Autobiography of Sir John Rennie, F.R.S., Past President of the Institute of Civil Engineers / Comprising the history of his professional life, together with reminiscences dating from the commencement of the century to the present time.

by Sir John Rennie

During this period I was requested by the Commissioners of the Ancholme Level, consisting of about 50,000 acres of low fen lands, bordering upon the Ancholme in North Lincolnshire, to give them my advice as to the best means of improving their drainage, and at the same time the navigation of that river.

The Ancholme takes its rise near Market Rasen, in the highlands of the north of Lincolnshire, and after a course of some miles it enters the lowland district of the valley, and proceeds through it in a northerly direction for a distance of about 18 miles, when it joins the Humber at right angles to its course. The valley varies from one mile in width at the upper end to three miles at the lower end, where it joins the Humber. It is bounded on the south by a ridge of chalk hills of considerable elevation, and on the north by a similar ridge of sandstone hills.

The Ancholme having very little fall where it enters the lowlands, and being prevented from discharging its waters with facility into the Humber on account of the great mass of water and high tides in the latter river, was forced back upon the lowlands, and frequently inundated them, so that they became little better than marshes, and the river itself was necessarily extremely circuitous. In 1806 the Commissioners applied to my father for advice, and he recommended, in the first place, that the river should be straightened as far as practicable, in order to utilize the fall of the current to the fullest extent; also that a sluice should be constructed to exclude the tides at Terreby; and a catchwater drain made on the south side, with separate sluice to discharge the highland waters into the Humber. This advice was only partly followed: the river was straightened; the catchwater drain only extended as far as Brigg; a lock was made for the navigation at Hortestow Green, where the river entered the lowlands; and a sluice with a lock was made at Terreby. In principle, these works were correctly designed and well adapted for the purpose as far as they went; but I am not exactly aware whether they were carried out according to his plan, or under his immediate direction; and twenty years had elapsed before I was invited to give my opinion.

When I visited them the level was very badly drained; the river was full of shoals; the navigation, which was intended for the Yorkshire coasting vessels up to Bishop’s Bridge, was only practicable a few miles beyond Brigg, and that in a very imperfect manner; and the works generally were in a very bad state.

After having inspected the works, I recommended, first, that the main river should be deepened, widened, and enlarged throughout the entire length of the level, so as to accommodate the full-sized Yorkshire coasting vessels drawing 6 ft. 6 in.; and that the river should be of ample capacity to contain the floods fully 2 to 3 feet below the level of the lowlands, so that they could not be overflowed, and might always be able to drain into it.

Secondly, that a lock should be made with a lift of 6 feet, so that coasting vessels might be enabled to get up to Bishop’s Bridge; and that as a great deal of sand was brought down by the upper part of the river, which continually produced shoals and filled it up, I recommended that at the upper end of the lock an overfall should be made, together with a capacious reservoir, into which the sand might be discharged, in order to prevent it from getting into the river; then it could be removed whenever necessary.

Thirdly, that a new sluice and lock should be made at Terreby, where the Ancholme joined the Humber; that all the new sluices should be laid 6 feet below the old one; and that new bridges should be made across the main river to replace the old ones, which were not of sufficient capacity.

Fourthly, that the south catchwater drain should be drained out and enlarged, and extended to the upper end of the level.

Fifthly, that a catchwater drain of the requisite dimensions should be made on the north side of the level, from the new sluice to the farther extremity of the level, and that the water should be discharged through a separate opening in the new sluice.