HR: 0800h
AN: H11C-0675    [Abstracts]
TI: Evaluating Channel Head Conditions for Environmental Impact Assessment in Northwestern Sonoma County, California
AU: * Sherwood, M N
EM: msherwood@oe-i.com
AF: O'Connor Environmental, PO Box 794, Healdsburg, Ca 95448, United States
AU: O'Connor, M
EM: matto@oe-i.com
AF: O'Connor Environmental, PO Box 794, Healdsburg, Ca 95448, United States
AU: Pennington, R
EM: robertp@oe-i.com
AF: O'Connor Environmental, PO Box 794, Healdsburg, Ca 95448, United States
AB: Erosion and sedimentation have been identified as processes significantly affecting water quality in northern California Coast Range watersheds. These watersheds, including the Gualala River watershed in northwestern Sonoma County, have been designated as having water quality impaired by sediment under provisions of the Clean Water Act Section 303(d). A study was performed to estimate potential increases in erosion rates resulting from proposed vineyard development of ridge top forestland in the Gualala River watershed. The study area has an extensive history of logging, with substantial ground disturbance from tractors. The study area is characterized by flat ridge tops with steeply incised drainages shaped by debris slides, rock slides and earth flows. Jurassic age sedimentary and meta-sedimentary rocks of the coastal and central belt Franciscan formation comprise the underlying bedrock. Channel head development and advancement has long been understood to play a key role in sediment delivery and is possibly the most sensitive to changes in the external factors such as changes in climate or land use (Dietrich and Dunne 1993). Quantifying the amount of sediment contributed by potential channel head incision and/or initiation is an objective of environmental analysis for the project. Field surveys were performed during the field seasons of 2005 and 2006 to acquire measurements of channel head locations and slope, channel dimensions and substrate associated with the proposed development sites. Analysis of this field data, including the use of ArcGIS, allowed us to examine the local relationships between variables that influence channel initiation. Variables considered include drainage area, slope, soil type, geology and vegetation. An initial analysis of a selection of area-slope data failed to produce an inverse area-slope relationship as has been found in previous studies by Montgomery and Dietrich (1988). A more complete evaluation of the entire data set is presented here.
DE: 0496 Water quality
DE: 1815 Erosion
DE: 1825 Geomorphology: fluvial (1625)
DE: 1861 Sedimentation (4863)
SC: Hydrology [H]
MN: 2007 Fall Meeting