Despite the fact that many studies on the stability of stones in bed protections under flowing water have been conducted, our knowledge is still far from advanced and reliable. Issues like how to quantify the hydraulic loads exerted on the stones on a bed and the associated stability of the stones are still central and most challenging in stone stability research.These two challenging issues are dealt with in this thesis. Its main focus is on the effect of hydraulic parameters, such as the velocity and the turbulence fluctuations, on the stability of stones in bed protections and on the establishment of the physical relationship between the hydraulic parameters and the bed damage. Experimental work is central in this study. The work has resulted into a new stability parameter to better quantify the hydraulic loads exerted on the stones. A physical relationship between flow parameters and the bed damage - expressed as stone transport formulae - has been established for non-uniform flow. Such a relationship provides consistent design criteria and allows an estimate of the cumulative damage over time which is important for making decisions regarding maintenance frequency and lifetime analysis of hydraulic structures.