Chapter 17 Water Use and Management

How much is fresh (as opposed to saline) and where is it? ( Practice Quiz 9)

2.4% is fresh water, nearly 90% is tied up in glaciers, ice caps, and snowfields. Most of this ice is located in Antarctica, Greenland, and the floating ice cap in the Arctic, alpine glaciers and snowfields supply water to billions of people. 97.6% is saline water.

Subsidence

A settling of the ground surface caused by the collapse of porous formations that result from a withdrawal of large amounts of groundwater, oil, or other underground materials.

Which is the largest consumer worldwide of water?

Agricultural is the greatest water consumer. Water use is divided into agriculture, domestic use and industrial use. worldwide, agriculture claims about two-thirds of total water withdrawal and 85% of consumption. The Aral Sea,, is a tragic example of this. Was once the fourth largest inland body of water in world, but it has now lost 90% of its volume since 1975 as the water was diverted for irrigation of rice and cotton crops. Commercial fisheries have also been lost.

Mountains act as cloud formers & rain catchers. Rain Shadow Effect:

Air sweeps up the (windward side) of a mountain, pressure decreases, and the air cools. Eventually saturation point is reached, and moisture in the air condenses. Rain falls on the mountaintop. Rain Shadow- Cool, dry air descends from the mountaintop down the other side of the mountain (leeward side) creating dry areas with very little precipitation. For example, at Mount Waialeale in Hawaii, rain on the east side of mountain is greater than 20 times that on the west side.

The Atmosphere: A Small Water Compartment

Among the smallest water reservoirs contains less than 0.001% of total water supply. Has most rapid turnover rate. Provides mechanism for distributing fresh water over landmasses and replenishing terrestrial reservoirs.

Renewable Water Supplies

Annual freshwater surface runoff plus annual infiltration into underground freshwater aquifers that are accessible for human use.

Groundwater Stores Large Water Resources: Aquifers, Artesian well, and Recharge Zones (Groundwater System)

Aquifers- Porous, water-bearing layers of sand, gravel, and rock below the earth's surface; reservoirs for groundwater. Artesian well- A pressurized aquifer from which water gushes without being pumped, due to the aquifer's intersecting the surface or being penetrated by a pipe or conduit; also called a spring. Recharge Zones- area where water infiltrates into an aquifer.

Diversion Projects: what are pros and cons?

Dams Pros: Provide inexpensive hydroelectric power. Provide jobs. Reduce flooding. Allow farming on lands that would otherwise be too dry. Dams Cons: Submerge farmlands and towns displacing people. Cause earthquakes. Block fish migration (e.g. salmon). Change aquatic habitats for native species. Reduce spring floods that drop sediment to enrich soils downstream.

Domestic Conservation

Estimates suggest we could save as much as half of domestic water usage without change in lifestyle. Largest domestic use is toilet flushing. Can use low volume toilets or waterless composting. Anaerobic digesters use bacterial to produce methane gas from waste in waterless systems. significant amounts of water can be reclaimed and recycled. Purified sewage effluent- San Diego pumps water from sewage plant directly into drinking reservoir.

Frozen Water

Glaciers, Ice, and Snow: 2.4% of world's water is classified as fresh. 90% in glaciers, ice caps, and snowfields. Climate change is shrinking glaciers and snowfields.

Groundwater/Infiltration/Zone of Aeration/Zone of Saturation

Groundwater is the second largest reservoir of fresh water. Infiltration- process of water percolating through the soil and into fractures and permeable rocks. Zone of Aeration-upper soil layers that hold both air and water. Zone of Saturation-lower soil layers where all spaces are filled with water. Water table- the top of this zone is the water zone. The water table is not flat, but undulates according to the surface topography and subsurface structure. Water tables also rise and fall seasonally, depending on precipitation and infiltration rates.

Quantities of Water Used

Human water use has been increasing about twice as fast as population growth over the past century, but impact varies with location. Canada withdraws less than 1% of its renewable supply per year. In Israel, Libya and Yemen groundwater and surface water withdrawals equal more than 100% of the renewable supply. This "mining" is not sustainable. US uses 20% of renewable water/yr.

The Hydrologic Cycle Redistributes Water

Hydrologic Cycle-water evaporates from moist surfaces, falls as rain or snow, passes through living organisms and returns to the oceans. 500,000 km3 of water evaporates each year from the world's oceans and enters the cycle. Greater than 90% of this water rains back into the oceans. Some is carried over land where it renews freshwater systems. Plants play a major role in the hydrologic cycle as they pump water from the soil and release it into the atmosphere. Solar energy drives the hydrologic cycle.

Water Consumption

Is loss of water due to evaporation, absorption, or contamination.

Water Withdrawal

Is the total amount of water taken from a water body. Much of this water could be returned to circulation in a reusable form.

Getting By With Less Water

Land Banking- Some farmers may decide to let some of their land lay fallow in dry years. Walking Wetlands- Other farmers may flood fields on a rotational basis to create temporary wetlands. These strategies allow for farmers to plan ahead and wetlands birds to have habitat. Money designated for endangered species protection will fund these new farming practices.

Saltwater Intrusion

Movement of saltwater into freshwater aquifers in coastal areas where groundwater is withdrawn faster than it is replenished.

Wetlands

Play a vital role in hydrologic cycle. Lush plant growth stabilizes soil and retards surface runoff, allowing more aquifer infiltration. Disturbances reduces natural water-absorbing capacity, resulting in floods and erosion in wet periods, and less water flow the rest of the year. Half of US wetlands are gone primarily due to agricultural drainage.

Lakes & Ponds

Ponds are generally considered small bodies of water shallow enough for rooted plants to grow over most of the bottom. Lakes are inland depressions that hold standing fresh water year-round with depths ranging from a few meters to greater than 1500 meters.

River & Streams

Precipitation that does not evaporate or infiltrate into the ground runs off the surface, back toward the sea. Best measure of water volume carried by a river is discharge. The amount of water that passes a fixed point in a given amount of time. Usually expressed as cubic feet per second.

Rain Shadow

Rain Shadow - a dry area on the downwind side of a mountain.

Water Supplies are Unevenly Distributed

Rain falls unevenly across the earth's surface. Some areas receive practically no precipitation and other areas receive heavy rain on a daily basis. Three principle factors control global water deficits and surpluses: Global atmospheric circulation, Proximity to water sources, and Topography.

Water Availability and Use

Renewable Water Supplies: Made up of surface runoff plus infiltration into accessible freshwater aquifers. About two-thirds of water carried in rivers and streams annually occurs in seasonal floods too large or violent to be stored effectively for human use. Readily accessible, renewable supplies are only about 400,000 gal/person/year.

Describe some problems associated with dam building and water diversion projects. (Practice Quiz 4)

Sediment carried by rivers eventually fills up dams. More than 10 million metric tons of sediment per year collect behind the Glen Canyon and Boulder Dams on the Colorado River. Within a century these reservoirs will be filled with sediment and useless for water storage or hydroelectric generation. In addition, downriver habitats lose nutrients and the beaches disappear as sediment is no longer available.

How can water supplies be increased?

Seeding clouds- condensation nuclei. Desalination- removing salt from ocean water or brackish water to get fresh water. Three to four times more expensive than most other sources. Oil-rich Middle East states produce 60% of desalinated water. Quicker showers.

Many Countries Suffer Water Scarcity

The United Nations considers 264,172 gallons per person per year to be the minimum necessary to meet human needs. Water Stress occurs when human and ecosystem needs exceed the renewable water supplies, resulting in competition. Periodic droughts create severe regional water shortages in semiarid zones where moisture availability is the critical factor is plant and animal distributions. The effects on water supplies may be the most serious consequence of global climate change.

Major Water Compartments

The distribution of water across the earth is often described as interacting water compartments. Water may reside briefly in one compartment and stay there for eons. The length of time water typically spends in a compartment is called the Residence Time. For example, the Average residence time of water in the ocean is about 3,000 years before the water evaporates and enters the hydrologic cycle.

The Oceans are a Major Water Compartment

The oceans hold 97% of all liquid water on the earth. 90% of the earth's biomass is found in the oceans. The oceans play a major role in moderating earth's climate. Ocean currents moderate the climate by redistributing warm and cold water around the earth.

Groundwater

Water held in gravel deposits or porous rock below the earth's surface; does not include water or crystallization held by chemical bonds in rocks or moisture in upper soil layers.

What is the difference between withdrawal, consumption, and degradation of water? (Practice Quiz 1)

Withdrawal is the total amount of water taken from a water body. Much of this water could be returned to circulation in a reusable form. Consumption is loss of water due to evaporation, absorption, or contamination. Degradation is deterioration in water quality due to contamination or pollution; makes water unsuitable for other desirable purposes.