Localized bedrock aquifer distribution explains discharge from a headwater catchment

Abstract

[1] Understanding a discharge hydrograph is one of the leading interests in catchment hydrology. Recent research has provided credible information on the importance of bedrock groundwater on discharge hydrographs from headwater catchments. However, intensive monitoring of bedrock groundwater is rare in mountains with steep topography. Hence, how bedrock groundwater controls discharge from a steep headwater catchment is in dispute. In this study, we conducted long-term hydrological observations using densely located bedrock wells in a headwater catchment underlain by granitic bedrock. The catchment has steep topography affected by diastrophic activities. Results showed a fairly regionalized distribution of bedrock aquifers within a scale of tens of meters, consisting of upper, middle, and lower aquifers, instead of a gradual and continuous decline in water level from ridge to valley bottom. This was presumably attributable to the unique bedrock structure; fault lines developed in the watershed worked to form divides between the bedrock aquifers. Spatial expanse of each aquifer and the interaction among aquifers were key factors to explain gentle and considerable variations in the base flow discharge and triplepeak discharge responses of the observed hydrograph. A simple model was developed to simulate the discharge hydrograph, which computed each of the contributions from the soil mantle groundwater, from the lower aquifer, and from the middle aquifer to the discharge. The modeling results generally succeeded in reproducing the observed hydrograph. Thus, this study demonstrated that understanding regionalized bedrock aquifer distribution is pivotal for explaining discharge hydrograph from headwater catchments that have been affected by diastrophic activities.Citation: Kosugi, K., M. Fujimoto, S. Katsura, H. Kato, Y. Sando, and T. Mizuyama (2011), Localized bedrock aquifer distribution explains discharge from a headwater catchment, Water Resour. Res., 47, W07530,

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“…Although piezometers can give significant, yet local, insights on the groundwater system (Kosugi et al 2011;Padilla et al 2014), their cost, their short lifespans in unstable areas and their poor representativeness make piezometers seldom used in landslide studies (Michoud et al 2013). Consequently, recent studies focus on indirect methods such as hydrochemistry surveys by monitoring springs for natural and artificial tracers (Bogaard et al 2007).…”

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