Vermuyden’s Subsidiary Drainage Works – sasses and sluices.

1629 – Court of Sewers appointed

In 1629, the Crown appointed a new Court of Sewers to oversee the “Level of Hatfield Chase,” a move intended to mark the completion of Cornelius Vermuyden’s great drainage project. This court was charged with maintaining the new network of drains, banks, and sluices that had reshaped the wetlands and opened large areas to arable farming. Its creation signalled a shift from engineering works to long‑term management of the altered landscape. Yet the appointment also revealed the deep tensions the drainage had created. Many local people felt their ancient rights to turbary, fishing, and grazing had been swept away along with the waters, and they challenged both the works and the authority of the commissioners. Instead of a neat conclusion, the 1629 Court of Sewers became the starting point for decades of dispute over land, water, and customary freedoms in Hatfield Chase.

The winter of 1628 brought catastrophic flooding to Fishlake and Sykehouse, overwhelming the low, medieval banks on the west side of Turnbridgedike. Local inhabitants argued that this was not a natural disaster but a direct consequence of Cornelius Vermuyden’s diversion of the River Don at Thorne. By blocking off the eastern branch of the Don and raising the embankments on the opposite side of Turnbridgedike, the drainage works had altered the hydrology of the entire northern Chase. Faced with rising water and damaged banks, the inhabitants petitioned for relief and in May 1630 agreed to pay Vermuyden £200 on the condition that he restore their ancient riverbanks, which had long protected the townships before the drainage scheme began.

Around this time a sasse (pound lock) on Turnbridgedike was constructed, positioned near its junction with the River Aire. The engineer was Hugo Spiering. This would have been a logical engineering response to the new hydraulic pressures created by diverting the River Don into the medieval channel of Turnbridgedike. A large outflow sluice was built alongside with 17 openings, each 6ft wide and 8ft high.

The first sasse to be constructed would have been at Thorne to permit the passage of boats through the Ashfield Bank to Vermuyden’s base at Sandtoft. Thorne sasse subsequently gave access to the ‘boating dikes’ which served the peat trade.

At their inaugural session, the newly appointed Commissioners of Sewers for the Level of Hatfield Chase reviewed the state of the drainage works and the complaints arising from the disastrous floods of 1627–1628. One of their earliest decisions was to require Vermuyden and the “participants” (the adventurers and local landowners who benefitted from the scheme) to construct another sasse, near Misterton on the River Idle/Bicarsdyke

Annotations on the 1633 map describe the sasses and sluices;
The Sasse at Turnbridge is 60 foot long nd 18 wyde
Dikesmarsh sluce hath 8 throughs 8 foot wide & 8 high
The great Sluce hath 17 throughs 6 fote wide & 8 high
The sasse at Thorne is 16 foot wide and 50 long
The sasse at Stokwith is like that at Turnbridge.

References
Jones, Pat. “Vermuyden’s Navigation Works on the River Don.” Journal of the Railway and Canal Historical Society 31, no. 5 (1994): 248–258.

Taylor, Martin. Thorne Mere and the Old River Don. York: Wm Sessions Ltd, 1987.