Current opening method - 1947 to present
Description of option
The manual opening of the lake at Taumutu using bulldozers and draglines, and more recently by hydraulic excavators. At present the machinery used includes: 22T/70T dragline (occasionally), D9 bulldozer, two D7 bulldozers & 20T excavator. A temporary cut (15m wide by 1.8m deep) is made up to 300m long through Taumutu beach crest. When fully developed mouth may be 100m wide and 3-5 m deep.
Opening, closing, and lake level control description
Based on Water Rights, National WCO (1990), Resource Consents, etc., the Lake is opened when the water level reaches 1.05m MSL (August to March inclusive) or 1.13m MSL (April-July inclusive). The opening closes naturally, so there is no control of when it closes, thus the Lake may drain to lower than desired water levels.
above 300 cumecs
Between 1947 and 1970 there were an average of 3.2 openings/year.
Cost of each opening ranges from 3-5 days work (approx $20,000) to 30+ days work (>$100,000). Plant costs $6,000 to $7,000 per day fully operational (8-10 hour day).
Fish passage benefit rating
Potential running impacts or benefits