oh no, how frustrating. i’m sure more mulching with compost will help the drainage in general. it might be worth planning over time to raise the level of the allotment with high raised beds etc to flood-proof your site as who knows whether this is how our climate will be from now on!
until i got access to this land my garden consisted of one raised bed in which the surface of the soil was 2 feet above a permanently swampy lawn – and the plants were happy in both drought and flood.