7B). Significant variation exists in active channel width ranging from ∼4.0 to 24 m. Cross sections measured at bridges and near the confluence with Anderson Creek (∼60 m upstream of the confluence) illustrate both deepening and widening of the channel in the downstream direction (Fig. 8). Terrace elevations (measured at the break in slope between the terrace surface and the channel bank) were surveyed whenever accessible from the channel (Fig. 7A). Average bank height (measured between thalweg and top edge
of the adjacent www.selleckchem.com/products/dabrafenib-gsk2118436.html terrace) is ∼4.8 m at upstream end of the study reach and increases to ∼8.0 m at the downstream end, a 40% change in bank height; the maximum bank height measured is 10.1 m (Fig. 7A). The difference between thalweg and terrace slope accounts for greater bank height downstream than in the upstream portion of
the reach, with reach average terrace slope VX-809 cell line of ∼0.0091, ∼20% less than the thalweg slope. Terraces have variable surface elevations that may result from erosion along the edge of the incised channel. For example, in one area between ∼425 m to 630 m on the longitudinal profile, a relict tributary channel is likely present, such that the tributary thalweg elevation remains hanging ∼2.0 m above the channel in Robinson Creek, lowering the apparent terrace elevation along the creek. Stratigraphic evidence suggesting that the incised alluvial unit represents one depositional environment is based on the characteristics of alluvial material exposed in vertical banks along the creek (Fig. 9). Stratigraphy exhibits a massive unconsolidated, fining upward, brownish alluvial unit. The unit is composed of rounded to subrounded sandstone gravel, cobbles and boulders, and subrounded to subangular
metamorphic cobbles, derived from the Franciscan formation rocks exposed in the upstream headwaters. The larger clasts are present within a matrix of finer gravel, sand, silt, and clay (Fig. 9). Local variation is present, with a few exposures exhibiting imbricated gravel clasts, sand lenses, Gefitinib manufacturer and some soil development at the surface. In several locations along the incised channel, yellowish-brown clayey sandy silt exposed beneath the alluvial unit appears to be the surface of a paleosol. The presence of this alluvial unit exposed in channel banks, appears to have been deposited in a single depositional environment, typical of vertically graded floodplain deposits (sensu Wolman and Leopold, 1957 and Allen, 1964), atop a paleosol, suggesting that incision has progressed through a component of Anderson Valley’s Holocene fill deposited prior to the “Anthropocene. Grain size distributions measured at eight locations in the study reach have D50 between 8.5 mm and 38 mm, a relatively large range from boulders to sand ( Fig. 10A). Eroding channel banks composed of unconsolidated non-cohesive alluvial material including cobbles and boulders contribute a portion of the large sized sediment present on the bed of the channel ( Fig.