Exam 2 Review - Rivers (1)

A...

1. Body of Water
2. Flowing Down-Slope in a
3. Physically Distinct Channel.

Rainfall, springs, or melting snow/ice.

Volcanic or tectonic processes.

From erosive action of overland flow.

When the amount of rain exceeds the surfaces ability to soak it up, you get water flowing over the surface.

How quickly water can soak into the ground.

1. How much water is there.
2. How fast is the water moving.

• Is the surface soft rock?
• Are there plant roots to bind the soil together?
• Is the surface poorly consolidated dust?

1. Erodibility of Surface
2. Erosiveness of Flow

1. They are highly erodible.
2. Experience very intense rainstorms.

1. Continental Divide
2. Major Drainage Divide
3. Minor Drainage Divide

• Very small
• Very large
• Or any size in between

A divide separating the Pacific drainage from the Gulf/Atlantic drainage.

• The arrangement of a stream and its tributaries.

• It reflects the geology (including rock types and structures) of the region.

Branches flow to the main stream.

1. Dendritic
2. Trellis
3. Parallel
4. Radial

Radial Drainage Pattern

Trellis Drainage Pattern

Q (discharge) = w (width) * d (depth) * v (velocity)

Q (discharge) = a (area) * v (velocity)

Discharge is a unit volume per unit time. Which is typically cubic meters per second, or cubic feet per second.

• Where river has shifting bed and bank patterns.

• Example: Where the river flows through very sandy material, constantly shifting.

Because velocity patterns vary across a river's cross-section.

That the water is moving slowest close to the bed and banks, and faster as you get further away from them.

As the area of a channel decreases, velocity increases.

As channel shape changes.

• It has a relatively large fraction of its water in contact with bed banks.

• Lots of friction therefore means slow flow.

• It becomes progressively more efficient.

• As the friction of the river in contact with the bed and bank decreases.

• Until the river is at its most efficient at the bank-full level.

When it is at low flow.

It becomes harder to raise the level of the river.

The amount of water they receive.

It will silt up and the channel will become smaller.

It will be moving very fast and therefore eroding, increasing the size of the channel.

A Drainage Basin System

Yes

Method One

• Direct Precipitation, rain or snow falling straight into the river channel.

Note: Not all that important as a water source, because the surface area of the river's channels is small in comparison to the surface area of the basin as a whole.

Method Two

1. Rainfall onto the surrounding slopes of the drainage basin.
2. Which soaks into the ground by infiltration.
3. Then flow through the soil into the river channel as throughflow.
   Note: Water is slow getting into the channel this way.

Method Three

1. Rainfall on the surrounding slopes of the drainage basin.
2. Which soaks into the ground by infiltration.
3. Then soaks on down into the underlying bedrock by percolation.
4. Then flows into the river channel as groundwater flow.

Note: Water is very slow getting into the river channel this way.

Method Four

1. Rainfall onto the surrounding slopes of the drainage basin.
2. Does not soak into the soil.
3. Flows over the surface as overland flow or surface runoff.

Note: Water is fast getting into the river channel this way.

A chart showing a rivers response to a rainstorm.

• It will have a very fast response to a rainstorm.
• Short lag time between peak precipitation and peak discharge.

Yes typically because impermeable surfaces (tarmac, parking lots, storm drains) force water to travel by overland flow into the river channel.