Welcome Geol 101 Lectures on Ch 15 Hydrology

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Welcome!Geol 101Lectures on Ch 15 Hydrology

• Dr Ken Sprenke
• ksprenke_at_uidaho.edu
• webct.uidaho.edu

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Water

• Evaporates from oceans
• Rises as water vapor
• Condenses as clouds
• 20 falls as precipitation onto land
• Returns to ocean, mostly as surface run off.

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Running water moves by laminar or turbulent
flowIn laminar flow, streamlines parallel one
another. Laminar flow only occurs naturally in
very slow moving streams
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In turbulent flow, stream lines intertwine.
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Most stream flow is turbulent
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Runoff

• sheet flow
• channel flow

Running water in any channel is called a stream.
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Gradient is steep in upper part of stream, but
gentle in lower reaches.
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Flow velocity, discharge, and stream
cross-section are related. A change in one
affects the others.
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Streams and their tributaries carry run off from
a drainage basin.
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Stream patterns reflect geology.
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Drainage basins are separated by divides.
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Streams erode by hydraulic action, abrasion, and
dissolution.
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The coarser part of a streams sediment load is
bed load. The finer part of a streams sediment
load is suspended load. The dissolved part of a
streams load is carried in solution.
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Competence

• measure of the maximum sized particle a stream
  can carry.
• related to stream velocity.

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Capacity

• measure of the total load a stream can carry
• related to discharge.

The Mississippi has low competence but huge
capacity.
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Braided streams are a complex of dividing and
rejoining streams.
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Braided streams occur where sediment supply
exceeds the capacity of the stream resulting in
sand and gravel bars.
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Meandering streams have a single sinuous channel
with broad looping curves.
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Meanders migrate laterally as the cut bank is
eroded and point bars form on the inner bank.
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Oxbow lakes are cutoff meanders in which
fine-grained sediments and organic matter
accumulate.
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Floodplains are flat areas paralleling stream
channels.
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Floodplains are composed of

• point bar deposits formed by lateral accretion
• mud accumulated by vertical accretion during
  floods.

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A delta is composed of alluvial deposits at a
streams mouth.
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Small deltas in lakes consist of

• bottomset beds
• foreset beds
• topset beds

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Marine deltas are complexes dominated by

• streams
• waves
• tides

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Alluvial fans are lobate alluvial deposits
consisting mostly of sand and gravel.
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Alluvial fans form in arid and semi-arid regions
where vegetation is scarce and erosion rates are
high during periodic rain storms.
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Sea level is the ultimate base level, the lowest
level to which streams can erode.
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Streams commonly have local base levels caused by
lakes, larger streams, and resistant rocks.
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A graded stream is one in which channel
irregularities have been eliminated.
Ungraded stream
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Graded streams have a smooth concave profile of
equilibrium.
In a graded stream, a balance exists among
gradient, discharge, flow velocity, channel
characteristics, and sediment load.
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In a graded stream, little or no deposition or
erosion occurs within its banks.
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Stream valleys develop by a combination of
processes including

• downcutting
• lateral erosion
• mass wasting
• sheet wash
• headward erosion

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Stream terraces are remnants of an older
floodplain at a higher level which indicate
renewed downcutting.
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Incised meanders are evidence of renewed
downcutting by a meandering stream.
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Goosenecks of the San Juan River---incised
meanders.
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Superposed streams cut into ridges directly in
their path.
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Superposed streams once flowed on a higher
surface and eroded downward into resistant rocks.
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Next Lecture Chapter 16 Groundwater