Factors Influencing Non-Perennial Stream Initiation in the Mt. Hood National Forest

First Advisor

Martin Lafrenz

Term of Graduation

Summer 2026

Date of Publication

9-25-2026

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Geography

Department

Geography

Language

English

Subjects

ephemeral, headwater, intermittent, Mt. Hood, non-perennial, stream initiation

Physical Description

1 online resource (vii, 37 pages)

Abstract

Historically, non-perennial headwater streams have been overlooked due to their small size and infrequent flow regimes, often leading to them not being recognized as legitimate streams, despite scientific evidence that has shown these streams significantly affect the quality of downstream waters. To combat this issue, environmental managers need to be able to accurately identify and delineate the origins of these streams; however, despite decades of research, an accurate, universal method for predicting how and where these streams commence has yet to be developed. Early studies conducted in steep, humid environments, identified a strong inverse linear relationship between the size of the source area above the channel head and the degree of the local slope measured directly above the channel head. However, many subsequent studies conducted in varying environments have not reported similar results.

To learn more about non-perennial stream initiation, this study evaluated the strength of the slope-area relationship in the Mt. Hood National Forest, and the influence of pedologic, climatic, and geologic variables on the initiation of these streams. To assess how these variables influence stream initiation, field-based and remote geospatial methods were used to survey 30 non-perennial streams, using their channel heads as a proxy for measuring the extent of the channels. Then simple linear regression models, and a multiple linear regression model were used to evaluate how each variable is associated with the initiation of non-perennial streams in the study area.

The regression models showed that a statistically significant relationship between slope and drainage area does not exist for non-perennial streams within the Mt. Hood National Forest. Instead, non-perennial stream initiation is more dependent on soil texture, precipitation regimes, and geology. Overall, throughout the study area, it is assumed that seepage from bedrock is the dominant streamflow mechanism, thus the upstream extent of the streams is primarily dependent on the location of bedrock fractures. However, it is assumed that for a few cases, saturation overland flow was responsible for eroding channels on shallow slopes, and in the western third of the Mt. Hood National Forest, it is assumed that subsurface stormflow, and landsliding may also be responsible for eroding a portion of those channels. Therefore, despite the assumed strong influence of bedrock, it is likely that slope-area, soil texture, and precipitation also partially influenced how and where the non-perennial streams began. In conclusion, to develop a prediction model suitable for management purposes, more research needs to be conducted in this area, specifically focusing on the local bedrock.

Persistent Identifier

https://archives.pdx.edu/ds/psu/45181

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