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Factors affecting storm hydrographs - Coggle Diagram
Factors affecting storm hydrographs
Precipitation type & intensity
highly intensive rainfall likely to produce land overflow.
low-intensity rainfall likely to infiltrate into the soil & percolate slowly into the rocks which increases the time lag & reduces the peak flow.
Precipitation which falls as snow sits on the ground until it melts - rapid melting can cause flooding & lead to high rates of overland flow
Drainage Basin size & shape
Smaller drainage basins respond more quickly to rainfall conditions
An example is the Boscastle Floods of 2004 drained an area of less than 15km squared, this meant that the peak of the flood occurred soon after the peak of the storm.
The Mississippi River is over 3700km long - it takes much longer for the lower part of the river to respond to an event that might occur in upper course of the river.
Circular basins respond more quickly than linear basins, where the response is more drawn out.
Rock type
Impermeable rocks
Granite & clay produce greater peak flows
Permeable rocks
Chalk & Limestone produce storm hydrographs with a much lower peak flow and a greater time lag.
Slopes
Steeper slopes create more overland flow,
Shorter time lags
Higher peak flows
Vegetation type
Summer:
Forest vegetation intercepts more rainfall especially in the summer. This then reduces the amount of overland flow and peak flow and increases time lag.
Winter:
Deciduous trees lose their leaves so intercept less
Land use
Impermeable surfaces or reduced vegetation cover reduced interception and increases overland flow.
If more drainage basins are built, then the water is carried to rivers very quickly, which means that peak flows are increased and time lags reduced.
Drainage Density
Basins with a high drainage density, such as urban basins with a network of sewers and drains, respond very quickly.
Networks with a low drainage density have a very long time lag
Porosity and impermeability of rocks and soils
Impermeable surfaces cause more water to flow overland, which causes greater peak flows.
Urban areas contain large areas of impermeable surfaces.
Rocks such as chalk and gravel are permeable and allow water to infiltrate and percolate, which reduces the peak flow and increases the lag time.
Sandy soils allow water to infiltrate whereas clay is much more impermeable and causes water to pass overland.
Temperature, evaporation, transpiration and evapotranspiration
temperature isn't the only thing that affects precipitation , also effects evaporation rates