Runoff generation processes estimated from hydrological observations on a steep forested hillslope with a thin soil layer

A paradigm shift in stormflow predictions for active tectonic regions with large-magnitude storms: generalisation of catchment observations by hydraulic sensitivity analysis and insight into soil-layer evolution

“…Stormflow generation was enhanced after HC was created by the water-flow connection in the entire hillslope. The matric potential near the soil surface had a clear positive relationship with the given rainfall intensity, as predicted theoretically from Darcy's law by Rubin and Steinhardt (1963), demonstrating the vertical water movement by the unsaturated flow through the soil matrix instead of the preferential flow (Tani, 1997).…”

“…A similar runoff process was estimated from two small forested catchments, KT (17.3 ha) and MN (Minamitani of 22.6 ha, an adjacent catchment of KT), in TEF (Tani, 1997). The soil was a clay loam derived from the sedimentary rock.…”

“…After the cumulative rainfall exceeds the threshold volume in a large-scale storm, almost all of the additional rainwater tends to be allocated to stormflow (Tani, 1997). Therefore, we can imagine that the entire catchment area eventually contributes to stormflow production, even though some rainwater may still be allocated to deep infiltration in catchments with geologies such as granite (Shimizu, 1980).…”

“…By tracer investigations (Pinder and Jones, 1969;Sklash and Farvolden, 1979), however, the important contribution of pre-event soil water to stormflow was detected, and many well-designed observations were conducted to explain the production of stormflow by soil water movement (Mosley et al, 1979;Pearce et al, 1986;McDonnell, 1990). We now understand that both quick preferential flow and slow water movement within the soil matrix play important roles in stormflow generation processes Tani, 1997), as is also reviewed in Sect. 2 of this paper.…”

Effects of bedrock groundwater on spatial and temporal variations in soil mantle groundwater in a steep granitic headwater catchment

“…Especially since the 1960s, increasing attention has been paid to subsurface flow as a dominant process for runoff generation in humid, soilmantled, and vegetated catchments. Detailed observations have been carried out at various study sites, including the Maimai catchment, New Zealand [Mosley, 1979[Mosley, , 1982Sklash et al, 1986;McDonnell, 1990], LI1 catchment at Llyn Brianne, Wales [Soulsby, 1992], Plastic Lake basin 1-08, Canada [Peters et al, 1995], and Tatsunokuchi-yama Experimental Forest, Japan [Tani, 1997]. The water flow processes in headwater catchments can generally be described as follows: in humid, soil-mantled, and vegetated catchments, most of the rainwater infiltrates into and flows downward through the permeable soil layers, eventually reaching a less permeable layer and forming a transient perched groundwater table.…”