The Middle Level - the area, the problems and the solutions
IntroductionThe Middle Level Commissioners are responsible for land drainage in that part of the Great Level Cambridgeshire Fens reclaimed during the l7th Century which lies between the River Nene to the north west and the Great Ouse (Old Bedford River) to the east, and which is bounded by low clay hills to the south and west and by the marine silts of Marshland to the north.
The Middle Level has a total catchment area of 70,000 hectares of which approximately 48,500 hectares are rateable fenland. The latter area, most of which lies below mean sea level, is divided into 39 Internal Drainage Districts from which run-off is pumped to the main Middle Level arterial drainage system by 78 pumping stations.
Formation of the Fens
In the distant past the British Isles were part of the continental land mass and the rivers of eastern England were tributaries of the River Rhine which flowed northwards over a flat plain and out into the sea just west of present day Norway. During the Ice Ages the Arctic ice caps spread southwards as far as the Thames Valley on several occasions moving clay from higher ground and depositing it to form the thick layers of clay which today lie beneath the fen deposits
Melting of the ice when it retreated caused a gradual rise in sea level and the sea advanced across the north sea plain, between the Lincolnshire Wolds and the heathlands of Norfolk and into the low lying area of present day fenland. When the sea subsequently receded the latter area became a freshwater swamp cut off from the sea by silt banks (estuarine deposits) which the rivers formed in the area now known as Marshland.
Inside the swamp the continuous growth and decay of trees and other vegetation formed thick layers of peat on top of the earlier glacial deposits. For a time this process was interrupted when the sea broke in again so that over much of the fens there are two layers of peat divided by a thin layer of buttery clay which was deposited by the sea. A maximum depth of approximately 9 metres of peat was deposited in the south west part of what is now the Middle Level Area.
Silt brought from inland by the rivers, combined with the peat deposits, slowly raised the ground levels but large expanses of water remained (Whittlesey Mere etc.) and the fenland rivers which followed slow meandering courses frequently overflowed and flooded the surrounding land. In places the underlying clay projected above the inundated area forming the islands upon which towns and villages have grown up.
Reclamation of the Fens
John Morton, Bishop of Ely, who in 1490 constructed a straight cut over 19 kilometres long from Stanground to Guyhirne, was aware that large straight drains were an answer to the problem of overflowing rivers. In this way large quantities of water from the hills inland could be conveyed straight to the sea without flooding the fens but the theory was not carried further until the l7th Century.
In 1630 the Earl of Bedford and thirteen other "Gentlemen Adventurers" employed the Dutch Engineer Cornelius Vermuyden to undertake the drainage of the fens. The object was not to drain the land so that it was permanently dry, but to provide lands fit for grazing in the summer ( "Summer Lands" ) and, in an attempt to achieve this, the Old Bedford River was cut 34 kilometres long between Earith and Salter's Lode to relieve the meandering course of the River Ouse.
In 1650 Vermuyden was again employed to execute a scheme which would make the fens dry all year round, and the New Bedford River was cut to the east of the Old Bedford (the latter had been found inadequate) with washlands in between to store flood water. The outer banks were built up to prevent overtopping into the adjacent fen areas. The works finally segregated the Middle Level Area completely from the adjacent fens and the Forty Foot, 'Twenty Foot and Sixteen Foot Rivers were constructed to direct drainage of the Middle Level to Salter's Lode and Welches Dam.
Drainage of the Middle Level since the Reclamation
Following reclamation it soon became obvious that the work of drainage would never finish and that constant maintenance and improvement work would be necessary, due to a continuous lowering of land levels caused by shrinkage of the peat soils.
In 1844, to provide an improved gravity outfall, the Middle Level Main Drain was excavated through the silts of Marshland to connect the Middle Level Area with a point some 14 kilometres down the River Ouse at St. Germans, where tidal levels were up to 2.5 metres lower than those at the existing upstream outfall at Salter's Lode. Since construction of the Main Drain, run-off from the entire Middle Level Area has been discharged into the River Ouse at St. Germans by one means or another.In 1862 the Middle Level was separated from the Bedford Level Corporation by Act of Parliament, and since that time the Middle Level Commissioners have executed a continuous Programme of improvement works, gradually lowering water levels to counteract the effects of peat shrinkage and increasing run-off. By the 1920's gravity drainage alone was no longer sufficient to protect the shrinking fens from flooding and construction of a pumping station on the Main Drain at St. Germans was imperative.