the drainage of deeping fen was again addressed in 1664, when the deeping fen act awarded the earl of manchester and others of land in return for the drainage works. they were also obliged to maintain the banks of the river, to ensure that both the welland and the glen were kept clean and free-flowing, and to ensure that no tolls were charged for navigation on any part of the river below east deeping. the inadequacy of the outfall and a spate of bad weather stopped them from completing their task. they tried renting out the land they had been granted, but many tenants were unable to pay the rent, due to the poor state of the drainage which reduced crop yields. in april 1729, the deeping fen adventurers received a letter from captain john perry, expressing the opinion that the only way to improve the drainage was to improve the river outfalls, and proposing the construction of scouring sluices on the river at spalding, on vernatt's drain at its outfall, and on the river glen at surfleet. perry was an engineer of some repute, who had set the standard for engineering reports in 1727, when he published his recommendations for the north level of the fens. his plans were approved, and the adventurers offered to give him land covering nearly in payment for the work. he sold one-third of the land to finance the project, and began work in 1730. cowbit sluice on the welland had six wide gates which were operated by chains connected to a treadwheel. at high tide, water was penned in cowbit wash, between banks which were set well back from the main channel. the bed of the river below the sluice was loosened by dragging wooden rollers with iron spikes over it. at low tide, the sluice gates were opened, and the flow scoured out the silt for some downstream. a navigation lock was constructed beside the sluice, so that vessels could still gain access to the river above. perry died in february 1733, and was buried in spalding churchyard. the lock lasted until it was removed by the welland commissioners in 1813.