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.