Describe and Explain the Factors that Influence the Flood Hydrograph, with particular reference to Rural and Urbanised Drainage Basins.

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Nazia Zia         Essay 2: Rivers        18/12/07

Describe and Explain the Factors that Influence the Flood Hydrograph, with particular reference to Rural and Urbanised Drainage Basins


In this essay I aim to find out the ways in which they affect the flood hydrograph, with particular reference to rural and urbanised drainage basins of Tokyo.

A drainage basin is an area of the land’s surface from which a river receives its supply of water. An imaginary line can mark the edge of a drainage basin. This is called the watershed. The other main features of a drainage basin are shown in figure 1.

The drainage basin relies on the atmosphere for its inputs of water, whilst water passes through the drainage basin leaves the system either to return to the atmosphere or to become an input into the coastal and ocean systems. A single drainage basin is one part of the whole hydrological cycle, but the hydrological processes taking place within it are most likely as those operating at the global scale. Figure 2 shows the hydrological processes taking place in a drainage basin, with its outputs, inputs, stores and processes. (On separate sheet).

The river flow out of the drainage basin is determined by the amount of precipitation, the losses in evaporation and Evapotranspiration and the gains or losses from the storage areas: surface storage, soil moisture and groundwater storage.

Using climate, it is possible to construct a water budget graph. Figure 3 (on a separate sheet) shows water budget graphs for a. Birmingham, UK and b. Athens, Greece.  This graph lest us know more about the processes that work in the drainage basin and it also allows us to compare different countries, I have used the examples of UK and Greece. Looking at figure 3, I can see that the rainfall in Birmingham is relatively constant during the year. Evapotranspiration is increased by high temperatures in the summer and therefore results in water deficit. Recharge in water is increased in autumn caused by an increased rainfall. Water deficit is much higher in Athens (a peak of 170mm) whereas in Birmingham it has a peak of 105mm), this is much lower than Athens as Athens has a higher summer temperature, which therefore causes an increase in Evapotranspiration, although this is reduced in the winter rainfall is not sufficient to create a water surplus in the soil.

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Flood hydrographs

A flood or storm hydrograph shows the relationship between rainfall and discharge. Studying this relationship in different drainage basins in different weather conditions can help to predict when and where flooding might occur. In this essay I am going to concentrate on the storm hydrograph of Tokyo before and after urbanisation, which will therefore help me describe the difference between rural and urban drainage basins using the factors.  

Figure 4 below shows a storm hydrograph with labels.


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