Factors affecting the shape of a hydrograph

Factors affecting the shape of a hydrograph

1. Antecedent rainfall

   • Heavy rain falling on a soil which is saturated from a previous period of wet weather
     • Produces steep rising limb

2. Impermeable rock types

   • 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.

3. Size of drainage basin

   • A small drainage basin tends to respond more rapidly to a storm than a larger one, so the lag time is shorter.

4. Vegetation

   • 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.

5. Urbanisation

   • Human impact. Reduces lag time and increases peak discharge. Impermeable surfaces (concrete/tarmac)
     • Drains/sewers
       • Transport water rapidly to river channels, reducing the lag time
     • 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.