River Processes & Pressures set

Erosion

Erosion

When a river wears away material from the landscape.

Abrasion

When pebbles grind along the river bank and bed like sand-paper

Attrition

When rocks that the river is carrying knock against each other. They break apart to become smaller and more rounded.

Hydraulic Action

The power of the water smashing against the river banks. Air gets trapped in cracks and causes the rock to break apart.

Solution

When the water dissolves soluble rocks (e.g. limestone)

Transportation

When a river carries material downstream. The material being transported is called the 'load'

Traction

pebbles are rolled / dragged along the river bed.

Saltation

pebbles are bounced along the river bed

Suspension

sediment is carried along in the water

Solution

dissolved rocks are carried in the water

Deposition

When a river drops off (deposits) its load. This happens when the water slows down and loses energy.

Source

The start of a river, usually found in hills and mountains. e.g. e.g The source of the river Ouse are tributaries such as Buckden Beck begin in the mountainous Yorkshire Dales

Tributaries

Smaller streams and rivers that join together to make bigger rivers

Mouth

Where the river meets the sea. e.g. The mouth of the Ouse is the Humber estuary where it flows into the North Sea

Velocity

The speed of a river

Discharge

Volume of water flowing through a river. Measured in cumecs (cubic metres per second)

Long profile

Graph showing how a river's gradient (steepness) changes over its course.

Bradshaw Model

Model showing how a river's characteristics change from source to mouth E.g. velocity and discharge increase as you go downstream. Sediment size decreases.

Upper course

Steepest, narrowest section of a river nearest its source.

Friction with shallow, rocky river bed slows the water down.

Discharge is low, erosion is vertical

Landforms: V shaped valleys, waterfalls, interlocking spurs

Interlocking Spurs

Hills that jut out into a V-shaped river valley.

The river cannot erode harder areas of rock so it winds around them

Waterfall

Step in river created when:

1/ River flows over hard then soft rock. Soft rock is eroded faster.

2/ This creates an overhang of hard rock and a plunge pool at base of waterfall.

3/ Eventually the overhang collapses and waterfall retreats, leaving a gorge.

Middle Course

Middle section of a river, with a gentler gradient.

Tributaries have joined together so the discharge is greater.

River is wider and deeper. Less friction with river bed increases velocity. Erosion is vertical and lateral

Landforms: Meanders and oxbow lakes

Meander

A bend in the river created by the helicoidal flow (corkscrew motion) of river water.

Water flows faster on the outside river bend, eroding the bank & creating river cliffs.

Water flows slower on the inside bend so deposition occurs creating slip-off slopes.

Ox-bow Lake

Over time, meanders gets bendier until the river cuts through the 'neck' leaving a horseshoe shaped lake

Lower Course

Final section of river, nearest its mouth. Flat gradient. River widens and deposition creates levees and mudflats

Flood Plain

Large flat area of land either side of a river. During floods, water spreads across flood plain and deposit alluvium (fine, fertile sediment)

Levees

Natural walls formed along the riverbanks.

When a river overflows the heaviest, largest sediment is deposited first, piling up next to river

Estuary/delta

When a river reaches the sea it fans out and deposits sediment, creating wildlife-rich mudflats and saltmarshes.

Weathering

When precipitation, temperature changes or organisms break down rocks at earth's surface.

Mechanical Weathering

E.g. freeze-thaw - water repeatedly freezes and melts in cracks. When frozen it expands 9%, widening cracks until rocks break off.

Biological Weathering

Weathering by plants & animals e.g. animals making burrows in rocks

Chemical Weathering

Rainwater is slightly acidic and over time this dissolves and wears away rock.

Mass Movement

Movement of soil and weathered rocks down slope due to gravity.

This can be rapid (e.g. landslides, rockfall) or slow (e.g. soil creep - when individual particles of soil move slowly down a slope)

Drainage Basin

The area of land drained by a river and its tributaries.

Watershed

The boundary of the drainage basin

Infiltration

When water soaks into the ground, slowing down its journey to the river.

Groundwater Flow

When water flows slowly underground towards the river

Impermeable

surfaces such as rock or concrete that water cannot infiltrate (soak into)

Surface run-off

surfaces such as rock or concrete that water cannot infiltrate (soak into)

Saturated

When ground can no longer hold any more water - e.g. after heavy, prolonged rainfall.

Interception

When plants and trees catch the rainfall before it hits the ground

Storm Hydrograph

Graph showing how a river responds to a rainfall event.

Peak Rainfall

The maximum amount of precipitation (in mm)

Peak Discharge

The maximum discharge of the river (in cumecs)

Lag Time

The time between the peak rainfall and peak discharge

Hard Engineering

Strategies using artificial structures (e.g. concrete) to prevent river or coastal flooding.

Flood Walls

Artificial barriers to raise height of river banks ensuring water flows quickly past vulnerable area

Dredging

Removing silt and material from the beds of the river

River Straightening

Digging a straighter channel for the river to follow

Soft Engineering

Working with natural processes to reduce the risk and impact of coastal or river flooding.

Flood Plain Retention/Zoning

Allowing only certain land uses on the floodplain so that river can flood without damaging important buildings.

Afforestation

Planting trees in rivers drainage basin to increase interception and lessen flood risk,

River Restoration

Using a variety of strategies to restore the river's original course

Environmental Agency

Government organisation responsible for protecting the environment. Part of its role is to monitor rivers and work out how to use flood defences to protect people and the environment.

Environmental Impact Assessment

Research to work out the effects of a proposed scheme on local residents, buildings, transport, wildlife, habitats, water quality etc.

Cost-benefit Analysis

Research to check whether a scheme would be good value for money