HYDROLOGIC CYCLE Precipitation Runoff or infiltration(groundwater flow and plant uptake) Flow to and/or gather in basin Evapotranspiration into air Condensation to form clouds Recycle

SURFACE WATER EROSION- The transport by water of weathered materials…

Major Erosive Agents: MASS WASTING (GRAVITY!) Running Water! Streams, Oceans, Precipitation GLACIERS

Where does the ENERGY for erosion come from? DISEQUILIBRIUM- elevation difference between higher elevations and BASE LEVEL (sea level or lake level)- GRAVITY controlled. SUN- provides kinetic (motion) energy to rain and wind and potential (rest) energy to snow.

STREAMS (the most important source of moving water…) ALL streams flow * fill in the blank * Streams begin at the HEAD and end at the MOUTH. Streamflow is contained within a CHANNEL or STREAM BED Streams carry different weathered material in different ways…

STREAMS (the most important source of moving water…) SOLUTION- smallest sizes, dissolved materials, includes salts. SOLUTION

STREAMS (the most important source of moving water…) SUSPENSION- particles are carried in the flow of water. SUSPENSION

STREAMS (the most important source of moving water…) SALTATION- larger sizes (sand and greater) can be “bounced” along the streambed. SALTATION

STREAMS (the most important source of moving water…) BEDLOAD (traction)- the largest (boulder) sizes are rolled along during heavy stream flow events. BEDLOAD

STREAMS (the most important source of moving water…) FLOTATION- the lightest sizes actually float along on the surface of the flow

Stream Erosion – starts with

Then expands to….. Then expands to…….

This is called a watershed

Idaho example Clearwater River system Subdivided by “divides” into smaller “basins”

Differential Erosion: In this picture, which layers are being eroded the most to cause undermining of other layers? …

Hint:

STREAM CHARACTERISTICS  Velocity – distance water travels in a given amount of time  Stream Gradient – steepness or slope of the stream  Discharge – volume of water that passes a certain point in a given time.

 Competence – a measure that describes the maximum size particles a stream can carry.  Capacity – total amount of sediment a stream can carry. STREAM CHARACTERISTICS -continued-

Velocity in 2 dimensions: Friction slows water close to banks and close to surface and bottom, slowing it. FASTEST= MIDDLE, JUST BELOW SURFACE!

Velocity due to steepness

PARTICLE SIZE vs. VELOCITY Different sized materials require different water velocities to be carried via suspension, saltation, or traction. This is illustrated by the size/velocity curve…

Discharge-the volume of water moved over time

Competence the maximum particle size transported increases with velocity the relationship between particle size and stream velocity small particles are cohesive and thus have a high erosional velocity but remain in suspension in running water (low depositional threshold) large particles are continuously transported and deposited intermediate particle sizes (coarse silt/fine sand) and most easily eroded by running water

Capacity maximum mass of suspended sediment transported by a stream difficult to determine because a sediment laden stream is transitional to a debris flow increases with discharge (i.e. faster than the increase of channel width or depth with discharge) as mass wasting and slope erosion in headwaters deliver sediment to tributary streams

So stream erosion is dependent upon……..

 Meandering streams wander side to side as they constantly seek out the lowest elevation. “Old Age”  This constant motion creates a series of S-shaped “loops”.  Stream Velocity varies from one side to the other side of the “S”, resulting in erosion in some places and deposition of sediments in others. MEANDERING STREAMS

Stream Velocity

Cut-bank - forms on outside of curve of meandering streams or rivers due to higher water velocity, which causes erosion on outside of curves.

Point bars - form on inside of curves of meandering streams or rivers

Eventually, it takes too much energy to keep meandering, so rivers will cut off a bend, resulting in an OXBOW lake…

Floodplain Features

MEANDERSMEANDERS

Braided streams

Braided stream

Alluvial fan

Delta

V-SHAPED VALLEY…

Steep gorge

Water Supplies

Use and re-use

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