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Introduction to Groundwater
Flow Modeling
Prof. Dr. Halil Önder
Fall 2008
Objectives and Scope
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Objectives:
To understand the processes of groundwater flow in an aquifer
To build models which enable the forecasting of the aquifer’s
response to planned activities
To provide the students with the necessary tools they need for
predicting the behavior of local groundwater as well as a regional
aquifer system, which are subject to natural and man-made
excitations
To present practical examples which will be of use in
groundwater development and management.
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Topics covered in the course
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The aquifer
The essentially horizontal flow approximation
Components of the groundwater balance
The motion equation in confined and phreatic aquifers
Storativity and mass balance equations for confined, phreatic and
leaky aquifers
Boundary conditions
The complete mathematical statement of a forecasting problem in
aquifers
Review of solution methods.
Fresh water-salt water interface in coastal aquifers
Mathematical models of aquifer management
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Hydrologic cycle
Schematic representation of the hydrologic cycle
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Hydrologic cycle
An engineering view of the hydrologic cycle
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Geologic Formations
Classification on the basis of water storing and
transmitting capability:
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Aquifer [water-bearing formation (bed, deposit,
stratum), groundwater reservoir, groundwater basin]
Aquitard [semi-pervious (leaky) formation]
Aquiclude [impermeable formation]
Aquifuge [non-porous, impervious formation)
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Geologic Formations:
Classification based on the origin and physical
properties
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Consolidated formation (Rocks)
 Igneous rocks (granite, basalt)
 Sedimentary rocks (sandstone, lime stone)
 Metamorphic rocks (marble, quartzite)
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Unconsolidated formation (soil)
 Gravel
 Sand
 Clay
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Water storing and transmitting capability
Geologic
Formation
Water Storing
Capability
Water Transmitting
Capability
Aquifer
Good
Good
Aquitard
Very poor, None
Fair
Aquiclude
Fair
None-Very Poor
Aquifuge
None
None
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Subsurface distribution of water
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Types of aquifers
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Various simplified aquifer boundaries
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Types of Interstices
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The portion of subsurface geological formation not occupied by
solid matter is the void space. It is also called as pore space,
pores, interstices, and fissures.
The interstices can be grouped in two classes:
Original Interstices
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They are created by geological processes at the time the rock was
formed, mainly in sedimentary and igneous rocks
Secondary Interstices
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They are developed after the rock was formed, mainly in the form of
fissures joints and solution passages
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Various types of interstices
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Roles (Main Functions) of Aquifers
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Source of Water
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Storage Reservoir
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Aquifer storativityPorosity
Conduit
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Renewable resource
Non-Renewable resource
Aquifer transmissivity
Permeability, Hydraulic Conductivity
Filter
Control of Base Flow
Water Mine
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Nonrenewable resource
One-time-reserve
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Groundwater Budgets
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A groundwater system consists of a mass of water flowing through
the pores or cracks below the earth’s surface. This mass of water is
in motion. Water is constantly added to the system by recharge from
precipitation, and water is constantly leaving the system as
discharge to surface water and as evapotranspiration. The total
amount of water entering, leaving, and being stored in the system
must be conserved. An accounting of all the inflows, outflows, and
changes in storage is called as water budget
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Human activities affect the amount and rate of movement of water in
the system, entering the system, and leaving the system. The
changes resulting from human interventions must be accounted for
in the calculation of the water budget
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Groundwater Balance
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1. Groundwater Flow and Leakage
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2. Natural Replenishment from Precipitation
3. Return Flow from Irrigation and Precipitation
4. Artificial Recharge (to enhance infiltration)
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Inflow and Outflow through Aquifer Boundaries
Leakage through Semipervious Layers
Surface spreading methods
Artificial recharge through wells
Induced recharge
5. River-Aquifer Interrelationships
6. Springs
7. Evapotranspiration
8. Pumpage and Drainage
9. Change in Storage
10. Regional Groundwater Balance
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Schematic representation of unconfined
ground water balance
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Groundwater System
Uncontrollable
Controllable
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Inputs
Excitation
Cause
SYSTEM
Outputs
Response
Effect
Detection
Identification
Prediction
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2
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Undesirable
Desirable
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Inputs
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Uncontrollable Inputs:
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Natural Recharge from
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Controllable Inputs:
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Policy Variables
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Precipitation
Irrigation return flow
Pumping and Injection Schedules
Artificial recharge
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Outputs
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Desirable Outputs:
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Undesirable Outputs:
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Reduction in Subsurface Outflow
Drying of a wetland
Drying of a spring
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System Characteristics
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System Characteristics:
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Aquifer Geometry
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Hydraulic Parameters
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Thickness
Lateral extent
Hydraulic conductivity
Transmissivity
Porosity
Storage coefficient
Specific yield
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Groundwater Systems and Three Unique
Problems
Detection (or instrumentation) problem
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The set of inputs to the system is unknown. It involves
determining the inputs given both the responses of the
system and the system outputs. The determination of
the recharge or leakage in semi-confined or
unconfined aquifers, from the response properties of
the aquifer system, is an example of instrument
problem.
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This problem is not considered an important problem
in groundwater hydrology
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Groundwater Systems and Three Unique
Problems
The identification (or inverse) problem
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It involves determining the parameters, which govern
the response of the system in particular this, requires
determining the coefficients of differential equation
which describes the response of the system. The
determination of the transmissivity and the storage
coefficient of a confined aquifer are typical examples.
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Identification is an extremely important problem in
groundwater hydraulics.
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Groundwater Systems and Three Unique
Problems
The prediction problem
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This requires the prediction of the fluctuating head in the
aquifers, given a range of groundwater recharge and
pumpage patterns both in temporal and areal distribution,
with known geometry and properties of the aquifer.
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Solving the prediction (forecasting) problem means solving
a model in order to obtain the future distribution of water
levels, or of piezometric heads produced in a specified
aquifer with known geometry and properties by an
anticipated natural replenishment and by any planned
schedule of future pumping and artificial recharge, as
envisaged in a proposed management scheme.
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Management concept
Intputs
Outputs
Uncontrollable
Undesirable
SYSTEM
Controllable
Desirable
User Judgment
Intputs
Outputs
Uncontrollable
Controllable
Undesirable
SYSTEM
Desirable
Judgment
Description
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