Hassan Vosoughi - M.Sc. Department of Civil Engineering, Islamic Azad University, Central Tehran Branch, Tehran, Iran.
Hooman Hajikandi - Assistant Prof., Department of Civil Engineering, Islamic Azad University, Central Tehran Branch, Tehran, Iran.

Pipelines are a very opportune means to transport oil, gas, water, waste water or other hydrocarbons from the sea bed or river crossing is current in water environments.Pipelines are widely used coastal structures, and scour around them can influence their stability. Pipelines installed on sandy sea beds in coastal areas are exposed towave and current action.Sumer and Fredsøe [3] demonstrated that the relative scour depth, S/D, is remarkably well correlated with the Keulegan–Carpenter (KC) number. The scour increaseswith increasing KC number. S/D can be expressed in terms of the KC number as follows: