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A flood hydrograph

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Introduction

A flood hydrograph is a graph of two axis, 'discharge' and 'time'. Plotted on the graph is the amount of discharge over a period of time. By looking at a hydrograph, a lot of information and data can be gathered about the river, the precipitation, the surrounding area and vegetation etc. The gradient, height and length of a line can tell you a lot of this information. There are many different factors that can affect the appearance and shape of a hydrograph. Certain conditions can cause the line on the hydrograph to be tall and thin and other conditions can cause it to be short and wide. Peak discharge is the term used to describe the maximum amount of discharge from the river over the period of time recorded; this peak discharge can be high or low depending on a lot of conditions. Climatic factors are the most obvious conditions that can affect the flood hydrograph. ...read more.

Middle

The rates of evapotranspiration affect the nature of a flood hydrograph. If there are high rates of evapotranspiration then the peak discharge maybe lower and the lag time greater. If the rates are low then the graph will not be affected by this factor. Soil types and characteristics can have a large impact on a hydrograph. If the soil is dry and permeable then it can hold lots of water and the hydrograph is more likely to look like line B on the right. If the soil is impermeable or it is a high antecedent soil that is already waterlogged the line is more likely to look like line A on the right. If the drainage basin has steep slopes then despite other factors the ascending limb can be a very steep gradient because the rainfall flows directly downhill to the river/streams without having time to infiltrate into soil. ...read more.

Conclusion

Vegetation prevents the water infiltration the ground as quick and reaching the river by means of overland flow or groundwater flow. If the drainage basin is greatly vegetated then the lag time is likely to be greater, the limbs are likely to be gentler and the length of the flood is likely to be longer. Forests and woodland intercept much rainfall and the roots encourage infiltration. If the drainage basin is bare and has little vegetation then there is likely to be more surface water. If there are lakes and backwater swamps upon the drainage basin then the movement of water to the channel is slowed. Another factor affecting the flood hydrograph is if the snow or ice that feeds the stream and rivers is melting quickly or slowly, this is decided by the weather. Flood hydrographs are useful and there are many different factors that can affect its from. Flood hydrographs could be slightly more useful if they were supplied with information about the precipitation, e.g. duration. ?? ?? ?? ?? Jonathan Burch 02/05/2007 Geography Essay 1 of 3 ...read more.

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