Kinloch Rannoch Weir is located at the head of Loch Rannoch in Scottish & Southern Energy’s (SSE) Tummel hydroelectric scheme and controls 1.637Mft3 of water. The Tummel Valley is well suited to a hydroelectric scheme, representing a large catchment area of 1839km2, with heavy annual rainfall. Its potential was recognized by the Grampian Electricity Supply Company which built power stations at Rannoch and Tummel Bridge in the 1930s.

The weir consists of three 12.2m wide floodgates which were installed in the 1930s and are to be replaced under this contract. The three weir gates at Kinloch Rannoch Weir control the flow of water from Loch Rannoch, and are of the undershot design. Originally designed, constructed and installed by Glenfield & Kennedy they are almost 80 years old and last year it was agreed they were in need of replacement.

Site Services, a division of Enterprise Engineering Services, the Aberdeen based engineering and fabrication services specialist, won the contract in May 2009. The Site Services division delivers onsite repair and maintenance across a wide range of sectors including hydro power, water control and the paper industries.

During the first few months of the Kinloch Rannoch Weir contract, the team undertook a detailed design phase and produced a 3D model of the gates in its Aberdeen workshop. It is anticipated that construction of gate one will be complete by the end of January 2010 (as we go to press) with installation following soon after.

A team of 10 staff from Site Services are involved in the ongoing project including project manager, construction manager, site supervisor, onsite engineers / welders, onsite electricians and manufacturing staff in the Aberdeen workshop. Kinloch Rannoch Weir is, to date, the biggest project the team has worked on.

Client objectives

Prior to the commencement of the design phase, several discussions took place between Sites Services and the client to agree key objectives:

• The gate should be designed to meet modern standards and provide an adequate design life based on the latest wave and flood modelling data available.

• The design of the gates must comply with modern design codes whilst still maintaining the original dimensions and weight restrictions of the existing civil works

• The mass of the new gate assembly should be no greater than the existing gate, as SSE wanted to retain the existing refurbished lifting gear without modification

• The new gate should be manufactured in several parts and subsequently re-assembled in situ, due to the SWL limitation on the overhead gantry system and the physical constraints of the existing civil works (i.e. the existing gate had been installed prior to the fitment of the headgear)

Design and installation

Although much of the work being carried out by Site Services is routine and has been completed many times before, the design phase has been particularly challenging as the replacement gates must comply with modern design codes whilst still maintaining the original dimensions and weight restrictions of the existing civil works. Finite Element modelling methods have been used in the design to cover the many load cases, including the requirement for seismic loadings to be taken into account.

Site load lifting limitations have also constrained the design of the gate to be of a three part modular construction employing bolted seams to complete the construction.

A bespoke overhead gantry system has been designed and installed by SSE to permit the installation of the stoplogs.

The SWL of the overhead gantry system, based on the maximum mass of a single stoplog, is 5 tonnes.

It was agreed by the team that this overhead gantry system would also need to be used to install the replacement gates as separate craneage access to the site is difficult.

Site Services manufactured a three part modular construction employing bolted seams to complete the construction due to the site load lifting limitations.

The Future

Site Services aims to deliver its part of the project on time and within budget despite the challenges it is being faced with. The team attributes its on-going successful completions of other projects to great communication and working closely with the main contractor to achieve goals.

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