Erosion and Sediment Yields in the Changing Environment (Proceedings of a symposium held at the Institute of Mountain Hazards and Environment, CAS-Chengdu, China, 11–15 October 2012) (IAHS Publ. 356, 2012). Copyright 2012 IAHS Press 364 Potential use of synthetic color-contrast aggregates and a digital image processing technique in soil splash measurements ABDULVAHED KHALEDI DARVISHAN 1 , SEYED HAMIDREZA SADEGHI 1 , MAHDI HOMAEE 2 & MAHMOOD ARABKHEDRI 3 1 Department of Watershed Management Engineering, Faculty of Natural Resources, Tarbiat Modares University, PO Box 46414-356, Noor, Iran a.khaledi@modares.ac.ir 2 Department of Soil Science, Faculty of Agriculture, Tarbiat Modares University, PO Box 14115-336, Tehran, Iran 3 Soil Conservation and Watershed Management Research Institute, PO Box 13445-1136, Tehran, Iran Abstract A digital computer-based method for measuring soil splash was evaluated in the present study. Accordingly, Synthetic Color-Contrast Aggregates (SCCA), having the same size, shape and specific gravity as those of natural soil aggregates were used as tracers for detecting particle movement. Subsequently, the amount and intensity of sheet erosion was inferred with the help of Digital Image Processing (DIP) techniques using MATLAB. The present study was conducted under laboratory conditions with a simulated rainfall intensity of some 90 mm h -1 and a slope of 30%, using sandy-loam soils taken from a summer rangeland in the Alborz Mountains, northern Iran. Soil erosion was mapped based on the DIP technique and finally compared with the density distribution of SCCA to evaluate the accuracy of the approach. The results show that the method can be used for measuring soil splashed downslope, and for estimating the amount and intensity of splash. Key words Alborz Mountains, Iran; digital image processing; erosion tracers; sheet erosion; soil splash; synthetic color-contrast aggregates INTRODUCTION The initial stage of splash-induced soil erosion is highly destructive and entails the dispersion and subsequent breakdown of soil aggregates. Splash also plays a synergistic role in soil erosion by decreasing surface infiltration rates and increasing runoff coefficients. The extent of splash erosion is a function of raindrop impact energy in conjunction with the stability of soil aggregates (Kukal & Sarkar, 2011). Although the bulk of eroded soils measured/sampled at the outlets of plots, slopes and watersheds are suspended sediments, splash-induced sheet erosion may contribute to a significant proportion of soil loss as a non-suspended type of soil movement that usually is ignored in soil erosion and sediment studies. The main reason for this may be due to the difficulties assoc- iated with sampling and measuring non-suspended particles at appropriate locations. To overcome this problem, a new, simple, innovative method with the potential for application in large-scale surveys is required. Computer-based methods, especially using the remote-sensing aspects of these techniques, may have the desired properties of both simplicity and large-scale application. Accordingly, a digital computer-based method for measuring soil splash has been developed for the present study. Synthetic Color-Contrast Aggregates (SCCA) having the same size, shape and density to actual soil aggregates (Ventura et al., 2002) were used to evaluate this approach. A detailed review of the current literature has indicated no similar study has yet been attempted. MATERIALS AND METHODS The present study was conducted under controlled laboratory conditions with a simulated rainfall intensity of 90 mm h -1 , an optimized rainfall duration of 10 min, and a 30% slope, using sandy- loam soils (14% clay, 24% silt and 62% sand) taken from the top layer (0–20 cm) of some summer rangelands in the Alborz Mountains in Northern Iran. The natural values for the bulk density, pH, EC, and organic content of the soil used in this study are 1.376 g cm -3 , 7.95, 75.5 μmohs cm -1 , and 2.167%, respectively. The soil was prepared for lab simulation following the methods of Kukal and Sarkar (2011).