Water, and running water

 

Water cycle

1.36 billion Km3 of water exists on the Earth

          97.2%  ocean

          2.1% ice cap and glaciers

          0.65% in the freshwater reservoar (atmosphere, lakes,                 rivers, groundwater)

The unending circulation of the Earthís water supply is the so called water cycle. The cycle itself is powered by the heat of the sun and gravitation

 

 Figure is from http://www.und.nodak.edu/instruct/eng/fkarner/pages/cycle.htm

Water from the ocean and from the land is continuously evaporating into the atmosphere, where it is transported by wind. Than clouds  are forming followed by precipitation.

Distribution of precipitation

1. part of the water soaks into the ground (infiltration);

2. other part after big rains runs off (runoff)

3. Some evaporates from the surface,

4. some will be adsorbed then released by plants (transpiration)

3 and 4 together is called Evapotranspiration

Some of the water can be stored on the surface for a while as snow (in glaciers)

FLUVIAL SYSTEM

RUNNING WATER

Running water may have the largest influence on human life.

1. drinking water

2. energy

3. travel

3. irrigation

Running water is divided into two big group:

1. Unconfined flow

       SHEETFLOW (water flowing on the surface)           

       usually depend on the infiltration capacity of the bedrocks.

       (after a while sheetflow will distribute into tiny                    channels RILLS).

       wave-cut clif

 

2. Confined flow (STREAM)

In Confined flow or stream water flows in channels, which are long narrow depressions eroded by the river or flow into the underlying rocks.

  If we check out the longitudinal profile of a stream from the headwater to the mouth we will see some major differences.

At the HEADWATER PART of the stream it has a typical V shape, where the stream occupy the bottom of the channel. There is absolutely no floodplain.

At  the MOUTH of the stream, it is flowing on a broad flat-floored valley. Here the stream channel is surrounded by wide floodplains.

The stream usually stays in the CHANNEL, where the side of the channel is called STREAMBANK

FLOW in the channel can be LAMINAR or TURBULENT

Laminar flow is usually slow and particles are moving straight, parallel with the stream banks:

In Turbulent flow water flows in erratic fashion that is often characterized by swirling, whirpool-like eddies.

 

Factors affecting stream erosion, and deposition:

1. Velocity

2. Discharge

1.Velocity

The speed at which water in a stream travels  is called stream velocity. (moderately fast (3 miles/hour) Fast (15 miles/hour)

Max. velocity in a channel usually is close to its middle (Friction is the smallest here). If there is a curve the centrifugal force pulles the highest velocity to the outer part of the curve!!!! Changes the channel shape!!!

HIGH VELOCITY:

River erode and transport sediment

LOW VELOCITY:

Deposition happens

VELOCITY of a stream IS CONTROLLED BY:

    a. Gradient

       downhill slope of the bed. (Feet/miles; or %)

       G=difference in elevation     (feet)  * 100                

              distance in course        (feet)

       Ex:. Changing gradient strongly influence wether the river   eroding or deposite.

    b. Channel shape and roughness

        As the water flows it wets the channel, and between the bank and the water            there is friction. The larger the channel the larger the bank, the larger the            friction. Friction slows down the flow.

     Roughness has the same affect. In smooth channel water flows faster.        (Changes shape as it flows on different rock types.)

2.DISCHARGE

The discharge of a river is the volume of water that flows through at a certain point in a unit of time.    

Discharge (m3/sec)= channel with(m)*channel depth(m)*velocity (m/sec)

MISSISIPI

D=17,715 m3   

Amazon 10 times more than Mississippi

DISCHARGE IS INCREASING DOWNFLOW

ST REAM EROSION

Streams usually cut their own valley by deepening and widening it for long time

Erosion can happen in three ways.

1. Hydraulic action (ability of the flowing water to pick up and move sediment

2. solution (carry chemicals in solution)

3. abrasion (grading, carving of river bed rocks)

       Potholes (abrasive action of sediment load makes these             holes).    

The sediment in a river can be carried as

       1. bedload

Large or heavy sediment particles that traven on or near the stream bed, and move by traction or saltation

       Movement by rolling, sliding or draging is called TRACTION

2.Suspended load

       Sediment which is carried in the flow all the time

       3.Dissolved load

       chemicalias in the stream                          

The max. sized sediment in the stream that the river can carry define its COMPETENCE, a factor related to flow velocity. CAPACITY on the other hand is the measure of the total load the stream can carry.

Stream Transportation of sediment

RIVERS IN US. CARRY 250 MILLION TONS of SOLID LOAD

300 MILLION TONS of DISSOLVED LOAD.

  STREAM DEPOSITION (CYCLIC

ALLUVIUM (river deposits)

       BAR

       FLOODPLAIN DEPOSITS

BAR IN A CHANNEL

       IN THE MIDDLE OR THE SIDE OF THE RIVER (CAN             MOVE)

Different stream types

Photos from:http://www.und.nodak.edu/instruct/mineral/101intro/slides/rivers/index.htm

ALLUVIAL FANS

Badwater fan

 
 
Badwater alluvial fan
Photo by Martin Miller
 
Slide 24
BRAIDED STREAM

Slide 5

NETWORK OF  INTERCONNECTED RIVULETS AROUND NUMEROUS BARS.

MAINLY IN HIGHER MOUNTAINS WHEN RIVER ENTERING TO FLAT AREA.

 

MEANDERING STREAM AND POINT BAR

FLAT, SLOW FLOWING RIVER

Slide 15

EROSION IN THE OUTSIDE CURVE,

Slide 17

DEPOSITION ON THE OPPOSITE SIDE.

 Slide 4Point bar

 

CUTOFF, OXBOW LAKE

 Slide 16

FLOOD PLAINS

NATURAL LEVEES

DELTAS (WITH LOTS OF DISTRIBUTARIES) DELTA SHAPE

Satellite view of the Indus River delta and surrounding coastline in Pakistan and India

NILE RIVER

NIGER RIVER (NIGER)

THE STREAM AS A SYSTEM

 

DRAINAGE BASINS

Each stream has a drainage basin.

Drainage basin is the total area drained by the given stream and its tributary                  

Tributary is a small stream flowing into a larger one.

Mississippi riverís drainage basin contain 1/3 USA, together with its tributary channels such as Ohio and Missouri rivers

DRAINAGE DIVIDE

A ridge or strip of high ground dividing one drainage basin from the other.

ex. CONTINENTAL DIVIDE

streams flowing to the PACIFIC from

streams flowing to the Atlantic and Gulf of Mexico

 

BASE LEVEL

WESLEY POWELL (1875) REALIZED, THAT THERE IS A DOWNWARD LIMIT OF EROSION, WHICH HE CALLED BASELEVEL.

Sea level = ULTIMATE BASE LEVEL

Lake level = TEMPORARY BASE LEVEL

THE CONCEPT OF GRADED STREAM

WHEN A STREAM JUST BEGIN TO DOWNCUT ITS LONGITUDINAL PROFILE IS IRREGULAR, WITH RAPIDS AND WATERFALLS ALONG ITS COURSE.

UNGRADED

MOST OF ITS ENERGY IS USED FOR                DOWNCUTTING, THE IRREGULARITIES (SMOOTHING).

GRADED

AS THE STREAM SMOOTHES ITS COURSE INTO A CONCAVE UPWARD SHAPE,  IT BECAMES GRADED.

BALANCE BETWEEN TRANSPORTING CAPACITY AND SEDIMENT LOAD AVAILABLE

LARGE SCALE EROSION

1.LATERAL EROSION

       WIDENING OF THE CHANNEL BY ABRASION OF BANKS +MASS MOVEMENT ALONG SIDES

2. HEADWARD EROSION

       SLOW UPHILL GROWTH OF THE CHANNEL

3. REGIONAL EROSION

       PENEPLAIN (FLAT ERODED AREA)

      

 

THE EVOLUTION OF A RIVER CAN BE DIVIDED INTO THREE

STAGES:YOUTH, MATURITY, AND OLD AGE

       -DOWNCUTTING YOUTH

       -LATERAL EROSION MATURE

       -PENEPLAIN (FLAT ERODED AREA) OLD

DRAINAGE PATTERNS

-DENDRITIC PATTERN (IRREGULAR BRANCHING)

Slide 26Slide 27

-RADIAL

-RECTANGULAR PATTERN