Short Notes: Well hydraulics and Aquifiers | Short Notes for Civil Engineering - Civil Engineering (CE) PDF Download

 Page 1


    
 
Well hydraulics and Aquifiers 
Aquifer 
An aquifer is an saturated geological formation, underground layer of water-bearing 
permeable and porous or unconsolidated materials (gravel, sand, or silt) from which 
groundwater can be extracted using a water well. 
Some Fundamental definitions: 
1) Aquiclude 
• These are the geological formations which, are highly porous but non-
permeable. Hence water cannot be extracted from these types of geological 
formations. 
e.g. Clay 
2) Aquitard 
• These are the geological formations, which are porous but possess very less 
permeability. Hence water does not readily flow out of these formations, but 
instead water seeps out. 
e.g. Sandy Clay 
3) Aquifuge 
• These are geological formations, which are neither porous nor permeable. 
e.g. Granite 
Type of aquifer 
1. Un-Confined aquifer 
2. Perched aquifer 
3. Confined aquifer 
1) Un-confined aquifer 
• Boundary of Un-confined aquifer extended from water table (water surface 
which is under atmospheric pressure) to impermeable bed strata. 
• Not subjected to any confining pressure and Water in Un-confined aquifer is 
under atmospheric pressure. 
• Un-confined aquifer are recharged by directly rainfall over the surface and 
water body. 
• This aquifer is also called non-artesian aquifer. 
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Well hydraulics and Aquifiers 
Aquifer 
An aquifer is an saturated geological formation, underground layer of water-bearing 
permeable and porous or unconsolidated materials (gravel, sand, or silt) from which 
groundwater can be extracted using a water well. 
Some Fundamental definitions: 
1) Aquiclude 
• These are the geological formations which, are highly porous but non-
permeable. Hence water cannot be extracted from these types of geological 
formations. 
e.g. Clay 
2) Aquitard 
• These are the geological formations, which are porous but possess very less 
permeability. Hence water does not readily flow out of these formations, but 
instead water seeps out. 
e.g. Sandy Clay 
3) Aquifuge 
• These are geological formations, which are neither porous nor permeable. 
e.g. Granite 
Type of aquifer 
1. Un-Confined aquifer 
2. Perched aquifer 
3. Confined aquifer 
1) Un-confined aquifer 
• Boundary of Un-confined aquifer extended from water table (water surface 
which is under atmospheric pressure) to impermeable bed strata. 
• Not subjected to any confining pressure and Water in Un-confined aquifer is 
under atmospheric pressure. 
• Un-confined aquifer are recharged by directly rainfall over the surface and 
water body. 
• This aquifer is also called non-artesian aquifer. 
 
Figure Various type of Un-confined aquifer 
2) Perched aquifer 
• Perched aquifer is small water body which is situated in unsaturated zone of 
soil above the main ground water table or main unconfined aquifer, separated 
by impervious strata. 
3) Confined aquifer 
• Confined aquifer bounded between two impermeable or very less permeable 
soil strata or rocks. 
• In confined aquifer, water is under pressure or artesian 
pressure (pressure above the atmospheric pressure) because in that case 
water is sandwiches between to impermeable layer or rock. 
• This is also called artesian aquifer. 
Figure Confined aquifer 
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Well hydraulics and Aquifiers 
Aquifer 
An aquifer is an saturated geological formation, underground layer of water-bearing 
permeable and porous or unconsolidated materials (gravel, sand, or silt) from which 
groundwater can be extracted using a water well. 
Some Fundamental definitions: 
1) Aquiclude 
• These are the geological formations which, are highly porous but non-
permeable. Hence water cannot be extracted from these types of geological 
formations. 
e.g. Clay 
2) Aquitard 
• These are the geological formations, which are porous but possess very less 
permeability. Hence water does not readily flow out of these formations, but 
instead water seeps out. 
e.g. Sandy Clay 
3) Aquifuge 
• These are geological formations, which are neither porous nor permeable. 
e.g. Granite 
Type of aquifer 
1. Un-Confined aquifer 
2. Perched aquifer 
3. Confined aquifer 
1) Un-confined aquifer 
• Boundary of Un-confined aquifer extended from water table (water surface 
which is under atmospheric pressure) to impermeable bed strata. 
• Not subjected to any confining pressure and Water in Un-confined aquifer is 
under atmospheric pressure. 
• Un-confined aquifer are recharged by directly rainfall over the surface and 
water body. 
• This aquifer is also called non-artesian aquifer. 
 
Figure Various type of Un-confined aquifer 
2) Perched aquifer 
• Perched aquifer is small water body which is situated in unsaturated zone of 
soil above the main ground water table or main unconfined aquifer, separated 
by impervious strata. 
3) Confined aquifer 
• Confined aquifer bounded between two impermeable or very less permeable 
soil strata or rocks. 
• In confined aquifer, water is under pressure or artesian 
pressure (pressure above the atmospheric pressure) because in that case 
water is sandwiches between to impermeable layer or rock. 
• This is also called artesian aquifer. 
Figure Confined aquifer 
Some important terminology used in well hydraulics 
1) Cone of depression 
• Cone of depression represent the water table during the drawdown of water 
with the help of well through homogeneous and isotropic aquifer. 
• In un-confined aquifer cone of depression represent the drawdown water 
table but in confined aquifer it represent the pressure drop (change in 
piezometric head) around the well. 
• Drop in water table from previous static water table is termed as drawdown 
depth or simply drawdown. 
 
Figure 3-d view of cone of depression 
 
 
Figure Cone of depression in confined aquifer 
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Well hydraulics and Aquifiers 
Aquifer 
An aquifer is an saturated geological formation, underground layer of water-bearing 
permeable and porous or unconsolidated materials (gravel, sand, or silt) from which 
groundwater can be extracted using a water well. 
Some Fundamental definitions: 
1) Aquiclude 
• These are the geological formations which, are highly porous but non-
permeable. Hence water cannot be extracted from these types of geological 
formations. 
e.g. Clay 
2) Aquitard 
• These are the geological formations, which are porous but possess very less 
permeability. Hence water does not readily flow out of these formations, but 
instead water seeps out. 
e.g. Sandy Clay 
3) Aquifuge 
• These are geological formations, which are neither porous nor permeable. 
e.g. Granite 
Type of aquifer 
1. Un-Confined aquifer 
2. Perched aquifer 
3. Confined aquifer 
1) Un-confined aquifer 
• Boundary of Un-confined aquifer extended from water table (water surface 
which is under atmospheric pressure) to impermeable bed strata. 
• Not subjected to any confining pressure and Water in Un-confined aquifer is 
under atmospheric pressure. 
• Un-confined aquifer are recharged by directly rainfall over the surface and 
water body. 
• This aquifer is also called non-artesian aquifer. 
 
Figure Various type of Un-confined aquifer 
2) Perched aquifer 
• Perched aquifer is small water body which is situated in unsaturated zone of 
soil above the main ground water table or main unconfined aquifer, separated 
by impervious strata. 
3) Confined aquifer 
• Confined aquifer bounded between two impermeable or very less permeable 
soil strata or rocks. 
• In confined aquifer, water is under pressure or artesian 
pressure (pressure above the atmospheric pressure) because in that case 
water is sandwiches between to impermeable layer or rock. 
• This is also called artesian aquifer. 
Figure Confined aquifer 
Some important terminology used in well hydraulics 
1) Cone of depression 
• Cone of depression represent the water table during the drawdown of water 
with the help of well through homogeneous and isotropic aquifer. 
• In un-confined aquifer cone of depression represent the drawdown water 
table but in confined aquifer it represent the pressure drop (change in 
piezometric head) around the well. 
• Drop in water table from previous static water table is termed as drawdown 
depth or simply drawdown. 
 
Figure 3-d view of cone of depression 
 
 
Figure Cone of depression in confined aquifer 
2) Radius of influence 
• It is the maximum distance up to the effect of drawdown is detected. 
• In other word, radius of influence represent the radial extent of cone of 
depression. And areal extent represent by area of influence. 
 
Note: 
• When we start drawdown from well, initially the drawdown surface not 
constant and changes with time (due to unsteady flow). After sufficient time 
equilibrium state is reached and flow become steady. 
• After attaining equilibrium state there is no change in drawdown surface, 
drawdown surface become constant with respect to time. 
• And after stopping pumping, accumulation of water in influence zone started 
and this phenomenon termed as recuperation or recovery of well. 
Different way of extracting water 
1) Infiltration Galleries: These are horizontal tunnels constructed at shallow 
depth of the 3-5 m along the bank of river in water bearing strata. 
 
Page 5


    
 
Well hydraulics and Aquifiers 
Aquifer 
An aquifer is an saturated geological formation, underground layer of water-bearing 
permeable and porous or unconsolidated materials (gravel, sand, or silt) from which 
groundwater can be extracted using a water well. 
Some Fundamental definitions: 
1) Aquiclude 
• These are the geological formations which, are highly porous but non-
permeable. Hence water cannot be extracted from these types of geological 
formations. 
e.g. Clay 
2) Aquitard 
• These are the geological formations, which are porous but possess very less 
permeability. Hence water does not readily flow out of these formations, but 
instead water seeps out. 
e.g. Sandy Clay 
3) Aquifuge 
• These are geological formations, which are neither porous nor permeable. 
e.g. Granite 
Type of aquifer 
1. Un-Confined aquifer 
2. Perched aquifer 
3. Confined aquifer 
1) Un-confined aquifer 
• Boundary of Un-confined aquifer extended from water table (water surface 
which is under atmospheric pressure) to impermeable bed strata. 
• Not subjected to any confining pressure and Water in Un-confined aquifer is 
under atmospheric pressure. 
• Un-confined aquifer are recharged by directly rainfall over the surface and 
water body. 
• This aquifer is also called non-artesian aquifer. 
 
Figure Various type of Un-confined aquifer 
2) Perched aquifer 
• Perched aquifer is small water body which is situated in unsaturated zone of 
soil above the main ground water table or main unconfined aquifer, separated 
by impervious strata. 
3) Confined aquifer 
• Confined aquifer bounded between two impermeable or very less permeable 
soil strata or rocks. 
• In confined aquifer, water is under pressure or artesian 
pressure (pressure above the atmospheric pressure) because in that case 
water is sandwiches between to impermeable layer or rock. 
• This is also called artesian aquifer. 
Figure Confined aquifer 
Some important terminology used in well hydraulics 
1) Cone of depression 
• Cone of depression represent the water table during the drawdown of water 
with the help of well through homogeneous and isotropic aquifer. 
• In un-confined aquifer cone of depression represent the drawdown water 
table but in confined aquifer it represent the pressure drop (change in 
piezometric head) around the well. 
• Drop in water table from previous static water table is termed as drawdown 
depth or simply drawdown. 
 
Figure 3-d view of cone of depression 
 
 
Figure Cone of depression in confined aquifer 
2) Radius of influence 
• It is the maximum distance up to the effect of drawdown is detected. 
• In other word, radius of influence represent the radial extent of cone of 
depression. And areal extent represent by area of influence. 
 
Note: 
• When we start drawdown from well, initially the drawdown surface not 
constant and changes with time (due to unsteady flow). After sufficient time 
equilibrium state is reached and flow become steady. 
• After attaining equilibrium state there is no change in drawdown surface, 
drawdown surface become constant with respect to time. 
• And after stopping pumping, accumulation of water in influence zone started 
and this phenomenon termed as recuperation or recovery of well. 
Different way of extracting water 
1) Infiltration Galleries: These are horizontal tunnels constructed at shallow 
depth of the 3-5 m along the bank of river in water bearing strata. 
 
 
Derivations: 
Discharge through element 
qx = ax*vx 
= (h*L)*k*ix (by Darcy’s law V= k*ix) 
= h*L*K* dh/dx 
Total Discharge 
Q= ?qx 
= ?h*L*k*dh/dx 
 
Q*R = k*L* [H
2
- h0
2
] 
Q = kL(H-h0)(H+h0)/(2R) 
2) Infiltration Well