Influence of bedrock groundwater on streamflow characteristics in a volcanic catchment

Abstract

Groundwater movements in volcanic mountains and their effects on streamflow discharge and representative elementary area (REA) have remained largely unclear. We surveyed the discharge and chemical composition of spring and stream water in two catchments: the Hontani river (NR) catchment (6.6 km2) and the Hosotani river (SR) catchment (4.0 km2) at the southern part of Daisen volcano, Japan. Daisen volcano is a young volcano (17 × 103 years) at an early stage of erosion. Our study indicated that deep groundwater that moved through thick lava and pyroclastic flows and that could not be explained by shallow movements controlled by surface topography contributed dominantly to streamflow at larger catchment areas. At the NR catchment, the deep groundwater contribution clearly increased at a catchment boundary defined by an area of 3.0 km2 and an elevation of 800 m. At the SR catchment, the contribution deep groundwater to the stream also increased suddenly at a boundary threshold of 2.0 and 700 m. Beyond these thresholds, the contributions of deep bedrock groundwater remained constant, indicating that the REA is between 2 and 3 km2 at the observed area. These results indicate that the hydrological conditions of base flow were controlled mainly by the deep bedrock groundwater that moved through thick lava and pyroclastic flows in the undissected volcanic body of the upper part of the catchment. Our study demonstrates that deep and long groundwater movements via a deep bedrock layer including thick deposits of volcanic materials at the two catchments on Daisen volcano strongly determined streamflow discharge instead of the mixing of small‐scale hydrological conditions. Copyright © 2015 John Wiley & Sons, Ltd.

An Increase in Specific Discharge With Catchment Area Implies That Bedrock Infiltration Feeds Large Rather Than Small Mountain Headwater Streams

“…Specific discharge did not increase systematically with catchment size over about 30 km 2 (O, P, and Q) in any of the three campaigns (Table 2 and Figures 4d, 4f, and 4h), but the number of locations was limited and the data were scattered, and therefore more information is required to validate this threshold area. Some previous studies have identified a catchment area in which constant specific discharge is reached (Fujimoto et al, 2016; Shaman et al, 2004). The threshold areas in volcanic rock catchments reported by Fujimoto et al (2016) coincided with the boundary between thick lava and pyroclastic flow deposition and a dissected channel that eroded headward, intersecting the flow paths of deep groundwater in the upper part of the catchment.…”

“…Some previous studies have identified a catchment area in which constant specific discharge is reached (Fujimoto et al, 2016; Shaman et al, 2004). The threshold areas in volcanic rock catchments reported by Fujimoto et al (2016) coincided with the boundary between thick lava and pyroclastic flow deposition and a dissected channel that eroded headward, intersecting the flow paths of deep groundwater in the upper part of the catchment. Meanwhile, in the catchment of Devonian sedimentary rock and glacial till deposits investigated by Shaman et al (2004), water infiltrated into bedrock through fractures and mostly discharged at the base of a steep slope.…”

“…The first pattern observed in such studies is that specific discharge is almost constant and independent of catchment area for areas up to about 100 km 2 (Figure 1a; see also Asano et al, 2009;Lyon et al, 2012;Wood, 1995). The second pattern is that specific discharge increases with catchment area (Figure 1b; e.g., Fujimoto et al, 2016;Shaman et al, 2004), presumably because of the contribution of groundwater flow paths, as demonstrated theoretically by Tóth (1963). The third pattern is a decrease in specific discharge with catchment area during low-flow conditions (Figure 1c; Floriancic et al, 2019;Tetzlaff & Soulsby, 2008).…”

“…In this study, we focused on the pattern of increasing specific discharge with catchment area (Figure 1b). Previous studies using geochemical tracers have shown that an increase in specific discharge is associated with increased deep groundwater/bedrock groundwater exfiltration (Egusa et al, 2016;Fujimoto et al, 2016;Shaman et al, 2004), which is less significant or absent in smaller catchments. Groundwater in weathered or fractured bedrock can contribute substantially to the response of runoff to rainfall in small catchments in steep headwaters (e.g., Anderson et al, 1997;Komatsu & Onda, 1996;Onda et al, 2001Onda et al, , 2006Uchida et al, 2003).…”

Climate, Landforms, and Geology Affect Baseflow Sources in a Mountain Catchment

“…The study area is separated by faulting from the regional groundwater of the High Cascades (Ingebritsen et al, 1994), indicating that the groundwater source to Cold Creek is likely local. Other studies have also illustrated that springs emerging from lava flow deposits are an important source of baseflow (Fujimoto et al, 2016;Jefferson et al, 2006).…”