Hydrographs Flashcards
What do flood hydrographs show? (Hydrographs rivers)
They record the amount of discharge from a river over time
What is the equation for river discharge? (Hydrographs rivers)
River discharge = velocity (m/s) x volume (m2)
What is velocity? (Hydrographs rivers)
The speed of the river
What is discharge? (Hydrographs rivers)
The amount of water flowing in a channel
What is basin lag time? (Hydrographs rivers)
Time between peak rainstorm and peak river flow
What factors affect lag time? (Hydrographs rivers)
Impermeable rocks
Permeable rocks
Steep gradient on basin
Less steep gradient on basin
How does impermeable rock affect lag time? (Hydrographs rivers)
Short lag time
Will not allow water through, resulting in large levels of surface run off and a greater flood risk
How does permeable rock affect lag time? (Hydrographs rivers)
Long lag time
High infiltration capacity and so will absorb the water very quickly
How does a steep gradient affect lag time? (Hydrographs rivers)
Shorter lag time
Greater overland flow
How does a less steep gradient affect lag time? (Hydrographs rivers)
Longer lag time
more time for infiltration
How does the shape of the drainage basin affect the shape of the hydrography? (Hydrographs rivers)
The larger the drainage basin, the slower the river responds. This is due to the distance the river has to travel
