Huritini/Halswell River Weed Screen Design and Build

Details

The Huritini/Halswell River weed barrier is located upstream of where the Halswell Canal discharges into Te Waihora/Lake Ellesmere. Its purpose is to capture weed cut by a weed cutting boat in Huritini/Halswell River before it reaches Te Waihora/Lake Ellesmere and degrades the water quality there. Weed is cut from the river as weed growth reduces its conveyance capacity, compromising the land drainage function that the river provides.
The existing weed barrier is very effective at capturing cut weed. However, it is nearing the end of its life and needs to be replaced. The methodology currently followed to erect the existing weed barrier has some health and safety risks that a new barrier may be able to mitigate. The existing screen does not have specific provision for fish passage, which is a requirement of the current consent and is important to stakeholders.
The existing weed barrier is similar in appearance to a chain link fence. When not in use the barrier lies flat on the base of the river. When required it is pulled out of the river and into position by shackling tension cables onto vehicles. The screen is further secured by attaching it to concrete blocks and lowering these into the river. Weed captured by the screen is removed by a dragline.
It is required that the existing barrier structure be replaced with a similar system at the existing location, utilising the existing dragline to remove weed. This shall provide the greatest surety around weed capture, and operational issues are understood and can be managed through changes to the design and mobilisation/demobilisation methodology. The design of a new structure shall incorporate features to manage operational issues, these being:
 Winch system to raise and lower the barrier in a safe manner (replacing the use of moving vehicles)
 Partial floating boom or other arrangement to preserve fish passage
 Partial floating boom or other arrangement to preserve high-flow conveyance
 Net fixed to the riverbed to avoid need to lower temporary ballast blocks into the river.
Environment Canterbury (ECan) require a suitable contractor to design and build the new weed screen at the existing location on the Huritini/Halswell River. Some key elements of design shall be undertaken by Beca Ltd i.e. piles. The existing screen shall be decommissioned and removed by the contractor.
We are looking for a contractor who has the ability to take part in an open and collaborative design approach.