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Chapter 13

Water Resources

Dr. Joao Santos

Chapter 13

Water Resources

Dr. Joao Santos

Case History: Long Island

• Groundwater pollution: A serious problem on the western end of the island since the beginning of twentieth century

• Groundwater is the sole water supply for the Nassau and Suffolk counties, 3 million people

• Groundwater below Nassau County is tremendous, yet intensive pumping causing as much as 15 m decline in water level

• Salt-water intrusion due to declination in water level

• Urbanization triggered more serious water pollution: Urban runoff, sewage and fertilizers, road salt, industrial and other wastes, and landfills (most of them have been closed)

Case History: Long Island

Water: A Global Perspective

• Cyclic nature

– Global movement of water between different water storage compartments

• Global distribution

– Abundance not a problem

– Distribution in space and over time a problem

– Supply versus use a problem

– More than 99 percent of Earth’s water is unavailable or unsuitable for beneficial human use (salt and ice), all people compete for less than 1 percent of Earth’s water supply

Global Water Cycle

• Water’s vertical movement

– Upflow: Evaporation, transpiration

– Downflow: Precipitation and infiltration

• Water’s horizontal movement

– Surface runoff

– Shallow subsurface through flow

– Groundwater flow

Global Water Cycle

Global Water Supply

Surface Water (1)

Surface runoff: Important effects on both the transportation and erosion

• Drainage network

• Drainage basin or watershed: An area of land that contributes water to a particular stream or river, a basic unit of landscape

• Drainage divide: The boundary between drainage basins

• Stream order and size of drainage basin

Surface Water (2)

Surface Water (3)

Surface Water (4)

Factors affecting runoff and sediment yield

• Geological factors: Type and structure of soils and rocks

• Topographic factors: Relief and slope gradient

• Climatic factors: Type, intensity, duration, and distribution of precipitation

• Vegetation factors: Type, size, and distribution

• Land-use practice factors

Surface Water (5)

Groundwater (1)

Groundwater (GW) profile

• Vadose zone (unsaturated zone, zone of aeration)

• Zone of saturation

• Water table: The boundary of the above two zones

• Perched water table: Local water table above a regional water table

Groundwater (2)

Groundwater (3)

• Aquifer: A unit capable of supplying water at an economically useful rate

• Aquitard or aquiclude: A confining layer or unit restricting and retarding groundwater flow

• Unconfined aquifer: No overlying confining layer

• Confining aquifer: With an overlying aquitard layer

• Perched aquifer: Local zone of saturation above a regional water table

Groundwater (4)

Groundwater (5)

Groundwater recharge and discharge

• Recharge zone: Area where water infiltrates downward from surface to groundwater

• Discharge zone: Area where groundwater is removed from an aquifer, such as spring, well, river, etc.

• Influent stream: Above the water table, recharge water to groundwater, may be intermittent

• Effluent stream: Perennial stream with the addition of groundwater when precipitation is low

Groundwater (6)

• Groundwater pressure surface: Generally declining from source along the flow from recharge area to discharge area

• Artesian well: Water self-rising above the land surface in a confined aquifer

• Cone of depression: Drawdown cone of groundwater in a well

Groundwater (7)

Groundwater Movement (1)

• Hydraulic gradient: The gradient of water table, generally following the topographic gradient

• Hydraulic conductivity: Ability of rock materials to allow water to move through (m3/day/m2)

• Porosity: Percentage of void (empty) space in sediment or rock to store water

• Permeability: Measuring the interconnection of pores in a rock material

Groundwater Movement (2)

Groundwater Use and Supply (1)

• Available groundwater estimated above the total flow of the Mississippi during the last 200 years

• Groundwater as primary drinking water source for ~50 percent of the U.S. population

• Groundwater overdraft problems (extraction rate exceeding recharging rate) in many parts of the country, particularly some states in the Great Plains region

• Estimated 5 percent of groundwater depleted, but water level declined more than 15 m (50 ft) in some areas

Groundwater Use and Supply (2)

Groundwater Use and Supply (3)

Groundwater Use and Supply (4)

Interactions Between Surface Water and

Groundwater

• Overdraft of groundwater : Leads to lower water levels of streams, lakes, reservoirs, etc.

• Overuse of surface water: Yields lower discharge

rates of groundwater

• Effluent stream (in groundwater discharge zone): Tends to be perennial

• Influent stream (in groundwater recharge zone above the water table): Often intermittent or

ephemeral

• Special linkage area: Sinkholes and cavern systems

in the karst terrains

Interactions Between Surface Water and

Groundwater

Karst Topography Problems

• Water pollution occurs where sinkholes have been

used for waste disposal.

• Cavern systems are prone to collapse, producing

sinkholes that may form in areas that damage

buildings on the ground surface, roads, and other

facilities

• In many areas underlain by limestone, such as the

Edwards Plateau in Texas, groundwater is being

mined. As a result of the mining, important karst

springs where water emerges from caverns are

being changed, causing a reduction in biodiversity

Karst Topography Problems

The Edwards Aquifer

• Mark Twain “Whisky is for drinking and water is for

fighting over.” Intense conflict over water in central TX

• One of the most prolific in N. America, providing water for

more than 2 million people, with a natural yield of 25,000

gallons per minute

• Recharged primarily through influent streams flowing over

the recharge zone where water sinks into the limestone

• Increased water demand for growing urban areas and for

irrigation

• Ecosystems dependent upon the spring water: the San

Marcos spring salamander, the fountain darter fish, and

Texas wild rice are endangered species

The Edwards Aquifer

Water Use (1)

• Offstream use: Removal or diversion from its surface water or groundwater sources temporarily (e.g., irrigation, thermoelectric, industrial use)

• Consumptive use: Type of offstream use of water without intermediate return to the surface water or groundwater, such as transpiration and human use

• Instream use: Navigation, fish and wildlife, recreational uses

Water Use (2)

Water Use (3)

In major urban areas

• Over withdrawal of groundwater

• Overuse of local surface water

• Threats of local urban landfills to the water supply (e.g., Long Island, NY)

• Water import issues and problems: What is distance to transport? How much water available? From where? Conflicts with other areas, litigations, and long-range planning

Water Use (4)

Trends in Water Use (1)

Based on the data from 1950–1995

• Surface water use far greater than groundwater use

• The rate of water use decreased and leveled off since 1980

• Irrigation and thermoelectric are major fresh consumptive water use

• Less fresh water use since 1980 due to new tech and water recycling

Trends in Water Use (2)

Trends in Water Use (3)

Water Conservation

• Improved agricultural irrigation could reduce water withdrawals by between 20 percent and 30 percent

• Engineering technology and structure (canals): Regulating irrigation and reducing evaporation

• Better technologies in power plants and other industries: Less use of water due to improved efficiency

• Domestic use of water (urban and rural) accounts for only 10 percent of the total national withdrawals, can be reduced at a relatively small cost with more efficient bathroom and sink fixtures

• Global water conservation: Virtual water budgets

Conservation of Water at the

Global Scale

Water Management (1)

Needs for water management

• Increasing demand for water use (population and economic development)

• Water supply problems in semiarid and arid regions

• Water supply problems in mega cities of humid regions

• Water traded as a commodity: Capital, market, and regulations?

Water Management (2)

Aspects to be considered: Leopold philosophy

• Natural environmental factors: Geologic, geographic, and climatic

• Human environmental factors: Economic, social, and political

• Strategies

– More surface water use in wet years, more groundwater use in dry years

– Reuse and recycle water regular basis as well as emergencies

Management of the Colorado River (1)

Managing the water

• Water appropriation to seven states in the United States and to Mexico

• Local needs versus regional needs (Colorado River compact of 1922)

• The United States versus Mexico (Treaty with Mexico in 1944)

• Human use versus needs of lands (1974 Salinity Control Act)

Management of the Colorado River (2)

Management of the Colorado River (3)

Managing the river

• Dam construction

• Impact on flood frequency

• Impact on sediment distribution, particularly downstream

• Impact on wildlife habitats

• Controlled and planned floods

Water and Ecosystems

• Ecosystems: Changes in response to climate, nutrient input, soils, and hydrology

• General tendency: Increased human use of water, increased degradation of natural ecosystems

• Overall reconciliation between multiple water uses

– Water resources development (dam, reservoirs, canals) and

associated impact on surface water environment

– Reconciling the uses of water: Agriculture, industry,

urbanization, and recreation

– Protection of wetland and water resources

Wetlands and Ecosystems

Wetlands: swamps, marshes, bogs, prairie potholes, vernal pools

• Wetlands are one of nature’s natural filters. Plants in wetlands may effectively trap sediment, nutrients, and pollutants

• Freshwater wetlands are a natural sponge. During floods, they store water, helping to reduce downstream flooding and release water after the flood, nourishing low flows of river systems

• Wetlands are highly productive lands where many nutrients and chemicals are naturally cycled while providing habitat for a wide variety of plants and animals

• Freshwater wetlands are often areas of groundwater recharge to aquifers. Some of them, a spring-fed marsh, for example, are points of groundwater discharge

Emerging Global Water Shortage

• Isolated shortage of water: Indication of a global

pattern of water shortage

• Depleted water resources: Over-drafted aquifers,

dried lakes (Aral Sea), troubled streams (Colorado

and Yellow River not reaching seas some years)

• Polluted limited water resources due to

development and increased wastes

• Demands for water resources tripled as populated

more doubled last 50 yrs and growing fast next

50 yrs

• Global warming: Causing more problems

End of Chapter 13