This work is supported by the National Science Foundation’s Transforming Undergraduate Education in STEM program within the Directorate for Education and Human Resources (DUE-1245025).

GEODESY AND WATER RESOURCES

Unit 3: Groundwater withdrawal and fluctuations in the height of Earth's

surface

OUTLINE

1. Groundwater Terrestrial Water Storage (TWS) Variations2. Groundwater Mining: a Global Problem3. GPS vertical position and hydrologic loading4. Subsidence: compaction and poroelastic effects5. Introduction to California physiography

TERRESTRIAL WATER STORAGE (TWS) AND GROUNDWATER

IN MANY LOCATIONS, CHANGES IN GROUNDWATER STORAGE DOMINATE VARIATIONS IN TWS.

1350.62 m

Depth to water7 m

Well depth18 m

Measure groundwater levels

Water level = (surface elevation) – (depth to water)

Depth to water table measured at a well

In > out replenished, water table/level goes upIn < out depleted, water table/level decline

porosity aread)replenishe(or volumedepletion increase)(or decline levelwater

RELATING CHANGES IN WATER TABLE TO CHANGES IN STORAGE

2. GROUNDWATER MINING: A GLOBAL PROBLEM

These figures are from Konikow, 2011See also Figure 2 from Famiglietti, 2014

3. GPS VERTICAL POSITIONSolid earth responds elastically to changes in load, such as water loss from regional groundwater pumping or drought

instantaneous, reversible, linear

Extract groundwaterTWS decreasesThe land surface moves up

HOW MUCH VERTICAL MOTION FROM TWS VARIATIONS?

Response to loading depends on elastic parameter, Young’s modulus (E)

E = tensile stress / extensional strain

Units, are force/area (N/m2) or pressure (Pa).

SPATIAL SCALE OF SENSINGDepends on horizontal scale of hydrologic loadFor large aquifers, unloading effects of pumping may be sensed 10’s of km away

0 250 500 500 250 Distance (km)

Disp

lace

men

t (m

m)

40 km wide2 m water equivalent

200 km wide0.5 m water equivalent

4. SUBSIDENCE: GROUNDWATER PUMPING MAY LEAD TO SUBSIDENCE

• Two effects– Compaction of aquitard sediments; generally

irreversible– Poroelastic effects; reversible

http://pubs.usgs.gov/circ/circ1182/pdf/04part1_intro.pdf

http://pubs.usgs.gov/circ/circ1182/pdf/04part1_intro.pdf

4. SUBSIDENCE: DECREASE IN SURFACE ELEVATION MAY EXCEED SEVERAL METERS!

4. SUBSIDENCE: GROUNDWATER PUMPING MAY LEAD TO SUBSIDENCE

• Effects are local – not extending beyond the pumped area.

5. California Physiography

Borsa et al., 2014

CENTRAL VALLEY GROUNDWATER: PRE AND POST DEVELOPMENTCROSS-SECTION FOR CENTRAL PART OF SAN JOAQUIN VALLEY

MAP

• Waiting on geologic map