Hydrologic Cycle

Aquifer—a body of rock or sediment that stores, filters, and transmits water through pore spaces and openings in the rocks

Henri Darcy, Dijon, France, 1855

Defined the term “hydraulic conductivity” to mean the ease with which a material transmits water.

K = hydraulic conductivity (m/day)I = hydraulic gradient (m/m)A = cross-sectional area (m2)Q = discharge (m3/day)

Darcy’s Law:

K = Q

AI

Artesian system—confined aquifer

Problems with groundwater withdrawal:

1.Overdraft—occurs when withdrawal from wells + natural discharge > recharge

High Plains(Ogallala)Aquifer

Center pivot irrigation

30 % of all groundwater withdrawn in USis taken from High Plains Aquifer, mostly for irrigation

Ogallala-- groundwater withdrawals for agriculture: 14 bgd

total water withdrawals: 0.78 bgd

Tennessee

groundwater withdrawals: 0.03 bgd

5.5% of 0.2% of

Changes in the water table levelin the Ogallala (1890-1999):

MAP of Changes in Ogallala

• 1900-1980—avg. water table decline: 10 ft (max. 175 ft)• 1980-2000— water table decline has

slowed due to regulations and more efficient irrigation techniques

2. Land subsidence• lowering of land surface due to groundwater withdrawal

Venice, Italy—land subsidence, coastal flooding

CentralValley,Calif.—land subsidence

MexicoCity

abaondonedwell casing,Mexico City

Karst—terrain having unique characteristics of relief and drainage due to dissolution

of carbonate rocks (limestone, dolomite)

Special problems with groundwater:

landfill

cave stream

Karst aquifers are typically not good filtersof groundwater pollutants

Winterpark, FL

“Oh no, my truck!”

Collapse sinkhole in Cookeville

TOTAL FRESHWATER WITHDRAWALS, 1995

Groundwater withdrawals and usesin the US (2000)

million gallonsUse per day (bgd) %

Irrigation 56.9 69Public supply 16.0 19Industry 3.6 4Other 6.6 8 Total 83.1 100

Fig. 4.2

Miss. R. aquifers (15%)

High plains aquifer (30%)California, Central Valleyand western basin aquifers (10%)

Water resources of Tennessee

% Tennesseans that rely on public water

1960……68%

1995….. 84%

TN -- Total water withdrawals:

Surface water (rivers, reservoirs): 96%Groundwater: 4%

East TN: some high-producing aquifers in areas of fractured bedrock

Middle TN: poor aquifers due to low-porosity, dense limestone bedrock

West TN: very productive aquifers, sand and gravel deposits

Note high withdrawals from TVA reservoirs. These supply major cities andprovide water for steam plants.