Pilot Sites - Hull, Humber
The Humber estuary is very dynamic with a tidal range of up to six metres near the mouth at Spurn Head. High water levels vary along the estuary, being up to one metre higher (and one hour later) at Goole than at Spurn. Severe storms can raise water levels by up to 1.5 metres above normal and result in waves up to four metres high near the mouth, although upstream of the Humber Bridge waves are rarely more than one metre high.
Sea levels have risen relative to the land at an average rate of about one mm per year over the last 4000 years, although over the last 100 years the rate has almost doubled. About 6 million tonnes (dry weight) of sediment enter the estuary each year, most of it from the North Sea and the eroding Holderness Coast with less than three per cent from the rivers. Much of the material brought in from the sea returns on the subsequent tide but it appears that enough stays to ensure that the estuary remains roughly in balance. Nevertheless the foreshore is eroding and threatening the defences in places, particularly along the Immingham frontage, near Winteringham and in the rivers (where regular works are needed to protect the banks).
In the future sea levels around the UK are predicted to rise more rapidly and severe storms to become more frequent, increasing the risk of tidal flooding on the coast and near estuaries. In the Humber, the rate of rise is expected to average about six mm per year over the next 50 years, so that sea levels will be about 300 mm higher than they are now. As a result there will be a dramatic reduction in the standard of protection provided by the estuary’s defences. In addition, model studies of the estuary indicate that seaward of Trent Falls the inter-tidal area in front of the defences (the area between high and low water) will decrease by up to 600 ha over the same period due to the predicted rise in sea level, a phenomenon known as ‘coastal squeeze’. The estuary’s defences protect nearly 90,000 ha of land from flooding, about 85% of which is farmed and is among the best and most productive agricultural land in the country. More than 300,000 people live or work in the floodplain, mostly in the towns and cities that occupy about eight per cent of its area.
The floodplain also contains major concentrations of industrial and commercial properties, particularly between North Killingholme, Immingham and Grimsby, near Hull and at Goole and Flixborough. These include power stations generating much of the country’s electricity, refineries producing much of its oil and the country’s largest port complex, which handles over 80 million tonnes of cargo each year.
The main aspects of relevance to the FloodProBE work programme are:
- Damage and repair measure for property – City of Hull on the north shore
- Flood embankment assessment and performance – Immingham on the south shore
Sites within the Humber estuary have been selected for UrbanFlood to take advantage of being able to set the localised UrbanFlood studies within the context of wider strategic studies being carried out across the whole estuary. These whole-estuary studies are supported by parallel UK-funded research programmes (Flood Risk Management Research Consortium 2 - FRMRC2; FLOODsite into Practice; Modelling and Decision Support Framework 2 - MDSF2). The studies involve carrying out a Risk Assessment for Strategic Planning (RASP) flood systems analysis study for the whole estuary to obtain an overall picture of the residual floodplain risk and the contribution to this from individual assets. In addition to this present day view, and following the logic set down in Tasks 14 and 18 of the FLOODsite project, future flood risk across will be explored for two well-defined management strategies for the existing defences over a 100 year timeframe.