Methods for and fish responses to channel remeandering and large wood structure placement in the Shibetsu River Restoration Project in northern Japan

Abstract

The Shibetsu River Restoration Project intends to reestablish a historic meander pattern by connecting a 3.5-km channelized reach with a series of oxbow lakes that were previously isolated by channel straightening. Prior to full-scale construction, a remeandering experiment (pilot) was conducted upstream of the project segment to assess the methods for and ecological responses to channel remeandering. Large wood (LW) structures were also installed in the experimental remeandering reach. The channel remeandering project with LW placement in a large lowland river is the first undertaken in Asia, and it has rarely been undertaken elsewhere. In this report, we present an overview of the Shibetsu River Restoration Project and the methods for and fish responses to channel remeandering and LW placement in the experiment.

Effects of configuration of instream wood on autumn and winter habitat use by fish in a large remeandering reach

“…Our study reach, which was 470 m long and 25-30 m wide, was located in the downstream section of the Shibetsu River, approximately 8.5 km upstream from the river mouth ( Fig. 1), and was an experimental remeandering reach that had been reconnected with the main channel in the spring of 2002 (Nagayama et al, 2008). The riverbed was composed of sandy gravel.…”

“…These materials were cabled tightly together, anchored to the shore by wires, and laid parallel to the stream current in the channel margin in June 2004. The root wads were placed at the upstream end of the engineered log jams, and the trees were left floating immediately downstream from the root wads (Nagayama et al, 2008). The fish species observed in our study were masu (Oncorhynchus masou) and chum salmon (O. keta), white spotted char (Salvelinus leucomaenis), rainbow trout (O. mykiss), Siberian stone loach (Noemacheilus barbatulus toni), one goby (Gymnogobius opperiens), three sticklebacks [Pungitius sp.…”

“…These indicate that the function of some engineered log jams as fish habitats declined considerably during the winter. This was attributed to the sedimentation of sand and gravel, which caused the burial of wood pieces and a decrease in the available habitats (Nagayama et al, 2008). Therefore, we need to develop installation methods and configurations of log jams that can serve to maintain fish habitats, and we need to recognize that engineered log jams can be used as a tool for interim habitat rehabilitation.…”

Impacts of river alteration for flood control on freshwater turtle populations

“…Artificial riverbank alteration for flood-and bank-erosion control measures, such as riprapping, removal of vegetation, and deepening of river bottoms, are regarded as primary causes of rapid and extensive declines in many freshwater fishes, invertebrates, and mossy vegetation (Miura and Uchida 2004;Nagayama et al 2008;Nakamura and Komiyama 2010). Therefore, various conservation countermeasures, such as reclamation of natural watercourses, removal of dams or weirs that interfere with up-and downstream migration, and facilitation of fish movement among rivers and surrounding shallow marshes for spawning and feeding, have been proposed and implemented (e.g., Wang et al 2002;Pretty et al 2003;Nakamura et al 2006;Nagayama et al 2008;Nakamura and Komiyama 2010).…”

“…Therefore, various conservation countermeasures, such as reclamation of natural watercourses, removal of dams or weirs that interfere with up-and downstream migration, and facilitation of fish movement among rivers and surrounding shallow marshes for spawning and feeding, have been proposed and implemented (e.g., Wang et al 2002;Pretty et al 2003;Nakamura et al 2006;Nagayama et al 2008;Nakamura and Komiyama 2010).…”