Hydrologic cycle`
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Hydrologic cycle`. I. Hydrologic Cycle: the movement of water through and over the Earth Water continuously traveling between oceans, atmosphere, continents, and mantle (by subduction and volcanism) . Hydrologic Cycle. I. Hydrologic Cycle: the movement of water through and over the Earth

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Hydrologic cycle`

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Hydrologic cycle

Hydrologic cycle`

I. Hydrologic Cycle: the movement of water through and over the Earth

Water continuously traveling between oceans, atmosphere, continents, and mantle (by subduction and volcanism)


Hydrologic cycle

Hydrologic Cycle

I. Hydrologic Cycle: the movement of water through and over the Earth

97.2%oceans

2.15%glaciers

0.62% groundwater

0.009%freshwater lakes

0.008%saline lakes & inland seas

0.005%soil moisture

0.001%atmosphere

0.0001%rivers

First we’ll examine streams and then groundwater


Hydrologic cycle

Hydrologic cycle – fresh water inventory


Hydrologic cycle

97.2%oceans

2.15%glaciers

0.62% groundwater

0.009%freshwater lakes

0.008%saline lakes and inland seas

0.005%soil moisture

0.001%atmosphere

0.0001%rivers

Hydrologic cycle


Hydrologic cycle

Streams

II. Stream Terminology

A. Stream (interchangeable with river): any surface water whose flow is confined to a channel.

B. Floodplain: the flat land immediately surrounding a stream channel, which would be submerged if the stream were to overflow it’s banks (wider in valleys than mountains)


Hydrologic cycle

Streams

II. Stream Terminology

C. Headwaters (Head): the origin or the source water of a particular stream

D. Mouth: the point downstream where the rivers empties into another body of water

E. Tributaries: smaller streams which supply water to a larger stream

F. Trunk Stream: a large stream into which smaller streams carry water and sediment


Hydrologic cycle

Streams

II. Stream Terminology

G. Distributaries: one of a network of small streams carrying water and sediment from a trunk stream into an ocean (located at the mouth of a stream)

H. Watershed or Drainage Basin: the total area which feeds a particular stream

Every stream, no matter how small, has a watershed (an area that it drains)

Square mile area drained by a small tributary

Mississippi River, 1.25 million square miles basin


Hydrologic cycle

Streams

II. Stream Terminology

I. Drainage Divide: area of higher topography which separates one watershed from an adjacent watershed

For example, Rocky Mountains divide watershed of Mississippi from that of the Colorado River

Or a low ridge dividing the watersheds of two tributaries

The most important drainage divide in North America is the Continental Divide. The divide separates streams that flow to the Atlantic from those that flow to the Pacific.


Hydrologic cycle

Streams

II. Stream Terminology

I. Drainage Divide: area of higher topography which separates one watershed from an adjacent watershed


Hydrologic cycle

Streams

III. Stream Flow

A. Velocity: the distance the water travels in a given amount of time (varies greatly).

Affects a streams ability to erode and transport material.

Straight channel: fastest in the center, just below the water’s surface.

Curved channel: fastest at the outside of the curve, just below the water’s surface.


Hydrologic cycle

Streams

  • III. Stream Flow

  • Velocity

  • Depends on:

  • 1. Gradient: slope of the stream, or it change in elevation over a given horizontal distance

  • Changes within a given stream, usually higher gradients near the headwaters, and gentler gradients at the mouth (general concave-up profile).

  • All else being equal:

  • steeper gradients = faster stream

  • 66 m/km to 0.1 m/km

  • Gradients are measured as vertical drop per horizontal distance)


Hydrologic cycle

Streams

  • III. Stream Flow

  • Velocity

  • Depends on:

  • 2. Size andShape of the stream channel

  • Slowest at the bottom and sides due to friction

  • Slightly slowed at the surface due to friction with the atmosphere


Hydrologic cycle

  • III. Stream Flow

  • Velocity

  • 2. Size andShape (continued)

  • Wetted perimeter: in cross section, the measure of the amount of surface contact between the water in a stream and it’s channel

  • Faster: small wetted perimeter : cross-sectional area (narrow & deep)

  • Slower: large wetted perimeter : cross-sectional area (wide & shallow)

  • When a given stream channel narrows, the stream must move faster

  • Analogy: put your thumb over a hose

Streams


Hydrologic cycle

Streams

  • III. Stream Flow

  • Velocity

  • 3. Roughness of channel

  • Slower over rough bed (large boulders).

  • Water bounces around more, energy put into upward, side-ways and up-stream directions, typically headwaters

  • Faster over smooth bed (clay, sand), typically further down


Hydrologic cycle

Streams

  • III. Stream Flow

  • Velocity

  • 3. Roughness of channel


Hydrologic cycle

  • III. Stream Flow

  • Velocity

  • B. Discharge

  • The volume of water passing a given point on the stream bank per unit of time

  • Measured as cubic meters per second)

  • 1. Formula for hypothetical rectangular stream channel:

Discharge = width x depth x velocity


Hydrologic cycle

  • III. Stream Flow

  • Velocity

  • Depends on:

  • B. Discharge

  • 2. Discharge also depends on:

  • a. size of drainage basin

  • b. amount of precipitation

  • Varies on daily cycles and seasonal cycles

  • 3. In a given stream, discharge increases from head to mouth

  • 4. Amazon: >12 times higher than Mississippi

  • One day discharge is equal to New York cities water needs for >5 years!

Streams


Hydrologic cycle

Discharge = width x depth x velocity


Hydrologic cycle

Discharge = width x depth x velocity


Hydrologic cycle

Streams


Hydrologic cycle

Problem Set 3

  • Due Monday, March 6th at beginning of class

  • Go to www.geology.cwu.edu and enter 101 in left navbar search field.

  • On G101 web page, download Problem Set #3, PDF file.

  • Discharge, stream velocity, wetted perimeter

  • Simple calculations

  • Need to understand units of calculations (e.g., m/sec or m3/sec)


Hydrologic cycle

Streams

  • IV. Stream Erosion

  • Most important geologic agent of surface change: they can erode, carry, and deposit sediment

  • Processes of Erosion: faster stream = more erosion

  • 1. Abrasion: scouring of the stream bed by transported particles

  • Fine particles suspended in the water constantly scrape the bed

  • Large pebbles my swirl in local eddies, carving out circular depressions called potholes


Hydrologic cycle

Streams

  • IV. Stream Erosion

  • Processes of Erosion

  • 2. Hydraulic lifting (erosion by water pressure)

  • Fast, turbulent water dislodges and lifts particles from the channel into the stream

  • Water forced into cracks with enough pressure to pry up rocks

  • 3. Dissolution

  • Water may dissolve underlying rock

  • For example: limestone or evaporites


Hydrologic cycle

Streams

IV. Stream Erosion

B. Base Level: the lowest level to which a stream can erode its channel

The level at which the mouth of a stream enters the ocean, lake, another stream

Ultimate base level = sea level

Local or Temporary base level = lakes, main streams, dams,

Or resistant layer of rock = waterfalls created, base level is lower on other side of rock

Headwaters: are way above base level actively eroding, downcutting

Near mouth: close to base level with less downward erosion, more side to side erosion


Hydrologic cycle

Streams

IV. Stream Erosion

C. Valley Geometry

1. Narrow: usually more toward head of stream = high gradients)

Where streams are high above base level = more down-cutting

Streams cut straight down into the underlying rock form valleys with vertical walls

Usually V-shaped due to overland flow and mass movements removing loosened material on the slopes


Hydrologic cycle

IV. Stream Erosion

C. Valley Geometry

2.Wide: usually toward the mouth of the river = lower gradients

Once a stream has cut near to base level: energy directed to side to side erosion

Widening of valley creates flood plain, either erosional or depositional


Hydrologic cycle

Streams

IV. Stream Erosion

C. Valley Geometry

3. Channel patterns:

a. Meandering Stream

Current fastest on outside of river bend - actively erodes cut bank

Current slowest on inside of bend - deposits load and creates a point bar deposit


Hydrologic cycle

IV. Stream Erosion

Current fastest on outside of river bend - actively erodes cut bank

Current slowest on inside of bend - deposits load and creates a point bar deposit


Hydrologic cycle

Streams

IV. Stream Erosion

C. Valley Geometry

3. Channel patterns:

a. Meandering Stream

Meanders progressively get more pronounced

Finally only separated by a thin strip

Stream may form a cutoff

Abandoned meander becomes an oxbow lake


Hydrologic cycle

Streams

IV. Stream Erosion

C. Valley Geometry

3. Channel patterns:

b. Braided Stream

Networks of converging and diverging stream channels

Separated by narrow sand and gravel bars

Develop in steams with very high sediment loads

More sediment load than its carrying capacity


Hydrologic cycle

Streams

IV. Stream Erosion

C. Valley Geometry

3. Channel patterns:

b. Braided Stream

Deposit their load in the stream bed  build up until they’re islands

Occurs: Where stream banks are loose unconsolidated material (lack vegetation) or

Where slope of stream decreases suddenly, base of mountain, steep tributary flowing into a gentle gradient main stream

End of glacier = abundance of glacial sediments


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