Open channel to Lake Forsyth then tunnel to sea

Year proposed

  1875

Status

  Not implemented

Location description

  Kaituna end of Lake Ellesmere to Lake Forsyth.  Bray (1875) Scheme No. 2 (see designs/drawings figure).

Description of option

  A 2.5 km long open channel from Lake Ellesmere to Lake Forsyth (via Birdlings Flat) was proposed, discharging 17.6 m³/s into Lake Forsyth. A tunnel of similar dimensions to a railway tunnel was then to be drilled into the rock on the seaward side of the lake to a length of 500m. The outlet to this tunnel was proposed to be subsurface.

Opening, closing, and lake level control description

  Allows continuous discharge.  Requires a higher lake level to obtain suitable hydraulic gradient; the lake level would have to be at least 0.66m.

Maximum discharge

  below 50 cumecs

Maintenance/Management description

  Potential gravel accumulation issues at tunnel outlet.

  Tunnel inspections/maintenance/repairs difficult or impossible (Bray, 1875).

Cost description

  High capital expenditure, similarity in levels of Lake Forsyth & Ellesmere, & short projected life of the expensive tunnel make this proposal uneconomic (Beattie, 2005).

  Costs estimated at 580,000 pounds (Askin & Grant, 1945)/$3,250,000 (1969).

Fish passage benefit rating

Potential running impacts or benefits

  Between 1875 and 1932, observed gravel deposits had increased in length along the shore by over 100m. It was estimated that the tunnel from Forsyth to the sea would be blocked within 100 years due to this aggradation (Bray,1875; Langbein, 1932).