Dams and Reservoirs - Hydrogeology: Objectives, Methods, Applications - page 296

The Hales Bar dam (USA) on the Tennessee River, is likely to set records.
Begun in 1905, without a geologic study, it was put into use in 1913, after
construction costs four times higher than predicted, due to injection work
in cavities encountered during construction. Losses were immediately
apparent and did not stop increasing, until they reached 250 m 3 ·s -1 in
1930, date at which construction halted. When the dam was purchased
by another company in 1939, the leaks fed thirteen large resurgences
immediately downstream, with a total discharge of 500 m 3 ·s -1 . The almost
total suppression of the leaks was nevertheless achieved, through the
creation of two impermeable curtains extending to a depth of 30 m below
the upstream facing of the dam (Gignoux & Barbier, 1955).
The Caramasa gravity dam in Catalonia (Spain), 92 m high, suffered
large losses as soon as it went into use in 1920. Their discharge showed
an annual increase of 5% and reached a value of 11 m 3 ·s -1 , fl owing over
a front of 1.2 km. After detailed studies, spread over several years, the
solution consisted of creating a 1 km long grout curtain, constructed using
224 boreholes totaling a length of 132 km, composed of individual lengths
between 112 and 394 m. The losses were brought down to a value of 2.5
m 3 ·s -1 , after the use of 1,90,000 metric tons of injected material, including
cement, scoria, sand, gravel, sawdust, sisal, and asphalt (Lugeon, 1933).
The Keban gravity dam (Turkey), 185 m high, was built on the Euphrates
(average discharge of 655 m 3 ·s -1 ), for the purpose of creating a 30 billion m 3
reservoir for irrigation and electricity production. During construction, a
karst cavity of 1,00,000 m 3 , the Crab cave, was discovered 300 m below the
construction site. It was fi lled with concrete and the waterproofi ng of the
rock below the dam was completed successfully, with the help of a grout
curtain. On the left bank, karst indicators were found during geologic
studies and during the excavation of a diversion gallery. A grout curtain
was put in place to isolate this area to a depth of 250 m, apparently not
enough given the depth of the Crab cave. The increase in leakage led, in
1976, to losses of 26 m 3 ·s -1 , when they were initially only of 6 m 3 ·s -1 , and
to the partial emptying of the lake, revealing the opening of a large cavity,
the Petek cave. It entrance was surrounded by a concrete chimney, in order
to reduce its absorption capacity, and it was then fi lled with the help of a
million m 3 of material, and a part of the left bank was waterproofed with
a concrete carpeting 50 cm thick. These projects decreased the leakage
to 9 m 3 ·s -1 , which represents only a little over 1% of the discharge of the
Euphrates and is therefore economically acceptable.
The Cheurfas dam (Algeria), after its reconstruction after its partial
destruction in 1885 (see chap. D4-2.1), required signifi cant waterproofi ng
work in order to curb the losses from its reservoir through its Tortonian
limestone base. The infi ltrated water reemerged immediately downstream,
at the level of several springs on the left bank of the Oued Mebtouh (Figure