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What is discharge?
- Total volume of water passing a point per unit time
- m3/sec or ft3/sec
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More land in contact with water = slower stream
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If the velocities are the same, all of these streams have
the same discharge.
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What’s the biggest river in the world in
terms of discharge?
Amazon River
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How and where does a river deposit its
load?
- floodplains and natural levees, leaving
- behind alluvium)
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What are floodplains?
- Flood plain are broad strips of land built up by
- sediment deposited on either side of a stream
- channel.
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What are natural levees?
- Natural levees occur where streams flood banks
- and deposit sediment directly on top of banks.
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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
- rejoining.
- Meandering streams-
- Single, sinuous channel (meanders) which erode on
- outside of each curve, and deposit a point bar on the
- inside.
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Ox-bow lakes form when parts of the channel are cut off and abandoned.
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What is a delta?
- River velocity drops as it
- enters the ocean or a lake,
- causing sediment to
- accumulate as a delta
-
Stream-dominated
deltas
- Long, finger-like sand
- bodies, e.g. Mississippi
-
Wave-dominated deltas:
- seaward margin of delta
- consists of islands reworked by waves
- e.g. Nile
-
Tide-dominated deltas:
- continuously modified into
- tidal sand bodies that parallel the direction of tidal flow
- e.g. Ganges-Brahmaputra
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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?
-
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
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How can we control floods?
- Flood control structures
- • dams
- • flood walls
- • channelization
- • levees
- Legal flood control
- • zoning to minimize
- • prohibition of rebuilding;
- • flood insurance
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