A SystemicToolforaMulti-value Stormwater Management System

Christchurch has always been prone to flooding due to its urban waterways, flat topography and low-lying nature. Water quality in the urban waterways has been further impacted by legacy of the city’s development. The Canterbury earthquakes and on-going urbanisation further increase flood vulnerability, and also Council and the local community are now putting more emphasis on the ecological and social values of the water environment; therefore, multi-value analysis and design tools that look at the system in its entirety need to be utilised moving forward.

A stormwater management approach focusing solely on improvement of stormwater conveyance is no longer best practice. An interdisciplinary method that can offer solutions to fulfill multiple functions is the more current course for stormwater management. Mathematical modelling of physical processes (e.g. wind impact, spring flow vs. stormwater flow etc.) is one of the important tools used to help designers and policy makers understand the overall behavior and interactions among some individual components within the system, and thus contributing to a better stormwater management outcome.

This paper examines how a computational modelling tool was used to provide multiple-value solutions to the stormwater challenges in a segment of the Heathcote River catchment. The design of the Sutherlands Basins stormwater system in the south west of the Heathcote River catchment was guided by the modelling results, which achieves functions such as: creating better places and connecting people with water through integrating cycleways, walkways and plantings, maintaining stream water quality and ecosystem health through reduction of fine sediments and separation of all stormwater from spring-fed stream, maintaining healthy flow regimes through reduction of urbanisation induced flood flows in the Heathcote River, and improving adaptability through consideration of fully developed scenarios. The model expands beyond the Sutherlands Basins to include the wider Sutherlands Eastman stormwater treatment facility, which is understood to be the largest stormwater treatment facility in the South Island.

This paper outlines the modelling approach selected and how the diverse functionality of the stormwater system designed was achieved through the aid of modelling tools. This paper also discusses some innovative techniques applied such as utilisation of drone in flood modelling, analysis of wind effects and offline stormwater to maintain water quality in spring fed streams.