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bagladesh

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Introduction

The recent past has seen a cluster of very wet winters - 1989/90, 1993/94 and 1994/95 each rank amongst the six wettest winters this century in southern England. In the autumn of 1993 a succession of active low-pressure systems on a southwesterly airflow brought abundant rainfall to southern counties. By mid-October the South Downs were saturated and rainfall infiltrating through the soil to the underlying Chalk caused groundwater levels to begin their seasonal recovery very early. After a respite the unsettled weather returned and a notable storm on the 28th November heralded a period of remarkably high rainfall. Over the next seven weeks rainfall totalled around 350 mm - equivalent to almost half the annual average for the Lavant catchment. ...read more.

Middle

In December 1993 alone the water tables rose 20 metres and groundwater levels were approaching the surface at year-end. On the 7th January the borehole became artesian (see left) and overflowed continuously for 18 days. Although the well has been known to overflow previously - most recently in 1974 (very briefly) and 1960 - available evidence suggests that January 1994 produced the longest period of continuous artesian flow on record. In order to develop appropriate flood prevention strategies it is essential to have an understanding of the relationship between flood size and their frequency of occurrence. This is difficult because, by their nature, extreme floods are very rare events and in most catchments a number of important floods are likely to have occurred before flow measurement facilities were in place. ...read more.

Conclusion

suggest that the peak flow was greater than any in the historical period. A frequency of less than once in a hundred years may be assumed. It is important to recognise that this rarity assessment assumes a stable climate. If global warming were to affect runoff variability in the UK this frequency could increase - underlining the need for more effective flood alleviation measures. Flooding can never be entirely prevented and in selecting a suitable flood alleviation strategy for a particular location a wide range of issues and options need to be considered. A Flood Relief Tunnel Construction of a flood relief tunnel beginning in the Westhampnett area, continuing below Chichester (following the general route of the existing culvert) and discharging south of the A27 bypass into the Chichester Channel and thence to the sea. Estimated cost: �8.6 million By Chloe Atkins 9 king ...read more.

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