Dr. G. Akbari - Department of Civil Engineering, USB, Zahedan, Iran
Dr. A. Hossein nezhad - Asst. Prof. Mech. Engineering, Univ. of Sistan and Baluchestan (USB), Za hedan, Iran

For natural real rivers having graded bed materials, simulating the actual active layer thickness in a bed coarsening and armoring model needs a broad attention and research investigations, because the thickness varies significantly with the variation of hydraulics conditions, geometry of the rivers, the length of the computational time-step, and the gradations and size of the bed materials etc. In a degrading situation, the rate of armoring will depend on the thickness of the active layer. There are various explanations for active layer thickness, bed coarsening, degradation, grain sorting and bed armoring terms used by different researchers. In this paper relative merits and disadvantages of most popular algorithms compared with a new approach, one developed by the Author is discussed. Introduced new approach was tested with field and experimental data, compared with most popular models available in literatures. Sediment deposition and gradation upstream of a river-reservoir, erosion downstream of a dam was studied to test the new model developed (NCMG) for the non-uniform complete solution of graded bed materials in rivers. The active layer introduced in the model worked well for a bed sorting and armoring phenomena investigated downstream of a dam.

Graded Rive Bed, Grain sorting, Armoring