Wood Load - Unglaciated Unconfined Channels
(Information compiled by Dan Cadol)
The unglaciated unconfined process domain hosts forests that include cottonwood, birch, spruce, and Douglas fir. Click here to go to riparian vegetation page. Wood recruitment to the channel occurs by transport of wood from upstream into the reach and by local recruitment from adjacent sources. Bank instability and channel meandering play an important role in delivering wood to the channel. As the channel migrates across the valley floor, it undercuts trees, causing them to topple into the channel. These large logs may exceed the transport capacity of the channel and persist for decades, potentially forming jams as smaller pieces transported from upstream accumulate on them.
This process domain has a large contributing drainage area, relative to the glaciated confined reaches, and will have a correspondingly higher stream power and transport capacity. However, it also has lower slopes than the confined reaches, which will lead to lower stream power and transport capacity. The balance of these two factors may change from reach to reach in this process domain, meaning that jam frequency and wood load may be variable.
Human land use is most likely to be present in this process domain. For this reason, anthropogenic wood removal is expected to be most prevalent here. Also, historic land uses are expected to have the longest lasting impact in this process domain. The relatively high mobility of wood in these channels suggests that once the jams were removed, the ability of the channel to retain wood was dramatically reduced and is unlikely to have yet recovered (Wohl and Jaeger, in press).
Aspect may affect wood load in the lower elevations. North-facing slopes retain moisture longer and are able to support larger and more closely spaced trees than are south-facing slopes. Where the channel approaches the valley walls, a north- facing slope will be more likely to supply wood to the channel.