Review:

# Prospects of Debris Flow Studies from Constitutive Relations to Governing Equations

## Shinji Egashira

NEWJEC Inc., Honjo Higashi 2-3-20, Kita-ku, Osaka 531-0074, Japan

The author thinks keys to debris flow studies lie in 1) sediment sorting in debris flow body, 2) phase shifting to or from fluid to solid, 3) difference between sediment concentration and flux sediment concentration, 4) constitutive relations and 5) governing equations employed in numerical simulation. In discussing 3)-5), the author stresses that 1) Eq. (1) predicts the spatial average sediment concentration of the flow body well from debris flow to bed load, and thus it should be prized, 2) researchers must be careful for the difference between sediment concentration and flux sediment concentration and for different flow structures over erodible and rigid beds, and realizes that 3) many problems associated with governing equations such as bed shear stress, erosion and deposition rates and correction parameters for sediment transport still remain to be solved.

*J. Disaster Res.*, Vol.6, No.3, pp. 313-320, 2011.

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