Global => Fresh stream-lakes
ice
ground water
Oceans
Physical Properties of Geologic Materials
Concepts:
Examples: quartz
sandstone
=> high porosity,
high permeability
clay minerals & micas =>
high porosity, low permeability
Subsurface W (all below ground)
Zone of saturation
= phreatic <=> ground water <=> soil moisture
Zone of areation =
vadose
Water table: top of phreatic zone not confined by impermeable overlying rock
Velocity
few cm/year < velocity < 250 m/day . Average = few cm/day
(avg)
__________________: (AF) Useful source of water; best: coarse clastic
R.
__________________: (AC) Not useful; does not allow extraction.
__________________: (AT) Intermediate properties; stores W- Flow slowed
______________to the surface
Aquifer Geometry:
Unconfined
large infiltration area: recharge
water table height
Confined
limited by AC or AT
under pressure
Artesian system: water rises above AF layer because of its own pressure
Potentiometric level : Height water would reach if unconfined because of its own pressure.
Availability: perched water table
Need to know 1. flow path (direction)
2. recharge zone
3. budget (use vs. consumption)
4. Divides in AF system (Pollution)
Sinkholes: circular depression
dissolution and collapse (underground cavern)
limestones large (tens of m)
gypsum
triggered drop in
water table
by
drop in water pressure overuse
drought
Karst topography: also dissolution
circular cracks
clues conical depressions
no streams
Water quality:
Hardwaters: 80-100 ppm => Ca, Mg
Zeolites: ion exchangers Ca - Mg by Na+
Surface vs Groundwater
groundwater...
Mining GW = draw too much too fast (recharge is slow)
Compaction - Subsidence: irreversible
Problems: structural damage
flooding of coastal areas
Solution: pump fresh water? From where?
Saltwater intrusion: upconing of salt water below cone of depression
in fresh water lens.
Water use and Supply
U.S.: 1800 gallons
/ person /day
biological need 1 gallon
Consumers vs Users: Municipal,
Rural,
Irrigation,
Industrial
Extension of supply
CHAPTER 10 - GROUNDWATER
Review Questions
1) Draw an unconfined aquifer and indicate its different components.
2) Characterize aquifer aquiclude and aquitard rocks. Define
each of those terms.
3) What is an artesian system?. Compare its recharge area to
that of an unconfined aquifer. Define potentiometric surface.
4) What factors need to be considered in order to assess groundwater
availability? Explain how any two of them influence the groundwater system.
5) Why and how do sinkholes form? Name rock types prone to produce
sinkholes.
6) What do you understand by hard waters? What does pH measure?
When is water considered alkaline and when acidic?
7) Name of the mineral group used as ion exchanger in water softeners.
How does it work? Is "softened" water good for everyone?
8) What is a cone of depression?
9) What clues point out to excessive groundwater withdrawal?
Mention its consequences. Explain why it is difficult to solve the problems
posed by excessive groundwater withdrawal.
10) What measures can be taken to mitigate the problem of dwindling
groundwater supply in areas where rain occurs as intense and but short
lived storms?
11) Analyze the use and consumption of water in the U.S. by the following
categories of users: municipal, rural (not including agriculture), agriculture
and industry. Order those sectors in decreasing order of water use. Order
those sectors in decreasing order of water consumption.
12) Mention two methods for desalination. Explain advantages and disadvantages
of each of them. Could they work to produce freshwater for irrigation purposes?
Yes, No, why?
13) How can conservation be applied to save water? Explain in detail
two options.
14) Water for agriculture in the High Plains is pumped out from the
Ogallala aquifer. Outline the perspectives for agriculture in the area
based on the present consumption of groundwater. (Read related Box in your
text).
15) Analyze the situation of surface water in the Colorado River Basin.
(Box in your text).