Integrated surface water and groundwater modelling to support the Murray Drainage and Water Management Plan, south-west Western Australia

Abstract

The Murray region in south-west Western Australia is characterised by a high water-table, sandy soils, wetlands of significance, and an extensive agricultural drainage system to relieve water-logging in winter months. Urban growth pressures in the region have led to the requirement of a Drainage and Water Management Plan (DWMP) to guide future water management. A key component of the DWMP involved the development of a regional surface water and groundwater model to determine groundwater levels and flows under various climate, drainage and development scenarios. The Murray regional model was constructed using the integrated surface water and groundwater model MIKE SHE, and consisted of unsaturated zone, saturated zone, channel flow and overland flow components. It had a constant grid spacing of 200 m, and covered an area of 722 km 2. Calibration was from 1985 - 2000 and validation from 2000 - 2009 using 45 groundwater bores and 7 surface water flow gauges. The normalised root mean square error of the calibrated model was 2.02%. Land development, drainage and climate scenarios were simulated and their results are discussed in this paper. The process of model conceptualisation, construction, calibration and simulation is discussed, and provides an appropriate framework for model evaluation and a high level of confidence in modelling results. The Murray MIKE SHE model provided regional groundwater levels, areas of groundwater inundation, estimated drainage volumes from development areas, effects of sea-level rise, and changes in surface water flows for a variety of climate, drainage and development scenarios. The results were used to determine regional-scale hydrology affects resulting from future urban development. The model grid size and calibration error may prevent the usage of the model for detailed drainage design; however the model is suitable to act as a basis for developing higher-resolution sub regional and local models that are more appropriate for this type of evaluation. The results of the Murray MIKE SHE modelling exercise were used in the Murray Drainage and Water Management Plan, a key deliverable to the Western Australian Planning Commission, used to guide stakeholders in future urban water management in the Murray region.