Outline•Today: Water cycle (Chapter 9, can skip the detail about different kinds of streams)

What is special about water? The water cycle The fresh water cycle –Runoff, Streams, and

Groundwater Human role in the global freshwater cycle

Where does YOUR drinking water come from?Review – answer your questions (plus a few of my own)

The Hydrologic CycleWater in the Earth System

Fixed amount of water circulates between atmosphere, ocean, cryosphere and biosphere

Atmosphere – as water vapor, Clouds – important reflectors of sunlight

Ocean – water contains salts (next week)

Cryosphere – frozen water in ice caps, mountain glaciers, snow (next week)

Land/ Biosphere – needed for life; distribution and availability governed by transport processes. Transpiration is evaporation through plants

People impact hydrologic cycle mostly in the freshwater reservoir

– mining of groundwater, use of stream runoff

Oki and Kanai 2006 Global Hydrological Resources and World Water Resources

The reservoirs –An estimate of global water distribution   Volume Percent of Total

Percent of (1000 km3) Water Fresh Water

Oceans, Seas, & Bays 1,338,000 96.5 -Ice caps, Glaciers,& Permanent Snow 24,064 1.74 68.7Groundwater 23,400 1.7 -        Fresh (10,530) (0.76) 30.1        Saline (12,870) (0.94) -Soil Moisture 16.5 0.001 0.05Ground Ice & Permafrost 300 0.022 0.86Lakes 176.4 0.013 -        Fresh (91.0) (0.007) .26        Saline (85.4) (0.006) -Atmosphere 12.9 0.001 0.04Swamp Water 11.47 0.0008 0.03Rivers 2.12 0.0002 0.006Biological Water 1.12 0.0001 0.003Total 1,385,984 100.0 100.0Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823.

All The Rest< 1%

Water Storage Changes over time in the Earth System

Figure 9.1, Skinner et al., 1999

The land, ocean and atmosphere exchange water over long time scales

•e.g. Glacial-interglacial Image of ice extent ~20,000 years ago

Recent satellite evidence suggests that there are short term variations as well

•e.g. on monthly and longer time scales

Fresh water on landPrecipitation can evaporate from the surface, or be taken up by plants and transpired (the sum of loss back to the atmosphere is evapotranspiration)

Precipitation/snowmelt that does not infiltrate into the soil “runs off” and travels downslope until it enters a stream (runoff or overland flow)

Once this flow enters a stream it is called streamflow.

Streams are also fed by water that travels through the subsurface, i.e. through the soil, after a storm has ended. This subsurface flow is called baseflow.

Water that we see flowing in streams is a combination of runoff, baseflow, and also, precipitation that has fallen directly on the stream http://ehp.niehs.nih.gov/docs/2001/109-12/runoff.jpg

Land freshwater cycle and residence time of water on land

Rivers2000km3

Flow into ocean45,500 km3/year

Precipitation on land111,000 km3/year

Evaporation from land65,500 km3/year

Precip – Evap=runoff 45,500 km3/year

Residence time of water in rivers 0.04 years or about 16 days

Stream behavior is controlled by:

1) average width and depth of channel

2) channel gradient

3) average velocity

4) discharge

5) sediment load (alluvium)

Sediment Transport by Rivers

Faster water flow – larger particles can be carried

Landforms resulting from stream deposition

Figure 9.14, Skinner et al., 1999

Floods

Before flooding and after flooding in 1993 on the Mississippi River, St. Louis

Flood occurs when a stream's discharge becomes greater than the capacity of the channel and water overflows the banks

Flooding can create alluvial valleys, with floodplains, terraces, and overbank flow

Figure 9.15, Skinner et al., 1999

Stream terraces in New Zealand

Alluvial FanWhen an large, fast stream leaves a mountain valley and enters a valley floor, it loses its energy and therefore and transporting capacity.

It deposits its load at the base of the mountain, forming a fan-shaped deposit of alluvium known as an alluvial fan

Lena River Delta

DeltaSimilarly, when a stream enters a standing water body, it loses its energy and ability to transport. The water deposits its load in the form of a delta

Figure 9.20, Skinner et al., 1999

Typical Groundwater System Less than 1% of total water, yet is still larger than all freshwater lakes, sea ice and glaciarsMostly found within 750m of surface

Aerated Zone- ground where holes between rock or soil solid fragments are still partly filled with airSaturated Zone- ground is saturated by water begins the “Water Table”

Movement of Groundwater

Figure 9.22, Skinner et al., 1999

Recharge- replenishment of ground water by rainfall of snowmeltDischarge- groundwater reaches surface to join rivers, lakes, etc.

Rivers2000km3

Flow into ocean45,500 km3/year

Precipitation on land111,000 km3/year

Evaporation from land65,500 km3/year

Putting groundwater in the freshwater cycle

Groundwater23,400,000 km3

~5000 km3/year? ~5000 km3/year?

Residence time in ground water ~5000 years

Precip – Evap - recharge 40,500 km3/year

Figure 9.23, Skinner et al., 1999

Time required for Recharge and Discharge varies with flowpath, porosity of rocks, and depth

Figures 9.25, 9.27, Skinner et al., 1999

Aquifers – water we use

Aquifer: a body of rock or regolith (weathered rock) sufficiently permeable to conduct economically significant quantities of groundwater to springs or wells

Gravels, sands and sandstones tend to make extensive and productive aquifers

The name “Fountain Valley” is derived from the city’s many artesian wells

(other cities, Artesia)

Figures 9.27, Skinner et al., 1999

Artesian aquifer:a confined aquifer with water pressure sufficient to make water in a well rise above the aquifer. Such a well is called an artesian well

Where does your water come from? Some water facts (from OCWD web site)

• 70% of California’s rivers have been engineered to redistribute water from northern to southern California

• Northern Orange County – 70% of water comes from groundwater recharged by Santa Ana River (includes Costa Mesa, Irvine)

• During summer most of the water flowing in the Santa Ana River is purified water from upstream treatment plants in Riverside/San Bernadino Counties; wetlands strip of residual nitrates and this water is used to recharge aquifers

• Southern Orange County – 100% of water imported (from Sierras and Colorado (Met WD) river)

http://www.spl.usace.army.mil/resreg/images/sar.jpg

http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16801

Newport Inglewood fault

Water being pumped out is rain that fell 100- 1000s of years ago depending on the depth

Issues

1)Saltwater intrusion

Solution:

Barriers

Pump freshwater In near coast;Stop removalsnear coast

2) Future watersupplies

http://www.ocwd.com/_assets/_pdfs/_hydrospectives/Hydro_Vol.2_Issue_1.pdf

Some Water-Related Environmental Issues

Allocation of Colorado River surface water

Groundwater mining, e.g. High Plains Aquifer, San Joaquin Valley

Groundwater contamination

Decreasing snowpack in the Western US

River restoration and dam removal

Coastal water quality

Etc…….

Rivers2000km3

Flow into ocean45,500 km3/year

Precipitation on land111,000 km3/year

Evaporation from land65,500 km3/year

Human impact on the hydrologic cycle

Groundwater23,400,000 km3

~5000 km3/year? ~5000 km3/year?

Residence time in ground water ~5000 years

Humans withdraw~3800 km3/year, about 10% of river flow

About 30% of evaporated water is from croplands

Runoff (annual precipitation minus evaporation)

is clearly related to river discharge – we will discuss later the reasons for these patterns

However, many regions with a lot of available water do not have a lot of people, while many regions with little rainfall have high water demand

Water scarcity index

The withdrawal of water by people annually divided by the annual runoff

Values >0.4 are water stressed (a very large fraction of water is being removed compared to what is available)

Places like the US Southwest have high population but low runoff

Figure 9.26, Skinner et al., 1999

From Rodell and Famiglietti, 1999

Groundwater Mining in the High Plains Aquifer

About 30% of the groundwater used for irrigation comes from the High Plains aquifer.

About 20% of irrigated land in the US is located here.

About 170,000 wells tap the aquifer, which is being depleted at rate that is faster than it is being recharged.

Its saturated thickness has declined by 50% (about 8 cm/year, in some parts more than 30 m)

What does the future hold for the High Plains?

Are similar things happening in the Central Valley?

How will climate change affect water scarcity?

(supply)How will population increase and higher demand for water

affect water scarcity?(demand)

Summary• Know the basic flows of the water cycle, which are the

biggest reservoirs, and the residence times in those reservoirs (approximate)

• Distribution of water among reservoirs has varied in the past

• The fastest flowing water carries the largest sediment particles

• Humans use about 10% of fresh water runoff for agriculture, domestic and industrial uses – however, water scarcity depends on both regional supply of runoff and local demand

• Climate change in the future will affect regional supply – population change and behavior will affect demand