ИСТИНА

The sediment yield in the rivers of the Caucasus varies widely, reaching their maximum (> 2500 ton km-2 yr-1) in the Eastern Caucasus. The sediment runoff of the mountain and piedmont rivers of the Caucasus is formed mainly during the warm season, when water flow increases due to the snow melting, glaciers and rains of varying intensity and duration. Observations at gauging stations generally show a good correlation between water and sediment discharges. However, direct measurements of water flow and turbidity during the passage of extreme floods are very rarely available, since in most cases the measuring equipment is destroyed. Only gauging stations located in the foothills sometimes it is possible to reliably determine the discharges of suspended sediments.. In this regard, data on reservoir siltation rates are the most reliable source of information on the contribution of extreme floods to river sediment runoff. For small streams of the low-mountain and high-mountain zones, similar data can be obtained based on the comparisons of the volumes of material delivered from the catchment slopes and its redeposition in the bottoms of the valleys, in the reaches of the valley bottoms located above the gauging station. This study presents data on the contribution of extreme floods to the sediment runoff of rivers in various altitudinal (from foothills to high mountains) and landscape (from subtropics to periglacial) zones of the Caucasus. It was found, that sediment yield associated with extreme events exceed the mean annual sediment yield in 4 -10 times depending from size of river basin and landscape zone.