ams fall swiftly from the mountains and have cut deep,
scenic gorges. The Struma and Mesta reach the sea through Greece. The
Maritsa forms most of the Greek-Turkish border after it leaves Bulgaria.

About 3,750 square miles of agricultural land have access to irrigation
waters. Dams provide the water for about one-half of the acreage;
diversions from rivers and streams serve about one-third; and water
pumped from the ground and from streams accounts for the remainder.

Of the dams, ninety-two are termed large state dams. Their combined
capacity is three times that of some 2,000 smaller dams. The sources of
four large rivers--the Maritsa, Iskur, Mesta, and Rilska (a major
tributary of the Struma)--are within a few miles of each other in the
high Rila. Water from the upper courses of these and several other
streams supplies the Sofia area with both water and electricity, and
they have a potential for further development. There are major dams on
the Tundzha, Iskur, Rositsa, and Struma rivers. The Danube is too
massive a stream to harness, and damming the Maritsa along most of its
course would flood too much valuable land. The rivers flowing north
across the Danubian plateau also tend to be overly difficult to use in
the areas where they are most needed.

The Vucha River, flowing from the Rodopi into the Maritsa River, is
often used to illustrate how rivers have been effectively harnessed to
provide a variety of benefits. Its cascade system of hydroelectric
development employs six dams having the capacity to generate over
600,000 kilowatts of electricity. The water they back up serves the
municipal water systems in Plovdiv and a number of other towns in its
vicinity, and the dams provide irrigation water for nearly 250,000 acres
of cropland. The reservoirs themselves are being developed as
recreational areas and mountain resorts.

Where a stream is difficult to dam or to divert, water is pumped from
it. This has been feasible only since about 1950, when low-cost diesel
engines and sufficient hydroelectric power became available from newly
constructed dams on other streams. About eighty-five huge pumping
stations have been set up along the Danube River, which furnishes about
three-quarters of the water acquired by this method; and in 1970 there
were about 1,200 lesser stations operating on smaller streams, most of
them on the Thracian Plain.

Climate

For so small an area, the climate varies widely and is unusually