2011.10.13

1. A numerical simulation to investigate the relation ofrivers and lake to groundwater flow systems inL. Kasumigaura watershed: Research planning 2011.10.13 FS研究勉強会 Graduate School of Life and Environmental Sciences University of Tsukuba Wang Shiqin

2. Research Backgrounds Groundwater is important for understanding lake systems because it can influence surface water budget, nutrient budget. Interaction between groundwater and surface water is important to understand the water quality change of a lake system. 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.

3. Previous studies in L. Kasumigaura area ：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 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) (内藤,2008) 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; )

4. To understanding the interaction between surface water and groundwater from a view of groundwater flow system Bs m Ac As 10 dt Lm Ns 0 Yc Ys -10 Yg -20 local regional (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. Dejima Lake

5. 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.

6. Interaction Mechanism between surface water and groundwater Flow Chart of the modeling Define Region 3-D Geology Model data collection Hydrologic data Field experiment Concept model Hydrogeo-chemistry Water chemicals Groundwater flow system Multi-tracers 2H, 18O, 15N, 3H, CFCs Numerical model Water budget Calibration Verification Water, salt, isotope Balance No Accept Yes Sensitivity analysis Model Revise Output

7. Groundwater model with a finite-difference method Infinitesimal volume of aquifer Q3 Modflow Q1 Q2 Partial Differential Equations Flow Most interaction between ground water and surface water is lumped into the W term Solute NO3- Denitrification: δt＝δ0＋εln(Ct/C0) (Mariotti et al., 1981)

8. Lake-aquifer and river-aquifer system USGS Head here is river head, HRIV science for a changing world Lake surface Length, L Lake bottom Lakebed thickness Lakebed Thickness, b Lake-aquifer Width, W Head here is aquifer head, Hi,j,k Tributary stream Vertical hydraulic conductivity is, Kv Outlet stream Conductance terms Surface runoff Interflow Evaporation Distance from base of lakebed to point in aquifer Precipitation Lake cell Aquifer Ground-waterdischarge Lakebed Lake leakage Aquifer cell with node Lake inflow or outflow: Lake stage: S. A. Leake Cross-sectional area Point in aquifer River-aquifer 7 CRIV= Kv (LW)/b

9. Groundwater concept model------as a case of Dejima region 1 2 3 4 1 2 3 5 6 Boundary Conditions: Water head boundary: Lake boundary, River boundary, Flow boundary: Mountain boundary, Upper boundary and bottom boundary. 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

10. Groundwater dynamics: 2007.5 2007.8 Water table (m) 2007.8 2007.5 0 Concentration of Nitrate (mg/l) The groundwater system could be described as a conceptual hydrologic model which was a six layer, heterogeneous, horizontal isotropy, three-dimensions, transient flow system.

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