Investigation on the dry and wet sieving soil granolometry indices and its application in water and wind erosion studies (Case study: Yazd plain)

Soil erodiblity or detachability is one of the most important and applicable index in wind and water erosion studies. Grain size distribution curve plays key role in estimating soil (wind and water) erodiblity. Two approaches of dry and wet sieve methods, are often used for determining of soil grain size distribution. Hydrometer and pipette methods are based on Stoke's law and free falling of soil particles in fluid (water). In wet sieving or hydrometer method, mechanical and chemical approaches have been applied to disperse the aggregates to finer particles. Whereas, in dry sieving method, texture indices are different in compare to wet methods, because aggregates dispersion doesn’t occur. In this research, 20 soil samples were taken from fine grain plains of Yazd. After preparing of soil samples, dry and wet sieving methods were applied in eight sieve classess (32μm < d < 2000 μm). Using G.R. Graph software, the important indices of grain size distribution including mean diameter, median diameter, skewness and sorting were calculated. Results show a significant different between all of the grain size distribution indices in 5% level. It can be concluded that in wind erosion and water erosion studies, using dry sieving and wet sieving are recommended, respectively that for describing the wind erosion phenomena it is prefer to use the dry sieving method as well as wet sieving for water erosion. The results also show that the average of mean diameter and median diameter in dry sieving, is approximately 2.5 times more than form average diameter of wet sieving.