Groundwater

P = Q + ET + G + DS

Floridan AquiferExtent

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

Also Lake City

Jasper

Geology

Land use

Conservation

Easement

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

Developed into a hole 300ft deep and

300ft wide

Hundreds of sinkholes developed over a

period of 6 hours.

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.

Invasion

Fire

Subsidence

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

Soil water movement across a watershed boundary.

P=Q+ET+G+ΔS

Qgroundwater= K A ΔH/L

Darcy’s Law

Darcy’s law is mostly used to calculate vertical leakage through a clay layer, but may also be used to calculate lateral flow.

Q is water crossing the defined area of the boundary in m3/day

K is hydraulic conductivityMost meaningful as saturated hydraulic conductivity Ksat (m/day). Why?

Q= K A ΔH/L

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?

Direction? 10

98

7

654

32

1

0

ΔH AD? Dir?

ΔH BF? Dir?

ΔH AF? Dir?

ΔH/L BF?

Q=K A ΔH/LK? A? ΔH? L?

Vertical leakage problem

Ksat=0.001m/d

Watershed=100 ha

0

1

2

3

4

5

6

Datum

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

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

Lateral leakage problem

Groundwater Flowpaths at Streams

Groundwater Discharges

Groundwater Flowpaths

Next Time…

• Soil Water Storage