Development of a Groundwater Model for the Western Davenport Plains
Knapton, Anthony; CloudGMS Pty Ltd
Northern Territory. Department of Environment, Parks and Water Security
E-Publications; E-Books; PublicationNT; WRD Technical Report 27/2017
Western Davenport Water Control District
CloudGMS has been commissioned by DENR to develop a numerical groundwater model of the aquifers within the central area of the WDWCD to improve confidence in the sustainability of the groundwater resources, as this is the area within the WCD with greatest potential for intensive development.
Made available by via Publications (Legal Deposit) Act 2004 (NT); Prepared for Dept Environment and Natural resources
Executive summary -- 1 Background -- 2 Physical -- 3 Available data -- 4 Conceptual model -- 5 Model design & construction -- 6 Parameter estimation -- 7 Water balances -- 8 Sensitivity analysis -- 9 Predictive scenarios -- 10 Conclusions -- 11 Reference -- 12 Document history and version control -- Appendix A - Groundwater level hydrographs - Appendix B - Alek range horticultural farm sub-regional modelling
Groundwater; Northern Territory; Western Davenport Water Control District; Conceptual mode
Northern Territory Governmnet
WRD Technical Report 27/2017
ix, 127 pages : colour illustration and maps ; 30 cm
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
https://hdl.handle.net/10070/842058 [LANT E-Publications: Development of a Groundwater Model for the Western Davenport Plains, version 1.1]
Western Davenport WCD Groundwater Model (v2.0) Executive Summary CloudGMS ii Model domain The model domain has been selected to encompass the major aquifer system in the Western Davenport Water Control District and the surface water catchment that provides recharge to this aquifer system. Although it could be argued that the Hanson River catchment to the west of the area considered provides recharge to the north eastern portion of the WDWCD, its inclusion in the model would require a considerably larger model, limited data exists and development in this region is arguable less likely due to the distance to transport and other infrastructure. Parameter estimation The calibration period of the simulation extends from 01/01/1970 to 01/01/2015 for a total of 45 years. The hydrologic boundaries of the model include areal recharge, overland flow, no-flow and fixed heads. Each boundary was included to represent a specific aspect of the groundwater-flow system. Groundwater pumping in the model represents public supply and horticultural use reported figures on actual usage and best estimated usage. Groundwater pumping data was compiled from Power and Water Corporation (PWC) and DENR to develop a pumping record for the period from 1990 to 2016. Site-specific pumping was used when available. Hydraulic properties in the model were assigned through discrete zones (large areas possessing the same property values) and pilot points. The value of each pilot point, as well as other discrete zone parameters, was adjusted through manual and automated methods to achieve a best fit of observed values of hydraulic head and water balance estimates. Simulated hydraulic heads were compared to 19936 measurements from 44 wells in the aquifers of Western Davenport WCD model area. Simulated hydraulic heads were generally in good agreement with observed hydraulic head values, following long term trends and reproducing the observed episodic recharge events. The average root mean square error value of hydraulic head for the steady state model of the Western Davenport WCD groundwater system was 7.34 metres and the scaled RMS is 3.7%. Predictive scenarios The model was used to simulate groundwater levels and water balance changes resulting from prolonged pumping to evaluate sustainability of current and projected water-use demands. Each of the scenarios utilised the calibrated model to simulate a 45-year period from 1970 to 2015. Groundwater resource sustainability Based on the predictive scenarios the groundwater systems within the Western Davenport WCD have adequate available storage, for example the saturated aquifer in the Central Zone, has of the order of 45000 GL in storage, which is more than 2 orders of magnitude greater than the applied groundwater extraction rate. However, there appears to be up to a 30% impact on GDEs as evidenced in the reduction in predicted evapotranspiration losses under the pumping scenario for predicted usage of all proposed allocations. The very large volume in storage is expected to provide a buffer to the impacts from groundwater abstraction provided development is not too close to areas sensitive to groundwater level decline. The robust nature of the aquifer system means an adaptive management approach can be applied where 5 10 year reviews of the water allocation plan would be appropriate. Current entitlements are likely to result in a minor drawdown response where regionally the effects of groundwater extraction will be undetectable from the natural scenario after a prediction period of 45 years. Longer predictions would result in propagation of the draw down across a wider area around the extraction sites, which would require projections of climate and the inherent uncertainty associated with lack of data on climate change in the Arid Zone.