River Operations Initiatives for Water Quality Management Presentation to Lower Opihi Catchment Group 23rd October 2014 Tony McCormick – CEO Opuha Water Ltd

Presentation Overview Opuha – scheme operation Water quality issues River Lake Flushing Flows Other Initiatives Conclusion

Max Irrigation Flow 6.6 cumecs Scheme Overview Lake Opuha Opuha River Hectares Kakahu 3200 Totara Valley 1766 Levels Plain 3296 Sutherlands 620 Above Dam 2100 Other 5018 Total 16000 Max Irrigation Flow 6.6 cumecs Opihi River Kakahu Scheme Fairlie Tengawai River Saleyards Bridge (min flow measured) Totara Valley Scheme Opihi River Sutherlands Scheme Pleasant Point Levels Plain Scheme Timaru

Opuha Dam and lake. Power Station is below dam (lower centre of picture)

Next slide is the view from here, looking downstream

View downstream from dam showing regulating pond and downstream weir (top right of picture)

Fusible Embankment 700+ cumecs Radial Gate 32 cumecs Fixed Spillway 80 cumecs Fusible Embankment 700+ cumecs View at downstream weir where water release to river is controlled

View of downstream weir: L to R – Gate (32 cumecs); Spillway (80 cumecs); Fusible Embankment (flood flow ~700+ cumecs) Fusible Embankment Radial Gate Spillway

Opuha Dam & Power Station Operation Dam 50m high Lake 710ha, 72 million m3, 22m range Power Station 50m head, 7MW, 16 cumecs Annual Generation 26 GWh Downstream Weir 16 - 35 cumecs 392m --- Lake Opuha Dam Power Station Downstream Weir 370m --- Regulating Pond Opuha River Regulating Pond level fluctuates with power station operation. River flow is maintained at steady rate through gate at downstream weir

Opuha Dam & Power Station Operation Dam 50m high Lake 710ha, 72 million m3, 22m range Power Station 50m head, 7MW, 16 cumecs Annual Generation 26 GWh Downstream Weir 16 - 35 cumecs 392m --- Lake Opuha Dam Power Station Downstream Weir 370m --- Regulating Pond Opuha River Regulating Pond level fluctuates with power station operation. River flow is maintained at steady rate through gate at downstream weir

Water Quality Issues River Lake Periphyton growth Didymo – nuisance Phormidium – toxic Water chemistry Lake Inflows – nitrate and phosphorous ???? Top of lake recreation (avian or bovine) ???? Limnological natural water chemistry when low oxygen conditions exist manganese and iron

Flushing Flows – Key Locations Dam site Lake Opuha Opuha River Skiptons (13km) (flow measured) Opihi River Kakahu Scheme Fairlie Tengawai River Confluence (26 km) Saleyards Bridge (min flow measured) Saleyards Bridge (42km) (flow measured) Totara Valley Scheme Opihi River Sutherlands Scheme SH1 Bridge (52km) (flow measured) Pleasant Point Levels Plain Scheme Timaru

2014 v 2013

Flow Attenuation

River Mouth – Opening & Timing

Periphyton Removal

Periphyton Removal Didymo removal 76%, 85% and 89% Improved on 2013 41%, 12% and 40%

River Temperature

Other Initiatives River Lake Operations Adaptive flow regime Investigations Enhanced monitoring (long term programme) Exposure/Drying Sand feeding Dissolved iron Lake Aeration enhancement

Conclusion No silver bullet Multi faceted issue On going investigations improve understanding and enable … Effective adaptive operations and management