As part of the Manapouri Second Tailrace project, DCII was committed to protecting the fragile marine ecosystem at Deep Cove. The Deep Cove portal, which provided construction access to the project, was 43m below sea level and required both a sheet pile coffer dam and deep well pumping system. The second tunnel was positioned within a groundwater “pressure shadow” around the existing tunnel to reduce total inflows and prevent the risk of tapping leakage flows from the existing tunnel.
To ensure that no unacceptable pollutants were introduced, sediments were removed from the water before it was discharged into the tailrace. The largest environmental task was incorporating the 1 million m3 of rock spoil, excavated by the tunnel boring machine, back into the environment. Waste rock dumps were contoured and replanted with locally sourced native plants and all construction waste and debris that could cause environmental problems was transported out of the national park. Divers monitored rare black coral to ensure that sediment released during channel excavation did not harm underwater plants or marine life.
Today, Deep Cove is the site of a New Zealand Department of Conservation camp featuring a hostel where schoolchildren come to study the variety of flora and fauna in the region, hike in the virgin native Podocarp Forest, go boating on the Sound, fish, and learn to interact and work as a team in one of the most remote places in New Zealand.