Open channel through Coopers Lagoon and on to Rakaia
Southern Lake Ellesmere near Taumutu to Rakaia Lagoon (10 km to the south);Bray (1875) Scheme No. 3 (see designs/drawings figure).
Description of option
As there are constant high flows from the Rakaia River into the Rakaia Lagoon, a Rakaia River mouth opening is naturally maintained by the river. A canal from Taumutu to the Rakaia River mouth was therefore proposed to pass Lake Ellesmere flows to the sea.
Opening, closing, and lake level control description
Allows continuous discharge. Requires a higher lake level to obtain suitable hydraulic gradient. Coopers Lagoon has maintained a permanent culvert outlet to the sea & could serve as a holding pond enroute to Rakaia.
below 50 cumecs
High rates of coastal erosion southwest of Taumutu could compromise any coastal canal structure or increase maintenance costs (e.g. may need dredging due to influx of seawater & gravels).
1969 cost : $1,000,000 conservative estimate (with gated outlet)
1875 cost: 79,310 pounds for a 5.25 mile long by 12 ft deep cutting (excl sluice gate cost).
Fish passage benefit rating
Potential running impacts or benefits
The dynamic nature of the Rakaia Lagoon is not fully known and Rakaia Huts could suffer increased periods of flooding due to an extra inflow.