Snellings Drain, being a timber lined drain in Burwood, discharges across Mairehau Road through an undersized culvert. There have been frequent floodings occuring downstream of Mairehau Road due to a combination of low lying land and limited hydraulic capacity. In March 2016 Isaac Construction was awarded by Christchurch City Council to carry out the Construction Works for Clare Park Wetlands.
The site clearance was established by first dewatering and clearing trees over the entire area of 91,000m2. The drains were cut from the internal wetlands to the Snellings Drain and the No.2 drain, filtering the drains with hay bales. The tree felling was the most difficult exercise of the entire project as there were many deep and soft areas in the middle of the wetland. Felled trees were used to bridge access for the 20T excavator.
Following site clearance, the bund walls bulk cut to fill earthworks commenced. The bund walls were built by two 20T excavators with machine-mounted GPS units. This allowed the operators to get all of the grades, including the underwater pond areas to a high level of accuracy. The bund construction was sequenced to give access to the wetland outlet first so that the construction of the deep outlet structures could begin and finish in the dry months. These outlet structures involved 4 pipelines, 2 large custom sumps, a 2m deep control chamber, 1 flap gate and a cut pipe rock wall.
The final drainage lines were 30m long running through the main entranceway road which runs through the centre of the wetland. Each line was constructed and reinstated in a half day so that the horse owners could get access after lunch each day. Following this the last drainage items were completed by Isaac Construction which were two 35m lengths of kerb that served as overflow weirs at low points in the bund walls.
This project was run in partnership by Isaac Construction and Rooney Earthmoving with a 50% division of work. Isaac was the head contractor and Rooney Earthmoving were a major subcontractor. Isaac Construction performed the project management, surveying, Health and Safety and QA requirements as well as the construction of all of the drainage structures. Rooney Earthmoving performed all of the site clearance and earthworks.