The (d50) Criterion in Estimating the Bedload in Earthen Channels

الملخص

It is a common tradition to depend on (d50) of the bed-material to estimate the sediment load in earthen channels and consider it appropriate to yield results of acceptable accuracy.The aforementioned concept is reviewed in this research through applications on a practical case study constituted nine existing channels, six of which are in the Middle-Euphrates area. Grain-size distribution analyses have been performed for the bed material of those six channels for the purposes of this research, whereas the available data for the other three were considered. The Einstein [1950] approach for estimating the bedload (as developed by Al-Delewy [2003] to make the approach fully amenable for solution by a computer) is used in this respect. Besides, some new additions were necessary to satisfy the requirements of the research.The bed material of each example channel has been classified into six size-classes. Estimates of bedload were performed, once based on (d50) and then for the classified soil; (PR) has been used to denote the ratio of the former to the latter.Despite that no rigid conclusion can be abstracted from relatively limited applications, the research indicated that the (d50) criterion in some cases is not more than a very rough indicator, particularly with very fine or coarse beds, and especially with mild bed- slopes; the ratio (PR) ranged from (0 %) to (1718 %).An indicator of the classified sizes, called texture coefficient, (TC), has been introduced in the research.....