HKDSE Geography/M2a/Hydrographs and Flooding

Flooding is the condition in which the water in a river overflows.

Hydrograph

TODO: Need actual hydrographs

• Peak discharge is the maximum river discharge during a certain period of time.
• A hydrograph's rising limb shows the time during which discharge increases.
• A hydrograph's falling limb shows when discharge decreases.

Factors

All the factors above that affect discharge affect flooding. The greater the discharge, the greater the flood risk. In addition:

• Elongated drainage basin → Time lag ↑ → Floods ↓
• Circular drainage basin → Time lag ↓ → Floods ↑

• Straight river → Time needed for river to flow away ↑ → Floods ↓
• Meandering river → Time needed for river to flow away ↑ → Floods ↓

• Lakes ↑ → Act as a buffer during floods → Capacity ↑ → Bankfull discharge ↑ → Floods ↓