مقايسه گرانولومتري و تيپ سه جريان سيلابي در حوزه آبخيز زيارت گرگان

Comparison of granulometry and type of three flood flows in Ziarat watershed, Gorgan

Rivers under different hydro-morphological regimes, demonstrate different flow behavior as normal, debris, mud and flood flows. Spatial and temporal differentiation of these flows according to granulometric characteristics of remainder sediments is of high importance in implementation of watershed management projects especially in river flood plains. The Ziarat watershed contains debris and mud flows in summer that threat the water reserviors of the Gorgan city and touristic sites along the main stream as flash and periodically. In this study for the differentiation of flood flows, after three flow events in 26/27 July 1999, 26 August 2000, and 15/16 October 2000, 37 sediment samples have been selected randomly along the suitable reach of main stream. Then, after granulometric tests by wet sieving and hydrometry, and related curves, key granulometric indices including Trask, Symmetry, Inclusive graphic standard deviation and Krumbein index have been calculated. The sedimentology studies showed that those three flow events were high sediment flows; the first one is determined debris flow and the other two events are known as mud flow. The statistical analysis of variance resulted that, there are significant differences between first and other two flow events at 0.05 levels. The analysis of variance also showed that for particles sizes of less than 50% frequency, the difference between three flood types is not significant but for particles of higher than 50% frequency, the differences are highly significant.