How Debris Flow Channels Refill in the Western Cascades Arianna Lambie Advisor: Frederick Swanson Ecosystem Informatics Summer Institute August 2007

Why we care Debris flows change landscapes and influence ecosystems

What influences flow impacts? Frequency Volume

My objectives 1) Quantify material volume Wood Sediment 2) Determine accumulation rates 3) Identify factors influencing accumulation

Methods

Study Site: HJ Andrews Forest

Data Collected Wood –diameter, length, orientation Sediment –width, length, depth, composition, obstruction Channel in general –Slope, width, other observations

Surveying the Channels

Results

Wood and sediment volumes correlate and increase over time

Approximating Accumulation Rates

Large wood is a primary sediment storage mechanism

The Sediment Story Sediment Wood Hillslump Remnant debris flow deposits Material in channel Root throw, Soil creep, and subsequent transport Slump earthflow Previous debris flow Fluvial transport Bedrock channel slope Forest management, Road building Size, age, health of trees Debris flow impacts Debris flow frequency Solid line = transport Dashed = influence

Extending the Study Fill and rework the influence diagram –Compile data from previous studies –Continue channel data collection, plantations Apply math –Fit equations to accumulation rates –Quantify influence pathways Investigate biologic impacts –In channel –Downstream

Summary Frequency Volume Important Debris Flow Characteristics HJ Andrews Forest Sediment and wood accumulate faster than in Coast Range Wood blocks 87% of sediment Implications for forest management that changes wood input Piecing together the sediment budget story