Drainage Basin Networks and Sources to Sink Flashcards
How does topography determine drainage direction? Give an example
Mountainous regions act as barriers and slopes that guides the flow of water within them. In the USA three rivers are guided by the Rocky mountains, Appalachian Mountains and post-glacier landscape to flow south in to the Mississippi river
What is discharge?
The measure of flow rate within rivers. The amount of water that passes by time unit thorugh a section of river.
What unit is used to measure discharge and how is it calculated?
Cumecs (m^3S^-1) = Area of River (Height x Width) x velocity (ms^-1).
What is bankful discharge?
the maximum volume that a channel can hols without flooding
What are the three determinants of river velocity?
Slope, Depth, Roughness
How do you calculate river velocity using its determinants?
Roughness x square root of (depth x slope)
What is river capture?
When the headward erosion of a river leads in to another channel. It captures that river within it.
What is an example of river capture?
Indus River used to flow through the Ganges but is now flowing through the Indus Fan.
What is river splitting?
This is when a flat plane develops in to two drainage basins following changes of the previously uniform rainfall pattern
Explain how river splitting happens
Initially there is an area which experiences uniform rainfall and tectonic uplift. Changes to the uniform rainfall over an area cause part of a plane to receive more than the other. This means that the same part will experience greater denudation. This will cause the area to rise at different rates creating a ridge of which either side there will be different sloped basins.
What is the most dominant and everyday determinant of changes within drainage basins?
Hydrological Cycle
What does the Hjulstrom curve represent?
The different flow velocities required to erode, transport and deposit different sized sediments along a logarithmic graph.
Explain clay within the Hjulstrom curve?
It initially requires a high velocity to be eroded due to it being so compact and coagulated. However, once release it is very fine and so forms part of the channel and has a very very low deposition velocity so much so that it cannot be represented on the curve
What is transport capacity?
Total amount of sediment that a body of flowing water can hold.
What is the transport rate?
The velocity at which the flow of water can carry the maximum transport capacity
What is the sediment delivery ratio?
the fraction of sediment eroded from the slope that reaches the drainage basin outlet
What tends to happen to sediment delivery ratio as you move downstream and why?
Sediment delivery ratio decreases downstream because there are more places within the channel that can trap and store sediment.
What are some of the parts of the channel that can trap and store sediment?
Floodplains, Braided Channels, Deltas, Meander Bars
How do you calculate sediment delivery ratio?
Sediment Output from Basin / Sediment eroded from slope
What is the sediment to sink concept?
The notion that as water and sediment travels downstream it goes through a ‘jerky conveyor belt’ system. This means that it gets stopped at different point within the system for different durations until it finally finds its way to the mouth. For example, in braided rivers it is only stored for a short period whereas in floodplains it can be stored for ever possibly.
What is Sediment Accommodation Space?
The space available to store sediment.
How does sediment accommodation space vary across the long profile and why?
Upstream there is very little because it is so steep and volatile. Downstream there is a greater accumulation of sediment and water that can carve space.
How can you increase sediment accommodation space upstream artificially?
Dams
What is the main site of study for sediment accommodation space?
Downstream
