Reliable Water Supply
Morven Glenavy Irrigation Ltd (MGI), commissioned us to design and construct an irrigation scheme that provided irrigation water to 3,300 hectares with water sourced from the Waitaki River MGI scheme. The new scheme irrigated areas including Douglas, Mount Harris Greenhill and through to Arno.
An open 9 km race took water to a 40,000 cubic metre capacity buffer pond. From there it was screened and pumped through six large 500kw pumps to a 30,000 cubic metre capacity upper buffer pond and piped to the remainder of the scheme. The vertical lift through 6km of 900mm diameter pipe was 126 metres from the lower to the upper buffer pond, thus providing an excellent head for the 35km of the distribution pipe network.
A total of 24 water users were fed irrigation water through 32 off take valves at pressure.
Project Scope:
- Construction of a concrete Labyrinth weir within the existing MGI irrigation supply race
- 9 km of open supply race to feed the lower buffer pond
- Construction of a 40,000 cubic metre lower, and 30,000 cubic metre upper earth buffer ponds
- Construction three pump houses protecting 6 separate 500kw, 250ltr/sec electric pump sets
- 6km of 900mm diameter 15bar GRP pressure pipe laid to a vertical height of 126 metres
- 35km of GPR and uPVC pipe ranging from 900mm to 150mm diameters
- 32 automated water offtake values spread across the 3300 hectares of irrigated land
Technical Constraints:
The labyrinth weir, main race offtake and supply race was constructed within the tight 120day widow of the irrigation off season. The control methodology of the water hammer created through the 126 metre pumping head also proved to be a challenge.
Outcomes:
The project was constructed successfully over 24 months providing irrigation water at pressure to over 3300 hectares of farmland. This scheme is expected to have a reliability level close to 100% due in part to the Waitaki river hydro scheme controlling flows within the Waitaki River.
