Groundwater modelling (an Introduction)
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Transcript of Groundwater modelling (an Introduction)
By : Putika Ashfar K
Groundwater Modelling ( Introduction)
References : Gang Ji, Zen.2008. Hydrodynamics and Water Quality: Modeling
Rivers, Lakes, and Estuaries. John Wiley & Sons, Inc., Kumar, C.P. 2013 Numerical modelling of ground water flow
using MODFLOW,Indian Journal of Science. 2(4). 86-92, O. Lehn Franke, Thomas E. Reilly, and Gordon D. 1987. Bennett
Definition of Boundary and Initial Conditions in the Analysis of Saturated Ground-Water Flow Systems – An Introduction. USGS - TWRI Chapter B5, Book 3,
Khadari, S.F.F., Pande, Chaitanya. 2016. Ground water flow modeling for calibrating steady state using MODFLOW software: a case study of Mahesh River basin, India.Model. Earth Syst. Environ. 2(39)
Winston, Richard B., Voss, Clifford I., 2004. SutraGUI - A Graphical User Interface for SUTRA, A Model for Ground-Water Flow with Solute or Energy Transport. USGS
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
1. Groundwater modeling is an important component in water resources system
2. With increasing of groundwater withdrawal,
the groundwater qualiity has been continously deteriorating
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Typically groundwater modeling purposes : 1. To know aquifer properties 2. To know aquifer characteristics 3. Stimulate the response of the aquifer 4. Identify recharge-discharge area 5. Identify groundwater levels
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
General Data Needs 1.Topographics
http://eros.usgs.gov/elevation-products
2. Water Elevation
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
General Data Needs 3. Geological Information
http://landsat.usgs.gov//metadatalist.php
4. Hydrogeologic Properties (maps of K, T distributions)
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
3. Climate data (rainfall, evaporation, precipitation, temperature)
https://pmm.nasa.gov/TRMM
4. Land use (LU)/ land cover (LC) data http://landcover.usgs.gov/landcoverdata.php#asia
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Data Classification Hydrological
1. Hydrograph of groundwater heads and surface water level
2. Maps of K, T distributions 3. Maps of storage properties of aquifer 4. Spatial and temporal distribution of rates of
evaporation, recharge, groundwater pumping, etc
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Data Classification Physical
1. Geological Map (cross section) which is showing the vertical system and boundary
2. Topographic map showing surface water bodies divides (details of drainage, springs, wetlands and swamps)
3. Land use map 4. Contour maps, showing the elevation of
confining bed 5. Isopach maps, showing the thickness of aquifer
and confining bed
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Boundary Types Constant/ Specific Head
Specific Flow
C
D
E
F G
I
H
A B
Constant head (ABC, EFG) Head Dependent Flow
-Could be recharge (CD)
-No flow (HI)
-Free surface / phrearatic surface (CD) -seepage surface (DE)
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Basic Types of Boundary Conditions
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Basic Types of Boundary Conditions Constant Head & Specified Head Boundaries
Specified Head: Head (H) is defined as a function of time and space. Constant Head: Head (H) is constant at a given location.
• Fully penetrating surface •water level
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Basic Types of Boundary Conditions No Flow and Specified Flow Boundaries Specified Flow: Discharge (Q) varies with space and time. No Flow: Discharge (Q) equals 0 across boundary. Hydraulic conductivity contrasts between units – Alluvium on top of tight bedrock. Assume groundwater does not move across this boundary - We can use ground-water divide or flow line
•Precipitation/rainfall •Recharge/discharge area •Wells
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Basic Types of Boundary Conditions Head Dependent Flow
Free Surface: h = Z, or H = f(Z) e.g. the water table h = z or a salt water interface
Seepage Surface: The saturated zone intersects the ground surface at atmospheric pressure and water discharges as evaporation or as a downhill film of flow. The location of the surface is fixed, but its length varies
•Rivers •Spring •Adjacent aquifer
Step 1
Define background
Define purpose(s)
Determine the types of model
Boundary Conditions
Collecting Data
Flow Model
or
Transport Model
Calculate both head and flow
Calculate concentration
h(x,y,t)
c(x,y,t)
output
output
Step 1
Flow Model
Transport Model
Fluid continuity storage Source/sink
h = hydraulic head Kx, Ky, Kz = hydraulic conductivity in x,y,z directions C = substance concentration t = time X = distance U = advection velocity (in x-direction) D = mixing and dispersion coefficient S = source and sink due to settling R = reactivity of chemical / biological process Q = external loading to the aquatic system from point/non-point source
Step 1
Flow Model Transport Model
Geometry
Aquifer Parameter
Inflow/Outflow
-Shape of model area -Thickness and elevation of aquifer
K, T, storage coefficient
-well recharge/discharge -groundwater recharge -boundary flow
Prescribed Head
Obserbved discharge
Initial Hydraulic Parameters
Boundary conditions
Effective porosity
Dispertivities
Input and abstraction of
pollutants
Decay constant
Adsorbtion parameters
Initial distribution of contaminants
Boundary conditions
Source/sink for contaminants
Contaminants loading function
Step 1
Flow Model Transport Model
1. Hydraulic head value (in space, time) 2. Groundwater fluxes (over space time)
1. Contaminants concentrations (in space, time)
2. Contaminant breakthrough curves at specific locations
Step 2
Determine the types of model
Choose code
Result
Verification and calibration
Groundwater modelling software example MODFLOW - MODULAR THREE-DIMENSIONAL FINITE-DIFFERENCE GROUND WATER MODEL, by US Geological Survey (USGS)
Step 2
Determine the types of model
Choose code
Result
Verification and calibration
Groundwater modelling software example Sutra - Model for Ground-Water Flow with Solute or Energy Transport by USGS
Step 2
Determine the types of model
Choose code
Result
Verification and calibration
The calibration process is undertaken until model simulations match the field observations to a reasonable degree. The subsequent sensitivity analysis should be used to test the overall responsiveness and sensitivity of the numerical model to certain input parameters.
match with field data
Not match
Collect field data
Is the result of the model is match with field data ?
Conclusion The model should be used to simulate impacts of human
activities on groundwater flow systems, to formulate sustainable groundwater resources development
scenarios, and to communicate the results to public and decision-makers.