The “Weir Construction Contract” aims at building two reinforced concrete weirs with tilting gates, the rotation axis of each gate roughly at riverbed level so as not to obstruct river flow when the gates are open. Each weir is equipped with a 13.0 m long gate.
An overflow concrete walkway has been designed for access, allowing flood overtopping; for that reason no lateral railing is provided.
Pedestrian access between the weirs follows a spillway path with a sill elevation of 144.25 m, slightly above the maximum admissible operating level of the water mirrors (144.10 m) and the top elevation of the fully closed gates.
This path materialises a broad-crested spillway with two main functions: auxiliary discharge for flood flow conveyance outside the bathing season, and emergency spillway — reducing flood elevation in unexpected situations and accidental discharges where high flow runs in the river without the gates being open.
As a complement to the path and spillway, the central island is regularised by demolishing rock outcrops above project elevations, so that no obstruction to flow occurs on approach to and downstream of the discharge of the path — at elevations 144.25 m and 144.00 m respectively.
For gate operation and control, two watertight machinery and control rooms have been built, one on each riverbank, accessible above the centennial flood elevation or higher from neighbouring land and roads.
The existing mill is preserved and a new 800 mm diameter supply pipe is constructed.
On the work front, Weir 1 “Right Bank” is built first, followed by Weir 2 “Left Bank”, with the works comprising:
- Site setup
- Construction of an embankment cofferdam to divert the Vouga river flow to the left bank, creating a working platform
- Demolition of existing elements and rock outcrops to project elevations
- Diversion of conflicting infrastructure
- Construction of the reinforced concrete structure as designed
- Gate installation — Weir 1
- Once the previous task is complete, construction of the Weir 2 cofferdam, diverting river flow to the right bank (already built)
- Demolition of existing elements
- Construction of the reinforced concrete structure
- Indoor and outdoor finishes
- Gate installation — Weir 2 with respective electromechanical and electrical equipment
- Installation of metalwork and decking walkway
- External landscaping