Water Cycle - Drainage Basins 3112 Flashcards Preview

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Flashcards in Water Cycle - Drainage Basins 3112 Deck (34):

What is a drainage basin?

A drainage basin is the area that supplies a river with its supply of water, including water found below the after table as well as soil water and any surface flow. Drainage basins are alerted from one another by highland called a watershed.


What is the highland separating drainage basins from one another called?



What is the input into a drainage basin system?

Precipitation. The nature, intensity and longevity of the precipitation have a direct bearing on what happens when the water hits the ground.


In general, when precipitation lands on a vexation cover, the vegetation acts as a store what is this called and how does it act as a store.

An interception store. This occurs on the branches and leaves of vegetation. Some vegetation is a better interception store than others. The density of the vegetation cover also plays a part. Studies show that forests made up of needle-leaf trees captured 22% of all rainfall whereas bread leaf deciduous forest intercepted 19% - this may be due to the density of the vegetation cover rather than the structure of leaves. Some tropical rainforests intercept as much as 58% of all rainfall.


What happens to the majority of of water captured by vegetation?

Evaporated back into the atmosphere.


What is it called when water makes its way from the leaves of trees to the ground by dropping/falling from one interception store to another until it eventually reaches the ground?



What is it called when water flows down stems of grasses etc, (in very heavy storms can flow down the trucks of trees)

Stem flow.


On reaching the ground, water soaks into the soil by the process of what?



What is the rate of which water soaks into the ground called?

Infiltration rate


What is infiltration?

The movement of water into the soil. This movement is controlled by gravity, capillary action and soil porosity. The most important factor is soil porosity.


What is a soils porosity controlled by?

Texture, structure and organic content.


What kind of soils have larger pores and fissures?

Coarse, textures soils.


What kind of soils have smaller pores and fissures?

Fine-grained soils.


If a soil has larger pores and fissures what does that mean?

They allow for more water flow.


How can pores and fissures in soil be made larger.

1. The burrowing of worms and other organisms and penetration of plant roots can increase the size and number of macro and micro channels within the soil.
2. As the soil moistens the clay particles absorb water causing them to expand. The expansion reduces the size of soil pores.
3. Raindrop impact breaks large soil clumps into smaller particles. These particles then clog soil surface pores reducing the movement of water into the soil.


What is soil storage?

The amount of water stored in the soil.


What is the structure of soil (regarding particles and pores)?

Soil consists of soil particles with pore spaces between them. Those pore spaces can be filled with air but also with water.


How does the amount of pores in soil vary between different types of soil?

The pores on clay soil account for 40 to 60% of the volume. In fine sand this van be from 20 to 45%


Describe vegetation storage

When plants remove water from the soil and store it in the structure of the plant.


What is it called when plants loose water through stomata on their leaves?



What is infiltration capacity?

If rainfall intensity is greater than the infiltration rate, the soil becomes saturated because it cannot infiltration any more water.


What happens once soil has reached infiltration capacity but rainfall continues?

Water will build up on the surface as surface storage - usually in the form of puddles (common in man made environments their occurrence in natural environments is quite rare as infiltration rate is usually greater than the rate of precipitation). Water can only build up on the surface after s long period of rain, an intense rainstorm or on an impermeable surface (man made e.g footpath or natural, bare rock or on frozen ground).


What happens once surface storage starts to collect?

Most of the surface storage is evaporated back into the eh atmosphere and is lost to the drainage basin.


Why is evaporation and transportation referred to as evapotranspiration?

It is difficult to separate evaporation from transpiration and so the total amount outfitted is referred to as evapotranspiration.


What happens if surface stores are full?

Overland flow or sheet flow will begin on slopes - this is very fast reaching the nearest channel.


What is the lateral movement of soil water downslope called?

Through flow - and eventually reached the nearest channel although tens to be much slower than overland flow. Generally the more vegetated an area the faster the rate of through floe because it is aided by root channels in the soil.


Flowing infiltration water moves vertically down through the soul and unsaturated rock by the process of what?



Water held in pore spaces in underground rocks is considered what?



Once water has percolated through unsaturated rock and has been held in the pore spaces in rock what happens next?

It then passes slowly into the zone of saturated rock where it can move vertically and latterly by the process of groundwater flow - this is a very slow movement and can feed rivers through long periods of drought.


What determines how much water a rock can hold?

How porous the rock is.


The sum of all the movements and stores add up and form the drainage basin hydrological cycle where do all the flows lead water to?

The nearest river or deep under ground water store.


What is the flow of water in a river called?

Channel flow


What is the amount of water than leaves the drainage basin as channel flow called?



Why does water move so quickly on/ through urban surfaces?

They are designed to move water quickly by having strategically placed slopes and very smooth surfaces.