Lecture 5 - Flooding and Landslides Flashcards
What is a region that is drained by a single stream?
A drainage basin/watershed/river basin/catchment
Gradient of a river?
The drop in elevation over distance
Where is the gradient of a river highest/lowest?
Greatest in headwaters, lowest at the river mouth
Bed load?
The particles of sand and gravel that slide along the bottom of a channel in rapidly moving water
Suspended load?
Silt and clay particles carried in the water (90% of total load)
Dissolved load?
Ions that are carried in solution in water
Discharge?
The volume of water flowing through a cross section of a river per unit time (V*A=Q)
What forms where a river deposits sediment?
Alluvial fan (on land) or delta (in water)
Braided channel?
A large number of intersecting channels
Anastomosing channels?
Two or more channels with stable islands/bars where sediment is stored
Meandering channels?
Migrate back and forth across a floodplain
Cutbanks?
erosion on the outside of curves due to higher velocity
Point bars?
deposition on the inside of curves due to slower movement
Avulsion?
riber abandons a looping section of the old channel
When does flooding of a stream begin?
When the stream achieves bankfull discharge
Flood Discharge?
the level of river surface at a point (stage)
Flood stage?
indicates that a river has reached a level likely to cause property damage
Recurrence interval?
Avg time between floods
Where do flashfloods occur?
Upper parts of watersheds and in small tributary basins of large rivers
What causes a flash flood?
Large quantities of rain in a short time
Downstream Flood?
- affect larger areas than flashfloods, more destructive
- produced by storms of long duration, or rapid melting of snowpacks
Glacial Lake Outburst Floods (GLOF)
Sudden-onset outburst floods that result from the failure of a moraine-dam, ice dam
Where are many GLOFs found?
SHIT TONS IN PERU
Dykes?
Thick wall constructed to prevent flooding
What are some natural service functions of floods?
- fertile land
- aquatic ecosystems
- sediment supply
Dynamic equilibrium?
River can maintain the gradient and cross-sectionalshape that provides the flow velocity it needs to move sediment load
- Forest –> agriculture increases the amount of sediment delivered, it must flow faster (opp is also true)
Levee
Naturally forming dyke
Flood proofing?
Construction methods to protect buldings from floods
Canada water conservation act, 1953
federal govt can hep people financially
Canada water act, 1970
planning on all water uses
Flood damage reduction program, 1975
agreement not to build on an area with flood risk, except for flood proofed structures
Quick Clay Landslide at Rissa, Norway, 1978
- farmer wanted a basement, was digging out dirt and making a pile
- shore line slid into the lake
- complete liquifaction of the quick clay
- only one person died
- waves moved across the lake and caused flooding in another town
Fall?
bounding of rocks
Slide?
downslope movement of a block of rock
Slump?
Failure plant curved upward
Flow?
All particles move semi-independently of each other, often with water
Debris flows?
Mix of mud/debris/water
Creep?
Very slow flow of rock/sediment
- Sackung large mass of rock
- Topple rock mass pivots about a point
Factor of Safety?
The ratio of resisting forces to the driving forces
- stable when greater than 1, unstable when less than 1
How does the shape of the slip surface affect the landslide?
Rotational slides: slumps are curved
Translational slides: planar
How does slope steepness effect the landslide?
The steeper the slope, the greater the driving force
What type of landslides are arid regions prone to?
Rock falls, debris flows, soil slips
What type of landslides are humid regions prone to?
Landslides, creep, slides, slumps
How can landslides be prevented?
- Drainage control
- Grading: material from the upper slope can be moved to the base
- Slope supports: retaining walls of concrete/brick
