Nature friendly hydraulic structures made of natural stones such as ripraps have attracted attention in recent years. However, those structures are subject to failure problem under flood flow. Therefore, the authors proposed tied gravels to increase its stability against flood flow. Coefficients such as the drag and lift force are necessary in designing those structures. However, the authorized values for those coefficients are not established yet, the coefficients used for concrete structures are therefore applied in designing structures made of stones at present condition. This study aims to clarify the drag and lift coefficient for gravels and tied gravels experimentally.
