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Edexcel IGCSE Geography 復習筆記 1.1.3 River Regime & Hydrographs

Category: IGCSE課程, 國際課程, 教材筆記, 福利干貨 Date: 2022年7月22日下午3:54

Edexcel IGCSE Geography 復習筆記 1.1.3 River Regime & Hydrographs

River Regimes & Storm Hydrographs

River regimes

The?discharge?of a river changes over time
The?river regime?is a record of these changes over a year
Many factors can influence the river regime including temperature, vegetation, land use and human activity

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

storm-hydrograph

Storm hydrograph in an urban area

Worked Example

Study Figure 1 which shows storm hydrographs for rivers A and B

T6o~P2mz_storm-hydrograph

Figure 1 Storm Hydrograph

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 6 hours from the start of the storm
- 6 hours - 2 hours and 30 mins = 3 hours and 30 mins

Answer

Lag time = 3 hours and 30 mins (1)

Exam Tip

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

Exam Tip

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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