Odeleite Dam

The design and development of the project comprised the following components:

Odeleite Dam

Located in the municipality of Castro Marim, Odeleite Dam is a rockfill embankment dam with a waterproofing coating of reinforced concrete on upstream face.

Main characteristics:

- Crest length/width: 350 m / 12 m;

- Maximum height above foundation level: 65 m;

- Upstream slope inclination: 1.3/1 (H/V);

- Downstream slope inclination: 1,4/1 (H/V);

- Area of the upstream concrete face slab: 22 800 m²;

- Volume of compacted fill: 1 x 106 m³.

The catchment area at the dam site is approximately 352 km² and the average annual inflow is around 89 × 10⁶ m³, corresponding to a runoff depth of 253 mm. The mean flow rate is 2.8 m³/s.

The location and crest elevation of the dam required the construction of a saddle dam on a saddle located on the left bank and an embankment across a valley on the right bank. This embankment, operating under balanced hydraulic loads upstream and downstream, was required to restore road connections, as National Road EN 122 became submerged along the approaches to the existing bridge. The crest elevations of these structures range between 63 m and 75 m.

Odeleite Dam is a rockfill embankment dam with a waterproofing coating of reinforced concrete on upstream face and supported on a concrete plinth. The dam crest, 12 m wide, extends for approximately 347 m at elevation 55 m. The height of the dam, measured from the lowest foundation level, is 65 m.

To enable construction of the dam, the Odeleite stream was diverted through a horseshoe-shaped diversion tunnel with a horizontal invert and a diameter of 7.7 m. Two cofferdams were constructed: an upstream cofferdam with crest elevation at 17.3 m and a downstream cofferdam with crest elevation at 11 m.

 Flow restitution was achieved through a hydraulic jump energy dissipation basin of trapezoidal section, 45 m long, with a width increasing from 14 m to 24 m.

The design discharge for the temporary river diversion, corresponding to a 50-year return period, is 485 m³/s.

The frontal spillway is located on the left bank, with its crest at elevation 42 m. It comprises two 6.7 m wide bays equipped with automatically operated radial gates. Upstream of the spillway crest, a 45° shaft connects to the temporary diversion tunnel, discharging into the stilling basin.

The temporary diversion tunnel was subsequently adapted to function as the bottom outlet. Upon completion of its role as a temporary river diversion, the tunnel was sealed with a concrete plug, inside which the bottom outlet conduit was installed, having a maximum discharge capacity of 50 m³/s.

The dam crest is at elevation 55 m. The Full Supply Level (FSL) of the reservoir is at elevation 52 m, the Maximum Flood Level (MFL) is at elevation 54 m and the Minimum Operating Level (MOL) is at elevation 26 m.

At the Full Supply Level, the reservoir has a flooded surface area of approximately 720 ha. Total storage capacity is approximately 130 × 10⁶ m³, while live storage capacity is approximately 117 × 10⁶ m³. The reservoir regulation index is 1.31, based on inflows from its own catchment.

A small water intake structure was also constructed on the left bank of the Odeleite reservoir, adjacent to the dam, to supply irrigation water to approximately 250 ha of agricultural land in the Odeleite valley as far as the banks of the Guadiana River.

This intake comprises a rectangular tower with an overall cross-section of 2.0 × 2.0 m, incorporating three intake openings measuring 0.8 × 0.8 m at Elevations 26.5 m, 35.5 m and 44.5 m. The gate is operated from a platform located at Elevation 55.0 m and connected to the bank by a footbridge approximately 50 m long and 1.6 m wide.

The Odeleite Dam was followed by these subsequent projects:

Beliche – Tavira Water Treatment Plant Conveyance System

The following constructions were carried out at this stage of the project:

Water intake at Beliche Reservoir: reinforced concrete intake tower with a pentagonal cross-section, 33 m high, incorporating three intake levels with openings fitted with gates and gratings;

Beliche Tunnel • PS1: approximately 350 m long, connecting the intake structure to Surge Tank No. 1, with the same cross-section as the Odeleite–Beliche Tunnel;

Surge Tank No. 1: circular section with an internal diameter of 11 m and 41 m in height;

Pumping Station PS1: equipped with horizontal split-case variable-speed pump units, comprising four pumps rated at 2.6 m³/s and two pumps rated at 1.3 m³/s, providing a maximum pumping capacity of 10.4 m³/s, an average pumping head of 80 m, an installed capacity of 14 MW and a 60 kVA substation;

Stretch of Pipe: of some 560m, from the EE1 to the Equilibrium Chimney Number 2 in reinforced and pre-stressed concrete pipe of DN 2500 mm, with rubber cord sealing joints;

Equilibrium Chimney nº 2: with a circular section and internal diameter of 11 m and 30 m in height;

Stretch of pipe: reinforced and pre-stressed pipe with rubber cord sealing joints of DN 2500 mm, some 25 km in length to the EE2, sized for pressures up to 1.4 Mpa and backfills up to 4 metres in height; along the length of the pipe are flow outlets for irrigation using 6 outlets with MONOVAR flow control valves;

Pumping station EE2: blower fitted with 3 horizontal axis 2.1m3/s electro pumps with elevation of 10 – 13 m. Installed power of 1.2 Mw;

Stretch of pipe: reinforced and pre-stressed concrete pipe with rubber cord sealing joints, DN 2500 mm, almost 3 km in length to the reservoir;

Sto. Estevão Reservoir: open air, hilly type, built using a perimeter dyke with variable heights between 0.5 and 15 m with a total capacity of 150,000 m3, surface area of some 2.8 hectares, covered with HDPE type plastic geo-membrane including a series of hydraulic security devices and outlets for the various users;

Pumping station EE3-U: installed at the reservoir, pumps the water to the Tavira ETA, equipped with horizontal axis electro pumps: 2 x 1.1m3/s and 2 x 0.55 m3/s. Elevation 21 metres. Installed power 900 Kw;

Stretch of pipe: for the supply of water to the Tavira ETA in DN 1200 mm reinforced and pre-stressed concrete with rubber cord sealing joints some 1.8 km in length. 

Odeleite – Beliche Tunnel

The Odeleite and Beliche reservoirs are connected by a tunnel so that they can operate as communicating vessels. The tunnel has a chamfered corner portal type section, 3.3 m in length and a useful height area of 9.5 m. Maximum flow through the tunnel is 25 m3/s.

The elevation of the Odeleite reservoir floor is 23 m, while that of Beliche is 26 m. The tunnel stretching for some 2950 m was clad in full with reinforced concrete.

Significant dimensions:

- Rectilinear length 2,958 m;

- Area of the excavation section of 17 m2;

- Section area after final cladding with reinforced concrete: 9.5 m2;

- Circular upstream and downstream shut-off towers with an internal diameter of 4 m, average wall thickness 0.3 m and height 32 m.

Tavira Water Treatment Station (1ª Stage)

Providing treatment of water supply to Sotavento Algarvio with a maximum production capacity of 2.2 m3/s. At this stage drinking water production of 1.1 m·/s is expected.