Groundwater Science, James Beach

Groundwater Science Aquifers

Wellsetc.etc.

James Beach, PGLBG-Guyton Associates

Special thanks to Robert Mace of TWDB Special thanks to Robert Mace of TWDB

for many slides

Outline

• big picture

• technical definitions (sorta)

• flow in aquifers• flow in aquifers

• pumping an aquifer

• miscellaneous important stuff

Groundwater in the World

From Freeze and Cherry (1979)

Major aquifers

Minor aquifers

Texas groundwater factoids

• 60% of the water used in Texas

• 81% of groundwater is used for irrigation

• groundwater provides 39% of water to cities

groundwater use in Texas (1937 to 2003)

TECHNICAL DEFINITIONS

Definitions

• Aquifer

• Aquitard/confining layer

• Vadose zone/unsaturated zone

• Water table• Water table

• Recharge

• Water level

• Unconfined aquifer

• Confined aquifer

• an aquifer is geologic media that can yield economically usable amounts of

what is an aquifer?

yield economically usable amounts of water.

Porous Media

Hickory Aquifer, sandstone

Edwards-Trinity (Plateau) Aquifer, limestone

Ogallala Aquifer, sand and gravel

• an aquitard is geologic media that can not yield economically usable amounts of water.

what is an aquitard?

of water.

• A confining layer is an aquitard that bounds an aquifer.

what is a confining layer?

the unsaturated zone

Unsaturated zone

the water table

Unsaturated zone

recharge

recharge – typical

recharge – not typical

the water level

water flows down gradient (to lower potential energy)

Groundwater Flowpaths (TOP view)

Groundwater Flowpaths (SIDE view)

Flat Ground

With Hills and Topography

RegionalSprings

LocalSpring

• An unconfined aquifer is an aquifer that is bounded by a confining layer at its bottom but not at its top.

unconfined aquifer

an unconfined aquifer

confined (or “artesian”) aquifer

Flowing “artesian” well

Catfish Farm Well Flowed 24,000 gpm

July, 1991

catfish farm well

Edwards aquifer

• flowing well at 40,000 gpm

• 1/4 of San Antonio’s use

• 9% of Annual Recharge

• world’s largest artesian well

National Geographic (1993)

confined or unconfined?

confined or unconfined?

same aquifer: unconfined and confined

Major aquifers

same location: confined and unconfined aquifers

Confined/Dipping Aquifer

Warning:Not to Scale

Confined/Dipping Aquifer

Edwards

Gulf Coast

Carrizo-Wilcox

Carrizo Aquifer

Leaky Aquifers

Water Table is Higher

Semi-Confined water level is lower

Why do you care?

Unconfined Confined

FLOW IN AQUIFERS

fundamentals

• Terms that describe the ease with which water flows through geologic

what is permeability?

hydraulic conductivity ?transmissivity?

which water flows through geologic media.

What determines flow?

• Hydraulic properties

Flow = KA dh / dl

• Hydraulic properties

• Water level variation

• Aquifer geometry

Edwards Group

Upper Trinity aquifer

Middle Trinity aquiferGuadalupe

River

SE model boundary

A2400

2200

2000

1800

1600

1400

Trinity cross-section

Middle Trinity aquifer River

CanyonLake

Edwards aquifer(BFZ)

No flow

No flowA’

1200

1000

800

600

400

200

sea level

Spring flow

0 5 10 15 mi

Recharge

Cross-formational flow

Surface water-groundwater interaction

Groundwater flow

DrainPumping

water flows down gradient (to lower potential energy)

PUMPING AN AQUIFER

pumping a well: unconfined

pumping a well: confined

Aquifer may not be

depleted

Pressure is decreased

• Storage properties describe the amount of water released from an aquifer when water level drops

what is storativity?

• Confined : “storativity”

• Unconfined : “specific yield”

• Unconfined aquifers0.01 to 0.3

Storage yields from aquifers

• Confined aquifers0.005 to 0.00005

Simple regional flow (sand)

Simple regional flow + well

Drawdown caused by well

Drawdown caused by well

Groundwater movement to well

After 50 years

Groundwater movement to well

After 100 years

MISCELLANEOUS IMPORTANT

STUFF

Miscellaneous

• spring and stream impact

• droughts and groundwater

• long-term impacts

• water quality • water quality

Springflow ImpactEdwards Aquifer

High correlation

• Observed springflow increase increase following several wet winter months

Outcrop Well

Page 71

Pumping Well

Middle Wilcox orSimsboro Aquifer

Outcrop

Outcrop Well

Outcrop and Downdip Hydrographsin Brazos and Robertson Counties

De

pth

to

Wa

ter

(fe

et)

Page 72

State Well Number, Screened Interval

Pumping WellDe

pth

to

Wa

ter

(fe

et)

Total water leveldeclines in themajor aquifers

800

400

600

Water level declines

-200

0

200

1880 200019601920

Year

Woodbine

Paluxy

TrinityLower

Water Levels in Carrizo Wells0

50

100

150

200

Dep

th t

o W

ate

r (f

eet)

Static Water Levels in Carrizo Aquifer Wells (Angelina and Nacogdoches Counties)

250

300

350

400

Jan

-45

Jan

-47

Jan

-49

Jan

-51

Jan

-53

Jan

-55

Jan

-57

Jan

-59

Jan

-61

Jan

-63

Jan

-65

Jan

-67

Jan

-69

Jan

-71

Jan

-73

Jan

-75

Jan

-77

Jan

-79

Jan

-81

Jan

-83

Jan

-85

Jan

-87

Jan

-89

Jan

-91

Jan

-93

Jan

-95

Jan

-97

Jan

-99

Dep

th t

o W

ate

r (f

eet)

Water Quality

~40,000 wellsDeep saline units not included

Water Quality

Edwards Aquifer

Drought Sensitivity - Major

Minor

Drought and Groundwater

• Most aquifers are drought tolerant

• Higher than usual water level declines in drought can be caused by increaseddrought can be caused by increasedpumping

• Important to discern between local short-term and regional long-term impacts

Take Home

1. Laws of physics are constant – however– geology, aquifers and groundwater can vary significantly over short distances

2. Good science is critical for developing appropriate rules and management

3. Good science takes time and money