Rivers Flashcards
What is a drainage basin?
an area of land drained by a river and its tributaries
What is a confluence?
The point at which two rivers join
What is a mouth?
Where the river flows into the sea or sometimes a lake.
What is the source?
The upland area where the river begins.
What is the watershed?
The boundary dividing one drainage basin from another - a ridge of high land.
What is a tributary?
A river that joins a larger river.
What is percolation?
The filtering of water downwards through soil and through the joints and pores of a permeable rock.
What is soil moisture store?
water stored in the soil
What does saturated mean?
The soil can’t hold any more water.
What is the field capacity?
When a soil is drained, some water cannot drain as it is stuck to the outside of water particles. The volume of this water is known as the field capacity. However, it can be used by plant roots and is know as soil moisture utilisation. It is called field capacity as there is an electric field which sticks the water to the soil particles.
What is the imput to a drainage basin system?
Precipitation.
What are forms of storage in the drainage basin system?
Interception storage (water droplets on trees and plants) surface storage (puddles or lakes) soil moisture storage (water in the soil) groundwater storage (water stored in porous rocks)
What are transfers of water in the drainage basin system?
Stemflow
Surface run off
Infiltration ( surface water soaking into soil)
Throughflow ( downhill through the soil layer)
Percolation (water moving downwards from soil into rocks)
Groundwater flow (slow movement through rock layers deep below surface, towards river.
What are outputs of the drainage basin system?
Channel output ( water leaving the system in a river, to the sea)
Transpiration ( water vapour released by trees and plants)
Evapotranspiration (transpiration and surface water lost through evaporation)
What is the water budget?
The relationship between inputs and outputs in a drainage basin system. Allows you to work out the amount of water in a drainage basin throughout the year. Can help predict flooding and water shortages.
P=Q+E+/- change in storage in soil or bedrock.
Where:
P= precipitation
Q= Run off
E = Evapotranspiration
How is river discharge calculated?
By determining the discharge in each subsection of a channel cross section and summing the subsection discharges to obtain a total.
Area = Depth x width
Discharge = Area x Velocity
Discharge is measured in cumecs (cubic metres per second)
What is a flood?
When a river bursts its banks and spills out onto the floodplain. Q>Qbf
discharge> bankfull storage
What is the lag time?
The time gap between peak rainfall and peak discharge.
What factors result in a short lag time?
- impermeable surfaces
- steep relief
- sparse vegetation
- shallow soil
- high drainage density
Which factors result in a long lag time?
- gentle relief
- lots of vegetation
- permeable surfaces for infiltration
- deep soil that can hold more water
- low drainage density
What is hydraulic radius and how is it calculated?
Hydraulic radius is the efficiency of a channel.
Hydraulic radius = cross sectional area/wetter perimeter
How does channel shape affect river velocity?
Greater wetter perimeter means increased friction so slower velocity. A narrow deep channel has a smaller wetter perimeter so flows faster than a wide shallow channel.
How does river gradient affect river velocity?
A steeper slope means a stronger gravitational force pulling the water downwards than there would be on a gentle gradient.
How does channel roughness affect river velocity?
More rocks and boulders in the channel increase its roughness and create more friction, reducing the velocity. Channels with minimal roughness have faster velocities.
How does volume of water affect river velocity?
An increasing mass of water (at confluences) mean the water is more capable of erosion, resulting in wider deeper channels which allows water to flow faster as there is less resistance.
What is sinuosity?
The bendiness of a river channel. Sinuous index is calculated by:
Channel length/down valley length (direct route)
What is a river’s capacity?
The total volume of sediment a river can transport?
What is river competence?
Largest sized sediment a river can transport.
What is abrasion?
When a river picks up material and then rubs it against its beds and banks. Erosion occurs by the process of abrasion and is most effective during times of flood.
What is attrition?
When boulders collide with one another as they move down the river and break into smaller pieces. The rocks become more smooth over time.
What is hydraulic action?
The force of water that hits river banks and pushes water into cracks exploiting weakness in the bank and causing the river bed to in time collapse.
What is corrosion?
A continual process as a result of the chemical composition of the water.
What are the main factors leading to deposition?
- Low rainfall reducing precipitation
- Increase in load
- Water becoming shallower, energy dissipates
- River overflows its banks, depositing material on flood plain.
- A river entering a sea or lake, reducing velocity.
What type of channel does vertical erosion result in?
- Faster flowing rivers with energy to downcut
- Larger, more angular bedloads
- Steep sided valleys.
What does lateral erosion result in?
- Floodplain
- Meanders
What is the Hjulstrom curve?
This illustrates the relationship between velocity and competence. It shows the velocities at which sediment will normally be eroded, transported or deposited, depending on its size.
How do interlocking spurs form?
When the river winds around protrusions, hills or ridges of land.
What factors does the shape of the valley depend on?
Climate- sufficient water needed for high discharge levels to produce more vertical erosion and move sediment.
Geology- the type of rock and its structure may tend to a steep or gentle relief.
Vegetation - more vegetation helps bind the soil leading to stable valley sides.
When do rapids form?
Rapids form where there is a sudden increase in the slope of the channel or where the river flows over a series of gently dipping harder bands of rock. Water becomes more turbulent so its erosive power is greater.