subtitle

Hydrology...an Introduction to

Groundwater & Surface Water

1st – General Perspective on the

Hydrosphere

2nd – Groundwater

3rd – Surface water

General Perspective on the

Hydrosphere

Classroom Resources Animation “draining the oceans” giving a feel for water in the oceans – largest water reservoir

Cryosphere – 2nd

largest reservoir

of water on Earth

Groundwater Focus Although groundwater is

not very globally significant

in volume, it is a critical

source of domestic water,

because it is part of the

limited budget of fresh

(non-saline) water.

It can be viewed as a

partially-renewable

resource:

It is possible to withdraw it

faster than nature

recharges it.

Simplified Hydrologic Cycle

Hydrological Cycle: More Detail

Classroom Resource

WHY HYDROLOGY IS IMPORTANT

• Demand for and use of freshwater has tripled over the past half

century, as world population has grown from 2.5 to 6.45 billion people

Sources: Asian Development Bank; BBC; Earth Observatory; UNEP; UNESCO

• Of the 0.5% useable freshwater, irrigation accounts for 70%, industry

20% and household 10%

• By 2025 global water needs will increase with 40% more required for

cities and 20% for growing crops

• The satellite photos show major freshwater depletion taking place on all

continents, notably in the Dead Sea, the Aral Sea, Lake Chad, the

Mesopotamian Marshlands, the Everglades and other water sources

• According to UNESCO estimates, by 2030 global demands for fresh

water will exceed the supply with potentially disastrous consequences

• Of total world water, 97.5% is salty water and only 2.5% is

freshwater of which useable freshwater accounts for about 0.5%

• Water withdrawals are causing major rivers—such as the Colorado, the

Nile, the Yellow Rivers—to run dry in sections, lakes to vanish and

groundwater tables and aquifers to drop in many places

• In 2002, around 3.16 billion people (82%) in the Asia Pacific region had

access to improved water supplies, up from 74% in 1990

Sources: Asian Development Bank; BBC; Earth Observatory; UNEP; UNESCO

• Over the next 20 years, average water supply per person is estimated

to drop by a third, potentially endangering human health, agriculture and

the environment

• Water pollution is a serious threat to the world’s water supply

• Water volume in the Aral sea has dropped by about 80% since 1960s,

due to extensive irrigation primarily for cotton production

• Current water levels in Lake Victoria are below normal and the lowest

level since September 1961

WHY HYDROLOGY IS IMPORTANT

Groundwater Groundwater & surface water

are a most precious natural

resources.

According to U.S. estimates, groundwater provides:

• 34% of agricultural use (mostly for

irrigation)

• 40% of the public water supply

withdrawals

• 53% of all drinking water for the total

population

• 97% of drinking water for the rural

population

Introduction to Groundwater The zone of

saturation occurs where water

completely fills the open spaces in the soil and rock.

The upper limit of this zone is called the water table.

The zone above the water table is called the zone of

aeration.

How water

gets into the

zone of

saturation

(well water)

The Water Table Material

saturated with

water lies below

the water table.

Materials that

conduct water (are porous and

permeable) are

aquifers.

Materials that do

not conduct water (are well-

cemented,

unfractured, etc.)

are aquicludes &

aquitards. One inch of rain on one acre of ground

results in 27,192 gallons of water (~100,000 L).

Perched aquifers are common, since the geology of the near-surface can be

fairly complex. Parts of an aquifer can become perched as a result of slight

variations in the clay content of sediments.

Clay-rich sediments tend to be impermeable and retard water flow.

Groundwater: aquifers must be

permeable and porous

• Any geologic unit

through which

water can move

easily (i.e. it’s

permeable)

• Porosity: how

much water a

geologic material

can hold

Porosity and Permeability

Porosity: volume proportion made up of voids

Permeability: connectedness of voids, dictating

capacity to transmit flow

Porosity & Permeability for Life

Used in adult demonstration only

Gravel – great aquifer

Permeable & Porous

Opposite of an aquifer? • Aquitard / aquiclude Retards or Precludes the flow of groundwater

– Shale (compressed mud) is the example

Permeability

Aquicludes

or Aquitard

Aquifers

Groundwater in a Humid Landscape

• Water infiltrating the ground is recharge.

• Groundwater flowing out from the ground is discharge.

• But water moves slowly (typical range 0.1 to 100 m/day)

Characteristic US Aquifers

Great Plains: water derived

from the Colorado Front Range

Atlantic Coast: water moves

through young, poorly

hardened sediment

Basin and Range: waters

concentrate in gravels &

sands of alluvial fans

Great Plains:

Ogallala

Aquifer being

depleted in

most places

as water table

declined 10 to

> 100 ft.

Water Use in the USA

The blue areas had relatively little water withdrawals in 1990.

Animated map (gif)

Will play inside a powerpoint presentation,

showing increasing reliance on

groundwater withdrawal

Natural Recharge

In arid regions, recharge often

through streams

Drawdown through Wells Whenever water

is withdrawn

from a well, the

water table

around the well is

lowered. This is

called drawdown.

The conical shape

of the drawdown

region near well

has led to it being

called the cone of

depression.

Classroom

Resource

Groundwater Contamination

A. The groundwater

moves too rapidly

through the

cavernous limestone

to be naturally

purified.

B. Groundwater

movement in the

permeable sandstone

aquifer is slow

enough to allow

natural purification.

Flow direction can change

What causes

groundwater

contamination?

� Leaky underground

storage tanks

� Poorly constructed

landfills and septic

systems

� Improperly abandoned

mines and wells

� The overuse of

fertilizers, pesticides,

and road salts

� Runoff from livestock

confinement areas

� Careless industrial

and manufacturing

organizations

� From groundwater.org

Subsidence

Land subsidence due to

groundwater

withdrawal in the San

Joaquin Valley of

California began in the

mid 1920’s and locally

exceeded 8 meters (28

feet) by 1970.

Classroom Resource

• Animation illustrating

that groundwater

removal allows grains

to compact, and that

compaction causes

subsidence

• Like squishing a moist

sponge – once the

water is gone, you can

compact the sponge

Arizona Land Subsidence

Aquifers Susceptible

to Subsidence

Groundwater returns to surface

as baseflow to streams (in humid areas)

Perennial is possible, because

Groundwater returns to surface

as baseflow to streams (in humid areas)

Intermittent Streams:

Wet season raises water table so

base flow feeds stream

Groundwater returns to surface as springs

Can return as Artesian Wells Water flows freely out of an artesian

well.

Two requirements must be met:

-The aquifer must be inclined so that it is exposed to

recharge.

-The aquifer must be confined by aquitards above and below so the water does not

escape.

US Southwest has Artesian

Conditions

Online Video Resource on

Groundwater

EPA Lessons

on

Groundwater

Surface Water – starts with

Infiltration capacity (how much rain can ground absorb before water runs off)

determines what land will look like

HIGH –

water

sinks

in

LOW –

water

runs

off

High infiltration capacity landscapes

look like this:

Water sinks into ground supports plants & high water table

Low infiltration capacity

Means that water does not sink in, but runs off

and erodes channels (tiny rills to big gullies)

Rainsplash ejects particles into flowing

water

Eroding landscapes from overland

flow starts with RAINSPLASH

Rainsplash Video

• This is a high-speed video sequence of rainsplash. A single raindrop impacts dry sand. Time between individual video frames is 1/240th of a

second. The full video sequence is 0.1 seconds in real time. (Prof. Schmeeckle, ASU Geographical Sciences)

• http://www.markschmeeckle.com/rainsplash.html

Rainsplash puts smaller pieces into

the flow, leaving behind pedastals

Overland flow – then concentrates

into tiny channels to erode rills

Rainsplash

Rill

Larger Rill

Classroom Resource

Experiment showing how overland flow

starts in a desert (near Tombstone, AZ)

Rills

Rills grow into gullies

Low infiltration capacity means that

water runs off quickly into streams

as flash floods

Gypsum Wash – Near Las Vegas, NV

Flood deaths – 2nd to

Heat

Idiots on parade – or

Stupidity on summer

vacation

Why FLASH FLOODS HAPPEN 4

1. Intense Rain

2. Low infiltration capacity of ground (so

water sent quickly to streams)

[there is a threshold that will raise water to

point where stream rises quick & floods]

2. Low infiltration capacity of ground –

means that there is a high “drainage

density” (lots of channels in an area to

feed water to larger streams)

Why FLASH FLOODS HAPPEN 4

3. The water collection area combines at

stream junctions at the same time

Why FLASH FLOODS HAPPEN 4

Why FLASH FLOODS HAPPEN 4

4. Worst in slot canyons, where the

increased water makes height rise

quickly

Classroom Resource

Flash flooding movies

Science of

Hydrographs

Q is “Discharge” (cubic volume per second)

Q = width x depth x velocity

Discharge measured at

Gauging Station

Hydrograph – how discharge

changes over time (minutes, hours,

month, year, decade)

Example of response to single storm

Before

Rain

After

Rain &

water

moves

to streams

Water sinks in

so baseflow feeds

streams slowly

Water runs off fast

so stream

discharge rises

fast

Lag time between rain and stream

rising (long in forest & short in

desert or urban)

Floods and Urbanization

Surface runoff vs. Infiltration

Natural land cover vs. Urban area

Classroom Resource

Animation of how urbanization changes a hydrograph – making a forested region behave more like a desert in “shedding water” rapidly causing urban flash floods

Classroom Resources

Clips: flash flooding in urban settings

Influent and Effluent

When groundwater flows

into streams they are called

effluent.

When the water table is low,

streams become influent,

and water leaks from the

stream bed into the ground.

- During dry season

- Permanently in deserts

Core Concept in Surface Water

Hydrology: DRAINAGE BASIN

Synonym:

Watershed

Drainage Divide separates basins

The Continental Divide

In North America, the continental divide

separates watersheds that drain to the

west from those that drain to the east

(and the arctic).

Different sizes of drainage basins

Policies need to be different for

different types of drainage basins

Classroom Resource

Animation illustrating Drainage Basin of

Mississippi River (12th order stream)

Airplane Entertainment & Drainage

Patterns

Question: Is the pattern distributary (flow

splits) or tributary (flow combines)?

Tributary Distributary:

Delta & Alluvial Fan

Distributary: Alluvial Fan, Tibet

Alluvial fan

Distributary

Deltas -

distributary

Ganges,

So. Asia

Tributary – patterns you see from

the airplane tells you the geology

Dendritic

same rock type

Rectangular

Jointed & faulted

Trellis

Big stream cuts across anticline folds

Radial

Volcano

Out from Center

Radial – outward from center

Dendritic Tributary

Pattern

Rectangular

Tributary Pattern

Trellis Tributary

Pattern

Online Resources

Watersheds and Hydrologic Cycle

http://serc.carleton.edu/NAGTWorkshops/visualization/collections/watersheds.html

Groundwater Animations

http://serc.carleton.edu/NAGTWorkshops/visualization/collections/groundwater.html

Cryosphere Visualizations (frozen water)

http://serc.carleton.edu/NAGTWorkshops/visualization/collections/cryosphere.html