Running water

• 97.2 % oceans• 2.2 % ice• 0.6 % liquid fresh water most of

which is ground water• Water is always on the move in

the water cycle

Water Cycle

• Infiltration = soak in• run off - surface flow• evaporation = back into the

atmosphere• transpiration = back into the

atmosphere by plant• evapotranspiration - combined

Running water• Run off begins as sheet flow.• How much goes into the ground depends

on the infiltration capacity of the soil• Factors of infiltration

– intensity and duration of rain fall– soil wetness(saturation)– soil texture– slope– vegetation

Running water

• Rills - tiny channels • Gullies - larger channels• stream - any running body of water

– sometime called rivers if really large

Stream characteristics

• Gradient or slope is the vertical drop of the stream over a fixed horizontal distance,– The steeper the slope the more energy

available for stream flow.

• Cross-sectional shape determines the amount of drag.– The less drag the faster the water can flow– Size and roughness also influence drag

Stream characteristics

• Discharge is the amount of water flowing past a certain point in a given amount of time– Discharge (meter 3/ second)= – channel width(meters) X depth

(meters) X velocity (meters/second)

Changes downstream

• Longitudinal profile - a look at the stream from head to mouth– gradient decreases downstream– discharge increases downstream– width, depth and velocity increase

downstream

• When gradient is high, discharge is small

Base level

• Running water in a stream will erode downward over its course until it reaches a balance point.

• This balance point is called the base level.

• Base level is the lowest elevation to which a stream can erode.

• Two types of base level

Base level

• Ultimate base level - sea level• Temporary ( local) base level -

anything which has the capacity to limit downward erosion.– Lakes, resistant bedrock, or a larger

stream

• Kalamazoo River – Ultimate base level the Atlantic ocean– Local base level Lake Michigan

Base level

• Base level can be changed.– Raised base level results is velocity

dropping and deposition begins up stream.– Lowered base level results in velocity

increasing and erosion increasing.

• How do you raise base level? Build a dam.

• How do you lower base level? Uplift the land or lower sea level.

Base level

• Sooner or later a stream will reach base level and be neither eroding or depositing just transporting.

• A graded stream is at base level

Stream Erosion• Waters in streams are turbulent. They

whirl and eddy.• The material in streams (sand, gravel,

silt, and clay sized particles, plus dissolved minerals) abrades the streambed and become rounder and smoother with transport. This is called the load.– Potholes are gouged by gravel caught in

an eddy.

Stream Transport

• Dissolved load - minerals dissolved by ground water and added to the stream.

• Suspended load - usually the largest load of a stream. Fine sand, silt and clay sized particles.– How much suspended sediment depends

on velocity of the stream and settling rate of the sediment.

Stream Transport

• Bed Load - the material on the stream bed too large to be carried by suspension.– This is the stuff that does the grinding to

produce downward erosion.

• This material moves by rolling, sliding and saltation.– Saltation is jumping or skipping down

stream

Stream Transport

• The ability to carry material is measured in capacity and competence.

• Capacity is the maximum load a stream can carry.

• Competence - the maximum sized particle a stream can carry. – The greater the stream’s discharge the

greater the capacity and competence.

Stream deposition

• When velocity slows the stream can no longer carry its load.

• Particles will be deposited by size with the largest settling out first.

• This sorting explains why particles of the same size are found together.

• Alluvium is the term for all stream deposited sediments

Stream deposition - channel• Channel deposits - the materials

deposited mid-stream usually sand or gravel in bars.

• Point Bars form in the inside bend of a stream meander.

• Braided streams have bars mid channel. – Merger of two streams with different velocity,– after glacial melting, or– after heavy down pour.

Stream deposition- floodplain• Floodplain - the area adjacent to a

stream that is covered with water during a flood.

• Natural levees flank the stream and are an accumulation of gravel deposited during a flood when the water lost it competence and capacity upon leaving the channel.

Stream deposition- floodplain• Some levees are so high that

tributary streams can’t enter the main stream.

• These streams (Yazoo tributaries ) flow along the flood plain of the larger stream in swampy (back swamp) poorly drained areas.

Stream deposition- Fans and Deltas• When a stream loses its competency

abruptly it will drop its load.• Alluvial fans will form if the

deposition occurs on land. These are fairly steep.

• Delta will form if the deposition occurs under water.These are fairly shallow.

Stream deposition- Fan

• Alluvial fans form when a high gradient stream in a narrow mountain valley enters a broad flat basin.

• The change is gradient is drastic resulting is immediate deposition.

• Coarse material is deposited at the top of the fan while finer material is carried lower.

Stream deposition- delta

• Deltas form when a stream enters a lake or the ocean.

Stream deposition- delta

• The main stream will become sediment choked, so it will seek a higher gradient route to base level.

• It may do so by splitting into branches called distributaries.

Stream deposition- delta

• Mississippi River Delta - a bird-foot delta.– This delta extends far out into Gulf of

Mexico .– Many Smaller sub deltas have grown since

the ice age.

• Threat to the Mississippi includes a potential capture and diversion of water further upstream.

• Could spell disaster for New Orleans.

Stream Valleys

• Playfair’s law - all streams have a main trunk, fed by branches and have carved the valley in which they exist.

• Two types of stream valleys– narrow V shaped valleys– wide valleys with flat floors

Stream Valleys - V shape

• Characterized by – downcutting– narrow canyons with steep wall– rapids and waterfalls

• Valley walls undergo weathering and mass wasting at the top to help with the profile.

Stream Valleys - Wide valleys• More common in a graded stream • Erosion shifts from down-cutting to lateral.• Streams flow in floodplain is sweeping

bends called meanders.• Erosion takes place on the outside of the

bend at the cut bank.• Deposition takes place on the in side of

the bend at the point bar• Causes the meander to migrate laterally

and downstream

Stream Valleys - Wide valleys• Sometimes one meander will cut off

another to create a shorter channel• The abandoned meander is called an

oxbow lake.• Eventually the lake fills with

sediment to create a cut off scar• Incised meanders- form when there

is a rapid change in base level.

Drainage networks

• All streams drain to an ocean.• The drainage basin is all the land

contributes water to the stream.• A divide is the imaginary line that

separates two drainage basins.• Individual drainage basins have one

of four patterns depending on the material on which they flow.

Drainage Patterns

• Dendritic - the most common - tree like branches emptying into larger trunks

• Radial - like spokes on a bike tire draining the side of an isolated cone or dome.

• Rectangular - flowing over jointed rocks making sharp right angle turns

• trellis - also rectangular but looking more like a trellis with lots of branches.

Stream Piracy - Ahrg!!

• Streams erode headward, downward and laterally.

• As Niagara Falls erodes it is doing so up stream (headward erosion)

• When the headward erosion of one stream breaches the divide it can divert water from a slower stream. This is stream piracy.

Floods and Flood Control

• What causes floods? Too much water from rain or melt water.

• Controls include building artificial levees, dams,channelization (dredging) and better flood plain management (non-structural controls).