Chapter 15 - River Systems Flashcards
River
a river is water in a channel on the surface of the Earth moving downhill due to gravity
Drainage Basin
the area of land drained by a river.
Drainage divide
the high point of land that separates water flow. The limits of a drainage basin marked by ridges and highlands.
Summarize the process of water flow down a drainage basin
3 STEPS
- The water that collects high in the drainage basin, nearest the divide, is in many small channels.
- converge into fewer, larger channels
- eventually all the water flows out of the basin in a single large channel.
Summarize the process of water flow down a drainage basin through channels
3 STEPS
- the water that collects high in the drainage basin, nearest the divide, is in many small channels.
- these channels eventually converge into fewer, larger channels
- eventually all the water flows out of the basin in a single large channel.
Deranged Pattern
- common in Canadian North
- result of three contributing factors:
- the ground is permanently frozen (permafrost).
- there is a lot of exposed bedrock
- there are many old glacial deposits
How is permafrost a contributing factor to the formation of a Deranged drainage pattern?
Because the ground is frozen, it’s difficult for surface water to erode a channel.
How are exposed bedrock and old glacial deposits contributing factors to the formation of a Deranged drainage pattern?
They block or deflect flow.
Two common types of river
- Meandering
2. Braided
Braided River Features
- Number of channels:more than 1
- Size of channel:smaller
- Shape of Channelwide and shallow
- Discharge:variable
- Sediment Load:poorly sorted coarse or large moving as bedload
- Gradient:Steep
Meandering River Features
- Number of channels:1
- Size of channel:larger
- Shape of Channelwide and Deep
- Discharge:consistent and stable
- Sediment loadwell sorted, fine or small moving in suspension
- Gradient
shallower
Fluvial or river erosion
The way in which a river sets sediment in motion
3 ways fluvial erosion occurs
THE IMPACT OF
- moving water
- sediment that is already moving
Together these two processes are ABRAISION
- Hydraulic lift
Hydraulic lift
When moving water flows around a grain and it cannot move, it speeds up (velocity increases)
At the the same time, pressure decreases as the water flows around this grain
As a result the grain is lifted upward and set in motion.
If it doesnt lift the sediment grain off the river bed, it reduces contact so that the water around it can move it.
Fluvial Transport
How sediment already in motion is moved by a river.
Fluvial Transport modes
- Solution
- Suspension
- Saltation
- Traction
SOLUTION as a mode of Fluvial Transport
Dissolved elements or molecules carried throughout the river. These are deposited when they precipitate.
example: sodium and chlorine dissolved in the water, and they precipitate (salt).
SUSPENSION as a mode of Fluvial Transport
The finest/smallest solid particles that are carried in the water. This sediment rarely makes contact with the channel bottom.
SALTATION as a mode of fluvial transport
These are larger sediment grains that bounce along the bottom making frequent but only short term contact with the channel bottom.
TRACTION as a mode of fluvial transport
The largest sediment in motion. These grains roll or slide along the bottom. (too heavy!)
Traction and saltation together make up…
BEDLOAD
Fluvial Deposition
How sediment in a river stops moving.
When does deposition of solid particles occur?
when water velocity drops
Threshold or critical velocity
The water velocity necessary to set in motion (erode) a grain of a certain size
Why are very small grain sizes (<0.002mm) harder to erode?
Because they often contain clay minerals. Clay minerals are flat, sheet-like grains.
Clay minerals are flat, sheet-like grains that have an electric charge on their surface. This means that clay minerals stick together and are hard to erode.
Thalweg
The place in the river where the deepest, fastest water is..
Cut Bank is a product of ____
erosion
Point Bar is a product of _____
deposition
Where is the fastest water (Thalweg) found?
The fastest water is found next to the outside bank of the river where it erodes sediment to produce a CUT BANK.
Where is the slowest water found?
next to the inside bank of the river where it deposits sediment to produce a POINT BAR
Once a bend or meander in a river starts to form the process will continue until..
well developed meanders form as channels migrate laterally
3 FACTORS controlling the FORMATION OF A DELTA
- River (dominated delta)
- Wave (dominated delta)
- Tide (dominated delta)
River dominated delta
- the delta grows into the lake or ocean.
- a number of longer, linear extensions grow as multiple channels transport and deposit sediment.
Example: Mississippi “Bird Foot Delta”
Wave dominated delta
Waves originating on the lake or ocean will rework sediment at the front of the delta to create beaches.
Tide dominated delta
Sediment on the surface of the delta is reworked into a series of linear bars by the back and forth motion of water as the tide rises and falls.
Rivers flood only ____ly and when they do the size of the flood will ___. Not all rivers have flood ___
Rivers flood only rarely and when they do the size of the flood will vary. Not all rivers have flood plains
flood plain
A flat, low-lying area along a stream channel, created by and subject to recurrent flooding
Flooding can be prevented, or at least minimized by artificial structures such as ___
Levees
Flood hydrograph
A graph plotting river discharge over time
Describe flooding in urban settings (hydrograph)
In an urban setting water collects quickly due to hard, impermeable surfaces and enters the river channel quickly It also drops quickly.
Describe flooding in rural settings (hydrograph)
In a rural setting the ground is more porous i.e. farm fields and covered in vegetation. These ensure that water collects more slowly and moves through the river system over a longer period of time
Describe flooding in rural settings (hydrograph)
In a rural setting the ground is more porous i.e. farm fields and covered in vegetation. These ensure that water collects more slowly and moves through the river system over a longer period of time
Levees
elevated banks of a river
Fluvial processes
processes that are related expressly to streams and rivers
Drainage density
total length of all stream channels in the basin divided by the total area of the basin
Base Level
level below which the stram cannot erode its valley
Discharge
Volume of flow in a river that passes by a given point in a given unit of time. (cubic metres per second)
Most important thing to remember about the four things used to define a river
They are all related
The dominant processes controlling channel processes is..
climate which controls precipitation, which . controls discharge
