AQA AS Geography Rivers: River Discharge and the Storm Hydrograph

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  • Created on: 22-08-13 19:59
Preview of AQA AS Geography Rivers: River Discharge and the Storm Hydrograph

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River Discharge
River discharge is the volume of water, in cubic metres, that flows in a river per second.
Hydrographs are graphs of river discharge over time.
They show how a drainage basin responds to a period of rainfall.
They are useful in planning for flood situations and times of drought as they show the
discharge reaching the channel via surface runoff, throughflow and base flow that
originated as precipitation.
Peak discharge Highest point on the graph, when river discharge is at its greatest
Lag time The delay between peak rainfall and peak discharge
Happens because it takes time for the rainwater to flow into the river
A shorter lag time can increase peak discharge.
Rising limb The part of the graph up to peak discharge
The river discharge increases as rain flows into the river
Falling limb Part of the graph after the peak discharge
Discharge is decreasing because less water is flowing into the river

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The Storm Hydrograph is affected by Physical Factors
Drainage basin characteristics
Larger drainage basins Can catch more precipitation so higher peak discharge
Shorter lag times
Smaller drainage basins Precipitation has a shorter distance to travel
Steep-sided basins Shorter lag times
Water flows more quickly downhill
Increases peak discharge
Lots of tributaries Increases peak discharge
Decreases lag time
The amount of water already
Saturated soil If the ground is already saturated then infiltration is
reduced and surface runoff increases.…read more

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Vegetation Intercepts precipitation and slows its movement to the
river channel
Increases lag time
Interception is at its highest when there's lots of
The more vegetation there is, the more water is lost
directly from the vegetation before it reaches the
river, reducing peak discharge
Intense storms Generate more precipitation and so peak discharge
Type of precipitation
Snow that's fallen can melt and flow into the river
giving it a very long lag time and also increasing peak
Hot,…read more

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The Storm Hydrograph is affected by Human Factors
Type of area
Urban Much of the soil is covered with man-made
impermeable materials such as concrete and
tarmac.…read more

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