Factors affecting river discharge Flashcards
What does the unit cumec actually mean?
Cubic meters per second.
What does a storm hydrograph show?
Variations in a river’s discharge over a short period of time, usually during a rainstorm.
Label this storm hydrograph.
How does the intensity and duration of a storm affect the shape of the hydrograph?
If both are high they produce a steep rising limb as the infiltration capacity of the soil is exceeded.
How does the atecedent rainfall affect the shape of the hydrograph?
Heavy rain falling on soil which is saturated from previous wet weather will produce a steep rising limb.
How does snow affect the shape of the hydrograph?
The discharge will be increased when the melting occurs, as massive amounts of water will be released.
Water may reach the channel even quicker if the ground is frozen as infiltration is restricted.
How does porous soil types/permeable rock types affect the shape of the hydrograph?
E.g limestone
Produces less steep hydrographs because the water is regulated more slowly through the natural systems.
How does impermeable rock types affect the shape of the hydrograph?
E.g granite and clay
Tend to have higher densities of surface streams (higher drainage densities).
The higher the density, the faster the water reaches the main river channel, causing rapid increase of discharge.
How does the size of the drainage basin affect the shape of the hydrograph?
Smaller drainage basin has a shorter lag time.
This is because a smaller drainage basin responds more quickly to a storm than a larger drainage basin.
How does the shape of the drainage basin affect the shape of the hydrograph?
Rainfall reaches the river more quickly from a round basin, than an elongated basin.
How does temperature affect the shape of the hydrograph?
High temperatures mean more evapotranspiration, so the discharge is reduced.
Cold temperatures freeze the ground so there is restricted infiltration, increasing overland flow and discharge.
How does vegetation affect the shape of the hydrograph?
In summer there are more leaves on deciduous trees.
Interception is higher and the peak dischargeislower.
How does land use affect the shape of the hydrograph?
Water runs more quickly from impermeable land e.g caravan parks.
Lag time is reduced and peak discharge is increased.
How does urbanisation affect the shape of the hydrograph?
The following reduces the lag time and increases the peak discharge:
- Removal of topsoil and compaction of the ground with eath-moving machinery during building work
- Building of roads which incresaes the impermeable surface area
- Building of drains and sewers that transport water rapidly to river channels
- Straightening of river channels and lining with concrete
