GLG110 Geologic Disasters and the Environment

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GLG110 Geologic Disasters and the Environment
Today Chapter 10 Water Resources
Instructor Professor Stan Williams Email
stan.williams_at_asu.edu
TA Carol Butler Email clbutler_at_asu.edu
Course Website http//glg110.asu.edu
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Overview

• Essential terms and concepts of Rivers
• Review of Floods from Tuesday
• Introduction to Groundwater

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The Parts of a River

• Slope (or gradient)
• vertical drop of the channel over some horizontal
  distance (nearly vertical slope waterfall)
• Base Level
• lowest level to which a river may erode
• most often sea-level
• Drainage Basin
• area drained by a single river or river system

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Channel Types

• Braided Channels
• characterized by many gravel bars and islands
  around which the river divides and reunites
• relatively steep slope
• coarse sediment
• wide and shallow

Polychrome Pass, Denali N.P. Alaska
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Channel Types

• Meandering Channels
• develop when the river winds sinuously across a
  plain
• flat floodplain
• finer sediment
• relatively narrow and deeper
• Oxbow Lakes form in abandoned channel bends

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Channel Types

• Meandering Channels
• Pools develop where the channel is deeper and the
  water is slow
• Smooth, glassy surface
• Riffles form in shallow areas where a lot of
  sediment has been deposited
• Rough, white-water surface rapids

Pool
Riffle
Sims Creek, Blowing Rock, North Carolina
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Rivers and Sediment

• Rivers carry and move large quantities of
  sediment
• Total Load the total quantity of sediment
  carried in a river
• Bed Load particles moving along the river
  bottom
• Suspended Load the sediment carried within the
  flowing river
• Capacity the total load of sediment that a
  river carries in a given period of time

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Rivers End

• When the river slows down and spreads out it can
  no longer carry its sediment
• Alluvial Fan
• Delta

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Alluvial Fan

• Alluvial Fan triangular-shaped deposit formed
  when streams flow from mountains onto the plains
• Popular place to build - great views of
  mountains, elevated above the plain
• Do you think that is wise?

Caraballeda, Venezula
Image USGS/Matthew C. Larsen
Badwater, Death Valley, California
Image Martin Miller
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Venezula, December 1999

• Storms in the mountains or snow melt can cause
  flooding - bad news if you live there

Marks on walls show height of debris deposit
Person for scale
Images USGS/Matthew C. Larsen
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Delta

• Delta triangular-shaped deposit that forms
  under water when a river enters a lake or ocean
• river often splits into distributory channels

New Orleans
Images NASA
Mississippi River Delta
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Mississippi Delta over time
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Discharge

• Discharge (Q) W x D x V
• Discharge is the volume of water moving by a
  specific spot in a river in a specific amount of
  time
• Measured in cubic meters per second (cms)
• W width of the flow meters
• D depth of the flow in meters
• V average velocity of the flow in meters per
  second

W
D
V
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Discharge
Grand Canyon N. P. Arizona

• If both rivers had the same velocity which would
  have the higher discharge?

Rio Grande, Colorado
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Dams

• Construction of a dam causes considerable changes
  both up and downstream from the structure
• Deposition upstream, especially within reservoir
• Erosion downstream because water is sediment free
  and flow has been disrupted
• Dams and Floods
• If a dam breaks the reservoir drains causing
  devastating flooding downstream with little time
  to evacuate

• Controlled flooding in some cases to help restore
  environment

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Urbanization Floods

• Impervious Cover cement, asphalt, pavement,
  roofs, etc. that cover the Earths surface and
  alter water drainage patterns

• The magnitude and frequency of the floods is
  affected by the percentage of impervious cover
  and the percentage of area served by storm sewers

Santa Barbara, California
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Urbanization Floods

• The magnitude and frequency of the floods is
  affected by the percentage of impervious cover
  and the percentage of area served by storm sewers

more people
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Urbanization Floods
Lag time- before

• Urbanization increases runoff because less water
  infiltrates the ground
• Urbanization reduces Lag Time, the amount of time
  between the when the rainfall occurs and a flood
  is produced

Lag time- after
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ReviewFactors that Affect Flood Damage

• Land-use on floodplain
• Depth and velocity of water
• Frequency of flooding
• Rate of rise of floodwater
• Duration of flood
• Season
• Sediment load deposited
• Effectiveness of forecasting

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ReviewAdjustments to Flood Hazards

• Levees constructed earthen embankments
  constrain path of river
• Channelization straightening, deepening,
  widening, clearing, or lining existing channels
• cited to control floods and increase drainage
• objections eliminates habitats, eliminates
  vegetation, changes flow patterns

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Review Floodplain Regulation

• Objective to obtain the most beneficial use of
  floodplains while minimizing flood damage and
  cost of flood protection
• Map the flood hazards
• Determine appropriate development zones
• Relocate and redesign where appropriate

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Flood Hazards

• Flash Floods Fast response to severe storms or
  dam failure
• Too much water in very short duration, ground
  cant absorb
• Cause flooding down washes where there was no
  visible sign of the storm
• Climb to safety
• July 1976
• Big Thompson Canyon, CO
• Rained 14 inches in 4 hours
• 144 people killed

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Flood Hazards

• Long-term Floods Waters rises over time due to
  prolonged rain in region or in response to snow
  melt from above average winter storms
• Strong currents and undertow (just 6 inches of
  rapidly moving flood water can knock a person
  down)
• Hidden objects
• 80 of flood deaths occur in vehicles, most when
  trying to drive through flood waters.
• A mere 2 feet of water can float a large vehicle
  even a bus.
• 1/3 of flooded roads and bridges are so damaged
  by water that any vehicle trying to cross stands
  only a 50 chance of making it to the other side
• Storm Surge - hurricanes

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Associated Hazards

• Floods are a hazard which can cause additional
  hazards
• Fire
• Exposed electrical sources
• Pollution
• Water may contain sewage or chemicals
• Erosion / Landslides
• Flood waters may undercut river banks
  jeopardizing hillslope and structures above
• Strong floods may move large quantities of
  sediment

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Water Resources Overview

• Hydrologic Cycle
• Surface water and rRunoff
• Groundwater
• Aquifers and Aquitards
• Groundwater Movement and Supply
• Interactions Surface Water and Groundwater
• Groundwater Related Hazards

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Hydrologic Cycle
Starting with a raindrop, show all the pathways
it can take before ending up as a raindrop again
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Hydrologic Cycle
----Evaporation-----
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Drainage Basins

• Drainage Basin area of land that contributes
  water to a particular stream or river
• Includes streams and rivers as well as surface
  runoff

Basin A
Basin B
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Surface Water

• Surface Water runoff is directly related to
  sediment erosion, transport, and deposition

Moving water carries sediment
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Factors influencing runoff and sediment yield

• Geologic factors
• different rates of infiltration and erosion
• Topography
• relief (difference in local elevations)
• Climate
• storm types, annual variation
• Vegetation
• may resist erosion and absorb precipitation
• Land use
• Agriculture or urbanization

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Vegetation and Runoff

• Normal conditions
• May decrease runoff by absorbing rainfall
• May reduce stream-bank erosion because soil bound
  by roots
• Large amounts of organic debris affect
  stream-channel form and development of pool
  environment

• Loss of vegetation
• By clearing, grazing, fire, climate results in
  increased runoff and erosion

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Groundwater

• Groundwater water (most from precipitation)
  that flows through the soil and rocks beneath the
  surface

Vadose Zone all Earth materials above the zone
of saturation water moves through the vadose
zone to reach the saturated zone
Water Table the top of the zone of saturation
Zone of Saturation layer in which the pore
space in the soil and rocks is filled with water
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Aquifers and Aquitards

• Aquifer zone of Earth material from which
  groundwater can be extracted at a useful rate via
  a well
• good aquifers include gravel, sand, soils,
  fractured sandstone
• Aquitard zone of Earth material that will hold
  water but not transmit it fast enough to be
  pumped from a well
• often forms a confining layer that restricts
  water flow

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Aquifers and Aquitards
Perched Aquifer local zone of saturation above
the water table
Groundwater Recharge any process that adds
water to an aquifer
Spring forms when water flowing in an aquifer
intersects with the Earths surface
Confined Aquifer aquifer beneath an aquitard
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Groundwater Movement

• Hydraulic Gradient groundwater flows downslope
  depending on the type of material that comprises
  the aquifer
• Cone of Depression a funnel shaped depression
  in the water table caused by pumping groundwater
  out through a well

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Groundwater Supply
50 of the U.S. population uses groundwater as a
primary source of drinking water
In many parts of the country groundwater
withdrawal exceeds recharge
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InteractionsSurface Water Groundwater

• Withdrawal of groundwater by pumping can
• Reduce stream flow
• Lower lake levels
• Reduce water in wetlands
• Withdrawal of groundwater can cause streams to
  dry up habits may be lost
• Withdrawal of surface water can deplete
  groundwater resources

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Groundwater Related Hazards

• Groundwater withdrawal may cause subsidence of
  overlying surface
• Fissures may develop and grow with time

Fissure in Harquahala Valley, Arizona
Image Raymond C. Harris
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Fissures
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Groundwater Related Hazards

• Water pollution in surface streams may filter
  down into groundwater and pollute drinking water
• Pollution on dry surface may be filtered into
  soil and groundwater with precipitation or
  occasional flooding

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Karst Topography

• Karst Topography forms when surface water is
  diverted to subterranean routes through limestone
  which is dissolved and results in unique landforms

• Sinkholes result from
• solutional weathering at surface, or
• collapse of surface material into underground
  caverns
• Karst Plain surface pockmarked by numberous
  sinkholes

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Sinkhole Hazards

• Sinkholes are occasionally used for
  waste-disposal (generally illegally) bottom of
  sinkhole is near water-table which injects
  pollution into groundwater
• Sinkholes may form in urban areas causing
  structural damage to homes or businesses

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Sinkhole Hazards

• April 1998
• Springhill, Florida
• 150 ft diameter sinkhole opened
• Wells in vicinity were shut down to hopefully
  prevent further depressions from developing

Images Hernanda County Emergency Management
150 ft
Rim of sinkhole
Water and debris on floor of sinkhole
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Be Aware of Hazards When You Buy a Home
http//www.azgs.state.az.us/Home20Buyers20Guide.
htm