Chapter 11 – WATER ON THE GROUND. The Hydrologic Cycle Hydrologic cycle –How water moves through...

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


• Streams and stream flows– Niagara Falls

• Knick point = rapids & waterfalls



– Channel• Clearly defined passageway where

stream flows– Straight

• Rare– Braided

• Interwoven channels

– Meandering• Curving channel• Cut bank• Point bar• Oxbow lake


– Meandering streams• Cut bank (outside)• Point bar (inside)• Early vs. Mature vs. Old Age


– 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


• Stream deposit– Delta

• Sediment build-up where stream flows into standing water

• Triangular shape


• Drainage basin– Total area from which water flows into

stream• Divide

– Topographic high separating adjacent drainage basins


• 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


• 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

• 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

• Surface water resources– Reliable water supply critical to

human survival & health, agriculture & other economic activities

– Nearly 250 million people are water-scarce


Chapter 11 – WATER ON THE GROUND. The Hydrologic Cycle Hydrologic cycle –How water moves through...

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