Editing River Ouse, Sussex (section)

==Inundation and drainage==
When the [[Domesday Book]] was produced in 1086, the Ouse valley was probably a tidal inlet with a string of settlements located at its margins.{{sfn |Robinson |Williams |1983 |p=3 (pdf)}} In later centuries the river was draining the valley sufficiently well for some of the marshland to be reclaimed, by building embankments to create highly prized meadow land.{{sfn |Brandon |1971 |p=96}} However, by the 14th century the Ouse valley was regularly flooding in winter, and frequently the waters remained on the lower meadows through the summer. In 1422 a [[Commission of Sewers]] was appointed to restore the banks and drainage between the coast and Fletching, around {{convert|20|mi|km}} inland, which may indicate that the Ouse was affected by the same storm that devastated the Netherlands in the [[St. Elizabeth's flood (1421)|St Elizabeth's flood]] of 1421. Drainage became so bad that {{convert|400|acre|km2}} of the [[Archbishop of Canterbury]]'s meadow at Southerham were converted into a permanent fishery (the Brodewater) in the mid-15th century, and by the 1530s the entire [[Lewes and Laughton Levels]] comprising over {{convert|6000|acre|km2}}, were reduced to marshland again.{{sfn |Brandon |Short |1990 |pp=107-108}}

Part of the problem of flooding was caused by [[longshore drift]] creating a huge [[shoal|shingle bar]] across the river mouth, which had gradually moved eastwards to [[Seaford, East Sussex|Seaford]], some {{convert|2|mi|km}} from its position in Roman times. The bar prevented the river from draining effectively, and made it difficult for ships to enter the estuary.{{sfn |Brandon |1971 |p=98}} Prior Crowham of [[Lewes Priory]] sailed to [[Flanders]] and returned with two drainage experts. In 1537 a water-rate was levied on all lands on the Levels to fund the cutting of a channel through the shingle bar at the mouth of the Ouse, below Castle Hill at Meeching, to allow the river to drain the Levels. This canalisation created access to a sheltered harbour, [[Newhaven, East Sussex|Newhaven]], which succeeded Seaford as the port at the mouth of the Ouse.<ref>{{cite journal|author=The Conservation Studio, Cirencester|title=Piddinghoe Conservation Area Appraisal|year=2007|url=http://www.lewes.gov.uk/Files/plan_CAA_Piddinghoe.pdf|archive-url=https://web.archive.org/web/20120213104615/http://www.lewes.gov.uk/Files/plan_CAA_Piddinghoe.pdf|archive-date=13 February 2012|access-date=2009-01-26|url-status=dead|df=dmy-all}}</ref>

The new channel was completed by 1539{{sfn |Brandon |1971 |p=99}} and drained the Levels so that much of the valley floor could be reclaimed for pasture. However, shingle continued to accumulate and so the mouth of the Ouse began to migrate eastwards again. In 1648 the Ouse was reported to be unfit either to drain the levels or for navigation.{{sfn |Brandon |1971 |p=101}} 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 {{convert|0.5|mi|km|1}} further to the east, at the site of a tide mill.{{sfn |Brandon |1971 |p=104}} The outlet at Newhaven had been reinstated by 1731,{{sfn |Brandon |1971 |p=106}} when the Newhaven Harbour Commissioners were established by act of Parliament.{{which|date=August 2024}} The engineer John Reynolds carried out some work for them on the piers at the entrance to the river, and constructed a sluice across it at Piddinghoe between 1731 and 1733, working for the Drainage Commissioners, but that was short lived, as it was damaged in 1736 and taken down rather than repaired.{{sfn |Skempton |2002 |p=571}} By the 18th century the valley was regularly inundated in winter and often flooded in summer.{{sfn |Woodcock |2003 |pp=1-16}}
[[File:Cliffe Cut.jpg|thumb|This straightened tidal stretch of the River Ouse just south of Lewes is called Cliffe Cut. It was made when the Ouse was canalised in the late 1790s. The original course of the river meandered in the foreground.]]

===Smeaton's survey===
In 1767 the Commissioners for the Lewes and Laughton Levels employed the engineer [[John Smeaton]] to survey the river and the drainage of the levels, which he did over four days in June following a period of wet weather. He found that the meadows, which were locally known as brooks, were in many cases under water, but that their condition, and therefore the remedies that would be required, were variable. 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. At high tide, the level of the river was above that in the meadows. The same applied to Ranscombe brooks, to the north of the junction between the Ouse and the Glynde, Further down river, at White Wall and Tarring, the brooks were generally dry, which he attributed to the land surface being higher, the walls being higher and well maintained, and the outfall sluices from the meadows being arranged at a lower level in relation to the river.{{sfn |Smeaton |1812 |p=340}}

He noted that the rise and fall of the tide below Piddinghoe was some {{convert|8|ft|m}}, but this was reduced to just {{convert|6|in|cm}} at the mouth of the Glynde, and was barely visible at Lewes Bridge. A series of shoals, combined with the narrow and winding channel, held water back and prevented it from draining from the levels. 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 {{convert|6.5|ft|m}} lower at low tide.{{sfn |Smeaton |1812 |pp=340-341}} 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 hampered 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. There was again no gradient on that river, which followed a winding course, but he was confident that if the drainage of Ranscombe could be solved, the drainage of the Laughton Levels would also be.{{sfn |Smeaton |1812 |p=341}}

His first proposal to achieve the drainage of the levels was to straighten the river, to remove all of the obstructions, and to construct an outfall sluice, to prevent the tides entering the river. The brooks on the west level and at Ranscombe would need better embankments, and adequate sluices to allow water to drain away when required. A second option involved raising the banks on all of the meadows, and constructing a separate sewer to carry surplus water from them to the sea, leaving the main river largely unaltered.{{sfn |Smeaton |1812 |p=342}} The outfall sluice would have been located at Tarring Tenantry near Piddinghoe, and would contain three openings, two of {{convert|13|ft|m}}, each with a set of pointed doors facing in opposite directions, to prevent the sea entering the river, and to retain water in the river during dry periods. The third opening would be {{convert|14|ft|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.{{sfn |Smeaton |1812 |p=343-344}}

He estimated the cost of the first scheme to be £10,800,{{sfn |Smeaton |1812 |p=350-352}} and the commissioners implemented some of his suggestions, improving the channels below Lewes in 1768, by dredging to remove shoals and making the channel wider in places. However, they did little to straighten the river, and Smeaton's great sluice was not constructed.{{sfn |Brent |1993 |p=21}}