B-Test Soils and Rivers
Soils
Formation
There are 2 main stages in Soil formation:

Parent or underlying rock is weathered to give a layer of loose, broken up material known as regolith.
Regolith may also result from the deposition of material by water, wind, ice and volcanic activity.

The addition of water, gases (air), living organisms (biota) and decayed organic matter (humus).
Factors affecting the formation of soil:

Parent rock (Geology) affects :
o Permeability (drainage)
o Mineral content (nutrients)
o Acidity or alkalinity
o Depth, color, texture

Topography (Relief) affects :
o Altitude (height)
o Steepness of slope
o Aspect

Fauna and flora affect :
o Flora (type of vegetation)
o Fauna (type of animals)
o Micro-organisms affect the rate at which humus forms.

Climate
o Temperature affects the rate of weathering
o Precipitation affects the type of vegetation, and movement of water within the soil.
o Affects the rate of vegetation decay and the formation of humus.

Time
o

It takes 3 000 to 12 000 years to create a layer of soil deep enough to support agriculture.
Human interference
o This factor is rapidly altering many of the world’s natural soils, with the result that in many
parts of the world’s soil, which is normally a sustainable resource, being eroded and lost.
World Soils, there are 3 different types of soils :

Brown Earths → found in Southern UK

Podsols → Northern UK

Tropical red earths →Equatorial areas
Soil profile model
A layer
Upper part is dark/brown due to high humus content. High organic activity
Lower part is bright due to in washing of nutrients and iron
B layer
Brighter color due to in washing of nutrients from above, less humus
C layer
Weathered parent material
Soil erosion
Some causes and effects of soil erosion :

Mining ruins large areas

Cutting down trees and removing hedges leaves soil exposed to wind and increases water erosion
which forms gullies. In tropical areas, deforestation increases leaching and surface runoff.

Ploughing up and down the hill increases surface runoff.

Overgrazing exposes land to erosion by wind and water.

Heavy machinery compacts the ground.

Agribusiness has little regard for the ground.

Overcroping and monoculture impoverishes the soil.
Soil erosion
It can take between 3 000 and 12 000 years for a sufficient layer for agricultural use. At present only 11 percent
of the Earth’s surface is classed as prime agricultural land. This land is needed for an ever growing world
population. The capacity of the soil to produce enough soil is being stretched to the limit. This problem is
aggravated where human development is actually ruining this essential resource.
Removal of vegetation
Most damage to the soil results from the removal of vegetation, with deforestation being the major cause.
Where there is no vegetation left to protect the humus, no interception of ran by plants, and no roots will bind
the soil together the soil will be washed downhill. And removed by rivers to leave deep unusable gullies. The
removal of hedgerows will also increase the erosion by wind and water.
Overcultivation and overgrazing
Overcultivation occurs when crops are grown on the same piece of land year after year. Overgrazing is when
there are too many animals on the amount of grass available.
Soil management
Soil is a sustainable resource, but only if it is managed carefully. Without careful soil management, soil,
which may have taken centuries to form will be lost in days, and in some extreme cases even minutes. Some
suggested methods of preventing, or at least limiting, soil erosion, while at the same time sustaining its
productivity are shown below :
-
-
Windbreaks
o Trees, bushes and grass can improve water retention, and bind the soil together.
Terracing
o When artificial steps are cut into steep hillsides, to make it useable.
o Bunds are stone or mud walls retain water
Contour farming
o When crops are planted around the hillside rather than up and down the hill
Strip farming
o When two or more crops are grown in the same field
o Sometimes a crop may grow under the shelter of another
Some cause of soil erosion
-
-
Deforestation
o Surface runoff
 Gullies
o Leaves soil exposed
Mining
Wind
Overcultivation
Urbanization
Inadequate draining of irrigation
Overcroping
Agribusiness
Monoculture
Heavy machinery
Overgrazing
Ploughing up and down the hill
o Surface runoff
o
≠contour ploughing
Some attempts to reduce soil erosion
-
Terracing
Contour ploughing
Hedgerows replanted
Crops alternated over the years
Strip cultivation
Afforestation
o Planting trees in order to form a forest
Resistant bushes planted to act as windbreaks
Overgrazing reduced
o By using smaller but better quality herds
Gullies filled with soil and replanted
Stone lines laid
o To trap surface water and soil runoff
Natural manure used wherever possible
Drainage basins and rivers
Drainage basins
A drainage basin or river basin is an area of land drained by a main river and its tributaries. Its boundary
marked by a ridge of higher land is called a watershed. A Watershed, therefore separates on drainage basin
from another. Size is less important than drainage density which is calculated by dividing =
The density is highest on impermeable rocks and clays, and lowest on permeable rocks and sands. The higher
The total length of all stream in the drainage basin
The total area of a drainage basin
thee density the greater the risk of flooding. Especially as a result of a flash flood.
Drainage basins can store water either within the river or channel itself, or in lakes or in the ground.
Excess water is carried back to the sea by rivers. Rivers form part of the hydrological water cycle. The seas and
oceans contain about 97 % of the world’s water, but being salty, is not suitable for use by terrestrial, plant,
animals and people. 2% of the world’s water is stored as ice in snow and alpine areas.
That leaves 1% which is either fresh water on land or vapor in the atmosphere. As the amount of fresh
water and vapor is limited, so it has to be recycled over and over again. It is this constant recycling of water,
which is called the hydrological water cycle. As no water is lost or added to the system, it is said to be a closed
system.
The drainage basin system
A drainage basin forms part of the hydrological cycle, but unlike the hydrological cycle, it is an open system.
It is an open system because it has :

Inputs : where water enters the system through precipitation (water and snow)

Outputs : where water is lost through the system.
A typical water drainage system
Flood charge and hydrographs
Volume = the amount of water in the river system (m²)
Verlocity = the speed of the river ( m/s)
Discharge = Velocity x Volume (m²/s)
Hydrographs = a graph showing the discharge from a river at a given point
Lag time = the time between the peak rainfall and the peak discharge
A river with a short lag time and a high discharge is more likely to flood. Causes of a short lag time :

Fast runoff on steep slopes

Surface runoff on impermeable rock

Very thin soil, less infiltration

Very thin grass, less interception

Urbanization : impermeable ground

Limited water extracted

Higher density
River processes
The 4 types of transportation :

Traction

Saltation

Suspension

Solution
The 4 types of erosion :

Attrition (big boulders)

Hydraulic action (power of the river slamming the rocks against the ground)

Corrasion (smaller material rubbing against the river floor)

Corrosion (acids in the river dissolve the rock)
Deposition occurs when a river lacks the energy to carry its load. This can occur after a dry spell or when a
powerful river slams into a (slow) sea, that last one can create DELTAS.
My notes on River landforms in a highland area
Lowland river landforms