2011.10.13
FS研究勉強会
A numerical simulation to investigate the relation of
rivers and lake to groundwater flow systems in
L. Kasumigaura watershed: Research planning
Graduate School of Life and Environmental Sciences
University of Tsukuba
Wang Shiqin
Research Backgrounds
Groundwater is important for understanding lake systems because it can
influence surface water budget, nutrient budget.
•
In L. Kasumigaura region, though many policies have been designed to prevent
environmental degradation in the catchment area, the quality of the lake has not
recovered greatly.
•
Nitrogen concentrations in river water are two or three times higher than those in the
lake. And nitrogen concentrations in groundwater are one order of magnitude higher than
those in the lake.
Interaction between groundwater and surface water is important to
understand the water quality change of a lake system.
Previous studies in L. Kasumigaura area
Results of interaction between surface water and groundwater:
1. River and aquifers: surface water receive groundwater inflow.
2. Lake and aquifers: predominant by the inflow of groundwater; there are outflow
in the south.
(村岡・細見,1981;山本,1992; 内藤,2008;中山・渡辺 ,2008; )
：湖水に流出入を繰り返す地点
図．平均動水勾配の分布傾向
(内藤,2008)
Darcy’s law
NICE –LAKE
model
Flow (G/R)
1%, >1%
10%
Nitrate load
(G/R)
1～4.5%
30%
Spatial scale
Around lake
boundary
3-D
Time scale
Determined
period
Transient
The exchange of water and solutes
between groundwater and lakes is
complex and there is still a challenge in
understanding the temporal and spatial
variability across different scales.
(Nakayama and Watanabe, 2008)
To understanding the interaction between surface water
and groundwater from a view of groundwater flow system
local
regional
(J.Toth, 1963)
Exchange flow between lake water
and groundwater is defined by the
local and regional groundwater flow
system.
(大井信三,国土地理院）
Lake
Dejima
m
10
0
-10
-20
Bs
Ac
As
dt
Lm
Ns
Yc
Ys
Yg
Objectives of this research
• To set up a numerical model simulating the
interaction between surface water and
groundwater based on the understanding of the
groundwater flow system.
• To recognize the source of nitrogen in surface
water and groundwater and to study the
mechanism of solute transport (nitrate) from
groundwater to the lake.
• To quantity the temporal and spatial variation of
the flow and Nitrogen load between aquifers and
the lake.
Flow Chart of the modeling
Define
Region
3-D Geology
Model
data
collection
Concept model
Hydrologic
data
Field
experiment
Groundwater flow
system
Hydrogeochemistry
Water
chemicals
Numerical model
Multi-tracers
Calibration
Water budget
Verification
Water, salt, isotope
Balance
No
2H, 18O, 15N,
3H,
CFCs
Accept
Yes
Sensitivity analysis
Model Revise
Output
Interaction Mechanism between
surface water and groundwater
Modflow Groundwater model with a
finite-difference method
W  Q1  Q2  Q3  ...Qn
Partial Differential Equations
Flow
Most interaction between ground
water and surface water is
lumped into the W term

h

h

h
h
( K xx )  ( K yy )  ( K zz )  W  S s
x
x y
y z
z
t
Q3
Solute
 ( C ) 
C


( Dij
)
( vi C K )  qs Csk   Rn
t
xi
x j
xi
K
K
K
K
C
 Rn   b t  1 C K  2 b C
NO3-
Denitrification:
δt ＝δ0＋εln(Ct/C0) (Mariotti et al., 1981)
Infinitesimal
volume
of aquifer
Q1
Q2
Lake-aquifer and river-aquifer system
Lake-aquifer
Lake surface
Tributary
stream
Outlet stream
Surface
runoff
Interflow
Evaporation
Lake bottom
Lakebed
thickness
Conductance terms
Clkbd 
Precipitation
Caq 
Lake cell
Aquifer
cell with
node
Ground-water
discharge
K lkbd
Aaq
thicklkbd
K aq
thick aq
Aquifer
Distance from base of
lakebed to point in aquifer
Aaq
Cross-sectional area
Point in aquifer
Lakebed
Lake
leakage
S. A. Leake
Lakebed
Lake inflow or outflow:
Lake stage:
Head here is river head, HRIV
River-aquifer
7
Thickness, b
Head here is aquifer head, Hi,j,k
Vertical hydraulic conductivity is, Kv
CRIV= Kv (LW)/b
Groundwater concept model
------as a case of Dejima region
Hydrogeology construction
•
Upland: １関東ローム層 （ＹＬ）；２．常総層（Ｊ）；３．木下層 （Ｋi）；4. 上岩橋層（Ka）；
5. 上泉層（Km）；6. 藪層 （Yb）.
Lowland （桜川低地）: 1. 沖積層（A）；2. 桜段丘体積物及び相当層；３．木下層 （Ｋi）
；4. 上岩橋層（Ka）；5. 上泉層（Km）；6. 藪層 （Yb）.
Lowland （霞ヶ浦低地）: 1. 表土（Bs）；2. 砂質帯水層（As）；３．木下層 （Ｋi）；4. 上岩
橋層（Ka）；5. 上泉層（Km）；6. 藪層 （Yb）.
（３．木下層 （Ｋi）；4. 上岩橋層（Ka）；5. 上泉層（Km））=成田層
•
•
•
1
2
3
4
1
3
2
5
6
Boundary Conditions:
Water head boundary: Lake boundary, River boundary,
Flow boundary: Mountain boundary, Upper boundary and bottom boundary.
Groundwater dynamics:
36.15
36.15
36.1
36.1
2007.5
2007.8
36.05
140.15
140.2
140.25
140.3
140.35
140.4
36.05
140.15
140.2
140.25
140.3
140.35
140.4
Water table (m)
2007.5
Concentration of Nitrate (mg/l)
2007.8
0
The groundwater system could be described as a conceptual hydrologic
model which was a six layer, heterogeneous, horizontal isotropy, threedimensions, transient flow system.
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