Geography - Flooding + Flood Hydrograph definitions gcse 9-1
- Created by: becca14802
- Created on: 07-05-17 13:03
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- Geography: Flooding
- Flood Hydrographs
- Recession limb: Falling flood water in the river
- Peak flow: Maximum discharge in river
- Basin lag time: Tine difference between the peak of the rain storm and the peak flow of the river
- Rising limb: The rising flood water in the river
- Base flow: Normal discharge of river
- Discharge in m3/s, as a line graph
- Overland flow + Through flow = Stormflow
- Rainfall shown in mm, as a bar graph
- Definitions
- The more infiltration occurs the longer the lag time and shallower the rising limb
- Infiltration is generally greater on thick soil, although less porous soils e.g. clay act as impermeable layers
- Land
use
- Afforestation - intercepts the precipitation, creating a shallow rising limb and lengthening the lag time
- Urbanisation - concrete and tarmac form impermeable surfaces, creating a steep rising limb and shortening the lag time
- Slope Channel flow can be faster down a steep slope therefore steeper rising limb and shorter lag time
- Drainage density Drainage density is the total length of all the streams and rivers in a drainage basin
- Slope Channel flow can be faster down a steep slope therefore steeper rising limb and shorter lag time
- Tidal Conditions: High spring tides can block the normal exit for the water, therefore extending the length of time the river basin takes to return to base flow
- Shape Why does the drainage basin shape matter? An elongated basin will produce a lower peak flow and longer lag time than a circular one of the same size
- Precipitation & Temperature
- If there have been extreme temperatures, the ground can be hard (either baked or frozen) causing rapid surface run off
- Short intense rainstorms can produce rapid overland flow and steep rising limb
- Snow on the ground can act as a store producing a long lag time and shallow rising limb. Once a thaw sets in the rising limb will become steep
- Area Large basins receive more precipitation than small therefore have larger runoff Larger size means longer lag time as water has a longer distance to travel to reach the trunk river
- Flood Hydrographs
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