Jafar Chapokpour - Department of Irrigation and Reclamation Eng. College of Agricultural Engineering and Technology University of Tehran, Karaj, Iran
Ebrahim Amiri Tokaldany - Department of Irrigation and Reclamation Eng. College of Agricultural Engineering and Technology University of Tehran, Karaj, Iran

Rockfill structures are one of the most applicable structures in hydraulic engineering. Rockfill dams are always used to mitigate flood in the river to prevent damage in downstream of river basin. Since this typedetention dams should carry large amount of sediment particles. Therefore a consideration should be taken toprevent from siltation of its pore system. To achieve this subject a minimum hydraulic gradient should be existed on the structure which is called critical hydraulic gradient for initiation of motion. Previously some semi theoretical researches were done on this aspect with different investigators but any general consideration wasnot accomplished to develop an equation which covers all available data series. In this research tried to collectall available data series for extraction a relationship with acceptable accuracy in the subject of sediment transport in porous media. An alteration was made on two basic existence relationships because of deflection from Darcy law. Then the coefficients of developed equation related to geometrical characteristics of rockfill media. Ultimately a favorable equation obtained with acceptable accuracy

Rockfill structures; Sediment Transport; Critical hydraulic gradient; Non-Darcy flow