A hydrograph is a graph that reflects the discharge of a river over a period of time. Discharge is the volume of water that flows about a certain point per unit of time.
Discharge: volume of water in the river at a given time.
- Rising limb: The rising flood water in the river
- Peak flow: Maximum discharge in the river
- Recession limb: Falling flood water in the river
- Basing lag time: Time difference between the peak of the rain storm and the peak of the river
- Base flow: Normal discharge of the river
- Overland flow: Volume of water reaching the river from surface run off
- Through flow: Volume of water reaching the river through soil and underlying rock layer
- Storm flow = Overland flow + Through flow
1. Size of the drainage basin (Area):
Larger basin receives more pricipitation -- larger runoff
Larger basin means water will take longer to reach the river -- longer lag time
2. Shape of the drainage basin:
Elongated basin -- lower peak flow and longer lag time than circular one
Steep slop -- steeper rising limb and shorter lag time
4. Characteristics of the Drainage Basin:
Permeable rocks and soil mean rapid infiltration and little overland flow -- longer lag time and shallow rising lime
5. Land use and Human impact:
Afforestation -- intercepts the precipitation -- shallow rising limb and longer lag time
Urbanization -- tarmac and concrete form impermeable surface -- steep rising limb and short lag time
River management: the presence of a dam will allow flow to be controlled, reducing flood risk and allowing rivers to gradually respond to heavy rainfall in a controlled way.
Hope you have learnt something. Thank you :)
Xu Ao, JH405, 14