Chapter 11 – WATER ON
THE GROUND
The Hydrologic Cycle
• Hydrologic cycle
– How water moves
through 4 spheres
• Evaporation
– Change from liquid to
vapor
• Transpiration
– Water from plants
passes into atmosphere
• Condensation
– Change from vapor to
liquid
The Hydrologic Cycle
• Water in Earth system
– Deposition
• Changes from vapor to solid
– Precipitation
• Condensed water falls back to
surface (rain, snow, hail)
– Surface runoff
• Excess precipitation drains over land
or via stream channels
– Infiltration
• Water soaks into ground via small
soil openings
The Hydrologic Cycle
• Water in Earth system
– 97.5% of water in hydrologic cycle found in oceans
– 75% of freshwater is found in glaciers/ice caps
– 98.5% unfrozen freshwater is found underground
How Water Affects
Land
• Streams and stream flow
– Overland flow vs. stream flow
– Runoff
– Stream
• Body of water that flows
downslope along clearly defined
natural passageway
How Water Affects Land
• Streams and stream flows
– Gradient
• Steepness of stream channel
• Change in elevation divided by distance
– Discharge
• Amount of water passing by point on channel’s bank during unit of
time
• Width x Depth x Velocity
– Bed texture
• Material that makes up
streambed
How Water Affects Land
• Streams and stream flows
– Load
• Sediment carried or by
stream
• Bedload
– Saltation vs. Traction
• Suspended load
• Dissolved load
• Capacity vs. Competence
– Base level
• Lowest elevation stream
can erode its channel
• Ultimate vs. local base level
How Water Affects Land
• Streams and stream flows
– Niagara Falls
• Knick point = rapids & waterfalls
How Water Affects Land
• Streams and stream flow
– Channel
• Clearly defined passageway where stream
flows
– Straight
• Rare
– Braided
• Interwoven
channels
– Meandering
•
•
•
•
Curving channel
Cut bank
Point bar
Oxbow lake
How Water Affects Land
• Streams and stream flow
– Meandering streams
• Cut bank (outside)
• Point bar (inside)
• Early vs. Mature vs. Old Age
How Water Affects Land
• Streams and stream flow
– Stream drainage patterns
• Controlled by topography
– Dendritic
– Radial
• Controlled by
underlying geology
– Centripetal
– Rectangular
– Trellis
How Water
Affects Land
• Stream deposit
– Floodplain
• Flat valley floor adjacent
to stream channel
• Inundated when stream overflows
– Alluvium
• Stream sediment
– Natural levee
– Alluvial fan
How Water Affects Land
• Stream deposit
– Delta
• Sediment buildup where stream
flows into
standing water
• Triangular shape
How Water Affects Land
• Drainage basin
– Total area from which water flows into stream
• Divide
– Topographic high separating adjacent drainage
basins
How Water Affects Land
• Tributaries
– Smaller channels that feed into larger
streams
– More numerous around headwaters
• Distributaries
– Smaller channels that distribute water
near mouth of stream
– Form due to excess
sediment in main
stream channel
How Water Affects Land
• Lakes
– Standing bodies of open water
surrounded by land
– Ephemeral lakes
Water as a Hazard
& a Resource
• Floods
– Event in which body of water
overflows its banks
– Storm runoff
– Storm surge
Water as a Hazard & a Resource
• Hydrographs of stream discharge
– Crest
– Hydrologic station
Water as a Hazard & a Resource
• Flooding and urban development
– Impermeable
surfaces
Water as a Hazard & a
Resource
• Flood prediction and prevention
– Flood frequency curve
– Recurrence
interval
– Channelization
– Artificial levees
– Flood control
dams
– Diversion
channels
– Floodplain
zoning
Water as a Hazard
& a Resource
• Surface water resources
– Reliable water supply critical to
human survival &
health, agriculture
& other economic
activities
– Nearly 250
million people
are water-scarce