A flood hydrograph

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Jonathan Burch        02/05/2007        Geography Essay


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. If the precipitation is very intense and there is a lot of it then the hydrograph is likely to have a high peak discharge where as if the precipitation is low-intensity and there is a small amount then the graph will have a gentle ascending limb.

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The ascending limb is the first part of the line on a hydrograph that rises to the peak discharge. If the gradient is steep (like the example on the right) then this can indicate that the amount of rainfall becoming overland flow is very high, the result of this is that all the water reaches the river very quickly and all in a short period of time, this gives the immediate steep ascending limb on the hydrograph.

Reasons for large amounts of rainfall becoming overland flow can be little vegetation and maybe impermeable rock below the surface. Being ...

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