1. Sculpting Earth’s Surface
Rivers
Sculpting Earth’s Surface

2. Rivers of the World Not a large proportion of Earth’s water
A major contributor in sculpting the landscape

3. Types of Flow Turbulent Flow Laminar Flow Low velocity High velocity
Particles flow in straight lines
No mixing
Rare in water systems
Turbulent Flow
High velocity
Particles move in irregular paths
Mixing
Most common type of flow
Laminar flow occurs when the water particles move along straight lines, called stream lines that are parallel to each other.
Turbulent flow tends to occur when the velocity of water and the vicosity and friction are low.

4. Flows in Rivers Velocity Factors in velocity
distance per unit of time (ft/s or m/s)
Factors in velocity
gradient
Velocity. Stream velocity is simply the distance that the water in a river or stream travels over an interval of time, measured in ft/s or m/s. The velocity is related to the discharge of a river, the slope angle of the river bed, and the type of flow.
size & roughness
discharge
Fastest in center; slowest at edges

5. Gradient Gradient (slope) vertical drop over distance
Longitudinal profiles, as shown in below, provide a useful way of looking at rivers. The slope, or gradient, of the river is highest near the headwaters and lowest at the mouth of the river, where it is terminated in a larger body of water, such as a river or ocean.
Gradient
As discussed previously, streams and rivers tend to flow from a source in a higher elevation, called the headwaters, downward towards a terminus, called a base level, at a lower elevation. The gradient of a stream is a measure of how far a river drops in elevation as it travels a certain horizontal distance. The gradient is the drop in elevation of the river, divided by the run, or horizontal distance the river has traveled, as shown in the equation below:
Gradient (m/km) = rise / run = elevation change / horizontal distance
The gradient of a river tends to be highest at the headwaters; decreasing to essentially zero at the base level, as shown in the longitudinal profile.
Gradient (slope)
vertical drop over distance
headwater; lowest near base

6. Channel Characteristics
Size
larger channels have more efficient flow
Roughness
Smooth channels promote more uniform flow
Irregular channels create turbulent flow

7. Discharge
Volume of water flowing past a certain point in a given unit of time (m3/s)

8. Erosion, Transportation and Deposition
Rivers typically display three different behaviors
Erosion – breakdown and removal of material
Transportation – movement of material down a river
Deposition – accumulation along banks and beds of rivers

9. Anatomy of a River Headwater Plains Delta high slope area
erosion dominant
Plains
gradient decreases
transportation dominant
Rivers tend to start in mountainous or high slope areas. This part of the river is called the headwaters of the river. The river channel tends to be steep and V-shaped, and the bed is rough and irregular.
As the river exits the foothills, it flows into the plains. The gradient of the river in the plains tends to decrease rapidly, and the river channel broadens and deepens. The river bed is smoother and the path of the river often meanders.
Eventually the river flows into the base level, forming a delta. The delta is a feature that forms when the sediment carried by the river is deposited at the base level (sea level or a lake).
Delta
Base level
Deposition dominant

10. X-section of a River Features Constantly decreasing gradient
Overall, smooth and concave upward curve

11. Erosion Particles are dislodged from channel and lifted
The stronger the flow, the more particles
More particles, increase erosion (sandpaper)

12. Transportation Bed load – moves along bottom by skipping or sliding
Streams typically carry large amounts of rock fragments and sediment as they move towards their base levels. This material is called the stream load, and it is composed of bed load, suspended load, and dissolved load.
Bed load – moves along bottom by skipping or sliding
Suspended load – fine sediment carried above channel – silt and mud
Dissolved load – sediment carried in solution - salt

13. Transportation Criteria of a stream’s ability to carry a load
Competence
Measures maximum size
Related to velocity
Capacity
Maximum load
Related to discharge

14. Transportation - Landforms
Braided Stream
Complex stream channels separated by sand bars
Coarse material; bedload
Meandering Stream
Curving stream that migrates side-to-side
Fine grained; suspended load
Oxbow Lake
A curved lake produced when a stream cuts off a meander

15. Landform Formation Examples of erosion and deposition:
Cutbank – banks that are eroded
Point Bar – areas of deposition

16. Fluvial Landforms Examples
Meandering
Oxbow
Braided

17. Deposition When velocity approaches 0 m/s, deposition occurs
Base level – limit to where a stream can no longer erode
Sea level – ultimate base level
Lakes and dams local base level

18. Drainage Basins
Drainage Basin – The surface area that contains tributaries and supplies the surface runoff that feeds the river
Every river system is provided with water from a variety of sources. These include tributary streams, surface runoff, and groundwater. The surface area that contains the tributaries and supplies the surface runoff that feeds the river is called the drainage basin. Typically, ridges that form a valley or bowl-shaped depression that channels the water towards the river bound the drainage basin
Dendritic – irregular branching; uniform underlying material
Radial – diverge from a central area; volcanic domes
Rectangular – right angle bends; contains joints and faults
Trellis – parallel; alternating bedrock

19. Floods
New Orleans, 2005
Overflow of a stream channel when discharge exceeds channel capacity
The most common and destructive geologic hazard

20. Floods Causes of Flood Major storms Rapid snow melt Hurricane
Sepulveda Basin
Causes of Flood
Major storms
Rapid snow melt
Hurricane
Pittsburgh 1996
Floods are among the most difficult natural hazards to mitigate although they have occurred since the beginning of recorded history. Property damage in the U.S. from floods topped $12 billion in 1993, and the number of deaths due to flooding is the only natural hazard-related death figure to rise on an annual basis since Floods can destroy entire towns and cities. In 1931 the flood of the Hwang Ho River, in China resulted in more than 4 million people drowning when it suddenly overflowed its banks in a violent flood. The lethal nature of this flood was due to the unconfined nature of the Hwang Ho River valley. The Hwang Ho flowed over a flat plain as it moved toward its terminus. The level of the channel bed had also risen with time, resulting in a greater sensitivity of the area to flooding. When increased discharge caused water levels to rise, there was little to hold back the flood waters.

21. Flood Control
Artificial Levees
Channelization