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

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

3. Max Irrigation Flow 6.6 cumecs
Scheme Overview
Lake Opuha
Opuha River
Hectares
Kakahu
Totara Valley
Levels Plain
Sutherlands
Above Dam
Other
Total
Max Irrigation Flow 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

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

5. Next slide is the view from here, looking downstream

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

7. 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

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

9. 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 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

10. 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 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

11. 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

12. 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

13. 2014 v 2013

14. Flow Attenuation

15. River Mouth – Opening & Timing

16. Periphyton Removal

17. Periphyton Removal Didymo removal 76%, 85% and 89%
Improved on %, 12% and 40%

18. River Temperature

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

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