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Influences on storm hydrographs - Coggle Diagram
Influences on storm hydrographs
Climate
Precipitation
Type
Rain means there is less lag time.
Precipitation that falls as snow sits on the ground until it melts - sudden, rapid melting can then cause flooding and high rates of overland flow and high peak flows.
Intensity
Low intensity more likely to infiltrate into the soil and percolate slowly into the rock, reducing peak flow.
Highly intensive rainfall is likely to produce overland flow and high peak flow.
Temperature, evaporation, transpiration and evapotranspiration
Temperature/evaporation - high temperatures lead to more evaporation and so less water getting into rivers. Warm air can hold more water so potential for high peak flows in hot areas is raised.
Transpiration - vegetation cover intercepts some rainfall and may return some of the rain through transpiration so reduces the amount of water reaching stream channels.
Evapotranspiration - the higher the return through evapotranspiration, the less water able to reach stream channels so peak of hydrograph lower.
Antecedent moisture
If it has been raining previously and the ground is saturated, rainfall will quickly produce overland flow, a high peak flow and short time lag.
Drainage basin characteristics
Drainage basin
Size
Smaller drainage basins respond quicker to rainfall conditions. It means that peak of the flood occurs soon after peak of the storm.
Large drainage basins means that it takes much longer for lower part of the river to respond to an event that might occur in the upper course of the river.
Shape
Circular basins respond more quickly than linear basins, where the response is more drawn out.
Drainage density
Basins with a high drainage density (urban basins with a network of sewers and drains) respond very quickly. Networks that have low drainage density have a very long time lag.
Porosity and impermeability of rocks and soils
Impermeable surfaces cause more water to flow overland causing 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 reducing peak flow and increase time lag.
Sandy soils allow infiltration whereas clay is more impermeable and so more water passes overland.
Rock type
Impermeable rocks such as granite and clay produce greater peak flows with a quicker response.
Permeable rocks like chalk and limestone produce storm hydrographs with a much lower peak flow and with a delayed response and greater time lag.
Slopes
Steeper slopes create more overland flow, shorter time lags and higher peak flows.
Vegetation type
Forest vegetation intercepts more rainfall, especially in summer, and so reduces the amount of overland flow and peak flow and increases time lag. In winter, as deciduous trees lose their leaves, less water is intercepted so there is more overland flow.
Land use
Land use that create impermeable surfaces, or reduce vegetation cover, reduce interception and increase overland flow.
If more drainage channels are built (sewers, ditches, drains), any water is carried to rivers very quickly. This means that peak flows are increased and time lags reduced.