Evaluation of Alternative Rebuild Options
When weighing up wastewater asset rebuild options, SCIRT designers made decisions on a "whole of life" basis. To help decision-making, a Net Present Value (NPV) analysis was used.
NPV is a fundamental calculation required to assess project options by providing whole of life costing analysis that enables SCIRT to make reliable decisions about which options provide the best value.
The methodology was originally designed to evaluate wastewater network options but was subsequently applied to other asset rebuild option evaluations, including structures and roading options.
The NPV calculation valued the relative resilience offered by different asset rebuild options by including earthquake risk (as measured by GNS Science earthquake expectation data) and earthquake-related repair and service restoration costs. Other capital renewal and operating and maintenance costs also formed part of the analysis.
The evaluation was a key input into papers presented to the Scope and Standards Committee. SCIRT designers presented papers to the Scope and Standards Committee when proposed designs deviated from approved scope or design standards.
Design Guideline 27 was created to provide guidance to designers using the methodology, along with a uniform approach tool (see calculating spreadsheet below).