EASTMANS INLET CONTROL STRUCTURE - CHCH
Jan 2023 – Current
Christchurch City Council
The Eastman Wetland Control Structure works are situated in the low-lying area adjacent to the recently completed Hoon Hay Basin and Tu Kuru wetlands. The whole area, when finished will be a series of wetlands and stormwater retention ponds that will increase the quality of water flowing across this land and provide habitat for a range of wetland birds and aquatic life.
The works involve construction of an in-situ reinforced concrete culvert structure with a mechanised penstock and then realigning a section of Miln’s Drain to flow through the structure. Miln’s drain flows into Cashmere Stream, which in turn flows into the Heathcote River. Construction of the concrete culvert structure required a large excavation that had sides supported by 8m sheet piles driven into the ground. A shallow groundwater aquifer exists below the work area, thorough planning and accurate execution was needed to avoid puncturing this aquifer.
A 300m long access track including a temporary bridge crossing Miln’s Drain was constructed to allow access to the site, great care has been taken to minimise impact to the partially completed basins, wetlands, and waterways in the area. A tidy site has been maintained during the project in wet and challenging conditions.
Hunter Civil engaged a specialist to prepare a Fish Management plan for the project. The ecologist also completed fishing of a section of the old Miln’s Drain prior to its redirection and backfilling. Close to 300 fish and eels were salvaged from the filling process.