Factors Affecting The Hydrological Cycle Flashcards
How does the antecedent rainfall affect the shape of the hydrograph?
Heavy rain falling on a soil which is saturated from a previous period of wet weather will produce a steep rising limb.
How does snow affect the shape of the hydrograph?
Heavy snowfall may not initially show on a hydrograph since the water is being ‘stored’. Water levels in a river may fall during a prolonged period of snowfall and cold weather. When temperatures rise discharge increases. This water may reach the river channel even quicker if the ground remains frozen and restricts infiltration.
How does the intensity and duration of the storm affect the shape of the hydrograph?
If they are both high they produce a steep rising limb as the infiltration capacity of the soil is exceeded.
How do porous soil types and/or permeable rock types affect the shape of the hydrograph?
E.g. Limestone- these produce less steep (or less flashy) hydrographs because water is regulated more slowly through the natural systems.
How do impermeable rock types affect the shape of the hydrograph?
E.g. Granite and clay- these 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 increases in discharge.
How does the size of the drainage basin affect the shape of the hydrograph?
A small drainage basin tends to respond more rapidly to a storm than a larger one, so the lag time is shorter.
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 from an elongated basin.
How can a sloping angle affect the shape of the hydrograph?
In steep sided upland river basins the water reaches the channels much more quickly than in gently sloping lowland river basins, producing a steeper rising limb and shorter lag times.
How can temperature affect the shape of the hydrograph?
High temperatures increase the rate of evapotranspiration thereby reducing discharge. Cold temperatures may freeze the ground, restrict infiltration, increase overland flow and increase river discharge.
How does vegetation affect the shape of the hydrograph?
This varies with the season. In summer there are more leaves on deciduous trees, so interception is higher and peak discharge lower. Plantations of conifers have a less variable effect.
How does land use affect the shape of the hydrograph?
Water runs more quickly over impermeable surfaces such as caravan parks or agricultural land which has been trampled by cattle. Lag time is reduced and peak discharge increased.
How does urbanisation affect the shape of the hydrograph?
This is the main human impact on a storm hydrograph by reducing lag time and increasing peak discharge.
What processes of urbanisation alter the shape of the hydrograph?
- Removal of the top soil and compaction
- Roads- impermeable
- Drains and sewers
- Straightening of river channels and lining with concrete
