Debris Flow Occurrence and Sediment Persistence, Upper Colorado River Valley, CO

Area of Science:

• Geomorphology
• Hydrology
• Environmental Science

Background:

• Understanding debris flow dynamics is crucial for assessing landscape change and establishing historical range of variability (HRV).
• The Upper Colorado River valley's geomorphic setting and potential human influences on natural processes warrant investigation.

Observation:

• Debris flow magnitudes and frequencies were analyzed using dendrochronology, field mapping, and aerial photography.
• A 19th-century earthen water-conveyance ditch was examined for its potential impact on debris flow occurrence in the Colorado River headwaters.

Findings:

• No significant difference in debris flow frequency was observed between the east and west sides of the valley over the last century.
• Four of the five largest debris flows originated on the west side, associated with the earthen ditch, suggesting human alteration of the debris flow regime.
• Valley confinement significantly influences debris flow deposit volumes and sediment persistence.

Implications:

• The earthen ditch has likely increased the frequency of large debris flows, exceeding the historical range of variability.
• Valley confinement ratios are valuable tools for land managers to delineate areas susceptible to persistent debris flow effects.
• Altered debris flow regimes due to human activity have long-term geomorphic consequences.