What is discharge?
- Total volume of water passing a point per unit time
- m3/sec or ft3/sec
More land in contact with water = slower stream
If the velocities are the same, all of these streams have
the same discharge.
What’s the biggest river in the world in
terms of discharge?
How and where does a river deposit its
- floodplains and natural levees, leaving
- behind alluvium)
What are floodplains?
- Flood plain are broad strips of land built up by
- sediment deposited on either side of a stream
What are natural levees?
- Natural levees occur where streams flood banks
- and deposit sediment directly on top of banks.
What is the difference between braided and meandering streams?
- Braided streams-
- Carry large quantities of sediment (often as bedload)
- typically in deserts or glacial areas.
- Channels get clogged with sediment and keep splitting and
- Meandering streams-
- Single, sinuous channel (meanders) which erode on
- outside of each curve, and deposit a point bar on the
Ox-bow lakes form when parts of the channel are cut off and abandoned.
What is a delta?
- River velocity drops as it
- enters the ocean or a lake,
- causing sediment to
- accumulate as a delta
- Long, finger-like sand
- bodies, e.g. Mississippi
- seaward margin of delta
- consists of islands reworked by waves
- e.g. Nile
- continuously modified into
- tidal sand bodies that parallel the direction of tidal flow
- e.g. Ganges-Brahmaputra
What’s an alluvial fan?
- • Form where gradient suddenly flattens, usually when a
- fault has been crossed
- • Generally in arid climates with little vegetation to prevent
- rapid erosion
- • Mudflows are common
What’s a flood? How dangerous are they?
- Floods are any high flflows of surface waters that overtop normal confifinements or cover
- land normally dry
- Floods are the most devastating of all geologic agents -
- exceeded only by plagues, world wars and the Holocaust in
- loss of life.
What is the recurrence interval?
- – Average time between floods of a given size
- – 100 year flood
- • occurs on average every 100 years
- • 1% chance in every year to experience 100 year flood
How can we control floods?
- Flood control structures
- • dams
- • flood walls
- • channelization
- • levees
- Legal flood control
- • zoning to minimize
- • prohibition of rebuilding;
- • flood insurance