A Step Forward in the Wellington Region’S Water Modelling Journey

In September 2014, Wellington Water was created following the merger of the Water Supply Group of Greater Wellington Regional Council with Capacity Infrastructure Services Limited. The decision to amalgamate was part of a wider push by councils in the region to realise the benefits of shared services across the region. 

Wellington Water is a shared service, council-controlled organisation jointly owned by Hutt, Porirua, Upper Hutt and Wellington City Councils, and the GWRC. Wellington Water manages the drinking water, stormwater and wastewater networks on behalf of its client councils and provides advice about how best to invest in their future development. 

In 2014/15 Wellington Water along with MWH embarked on a water model build project on behalf of Hutt City Council. The model is a key planning activity to: 

• understand how systems operate under various scenarios now and in the future, 
• assess system performance under normal conditions and critical asset failure scenarios, 
• assess implications of developments, upgrades, renewals and operational modifications, and 
• produce supporting information for planning studies. 

Wellington Water wishes to improve the quality of its asset data information (including water network models) by using the economies of scale enabled by the amalgamation of the water service utilities. In this context, Wellington Water is rationalising its modelling work so that outcomes are consistent and comparable. This involves developing consistent tools in terms of software package, data schemes, calibration standards and documentation. Consequently, the first element of the project was to update the previous Regional Water Modelling Specification to bring it in line with national best practice. A modelling report template was also prepared for consistency in documentation. This is a corner stone of the modelling strategy as it allows, if required in the future, the possibility to combine all water models into a combined model and a better integration with the asset data system, GIS and live SCADA. 

Innovation was encouraged within this project. Paper plans were abandoned in favour of a single online Google Map for the planning, execution and documentation of the field test. This simple but efficient change saved time and money and improved significantly the communication between the parties involved in the field test (Wellington Water, Council, contractor, consultant, fire service, operations). 

The project also highlighted the benefits of further preliminary analysis work of SCADA information: discrepancies were found in the balance between inflow, outflow and water level for several reservoirs or for flow meters in series with one another. These could have been identified earlier in the project through reservoir balance checks, complete demand disaggregation and preliminary model run. This would have allowed to flag potential significant discrepancies or gaps, allowing enabling works to be undertaken prior to the field test and possibly a finer demand allocation to be achieved. 

This paper demonstrates the step change in water modelling practice within the Wellington region following the water services amalgamation.