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
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 – fresh water inventory
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
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)
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
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
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.
Streams
II. Stream Terminology
I. Drainage Divide: area of
higher topography which
separates one watershed from
an adjacent watershed
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.
Streams
III. Stream Flow
A.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)
Streams
III. Stream Flow
A.Velocity
Depends on:
2. Size and Shape of the
stream channel
 Slowest at the bottom and
sides due to friction
 Slightly slowed at the
surface due to friction with
the atmosphere
Streams
III. Stream Flow
A.Velocity
2. Size and Shape (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 : crosssectional 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
III. Stream Flow
A.Velocity
3. Roughness of channel
Slower over rough bed (large
boulders).
Water bounces around more,
energy put into upward, sideways and up-stream
directions, typically
headwaters
Faster over smooth bed (clay,
sand), typically further down
Streams
III. Stream Flow
A.Velocity
3. Roughness of channel
III. Stream Flow
A.
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
Streams
III. Stream Flow
A.
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!
Discharge = width x depth x velocity
Discharge = width x depth x velocity
Streams
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)
Streams
IV. Stream Erosion
Most important geologic agent of
surface change: they can erode,
carry, and deposit sediment
A. 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
Streams
IV. Stream Erosion
A.
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
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,
Headwaters: are way above base level
actively eroding, downcutting
Near mouth: close to base level with less
downward erosion, more side to side erosion
Or resistant layer of rock =
waterfalls created, base level
is lower on other side of rock
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
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
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
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
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
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
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