Eccl. 1:7 "All the rivers run into the
sea; yet the sea is not full; unto the place from whence the rivers
come
thither they return again" or "All the rivers flow into the sea, yet
the
sea is not full. To the place from which the rivers come, there they
return"
The water cycle...good
site from USGS
Stream - body of running water
confined to a channel and flowing
downhill under the influence of gravity.
Sketches that show the
longitudinal profile
of a river and cross profiles (3)
Surface runoff
Overland flow
River Types
(What
is the difference between a stream and a river?)
1) Perennial Rivers: These are rivers that have water in their channels throughout the year.
2) Intermittent Rivers: These are seasonal rivers
3) Ephemeral Rivers: Have water in their channels only after heavy downpour or melting of 4) Exotic Rivers: These are perennial
rivers
that flow through arid regions. The Nile and
Colorado are two good
examples of exotic rivers
5) Influent Rivers: These are rivers that lose water to ground water
6) Effluent Rivers: These receive water
from
ground water (A river could be an influent river at
one time and become
an effluent
river at another time).
Sheet wash and rills are not types of rivers, but could be the
begining of a river
Sheet wash - thin layer of un-channel- water flows down slope
This leads to sheet erosion (Prevention: contour plowing, strip
planting, terracing)
Rills- small channels
Notion of Drainage Basin (watershed)- tributary, drainage divide
Continental drainage divide in Fort Wayne (use map)
Flooding ~ 25% of rainfall ends up as surface runoff to rivers.
What is a flash flood?
What can lead to a river flooding?
Rain - intensity and duration
Clearing of the drainage basin
Chocking of the river channels
Urbanization
Flood plains - a broad strip of land built by sediments on either
side
of a stream channel. The sediments get deposited during flooding (note:
in other words, no flooding no flood plains?)
Three types of flood plains
1) Point bars of sand and gravel
2) Flood deposits of silt/clay
3) Combination of 1 and 2
Discuss the floods (1912? and 1982) of Fort Wayne and the great Midwest flood of 1993
What lead to the 1982 flood in Fort
Wayne?
The great flood of 1993 in the Midwest and the Floods of 2003 and 2004
in Indiana and Ohio...check them out
Factors affecting stream erosion and deposition
Velocity and to a lesser extent discharge
1. Velocity - speed of water and this depends on (sketches to illustrate)
gradient numbers (some maths)
channel shape (cross section)
roughness of the channel
2. Discharge(Q)
Cross sectional = area * velocity
Cross sectional area = width * depth
Q = V * A [cubic feet per second (cfs) or cubic meters per second
(cms)]
Stream discharge typically increases downstream due to input from
groundwater
and tributaries.
Stream erosion
A stream erodes rock/sediments in three ways
1) Hydraulic action...wave activities
2) Solution... dissolution
3) Abrasion - grinding away of rocks (develops potholes at weak
spots)
Stream Transportation
Materials moved by streams are called loads and there are three
types
of loads
1- Dissolved
2- Suspended - (by turbulence)
3- Bedload
Traction...rolling, sliding, and dragging
Saltation
The ability of a stream to carry sediments can be described using 2 terms
1. Capacity - the total load of a sediment that the stream can carry (this increases with discharge)
2. Competence - measured by the largest particle size
the
river can carry (this increases with velocity)
Stream Deposition
Temporary deposition- bars, flood-plain deposits, end in
Delta,
alluvial form
1. Bar- a ridge of sediment (sand, gravel) deposited
in the
middle or along a bank of a river
2. braided streams- Mid-channel
bars could lead to(a stream
tends to become braided when it is heavily loaded with sediments and
has
banks that are easily eroded.
3. Meanders- Rivers with fine-grained silt/clay in
suspension
tend to be narrow and deep and to develop pronounced sinuous curves
called
meanders
4. Point bars - sediment deposited on the inward side
of
a curve due to slow velocity
5. Flood Plain - a broad strip of land built up by
sedimentation
on either side of a stream channel
6. Delta - A stream flowing into a standing water, usually builds a delta, a body of sediment deposited at the mouth of a river when the river's velocity decreases. The surface of most deltas is marked by distributaries
Examples Nile, Mississippi, Amazon, Niger(locations in a world map)
Internal construction of a small delta(sketch...top set, fore sets,
and bottom set)
7. Alluvial fan - occur mostly in dry climates
Valley Development
Down-cutting and base level (the lowest level of cutting)
Downward cutting produces 'V' shaped valley and mass wasting sheet erosion widens the valley to a broader, open, v-shaped canyon.
Downward cutting will continue until the base level is reached.
A graded stream is one that exhibits a delicate
balance
between its transporting capacity and the sediment load available to
it.
Lateral erosion - widens the valley by undercutting
valley
walls and eroding headward.
Regional Erosion
2 ideas-
i) Rugged mountains are worn by erosion to form peneplain and
ii) slopes retreat (parallel retreat of slopes)
Slopes are controlled by rock type, climate, and rock structure
Rock structure (folds and faults)
1. Radial (Hill)
2. Rectangular (Fractures)
3. Trellis (Ridge/valley)
4. Dendritic (uniform)
5. Parallel (broad valleys)
6. Annular (rugged mountain)
7. Deranged (found in yound terrains)
Stream terraces (step-like land forms)
Incised meanders
-river meanders are cut vertically downward following uplifts
-lateral erosion/down-cutting proceed simultaneously
Stream piracy ...antecedent stream
Pollution of Surface Waters
Possible sources of pollution
1. Herbicides/pesticides
2. Lawn conditioners
3. Deicing salt
4. Fertilizers/detergents
5. Acid mine drainage
6. Toxic metlas
7. Thermal (cooling plants)
Others.......
