Focus on Manapouri

Meridian undertakes a number of monitoring projects that relate to the consent conditions for the operation of the Manapouri Power Scheme.

The Upper Waiau

These projects include five-yearly monitoring of periphyton communities and aquatic plants in the upper Waiau River at five established sites. The third survey in this series was carried out in 2006/07. No long-term changes in periphyton or macrophyte communities were detected as a result of hydrological flow regimes, however community changes over the five years 2002 – 2007 were mainly attributed to the arrival of didymo. Didymo dominated the communities at three of these sites, while the other two sites were dominated by organisms commonly recorded in previous years.

The Lower Waiau

In the lower Waiau River – upstream of the Monowai River confluence - populations of periphyton and invertebrates are monitored each year. The aim is to monitor the impact that the river flow regime has on the communities of these organisms. The tenth such survey was carried out in February 2007. As with the previous two years' results, the presence of didymo in the river system strongly influenced survey outcomes and levels of the algal biomass continued to be very high compared with all years prior to 2005. However, invertebrate densities were at the highest level recorded in the entire sampling programme. No significant relationships existed between periphyton biomass and a range of hydrological variables. The survey will continue to be completed annually so that a better understanding can be gained about the longer-term growth patterns of didymo and also to gain a long-term understanding of the relationship between flow and algal biomass.

Deep Cove, Doubtful Sound

Meridian continues to regularly monitor the physical environment where the discharge of tailrace water from the Manapouri hydro-electric power station enters the marine environment at Deep Cove, Doubtful Sound. Detailed monitoring has been carried out since 1997 as part of consent conditions and to determine whether there are any ecological effects on the Doubtful Sound marine environment as a result of commissioning the second tailrace tunnel. This includes annual monitoring of sub-tidal rock wall communities and black coral colonies located at depths that could potentially be influenced by changes in the low salinity layer within the Doubtful Sound system. The most recent survey, carried out in early 2006, found that the inter-tidal communities at each of the monitoring sites have displayed consistent levels of species richness since 1997. Estimates of species richness in the subtidal zones were higher in 2006 than they were at most sites in 2005. The findings indicate that there are no changes in the rock wall community that appear to be linked to the commissioning of the second tailrace.