Lecture 21 Flashcards
Causes of stream floods (4)
1) Increase stream discharge
2) Alter stream flood hydrograph
3) Dam failure
4) Flooding of deltas
Why are most large deltas sinking and flooding?
Sediment compaction from removal of oil, gas, and water from underlying sediments
trapping of sediment in reservoirs upstream
Flood mitigation
Structural and Non-structural responses
Primary controls on streams (2)
Discharge of water
Base level
Secondary controls on streams (6)
1) Sediment
2) Resistance of bedrock to incision
3) Roughness of stream bed
4) Gradient of stream
5) Channel pattern
6) Frequency in variations of these
If base level is the ocean
Will cause river to flood if sea-level rises
If base level is another stream
Will cause river to flood if another stream rises
Sea level change
Due to climate change and glaciation
Tectonics causing base level change
Basin is on hanging wall which drops relative to mountains on footwall
Structural responses to flooding
Damns, building levees and dikes, channelization (straightening, widening, deepening, removal of debris, sandbagging)
Non-structural responses to flooding
Forecasting Zoning Insurance programs Evacuation planning Education
1996 Saguenay floods
Erosion, loss of houses, new channel, destruction of infrastructure Major rainstorm 290mm rain in 36 hours 16000 people evacuated 20 major bridges affected 10 deaths $1bil Antecedent rainfall days before had saturated the ground
Badger, NFLD, 2003
Confluence of 3 major rivers (Badger, Exploits, Red Indian) Major floods in 1978, 1982, 1985 Winter/spring breakup and ice damming February 900 homes affected, many cars destroyed
Calgary, 2013
200+ mm of rain from a frontal storm
40 mm of antecedent rain
Ground still frozen in places, so flashier flood hydrograph
Steep mountain streams cause water to flow more quickly instead of seeping into soil
Engineered hydrology systems underestimated true flood stages
100,000 people evacuated
$6 bil
14,000 homes, 80 schools, 10 health clinics, railways, roads, etc
