Stormflow generation in steep forested headwaters: a linked hydrogeomorphic paradigm

Abstract

Abstract:Headwater catchments are sources of sediments, nutrients, and biota for larger streams, yet the hydrologic pathways that transport these materials remain unclear. Dynamics of storm¯ow generation related to landform attributes and antecedent rainfall were investigated in a steep forested headwater catchment at Hitachi Ohta Experimental Watershed, Japan. Such headwater catchments are deeply incised: the narrow riparian corridors have limited capacities to store and transmit water to streams. Storm runo was monitored at several nested scales within the catchment: (1) 2 . 48 ha ®rst-order drainage (FB); (2) incipient 0 . 84 ha ®rst-order drainage (FA) comprized of two zero-order basins; (3) 0 . 25 ha zero-order basin (ZB); and (4) 45 m 2 hillslope segment (HS), including subsurface matrix¯ow (MF) and preferential¯ow (PF). Results from applied tracer and staining tests as well as observations of piezometric, tensiometric, and subsurface temperature responses were also employed to elucidate hydrologic pathways during storms. During the driest conditions, water yield from FB was only 1%; runo occurred as saturated overland¯ow from the small riparian zone and direct channel interception. For slightly wetter conditions, subsurface¯ow from the soil matrix augmented storm¯ow. As wetness increased, two signi®cant non-linear hydrologic responses occurred: (1) threshold response in geomorphic hollows (zero-order basins) where runo initiated after an accumulation of shallow groundwater; and (2) selforganization and expansion of preferential¯ow pathways, which facilitate subsurface drainage. Storm¯ow increases observed during periods of increasing antecedent wetness depend upon temporal and spatial linkages and the unique hydrologic behavior of three components: (1) narrow riparian corridors; (2) linear hillslopes; and (3) geomorphic hollows. These linkages form the basis for an emerging hydrogeomorphic concept of storm¯ow generation for steep forested headwaters. Knowledge of storm¯ow response is critical to the assessment of management practices in these headwater areas as well as the routing of water and materials to larger stream systems.

The significance of soil moisture in forecasting characteristics of flood events. A statistical analysis in two nested catchments

“…This indicates that the soil moisture measured at and near the base of a valley appears more important than the soil moisture conditions at the upper and the middle hillslope. This is consistent with results published by Sidle et al (2000), McGlynn and McDonnell (2003), McGlynn and Seibert (2003) and Klaus et al (2015), who also emphasize the importance of the riparian zone for the runoff response of a catchment. Woods et al (1997) additionally indicate the relevance of riparian zones in the forefront of convergent hillslopes.…”

Contributing sources to baseflow in pre‐alpine headwaters using spatial snapshot sampling

“…sustain baseflow (Tetzlaff and Soulsby, 2008). Other studies showed that during baseflow conditions the riparian zone acts as the main input to streamflow generation (Penna et al, 2014;Sidle et al, 2000). Our studied headwaters were lacking such a valley aquifer and riparian zone.…”

“…The wetlands are prominent landscape units with large storage capacity and areal extent (30-60% of the subcatchment area) but during baseflow these features mostly act as passive units not significantly contributing to baseflow. Consequently, pre-alpine headwaters with similar climate, geology and topography are, during baseflow, not just the sum of different landscape units, but are rather dominated by the arrangement of connected (active) or disconnected (passive) landscape units as conceptualised by Sidle et al (2000) and Ambroise (2004).…”

“…Many mountainous headwaters are characterized by high amounts of precipitation, steep gradients, shallow soils and a mosaic of different landscape units such as forests, meadows and wetlands. Along the steep and deeply incised mountainous stream channels the riparian zone is generally missing (Sidle et al, 2000). For these heterogeneous mountainous headwaters it is still not fully clear which landscape units predominantly contribute to streamflow, and in particular sustain baseflow.…”

The effects of human land use on flow regime and water chemistry of headwater streams in the highlands of Chiapas

“…It is not clear whether this intermittency correspond to the natural flow regime of the study streams or it is caused by land use changes because there are not historical flow records for the study area. Hydrological variability among headwater catchments can be high due to spatial variation in geology, soil depth, topography, and vegetation, and this variation decreases as drainage area reaches 1 km 2 (Woods et al, 1995;Siddle et al, 2000;Gomi et al, 2002;Bruijnzeel, 2004), which is greater than the area of half of our study catchments (Table I). This natural variation among small catchments could explain, in part, differences in flow regime among the study streams.…”