A numerical simulation to investigate the relation ofrivers and lake to groundwater flow systems inL. Kasumigaura watershed: Research planning
2011.10.13FS 研究勉強会
Graduate School of Life and Environmental SciencesUniversity of Tsukuba
Wang Shiqin
Research Backgrounds
• 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.
Groundwater is important for understanding lake systems because it can influence surface water budget, nutrient budget.
Previous studies in L. Kasumigaura areaResults 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; )
(Nakayama and Watanabe, 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.
To understanding the interaction between surface water and groundwater from a view of groundwater flow system
(J.Toth, 1963) (大井信三 ,国土地理院)
Exchange flow between lake water and groundwater is defined by the local and regional groundwater flow system.
10m
-10
-20
0
BsAcAsdtLmNsYcYsYg
LakeDejima
local
regional
• 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.
Objectives of this research
data collection
3-D Geology Model
3-D Geology Model
Groundwater flow system
Groundwater flow system
Concept modelConcept modelField
experiment
Water chemicals
2H, 18O, 15N, 3H, CFCsNumerical modelNumerical model
VerificationVerification
CalibrationCalibration
Accept
Sensitivity analysisSensitivity analysis
OutputOutput
Water budget
Define Region
Water, salt, isotope BalanceNo
Yes
Model Revise
Flow Chart of the modelingFlow Chart of the modeling
Multi-tracers
Hydrogeo-chemistry
Hydrologic data
Interaction Mechanism between surface water and groundwater
Groundwater model with a finite-difference method
( ) ( ) ( )xx yy zz s
h h h hK K K W S
x x y y z z t
Partial Differential Equations
Modflow
( )( ) ( )
K KK k
ij i s s ni j i
C CD vC q C R
t x x x
1 2
KKK
n b b
CR C C
t
FlowFlow
SoluteSolute
NO3-
δt = δ0 + εln(Ct/C0) (Mariotti et al., 1981)
Denitrification:
nQQQQW ...321
Infinitesimalvolumeof aquifer
Q1 Q2Q3
Most interaction between ground water and surface water is lumped into the W term
Lake-aquifer and river-aquifer system
Lake inflow or outflow:
Lake stage:
Lake-aquifer
River-aquifer
Lakebed
Lake cell
Surface runoff
Interflow
Precipitation
Lake leakage
Outlet stream
Evaporation
Ground-waterdischarge
Aquifer cell with
node
Tributary stream
Lake surface
Lake bottomLakebed
Point in aquifer
Distance from base of lakebed to point in aquifer
Lakebed thickness
Conductance terms
Aquifer
aqaq
aqaq A
thick
KC
aqlkbd
lkbdlkbd A
thick
KC
Cross-sectional area
S. A. Leake
CRIV= Kv (LW)/b
Head here is river head, HRIV
Head here is aquifer head, Hi,j,k
Vertical hydraulic conductivity is, Kv
Length, L
Width, W Thickness, b
7
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 (K i);
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 (K i); 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 (K i); 4. 上岩橋層( Ka); 5. 上泉層( Km); 6. 藪層 ( Yb ) .
• (3.木下層 (K i); 4. 上岩橋層( Ka); 5. 上泉層( Km)) = 成田層
Boundary Conditions: Water head boundary: Lake boundary, River boundary, Flow boundary: Mountain boundary, Upper boundary and bottom boundary.
1
2
3
4
5
6
23
1
140.15 140.2 140.25 140.3 140.35 140.436.05
36.1
36.15
140.15 140.2 140.25 140.3 140.35 140.436.05
36.1
36.15
The groundwater system could be described as a conceptual hydrologic model which was a six layer, heterogeneous, horizontal isotropy, three-
dimensions, transient flow system.
Groundwater dynamics:
Water table (m)
Concentration of Nitrate (mg/l)
2007.5
2007.82007.5
2007.8
0
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