Author: Jim Wheelhouse, Project Delivery Catchment Services, GMW.
Cairn Curran Reservoir is part of the Loddon System and is located on the Loddon River, upstream of Baringhup near Maldon in Victoria. Cairn Curran Reservoir is operated in conjunction with Tullaroop and Laanecoorie Reservoirs.
The outlet works are situated through the main embankment, and comprise a wet intake tower, a concrete culvert housing the two outlet conduits, and a power station and outlet valve at the downstream end.
The service gate, in the intake tower, comprises two separate gate sections which can be coupled together to close off both the penstock and irrigation conduit. The service gate is suspended from an electrically driven wire rope hoist housed in the top of the tower. The service gate(s) travels down guide rails which run the height of the 32m tower and control the position of the gate(s) to the bottom of the tower. Near the bottom of the tower the gate(s) additionally engage heavily constructed main rails designed to take the water forces acting on the gate(s).
Records show that the hoist was originally tested (circa 1958) with both gates suspended and moved down and up the tower to close off both conduits, also that the larger gate (only) was closed into partial flow. Since this time only the larger of the two gates has been suspended from the hoist, the smaller gate has been uncoupled and unused, stored in an alcove below the tower operating deck.
The primary purpose of the service gates is to act as an emergency closure guard gate in the event of a failure of the downstream equipment in the outlet. The Cairn Curran Outlet Works Upgrade – Final Report for Review of Emergency Guard Operation (GHD 2012) confirmed that the combined weight of the two gates (20 tonne) is necessary to ensure closure under flow conditions.
Since construction in the 1950’s, the carbon steel rails had corroded to a point where they were no longer serviceable and there was a real risk of the gates not being able to be closed, particularly in a water flow situation. The condition of the main thrust rails was such that they were likely to prevent closure of the gate in a close into flow event due to high friction forces.
The Service Gate Upgrade Project, undertaken in 2013, included the following works:
- The original carbon steel main rails were replaced with identical rails machined from stainless steel 431;
- The original carbon steel guide rails were replaced with stainless steel 304 channels;
- The original carbon steel service gate and balance beam guide wheel assemblies were replaced with stainless steel 304 assemblies to suit the new guide channels;
- Construction of a hydraulically operated hinged maintenance platform over the tower shaft;
- Construction of hydraulically operated equipment to enable the lower service gate to be moved from storage out into the centre of the tower shaft so it can be attached to the bottom of the upper gate;
- Fabrication of hinge brackets to connect the two service gates so they can be operated simultaneously; and
- A thorough current condition assessment of the hoist to confirm the hoist is adequate for continued service carrying both gates.
A major project challenge was working with leakage through the existing closure stop logs at a rate of 4 ML/d. The leakage was managed by lowering a tarp down the tower shaft to direct leakage to the floor and away from the work and by lowering a plastic membrane down the front of the intake tower which was drawn in by the leakage. Another challenge was working with heavy components while suspended in a work basket with a rated WLL of 350 kg. In addition to the work basket, a one tonne WLL materials hoist with the same hoist speed as the work basket was used for removal and installation of the components, weighing up to 600 kg individually.
Among other things, a key project objective was to update the Operating and Maintenance Manual to include the new equipment and develop safe operating and maintenance procedures for operation of the hydraulic equipment and coupling together of the two service gates.
The work was programmed to commence at the end of the irrigation season (15th May) and be completed prior to the start of the next irrigation season (15th August) and was completed in 13 weeks at a cost of $591,000. During the outage, riparian releases were passed downstream through a low flow valve attached to one of the radial flood gates. Stage 2 works will include replacing the electrical and control system, replacing conduit air valves and automation of the irrigation conduit guard gate.