ACG08-01

会場:301A

時間:5 月 24 日 15:15-15:40

森林流域における小流域のばらつきを考慮した地下水流出と集水面積の関係
Relationship between groundwater discharge and catchment area in considering smallscale variability
江草 智弘 1∗
EGUSA, Tomohiro1∗
1
1

東京大学大学院 農学生命科学研究科
Graduate school of Agricultural and Life Sciences, The University of Tokyo

In forested catchments, most of the rainfall infiltrates into the ground, is influenced by evapotranspiration, passes through various pathways, is stored in soil and bedrock layers, and finally discharges to streams. The flow pathways and locations of storagesites regulate the chemical evolution of groundwater. Therefore, to predict stream water discharge and chemistry in forested
catchments, it is necessary to acquire a sufficient understanding of the groundwater dynamics. Many studies, including model
calculations and empirical research, have targeted the relationships between groundwater dynamics and catchment area. Most ofthese studies indicted increases in both groundwater discharge and the contribution of deeper groundwater with catchment area.
However, few studies have considered the spatial variability of groundwater discharge among small catchments. In addition,
there have been few studies with multiple observations of water discharge and chemistry. Therefore, it remains unclear how the
relationships between groundwater and catchment area differ among groundwaters with different flow pathways and whether
there is a disconnection of groundwater discharge processes between small and large catchments. Inokawa catchment (5.07
km2 ), with bedrock consisting of Neogene age sedimentary rock, was examined. Stream water discharge and chemistry were observed at multiple points, and soil water and groundwater chemistry were observed in a hillslope (0.01 km2 ). Using end-member
mixing analysis (EMMA), stream water was separated into a shallow groundwater component, which mainly passes throughand is stored in the soil layer, and a deep groundwater component, which mainly passes through and is stored in the bedrock
layer. The deep groundwater was further divided into three types, CaHCO3 , NaHCO3 , and NaCl types, based on the chemical
characteristics. The relationships between groundwater discharge and catchment area were then examined. Shallow groundwater
discharge decreased with catchment area, while deep groundwater discharge increased with catchment area. In addition, thecontributions of NaHCO3 type and NaCl type groundwater, which were thought to pass through deeper bedrock than CaHCO3
type groundwater, increased largely with catchment area. Both shallow groundwater discharge and all types of deep groundwater
discharge showed large variability in small catchments (<0.1 km2 ). The observed values in larger catchments were all within
the range of observed values in small catchments. The results indicated that a disconnection of groundwater discharge processes
did not occur at this site. However, the NaHCO3 and NaCl types of groundwater were observed at fewer sampling points than
CaHCO3 type groundwater. Therefore, if deeper groundwater pathways become dominant, the disconnection of groundwater
discharge processes between small and large catchments would be expected to become more obvious.
Keywords: groundwater discharge, catchment area, water chemistry, EMMA, scaling

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ACG08-02

会場:301A

時間:5 月 24 日 15:40-15:55

UNCERTAINTY OF DIRECT RUNOFF ESTIMATION FOR FLOOD PREDICTION
BASED ON TOTAL RAINFALL-TOTAL RAINFALL LOSS RELATIONSHIPUNCERTAINTY OF DIRECT RUNOFF ESTIMATION FOR FLOOD PREDICTION
BASED ON TOTAL RAINFALL-TOTAL RAINFALL LOSS RELATIONSHIP
SUPRABA, Intan1∗ ; YAMADA, Tomohito J.1
SUPRABA, Intan1∗ ; YAMADA, Tomohito J.1
11

Hokkaido University
Hokkaido University

One of the main objectives of research in hydrology is to improve the accuracy of direct runoff estimation for enhancing flood
prediction. Rain water falling to the ground surface will infiltrate into the soil and the excess rainfall (effective rainfall) will bedirect runoff. Rainfall loss which is defined as the difference between the observed rainfall and effective rainfall consists mainlyof infiltration with some allowance for interception and depression storage. A previous study applied total rainfall-total rainfall
loss relationship to many catchments in Japan for estimating effective rainfall intensity to simulate direct runoff, and results
showed that the runoff parameters (a and b ) consists of standard deviation values. The standard deviation value of parametera is to show the range of the uncertainty of obtained parameter a which represents the effects of evaporation that affects theinitialization of soil moisture, interception by vegetation cover, or depression storage on the land surface. The purpose of thisstudy is to estimate the uncertainty of direct runoff by using different sets of runoff parameters.
キーワード: Uncertainty of Direct Runoff, Flood Prediction, Total Rainfall-Total Rainfall Loss
Keywords: Uncertainty of Direct Runoff, Flood Prediction, Total Rainfall-Total Rainfall Loss

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ACG08-03

会場:301A

時間:5 月 24 日 16:15-16:40

分布型流出モデルと時空間起源追跡法による基岩地下水の寄与率推定
Estimation of bedrock groundwater contribution with a distributed rainfall-runoff modeland Time-Space Accounting Scheme
佐山 敬洋 1∗ ; 岩見 洋一 1 ; 小杉 賢一朗 2
SAYAMA, Takahiro1∗ ; IWAMI, Yoichi1 ; KOSUGI, Ken’ichirou2
1
1

土木研究所 ICHARM, 2 京都大学大学院農学研究科
ICHARM, PWRI, 2 2) Graduate School of Agricultural Science, Kyoto University

Recent field studies with deep groundwater wells in headwater catchments have demonstrated the importance of groundwaterin weathered bedrock in mountainous regions for controlling the dynamics of streamflow. On the other hand, currently used distributed rainfall-runoff models typically simulate for flows in subsurface soil and on surface by assuming impermeable bedrock.
This may hamper the reasonable representation of rainfall-runoff process at a catchment scale, especially in terms of temporaland spatial source of water.
This study proposes a simple Boussinesq-type distributed rainfall-runoff model simulating for groundwater in weathered
bedrock and unsaturated, saturated subsurface flow in a soil layer as well as overland flow. We apply the model in a Japanesecatchment in Rokko mountain region underlying by weathered granite bedrock. We introduce also Time-Space Accounting
Scheme (T-SAS) for analyzing temporal and spatial sources of water in simulated hydrographs. In particular, this study extends
the original T-SAS algorithm to evaluate flowpath within the model to quantify the contribution of bedrock groundwater. The
case study suggested the importance of the interaction between bedrock groundwater and saturated subsurface flow and the considerably high ratio of groundwater contribution especially during a low flow season. The developed model with T-SAS can be auseful tool to understand hydrologic processes including bedrock groundwater in mountainous catchments.

キーワード: 地下水, 基岩, ブーシネスク式, 貯水量, 花崗岩, 流出経路
Keywords: groundwater, bedrock, Boussinewq equation, storage, granite, flowpath

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ACG08-04

会場:301A

時間:5 月 24 日 16:40-17:05

確率過程論に基づく流出解析における不確実性評価
Uncertainty Estimate in Runoff Analysis Based on Theory of Stochastic Process
Yoshimi Kazuhiro1∗ ; ; 山田 正 2 ; 山田 朋人 3
YOSHIMI, Kazuhiro1∗ ; WANG, Chao-wen1 ; YAMADA, Tadashi2 ; YAMADA, Tomohito3
1

中央大学理工学研究科, 2 中央大学理工学部, 3 北海道大学大学院工学院
Graduate School, Chuo University, 2 Department of Civil and Environmental Engineering ,Chuo University, 3 Graduate Schoolof Engineering, Hokkaido University

1

The aim of this paper is to provide a theoretical framework of uncertainty estimate on rainfall-runoff analysis based on theoryof stochastic process. In this study, we applied SDE (stochastic differential equation) and Fokker-Planck equation to estimate
uncertainty of rainfall-runoff analysis. SDE (stochastic differential equation) based on this theory has been widely used in thefield of mathematical finance due to predict stock price movement. Meanwhile, some researchers in the field of civil engineering
have investigated by using this knowledge about SDE (stochastic differential equation) (e.g. Kurino et.al, 1999; Higashino andKanda, 2001). However, in the field of civil engineering, there have been no researches about uncertainty estimate by using
correspondence relationship of SDE (stochastic differential equation) and Fokker-Planck equation. The Fokker-Planck equation
is a partial differential equation that describes the temporal variation of PDF (probability density function), and there is evidence
to suggest that SDEs and Fokker-Planck equations are equivalent mathematically.
In this paper, therefore, the uncertainty of discharge on the uncertainty of rainfall is explained theoretically and mathematicallyby introduction of theory of stochastic process. The rainfall data is generally used as input data for rainfall-runoff analysis. The
lumped rainfall-runoff model is represented by SDE (stochastic differential equation) due to describe it as difference formula,because the temporal variation of rainfall is expressed by its average plus deviation, which is approximated by Gaussian distribution. This is attributed to the observed rainfall by rain-gauge station and radar rain-gauge system. Moreover, we obtained
the time evolution of PDF (probability density function) of water level or discharge from correspondence relationship of SDE(stochastic differential equation) and Fokker-Planck equation.
As a result, this paper has shown that it is possible to evaluate the uncertainty of discharge by using the relationship between
SDE (stochastic differential equation) and Fokker-Planck equation. Moreover, the results of this study show that the uncertainty
of discharge increases as rainfall intensity rises and non-linearity about resistance grows strong. These results are clarified by
PDFs (probability density function) that satisfy Fokker-Planck equation about discharge. It means the reasonable discharge canbe estimated based on the theory of stochastic processes, and it can be applied to the probabilistic risk of flood management.
Keywords: uncertainty, runoff analysis, lumped model, SDE, Fokker-Planck equation

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ACG08-05

会場:301A

時間:5 月 24 日 17:05-17:20

長期的なトレーサー情報を用いた流域水貯留量の推定
Estimation of catchment scale water storage using high frequency and long-term tracer
information
小田 智基 1∗
ODA, Tomoki1∗
1
1

東京大学大学院農学生命科学研究科
Graduate School of Agricultural and Life Sciences, The University of Tokyo,

In forested catchments, streamwater runoff process and streamwater chemistry are related catchment water storage. To investigate the mechanisms of water flow in forested headwater catchment, water sources, pathways, transit time and water storage
have been estimated using chemical tracer information. Recent studies have modeled catchment streamflow and the responseof isotopes and chemical composition during storm events using a conceptual model and estimated the water storage and transit
time distributions within the flow regime and the relationship to the water source and flow paths.
Considering the field-based water source and time relationship, for example, previous studies have estimated the bedrock
groundwater contribution using the mean transit time (MTT) of bedrock groundwater and streamwater during baseflow. However, the studies that estimated the MTT using tracer information were usually in the baseflow condition. The transit times
during storm events are not clear, as field observations have not been made to test the model results. A newer methodology andobservation system are needed to determine the high spatial and temporal variation in the water time and the source in forested
catchments. In this study, to estimate the catchment scale water storage and the contribution on the water runoff, we considered adata collection strategy using a case study involving long-term high-frequency tracer measurements using the signal of an entire
clear-cut catchment in the Fukuroyamasawa Watershed in the Tokyo University Forest, Chiba, Japan. A time series of Cl concentrations during each flow condition was used to estimate the MTT for various flow regimes. The estimated MTT was 300 to 400
days during high flow, and more than 1200 days during baseflow. From the MTT, the water storage in the catchment could be
estimated. The water storage in the catchment could not be explained by the storage capacity of the soil layer alone; the bedrock
water storage might contribute to water runoff and streamwater chemistry. This suggests that long-term high-frequency tracer
data and focusing on the variation in tracer composition in each flow condition could be used to express the relationship between
the water source and time in the flow regime.

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ACG08-06

会場:301A

時間:5 月 24 日 17:20-17:35

風化基岩流域における複数の手法を用いた地下水流動の推定
Estimation of bedrock groundwater movements using multiple investigation methods at aweathered granite mountain, Japan
藤本 将光 1∗ ; 小杉 賢一朗 2 ; 下垣内 裕哉 1 ; 馬場 直輝 1 ; 正岡 直也 2 ; 深川 良一 1
FUJIMOTO, Masamitsu1∗ ; KOSUGI, Ken’ichirou2 ; SHIMOGAKIUCHI, Yuuya1 ; BANBA, Naoki1 ;MASAOKA, Naoya2 ; FUKAGAWA, Ryoichi1
1
1

立命館大学, 2 京都大学
Ritsumeikan University, 2 Kyoto University

Introduction
Previous studies have noted that bedrock groundwater is one of the important factors influencing stream discharge andstreamwater chemistry. However, most previous studies were conducted not by direct measurement of bedrock groundwater
but by using indirect methods, such as solute tracers and water budget analysis. Thus, the movement and flow path of bedrock
groundwater remain incompletely understood based on direct measurements of bedrock groundwater. To better understand the
dynamics of bedrock groundwater, we evaluated the flow path of bedrock groundwater based on groundwater table movement,water chemistry of bedrock groundwater and elution experiment of bedrock using dense borehole wells at a small catchment ina mountainous area.
Methods
The study was performed at the Fudoji Experimental Watershed located in the Tanakami Mountains in the southeastern part of
Shiga Prefecture, central Japan. Precipitation was monitored using tipping-bucket rain gauges, and discharges were observed ateight small catchments, ranging in area from 0.1 to 2.3 ha. Seven small catchments (subcatchments) were included in the largest
catchment (2.3 ha), within which we installed 61 borehole wells. The water table of bedrock groundwater was then observed atthese borehole wells. Rainwater, streamwater from the small catchments and bedrock groundwater from the borehole wells were
sampled, and the concentrations of major ions and SiO2 as well as the water stable-isotope ratios d18 O and dD were measured in
the Graduate School of Agriculture, Kyoto University. The elution experiment of bedrock obtained by borehole excavation was
conducted to evaluate the elute potential of rock itself. The elution water was analyzed by chemical analysis as described above.
Results and Discussion
The results of the analysis of the groundwater table of bedrock groundwater indicated that there were several fluctuating characteristics and that these characteristics of groundwater table change had locality. At the area having higher altitude in the ridge,
the bedrock groundwater-table changes were gradual but the ranges of fluctuation were larger than those of the lower wells. At
the lower-altitude points, although the bedrock groundwater table responded rapidly, the ranges of fluctuation of the groundwatertable were small relative to those of the higher points. Some areas responded only to peak rainfall over a short time. Based on
the groundwater flux analysis, bedrock groundwater moves across the surface divide. A catchment inflowed by a neighboringcatchment showed a high specific discharge.
The relationships among chemistries derived from the chemical weathering of bedrock indicated that although the weathering
processes were similar in the catchment, the weathering level varied among the borehole wells. The chemistries of bedrock
groundwater at each catchment and of streamwater at each catchment showed large variability. The results of elution experimentand chemical variability of bedrock groundwater suggested that the concentrations of Na+ were high when the bedrock depth
was shallow and the degree of hardness of bedrock was low. In addition, the concentrations of Ca2+ were high as the bedrock
depth deep and the hardness degree of bedrock was high. The concentrations of Na+ and Ca2+ with local characteristics may be
explained by specific flow path and different flow paths of bedrock groundwater across the surface divide. Our study indicatedthat groundwater movements assumed by the groundwater table were different with those estimated by chemical characteristics,
suggesting that complex processes of groundwater flow path and chemical dynamics occur in the weathered bedrock.

キーワード: 基岩地下水, 風化花崗岩, 高密度ボーリング孔, 水質の空間分布, 溶出実験
Keywords: bedrock groundwater, weathered granite, densty borehole, spatial variavility of chemistries, elution experiment

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ACG08-07

会場:301A

時間:5 月 24 日 17:35-17:50

基岩内地下水位の集中観測による流域水貯留量の推定
Intensive monitoring of bedrock groundwater level for estimating water storage capacity
in a headwater catchment
正岡 直也 1∗ ; 小杉 賢一朗 1 ; 杉本 康平 1 ; 藤本 将光 2 ; 水山 高久 1
MASAOKA, Naoya1∗ ; KOSUGI, Ken’ichirou1 ; SUGIMOTO, Kohei1 ; FUJIMOTO, Masamitsu2 ;MIZUYAMA, Takahisa1
11

京都大学大学院農学研究科, 2 立命館大学理工学部
Graduate school of Agriculture, Kyoto University, 2 Collage of Science and Engineering, Ritsumeikan University

1. INTRODUCTION
The mechanisms of bedrock groundwater flow in headwater catchments and their significant contribution to catchment hydrology have been emphasized in recent studies, involving the direct monitoring of bedrock groundwater in intensively drilled
bedrock wells in granitic regions (e.g., Kosugi et al., 2011). The principal goal of these investigations was to clarify the contribution of bedrock groundwater to water storage capacity of a watershed and a discharge hydrograph. In this study, we observed
bedrock groundwater levels from monitoring nested bedrock wells and estimated the amount of bedrock groundwater storage ina mountainous watershed.
2. METHODS
Observations were conducted in the Fudoji Experimental Watershed, underlain by Cretaceous granite. The whole study watershed is referred to as F0, the area of which was 2.3 ha (Figure 1a). Discharge was measured at a V-notch weir at the outlet of thewatershed. Groundwater levels were measured at 67 bedrock wells with depths of 2-42 m. In each well, bedrock groundwater
storage was calculated by multiplying the amount of elevation in groundwater level by local porosity, which was estimated fromweathering class and fissure distribution in each core sample. Within whole watershed, groundwater storage was estimated byinterpolation of wells using kriging method.
3. RESULTS AND DISCUSSION
Figure 1b shows the 2D contour map of the groundwater level (annual average in 2013). In general, the groundwater surface
shows a main valley line, which roughly corresponds to the ground surface topography (Fig. 1a). On the slopes on both sidesof the main valley line, however, the groundwater surface across the slope is mostly planar and does not correspond to the reliefof the ground surface topography. Thus, the bedrock groundwater in both side slopes flows towards the main valley line, mostly
independent of the ground surface topography.
The amount of bedrock groundwater storage showed gradual variation and ranged approximately 80 mm from minimum tomaximum in a year. The waveform of the groundwater storage corresponded to the base flow of discharge hydrograph. Thebase flow can be fitted well by quadratic function of the groundwater storage. However, after the heaviest rainfall event duringobservation period (total: 328 mm), the volume of observed base flow was lower than that of estimated from groundwater storage. This trend lasted for a month after the rainfall event. During that period, the contour map of the groundwater level showeda characteristic shape indicating that a considerable amount of groundwater flows out from F0 across the watershed boundary.
Future studies should analyze long-term data to further clarify the effect of bedrock groundwater on the water budget of specificwatersheds.

キーワード: 基岩内地下水位, 水貯留量, 地下水流, 基底流
Keywords: bedrock groundwater level, water storage capacity, groundwater flux, base flow

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ACG08-07

会場:301A

時間:5 月 24 日 17:35-17:50

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