1. introduction dust phenomenon which occurs in arid and semiarid lands of the world is closely related to climatic characteristics of the region. according to the world meteorological organization (wmo), whenever wind speed exceeds 15 meter per second and horizontal visibility reduces to less than 1 km in a station, dust storm is reported (goudie & mideleton, 2006). great storms are created wh...

introduction the floods particularly in arid regions of iran damage railroads each year. most of the damages are in the rail bridges on stream channels because of the channel bed replacements, sudden rainfalls and disjointed bed materials. dry channels of the streams, the flat surface of the ground, and lack of vegetation cover result in seasonal and annual channel bed replacements. these chann...