Effect and design of an underminer structure.

Wooden debris structures are commonly used in stream restoration to alter sediment transport and flow distributions to improve fish habitats in degraded streams. Various wooden structures were tested in a laboratory flume to determine their ability to change flow patterns, resulting in local scour. A parametric study was made to predict scour hole depth. The results indicate that the underminer structure should cover the full channel width and divert the whole flow below the structure. Maximum scour depth was obtained with a single structure perpendicular to the flow direction and overall scour depth was governed by structural height and sediment particle size distribution. With increasing structure angle with respect to flow, the area and volume of the scour hole increase, whereas the scouring depth decreases. Coarser sediment size reduces scour depth for both single and consecutive structures. The optimum underminer spacing ratio was found to be 2 to 3 times the channel width. [ABSTRACT FROM AUTHOR]