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Drainage Basins


Examine the functioning of a drainage basin as an open system with inputs, outputs, transfers, stores and feedback loops

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Drainage Basins


Examine the functioning of a drainage basin as an open system with inputs, outputs, transfers, stores and feedback loops

 
 

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)

  1.  
 

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 stream discharge. Examine its relationship to stream flow and channel shape.

Discharge


Define stream discharge. Examine its relationship to stream flow and channel shape.

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
 

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.
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Hydrographs


Describe the characteristics of a hydrograph.
Examine the reasons for spatial and temporal (short-term and long-term) variations in hydrographs.
Examine the role of hydrographs in forecasting the magnitude, spatial extent and timing of floods.

Hydrographs


Describe the characteristics of a hydrograph.
Examine the reasons for spatial and temporal (short-term and long-term) variations in hydrographs.
Examine the role of hydrographs in forecasting the magnitude, spatial extent and timing of floods.

 
 

presentation

 
 

task

  1. Complete the task below from geographyalltheway.com
  2. Read and make notes on pp 111-113 Core Book
 

plenary

How would the following factors affect the shape of a flood hydrograph? (Source)

Write the factor > effect on drainage basin process > effect on shape of hydrograph

 
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Floods


Discuss the natural and human causes and consequences of the 2005 Swiss flood of the river Aare

Floods


Discuss the natural and human causes and consequences of the 2005 Swiss flood of the river Aare

Why is Switzerland prone to flooding? (relief, geology, distance from sea, altitude, snow)

The “Wasserschloss” (the confluence of the rivers Aare, Reuss and Limmat in the Canton of Aargau) during the flood of August 2007.

The “Wasserschloss” (the confluence of the rivers Aare, Reuss and Limmat in the Canton of Aargau) during the flood of August 2007.

 

why is switzerland at risk from flooding?

 
 

the river aare

The Aare River Basin, northern Switzerland.

TASK

  1. Draw a simple sketch map of the Aare river basin.
  2. Describe the Aare's course, naming major cities.
 

CAUSES AND CONSEQUENCES OF THE 2005 FLOOD IN SWITZERLAND

TASK

  1. Read the document.
  2. Highlight causes and effects using two different colours.
  3. Transfer these to a grid in your book, separating natural and human causes and consequences.
  4. Use this information to write an answer to the exam question below.
 
 

how engineering can prevent future flooding

 
 

EXAM QUESTION