Sediment that is small or light enough to be lifted

Sediment that is small or light enough to be lifted by the water
(deposited when velocity decreases)
o Bed load
 Traction = stays in contact with bed
 Saltation = series of short leaps or bounces
STREAM DEPOSITION
 As velocity falls, largest particles settle out
 Results in sorting of sediment in river deposits = alluvium
 Most transport takes place during floods; most deposition occurs as flood waters fall
 Stream deposits include

o Bars
 Ridge of sediments (sand or gravel)
 Alluvial placer deposits – concentrations of heavy particles, such as
gold, platinum, other metals or gemstones
 Ex: Barra del Puerto
o Braided streams
 A stream heavily loaded with sediment
 Sediment collects as bar deposits which separate the stream into
several different channels
 Arid/semiarid environments
o Meandering streams and point bars
 Meandering streams – single, continuous channel with meanders
 Cut bank
 Point bar
 Oxbow lake
o Flood plains
 Sediments are deposited as a river floods its banks and the water
velocity slows.
 Natural levees
 Back swamp deposits
 Yazoo stream
o Deltas
 Where the stream deposits at the mouth od a body water
 Distributaries
 Stream dominated delta
o Long, finger- like sand bodies
o Mississippi
 Wave-dominated deltas
o Seaward margin of delta consists of islands reworked by
waves
o Nile
 Tide dominated delta
o Continuously modified into tidal sand bodies that
parallel the direction of tidal flow
o Ganges-brahmaputra
o Alluvial fans
 Is like a delta except it forms with temporary streams
 Usually deposit in arid and dry areas, when there is snow this rivers
can flood.
 Bajada
FLOODS

 Most deposition occurs when rivers flood.
 Floods are the most devastating of all geologic agents - exceeded only by plagues,
world wars and the holocaust in loss of life.
 $5 BILLION annually in the US, NOT including coastal flooding due to hurricanes.
 River floods can occur quickly and recede after hours/days
o Flash floods- can be caused by rapid, heavy rainfall, dam failures, etc.
CAN FLOODS BE PREDICTED/CONTROLLED
 Controlling Floods
o Dams
o Flood walls
o Levees
o Floodways – built for excess water to flow through
o Channelization – speed up the flow of water and thus prevent flooding
o Dikes
 Zoning to minimize development
 Prohibition of rebuilding; moving town
o Not a realistic option for larger towns
o Martin, KY – has flooded 37 times since 1862
NORTH AMERICAS DRAINAGE DIVIDES
 Drainage basins
o Mississippi River Drainage basin
 40% of US area
 Tributaries
 Divides
DRAINAGE PATTERNS
 The arrangement, in map view, of a river and its tributaries
o Dendritic
 Like tree branching
 Gently sloping surfaces
o Radial
 Flows outward in all directions
o Rectangular
 Right-angle bends
 Controlled by geologic structures
 Ex. jointing
o Trellis
 Parallel main streams
 Tributaries at right angles

STREAM VALLEYS
