Water Needs and Their Evolution - Hydrogeology: Objectives, Methods, Applications - page 176

3 TECHNICAL USES OF GROUNDWATER
3.1 Hydraulic energy and hydroelectricity
The transfer of mechanical energy from groundwater into usable energy
is rare. However, a few examples can be cited, in France, in China, and in
Croatia.
The Eylies (Ariège) hydroelectric plant is powered by the capture of
karst groundwater in the Cigalère cave. The Miégebat plant in the Ossau
valley diverts the underground river in the Eaux Chaudes cave through a
514 m long gallery feeding a waterfall 400 m high. There was an unsuccessful
attempt to harness the underground river of the Pierre Saint Martin (Atlantic
Pyrenees) in the 1960s.
A few examples of underground dams harnessing karst rivers for
hydroelectric production are known in China, including the dam in
Luota (Hunan), in a Permo-Triassic limestone syncline perched above
impermeable coal beds, where an underground excavation created a 3
million cubic meter reserve powering a 10 MWe facility. In France, a dam
was built in the entryway to the Bournillon cave (Vercors), in order to power
the plant with the same name in the Bourne gorges.
In order to take advantage of abrupt topography with a number of
levelled poljes, many hydroelectric installations were built in Croatia,
intercepting the water circulating in Dinaric poljes before it disappears
below ground into sinkholes. The water is then carried through subterranean
galleries over several kilometers towards poljes or rivers at a lower elevation,
where it passes through turbines. These installations do not directly use
groundwater, but, by intercepting the water before its natural descent
into the endokarst, they greatly modify the behavior of the different karst
systems in the region. Figure 94 illustrates the hydroelectric infrastructure on
the Trebisnjica River, north of Dubrovnik. Part of the water in the Nevensinje,
Dabar, and Fatnicko poljes, which contributes to the dicharge in the Buna
and Bregava springs, is diverted from the system. Forty or so peripheral
springs were monitored regularly over the course of several years. The
average spring discharge underwent a general decrease. The Ombla spring,
for example, went from an average discharge of 34 to 24 m 3 ·s -1 after the
construction. The dry season discharge, however, is sometimes greater,
thanks to leakage from the dammed lakes and the subterranean reservoirs
maintaining underground circulation (Milanovic, 2001).
Such projects can, however, exist only in very particular geologic
environments.