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Drainage Basins


Explain the drainage basin as an open system with inputs, outputs, flows and stores

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Drainage Basins


Explain the drainage basin as an open system with inputs, outputs, flows and stores

 
 
 

Summary

Drainage basins are open systems, with inputs, stores and outputs. The main input is precipitation which is regulated by various means of storage. Outputs include channel runoff, evapotranspiration and groundwater flow.

 

The Drainage basin system

Drainage basin flow chart

Drainage basin flow chart

 
 
Drainage basin system diagram. (Click on the image above to obtain a downloadable PDF)

Drainage basin system diagram. (Click on the image above to obtain a downloadable PDF)

 

TASK

  1. Complete the system diagram using information from the flow chart

  2. Identify and annotate a feedback loop on your system diagram

  3. Make notes on pp 104-106 Core Book

 

water balance in a drainage basin

Water balance in a drainage basin ( Source )

Water balance in a drainage basin (Source)

The water balance is the relationship between inputs (precipitation) and outputs (evapotranspiration). It is influenced by a number of factors:

  • Soil moisture deficit - the degree to which soil moisture falls below its capacity

  • Soil moisture recharge - precipitation > potential EVT

  • Soil moisture surplus - soil is saturated leading to overland flow

  • Soil moisture utilisation - water is drawn to the surface by the capillary action of plants, which is then used or evaporated

These factors may change over time (seasons, long term changes in ice/water balance) or space (precipitation, EVT and runoff vary between countries).

 

PLENARY

Match the words with the definitions to create a circle

Click to open

Click to open

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Discharge


Define river discharge and its relationship to stream flow, channel characteristics and hydraulic radius

Discharge


Define river discharge and its relationship to stream flow, channel characteristics and hydraulic radius

River discharge is the volume of water flowing through a river channel. This is the total volume of water flowing through a channel at any given point and is measured in cubic metres per second (cumecs)

Discharge is calculated as follows:

cross sectional area of a river or stream   x mean velocity of water

 
 
  1. Describe three relationships shown on the diagram above e.g. as discharge increases, velocity increases

WETTED PERIMETER

The wetted perimeter of a river refers to that part of the channel that is in contact with water. It represents the friction that slows down the river velocity.

The longer the wetted perimeter, the more friction between channel and water.

 

HYDRAULIC RADIUS

The hydraulic radius is a measure of efficiency in a river channel. It is calculated by comparing the wetted perimeter with the cross-sectional area of the channel.

Hydraulic radius = cross-sectional area / wetted perimeter

The higher the hydraulic radius, the more efficient the river.

 

ACTIVITIES

  1. Make simple sketches of the diagram above
  2. Read 107 - 109 (Core Book): Discharge, stream flow and channel shape.
  3. Make detailed notes under the different headings.
niagra waterfall river water.jpg

Stream Processes & Landforms


Describe and explain river processes of erosion, transportation and deposition and spatial and temporal factors influencing their operation, including channel characteristics and seasonality

Describe and explain the formation of typical river landforms, including waterfalls, floodplains, meanders, levees and deltas

Stream Processes & Landforms


Describe and explain river processes of erosion, transportation and deposition and spatial and temporal factors influencing their operation, including channel characteristics and seasonality

Describe and explain the formation of typical river landforms, including waterfalls, floodplains, meanders, levees and deltas

river profile.jpg
 
 

river erosion processes

river transportation processes

 

TASK

  1. Watch the video and read the overview above

  2. Describe two ways that rivers erode (2 + 2 marks)

  3. Describe two ways that rivers transport matieral (2+2 marks)

 
 

river landforms

 
 

TASK

  1. Watch video above
  2. Read pp 120-122 Core book
  3. Explain how two different landforms are produced by river processes:
    • Meanders and oxbow lakes
    • Levées