Support systems KQ1- Hydrographs Flashcards
What do hydrographs show?
Continuous recordings of river discharge
What is river discharge?
Volume of water passing a given point in a given time
What is river discharge measured in?
Cumecs (m cubed, seconds to the minus one)
Why are hydrographs important?
- used to compare drainage basins and how they respond
- speed and scale of the rise in discharge can be worked out
- assess the risk of flooding
- changes in the management can be monitored
What is peak discharge?
Maximum discharge recorded after a rainfall event
What is the rising limb?
When discharge begins to rise due to overland flow
What is the recession limb?
When discharge begins to fall as inputs to the channel decrease
What is base flow level?
The level at which the stream maintains in dry spells due to ground water flows
What is lag time?
Time between maximum rainfall and peak discharge
What is peak rainfall?
Maximum rainfall value
What is storm flow?
The area under the graph above base flow level
Why is there a lag time?
Water takes time to reach the river
What are the features of a ‘flashy’ hydrograph?
- steep rising and falling limb
- reaches high peak discharge
- shorter lag time
What are the features of a ‘non flashy’ hydrograph?
- flat hydrograph
- reaches lower peak discharge
- longer lag time
Give some factors which might produce a ‘flashy’ hydrograph
- steep relief of area
- small drainage basin
- saturated soil
- heavy prolonged rain
- urban area
- frozen ground
