Cross sections surveyed by Mendocino County Water Agency between 1996 and 2005

further downstream at Mountain View Bridge indicate fluctuations typical of short-term geomorphic change, with ∼0.8 m of incision during the water year 1998 flood, followed by an increase in bed elevation back almost to the 1996 level in 2001. Between 2001 and 2013, incision lowered the bed by about 0.37 m. Bed elevation fluctuation of erosion or deposition during any one flood is common and longer-term monitoring data is warranted to assess trends. Measurements in a reach of Robinson Creek ∼2.4 km upstream of the mouth measured incision using exposed Akt inhibitor roots of riparian California Bay Laurel Trees as an indicator. In this location, the root systems of numerous trees are fully exposed along both banks of the incised channel. Measured bank heights between the channel bed and the surface of the lateral roots in 2008 reached 2.0 m on average (Fig. 6A). Because trees establish on level alluvial surfaces such as on a creek’s floodplain, vertical banks present below the tree’s root systems clearly indicate incision. In 2013, we assessed tree rings in a core from one of

the undercut trees (main stem diameter ∼198 cm) and assume it is representative of numerous nearby undercut trees of similar size. Portions of the core are indistinct, selleck kinase inhibitor including the heart of the core (Fig. 6B); and because the tree rings are not cross correlated or dated, the core does not give an absolute age. However, about 83 rings are visible, suggesting that the tree established prior to 1930. Because these trees can reach 200 years when mature, we estimate these stream-side trees established sometime after about 1813 and before 1930—and that incision began after their establishment. We examined incision in the study reach through surveyed thalweg, bar crest, and top of bank/edge terrace elevation profiles (Fig. ROS1 7A). The thalweg profile has a reach average slope of ∼0.012. Contrasting the

three channel segments between bridges (Table 1) illustrates that the downstream portion of the reach is steeper than the upstream portion. Variation in bed topography is present despite incision; the thalweg profile exhibits irregularly spaced riffles and pools (Fig. 7A). However, pools present have relatively shallow residual depths (the maximum depth of the pool formed upstream of a riffle crest; sensu Lisle and Hilton, 1999); 60% have a residual depth less than 0.6 m. Several pools contained water during the summer of 2005 and 2008 when the majority of the channel was dry. Variation in bed topography is also exhibited in steeper than average apparent knickzones, with slopes of ∼0.018 ( Fig. 7A). Bars are present in the channel (Fig. 7A); the reach averaged bar crest slope is similar to the thalweg slope, 0.012. Average bar height is ∼0.6 m above the thalweg.