Groundwater Modelling of Ganga Basin

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Prof. S. N. PandaHead, School of Water Resources

• Groundwater Modelling of Ganga Basin
  Opportunities and Challenges

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Physiography and groundwater flow of Ganga basin
(Source Ministry of Environment and Forests,
Government of India)
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Annual groundwater draft in comparison with net
annual availability in Ganga basin
(Source Ministry of Environment and Forests,
Government of India)
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Annual replenishable groundwater in comparison
with annual draft in Ganga basin
(Source Ministry of Environment and Forests,
Government of India)
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Schematic illustration for evaluating
stream-aquifer interaction
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• Problems with groundwater in the Ganga Basin
• Imbalance in groundwater draft
• Waterlogging and salinity in canal commands
• Groundwater pollution

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Types of Terrestrial Water
Surface Water
Soil Moisture
Ground water
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Movement of water through the hydrologic cycle
(Source usgs.gov)
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Effluent and influent streams
Gaining stream
Losing stream with shallow watertable
Losing stream with deep watertable
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Water Balance Concept

• The basic concept of groundwater balance is
• Input to the system - outflow from the system
  change in storage of the system (over a period of
  time)

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Flow components for assessing groundwater balance
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Groundwater Balance Equation Considering the
various inflow and outflow components in a given
study area, the groundwater balance equation can
be written as Rr Rc Ri Rt Si Ig
Et Tp Se Og ?S
where, Rr recharge
from rainfall Rc recharge from canal
seepage Ri recharge from field
irrigation Rt recharge from tanks
Si influent seepage from rivers Ig
inflow from other basins Et
evapotranspiration from groundwater Tp
draft from groundwater Se effluent
seepage to rivers Og outflow to other
basins and ?S change in groundwater
storage
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Groundwater Survey and Investigation

• Water table contour map

Water table contour map showing a local mound and
depression in water table and direction of
groundwater flow
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Flow net
Flow net technique for estimation of subsurface
horizontal flow
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Depth-to-Water Table Map or Isobath Map
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Groundwater Quality Map
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• Components of a Mathematical Model
• Governing Equation
• (Darcys law water balance equation) with head
  (h) as the dependent variable
• Boundary Conditions
• Initial conditions (for transient problems)

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General governing equation for steady-state,
heterogeneous, anisotropic conditions, without a
source/sink term
with a source/sink term
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Change in concentration with time

• is porosity
• D is dispersion coefficient
• v is velocity

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Model Grids
Finite Element Grid
Finite Difference Grid
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Modelling Process
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Opportunities and Challenges in the Ganga Basin

• Wide variation in climate from semi-arid to
  sub-humid/sub-tropical regions
• Large-scale spatial variation in
• Soil texture and land-use
• Type of aquifers and its properties
• Spatio-temporal variation in
• - meteorological parameters associated
  with uncertainties
• - groundwater recharge and discharge
  components
• Groundwater level monitoring is not being done
  regularly and intensively
• Setting up/optimising monitoring networks and
  setting up groundwater protection zones
• Groundwater resources too need to be planned and
  managed for maximum basin-level efficiency.

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THANK YOU
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• Diversified geological climatological and
  topographic set-up, giving rise to divergent
  ground water situations
• Excessive use of our rivers, are causing
  downstream problems, of water quality and
  ecological stress.
• Climate change impacts directly on the
  availability of water resources both in space and
  time.
• The precarious balance between growing demands
  and supplies brings forth the importance of
  maintaining quality of both surface and ground
  water.

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• Application of existing groundwater models
  include water balance (in terms of water
  quantity)
• gaining knowledge about the quantitative aspects
  of the unsaturated zone
• simulating of water flow and chemical migration
  in the saturated zone including river-groundwater
  relations
• assessing the impact of changes of the
  groundwater regime on the environment

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State-wise distribution of the drainage area of
Ganga river
(Source Status paper on river Ganga, NRCD, MoEF,
2009)
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Soil types in Ganga basin
(Source Central Pollution Control Board,
National River Conservation Directorate (MoEF)
(2009))
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• Data requirement for groundwater balance study
  over a given time period
• Precipitation
• River
• Canal
• Tank
• Water table
• Groundwater draft
• Aquifer parameters
• Land use and cropping patterns

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• Management of a groundwater system, means making
  such decisions as
• The total volume that may be withdrawn annually
  from the aquifer.
• The location of pumping and artificial recharge
  wells, and their rates.
• Decisions related to groundwater quality.
• Groundwater contamination by
• Hazardous industrial wastes
• Leachate from landfills
• Agricultural activities such as the use of
  fertilizers and pesticides

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Groundwater Modelling

• The only effective way to test effects of
  groundwater management strategies
• Conceptual model Steady state model
  Transient model
• Processes
• Groundwater flow (calculate both heads and
  flow)
• Solute transport requires information on flow
  (calculate concentrations)

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Model Design

• Conceptual Model
• Selection of Computer Code
• Model Geometry
• Grid
• Boundary array
• Model Parameters
• Boundary Conditions
• Initial Conditions
• Stresses

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Modelling Process
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General governing equation for transient,
heterogeneous, and anisotropic conditions
Specific Storage Ss ?V / (?x ?y ?z ?h)
Kx, Ky, Kz are components of the hydraulic
conductivity
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• Types of Solutions of Mathematical Models
• Analytical Solutions h f(x, y, z, t)
• Numerical Solutions
• Finite difference methods
• Finite element methods

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Model Design

• Conceptual Model
• Selection of Computer Code
• Model Geometry
• Grid
• Boundary array
• Model Parameters
• Boundary Conditions
• Initial Conditions
• Stresses

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Managed Aquifer Recharge
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• Suitability of groundwater in increasing dry
  season productivity in the coastal region of the
  Ganga basin
• How the recharge mechanisms can be used to reduce
  salinity.
• Climate change impact on groundwater.

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Methods for groundwater recharge
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• Management of Excess Rainwater

• Mismatch between water supply and demand

• Possible solutions

• Rainwater conservation and recycling

• Multiple use of harvested water

• Managed aquifer recharge

• Management of stagnant water in lowland areas

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Rainwater Conservation

• a. Storage of rainwater on surface reservoir
• b. Recharge to ground water
• Pits
• Trenches
• Dug wells
• Hand pumps
• Recharge wells
• Recharge shafts
• Lateral shafts with bore wells
• Spreading techniques

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Methods of Rainwater Storage

• Infiltration
• Injection

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Benefits

• Ideal solution to water problems in water stress
  areas
• Capture and storage of water in monsoon when
  rainwater is abundant
• More water will be available for summer use
• Rise in groundwater level - Improves declining
  aquifers
• May increase base flow to streams
• Mitigates the effects of drought
• Reduces the runoff which chokes the storm water
  drains
• Flooding of roads and low land areas are reduced
• Quality of water improves
• Soil erosion will be reduced
• Saving of energy per well for lifting of ground
  water 1 m rise in water level saves about 0.40
  KWH of electricity

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What is Managed Aquifer Recharge (MAR)?

• Managed Aquifer Recharge is
• The infiltration or injection of water into an
  aquifer
• Water can be withdrawn at a later date but also
  left in the aquifer (e.g. to benefit the
  environment)

Why Consider MAR?

• Allows storage of water in wet seasons
• Improvement in groundwater quality
• Allows increased use of groundwater from other
  parts of the aquifer systems
• To stop seawater intrusion in coastal areas
• To maintain or increase available water supplies
  for use in agriculture, drinking water supply,
  and industry

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The point of origin of the Ganga, known as the
Gangotri (left) and Devprayag, the point of
confluence of the Alaknanda (from right) and
Bhagirathi (from left) to form the Ganga (right).
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Ganga River Basin, India

• The river systems in India are grouped into four
  broad categories
• The Himalayan rivers
• The Peninsular rivers
• The Coastal rivers
• The Inland rivers
• The Ganga River (length 2525 km long catchment
  area 861404 km2) is fed by runoff from
• Vast land area bounded Himalaya in the north.
• Peninsular highlands and the Vindhya Range in
  the south.
• The states of Haryana, Rajasthan, Uttar Pradesh
  and West Bengal, comprising 50 of the basin
  area.
• The basin spreads over four countries India,
  Nepal, Bangladesh and China.

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Soil and rainfall (isohyetal) map of Ganga
Basin(Source Ministry of Environment and
Forests, Government of India)
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Vegetation Types of Ganga Basin(Source
Ministry of Environment and Forests, Government
of India)
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• Groundwater
• An important component of water resource systems
  and source of clean water.
• More abundant than Surface Water
• Extracted from aquifers through pumping wells and
  supplied for domestic use, industry and
  agriculture.
• With increased withdrawal of groundwater, the
  quality of groundwater has been continuously
  deteriorating.
• Linked to Surface Water systems and sustains
  flows in streams

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Groundwater in Hydrologic Cycle
(Source physicalgeography.net)
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Dynamic Groundwater Resources of India

• Total replenishable groundwater in the country
  433 BCM
• 5,723 units (blocks, talukas, mandals, districts)
  assessed
• 15 over-exploited
• 4 critical
• 10 semi-critical
• Delhi, Haryana, Punjab, Rajasthan are overusing
  their groundwater resources.
• Andhra Pradesh has the highest number of
  over-exploited units.
• The agricultural (tube-well dependent) state of
  Punjab has developed (usage compared to
  availability) its groundwater upto 145.
• Delhi is mining 170 of its groundwater.
• Countrywide percentage of groundwater development
  is 58.

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Annual replenishable groundwater in comparison
with annual draft in Ganga basin
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• Ground Water and Surface Water Interaction
• Ground water and surface water contained in the
  hydrological system are closely interrelated
• The studies examines the processes of ground
  water flow generation and estimation of ground
  water discharge including ground water discharge
  to rivers (base flow)
• In a ground water basin, it is common to identify
  several aquifers separated either by less
  permeable or impermeable layers

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• the upper aquifer is recharged through the bed
  and banks of the river. The lower aquifer is
  recharged through the intervening aquitard
• finite difference equations describes the
  response of the aquifer system to applied
  stresses
• quasi three-dimensional model simulates a ground
  water system having any number of aquifers

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• The studies on the ground water/surface water
  interrelationship made it possible to solve a
  number of important scientific and practical
  problems
• to estimate base flow and, therefore, sustained
  low river discharges of different probabilities
• to estimate the ground water contribution to
  total water resources and the water balance of
  regions
• to evaluate quantitatively the natural ground
  water resources for determining the prospects of
  their use within large areas and as a component
  of the safe ground water yield

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• The methods for estimating the ground water
  discharge of the upper hydrodynamic zone are
  fairly well developed as compared to deep
  artesian aquifers and their contribution to
  surface runoff

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• Seawater Intrusion
• A natural process that occurs in virtually all
  coastal aquifers.
• Defined as movement of seawater inland into fresh
  groundwater aquifers, as a result of
• higher seawater density than freshwater
• groundwater withdrawal in coastal areas

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• Sea Water Intrusion
• In the coastal margins of ground water basin, the
  lowering of water level or potentiometric head
  results in the intrusion of sea water
• Inland gradient for saline intrusion result from
  pumping at rate higher than the recharge to the
  ground water basin
• wedge-shaped intrusion occurs as sea water is
  approximately 1.025 times heavier than fresh
  water

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• Field surveys (geophysical and geochemical
  studies) can only reveal the present state of
  seawater intrusion but can not make impact
  assessment and prediction into the future
• Mathematical models are needed for these purposes
• Ghyben-Herzberg relation is a highly simplified
  model
• Dynamic movement of groundwater flow and solute
  transport needs to be considered
• A density-dependent solute transport model
  including advection and dispersion is needed for
  the modelling

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• Ground Water Pollution
• Restoration to the original, non-polluted state
  of polluted ground water is more difficult than
  surface water
• Geologic and hydrogeologic setting along with
  magnitude of the pollution hazard for a specific
  incident must be evaluated.
• Movement of contaminants and its control largely
  depends on the hydrogeologic environment
• Processes of migration and alterations present in
  ground water are also present in the unsaturated
  zone

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• Remedial action can be classified into three
  broad categories
• Physical containment measures, including slurry
  trench cutoff walls, grout curtains, sheet
  piling, and hydrodynamic control
• Aquifer rehabilitation, including withdrawal,
  treatment, reinjection (or recharge), and in-situ
  treatment such as chemical neutralization and
  biological neutralization
• Withdrawal, treatment and use

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• use of models provide more appropriate and
  rigorous method for integrating all the available
  data together
• It evaluates the response of the aquifer system
  to a contamination event
• The models are derived from the expression of the
  flow and transport processes in terms of
  mathematical equations
• Equations are solved by incorporating appropriate
  parameter values and boundary conditions

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Seawater Intrusion
Before extensive pumping
After extensive pumping by many wells
Pumping causes a cone of depression and draws the
salt water upwards into the well.
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• Groundwater
• An important component of water resource systems.
  
• Extracted from aquifers through pumping wells and
  supplied for domestic use, industry and
  agriculture.
• With increased withdrawal of groundwater, the
  quality of groundwater has been continuously
  deteriorating.
• Water can be injected into aquifers for storage
  and/or quality control purposes.

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• MANAGEMENT means making decisions to achieve
  goals without violating specified constraints.
• Once contamination has been detected in the
  saturated or unsaturated zones, requires the
  prediction of the path and the fate of the
  contaminants, in response to the planned
  activities.
• Any monitoring or observation network must be
  based on the anticipated behavior of the system.
• The tool for understanding the system and its
  behavior and for predicting the response is the
  model.
• Usually, the model takes the form of a set of
  mathematical equations, involving one or more
  partial differential equations. We refer to such
  model as a mathematical model.
• The preferred method of solution is the
  analytical solution.

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• For most practical problems we transform the
  mathematical model into a numerical one, solving
  it by means of computer programs.

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What is a model?

• Any device that represents approximation to
  field system
• Physical Models
• Mathematical Models (Analytical and Numerical)
• Modeling begins with formulation of a concept of
  a hydrologic system and continues with
  application of, for example, Darcy's Law to the
  problem, and may culminate in a complex
  numerical simulation.

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TYPES OF MODELS CONCEPTUAL MODEL MATHEMATICAL
MODEL ANALOG MODEL PHYSICAL MODEL
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Line diagram of the Ganga with major tributaries
(Source Status paper on river Ganga, NRCD, MoEF,
2009)
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• Importance of ground water flow models
• Construct representations and helps understanding
  the interrelationships between elements of
  hydrogeological systems
• Efficiently develop a sound mathematical
  representation
• Make reasonable assumptions and simplifications
• Understand the limitations of the mathematical
  representation and interpretation of the results

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• Groundwater models can be used
• To predict or forecast expected artificial or
  natural changes in the system.
• To describe the system in order to analyse
  various assumptions
• To generate a hypothetical system that will be
  used to study principles of groundwater flow
  associated with various general or specific
  problems.

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• Processes to model
• Groundwater flow
• Transport
• Particle tracking requires velocities and a
  particle tracking code. calculate path
  lines
• (b) Full solute transport requires velocites
  and a solute transport model. calculate
  concentrations

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• Processes we need to model
• Groundwater flow
• calculate both heads and flows (q)
• Solute transport requires information on flow
  (velocities)
• calculate concentrations

Requires a flow model and a solute transport
model.
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Modelling Process

• Establish the Purpose of the Model
• Develop Conceptual Model of the System
• Select Governing Equations and Computer Code
• Model Design
• Calibration
• Calibration Sensitivity Analysis
• Model Verification
• Prediction
• Predictive Sensitivity Analysis
• Presentation of Modeling Design and Results
• Post Audit
• Model Redesign

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• Mathematical model
• Simulates ground-water flow and/or solute
  fate and transport indirectly by means of a set
  of governing equations thought to represent the
  physical processes that occur in the system.
• (Anderson and Woessner, 1992)

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General 3D equation
2D confined
2D unconfined
Storage coefficient (S) is either storativity or
specific yield. S Ss b T K b
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Groundwater flow is described by Darcys
law. This type of flow is known as advection.
Linear flow paths assumed in Darcys law
True flow paths
The deviation of flow paths from the linear Darcy
paths is known as dispersion.
Figures from Hornberger et al. (1998)
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In addition to advection, we need to consider two
other processes in transport problems.

• Dispersion
• Chemical reactions

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advection-dispersion equation
groundwater flow equation
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advection-dispersion equation
groundwater flow equation
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Flow Equation
1D, transient flow homogeneous, isotropic,
confined aquifer no sink/source term
Transport Equation
Uniform 1D flow longitudinal dispersion No
sink/source term retardation
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Flow Equation
1D, transient flow homogeneous, isotropic,
confined aquifer no sink/source term
Transport Equation
Uniform 1D flow longitudinal dispersion No
sink/source term retardation
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Conceptual Model A descriptive representation of
a groundwater system that incorporates an
interpretation of the geological hydrological
conditions. Selection of Computer Code Depends
largely on the type of problem(Flow, solute,
heat, density dependent etc. along with 1D, 2D,
3D) Model geometry It defines the size and the
shape of the model. It consists of model
boundaries, both external and internal, and model
grid. Grid In Finite Difference model, the grid
is formed by two sets of parallel lines that are
orthogonal. In the centre of each cell is the node
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• Boundaries
• Physical boundaries are well defined geologic and
  hydrologic features that permanently influence
  the pattern of groundwater flow (faults, geologic
  units, contact with surface water etc.)
• Hydraulic boundaries are derived from the
  groundwater flow net and therefore artificial
  boundaries set by the model designer. They can be
  no flow boundaries or boundaries with known
  hydraulic head.

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• Model Parameters
• Time, Space (layer top and bottom), Hydrogeologic
  characteristics (hydraulic conductivity,
  transmissivity, storage parameters and effective
  porosity)
• Initial Conditions
• Values of the hydraulic head for each active and
  constant-head cell in the model.

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Calibration and Validation

• Calibration parameters are uncertain parameters
  whose values are adjusted during model
  calibration.
• Typical calibration parameters include hydraulic
  conductivity and recharge rate.
• Model validation is to determine how well the
  mathematical representation of the processes
  describes the actual system behavior.

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• Groundwater Flow Models
• MODFLOW
• (Three-Dimensional Finite-Difference Ground-Water
  Flow Model)
• When properly applied, MODFLOW is the recognized
  standard model.
• Ground-water flow within the aquifer is simulated
  in MODFLOW using a block-centered
  finite-difference approach.
• Layers can be simulated as confined, unconfined,
  or a combination of both.
• Flows from external stresses such as flow to
  wells, areal recharge, evapotranspiration, flow
  to drains, and flow through riverbeds can also be
  simulated.

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• Other Models
• MT3D (A Modular 3D Solute Transport Model)
• FEFLOW (Finite Element Subsurface Flow System)
• HST3D (3-D Heat and Solute Transport Model)
• SEAWAT (Three-Dimensional Variable-Density
  Ground-Water Flow)
• SUTRA (2-D Saturated/Unsaturated Transport Model)
• SWIM (Soil water infiltration and movement
  model)
• VISUAL HELP(Modeling Environment for Evaluating
  and Optimizing Landfill Designs)
• Visual MODFLOW (Integrated Modeling Environment
  for MODFLOW and MT3D)

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• Several methods to control saline intrusion
• Reduction of ground water extraction
• Artificial recharge by spreading
• Physical barrier
• Mathematical modelling of unsteady flow of saline
  and fresh water in aquifer