ENVI 485 02/13/07

1
ENVI 485 02/13/07

• SOILS (cont.)
• Soil erosion
• Causes
• prevention
• Sediment pollution
• My research project
• Soil degradation
• Soil as a natural hazard
• INTRO. TO NATURAL HAZARDS DISASTERS
• STEAMS AND FLOODING

2
(No Transcript)
3
Figure 11.16 b
4
(No Transcript)
5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
Figure 11.16 a
9
(No Transcript)
10
Figure 11.15
11
Human activities that enhance soil erosion

• Deforestation
• Over exploitation for fuel wood
• Overgrazing
• Agricultural Activities
• Industrialization/Urbanization

12
Strategies for Reducing Erosion

• Protect from wind
• Plant wind breaks perpendicular to dominate wind
  direction
• Protect the soil from fast moving water
• Reduce the slope
• Plow fields parallel to contours
• Terrace fields
• plants with extensive root systems
• Scheduled grading construction activities
• Sediment ponds and traps

13
Figure 11.18 a
14
(No Transcript)
15
(No Transcript)
16
Figure 11.19 c
17
(No Transcript)
18
Sediment Pollution

• Eroded soil

19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
MY CURRENT RESEARCH PROJECT
23
The impact of terrestrial sediments on the coral
reefs

• What is the pathway of sediment dispersal and the
  quantity and type of sediment reaching fringing
  reefs from
• Drainage basins impacted by development?
• Drainage basins with little development?
• Is there a relationship between sedimentation and
  parameters of coral reef health?

24
Problem/issues

• Sedimentation is detrimental to corals in several
  ways
• Negative impact of sedimentation depends on
• Sediment composition (mineralogy, organic
  content, grain size, etc)
• Water nutrient concentration
• Coral species
• Colony size
• Nature and duration of sedimentation event

25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
Construction on St. John
(Reference The State of Coral Reef Ecosystems of
the U.S. Virgin Islands)
29
(Reference The State of Coral Reef Ecosystems of
the U.S. Virgin Islands)
30
(Reference The State of Coral Reef Ecosystems of
the U.S. Virgin Islands)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
National Park Boundary
35
Great Cruz Bay
36
(No Transcript)
37
(Reference WRI and NOAA, 2005. Land-based
Sources of Threat to Coral Reefs in the U.S.
Virgin Islands. Washington, DC)
Mean Vulnerability to erosion by watershed
38
Methods Sediment traps
(http//coralreefs.wr.usgs.gov/sediment.html)
39
Methods Camera and gridded block
(http//coralreefs.wr.usgs.gov/sediment.html)
40
Methods Sediment traps
41
Soil Degradation

• Leaching modifies soil chemistry
• Application of fertilizers, herbicides and
  pesticides alters soil chemistry
• Human activity modifies soil chemistry
• Runoff water from irrigated fields carries off
  toxic chemicals
• These chemical can collect in lowland areas or
  wetlands

42
Desertification

• Conversion of land from a productive state to one
  resembling a desert
• Overgrazing
• Deforestation
• Adverse soil erosion
• Poor drainage of irrigated land
• Over-draft of water supplies
• Damage from off-road vehicles

43
(No Transcript)
44
The Soil ResourceThe Global View

• Soil degradation is a global issue
• Destructive processes exist such as
• Desertification
• Erosion
• Deterioration of lateritic soil
• Contamination from pollution
• Chemical modification to soil by humans
• These processes combine to the loss of soil, loss
  of soil quality, and degraded acreage left to
  grow enough food for a hungry world. Land area is
  finite.

45
Figure 11.23 a
46
Natural hazards soils

• Unstable soil
• Shrinking and swelling clays
• Liquefaction during earthquakes
• Role in mass wasting
• Role in reducing flood coastal hazards
  (wetlands)

47
(No Transcript)
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
Hazards Risks

• To know ones ignorance is the best part of
  knowledge.
• Lao Tzu, The Tau, 71

52
Types of hazards

• Natural
• Technological
• Mixed (natural influenced by humans)

53
Types of hazards

• Condition
• Process
• Event

54
To predict a hazardous event

• 1. Historical knowledge
• 2. Monitoring and data gathering
• 3. Understanding of hazardous process
• 4. Must have rules to determine success

55
Risk how safe is safe?

• What is risk?
• What is acceptable risk?
• Depends on your VALUES
• What is our society willing to pay for our
  quality of life and life style?
• Paradox of risk reduction

56
RISK ASSESSMENT

• An attempt to assess objectively a public health
  or other environmental risk

57
Human response to hazardsRisk and Policy

• 1. Modify the hazards through human intervention
• 2. Redistribute the losses caused by a hazard
• 3. Decrease the vulnerability (Planning)

58
Magnitude vs. frequency

• Usually inversely related
• Affects hazard perception

59
Disaster prediction and warning

• Location
• Probability occurrence
• Forecasting
• Warning
• Go public
• Problems?

60
Catastrophe

• When a natural disaster results in damages
  (people or property) that require a long involved
  process of recovery

61
Model of recovery

• Phase 1 emergency
• Phase 2 restoration
• Phase 3 restoration I
• Phase 4 restoration II

62
Phase 1 Emergency(days)

• Normal activities stop
• Search and rescue
• Emergency shelter/feeding
• Capital damaged or destroyed

63
Phase 2 Restoration(weeks-months)

• Normal activities return but at minimal levels
• Restoration of urban services
• Return of refugees
• Capital patched

64
Phases 3 4 Reconstruction I
II(months-years)

• Normal activities return to predisaster levels
• Capital rebuilt (replaced)
• Activities improved and developed
• Capital improved beyond predisaster levels
• Disaster preparedness response improved

65
(No Transcript)
66
Effects of Selected Hazards in the U.S.
67
Effects of Selected Hazards in the U.S.
68
Streams and Rivers

Stream Small river River components Formed from streams Watershed or drainage basin Base level and gradient
69
(No Transcript)
70
Sediment in Rivers

Stream total load Bed load Coarse particles moving along the bottom of river channel Suspended load Accounts for about 90 of its total load Dissolved load Carried in chemical solutions
71
(No Transcript)
72
(No Transcript)
73
Discharge and Profile

• Streamflow
• Factors that determine velocity
• Discharge the volume of water moving past a
  given point in a certain amount of time
• Changes from upstream to downstream
• Profile
• Cross-sectional view of a stream
• Viewed from the head (headwaters or source) to
  the mouth of a stream

74
Longitudinal Profile Gadient
75
Drainage basin and cross sections at the
headwater and near base level
76
Variables

• Changes from upstream to downstream
• Profile
• Profile is a smooth curve
• Gradient decreases downstream
• Factors that increase downstream
• Velocity
• Discharge
• Channel size

77
Factors in Stream flow

• Several basic factors control the way a stream
  behaves
• Gradient h/x (expressed in meters per
  kilometers)
• Stream-cross-sectional area A
• (width average depth, expressed in square
  meters)
• Average velocity of water flow v
• (expressed in meters per second)
• Discharge Q (expressed in cubic meters per
  second)
• Load (expressed in kilograms per cubic meter)
• Dissolved matter generally does not affect stream
  behavior

78
Changes Downstream

• On steep mountain slopes, discharge is low so the
  flowing water is shallow
• The stream bed causes much more resistance to the
  flow of shallow water
• Discharge increases downstream as each tributary
  (a stream joining a larger stream) and inflow of
  groundwater introduce more water
• To accommodate the greater volume of water,
  velocity increases together with the
  cross-sectional area of the stream

79
Discharge, Velocity, Channel Shape

• The relationship of discharge, velocity, and
  channel shape for a stream can be expressed by
  the equation
• Q A V
• Discharge Cross-sectional
  Average
• (m3/s) area of stream
  velocity
• (width x average
  (m/s)
• depth) (m2)

80
River Erosion

Erosion types Abrasion by sediments transported by river Hydraulic action of moving water Chemical corrosion Erosion location Down cutting Lateral Concentrating on the outer bends Headward erosion
81
07_14a Meandering River, showing forms and
processes
82
Meander on the Colorado River
83
Erosion
84
Koyakuk River, Alaska, showing meander bends,
point bar, and cut bank
85
Pool and Riffle, Seems Creek near Blowing Rock,
North Carolina. Pool deep areas (see middle
distance) produced with scour at high flow.
Riffle shallow areas (see far distance)
produced by depositional processes
86
Braided channels in Granada, southern Spain with
multiple channels, steep gradient, and coarse
gravel
87
(No Transcript)
88
Effects of Land-Use Changes (1)

Changes in infiltration rate Change of the amount of water flowing into a river Soil erosion Change in the amount of sediments in a river Amount of water and sediments in river Changes in the velocity of water flow Changes in rivers velocity Leading the change in river dynamics

89
Effects of Land-Use Changes

Forest to farmland Increases soil erosion, stream deposition Increases gradient and velocity Increases river-channel erosion Urban build-up Increases impervious cover Increases certain flood frequency Reduces the lag time of flood
90
Effect of dam on erosion
91
07_19 Urbanization increases runoff (Santa
Barbara, CA)
92
Flood

• A flood occurs when a streams discharge becomes
  so great that it exceeds the capacity of the
  channel, therefore causing the stream to overflow
  its banks
• Geologists view floods as normal and expected
  events
• As discharge increases the water rises in the
  channel and erosion scours the bed.

93
Flooding

Flooding Overbank flow condition, discharge greater than channels holding capacity Stage The height of the water level in a river at a given location at a given time Hydrograph Graphic representation of a rivers discharge over time Lag time The amount of time between the occurrence of peak rainfall and the onset of flooding

94
Flood and Hydrograph

• Unusually large discharges associated with floods
  appear as major peaks on a hydrograph
• A hydrograph is a graph that plots stream
  discharge (Q) against time (t)
• Regardless of the size of the stream basin, as
  discharge increases during a flood, so does
  velocity
• This velocity increase has the double effect of
  enabling a stream to carry
• Greater load, i.e., capacity
• Larger particles, i.e., competence