THE FLUVIAL ACTION OF THE KARLA BASIN STREAMS IN A NATURAL AND MAN – MADE ENVIRONMENT
This study investigates the fluvial action of streams draining the Lake Karla basin, located in the plain of Thessaly, in Central Greece. Until a few decades ago, a large part of this area had been occupied by a lake. In order to find out the relation between the channel bed morphology and the oscillations of the local base level due to variations in water level and human intervention in the lake, the following streams were investigated: the flumes of Mpegiatiko, Bagiorema, Bathurema, Xerias and Maurorema. The width and the length of all channels were measured with a laser range finder while the incision and the erosive events were recorded by GPS with sub-meter accuracy. Furthermore, an integrated GIS analysis was undertaken in order to illustrate the changes in the water level of Lake Karla coupled with historical data and data from previous studies. It will be shown that there were two main evolutionary stages which controlled the local base level changes of the studied area. The first one is connected to the continuous changes in the lake’s water level and its reduction from 64m to 45m a.s.l. This resulted in the incision of the channels and the creation of characteristic knick points upstream. The second stage is associated with the draining of Lake Karla in 1962. This intervention mostly altered the streams that developed into fine-grained material channel beds.