Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 12 The Hydrologic Cycle and Groundwater
Hydrologic Cycle and Groundwater M. L. Sinibaldi/Stock Market
Groundwater The study of groundwater and its effects is called Hydrology. Uses of Water: LivingEngineeringRecreation DrinkingCoolingSwimming PhotosynthesizingHeatingFishing RespiringCleaningSailing MetabolizingFlushingSkating IrrigatingSkiing
Fig Distribution of H 2 O on Earth
Uses of Groundwater Why is groundwater such a valuable resource? 1.Abundant - 70 times more in the subsurface than in surface reservoirs. 2.Because groundwater moves so slowly it is stored in the earth and remains available even in dry periods. 3.In some regions groundwater flows from humid environments to dry ones, making water available.
Groundwater Water contained in spaces within soil, bedrock, and regolith Less than 1% of all H 2 O on Earth 40 times more abundant than water found in lakes and streams
Hydrologic Cycle Fig. 12.2
Rain Shadow Deserts Fig. 12.3
Fig. 12.4a Average Annual Precipitation in the U.S.
Average Annual Runoff in the U.S. Fig. 12.4b
Fig Swamps as Reservoirs
Groundwater terms zone of aeration zone of aeration: portion of soil and rock near the surface in which open spaces are filled primarily with air (a.k.a vadose zone) saturated zone saturated zone: zone in which pore spaces are filled with water water table water table: boundary between zone of aeration and saturated zone
Geologic activity of groundwater Dissolution (most important in carbonates and evaporites) Cementation Replacement
Springs Locations where a perched water table intersects the ground
Soils and rocks are not completely solid. porosity: portion of volume of a material that consists of open spaces permeability: measure of the speed at which fluid can travel through a porous medium Imagine two vertical pipes, one filled with gravel, one with sand. Out of which one will the water flow faster?
Fig. 12.7a Porous Sandstone
Fig. 12.7b Cemented Sandstone
Fig. 12.7c Well-sorted Sandstone
Poorly-sorted Sandstone Fig. 12.7d
Unfractured Shale Fig. 12.7e
Fractured Shale Fig. 12.7f
More groundwater terms aquifer aquifer: body of rock that is sufficiently water permeable to yield economically significant quantities to wells and springs aquitard aquitard: body of rock that retards but does not prevent flow of water to or from an adjacent aquifer aquiclude aquiclude: body of relatively impermeable rock that is capable of absorbing water slowly but does not transmit it rapidly enough to supply a well or spring
Fig Groundwater Table
Groundwater Movement in Temperate Regions Fig. 12.9
Wet Period Fig
Dry Period Fig
Fig Confined Aquifer
Fig Perched Water Table
Fig Drawdown Due to Pumping
Fissures and Depressions Caused by Overpumping Fig James W. Borchers/USGS
Saltwater Intrusion Fig
Rates of groundwater movement Slow to very slow (depending on permeability) Generally within the range of 10 to 100 cm per day
Darcy’s Law Q = discharge (m 3 /sec) A = cross-sectional area (m 2 ) K = coefficient of permeability (m/sec) h 1 = beginning height (m) h 2 = ending height (m) l = length of flow (m) Q = AK(h 1 – h 2 ) l
Fig Darcy’s Law
Fig U.S. Groundwater Withdrawals 1950–1995
Ogallala Aquifer: “Mining” Groundwater
Fig David Muench
Fig Sinkhole in Florida Leif Skoogfors/Woodfin Camp.
Major Features of Karst Topography Fig
Water Quality and Groundwater Movement Fig
Fig Groundwater Contamination
Fig Groundwater Distribution in a Typical Section of Continental Crust
Fig Geyser Peter Kresan