An Investigation of Factors Affecting Runoff Generation in Zanjan Province Marl Units of Formations Geological using Simulation Rainfall

Marl unit include of about 4438 km sq. (some %20) of total surface area of Zanjan province. A study on the relationship among the runoff threshold, volume and run-off coefficient at Marl unit shows a quadratic regression equation to express the variations. Statistical data analysis shows the significant effects of the Marl units and slope on the runoff threshold (p<0.05). While, there is no significant effect of the climate on it. Marl unit can be classified in to three groups, based on the runoff threshold, so that Marls of Pliocene (PL) and Qom (OM) are in a separate class and upper-red (Mu), lower red and Eosen (EM) Marl units are in a unique group. These 3 groups differ significantly of view point of the runoff threshold resulted by the physico-chemical differences among them. So that the more silt content, the more rapid runoff threshold, because of lack or scarcity of water absorption capacity in these units. Investigation suggests that combined effects of slop and climate are significant on the runoff threshold.