Groundwater
P = Q + ET + G + DS
Floridan
Aquifer
Extent
Geologic
Profiles
(Stratigraphy)
Confinement
Groundwater and Wetlands
Transmissivity
• How much water can
be moved
horizontally
– Function of thickness
and Ksat
– Good measure of well
productivity
– Floridan is the most
transmissive aquifer in
the world
Loss of
Potential
Potentiometric
Surface
• Elevation of “free
water surface”
• Where this surface
and the ground
intersect (and there’s
no confinement)
water seeps
Relevant Questions
• Where is the water going?
– Potentiometric (piezometric) surface
• How much water is moving? How quickly?
– Potentiometric surface and Darcys Law
• What level of natural assimilation is occuring?
– Water quality modeling
Gainesville’s Well Field
Geology
Land use
Conservation
Easement
Also Lake City
Jasper
Murphree Wellfield Cone of
Depression
1988 (Observed)
2010 (Predicted)
How to make a sinkhole
Pray for lots of Rain
Suck a lot of water
Drilling and pumping
Hundreds of sinkholes developed over
a period of 6 hours.
Developed into a hole 300ft deep
and 300ft wide
Freeze Protection
• To protect strawberry yield during a January
freeze in 2010, ~ 2 billion gallons per day of
water pumped over a 5 day period. Voila.
Subsidence
Invasion
Fire
Degraded wildlife habitat
Artesian Springs
• Where a confining layer exists, there may be a
pressure potential in the aquifer HIGHER than
the gravity potential of the surface.
• When tapped, water flows upwards
P=Q+ET+G+ΔS
Soil water movement across a watershed boundary.
Q
= K A ΔH/L
groundwater
Darcy’s Law
Q is water crossing the
defined area of the
boundary in m3/day
Darcy’s law is mostly used to calculate vertical
leakage through a clay layer, but may also be
used to calculate lateral flow.
Q= K A ΔH/L
K is hydraulic conductivity
Most meaningful as saturated hydraulic conductivity Ksat (m/day). Why?
ΔH is the difference in H between two points
Water flows from high ψtotal to low
ψtotal (could be “up”)
Point
ψG
ψP
H
A
B
C
H = Ψgravity + Ψpressure
H = level of water in an open well
above some datum
HA = ? HB = ? ΔH = ?
Flow Direction?!?
H @ D?
H@F?
ΔH?
10
9
8
7
6
5
4
3
2
1
0
Direction?
ΔH AD? Dir?
ΔH BF? Dir?
ΔH AF? Dir?
ΔH/L BF?
Vertical leakage problem
Watershed=100 ha
6
5
4
3
Ksat=0.001m/d
2
1
0
Datum
K?
A? ΔH? L?
Q=K A ΔH/L
Q = K * A * ΔH/L
K = 0.001 m/d
A = 100ha = 1,000,000 m2
ΔH = 5-3 = 2m
L = 2m
Q = 0.001m/d x 1,000,000m2 x 2m / 2m
Q = 1,000 m3/day or 365,000 m3/year
Q surface depth = 365,000 m3 / 1,000,000 m2= 0.365m
Lateral leakage problem
Q=K A ΔH/L
K=0.1m/d
A=100m x 50m
=5,000m2
ΔH=108m-105m
=3m
L=1,000m
Qm3/d= 0.1m/d * 5,000m2 *0.003 = 1.5m3/d
Groundwater Flowpaths at Streams
Groundwater
Discharges
Groundwater Flowpaths
Next Time…
• Soil Water Storage