The Hydroelectric Power Plant of Pont Ventoux-Susa · The hydroelecTric Power PlanT of Pont Ventoux-SuS a www .ir enener gia.it Iren Energia is the company in the Iren Group whose

T h e h y d r o e l e c T r i c P o w e r P l a n T o f P o n t V e n t o u x - S u S a

w w w . i r e n e n e r g i a . i t

Iren Energia is the company in the Iren Group whose core

businesses are the production and distribution of electri-

city, the production and distribution of thermal energy for

district heating and the provision of technological services

Iren Energia, which has always been sensitive to envi-

ronmental protection issues, produces electricity and heat

from renewable energy sources (hydroelectric power

plants) or similar sources (cogeneration plants).

Iren Energia constantly pursues its objectives, which are qua-

lity, reliability, sustainable development, energy efficiency

and a close relationship with the areas in which it operates.

The hydroelectric power plant of Pont Ventoux-Susa has

an installed capacity of 150 MW and uses water from the

river Dora Riparia and its tributary Rio Clarea.

The water is conveyed along an off-take canal in a tun-

nel to the Clarea Valley reservoir, the starting point of the

pressure tunnel leading to the forced pipeline, which, in

turn, leads to the plant in the cavern.

Downstream of the plant the water is returned to the Gor-

ge della Dora reservoir and may be pumped back at night-

time to the Clarea Valley reservoir, so that it can be reused

to produce electricity during the daytime.

MaIn PLant CHaRaCteRIStICS

Pont Ventoux intake works Altitude considered normal 1,046.30 m a.s.l.

Clarea Valley reservoir Altitude considered normal 1,030.50 m a.s.l.

Capacity 561,000 m3

Gorge reservoir Altitude considered normal 531.20 m a.s.l.

Capacity 442,000 m3

General information Subtended catchment basins 536 km2

Maximum net head 502.92 m

Efficient power 150 MW

Mean energy coefficient 1.23 kWh/m3

Mean power output per year of over 350 GWh

Iren energia S.p.a.Corso Svizzera, 9510143 Torino - ItalyTel. +39 011 5549 111Fax +39 011 53 83 13

Cutaway of plant in cavern (three-component unit)

The Hydroelectric Power Plant of Pont Ventoux-Susa




























Capacity 561,000 m3


Capacity 442,000 m3




































Capacity 561,000 m3


Capacity 442,000 m3









Pont Ventoux-Susa plant

Salbertrand-Chiomonte and Chiomonte-Susa plants

In Clarea Valley, on the right side of the

valley outside the bed of the Clarea tri-

butary, a daily regulation reservoir has

been built with a net regulation volume

of 571,233 m3, which corresponds to a

maximum regulation level of 1,030.50

m a.s.l. The total length of the crest of

the reservoir is 852 m.

The reservoir was constructed by cre-

ating an artificial bed in the Clarea tri-

butary running alongside the reservoir.

The design solution adopted maintains

the surface flow of the Clarea tributa-

ry continuous without its water mixing

with the water in the river Dora Riparia

contained in the reservoir.

This was done to safeguard the flu-

vial ecosystem of the Clarea tributary

downstream of the regulation reservoir.

All the hydraulic works necessary for the

supply of the reservoir, diversion and di-

scharge of the water were built under-

ground, on the rocky right side of the

valley. The discharge works were tested

by hydraulic physical modelling.

A pressure tunnel with a circular cross

section dug with a TBM, 4.3 km long and

with a final diameter of 4.05 m, sized for

a maximum flow rate through the tur-

bine of 34 m3/s, links the regulation re-

servoir of Clarea Valley to the upstream

piezometric well. The latter consists of a

cylindrical shaft with a height of about

80 m carved into the solid rock.

The piezometric well is the starting

point of the forced pipeline, which is

also entirely carved into the rock and

consists of a metal pipeline 1,320 m

long with a variable diameter (3.50 –

3.20 – 2.80 m).

The Pont Ventoux-Susa run-of-river plant

is regulated on a daily basis and takes

water mainly from the river Dora Ripa-

ria between Pont Ventoux (municipality

of Oulx) and Susa but also from the left

tributary, Rio Clarea.

The main diversion works on the river

Dora, situated at Pont Ventoux, con-

sist of a barrier dam including a fish

ladder, intake works and a moderator

canal on the left bank that houses the

gravel and sand removers.

The altitude to which the reservoir is

normally regulated upstream of the

barrier is 1,046.30 m a.s.l.

The design of the hydraulic works

in the river bed, including the dikes

upstream and downstream of the bar-

rier was tested by physical modelling.

A minimum instantaneous release

(minimum vital flow) from the bar-

rier is guaranteed to preserve aquatic

life in the river before other tributari-

es flow into it.

The water from the river Dora Riparia

(mean diverted flow rate 9.51 m3/s)

is conveyed into an off-take canal in

a free-surface tunnel, sized for a ma-

ximum flow rate of 33 m3/s.

The canal runs on the left side of the

river Dora Riparia for about 14 km to

the Clarea Valley reservoir.

The electric power plant was built in an

underground cavern with an excavation

volume of about 35.000 m3.

The machine room level is situated at

495.00 m a.s.l. and is accessible from

the mouth of the cavern situated at a

height of 575.00 m a.s.l., on the Susa-

Venaus road, through a large tunnel su-

itable for the transit of lorries and about

1,170 m long.

The plant is also equipped with an esca-

pe tunnel about 460 m long. The tran-

sformers are installed in underground ca-

verns independent of the machine room.

The plant in the cavern houses the

hydraulic and electrical production ma-

chinery: a two-component unit (Fran-

cis turbine and generator) and a th-

ree-component unit (Francis turbine,

generator and pump), both with a ver-

tical axis and an overall efficient power

of 150 MW.

The pump, which has a maximum ca-

pacity of about 13 m3/s, transfers wa-

ter from the Gorge reservoir of the ri-

ver Dora Riparia to the regulation Clarea

Valley reservoir.

In this way, the water is made available

again in the Clarea Valley reservoir, thus

ensuring a significant additional pro-

duction of electricity for use during the

daytime when the demand is higher,

thus optimizing the use of the amount

of water available.

The high-voltage connection with the

national transmission grid is made at

the Terna transformer station in Ve-

naus by means of underground cables

to the armoured electric power plant

situated at the mouth of the tunnel for

access to the plant in the cavern.

Downstream of the plant is situated

the tunnel pressure return canal, which

is about 1.6 km long and leads into the

bed of the river Dora Riparia upstream

of the town of Susa. In order to ensu-

re the necessary demodulation of the

flows and pump storage, a concrete

arch-gravity dam was built to form a

reservoir at the gorge of the river Dora.

The body of the dam, which has a vo-

lume of about 48.000 m3, reaches a

maximum height above the river bed

of about 30 m, and has a crest about

90 m long. The net storage volume

at its maximum regulation height of

531.20 m a.s.l. is 442,200 m3.

The entire barrier permits overflowing

via four overflow thresholds that con-

verge towards a damping reservoir

downstream of the dam.

A concrete cofferdam was built im-

mediately upstream of the dam to al-

low dam construction and subsequent

maintenance work to be carried out.

The water diverted and used is retur-

ned to the river Dora Riparia down-

stream of the Gorge dam: in part

through a regulation valve situated on

the body of the dam, which ensures a

minimum vital flow and in part throu-

gh a demodulator tunnel with a circu-

lar cross section, which branches off

from the pressure return tunnel and

conveys the water to a point about

700 m downstream of the dam.

The Plant of

Pont Ventoux-Susa










































3.20 – 2.80 m).
























es flow into it.


















1,170 m long.












of 150 MW.





Valley reservoir.







of water available.























531.20 m a.s.l. is 442,200 m3.




















The Plant of

Pont Ventoux-Susa










































3.20 – 2.80 m).
























es flow into it.


















1,170 m long.












of 150 MW.





Valley reservoir.







of water available.























531.20 m a.s.l. is 442,200 m3.




















The Plant of

Pont Ventoux-Susa










































3.20 – 2.80 m).
























es flow into it.


















1,170 m long.












of 150 MW.





Valley reservoir.







of water available.























531.20 m a.s.l. is 442,200 m3.




















The Plant of

Pont Ventoux-Susa




























Capacity 561,000 m3


Capacity 442,000 m3









Documents

The Hydroelectric Power Plant of Pont Ventoux-Susa · The hydroelecTric Power PlanT of Pont Ventoux-SuS a www .ir enener gia.it Iren Energia is the company in the Iren Group whose