River Regime & Hydrographs (Edexcel IGCSE Geography)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
River Regimes & Storm Hydrographs
River regimes
The discharge of a river changes over time
The river regime is a record of these changes over the period of a year
Many factors can influence the river regime as outlined in the table below
Storm hydrographs
A storm hydrograph shows the changes in river discharge after a storm event
The graph shows a short period of time, usually 24 hours
The storm hydrograph has a number of features:
Base flow
Peak rainfall
Rising limb
Peak discharge
Lag time
Recessional limb
Worked Example
Study Figure 1 which shows storm hydrographs for rivers A and B
River A River B
Figure 1 Storm Hydrographs
What is the lag time for river A? (1)
To work out the answer you need to calculate the difference between the peak rainfall and peak discharge:
The peak rainfall is between 2 and 3 hours from the start of the storm, taken at the mid point this would be 2 hours and 30 minutes.
The peak discharge is at 8 hours from the start of the storm
8 hours - 2 hours and 30 mins = 5 hours and 30 mins
Answer
Lag time = 5 hours and 30 mins (1)
Examiner Tips and Tricks
Remember a hydrograph shows the changes in discharge over a short period after a storm event, whereas the river regime shows changes in discharge over a long period, usually a year.
Factors Affecting Regimes
There are many factors which affect the discharge or regime of a river
The shape of storm hydrographs is also affected by these factors
Factors which increase overland flow lead to:
shorter lag times
increased discharge
steeper rising limb
Factors which Influence River Regimes
Factor | Effect |
|---|---|
Climate | Snow and ice melt leads to higher discharge - usually in the spring months High temperatures increase evaporation and reduce river discharge Higher rainfall in autumn and winter increases river discharge Convectional rainfall in summer or hot, moist climates increases river discharge |
Vegetation | Vegetation increases interception and infiltration leading to reduced overland flow and so lower river discharge Deciduous trees lose their leaves in winter decreasing interception, increasing overland flow and river discharge |
Land Use | Concrete and tarmac in urban areas and built environments are impermeable leading to high overland flow - this is rapidly taken by drainage systems to the rivers/streams, increasing river discharge |
Geology | Permeable rocks increase infiltration and percolation which reduces overland flow and decreases river discharge |
Soils | Soils which are compacted or frozen reduce infiltration, increasing overland flow and river discharge |
Abstraction | Water taken for irrigation and domestic use decreases the river discharge |
Dams | Dams control the flow of water, so can both increase and decrease river discharge Reservoirs experience higher levels of evaporation which can decrease river discharge |
Relief | Steep slopes increase overland flow which leads to increased river discharge |
Drainage density | High drainage density leads to increased discharge, particularly after a rainfall event |
Examiner Tips and Tricks
Remember all the factors which affect river regimes also affect the risk of flooding. Any factor which increases overland flow and discharges also increase the risk of flooding.
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