Effects of hillslope topography on hydrological responses in a weathered granite mountain, Japan: comparison of the runoff response between the valley‐head and the side slope

Abstract

Abstract:To evaluate the effects of hillslope topography on storm runoff in a weathered granite mountain, discharge rate, soil pore water pressures, and water chemistry were observed on two types of hillslope: a valley-head (a concave hillslope) and a side slope (a planar hillslope). Hydrological responses on the valley-head and side slope reflected their respective topographic characteristics and varied with the rainfall magnitude. During small rainfall events (<35 mm), runoff from the side slope occurred rapidly relative to the valley-head. The valley-head showed little response in storm runoff. As rainfall amounts increased (35-60 mm), the valley-head yielded a higher flow relative to the side slope. For large rainfall events (>60 mm), runoff from both hillslopes increased with rainfall, although that from the valley-head was larger than that from the side slope. The differences in the runoff responses were caused by differences in the roles of lower-slope soils and the convergence of the hillslope. During small rainfall events, the side slope could store little water; in contrast, all rainwater could be stored in the soils at the valley-head hollow. As the amount of rainfall increased, the subsurface saturated area of the valley-head extended from the bottom to the upper portion of the slope, with the contributions of transient groundwater via lateral preferential flowpaths due to the high concentration of subsurface water. Conversely, saturated subsurface flow did not contribute to runoff responses, and the subsurface saturated area at the side slope did not extend to the upper slope for the same storm size. During large rainfall events, expansion of the subsurface saturated area was observed in both hillslopes. Thus, differences in the concentration of subsurface water, reflecting hillslope topography, may create differences in the extension of the subsurface saturated area, as well as variability in runoff responses.

Topographic controls on shallow groundwater dynamics: implications of hydrologic connectivity between hillslopes and riparian zones in a till mantled catchment

“…Advances in using digital elevation models (DEM) to generate simple topography-based run-off predictions have highlighted the need for detailed field data to characterize how surface topography specifically influences soil moisture, shallow water tables, and run-off Western et al, 1999;Fujimoto et al, 2008). The use of a similarity approach to hydrologic modelling likewise often relies on a DEM to subdivide a watershed into elementary units defined by topography, climate, and soils as a means of characterizing physical processes (Aryal et al, 2002;Harman and Sivapalan, 2009).…”

Characteristics and controls of variability in soil moisture and groundwater in a headwater catchment

“…Anderson and Burt (1978) showed that topography can control matric potential and downslope flow: at their field site, hillslope "hollows" had specific discharge an order of magnitude higher than hillslope spurs. Fujimoto et al (2008) found that topography interacts with storm size to control subsurface processes. For small storms, a concave hillslope stored more water than a planar slope and produced less runoff, whereas for larger storms, transient groundwater in the concave slope caused greater expansion of the saturated area than in the planar slope, and correspondingly greater runoff.…”

Soil thickness effect on hydrological and erosion characteristics under sloping lands: A hydropedological perspective

“…For instance, at the plot scale, Peters et al (1995) found that the runoff hydrographs of the shallow soil plots, compared with the deeper soil plots, closely resembled the shapes of the hyetographs, which were highly responsive to incoming rainfall, with synchronous peak intensities, and showed high recession rates after rainfall cessation. At the hillslope scale, Fujimoto et al (2008) noted that convergent hillslopes with deep soils had delayed runoff responses, whereas hillslopes with shallow soils produced highly peaked hydrographs.…”