UNUSUAL FLOODS IN HIGH KARST PLATEAU OF MONTENEGRO, YUGOSLAVIA

Banjani karst plateau in western Montenegro, Yugoslavia, is an area of about 400 square kilometers without any rivers or even springs. Velimlje polje, more than a dozen uvalas, thousands of dolines, and more than two dozen caves are dry even though this area receives around 2,000 mm (80 in) of precipitation in a year. However, on some exceptional occasions, Velimlje polje and uvalas Rijecani and Rudine get flooded.

The total amount of rain is not the key to understanding why flooding occurs on this high plateau. The nature of precipitation during the late summer and fall is the key to understanding these rare floods. In all recorded floods the second half of the summer was very dry, with little or no rain. The first rains, in late September or early October, were heavy downpours that washed away sun-baked terra rosa and soil into underground fractures and cavities. Another dry spell of weather (between two to five weeks) preceded the next rainy period. During those rains within three days time at least 250 mm (10 in) of rain fell down before flooding of Velimlje polje began. In the last 60 years Velimlje polje flooded six times, the shortest flood lasting three and the longest eleven days. In all instances temporary lakes had ‘flooding stage’ lasting two to six days, and ‘withdrawal stage’ that lasted one to five days. In 1985 flood waters were coming out from the fractures along the sides and the floor of the Velimlje polje, with all ‘springs’ yielding some 9.6 cubic m/sec. Withdrawal of water was always faster, and it was on average 12 cubic m/sec during 1985 flood. A lot of soil, terra rosa, sand and gravel were found near those fractures after waters receded.