Following a surge of requests, since it was originally reported on the T&TI web site in early August, interested parties have had two extensions to the availability of prequalification documents for the 660MW Porce III hydroelectric project in Colombia, which includes over 16km of tunnels.

Porce III is being developed by Empresas Publicas de Medellin ESP (EEPPM) in the region of Antioquia. It features a concrete face rockfill dam, intake structures, headrace tunnel and surge tanks, powerhouse, transformer cavern and tailrace tunnel. There are also three access adits varying from 465m to 649m long.

The prequalification documents were originally only available until 6 August, however, this was extended to 17 August and finally the period was lengthened to 2 September. Requests to prequalify are now due to be returned by 16 September, after which successful contractors will be invited to bid for the project.

In 2001, EEPPM carried out a conceptual design on the scheme and updated the environmental impact assessment. A year later, in January 2002, a consortium of Ingetec SA and Klohn Crippen Consultants Ltd, was awarded the contracts for detailed design and advice during construction. By early 2003, the environmental division of the state government approved the project.

Water will be diverted to the reservoir by means of a 653m long tunnel, 10.5m in diameter. Reservoir filling is controlled by a bottom discharge that will also allow emergency drainage and an ecological discharge of 2m3/s. A radial gate will regulate a bottom discharge tunnel.

Headrace tunnel works take the form of a 12.3km long upper section of 10.2m diameter, averaging a 1% slope. A 304m long lower section, also 10.2m in diameter, will be driven at a 7.7% slope. A vertical shaft 149m deep of 10.3m diameter will connect these two sections. Three access adits will be driven to provide multiple workfronts for the headrace works.

An underground powerhouse 121m long will accommodate four 172MW turbines. At 18.2m wide by 40.7m high, the excavation will also house the associated generators, access is provided by a 7m diameter, 493m long tunnel.

The tailrace works consist of four draft tube tunnels from 50m to 57m, a 76m long horseshoe tunnel that will be shotcrete lined and of variable width between 5.7m and 10.4m, as well as an 827m long tailrace tunnel of horseshoe profile that is 4.9m to the shoulder and has a vault radius of 5.1m. A 348m long downstream surge tunnel will start at the powerhouse access tunnel and will be used as a construction tunnel.

Porce III will be the biggest power station in EEPPM’s generation system. With its completion, EEPPM will continue being the leading power generator in Colombia, up to the maximum percentage allowed by law equal to 25% of the national installed capacity.

Related Files
Diagram showing the scope of underground works for the Porce III hydroelectric project in Colombia