Eastman Wetland Stage 1 – Design

Client:  Christchurch City Council
Date:  2012

We were commissioned by Christchurch City Council (CCC) to design, consent, tender and supervise the construction of the Eastman Wetlands – Stage 1.  The project involved the design and construction of two large stormwater detention basins, totalling approximately 30,000m3 of flood storage and associated infrastructure to mitigate the effects of flood flows into the upper Heathcote River.  The basins were designed to fit around an existing First Flush Basin and drain realignment, constructed in 2012.  In addition, they were required to integrate into the future construction of a proposed treatment wetland on the site.

We were set the challenge by CCC to take this project from the concept design phase through to construction completion in eight months.  To achieve this we identified the importance of CCC operational and asset staff involvement in the design phase; their involvement leads to workable solutions and design approaches to key design elements such as outlet structures, inlet channels, control structures and weirs.  Hydraulic modelling of the existing and proposed elements was used to confirm design decisions and prove the operational effectiveness of the new elements.  Concept, preliminary and detailed design reports were prepared for CCC approval at key progression points.

Key Aspects:

  • Hydraulic modelling to confirm operational effectiveness
  • Detailed design of detention basins and associated structures
  • Resource consenting
  • Ecological assessment
  • Geotechnical investigation
  • Coordination of landscape design and construction management
  • Splitting the detention basin inverts into two “cells” with independent outlets to maximise basin volume.
  • Innovative outlet design to meet requirements identified by maintenance staff.
  • The use of precast components for large outlet structures provided a $70k saving to CCC compared to the cast in situ equivalent
  • Achieved completion of concept design phase through to construction in eight months
  • Integration of new design elements with existing features and hydraulic limitations

Client:  Christchurch City Council
Date:  2012

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