Rainfall‐triggered slope failures in eastern Ireland

Abstract

A rain storm (>1‐in‐200 yr) following high antecedent rainfall in August 1986 triggered four debris slide‐flows on the slopes of the Cloghoge Valley in eastern Ireland. Failures occurred at the bedrock interface underlying shallow (∼1 m) soils on slopes between 19° and 35°. Resistance to shear of the soil ranges from 26 to 32 kN/m² and liquid limits range between 34 percent and 58 percent and these thresholds were exceeded. The debris slides were rapidly transformed into high velocity debris flows that felled trees, stripped bark and incised gullies. The average velocities were estimated to be between 3 and 7 m/s. Factors influencing failure location include local slope morphology, soil depth, preferential groundwater seepage, and natural and anthropogenic surface runoff routing. Conclusions are drawn as to the general mechanisms of small‐scale slope failures resulting from saturating rainfall on upland glaciated slopes.

Key index words:

• Debris flow
• peat slide
• high magnitude rainfall.

Notes

Currently at the Planetary Science Institute, Arizona, USA