Model of alluvial fan development based on channel pattern and gravel size

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In Czech and Slovak the author found some alluvial fans which have a free meander stage on an alluvial fan, an incised meander stage, and development stage of terrace scarp by a straight channel like Polish alluvial fans (Saito, 2002a). Confirming such processes of the fans, the author collected references not only on geomorphological studies but also on sedimentological studies. Hence, the definition of an alluvial fan seems to be serious problem on sedimentological studies. Consequentlty, the problem was explained in detail (Saito, 2001a) and the paper of Blair and McPherson (1994) was translated (Saito, 2001b). In particular, Blair and McPherson (1994) asserted that there are no depositional slopes ranging from 0.5° to 1.5° in nature, but no gap exist on the mean slopes of alluvial fans with over 2km^2 in Japan. Moreover, the author made a list of research areas and keywords on regions of alluvial fans (2002b). In consequent, it is important to get the criteria of a gentle-slope alluvial fan and a steep-slope one and the confidence of the lowest gradient of alluvial fan, probably 1 ‰. Besides, former fan consists of fluvial deposits, while latter one is made of debris flow.