MIDDLE LEVEL. Under the heading BEDP ItD LEVEL, a remarkable district, cov ering 400,000 acres, is described, boundino. the Wash on all sides except seaward, extend ing -landward nearly to Brandon, Cambridge, Peterborough, and Bolingbroke, and embracing portions of the six counties of Northampton, Huntingdon, Cambridge, Lin coln, .Norfolk, and Suffolk. It nearly coincides in area with what is popularly known as the Fens. The whole region was, centuries ago, converted into an unprofitable marsh by repeated incursions of the sea, coupled with obstructions to the outward flow of the rivers Nene, Cain, Ouse, Welland, etc: Vast operations have been carried on ever since the time of Charles I., by digging new channels and outfalls, and employing windmills and steam-engines to pump the water from the marshes and ponds into these artificial channels. The Bedford level is divided into the _A'orth, the Middle, and the South levels, managed by commissioners, whose powers are derived from special acts of parliament. The improved value of the land is the fund out of which the expense of the engineering works is defrayed. It waS in one of these districts (the Middle level, between the Nene aud the Old Bedford river) that an irruption took place in 1862, which strikingly illus trates the dependence of the safety of the whole region on well-formed and well-main tained embankments. There was a sluice, Tailed St. Germain's sluice, situated at the confluence of the Middle level main outfall drain with the river Ouse, near the upper end of another artificial channel, known as the Eau Brink cut. The drain was made in 1847, and was enlarged ten years afterwards to a bottom-width of 48 ft., a side-slope of 2 to 1, and a level of 7 ft. below low-water spring-tide in the river; the rise of high water spring-tide at that point was 19 ft., and the sill of the sluice was 6 ft. below low wafer spring-tide.
On May 4, 1862, this sluice gave way without the slightest warning: the tidal waters undermined the brickwork, 'and formed a hole in tlie bed of the -river, into which the Works of the sluice sank. The tidal waters rushed up the opening, and ebbed and flowed throughout a distance of 20 miles. The commissioners of the Middle level applied to Mr. Hawkshaw, the engineer, to devise means for repairing the disaster. An earth and -cradle-dam was attempted to be thrown across the drain, at about 500 yards from the fallen sluice; but this was relinquished in favor of a permanent coffer-datn of pile-work. .at a distance of half a mile from the sluice; and after incessant exertions from _May 10 to June 19, the tidal waters were at length effectually shut out by a strong dam. The failure of the St. Germain's sluice was'not the only irruption that had to be battled with; eight days after that failure, under the pressure of a high spring-tide, the west bank of the drain gave way, on May 12, at a point about 4 miles from the sluice; the bank had been built only to resist upland waters, and not a rush and a pressure of the sea. The rupture
carried away 70 yards of the bank, scouring out a hole 10 feet deep at the spot, and admitting a rush of water which covered 6,000 acres of fertile land to a depth of 2 or 3 feet, increased at successive high-tides to 10,000 acres.
When the finishing of the dam had enabled Mr. Hawkshaw to shut out the tidal waters, means had to he devised for getting rid of the flooding waters, and providing an outlet for the usual rivers and laud-drainage of the _Middle level. It was resolved to utilize some of the old outlets at other spots, and to supplement their action by enormous siphons. placed over the coffer-dam. Sixteen siphons were provided. They were made ,of cast iron, feet 6 in. internal diameter, and somewhat over 1 in. thick; they rested on the top of the dam, mid on inclined framework supported by piles at the sides. The valves were so arranged, that the siphons could be put in operation, either by exhausting the air or by filling them with water. When only six of the siphons were in position, they -carried 50,000 gallons of water per minute over the dam.—For more minute details of the dam and the siphons, see Mr. Hawkshaw's paper read before the institute of civil •engineers in 1863.
There are large items both of cost and of compensation in works of this kind. Nearly the whole of the Middle level is 15 feet below high-water spring-tides; it is difficult to keep out the sea-water, and at the same time to preserve an outlet for the land-water, especially Whittlesea mere; there are 130,000 acres to be drained somehow or other; but as the laud is rich for farming, the commissioners, in past years, did not hesitate to spend L.400,000 ou 11 miles of drain, and S;30,000 on the sluice. The drain runs through a dis trict called Marshland, between Linn and Wisbeach; and as the bursting of the hank caused this district to be deluged with water, the commissioners have had to compensate the Marshland farmers and others; the amount of this compensation was frequently liti gated between 1862 and 1867. A_s concerns the land itself, it is found to be more fertile after such inundations than before, owing to the amount of silt deposited on the fields. After repairing the breach in the bank, the 10,000 inundated acres were drotined without much difficulty, through the Marshland, Smeeth, and Fen drain, and the Marshland sewer; the siphons are permanent channels, to carry off the usual land-waters regu larly. The siphons were subjected to a severe trial in Jan., 1867, by the ice which accu mulated around their lower ends; but iron gratings effectually resisted the entrance of the ice into the siphons.