Mystery? The plot thickens…

Nestled among the sheds and veg of Birchall and Cranbrook Road allotments is a small brick shed with these enormous pipes outside – what on earth? – is someone growing giant mushrooms or even captured Triffids?
Neither, but the gardeners will never forget the day in 1986 when they were all turned off their allotments. All their hard work replaced by a massive crater which occupied the entire site and was nearly three storeys deep. But why? The answer lay in a problem that had bedevilled Bristol’s history down the centuries, and one which sadly still distresses many communities even today.

Bristol, the city of hills and steep sided valleys, has many streams and rivers emptying to the River Avon and eventually to the Severn Estuary. Homes in the valley bottoms were always prone to serious flooding, and down the centuries many were destroyed and lives lost.

In the 1900s, endeavouring to reduce the cacophony of iron rimmed cart -wheels, the city laid eighteen miles of hardwood block paved roads. The junction of Cheltenham, Cranbrook and Zetland roads was one such, but in 1902 it was flooded thoroughly, soaking the wood blocks, which swelled to such an extent that they rose forming a wooden ‘bubble’ about three feet, (nearly a metre), high.

But what has this to do with the allotment holders’ distress?

Beneath the junction of Gloucester and Cheltenham Roads there is a large brick chamber where the culverted waters of the stream flowing between Cranbrook and Elton Roads joins the Horfield Brook which, culverted, becomes the Cutler’s Mill Brook to continue behind Cheltenham Road before joining the River Frome, and onto the Avon.

Flood plains weren’t possible in an urban environment, and the usual solution was to have holding tanks where the storm water could be stored and slowly released.

By the 1980s it was realised the problem of repeated flooding required drastic action – bigger holding tanks, but where? Unfortunately for the allotment holders, theirs was the only open space in the problem catchment area. Therefore in 1986 allotments between Birchall and Cranbrook Road were cleared enabling Bristol City Council’s Engineering department and Wessex Water to dig a colossal storm water relief tank.

The tank occupies the entire allotment site and is nearly three storeys deep. Not until 1990 were the allotments re-instated so that veg and flowers could once more flourish.

Nowadays, among the veg, fruit and flowers the only evidence of this engineering feat is a small water control blockhouse and these massive set of pipes which are needed to vent the rush of air when storm water fills the tanks.