Physical Geography (GEOG 1301.01)

Spring 2005

Chapter 9: Water Resources

Important Concepts

Water is a renewable resource (but think of ways it can be non-renewable.)

Next 50 years, water availability per person will drop 74% (due to population/demand growth)

Energy exchanges between water and atmosphere drive weather systems.

Water flow links the spheres through exchanges of energy and matter.

There are Spatial and temporal components of water availability

(Precipitation = receipt) and (evapotranspiration = expenditure)

Hydrologic Cycle (page 247):

Know all of the components and their percentages.

Ocean = 86% of evaporation

Land gets 22% of precipitation (20% of moisture from ocean)

Runoff is 8% (of the 20%- above- from ocean)- overland flow and streamflow

Regional weather patterns associated with short residence times (average of 10 days)

Long residence times act to moderate temperature and climates

Components of the model:

Precipitation- input of water

Interception- trapping and redirecting water from falling straight to the ground (trees and roofs)

Infiltration- water soaking into the subsoil

Percolation- downward movement of water into sol or rock

Runoff- overland flow (after soil is saturated)

Evapotranspiration- water transpired by plants or evaporated by insolation

Earth’s water budget:

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/bdgt.rxml

Soil-Water-Budget Concept

This section requires a great deal of careful reading (pages 248-256)

Soil-water Budget (soil-moisture environment- figure 9.3 on page 248):

Measures precipitation input against demands of evaporation, transpiration and soil moisture storage

Use the soil-water balance equation to model this (PAGE 249)

Evapotranspiration is reduced when air is cold (holds less moisture) or with high humidity (at or near saturation) and increase when air is hot (can hold more moisture) and dry (not near saturation.)

Precipitation: The input (moisture supply) into the equation = rain, sleet, snow, etc.

Actual Evapotranspiration = evaporation (movement of water from wet to air) and transpiration (plant cooling process)

Potential Evapotranspiration = PE = The amount of evapotranspiration that could happen given optimal moisture conditions. It needs adequate precipitation and soil moisture supply (Thornthwaite calculated from monthly mean air temperature and daylength. Estimated with evaporation pans.

Soil Moisture Storage = Volume of water stored in soil accessible by plant roots

Soil moisture has 2 kinds of water:

1. Hygrosopic- (molecule-thin layer of water, unavailable to plants) and

2. Capillary- (accessible to plants- available to plants)

Field capacity- amount of water available to plant after drainage (runoff and percolation)

Wilting point- condition of soil when only remaining water is unextractable by plants

Goal of irrigation: avoid soil moisture deficit and reduction of plant growth

Understand the water budgets on pages 248-255.

Sample Water Budget (Page 254, Figure 9.11): Must Know- Important to understanding relationship between precipitation, temperature, soil moisture and evapotranspiration

Types of streams: perennial (year long) or intermittent (temporary flow) from surface runoff, subsurface flow and groundwater.

Drought Monitor (monitoring rainfall :

Drought: a moisture deficit bad enough to have social, environmental or economic effects (notice the human emphasis of this definition)

Regular drought conditions map found on the web at:

http://www.drought.unl.edu/dm/monitor.html

Groundwater

Aquifer: rock layer that is permeable to groundwater flow. Bordered by an aquiclude.

Water table: upper limit of water that collects in the zone of saturation (where subsurface water accumulates.)

Ground water tends to move to areas of low pressure and elevation (creating springs.)

Review sections on Overuse and Pollution of groundwater (page 262-266)

Pollution (saltwater intrusion too) and aquifer collapse are irreversible

Know groundwater profile and parts of an aquifer (USGS site):

http://ga.water.usgs.gov/edu/earthgwaquifer.html

http://capp.water.usgs.gov/aquiferBasics/

Texas Aquifers

Edwards: http://www.edwardsaquifer.net/

Texas Water Foundation: http://www.texaswater.org/default.htm

What is the problem with the high plains aquifer (page 263)?

Ogallala: http://www.npwd.org/Ogallala.htm

Identify consumptive and nonconsumptive uses.

Key Terms

Hydrologic cycle	Interception
Infiltration	Percolation
Soil-water budget	Precipitation
Transpiration	Evapotranspiration
PET/AET	Overland flow
Total Runoff	Wilting point
Capillary water	Available water
Field capacity	Porosity
Permeability	Groundwater
Zone of saturation	Zone of aeration
Aquifer	Aquiclude
Confined/unconfined aquifer	Potentiometric surface
Drawdown	Cone of depression