An international tender is underway for the Mazar Project, a US$238M hydroelectric scheme with approximately 4km of tunnels in Ecuador. Precontract documents were available until March and the construction contract bid competition closes on 11 June.
With an estimated construction period of four years the project incorporates a concrete face rockfill dam across the river Paute near its confluence with the river Mazar, as well as various tunnels and underground works. The diversion tunnel is 1.2km long, driven as a horseshoe section of 12m by 12m.
Preliminary documents describe a concrete lining in the invert and the lower 6m of the walls. For the final 192m of its length, a rectangular section of 12m by 12.35m has been adopted with a concrete invert and walls up to 5m. A bottom outlet tunnel is incorporated into the design to allow drainage of the dam in an emergency, to maintain protected water flows when maintenance would normally limit throughput and to ensure evacuation of fine sediments from the power generation system. The outlet is 403m long, of similar horseshoe section as described above, but in this instance completely lined in concrete.
The intake leads to a 384m long headrace tunnel of 6.3m diameter. A surge tank is provided in the form of a 77m deep, 15.2m diameter circular shaft within the complex that is concrete lined. It is connected to the headrace by means of a 25m long L-shaped throat section. There are 160m of approximately 6m section horseshoe tunnels to be used for other installations and a 64m long by 20m wide and 39m high cavern for the powerhouse which will contain two 97MW generating units. A 60m shaft, which tapers from 6.1m to 5.6m as it varies from concrete lined to an armoured pipe, is used to harness the force of the water for the turbines. Discharge back into the river is by an 8m horseshoe section tunnel that runs for 642m to a floodgate control.
For maintenance and access purposes, a 170m deep, 10m diameter shaft gives a space of 4.1m by 7.5m for cables, elevator, stairs and equipment transport. A 450m long tunnel will connect it to an 854m long main access tunnel.
Client, Hidropaute SA, has also been seeking a consultant to act as project manager and assist with finalisation of the designs. Bids were due to be opened at the end of April and announcement of the successful bidder should be imminent.
