, 1984, Schumm et al., 1987, Harvey, 2002 and Storz-Peretz et al., 2011). In the concept of “complex response” (Schumm and Parker, 1973 and Schumm, 1977)

suggests that baselevel lowering in a main river channel will influence upstream areas as tributaries or the upstream portion of the main channel incise because of headward knickpoint migration. Erosion in upstream areas increases sediment supply to the downstream channel and may cause it to aggrade. In turn, the downstream channel readjusts through a complex series of responses, including reworking sediment into bars or other landforms and transferring sediment further downstream. Because a lag time often exists between processes and responses, and because one perturbation such as baselevel lowering may lead to multiple Selleck VE-822 responses (e.g. migration of multiple knickzones), understanding and predicting incised channel evolution is challenging. For example, in a southern California system, variable responses

Selumetinib to one wet period occurred because of various controls on sediment storage and transfer at the scale of the watershed (Kochel et al., 1997). During the “Anthropocene,” numerous human activities alter baselevels and influence upstream channel profile development. Examples include: excavation of sediment from channels for aggregate (Florsheim et al., 1998, Marston et al., 2003 and Comiti et al., 2011), flood conveyance (Ellery and McCarthy, 1998), or maintenance of culverts under highways (Florsheim et al., 2001) that may lower baselevel and initiate headward migration of knickzones and incision in upstream reaches. Dam removal for restoration also creates a lowering of baselevel for upstream reaches (Simon and Darby, 1997) where channel adjustments include headcut migration as incision translates upstream through sediment deposited upstream of the former dam (Doyle et al., 2003 and Cantelli et al., 2004). Removal of large woody debris (Williams, 2010 and Wohl, 2013) or artificial grade control

structures those that trap sediment upstream causes similar upstream channel adjustments as when a dam is removed. Numerous human activities may contribute to channel incision locally by altering channel pattern, channelizing reaches that inhibits widening, or lowering channel bed elevations through direct removal of the channel bed sediment. Pervasive channel realignment has caused increases in slope in lowland agricultural systems where channels were straightened to follow property boundaries and roads (Brookes, 1988 and Florsheim et al., 2011). Channelization utilizing hard bank material prevents widening such that flows capable of mobilizing sediment entrain sediment from the bed of the channel, without the ability to adjust channel size to accommodate variability in watershed hydrology or sediment supply (Simon and Rinaldi, 2006 and Hooke, 2006).