integrated catchment management planning - dealing with uncertainties to achieve an optimal ersult

Understanding future uncertainties is critical for the development of a realistic and successful capital investment plan. For the Grey Lynn catchment the main uncertainties were as follows:

• The stormwater solutions in most areas involved partial separation, which takes stormwater from the roads into the new stormwater system, reducing flow into the combined lines. The impact of this on overflow performance is uncertain
• The effect of planned upgrades to the Watercare trunk network.

A phased programme was developed. The first phase consisted of projects that will deliver immediate benefit with limited capital investment, and are not dependent on future uncertainties. The subsequent phases occur after the effect of the uncertainties can be measured, and will complete the programme to achieve the target level of service (LOS) in the catchment.

The benefits of this approach are the deferral of capital expense, the minimisation of sunk costs for assets that may become obsolete in the near future, the provision of benefits in the short-term to address community concerns, and the layout of a path towards addressing target LOS.

Additionally, the integrated approach to drainage planning taken in this catchment mean cost efficiencies and the ability to programme projects together, allowing construction disruption to be minimised.