Managing water in a flood plain

Rosybee is situated in the flood plain of the Thames valley in South Oxfordshire. The site itself is a flat sheet of clay with slight ridge and furrow from the ancient ploughing.  When we bought this site, we knew it was prone to flooding but as my planning advisor said, 'so what, you are building a floodable building'.  That is true but even though the polytunnel comes to no harm with a few inches of water, and our plants are all off the ground on benches but its not nice and makes hygene difficult. Last year we only had water cover the floor once but it got a bit boggy serveral times. We all now know that 2012 was a very wet year but we decided that we want to try and manage the flooding as best we can. Therefore, we worked in stages to reduce the risk and each time had to wait (not too long obviously!) for it to rain again, observe what was working and not and amend again.   I am very pleased to report that in the last wet spell just before Christmas, all the fields around us had standing water - or full lakes with swans in one case - we only had temporary standing water in the furrows and by the next day it was just damp.

We have achieved this through:

• reinstating  the ditches to the correct depth on three sides of the field including wide 50cm culverts  (above) where access is needed
• adding a new ditch from the centre of the field to the edge to help the central furrows drain
• put 'french drains' of gravel and porous pipe round 3 sides of the polytunnel
• installing a sump and pump with a float switch to automatically remove excess water round the polytunnel

The last step has meant that we can move the water quicker than gravity and ditches alone would allow and this means that we can keep dry even in heavy rain.