Ch 10: Water: Hydrologic Cycle & Human Use

10.1 Water: A Vital Resource 325 million cubic miles of water cover

Earth’s surface. 71% of the surface. 97.5% is salt water in ocean and seas 2.5% is fresh water (contain < 0.1%

salt) 2/3 in glaciers and ice caps. 0.77% of that in lakes, wetlands, and

streams Fresh water is a continually renewable

resource.

10.2 Hydrological Cycle: Natural Cycle, Human Impacts

Evaporation-> Liquid water turning in to a gas (water vapor) after absorption of heat.

Humidity-> Amount of water vapor in the air.-> Relative humidity: amount of water vapor air can hold at a particular temperature

Condensation-> The process of water vapor returning to a liquid form

Purification-> The process of evaporation and condensation purify water naturally.

Rain ShadowThe dry region downwind of a mountain range.

Groundwater Infiltration-runoff ratio: The amount of

precipitation that soaks into the ground compared with the amount that runs off.

Watershed: All land area that contributes water to a particular stream, river, or major water body.

Surface waters: All waters on the surface of the Earth

Capillary Water: Water that held in soil. Returns to the atmosphere by evaporation or transpiration.

Gravitational Water: trickles or percolates down through pores and cracks through gravity.

Groundwater: the accumulation of gravitational water at an impervious surface.

Recharge-> Aquifers: layers of porus materials through which groundwater moves.-> Recharge area: area where water enters an aquifer

99% of all liquid fresh water found in aquifers

Purification-> Through percolation, bateria, soil and detritus are removed from water.-> Minerals are leached through percolation

Natural exits for groundwater:1. Seeps: water flows out over wide area2. Springs: water exits the ground as a

significant flow from a small opening.

The Human Impacts Changing the Earth’s surface

-> Floods Climate Change Atmospheric Pollution Withdrawing water supplies

10.3 Water: A Resource to Manage, a Threat to Control Nonconsumptive Uses

-> remains available to humans for the same or other uses if treated and enough supplyElectric power 580 gal/day & Domestic use 164 gal/day

Consumptive uses-> water does not return to the water resource.Irrigation and other agri. use 485 gal/day

Sources 40% of domestic water from ground

water 60% from surface water

-> surface waters are susceptible to pollution 90% of wastewater in developing

nations goes in to surface water; UNTREATED

1.7 million people die of contaminated water in dev, countries each yr. -> 90% are children

Surface Waters

75,000 dams are in the United States (at least 6ft in height)

Dam Impacts Waterway below dam is deprived of

water-> Impacts aquatic organisms-> Wildlife affected as well

95% mortality rate of juvenile salmon in the Columbia & Snake rivers

San Francisco Bay 60% of fresh water that once

flowed into the bay has been diverted

Irrigation in the Central Valley (4.5 million acres)

Municipal Use in S. Cali. (22 million people)

Groundwater ¾ of all groundwater is non renewable Saltwater Intrusion

-> happens in coastal area through wells Falling Water Tables

-> withdrawal > than recharge Diminishing Surface Water

-> Wetlands, springs, seeps dry up due to falling water table Land Subsidence

->The gradual settling of the land due to water table dropping-> Sinkholes

10.4 Water Stewardship: Public Policy Challenges

Obtaining More Water More Dams to capture runoff

-> Three Gorges Dam-> 500 dams have been destroyed in US-> Wild Rivers and Scenic Rivers Act 1968

Tapping More Groundwater-> Tapping nonrenewable groundwater

Desalting Seawater-> Desalinization (Microfiltration & Distillation)

Using Less Water Agriculture

->30%-50% of water used in irrigation lost to evaporation, percolation, or runoff (using current methods)->Drip irrigation (reduce waste by 30%-70% & increase production)-> Surge Flow (computer controlled)

-> Treadle pumps (allow irrigation during dry seasons)

Municipal Systems

100 gallons per day used in homes Flushing Toilets: 3-5 gallons per flush Showers: 2-3 gallons per minute Laundry: 20-30 gallons per wash Xeriscaping: using desert plants that

use little to no water Recycling grey water (sink and shower

water collected the used for watering lawns and washing cars.

Public Policy Challenges Humans Use

-> 26% of total terrestrial evapotranspiration-> 54% of accessible precipitation runoff-> Many players in the water cycle

Natural Water Policy The Clean Water Act

Authorizes EPA to develop programs to protect the nation’s water quality

Key Issues1. Water efficiency must be promoted as the primary

strategy for meeting future water needs.2. Water subsidies need to be reduced or eliminated.3. Polluters must be charged according to their effluents.4. Watershed management must be integrated into the

pricing of water.5. Water authorities must regulate dam operations as that

river flow is maintained to simulate nature.6. The U.S. must respond to the global water crisis with

adequate levels of international development aid.7. Much more research and monitoring are needed to provide

the basic data for making informed policy decisions.