Click here to load reader

Flooding in York

  • View

  • Download

Embed Size (px)

Text of Flooding in York

Flooding in York1st November to 11th November 2000.

The Flood event which occurred in November 2000 had a return period estimated to be 1 in 80 to 90 years. In November 2000 York suffered its worst floods since records began some time in the 17th century. The water was over six metres higher than it should have been and came within five centimetres of breaching York's flood defences.

Knavesmire Road (between the line of trees)

Flood defences, North Street

Flood defences , end of North Street

View from Leeman Road towards Marygate

Car Park, Leeman Road

River Ouse beside Lendal Bridge

Kings Arms

Environmental Agency

Streets in Clementhorpe

The purple line shows all flood defences built in the last five years to protect against river floods with a 1% (1 in 100) chance of happening each year, or floods from the sea with a 0.5% (1 in 200) chance of happening each year, together with some, but not all, older defences and defences which protect against smaller floods. Flood defences that are not yet shown, and the areas that benefit from them, will be gradually added. Hatched areas benefit from the flood defences shown, in the event of a river flood with a 1% (1 in 100) chance of happening each year, or a flood from the sea with a 0.5% (1 in 200) chance of happening each year. If the defences were not there, these areas would be flooded. Flood defences do not completely remove the chance of flooding, however, and can be overtopped or fail in extreme weather conditions.

Photographs of the historic walled city of York, where the river reached a peak of 17ft 8ins (5.3m) above normal at 0330 GMT on Saturday 4th November 2000, within two inches of breaching flood defences

Lendal Bridge Flood Defences

Foss Barrier

Catchment area: Rivers Ouse & FossRight: This map shows the Ouse catchment area upstream of York a total of 3,000 square kilometres. The River Ouse is fed mainly by the rivers Swale, Nidd and Ure which carry water from the Dales and the Pennines. When there is heavy rain or melting snow on the high ground, the level of the Ouse in York can rise dramatically.

Clifton IngsThis is a natural flood plain upstream of York which can store 2.3 million cubic metres of water, lowering the peak flood level in the city by 150mm. In 1982, at a cost of 1.25 million, the existing floodbanks were raised and new embankments constructed to provide this greater storage. Sluice controls for letting flood water in and out of the Ings were also put into operation. This system is extremely effective for medium order floods of up to 14 feet (4.27 metres) above normal. For higher order flooding, the site is designed to let the banks overtop, allowing the full capacity of the Ings to be utilised in such an event.

View of Clifton Ings filled with flood water during the 1995 event looking downstream of the Ouse towards the city. Utilising these washlands can reduce the effects of high water levels in the river. Flood water is returned to the Ouse when the river has fallen to a safe level.

Leeman RoadThe Leeman Road area of York consists primarily of 19th Century ex-railway workers' houses. It was extremely prone to flooding both from the River Ouse and the adjacent Holgate Beck. In 1978, 225 houses were seriously flooded. In 1980 a floodbank was constructed in front of the houses to protect them from flood water. The sewage system was also improved drastically, allowing sewage to be pumped when the river levels were high. During the 1982 flood, high winds blowing over Clifton Ings generated large waves which overtopped the Leeman Road defences. The floodbank was raised in response to this effect.

Lower Ebor StreetThis area of 19th Century housing was badly flooded in 1978. Work had already begun to protect the area when it flooded again in 1982. Since then, a combination of concrete flood walls with steel trench sheeting have beenconstructed, as well as earthen embankments. Valves have been installed to isolate the sewage system incorporating a small pump to evacuate sewage when river levels are too high

Holgate BeckIn order to prevent flooding in the Acomb area of the city, and near the racecourse, upstream tributaries of Holgate Beck were diverted to discharge flow directly into the Ouse downstream of York. Upstream of York, where Holgate Beck joins the Ouse, a two-pump station was built to control water levels.

The Foss BarrierThe River Foss is a large tributary which flows through York, joining the River Ouse just downstream from York Castle. Because of the delicate relationship between these two rivers, rising water in the Ouse can often result in a dangerous reaction in the Foss. A rapid increase in the volume of water in the Ouse would force the Foss back on itself, causing it to overtop its banks and flood surrounding properties. It was this dramatic effect that contributed to the severity of the floods in 1947, 1978, and 1982. A solution for the Foss had to be found.