River Environments Flashcards
What are the features of a drainage basin?
Source, watershed, channel network, mouth.
Define source.
The upland area where the river starts.
Define tributary.
A much smaller river, which joins onto a larger river.
Define confluence.
The point at which two rivers join.
Define mouth.
Where the river flows into the sea.
Define drainage basin.
The area which is drained by a river and its tributaries.
Define watershed.
The boundary between each drainage basin.
What are the characteristics of the hydrological cycle?
- There is a finite (fixed) amount of water.
- There is never more or less in the global system.
- It is a closed system.
- The water is infinitely recycled.
What are the stores in a hydrological cycle?
The atmosphere, snow and ice, interception storage, surface storage, soil moisture, groundwater in rocks, seas and oceans.
What are the transfers (flows/main water movements) in the hydrological cycle?
Evaporation (from land and sea). Precipitation (from condensed water in the atmosphere). Wind (causing a net movement of water inland by blowing clouds inland). Overland flow. Infiltration. Percolation Through flow. Groundwater flow.
Define hydrological cycle
A global circulation of water which is also a closed system.
when precipitation does not infiltrate the soil and flows on the surface of the land to the sea/lake
Define precipitation
The transfer of water in any form from the atmosphere to the land or sea surface.
Define condensation.
The change in the atmosphere when water vapour cools and becomes a liquid: the water takes the form of water droplets that appear in the atmosphere as clouds.
Define transpiration.
Plants take up liquid water from the soil and ‘breath’ I into the atmosphere as water vapour.
Define evaporation.
The hydrological cycle starts with evaporation due to the heat and solar energy emitted by the Sun. Water is converted from a liquid to a gas (water vapour). This takes place on the surface of the sea and from water surfaces (ponds and lakes) on land. Evaporation is particularly important in the transfer of water from the sea store into the atmosphere.
Define evapotranspiration.
The loss of moisture from the ground by direct evaporation from water bodies and the soil, plus transpiration from plants (water evaporated directly from the leaf and water released in transpiration).
Define through flow.
This takes place between the ground surface and the top of the groundwater store. As a exult of gravity, water moves slowly through the soil until it reaches a stream or river (horizontal movement).
Define groundwater flow.
This happens in the rocks of the aquifer and is the underground transfer of water to rivers, lakes and the sea.
Define channel.
The flow of water through a river.
Define system.
A series of inputs, processes and outputs. Systems can be open or closed.
Define open system.
A set of interrelated objects in which there are both inputs and outputs.
Define closed system.
A set of interrelated objects in which there are no inputs or outputs.
Define surface runoff.
When precipitation doesn’t infiltrate the soil and flows on the surface of the land to the sea/lake.
Define infiltration.
Water seeping into the soul after falling on the surface (vertical movement).
Define percolation.
Water which has infiltrated the soil and is flowing between cracks in the bedrock (vertical movement).
What would happen to the movement of the water if the rock was saturated?
There will be an increased amount of water moving through the soil as through flow if the rock is saturated (‘full’ to capacity with water).
What would happen to the movement of the water if the soil was saturated?
When the soil is saturated, no infiltration takes place and water will flow on the surface towards the river. This is known as surface runoff or overland flow.
Define river regime.
The difference in the discharge of the river throughout the year (as river discharge can vary).
It closely reflects the local climatic conditions, particularly rainfall.
Define river discharge.
The volume of water carried by a river at any one time (measured in cumecs - m3/s of water passing a particular point along the river’s course).
Depends on precipitation, evapotranspiration and storage factors.
What is a hydrograph?
A graph showing the discharge of water over a given period of time.
What are the factors affecting river regimes?
- Amount and intensity of rain.
- Temperature.
- Slope of the surface (gradient).
- Rock type.
- Vegetation and land use.
- Human intervention.
How does precipitation affect river regimes?
Heavy rain will not sink into the ground but enter the river due to increased overland flow.
How does temperature affect river regimes?
Affects the form of precipitation (eg. Below freezing, there would be snow which could take weeks to melt and enter the river, and if the ground remains frozen, melting snow on the surface can reach the river quickly).
How does the gradient of the surface affect river regimes?
A steep surface will cause rapid surface runoff, so water will reach the river more quickly, however, water may infiltrate into the soil if the land is flat or gently sloping, delaying it from entering the river.
How does rock type affect river regimes?
Impermeable rocks don’t allow percolation, so surface runoff is increased, but permeable rocks allow percolation to occur, so the delivery of water to the river is delayed.
How does vegetation and land use affect river regimes?
Trees and other plants intercept and delay the rain from reaching the ground, whereas loose soil and rocks speed up the runoff and reduce lag time (same with tarmac and concrete in urban areas).
How does human intervention affect river regimes?
Dams hold back discharge and reduce the risk of flooding while reservoirs control the flow of water by opening and closing sluice gates for abstraction of water from rivers for a range of human needs.
What is a storm hydrograph?
These record the changing discharge of a river after a rainstorm.
They record the discharge of a river as being made up of two flows:
- Base flow (the ‘normal’ discharge of the river).
- Storm flow (the additional discharge of the river as a result of the rainstorm).
What is the lag time?
The delay between peak rainfall and peak discharge.
The shorter the lag time, the the quicker the water reaches the river channel. A short lag time causes the river discharge to rise quickly, forming a steep gradient on a storm hydrograph. The steeper the rise in discharge, the greater the chances of flooding. It is possible to mark on the storm hydrograph the level of discharge above which the river will flood. Once the storm and its peak discharge have passed, the amount of water in the river starts to decrease.
What are the main processes in a river and its drainage basin?
- Weathering (physical, chemical and biological)
- Erosion (corrosion, solution, hydraulic action, attrition)
What is weathering?
The breakdown and decay of material and bedrock in one place. The weathered material doesn’t move (in situ) unless by gravity.
What is physical weathering?
Breaking of rocks into smaller and smaller pieces by force (and changes in temperature)
Eg. Freeze to thaw weathering (thawing in rock cracks)- liquid turned into solid ice when rainfall in rock cracks freezes. Forces are exerted as solid ice expands.
What is chemical weathering?
Rocks decaying and disintegrating by the changing chemical composition of rock through chemical reactions.
Eg. Limestone + water —> carbonation
What is biological weathering?
Material broken down by the action of living things (bio).
Eg. Trees growing into the cracks of the rocks and gradually splitting the rock apart.
Rabbits digging holes weakens the rock.
What are the two main mass movement events?
- Slumping (fast)
- Soil creep (slow)
Weathered or loose material is called ‘scree’ or ‘regolith’.
Movement of loose material by gravity can be catastrophic.
What is erosion?
The breakdown and transportation of material from one place to another, where it is deposited (always involves an agent of erosion: river/sea/water, wind, ice (glaciers).
What are the four main types of erosion that occur in a river and its drainage basin?
Corrosion (abrasion). Attrition. Solution. Hydraulic action/power. (Mnemonic = CASH)
What is corrasion/abrasion?
‘Sand paper’ action of load (material that has been washed or has fallen into the river) between the sides and floor of the channel.
What is attrition?
The load becoming smaller as it collided with each other.
Doesn’t cause erosion of river channel or valleys
