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

Abstract:This article discusses preferential flow paths through soil and rock and how these contribute to the style and timing of landslides. The importance of geological compartmentalization because of the presence of aquicludes such as weathered dykes and faults is emphasized as is channel flow through fracture networks and through natural pipes in soil-like material. Although piping is a contributing factor to some landslides, as generally recognized, it can also be a sign of inherent distress in a developing landslide where water flow exploits cracks in the dilating rock mass. It is suggested that the association might be targeted in ground investigation. Inactive or low activity pipe systems can be identified by the anomalous presence of alluvial sediments at depth in the geological profile, whereas active pipe systems may simply comprise voids that could be misinterpreted as core loss during ground investigation. Examples of pipe systems encountered during ground investigations are given for various landslides and several case studies are illustrated in this article. Mitigation measures for preventing landslides triggered by rainfall are discussed together with the difficulties associated with preferential flow paths.

Section: Preferential Flows and Landslidessupporting

confidence: 69%

Preferential flow paths through soil and rock and their association with landslides

Hencher

2010

“…Montgomery and Dietrich (2002) also noted the contribution of rapid lateral flow and slow bedrock flow to runoff generation in a small catchment. In headwater catchments, bedrock is important in controlling soil mantle groundwater generation and water flow processes (Katsura et al , 2008). Therefore, the weathering properties and resultant hydraulic properties of the soil and bedrock are more important than the geomorphic factors in small catchments.…”

Section: Discussionmentioning

confidence: 99%

Connection between streamwater mean residence time and bedrock groundwater recharge/discharge dynamics in weathered granite catchments

Katsuyama

Tani

Nishimoto

2010

We examined the connection between the mean residence time (MRT) of streamwater and the bedrock groundwater recharge/discharge dynamics in weathered granite catchments, the Kiryu Experimental Watershed (KEW), Japan. Several hydrological parameters including discharge, direct runoff ratio, baseflow recession, and bedrock infiltration were measured or estimated at subcatchments within KEW. Although large differences in the rainfall–runoff characteristics were observed among the small catchments, the differences became smaller and stabilized at the larger catchment scale. The key factor in the stabilization was the bedrock groundwater recharge and/or discharge dynamics, which reflected the differences in MRTs among the catchments. Our results suggest a dominant control of MRT by key geological factors, namely bedrock permeability and bedrock groundwater dynamics. In other words, MRT provides much information to consider when addressing hydrological scaling issues and/or estimating rainfall–runoff processes in a catchment, even an ungauged catchment. Copyright © 2010 John Wiley & Sons, Ltd.

“…Numerous studies have shown that this characteristic is due to the large storage capacity of deeply weathered granite bedrock, the depth of which is more than 10 m in the middle of hillslope (Katsura et al, 2008). For example, Kosugi et al (2006) conducted hydrometrical observations at subcatchments within the KI, where they demonstrated that the saturated and unsaturated infiltration from soil to bedrock is a dominant hydrological process at the soil-bedrock interface and that the annual bedrock infiltration ranged from 35% to 55% of the annual precipitation.…”

Section: Runoff Mechanisms and Dependencies On Forest Disturbances Inmentioning

confidence: 97%

“…A dominant contribution of bedrock water has also been confirmed by end-member analysis using SiO 2 and H 2 SO 4 at KI (Katsuyama et al, 2005) and by the water pressure and temperature measurements at F2 . Recently, Katsura et al (2008) directly measured the temporal variations of bedrock groundwater and found that the baseline of the annual runoff variation was controlled by that of the bedrock groundwater on the hillslope. Because of the high weight of bedrock infiltration, stormflow is produced by water escaping from the infiltration in a granite hillslope.…”

Section: Runoff Mechanisms and Dependencies On Forest Disturbances Inmentioning

confidence: 99%

Predicting the dependencies of rainfall‐runoff responses on human forest disturbances with soil loss based on the runoff mechanisms in granite and sedimentary rock mountains

Tani¹,

Fujimoto²,

Katsuyama³

et al. 2011

Self Cite

Abstract:Understanding the effects of severe human induced forest disturbances with soil loss on rainfall-runoff responses is important for future forest management. However, few studies have addressed this issue, which is methodologically difficult compared with the hydrological assessments of the effects of logging. In this study, several small catchments in Japan with different soil and geological conditions were compared using the runoff model HYCYMODEL to reveal their runoff characteristics. The results were then examined on the basis of runoff mechanisms to demonstrate the possible ranges of the effects derived from human disturbances for each geological type. For granite mountains, bare land can be considered the severest case of disturbances leading to high stormflow peaks, although a large baseflow remains because of the water storage fluctuation in weathered bedrock. For sedimentary rock mountains, the severest case may be a forest on the clayey soil without brown forest soil producing flashy runoff characteristics including a large stormflow volume with a sensitive response to the antecedent dryness and a low baseflow rate.