He suggested straightening and widening the river channel, raising the banks around meadows, and building a large sluice near Piddinghoe, to keep the tides out.
Improvements continued in the early 19th century under the leadership of John Ellman, a renowned agriculturalist who became the Expenditor for the Lewes and Laughton Levels.
[2] The gradient on the lower Ouse, between Lewes and Newhaven, is just 6 inches per mile (0.1m per km)[3] and changes in the relative levels of the land and sea, together with an increase in the number of storm tides, resulted in many of the meadows being submerged in winter by the later 14th century, and sometimes remaining flooded through the summer.
Such an area includes the valley of the Ouse as far upstream as Sheffield Bridge, and the Glynde Reach to Laughton, all of which had become an inland lake, suitable only for fowling and fishing.
[5] Part of the problem of flooding was caused by longshore drift creating a huge shingle bar across the outlet of the river, which had gradually moved eastwards to Seaford, some 2 miles (3.2 km) from its position in Roman times.
[8] At some time between 1676 and the publication of an Admiralty chart in 1698, the river flowed along the back of the shingle bar and broke through into the sea about 0.5 miles (0.8 km) further to the east, at the site of a tide mill.
It was designed to hold back the water in the river, so that it could be released at low tide to scour the channel, but it was short-lived, as it was damaged in 1736, and removed rather than repaired.
In particular, the brooks of Southover, Iford, Pool Bar, and Rodmell, which he called the West Levels, were badly affected as their embankments were low and poorly maintained.
[12] He noted that the rise and fall of the tide below Broad Salts, a little below Piddinghoe, was some 8 feet (2.4 m), but this was reduced to just 6 inches (15 cm) at the mouth of the Glynde, and was barely visible at Lewes Bridge.
He also commented on the great shingle bar crossing the mouth of the river at Newhaven, which if removed would allow the water levels to be around 6.5 feet (2.0 m) lower at low tide.
[13] The brooks above Lewes Bridge became gradually drier as he progressed towards Barcombe Mill, but with almost no fall on the river, its winding course and numerous shoals did little to assist the drainage of the meadows.
The brooks bordering the Glynde, to the east of Ranscombe, were generally at a higher level, but were affected by stagnant water lying on the surface.
The third opening would be 14 feet (4.3 m) wide, with double pointed doors facing in both directions, so that it could additionally be used as a navigation lock at all states of the tide and river.
The work would include 1,000 yards (910 m) of new cut, to resolve the worst of the meanders,[22] and a second Act of Parliament created the Lower Ouse Navigation Company in 1791.
Work to improve Glynde Reach took place from 1786 to 1803, resulting in better drainage for Ranscombe Brooks and Laughton Levels, although there were complaints from a group of chair-bottomers, whose source of reeds to make chair seats dried up.
Ellman is best known for his agricultural achievements, particularly the improvement of the Southdown sheep breed,[24] but he became part of the jury for the Commissioners of the Lewes and Laughton Levels in 1780, and its Expenditor in 1783.
He produced estimates for the improvements, and while his contribution to the drainage and navigation of the Ouse is not fully understood, due to the fragmentary nature of the evidence, it appears to have been considerable.
He retired from farming and the Commissioners in 1828, but the benefit of the work was demonstrated in April 1829, when although severe flooding occurred on the river below Lewes, the meadows had drained within 48 hours.
[30] Lewes District Council, who contributed £131,000 annually for the work of the IDD, opposed the setting up of an independent internal drainage board.