1 WATER ON AND UNDER GROUND Objectives • Define and describe the hydrologic cycle. • Identify the basic characteristics of streams. • Define drainage basin. • Describe how floods occur and what factors may make them worse. • Define recurrence interval and show how it is used to predict floods. • Define water table. • Identify two types of aquifers. The Hydrologic Cycle • Hydrology – The scientific study of water • Evaporation – Water changes from a liquid into water • Transpiration – Water taken up by plants passes into the atmosphere • Condensation – Water changes from a vapor into a liquid or a solid
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1
WATER ON AND UNDER
GROUND
Objectives
• Define and describe the hydrologic cycle.
• Identify the basic characteristics of streams.
• Define drainage basin.
• Describe how floods occur and what factors may
make them worse.
• Define recurrence interval and show how it is used to
predict floods.
• Define water table.
• Identify two types of aquifers.
The Hydrologic Cycle
• Hydrology
– The scientific study of water
• Evaporation
– Water changes from a liquid into water
• Transpiration
– Water taken up by plants passes into the atmosphere
• Condensation
– Water changes from a vapor into a liquid or a solid
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The Hydrologic Cycle
• Water in the Earth system
– Precipitation
• Water that has condensed in the atmosphere falls back to the surface
as rain, snow, or hail
– Surface runoff
• Precipitation that drains over the land or stream channels
– Infiltration
• The process by which water works its way into the ground though
small openings in the soil
– Evapotranspiration
The Hydrologic Cycle
The Hydrologic Cycle
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The Hydrologic Cycle
How Water Affects Land
• Streams and stream flow
– Stream• A body of water that flows
downslope along a clearly defined natural passageway
How Water Affects Land
• Streams and stream flow
– Channel• The clearly defined
passageway through which a stream flows
– Straight
– Meandering
– Braided
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Qu’Appelle Valley, Manitoba
Meandering Stream
Braided stream
How Water Affects Land
• Streams and stream flows
– Gradient
• The steepness of a stream
channel
– Discharge
• The mount of water passing by
a point on a channel’s bank
during a unit of time
– Load
• The suspended and dissolved
sediment carried by a stream
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Discharge is the amount of water that flows through a channel. Discharge is
calculated by first finding the cross-sectional area of a stream and then
multiplying this times the velocity. The result will always be in a measure of
volume per unit time. Rather than trying to measure streams everywhere all the
time, stream gages (measure points) are used to estimate flow.