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
• 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
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
• 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 build-up 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
How Water Affects Land
Water as a Hazard & a Resource• Floods
– Event in which body of water overflows its banks
– Storm runoff– Storm surge
• 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
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
• Surface water resources– Reliable water supply critical to
human survival & health, agriculture & other economic activities
– Nearly 250 million people are water-scarce
Water as a Hazard & a Resource