1. Changing River Environments

1. Changing River Environments

  • 1.1.1 Characteristics of rivers and drainage basins: the long profile, width, depth, speed of flow/velocity, discharge, wetted perimeter, channel, watershed, tributary, confluence, source, mouth.

    1.1.2 The Bradshaw model.

    1.1.3 How the drainage basin operates within the water cycle.

    1.1.4 Processes which operate in a drainage basin: precipitation, interception, infiltration, percolation, overland flow, channel flow, throughflow, groundwater flow, transpiration, evaporation, evapotranspiration.

    1.1.5 Processes which operate within a river:
    • erosion; hydraulic action, abrasion, attrition, solution
    • transportation; traction, suspension, saltation, solution
    • deposition.

  • 1.2.1 The characteristics and formation of landforms: waterfalls, rapids, gorges, V-shaped valleys, meanders, oxbow lakes, levées, floodplains, deltas, interlocking spurs, potholes

  • 1.3.1 The opportunities and hazards of living near a river.

    1.3.2 The human and natural causes of river flooding.

    1.3.3 The impacts of river flooding.

    1.3.4 An evaluation of the strategies and techniques used to manage river flooding; including sustainable.

    1.3.5 The human causes of river pollution.

    1.3.6 The impacts of river pollution.

    1.3.7 An evaluation of the strategies and techniques used to manage river pollution; including sustainable.

    1.3.8 One detailed specific example to include:
    • the causes and impacts of a flood for a named river
    • the strategies and techniques used to manage the flooding of the river; including sustainable.

    1.3.9 One detailed specific example to include:
    • the causes and impacts of pollution in a named river
    • the strategies and techniques used to manage pollution levels in the river; including sustainable.

1.1 The main hydrological characteristics and processes

1.1.1 Characteristics of Rivers and Drainage Basins

What is a drainage basin?

A drainage basin is the area of land drained by a river and all of its tributaries.

Water falling anywhere inside the drainage basin will eventually move towards the main river, unless it is stored, evaporated or removed in another way.

The edge of a drainage basin is marked by a watershed. Watersheds usually follow areas of higher land such as hills or ridges.

Remember:
The drainage basin is the whole area being drained.
The watershed is the boundary around it.

Source

The source is the place where a river begins.

Sources are commonly found in upland areas where rainfall is high. Water may enter the river from springs, surface runoff, melting snow or smaller streams.

Channel

The channel is the physical area through which the river flows.

  • bed – the bottom of the river

  • banks – the sides of the river

Confluence

A confluence is the point where two rivers or streams meet.

After a tributary joins the main river, the greater volume of water usually causes discharge to increase.

Watershed

A watershed is the line of high land that separates one drainage basin from another.

Rain falling on opposite sides of a watershed will flow into different river systems.

Why does the gradient decrease downstream?

In the upper course, the river flows across steep upland landscapes and vertical erosion can cut downwards into the valley.

Further downstream, the river is much closer to its base level. Vertical erosion becomes less important and lateral erosion, transportation and deposition become increasingly significant.

This produces the characteristic smooth, concave long profile of a river.

Mouth

The mouth is the end of a river where it flows into another body of water, such as a sea, lake or larger river.

By the time a river reaches its mouth it normally has a much greater discharge than it had near its source.

Tributary

A tributary is a smaller river or stream that flows into a larger river.

Tributaries add water to the main river and therefore usually increase its discharge.

The Long Profile of a River

A river's long profile shows the change in height of the river from its source to its mouth.

Most rivers have a concave long profile.

Near the source:

  • altitude is high

  • the gradient is steep

  • the channel is usually narrow and shallow

Further downstream:

  • altitude decreases

  • the gradient becomes gentler

  • the channel becomes wider and deeper

Eventually the river approaches its base level, usually sea level.