Solifluction is a process where soil is saturated and starts flowing over a slope. The first application that included solifluction in LAPSUS, was Temme and Veldkamp’s study in South Africa.
Case Studies: » South Africa
Knowledge of the controlling factors of solifluction is incomplete, though the positive influence of slope and seasonal saturation and the negative influence of vegetation are known (e.g.Matsuoka, 2001). Realizing moreover that solifluction is accelerated creep (Matsuoka et al., 2005) that behaves in a less diffusive way, Follain’s (2006) implementation of creep was adapted to describe solifluction.In this implementation, the sum of outflow and infiltration is used as a proxy for saturation. Moreover, the stabilizing role of vegetation is included:
Where qS is the volume of creep (m t-1), Ds is the diffusivity for solifluction under complete vegetation cover (m2 t-1), cellsize is in (m), tan α is the tangent of slope (-), V is relative vegetation cover (-) and with solifactor (-):
Where outflow and infiltration are in (m3). Minimum and maximum values for solifactor are set to 1 and 5. The difference in diffusive behaviour is captured with a variation of Holmgren’s multiple flow direction algorithm (1994):
Solifactor here determines the diffusivity of the flow of sediment, with solifactor=1 dividing flow proportional to the tangent of slope and solifactor=5 resulting in practically all flow directed to the steepest neighbour.
This implementation leads to more solifluction and less diffusive behaviour with increasing saturation of the soil.
Seasonality of rainfall is ignored in the implementation above. Yet, the distribution of rainfall over a year is crucial for solifluction because it determines seasonal saturation of the soil (Matsuoka, 2001). It seems a good idea to correct for differences in seasonality when data about them are available.
- Follain, S., Minasny, B., McBratney, A.B. and Walter, C., 2006. Simulation of soil thickness evolution in a complex agricultural landscape at fine spatial and temporal scales. Geoderma, 133(1-2): 71-86.
- Matsuoka, N., 2001. Solifluction rates, processes and landforms: a global review. Earth-Science Reviews, 55(1-2): 107-134.
- Matsuoka, N., Ikeda, A. and Date, T., 2005. Morphometric analysis of solifluction lobes and rock glaciers in the Swiss Alps. Permafrost and Periglacial Processes, 16(1): 99-113.