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What was the impact of building Harlow new town on Canon's brook? Describe the changes in the river's response to rainfall events and explain why these changes have occurred.

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Introduction

What was the impact of building Harlow new town on Canon's brook? Describe the changes in the river's response to rainfall events and explain why these changes have occurred. There are likely to be many effects of building a town on a brook. We can see that the most probable responses would be that more water flows into the river and the flood risk increases. However, there are likely to be many other contributing factors and other responses to these rainfall events. In this essay, I am going to examine how the changes to the response of the river occur and what these changes actually are. The river responded to rainfall very differently in three different time periods. In 1950, the peak discharge was about 1.8 cumecs. In 1950, the lag time would have been much longer due to the fact that there were no drainage systems. Water flows into the drains, and is taken straight to the nearest river which would greatly decrease the lag time. As the drainage system developed, the lag time would decrease, and this is shown as in later years the lag time is much lower. The flood risk for the area in 1950 is quite low because there is not a lot of water being discharged from the river. ...read more.

Middle

At the third time period, the town had industrialised, and there were many new buildings and roads covered with tarmac. Overall, the land use has changed significantly from being mainly arable and rural, to an urbanised area. The drainage basin is mainly used for water extraction, which is used for industry, and irrigation. The rivers response has changed dramatically over time. In the 50's, there had not been mass urbanisation, and the land use was much different. This meant that there were not many buildings or a lot of tarmac covered roads. Therefore, there would have been less water going into the river as there would have been more trees, which would have intercepted and absorbed some of the water, and also there would have been far more permeable rocks that water could infiltrate through, instead of tarmac which is impermeable. This would all lead to a decrease in the peak discharge. However, we can see that the peak lag time for 1958 is dramatically higher, at 5.1 cumecs, and for 1966 is 8 cumecs which is an enormous difference from 1.8 cumecs in 1950. This is for a number of reasons, due to the land use changing and urbanisation. ...read more.

Conclusion

This would mean that the water could travel at its fastest speed as surface run-off to the river which would decrease lag time and increase the flood risk. Moreover, the water could now not percolate and infiltrate through the impermeable rocks which would lead to the flood risk increasing, and the lag time decreasing. Furthermore, the trees would have also been cut down. This would mean that there would be less interception and absorption and transpiration which greatly contributes to the amount of water flowing into the river. Also, the fact that more drains would have been introduced once the town had become urbanised, would mean that the lag time would decrease and the flood risk would increase. In conclusion, in believe that there were many impacts of building Harlow new town on Canon's Brook. By building the town, and urbanising the area, it means that there would be more tarmac on the roads and buildings being erected. Therefore, trees would be needed to be cut down in order fro this to happen and many permeable rocks would be covered by the tarmac. Consequently, this corresponds to the flood risk increasing for the area. This is a major drawback as if the river did flood; it would lead to many possessions being damaged and could even cause death. ...read more.

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