Advisor

Martin Lafrenz

Date of Award

Winter 3-4-2013

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Geography

Department

Geography

Physical Description

online resource (vii, 79 pages)

Subjects

Coarse woody debris -- Oregon -- Cummins Creek Wilderness, Fluvial geomorphology -- Oregon -- Cummins Creek Wilderness

DOI

10.15760/etd.658

Abstract

This study uses a spatial model to visualize LWD mobility areas in an approximate 1km reach of Cummins Creek, a fourth-order stream flowing through an old-growth Sitka spruce-western hemlock forest in the Oregon Coast Range. The model solves a LWD incipient motion equation for nine wood size combinations (0.1m, 0.4m, 1.7m diameters by 1.0m, 6.87m, 47.2m lengths) during the 2-year, 10-year, and 100-year discharge events. Model input variables were derived from a combination of field survey, remotely sensed, and modeled data collected or derived between June 2010 and July 2011. LWD mobility map results indicate the 2-year discharge mobilizes all modeled diameters, but mobile piece lengths are shorter than the bankfull channel boundary. Mobility areas for each wood size combination increases with discharge; 10-year and 100-year discharge events mobilize wood longer than average bankfull width within a confined section of the main stem channel, and mobilize LWD shorter than bankfull width within the main stem channel, side channels, and floodplain. No discharge event mobilizes the largest LWD size combination (1.7m / 47.2). Recruitment process was recorded for all LWD during June 2010, revealing that all mobile wood in the study reach was shorter than bankfull width. Based on these conflicting results, I hypothesize the distribution of wood in Cummins Creek can be described in terms of discharge frequency and magnitude, instead of as a binary mobile/stable classification. Mobility maps could be a useful tool for land managers using LWD as part of a stream restoration or conservation plan, but will require additional calibration.

Persistent Identifier

http://archives.pdx.edu/ds/psu/9270

Included in

Geomorphology Commons

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