ORIGINAL PAPER Temporal and spatial variations of the water erosion rate Jamal Mosaffaie & Mohammad Reza Ekhtesasi & Mohammad Taghi Dastorani & Hamid Reza Azimzadeh & Mohammad Ali Zare Chahuki Received: 18 June 2014 /Accepted: 4 September 2014 # Saudi Society for Geosciences 2014 Abstract Understanding the erosion dynamics and recogniz- ing sensitive times and places to erosion within the catchment are necessary for erosion control. The seasonal and spatial variability of soil erosion under different contrasting lithologic conditions was studied in Vartavan catchment of Qazvin province of Iran. For this purpose, sediment trappers and erosion pins were placed in each parent material unit and were monitored at the end of each season. The results showed that the erosion rate of Vartavan catchment has large variations spatially and temporally. Based on the average weight of sediments in trappers, soil erosion rate is reduced correspond- ingly in units of light tuff (178.2g), black shale (34.4 g), red mudstone (29.9 g), andesite (21.7 g), dark tuff (16.7 g), sand- stone (14.9 g), red sandstone (9.8 g), shale limestone (9.5 g), and eventually orbitolina limestone (6.5 g). The seasonal variation of erosion revealed that autumn has the maximum rate of erosion (71 %) which then decreases during the spring (19 %) and winter (10 %) until it reaches the minimum rate in summer. Understanding seasonal variations and identifying the critical months when the most amount of erosion occurs are essential for outlining soil conservation plans in specific lithological units. Keywords Sediment trapper . Erosion pin . Erosion dynamic . Vartavan catchment Introduction Watershed degradation as a result of soil erosion and sedimen- tation is considered to be one of the major environmental problems in Iran (Bagherzadeh and Mansouri Daneshvar 2013). This phenomenon is a highly dynamic and complex process which has negative onsite and offsite effects (Prasannakumar et al. 2012). It reduces not only the storage capacity of the downstream reservoirs but also deteriorates the productivity of the watershed (Arekhi et al. 2012a, b). After construction of Sefid-Rud dam, the measured sedimentation rate was about 45 million m 3 /year causing storage loss of over 30 % in 18 years. Hence, erosion control at catchments such as Vartavan located in the upstream side of this dam is essential. This highlights the need for data allowing delineation of critical periods and sediment source areas that need to be prioritized for soil conservation. Identification of such periods and hotspots will help in applying a targeted response directing resources to areas of high risk rather than spreading them equally across the landscape. This requires a basic understanding of the temporal and spatial variations of soil erosion and sediment transport at the scale of a river catchment (Haregeweyn et al. 2013). The parent material plays a key role in determining the geomorphologic processes affecting weathering rates, soil development, and slope forms (Cerdà 2002). Other factors such as rainfall characteristics, topography features, soil tex- ture, permeability, organic matter content, antecedent soil moisture, and soil management also affect runoff and soil J. Mosaffaie (*) : M. R. Ekhtesasi : H. R. Azimzadeh Faculty of Natural Resources, Yazd University, Yazd, Iran e-mail: jamalmosaffaie@gmail.com J. Mosaffaie e-mail: jamalmosaffaie@yahoo.com M. R. Ekhtesasi e-mail: mr_ekhtesasi@Yazd.ac.ir H. R. Azimzadeh e-mail: hazimzadeh@yazd.ac.ir M. T. Dastorani Faculty of Natural Resources and Environment, Ferdowsi University of Mashhad, Mashhad, Iran e-mail: dastorani@um.ac.ir M. A. Zare Chahuki Faculty of Natural Resources, University of Tehran, Karaj, Iran e-mail: mazare@ut.ac.ir Arab J Geosci DOI 10.1007/s12517-014-1628-z