Abstract
Importance of small-size material on invertebrate dynamics has been pointed out in previous studies. For clarifying the reference diameter that greatly affects the dynamics, invertebrate was sampled on the downstream riffle of Futase Dam. The average body length of the 4 invertebrates are around 4-14mm and related small particle size are supposed around 1.4-4.1 mm. Five methods for sampling large and small gravel-sand particles were tested. Image analysis that represents macro roughness has a possibility not to count small size particles. Combined method that uses appropriate methods for macro and micro roughness has been proposed. The method can represent the small size particle which is related to the drift phenomenon of invertebrates.
