scenarios The major question asked of this project is what is the likely impact of changes in river flow due to water extraction on water temperatures in the Daly River downstream from Dorisvale? The actual impact will depend on where the water is extracted, on what the background flow conditions are in the Daly at the time, and on the prevailing meteorological conditions. In the following analysis we adopt a scenario approach to analyse this problem. Each scenario is assumed to last for 58 days and utilises the 58-day record of measured meteorological conditions for 2001 that we have employed in the model analysis of the previous section. The flow alteration scenarios are the simplest possible; that is, the flows are specified to be constant in time and uniform in each of the river sections upstream and downstream of the spring at x = 29km. The scenarios are identified by their flow volume downstream from the spring, dQ . Upstream from the spring, the flow is assumed to be 3 -18m su dQ Q= . All scenarios use the time series of measured temperatures at Dorisvale as their upstream boundary condition. Figure 33 shows the results of the scenario analysis plotted as the time-averaged modelled temperatures between Dorisvale and Cattle Creek. The scenario entitled '2001 Flows' uses the measured flows and meteorology for 2001. Thus, unlike all the other scenarios, it allows the flow to change during the 58-day simulation period. The '2001 Flows' scenario illustrates some important features of the temperature response of the Daly River to meteorological forcing. The average temperature of the input water at Dorisvale for the simulation period is 23.6 0C. Downstream from Dorisvale the temperature gradually increases to 24.6 0C just upstream of the spring. The input of higher temperature water at the spring (x = 29km) causes a jump in river temperature of 0.6 0C at this point. Further downstream, the river water temperature continues to increase although at a slower rate than it did upstream of the spring. The measured average increase in temperature between Jinduckin Creek and Cattle Creek is 0.17 0C is consistent with the model-predicted increase of 0.16 0C, although it should be remembered that part of this agreement may be dictated by model calibration. Another possible cause of temperature increase in the real system is the inflow of warm springs along this section of the Daly River, which has been neglected by the model. The continuing increase of simulated water temperature between Dorisvale and Cattle Creek implies that the river did not reach thermal equilibrium with the 'average' meteorological conditions over its length. It would appear that the equilibrium river temperature is about


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