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Geography notes: Rivers

The drainage basin hydrological cycle

The drainage basin is an area of land drained by a river and its tributaries. The hydrological cycle is
the process by which water is moved within the drainage basin. The drainage basin hydrological
cycle is an open system as water is…

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Precipitation-This forms a major input into the system, though amounts vary over time and space.

Evapotranspiration ­ the two components of evapotranspiration (evaporation and transpiration)
contribute to form an output of the system. it is also possible to distinguish between the potential
and the actual evapotranspiration. For example, in deserts…

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Vocab Definition
Transpiration The biological process by which water is lost from a plant through the stomata in its leaves.

Evaporation The process by which liquid water is changed into water vapour and lost directly into the atmosphere from
water surfaces, including vegetation and the soil due to the effects…

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Percolation The slow vertical movement of water through underlying compact soil or rock layers. The rate of percolation
depends on the rock and impermeable rocks e.g. granite does not allow water to percolate.
Groundwater Storage of water caused by constant percolation in the underlying rock.
storage
Groundwater The slow vertical…

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The graph shows the water budget for a town in Ghana and shows
two distinct seasons. A dry season from November to March and
an increasingly wet season from April to October. When
evapotranspiration exceeds precipitation the water stored as soil
moisture storage is used soil moisture utilisation in October…

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Factor affecting Flashy Hydrograph Steady hydrograph
hydrograph

Annotated sketch




Precipitation Prolonged rainfall ­ soil becomes saturated If rain falls gently over a long period of time
therefore infiltration can't occur which it encourages infiltration therefore
leads to an increase of surface run off. This increasing soil moisture storage
decreases the…

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Soil This hydrograph may have clay soils which This soil may be deep therefore increasing
encourage surface run off due to their platy its soil moisture storage capacity. Thus
structure. They are difficult to infiltrate and there is a longer lag time as water
so little water infiltrates creating a…

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the wetted perimeter is large. Therefore more energy is lost through friction and the rivers
velocity therefore energy its energy level decreases. However, when the river contains large
quantities of water following heavy rain or snowmelt, it does possess the energy to perform great
amounts of erosion.

There are 4…

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Traction ­ large stones and boulders are rolled along the river bed by water moving downstream.
This process operates only at times of high discharge.

Saltation ­ small stones bounce or leap frog along the channel bed. This process is associated with
relatively high energy conditions. Small particles may be…

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There is an increase in the size of the load. This may be due to a tributary bringing in larger
particles, increased erosion along the rivers course or a landslide into the river.
The river floods and overtops its banks, resulting in a reduced velocity on the floodplain
outside the…

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