The Seventh Drain, in Three Maps

Three maps of the north-west marsh have been published in the town’s records. None of them, taken alone, tells the whole story. Taken together, they suggest a question that the Drainage Committee has so far declined to answer.

One: the Improvement Commissioners’ plan of 1826

The earliest is the plan annexed to the Improvement Commissioners’ award of 1826, which authorised the digging of what was then called, for no recorded reason, the Seventh Drain. The plan shows a channel running roughly north-south across the north-west marsh, from a point now identified as the headwall, before turning east, well south of the modern channel’s turn, and continuing to a confluence with the Old Eau.

The plan is careful. The Commissioners were paid by the yard, and their surveyors were not in the habit of imprecision. The angle of the turn, in particular, is recorded.

Two: the post-war revision of 1947

After the Great Flood, the parish records include a revised survey of the marsh, prepared for the rebuilding. The 1947 plan shows the Seventh Drain running, broadly, where the Commissioners had it. The turn is at a slightly different angle, and the channel is wider - the Flood having scoured it out, perhaps - but the route is recognisably the same.

The 1947 plan does not, however, account for the small differences in angle. It does not pretend to. It is a working surveyor’s plan, drawn for drainage engineers, and is content to record what is there.

Three: the 2022 contour survey

In 2022, a private contour survey of the marsh was prepared. The Gazette has not seen the original; what follows is from the careful account of it given by Della Finch to the Drainage Committee, and reproduced here with her permission.

The 2022 survey shows the modern channel running further north than the 1947 plan indicated. The turn, in particular, is some two hundred metres further north than either earlier plan recorded. The channel is also, in places, narrower than the 1947 survey would suggest.

What this does not show

This article has not, so far, made any claim about flow, depth, or the volume of water moving through the channel. Those are matters for the Drainage Committee, who maintain the sluice and the pumps. The Gazette has asked the Committee for a statement on the subject. The Committee has not, at the time of going to press, provided one.

The Gazette does not speculate. It reports.

A separate article collects the public clues that have appeared in the Gazette and elsewhere since 2022. It is at the mysteries page.