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The Parish of Bix & Assendon places of interest |
The Assendon Stream
"That Land-Springs, and fuch as run but once perhaps in many Years, have their Rife and Continuance from plentiful Showers, .......; whereof that of Affenton, near Henley upon Thames, is one of the moft eminent that I know of in England;"
"And fo they did lately, in an. 1674 with that Violence, that feveral Mills might have been driven with the Current; and had not the Town of Henley made fome Diverfion for them, their Fair-Mile muft have been drowned for a considerable time."
1705, Robert Plot, Late Keeper of the Ashmolean Museum, quoted from his essay on The Natural Hiftory of Oxford-Shire.
This stream is a geographical curiosity in that it rarely reaches as far as its natural outlet into the Thames at Henley via the pond in the grounds of Phyllis Court Club. The Stream last ran all the way to the Thames in February 2001. Previously, it flowed in the Spring of 1969, and this period of 32 years has proved to be the longest absence for the stream running in the last 150 years.
Once every forty years or so, sometimes less,
sometimes more, it causes havoc by flooding extremely fast down the Stoner
valley, through the Assendons along the line of the main road and including the
full width of the Fairmile before reaching the Thames. And on the way it floods
several houses and gardens in Northfield End.
This is largely because in the intervening years between floods the open ditches and enclosed culverts through which it should flow have fallen into disrepair and ceased to be of real use through lack of use! Not to mention lack of immediate knowledge of the stream's route making emergency remedial action somewhat difficult.
The stream rises from the valley floor in a field south of Stonor at a height of 77 metres above sea level. As the Chiltern Hills are mostly porous chalk deposits, rain water does not run off them on the surface such as in the Lake District making babbling brooks, but sinks into them slowly building up a reservoir within the hills themselves. When the groundwater level reaches 85.65 metres in the Stonor House well, the groundwater rises through the surface of the valley floor. It is at this point that the Stream starts to flow. When the water level falls the stream stops which may mean it has only flowed a mile or so. However in winters of excessive heavy rain that level continues to rise and rise much higher despite the stream flowing, thus making the stream flow further and further down the valley towards Henley. When the groundwater level drops the stream flow decreases and the Stream retreats back up the valley to its source..
Since appalling floods in 2001 devastated the whole area, the Parish Council has established a monitoring arrangement with the Environmental Agency, OCC and SODC so as to alert householders to acquire sandbags, clear ditches etc. It is hoped this will be maintained indefinitely.