Drainage Basin Systems

Revision notes on drainage basin systems for AQA A AS Geography Units 2 and 3.

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DRAINAGE BASIN SYSTEMS
THE RIVER SYSTEM AND ATMOSPHERIC PROCESSES
Rivers are open systems with
inputs & outputs of energy
(Evapotranspiration, solar
radiation,) and matter
(precipitation, runoff). Energy
and matter are stored within the
system and transferred between
the stores.
Factors affecting Drainage Basins:
Type of precipitation (e.g. snow has a delayed effect until melting).
Intensity of precipitation (e.g. a short shower leads to a faster movement of water
through the system, but affects only a small area).
Seasonal variations (e.g. may have more rain in winter and less in summer).
THE HYDROLOGICAL CYCLE
TERM TYPE DEFINITION
Interception Storage Precipitation that is trapped or temporarily stored on
Store vegetation.
Throughfall Transfer Precipitation that drips from vegetation to the ground.
Stemflow Transfer Precipitation that flows down plant stems to the ground.
Surface Store Storage Precipitation lying on the ground.
Overland Flow Transfer Movement of water over the ground surface to a river.
Transpiration Output Evaporation of moisture from the stomata of plants.
Infiltration Transfer The process by which water enters the soil.
Soil Water Store Storage Water stored in the soil.
Vegetation Store Storage Water stored in vegetation.
Throughflow Transfer Water that flows through the soil to a river.
Percolation Transfer Process by which water drains to the water table.
Groundwater Storage Water stored in the pores and crevices of rocks.
Store
Groundwater Transfer Water flowing in groundwater to a river.
Flow
Channel Store Storage Water stored in rivers.
Channel Flow Transfer Water flowing in a river.
River Runoff Output The total discharge from the river basin.
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FLOOD (STORM) HYDROGRAPHS
A hydrograph is the discharge of a river. They record the response of a drainage basin to an
individual precipitation event over a short timescale.
TERM DEFINITION
Base flow Water that reaches the stream via groundwater flow.
Runoff or Water that reaches the stream via overland flow and Throughflow.
stormflow
Peak discharge Time of maximum discharge after the precipitation event.
Rainfall peak Time of maximum precipitation in the precipitation event.
Lag time (basin The time between rainfall peak and peak flow.…read more

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Factors affecting the flood hydrograph:
SHORT LAG TIME LONGER LAG TIME
FACTOR (FLASHY) Lower peak and more gentle rising &
recession limbs.
Higher peak and steeper rising &
recession limbs.
Basin size Smaller Larger
Basin shape Circular Elongated
Relief Steeper slopes Gentler slopes
Type of Intense rainfall; rapid snow melt. Prolonged rainfall; slow snow melt.
precipitation
Vegetation Absent; Deciduous forest in Dense; Deciduous forest in summer.
winter.
Land use Deforestation; farming land; Reforestation; Natural vegetation;
desertification. Sustainable agriculture.
Urbanisation High density. Low density.
Geology Impermeable.…read more

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