Geogmorphological Evolutions of Polrud Delta in East of Guilan(From Quaternary period until now)

Delta is one of the compressible forms of river alluvium which are formed at the shallow main drainage near the river banks. Suitable slope, fertile soil, availability of water supplies, and the considerable size of Polrud delta, has made it a convenient and suitable ground for human activities, and that its size may very and become larger or smaller, as a result of delta’s evolution, because of the main river’s path, and other water network changes. The outcome of this evolution can have a positive or negative effect on its inhabitant. With respect to the importance of the matter and according to the surveys done, this delta is situated and Alborz Zone and its geological events have had an affective role in its developments. In the Quaternary period, it was effected by glacial age and interglacial age eras and has followed its development’s path in the Holocen epoch ,in such a way that at the present, this delta has been formed by two topographic slopes, river banks and plain, at the shallow basin of polrud. Delta’s medium slope is less 1% and has a very wet climate, in such a way that in the spring, the maximum (54.39 percent) and in the summer, minimum (9.14 percent) sediment are deposited. This research has been carried out according to aerial photographs and satellite pictures at three time periods (1967, 1994, 2006), ground measurements, topographic maps, library references, with the use of descriptive and analytic methods. The outcomes from the researches showed that this delta is of advancing type and has been formed under the effect of old and new river processes, and also the wave functions and effects at present era; therefore, it can ranked as a modern deltas.