The Natural Potential of Mountains in Bulgaria and Its Sustainable Use - Sustainable Development in Mountain Regions: Southeastern Europe - page 55

that has the highest contrast in Bulgaria is winter, followed by spring and autumn,
and summer is distinguished by the highest stability of weather (Fig. 5.4 b).

5.2.3 Assessment of Water

Bearing in mind the genetic formulation for the formation of water as a product
of climate, it may be pointed out that the mountains receive the highest amount of
precipitation. The mountains, with restricted evaporation conditions due to the rela-
tively low temperatures, are areas constantly generating water resources in Bulgaria.
More than half of the annual volume of river runoff is formed in the altitude belts
above 600 m, and including the belt within the range 300-600 m, their share exceeds
80% (Fig. 5.5 ). The highest water abundance belongs to the highest ridge locations -
above 800 mm, for a runoff coefficient above 80% with respect to precipitation in
these areas, and the lowest (more than 300 mm) belongs to the low-mountainous and
foothill areas, with a runoff coefficient above 50% (Fig. 5.6 ). It has to be noted that
with respect to precipitation and runoff conditions the East Rhodopes with their low
altitude (on the average 330 m) are comparable with the medium- and even high-
mountainous parts (with an average altitude of

1,000 m) of West and Middle Stara
Planina, the West Rhodopes, Rila and Pirin, i.e. this is one of the most water-bearing
low-mountainous parts of the country - with its occupied area of only about 4.5%,
more than 12% of the water resources of the country are formed here (Physical
geographic and social-economic regionalization, 1989). However, the river runoff is
with strongly expressed inconstant regime - with extremely high river floods usually
in winter-spring period and with continuous deep low-water during the summer-
autumn when even the bigger rivers become dry. On the contrary, the river runoff in
the high mountains is naturally regulated in the typical for them broadly spread ridge
and slope flattened areas, often with peat cover, thick forests, thick and permanent
snow cover and not on the last place with lower evaporation even in the summer.
In total 700 water reservoirs have been built for utilization of the water poten-
tial of the mountains in Bulgaria for different purposes (water supply, irrigation,
power generation), which are distributed irregularly in the height belts of the sin-
gle mountains and regulate a significant volume of the river water formed in these
mountain localities. The volume of the artificially regulated river discharge in the
water reservoirs of different size and location in the mountains by altitude belts
amounts approximately to 5 billion m 3 and represents 70% of the stored water
volume in the country (Mandadjiev, in: The natural and economic potential of the
mountains in Bulgaria, 1989 ).
The technically feasible usable hydraulic energy potential of the mountains is
estimated to be about 3,400 MWt, and the energy potential provided by the ca.
70 hydropower plants (HPP) that were constructed till the end of the 1980s at the
water reservoirs in the mountains, is 1,900 MWt. As one can see there is still
significant non-utilized hydraulic energy potential, which is one of the perspec-
tive renewable energy sources, in combination with climatic sources, for solving
problems of sustainable regional development in mountainous territories and in the

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