Surface Water and Stream Development

1
Surface Water and Stream Development
2
Surface Water

• The moment a raindrop falls to earth it begins
  its return to the sea.
• Once water reaches Earths surface it may
  evaporate back into the atmosphere, soak into the
  ground, or flow across the surface of Earth.
• Runoff- the movement of water across the surface
  of the earth

3
Factors Affecting the Rate of Runoff

• Rate of Precipitation more precipitation per
  unit time increases run-off.
• Topography The steeper the slope the greater
  the run-off.
• Level of Soil Saturation As soil pores get
  closer to saturation the level of run-off
  increases.
• Type of Soil Soils that have greater porosity
  and permeability will decrease the rate of
  run-off.

4
Factors Affecting the Rate of Runoff (continued)

• Amount of Vegetation Two effects
• Vegetation physically blocks the flow of surface
  water decreasing the rate of run-off.
• Vegetation, especially during the spring and
  summer months, absorbs much of the precipitation
  decreasing the rate of run-off.
• Presence of Man-made Structures Pavement and
  other developed surfaces prevent the absorption
  of surface water increasing the rate of run-off.

5
Watersheds / Drainage Basins

• All of the land area whose water drains into a
  stream system is called the streams watershed.
• Watersheds can be very small (lt2 Km2) to
  extremely large (The Mississippi watershed drains
  40 of the US land area.
• Watersheds are composed primary streams and their
  tributaries.
• Tributaries are smaller streams that contribute
  water to a larger stream.
• Watersheds are separated from one another by
  highland areas called Divides

6
Common Drainage Patterns
7
Watersheds of Virginia
8
Five Drainage Patterns

• Dendritic Form in regions in which the rocks
  have a uniform
• resistance to weathering. The
  pattern is very tree-like
• with tributaries making up the
  branches of the tree.
• Radial A pattern that forms on the slopes of
  large mountains
• Rectangular A pattern found where bedrock has
  been extensively
• faulted. The pattern has
  tributaries that meet at right
• angles.
• Trellis A pattern found where there has been
  extensive folding of
• rock strata. The tributaries flow
  along synclinal valleys. The
• pattern is typified by many
  tributaries that run parallel with
• one another.
• Braided A pattern found where water flows
  through a region of
• unconsolidated materials. Also
  found where changes in
• elevation are so minute as to
  produce no directional bias.

9
Characteristics of Moving Water

• Moving water is the single most important factor
  in shaping the Earths surface
• Water is set in motion by gravity
• Water shapes the topography of Earth by
• Weathering the soil and rocks through which it
  passes
• Transporting the resulting sediments
• Depositing those sediments at some remote distance

10
Mechanisms of Stream Erosion

• There are three mechanisms of stream erosion
• Hydraulic Action - is due to the force of moving
  water. Moving water can move both loose and
  consolidated materials along the bed of the
  stream. If this process removes material below
  the waterline on a stream bank, the bank may
  collapse in a process known as calving.
• Abrasion - Sediments carried along by the stream
  can impact on the streambed or with other
  sediment. The resulting abrasion gradually
  reduces the size of the sediment or removes
  material from the streambed if the channel is cut
  in bedrock
• Corrosion - Chemical erosion of rock and
  sediments due to acids in the stream water

11
Gradient and Potential Energy

• The amount of erosion that any moving body of
  water can accomplish is controlled by the
  gradient of the stream bed and the resulting
  potential energy.
• Gradient is a measure of the vertical drop over a
  defined lateral distance. In mathematics gradient
  is known as slope and is define as follows
• Slope (m) Vertical Rise/Horizontal
  Run
• The steeper the gradient the greater the
  potential energy of the stream.

12
Kinetic Energy and Competence

• The steeper the gradient of a stream the faster
  the rate at which the potential energy of the
  stream is converted to kinetic energy.
• Kinetic Energy Energy of motion
• KE ½ (mass)(velocity)2
• The greater the kinetic energy of the water the
  larger the particle size that the water is
  capable of carrying.
• Competence -The largest particle size that water
  can carry velocity determines the competence of
  a stream

13
Discharge and Capacity

• Discharge the volume of water that passes a
  point on the stream per unit of time
• Discharge Astream x VStream
• Capacity the maximum quantity of load that a
  stream can carry controlled by the discharge of
  a stream

14
Types of Stream Load

• Stream Load the mechanisms by which sediments
  are moved through a stream system. There are
  three types of stream load
• Bed Load Material that is rolled or pushed
  along the stream bed. This load typically
  includes all sediments larger than silt. Sand
  typically moves by saltation, while large
  sediments are pushed or rolled along the stream
  bed.
• Suspension Load Material that is small enough
  to be physically suspended in the water of the
  stream for long distances. It typically includes
  silts and clay sized sediments.
• Solution Load minerals that have dissolved out
  of rocks due to chemical weathering.

15
Stream Profile

• The profile of a stream is a cross-sectional view
  of a streambed as it flows from its head (highest
  point) to its mouth (lowest point), or, where it
  enters another body of water.
• Base Level The lowest level to which a stream
  can down cut. Most base level are temporary.
• Ultimate Base-Level Sea Level. No
  stream erosion can take place below sea level.

16
Formation of Stream Valleys

• All stream valleys share the following
  characteristics
• They are V-shaped.
• They are formed through a combination of down-
  and lateral- (side-to-side) cutting (erosion).
• The amount of down- versus lateral-cutting is
  determined primarily by the slope of the stream
  bed.
• There are three types of Stream Beds

17
Young River Valley

• Characteristics
• Deep, Narrow, V-shape
• Straight
• Fast Flow
• Down-Cutting Predominates
• Rapids and Waterfalls Common
• Occurs on Steep Slopes

18
(No Transcript)
19
Mature Stream Valley

• Characteristics
• Broad V-shape
• Intermediate Flow
• Down- and Lateral Cutting Occur
• Meanders Develop
• Flood-Plain begins to develop
• Occurs on Intermediate Slopes

20
Floodplain Structures
21
Cut-bank and Point-Bar Development
22
(No Transcript)
23
Stream Bed Shape
24
Old River Valley

• Characteristics
• Extremely Broad V-shape
• Low Flow
• Lateral-Cutting Predominates
• Well Developed Flood Plain
• Extreme Meandering
• Oxbows and Oxbow Lakes Present
• Occurs on Very Low Slopes

25
(No Transcript)
26
(No Transcript)
27
Formation of an Oxbow and Oxbow Lake
28
What Type of Valley Is It?
29
What Type of Valley Is It?
30
What Type is a Valley is It?
31
Additional Stream Features

• Deltas
• Watersheds/Drainage Basin
• Watersheds of Virginia

32
Deltas

• Named for their triangular shape which resembles
  the Greek capital letter D
• Formed when sediment laden stream enters a still
  body of water.
• Because slope is non-existent at a base level the
  water of the stream begins to carve random
  channels through the deposited sediment.
• These random channels are known as Distributaries
  

33
(No Transcript)
34
Further Examples of Deltas
35
Alluvial Fans
36
(No Transcript)
37
(No Transcript)