Geology, Geomorphology, and Salmonid Distribution in the
Upper Nehalem Watershed, Oregon
Brandon Snook and Dr. Steve Taylor, Dept. of Earth and Physical Science,
Western Oregon University, Monmouth, OR 97361
Background
Introduction
Mountainous watersheds are
fundamental landscape elements that
form an important setting for local
ecological interactions, human
occupation, and water resource
development. The western Oregon
landscape is associated with active
mountain building and extreme
precipitation patterns that result in a
dynamic geomorphic system
characterized by seasonal flooding,
slope failure, and debris flow activity
(Benda, 1990). Taylor (2002)
conducted GIS-based analyses of
Coast Range watersheds to elucidate
associations between bedrock
composition and slope gradients.
The study revealed that certain
bedrock types are associated with
significantly steeper slopes, wider
valley bottoms, and higher
occurrence of slope failure compared
to others. Understanding the controls
for routing and storage of sediments
in this region are a critical component
of habitat management plans. The
working hypothesis for this study is
that stream gradients, channel
network and valley morphologies will
statistically vary as a function of
bedrock composition and climatically
driven erosion patterns. The model
implies that spatial variation of
bedrock lithology is a primary factor
controlling slope, hillslope delivery
rates, and the resulting sedimenttransport efficiency of the channel
system. This work forms part of a
collaborative partnership between
Western Oregon University, the
Upper Nehalem Watershed Council
and a rapid bio-assessment program
funded by the Oregon Watershed
Enhancement Board (OWEB).
The Nehalem watershed is located in the Coast
Range of northwest Oregon (Fig. 1). This project
focuses on analysis of the geology,
geomorphology and salmonid distribution in the
Upper Nehalem watershed of western Oregon.
Geographic Information Systems, in conjunction
with emerging LIDAR technologies, are used to
analyze and interpret data collected from the
watershed to understand the associations
between bedrock geology, fluvial geomorphology
and fish habitat.
LIDAR Pilot Study
Rock Creek Fish Assessment
The Rock Creek sub-basin of the Upper
Nehalem serves as a key location for
understanding the affects that hillslope failure
and sediment transport has on salmonid
habitats. Emerging LIDAR data from this area
could be crucial in helping local efforts to restore
native salmon populations.
Percent
Summary
Figure 1 - Relief map created by Ryan Stanley
Geologic Setting
The Nehalem watershed is underlain by a
combination of early Tertiary basalts (Tillamook
Volcanics) and marine sedimentary rock (Keasey,
Pittsburg Bluff, and Sager Creek Formations),
both of which underlie a significant portion of the
Northern Oregon Coast Range drainage (Fig. 2).
Preliminary analysis of LIDAR data using GIS
software has proven effective in locating areas
that are prone to hillslope failure. This high
resolution imagery could be useful in analyzing
the effects of this active landscape on salmonid
populations in continuing research in the
Nehalem watershed.
Acknowledgments
Funding for this project provided by Oregon
Watershed Enhancement Board, Nehalem
Watershed Council, and the Oregon Space
Grant Consortium. RBA data collection by
Steve Trask and colleagues at Bio-Surveys,
LLC. Special thanks to Dr. Steve Taylor for his
continuing support and guidance on this project
and my education.
References
Benda, L., 1990, The influence of debris flows on channels and valley floors in the Oregon Coast Range, U.S.A.: Earth Surface Processes and
Landforms, v. 15, p. 457-466.
Taylor, S.B., 2002, Bedrock Control on Slope Gradients in the Luckiamute Watershed, Central Coast Range, Oregon: Implications for Sediment
Transport and Storage: American Geophysical Union Abstracts with Programs, Fall Meeting 2002, San Francisco, California.
Contact
Burns, W.J., and Madin, I.P., 2009, Protocol for Inventory Mapping of Landslide Deposits from Light Detection and Ranging (LIDAR) Imagery:
Oregon Dept. of Geology and Mineral Industries, Special Paper 42, 30 p.Davis, J.C., Statistics and Data Analysis in Geology, 3rd Ed.: Wiley and
Sons, 656 p.
Campbell, J.B., 2007, Introduction to Remote Sensing 4th Ed., The Guilford Press, 626 p.
Brandon Snook
Western Oregon University
bsnook06@wou.edu
Dietrich, W.E., and Dunne, T., 1978, Sediment budget for a small catchment in mountainous terrain:
Zeitschrift fur Geomorphologie Supplementband, v. 29, p. 191-206.
Lefsky, M. A., Cohen, W.B., Parker, G.G., and Harding, D.J., 2002, LIDAR Remote Sensing for Ecosystem Studies: BioScience Journal, v. 52,
no. 1, p.19-35.
Figure 2
Li, Z., Zhu, Q., and Gold, C., 2005, Digital Terrain Modeling: Principles and Methdology: CRC Press, Boca Raton, 323 p.