groundwater and surface water: a single...

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Groundwater and surface water:a single resourceSanta Cruz River, Tucson

1942 1989

1

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Groundwater basics

Groundwater is water found within the pore spaces of geologic material beneath the surface of the Earth. It exists in saturated layers of sands and gravels, in certain types of clay material, and in cracks within crystalline rock. -Cech, 2002

Are all pore spaces created equal?

2

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Porosity in different sediments. A. A porosity of 30 percent in a reasonably well-sorted sediment. B. A porosity of 15 percent in a poorly sorted sediment in which fine grains fill spaces between larger grains. C. Reduction in porosity in an otherwise very porous sediment due to cement that binds grains together. http://www.usd.edu/esci/figures/BluePlanet.html

http://www.usd.edu/esci/figures/158406.JPG

3

Arizona Water Issues © 2010 - The University of Arizona – HWR203

A B C

D E F

Pore Spaces

Typical grain packing showing: A and B) well sorted, well rounded grains; C) poorly sorted, well rounded grains; D) moderately well sorted, angular grains; E) platy uncompressed grains; and F) platy compressed grains . –Ferre, 2005.

Clay

Sand Gravel

4

Arizona Water Issues © 2010 - The University of Arizona – HWR203

• Typically, the water table separates the zone of aeration (vadose zone) from the saturated zone and fluctuates in level with seasonal changes in precipitation. • Corresponding fluctuations are seen in the water level in wells that penetrate the water table. • Lakes, marshes, and streams occur where the water table intersects the land surface. • In shape, the water table is a subdued imitation of the overlying land surface.

http://www.usd.edu/esci/figures/158405.JPG

http://www.usd.edu/esci/figures/BluePlanet.html

5

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Simplified ViewComponents of subsurface water:

6

Which way willwater flow?

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Groundwater Recharge

Precipitation and surface water infiltrate below ground until intercepted by plant roots or slowed down by a less permeable material such as clay, shale or bedrock.

This naturally occurring process of downward water migration that reaches the groundwater table is called groundwater recharge.

Cech, 2002

7

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Aquifers

An aquifer is a water-bearing geologic formation that can store and yield

usable amounts of water.

Latin orgin:“aqua” = water

“ferre” = to bear or carry

-Cech, 2002

8

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Aquifer terms

• Unconfined aquifer = Aquifer with no confining bed of material between the saturated zone and the land surface.

• Water table = the surface of the unconfined aquifer

• Confined aquifer = Aquifer that is overlain by a confining bed of geologic material

Cech, 2002

9

Arizona Water Issues © 2010 - The University of Arizona – HWR203

http

://lp

nnrd

.nrc

.sta

te.n

e.us

/imag

es/w

ater

/aqu

i_di

agra

m.jp

g

10

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Aquifer terms• Permeability = the measure of the ability of a material

to transmit fluids through it. – Wikipedia, 2006

• Aquitard = Geologic material with a relatively low permeability that yields low amounts of groundwater. - Freeze & Cherry, 1979– Examples: clay and bedrock

• Aquiclude = Impermeable geologic material that prevents groundwater movement. - Cech, 2002– Examples: highly compacted clays & bedrock

11

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Basin and Range

capp.water.usgs.gov/gwa/ch_c/C-basin.htmlB. Scarborough, Desert Museum, 2002

Aquiclude

Aquifer

Aquitard

12

Arizona Water Issues © 2010 - The University of Arizona – HWR203

http://www.usd.edu/esci/figures/BluePlanet.html

ConfinedAquifer

Aquitard

13

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Unconfined Aquifer

Water elevation in unconfined aquifer wells = water table elevation

Water table

Confined aquifer versus unconfined aquifer(plus respective water elevations in wells)

14

Arizona Water Issues © 2010 - The University of Arizona – HWR203

The High Plains aquifer is an example of an unconfined aquifer. A. This section across southeastern Wyoming and central Nebraska shows the eastward slope of the water table and the relation of the aquifer to underlying rock units.

http://www.usd.edu/esci/figures/BluePlanet.html

15

Arizona Water Issues © 2010 - The University of Arizona – HWR203

b) What zone is this?

a) What zone is this?

http://lpnnrd.nrc.state.ne.us/images/water/aqui_diagram.jpg

Saturated zone

Unsaturated zone

c) This is called?

d) This is called?a.k.a. what?

Name of well is?

Aquifer QUIZ!

What is thislevel called?

Aquitard

16

Arizona Water Issues © 2010 - The University of Arizona – HWR203

b) What zone is this?

a) What zone is this?

http://lpnnrd.nrc.state.ne.us/images/water/aqui_diagram.jpg

Saturated zone

Unsaturated zone

c) This is called?

d) This is called?a.k.a. what?

Name of well is?

Aquifer QUIZ!

What is thislevel called?

Unconfined

Confined

Water Table

Aquitard

Artesian well

17

Formation of “cone of depression”

Arizona Water Issues © 2010 - The University of Arizona – HWR203 18

Note: only occurs in

unconfined aquifer

Arizona Water Issues © 2010 - The University of Arizona – HWR203

How does groundwater flow?

19

Flow: Elevation Pressure, ∆head

Arizona Water Issues © 2010 - The University of Arizona – HWR203 20

No Flow

Flow

Arizona Water Issues © 2010 - The University of Arizona – HWR203

How does groundwater flow?

Above ground: Water flows downhill!Below ground: Water flows down gradient

Groundwater naturally moves to lower elevations due to the force of gravity. However, the direction and rate of movement are determined by lithology, stratigraphy, and structure of geologic deposits.

Cech, 2002

21

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Darcy Flow and Conductivity

Freeze & Cherry, 1979

Q h--- = -k * -----A l

Q = flowK = hydraulic conductivityh = hydraulic head

= elevation + pressurel = lengthA = cross-sectional area

• Factors that affect flow or conductivity– Sediments and their packing (permeability)– Fluid properties such as viscosity and density

• Orders of magnitude of K (m/s)Clay ~ 10-12, Slit ~ 10-8, Sand ~ 10-4, Gravel ~ 100

22

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Permeability

Relative Permeability Pervious Semi-Pervious Impervious

Unconsolidated Sand & Gravel

Well Sorted Gravel

Well Sorted Sand or Sand & Gravel

Very Fine Sand, Silt, Loess, Loam

Unconsolidated Clay & Organic Peat Layered

Clay Unweathered Clay

Consolidated Rocks

Highly Fractured Rocks

Oil ReservoirRocks

Fresh Sand-stone

Fresh Limestone, Dolomite

Fresh Granite

-Wikipedia, 2006 and Bear, Jacob, 1972. Dynamics of Fluids in Porous Media, Dover.

23

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Groundwater and surface water:Travel times

24

Geology break: stream cross-section

Arizona Water Issues © 2010 - The University of Arizona – HWR203 25

More simply:

stream

bench

terrace

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Recharge in mountain areasWater from mountaintop precipitation can follow several pathways:

A. Infiltration (slowest)

B. Transport in shallow water zone

C. Overland flow (fastest)

26

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Water Tables & Flow

Location of wells in map view (above)

Contours of equal hydraulic head may be drawn from water levels in wells

Flow lines are perpendicular to countour lines

Contouring groundwater from well data – how do hydrologists know which way water is flowing?

27

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Interactions: Gaining StreamsGaining streams

Contour plot of a gaining streamThis can be determined from water-table contour maps because the contour lines point in the upstream direction where they cross the stream

streams that receive water from the ground-water system

28

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Interactions: Losing streams

streams that lose water to the ground-water system

Contour plot of a losing stream

can be determined from water-table contour maps because the contour lines point in the downstream direction where they cross the stream

Losing streams

29

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Groundwater-surface water interactionsInfluence of increased surface water flow on groundwater

During high flow, stream water moves into the unsaturated portion of the stream banks as bank storage

30

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Groundwater-surface water interactions

A. Initially gaining stream

B. Flooding causes stream to rise, bank storage occurs

C. Additional bank storage water recharges groundwater (losing conditions) increasing height of the water table

Impact of increased surface water flow

31

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Human impacts on groundwater-surface water resources

32

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Development of sinkholes, subsidence

Sinkhole in Florida caused by overpumping of groundwater for irrigation

Subsidence fissure in Arizona caused by groundwater pumping

33

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Subsidence

WRRC, University of Arizona, 199934

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Impacts:Groundwater-stream interactions

1942 1989

Drawdown of aquifer causes Santa Cruz River to dry out and destroys riparian vegetation along stream banks

35

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Impact:Groundwater / surface water interactionsGaining stream: g.w. discharges into stream naturally

Installation of a well and pumping may intercept water discharging to stream

Increased pumping rates may draw water from the stream itself, creating losing stream conditions

36

Arizona Water Issues © 2010 - The University of Arizona – HWR203

GW-SW interaction - San PedroNatural cycle: groundwater recharges river

Today: increased groundwater withdrawls influence stream

37

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Impact: pollution

38

GW flow dir

Arizona Water Issues © 2010 - The University of Arizona – HWR203

Impact: saltwater intrusion

Coastal areas: freshwater flows over saltwater because it is less dense

Large draw downs of aquifers can cause underlying saltwater to migrate upwards into wells

39