Groundwater Modeling

Transcription

1 Groundwater Modeling -introduction and some applications in Delaware Presented by: Cangming He Delaware Geological Survey

2 Wat is a groundwater flow model? A groundwater flow model is a matematical representation of ground water system and includes assumptions and simplifications made for various specific purposes. R t S z K z y K y x K x s z y x = + +

3 Wy model? Understanding present groundwater systems -framework for integrating ydrologic data -establising data collection programs Prediction -forecasting future canges in water levels or concentrations -assessing future compliance wit regulatory criteria -analyzing remedial designs

4 Model Data Needs Geomoetric data (x,y,z) DEM, LiDAR, Drilling, Geopysical logs et al. Aquifer properties (k,s) Hydraulic parameters Water stresses (R) Pumping, Recarge, etc. R t S z K z y K y x K x s z y x = + +

5 Numerical Modeling R t S z K z y K y x K x s z y x = + + Inputs Results Visual ModFlow Package

6 Model Output Can develop useful grapics Maps of water level, drawdown, concentration Time series at points Flow vectors Animations

7 Notes: Groundwater flow model is a powerful tool in ydrogeology. A ground water model cannot be used as a substitute for data collection in te field. Model s accuracy/reliability is largely depended on te field data collection.

8 Example 1: Soutern New Castle County Groundwater modeling

9 400X320X9=1,152,000 grids Model Layer Delaware Maryland New Jersey (tis study) unit unit unit 1 Columbia Columbia Water table 2 Confining Confining Confining 3 Rancocas Aquia Vincentown 4 Confining Confining Confining 5 Mt. Laurel Monmout Mt. Laurel 6 Confining Confining Confining 7 Magoty Potomac A Patapsco prm upper 8 Potomac B Arundel (Confining) prm middle 9 Potomac C Patuxent prm lower

10 Aquifer property estimation Specific Capacity (Sc) vs. Transmissivity (T) TT = AA SS cc BB

11 Flow cart of modeling Construct Model Run Model Modify assumptions Adjust input data Compare to calibration targets Analyze outputs Assess model limitations Document, present, and debate results

12 Simulated eads Rancocas aquifer Mt. Laurel aquifer

13 Simulated eads Mag./Pt A aquifer Pt C aquifer Pt B aquifer

14 Head difference between aquifers = Mt. Laurel Mag./ Pt. A

15 Predictions Head canges due to increased pumping Rancocas aquifer Mt. Laurel aquifer Magoty/Pt. A aquifer Pt. B aquifer Pt. C aquifer

16 Example 2: Impacts of sea level rise on agriculture land use in St. Jones River watersed DNREC Sea-Level Rise Tecnical Workgroup 2007

17 Aquifer Two concerns: Water Table Rise Salt Water Intrusion Aquifer

18 Criterion 1: water table dept Effective rooting depts (ERD, Brisson et al., 2002, Mannering, 2007) of local crops. DD mmmmmm DD mmmmmm > 0.5m

19 Criterion 2: Irrigation water salinity Cloride concentration Less tan 600mg/L Delaware Kent County Agricultural Extension, 2007 Salt water

20 Assumptions: Tidal and seasonal variations of sea level are not simulated. Te mars is simulated as a drain. Groundwater discarges to te mars until te sea level rises above te mars land surface. Tereafter all submerged cells form a constant ead boundary. Te river stage, as well as salinity, increases troug time to account for te effect of a laterally encroacing tidal prism due to sea level rise. In te area were te land surface is lower tan te rising sea level, te first layer cells turn into constant ead boundaries wit ead values equal to sea level. Initial condition was obtained by running te model for 1000 years using a constant sea level.

21 Boundary Conditions

22 S1

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25 Ag land loss due to saltwater Ag land loss due to dept criterion Total Ag land loss ectares S1 S2 S3

26 Summary Groundwater flow model is an useful tool in groundwater resource management, even toug it is true tat all te models are wrong due to te simplifications and assumptions. Reliability of model largely depends on te acquirement of tremendous field data.

27 Te END