Factors affecting the shape of a hydrograph

Antecedent rainfall
1. Heavy rain falling on a soil which is saturated from a previous period of wet weather
  1. Produces steep rising limb
Impermeable rock types
1. such as granite & clay - tend to have higher drainage densities. The higher the density the faster the water reaches the main river channel, causing rapid increases in discharge.
Size of drainage basin
1. A small drainage basin tends to respond more rapidly to a storm than a larger one, so the lag time is shorter.
Vegetation
1. Varies with season. In summer there are more leaves on deciduous trees, so interception is higher and peak discharge lower. Plantations of coniferous have a less variable effect.
Urbanisation
1. Human impact. Reduces lag time and increases peak discharge. Impermeable surfaces (concrete/tarmac)
  1. Drains/sewers
    1. Transport water rapidly to river channels, reducing the lag time
  2. Straightening of river channels and lining of concrete - leads to faster delivery of water downstream of the urban area and increases the risk of flooding in downstream areas.

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