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

46 Flows at or above 40% Reduction (>16.1 cumecs) The maximum depth of all our identified breakpoints exceeded 0.5 m at flows, which were above 16.1 cumecs at Dorisvale Crossing (Table 15). Under these elevated flow conditions pig-nosed turtles would be able to move freely without impediment throughout the study reach (Table 15). The maximum length of the study reach was 73.7 km. The maximum and average depths of the river channel slightly increased as flow increased (Table 1) and the flow area, top width and wetted perimeter all decreased as flow decreased (Table 1). However, these differences were not significant. Table 15. Morphological parameters for the Daly River under five different flow conditions. Flow (km) Length (m) Flow area (m2) Top width (m) Wetted perimeter (m) Max channel depth (m) Average depth (m) 27.4 73.7 124.850.0 (13.1-268.2) 64.67.9 (15.7-148.8) 65.48.2 (16.1-149.7) 2.50.8 (0.6-4.3) 1.90.7 (0.3-3.4) 24.6 73.7 120.949.5 (12.1-257.8) 64.27.9 (15.2-146.5) 65.08.1 (15.6-147.4) 2.50.8 (0.6-4.2) 1.80.7 (0.3-3.4) 21.8 73.7 116.549.3 (11.3-245.1) 63.87.9 (14.5-144.2) 64.58.2 (14.8-145.0) 2.40.8 (0.6-4.2) 1.80.7 (0.3-3.4) 18.9 73.7 112.148.9 (10.1-235.5) 63.38.0 (13.7-141.4) 64.08.2 (14.1-142.0) 2.30.8 (0.6-4.2) 1.70.7 (0.2-3.3) 16.1 73.7 107.648.4 (9.2-229.5) 62.88.0 (12.9-137.4) 63.58.3 (13.2-137.9) 2.20.8 (0.5-4.1) 1.70.7 (0.2-3.2) Natural Regime and Fragmentation The magnitude of the flow at any given time is a measure of the availability or suitability of habitat and defines such river habitat attributes as pool length (space available for movement), emergent vegetation rooting zones (feeding grounds) and reproductive zones (nesting bank locations). In this study we have shown that there is a clear correlation between the percent of suitable habitat through river connectivity (i.e. number of pools) and flow (Figure 1). Hence, how often our simulated flow events occurred in a historical context (based on 40 years of gauged data) provides insight into how frequently turtle life history would have been compromised historically (Table 16). Base flow conditions where Q is less than 2.0 cumecs occurred infrequently (2.5% or 1 year out of 40). In contrast, extreme low flows (i.e. less than 3.0 cumecs) occurred on 27.5% of years and low flows (i.e. <10cumecs) occurred more frequently (95% of years). Increasing the frequency of occurrence of extreme low flow events would compromise turtle life history through limited access to resources, which are essential for reproduction (e.g. nesting banks) and feeding (e.g. Vallisineria meadows).