Hydro Lecture 7
Flow Lines continued…
Water flows from higher to lower hydrologic head
Geologic material is never actually homogenous, so flow lines refract when flows change subsurface structures or layers
If K1 is smaller than K2:
 water tends to flow vertically in K1 more than K2

 water flows nearly vertical in clay layers
 aquifers have horizontal flow more than vertical

Ground Water Investigation
Determining Groundwater Levels and Pressures
 Use existing wells
 Use open borings
 Use observation wells
 Use piezometers
Determining Groundwater Flows: Well Studies
 Useful for:
 extracting water for study
 relieving pressure under dams
 lowering water table for construction
 controling saltwater intrusion
 The Basic Purpose:
 compute drawdown (change in water level, hydraulic properties must be known)
 determine hydrologic and geologic properties for computation
Drawdown
insert slide image #1 (pg 3 of notes)
Steadystate flow time change is not considered, hydraulic head is constant
Transient flow hydraulic head changes with time
Types of pumping wells:
 Fully penetrating well (runs full thickness of aquifer)
 Partial penetrating well (really difficult to study due to altered vertical flows)
 Homogenous & isotropic (used for basic computations)
Flow in a completely confined aquifer
Basic Info:
 No recharge zone, no inputs
 Subsurface is always saturated
 elastic storage due to pressure changes after pumping
 Storativity is generally very small
 Pumping will affect large area of aquifer
Theis
 Discovered how to quanitfy drawdown circa 1935
 Theis (nonequilibrium) Equation: http://www.bae.uky.edu/sworkman/AEN438G/theiseq/theiseq.html
Q. insert
A. insert
Flow in a leaky, confined aquifer
Basic Info & Assumptions:
 Aquitard located above, below or on both sides
 if 2 aquitards, solution will be different
 HantushJacob formula deals with one leaky confining layer
 Water table in the source bed is originally horizontal
 Water table in the source bed does not fall during pumping
 Source bed is the geologic layer above the leaky, confining layer
HantushJacob Formula (1956)
insert math here
The HantushJacob curve is very generalized and very theoreticl, but it serves as a basis for computation of simple systems.
Flow in an unconfined aquifer
Basic Info & Assumptions:
 most difficult
 Neuman's solution (1980s) (still a really important guy)
 Vadose zone is ignored
 @beginning, water pumped is from elastic storage
 after beginning, water recharge due to gravity drainage
 specific yeild is at least 10x the elastic storativity
Three phases of an Unconfined Aquifer
 Early stage
 pressure drops, mostly due to specific storage
 behaves like an artesian aquifer
 flow is horizontal
 time:drawdown relates as Theis curve
 Second Stage
 water table declines, mostly due to specific yeild
 flow is horizontal and vertical
 time:drawdown is inversely related?
 Later Stage
 rate of drawdown decreases
 flow returns to horizontal
 time:drawdown reverts to Theis curve
Shlomo Neuman's Solution
 involves three parameters and an even more complicated charts
 vertical and horizontal hydraulic conductivity greatly affect the phases of the well
 insert math here
page revision: 8, last edited: 05 Oct 2011 02:09