Author(s): Athanasios Thanos Papanicolaou; Dimitrios Dermisis
Linked Author(s):
Keywords: Infiltration; Clast; Spawning gravel; Sand; Gravel bed; Deposition; Restoration
Abstract: Clogging of salmon nests by sediment particles has been reported in the literature as a problem of paramount importance, especially in the Pacific Northwest where large influxes of fine sediment intrude into gravel streambeds. Fine sediment intrusion restricts the supply of oxygenated water into the substrate, which leads to the asphyxiation of the incubating salmonid eggs. In the past, fish biologists and engineers have employed clasts (or boulders) in natural rivers to enhance salmon habitat (e.g., create shelter and rest areas). Little attention, though, has been given on how clasts may affect sediment infiltration within spawning gravels. The overarching objective of this study was to examine the effects of isolated clasts on sediment deposition within a gravel bed. To meet the goal of this study, detailed flume experiments were conducted under different flow conditions, with and without the presence of clasts. Results revealed that less sand was accumulated within the bed when clasts were present. Sand was mainly deposited within the first 8 cm, creating a surface seal. The formation of the surface seal hindered the penetration of sand deeper into the bed. An exponential decrease in the amount of infiltrated sand with depth was recorded below the 8 cm depositional stratum. In addition, clasts were found to work more effectively (i.e., regulate the percentage of sand that intrudes into the streambed) under moderate applied bed shear stress conditions. The findings of this study provide an improved understanding of the role of the clasts on regulating sediment infiltration that will result in more sophisticated science-based river restoration techniques.
Year: 2009