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Here you will learn about the impacts expected from climate change by the 2050s on flooding across the region. This includes assessments of:
Over recent years there have been an increasing number of extreme rainfall and flooding events that seem to occur on a more frequent basis. In Summer 2007 the worst flooding seen in decades hit areas around York and Humberside, as well as the Midlands, Gloucestershire and South East. Flooding affected an even greater number of properties (about five times as many) than had been flooded during the previous major events that had occurred during the Autumn of 2000, when serious flooding struck similar areas. Flooding claimed the lives of several people, over 55,000 homes and businesses were flooded across England and Wales, totalling an approximate £3 billion in insured losses alone, and key critical utilities were affected. Water supplies to 140,000 homes in Gloucestershire were cut off for up to two weeks, and almost 300 schools in Yorkshire and Humberside suffered damage. May to July 2007 was the wettest period since records began in 1766. The ground became saturated during May and early June followed by several periods of extreme rainfall, with some locations experiencing up to a month’s rainfall falling in a few hours. This led to widespread flooding across England and Wales. Intense rainfall produced some of the highest river levels on record and extensive flooding from the Rivers Don, Severn and Thames, as well as widespread surface water flooding, notably around South Yorkshire and Humberside. Two-thirds of the properties were flooded due to the overwhelming of drains or sewers by the heavy, intense rainfall. The extensive flooding events of Summer 2007 also showed the importance and criticality of key utility infrastructure, as water treatment works and electricity sub-stations were impacted which then affected significantly greater numbers of the surrounding population. As well as residents, many organisations rely heavily on constant power and water supply to support the local population, which highlights the criticality of these services to the wider community than that directly affected by flooding. The Government instigated a review into the Summer 2007 floods. The Pitt Review reports observations on the extents and impacts of the flooding, and makes recommendations for the regulation and organisation of flood risk management, the management of surface water flooding and drainage, emergency response to extreme events and the identification and protection of critical infrastructure. The Environment Agency also produced a Review of 2007 Summer Floods which also makes further recommendations for improvements. Looking to future flooding impacts associated with a changing climate, conclusions from the Office of Science and Technology’s Foresight Flood and Coastal Defence report estimate that at a national level the risk of flooding from rivers and the sea will at least double by the 2080s, and could increase by up to 20 times. The number of people at a high risk of flooding in the UK could rise from 1.5 million to between 2.3 and 3.5 million over this period, with the cost of flooding rising from the current £1 billion a year to between £1.5 billion and £21 billion. This clearly represents a significant threat to the lives of many communities and the way the country operates as a whole. Following sections assess how flooding may affect the region by the 2050s, based on the projected climate changes.
Description
There are several significant rivers within the region, most of which come together to form the Humber Estuary. The Humber is a major estuary and drains one fifth of the total land area of England and Wales. The River Ouse, and its tributaries: Swale, Ure, Nidd, Wharfe, flow from the north area of the Yorkshire Dales, with the River Derwent joining from off the North York Moors. The River Aire also originates in the Dales and is joined by the Calder, Don and Rother from off the Pennines. The region includes the lower sections of the River Trent and River Ancolme which also discharge into the Humber. In addition to the Humber tributaries, the River Esk is a separate river in the north of the region which discharges directly into the North Sea at Whitby. The main conurbations in the region are the cities of York, Kingston upon Hull, Leeds, Bradford, Huddersfield, Sheffield, Wakefield, Barnsley, Rotherham, Doncaster and Grimsby. As well as key railway routes, notably the North East mainline, Trans-Pennine route and Midlands-South-West connection, there is a network of principal motorways across the region, including the M1, A1(M), M62, and M18. Sources of flooding Significant areas on all of the major rivers and tributaries are also at risk of flooding from rivers, including York (River Ouse), Leeds and Castleford (River Aire), Dewsbury and Wakefield (River Calder), Sheffield, Rotherham and Doncaster (River Don), Beverley and Kingston upon Hull (River Hull). In addition to this there is likely to be extensive flood risk related to surface water/drainage across the region, particularly within heavily urbanised areas, although the key risk locations are not defined. There is limited coastal flooding due to the natural protection provided by the high cliffs. Historically, the significant flooding incidents that have occurred have been related to river flooding events. Previous major flooding has impacted across the region with two significant events in recent years. In October 2000, prolonged heavy rainfall led to major flooding across several of the main rivers causing widespread impacts on the Wharfe, Nidd, Ouse, Ure, and Swale, including 550 properties around York, 370 properties on the Aire near Keighley, and extensive flooding around Selby and Barlby. The River Ouse reached its highest level ever recorded. Following this, in summer 2007 the worst flooding seen in decades hit areas around South and West Yorkshire and Humberside affecting an even greater number of properties, about five times as many as in 2000. May to July 2007 was the wettest period since records began in 1766. The ground became saturated during May and early June followed by several periods of extreme rainfall, with some locations experiencing up to a month’s rainfall falling in a few hours. This led to extensive flooding across England and Wales and the biggest rescue effort in peacetime Britain. Flooding claimed the lives of several people, over 55,000 homes and businesses were flooded across England and Wales, and key critical utilities were affected. This resulted in national damages totalling approximately £3 billion in insured losses alone, with four years worth of claims being made during the two months of June and July. The intense rainfall produced some of the highest river levels on record as well as widespread surface water flooding, notably around York and Humberside, with two-thirds of the properties flooded due to the overwhelming of drains or sewers by the heavy, intense rainfall. In Kingston-upon-Hull one in five homes are reported to have been affected by the flooding. Across the Yorkshire and Humber region, approximately 25,000 homes and 4,000 businesses were flooded, as well as 248 schools, 65km of A-roads, 149 electricity substations and 23 sewage treatment works, affecting the service provided to more than 2.5 million people. This produced an estimated £2,100 million of overall damages, including £1,100 million in Sheffield and Rotherham (52%), £650 million in Hull (31%), £280 million in Doncaster (13%), and £80 million across Leeds, Wakefield and York (4%). The extensive flooding events of summer 2007 also showed the importance and criticality of key utility infrastructure, as treatment works and electricity sub-stations were impacted which then affected significantly greater numbers of the surrounding population. As well as residents, many organisations rely heavily on constant power and water supply to support the local population, which highlights the criticality of these services to the wider community than that directly affected by flooding. The Government instigated a review into the summer 2007 floods. The Pitt Review reports observations on the extents and impacts of the flooding, and makes recommendations for the regulation and organisation of flood risk management, the management of surface water flooding and drainage, emergency response to extreme events and the identification and protection of critical infrastructure. The Environment Agency also produced a Review of 2007 Summer Floods which also makes further recommendations for improvements.
Impacts A recent paper from Newcastle University concluded that recent trends in the UK are consistent with the climate projections which suggest an increase in the frequency and intensity of heavy rainfall. It showed that there has been a change in the timing of extreme rainfall with the majority now occurring during the autumn months. The paper also determined that the magnitude of recent extreme rainfall events has increased two-fold over parts of the UK since the 1960s, and that intensities previously experienced every 25 years now occur at approximately 6 year intervals. There is further evidence that winters during the 1990s were wetter than ever before, with a threefold increase in the number of wet winter days recorded at Whitby. Some climate predictions indicate a potential fourfold increase in the frequency of future wet winters with 60% more rainfall than the current average. In addition mean sea levels within the Humber Estuary and along the Yorkshire coast are estimated to have risen at rates of between 1.5 and 3.6 mm per year over the last 80 years. With future sea level rise projected, mean sea levels may rise by up to 300mm by 2050, based on current guidance from Defra, and extreme sea surge levels are likely to be even more exaggerated. Looking to future flooding impacts associated with a changing climate, conclusions from the Office of Science and Technology’s Foresight Flood and Coastal Defence report estimate that at a national level the risk of flooding from rivers and the sea will at least double by the 2080s, and could increase by up to 20 times. The number of people at a high risk of flooding across the UK could rise from 1.5 million to between 2.3 and 3.5 million over this period, with the cost of flooding rising from the current £1 billion a year to between £1.5 billion and £21 billion. This clearly represents a significant threat to the lives of many communities and the way the country operates as a whole. The various mechanisms and sources of tidal and river flooding across the Yorkshire and Humber region will be vulnerable to the following effects of climate change. Flooding from rivers and the sea
Flood defences
Surface water/Drainage More extensive, and higher risk, flooding problems are typically related to river or tidal flooding, although, as the events of summer 2007 have shown, localised flooding from foul and surface water sewers or directly from surface water runoff can be equally as devastating and often more numerous. In June 2007, two thirds of the properties that flooded were affected by surface water, rather than fluvial flooding. Despite this particular extreme occurrence, surface water flooding events typically occur with a fairly high frequency, but are generally of relatively low impact. Flooding incidents are often isolated and highly localised problems, and although prevalent and recurrent in many areas, particularly affect heavily urbanised areas, particularly low-lying areas. Problems can be exacerbated with high tide or river levels, when drainage outfalls may become tide-locked. This restricts the discharge from the outfalls and causes flows to back-up within the system and can lead to localised flooding. This is known to be a particular problem in Kingston upon Hull where much of the city is low-lying, with 90 per cent of the area below the high tide level. In addition, direct flooding from surface water runoff can occur where drainage provision is insufficient or non-existent, when rainfall directly runs off from the surrounding ground and does not issue from a watercourse and is not able to enter a local drainage system (often referred to as unconnected flooding). Surface runoff can be a significant cause of flooding, especially across urban areas and the steeper upland areas. Foul and surface water drainage systems potentially are vulnerable to the following effects of climate change:
As the previous recent major events have shown (York and Selby in 2000, Sheffield, Hull, Humberside, etc in summer 2007) the impacts of flooding to the population and country’s assets can be severe. The major impacts to the community are:
With future climate change, there is projected to be an increase in the potential flood risk extents which will affect a greater number of properties than are already identified to be at risk. The following critical infrastructure is estimated to be at risk of future flooding from rivers or the sea across the Yorkshire and Humber region:
and
From our discussions with various organisations within the region, one of the greatest threats posed by the weather on social wellbeing in the region was determined to be the serious potential for disruption to transport networks, as we have experienced during previous events. Also, the increased likelihood for vulnerable people and communities to be left without electricity, heating or water due to the flooding of critical infrastructure (as occurred during the summer 2007 floods). With regards to our flood defences, the maintenance of watercourses and the management of flood risk across the region, key impacts will include:
| North Yorkshire | West Yorkshire | Humber | South Yorkshire |
Description The area extends from beyond Settle in the west across to Whitby and Scarborough on the North York Moors coastline, and southwards to Goole at the head of the Humber estuary. The sub-region includes the city of York to the south and the major towns of Richmond and Northallerton in the north, Ripon in the centre and Harrogate and Selby in the south. The area is comprised of eight Local Authority districts, namely Scarborough; Ryedale; Hambleton; Richmondshire; Craven, Harrogate, York and Selby. The sub-region is predominantly rural with small towns and villages spread across the area and localised populations centred in the major towns. The upland areas are rugged and barren with agricultural land use mostly focused around the lower central and southern areas. The main A1(M) motorway bisects the area passing to the west of York and continuing northwards past Ripon and Harrogate. The Yorkshire Dales and North York Moors are significant National Park areas situated on either side of the sub-region. The North Yorkshire region is characterised by the numerous rivers which descend from the steep hills of the Yorkshire Dales and the North York Moors. The rivers from the National Park areas are steep and fast flowing leading to several major rivers. The River Swale discharges from the north of the Yorkshire Dales and falls southerly towards the Humber Estuary. In the upstream reaches the Swale is reputed for flash flooding along Swaledale during heavy rainfall. As it reaches its main valley through the centre of the sub-region the river is joined from the north by the River Wiske which discharges from the Cleveland Hills. Further downstream the Swale subsequently meets the River Ure from the west and continues southwards to become the River Ouse. To the north of York the River Nidd also joins the Ouse from the Dales to the west. The River Ouse continues southerly through the centre of York and on to meet the Rivers Aire and Trent at the head of the Humber Estuary. Due to the numerous tributaries that drain into the Ouse and its wide, flat floodplain, heavy rainfall can cause severe flooding in the adjoining catchments. Wharfedale and the River Wharfe act as a southerly boundary between the North and West Yorkshire sub-regions. The river is again sourced in the upland hills of the central Yorkshire Dales and flows through the tourist areas of Bolton Abbey, Ilkley and Otley to head past Tadcaster to join the River Ouse to the south of York. The River Derwent is another of the United Kingdom’s largest river catchments. The source of the river is within the upland moorlands of the North York Moors National Park. The river flows southerly through Ryedale District and continues along the boundary between the sub-region and East Riding of Yorkshire District to discharge into the lower section of the River Ouse. At its outfall, the Barmby Barrage is in place to prevent waters from the tidal Ouse from entering the non-tidal Derwent. The River Rye is a main tributary of the Derwent, which discharges from the Cleveland Hills through the rugged moorland and low-lying agricultural land and joins the Derwent to the north of Malton. Other main rivers within the sub-region include the River Esk, which discharges off the North York Moors and into the North Sea at Whitby; the Upper River Aire, which flows from Malham at the south end of the Dales and discharges southerly into the West Yorkshire sub-region towards Skipton; and the River Ribble, which originates within the Yorkshire Dales although flows out of the region beyond the westerly boundary to discharge into the Irish Sea at Lytham, Lancashire. Sources of flood risk Along the upper reaches of the Swale and Ure there is some flooding shown along the full lengths of the river valleys off the Dales. The areas are fairly consistent along its length, although with increased flooding on the Swale from Brompton-on-Swale to Skipton-on-Swale/A61 crossing, and around Hawes/Gayle, Middleham and Ripon on the Ure. Flooding increases where the two rivers converge affecting much wider areas, including the outskirts of Boroughbridge and Helperby. Along the Nidd the predicted flood zones are relatively small by comparison, with key flooding indicated at Ripley and along the downstream reaches beyond Knaresborough. The route of the River Ouse shows a wide flood plain along most of its length. The flood zone first widens through the City of York, and then further increases significantly beyond its confluence with the River Wharfe at Kelfield. At the lower boundary of the sub-region wide areas of the south-east corner of the Selby District are also affected by tidal flooding from the Humber Estuary. For a large river the Wharfe shows a relatively well contained flood plain. Flooding increases in the lower reaches affecting towns such as Conistone and Beamsley, and Ilkley and Otley on the West Yorkshire border. Beyond Otley, the flood zone gradually begins to expand through Tadcaster and into the Selby District, and approaching the confluence with the River Ouse, the flood zone widens substantially affecting local towns and villages, such as Kirkby Wharfe, Ulleskelf and Ryther. The River Ribble indicates key flooding at two main locations; the first near Horton-in-Ribblesdale, and the second, wider flooding, extending from Settle to beyond Wigglesworth. Much of the potential flood zone is within rural areas although there are more likely to be impacts at Settle. Along the River Rye significant flooding is shown along much of its length, notably as it approaches the confluence with the Derwent affecting wide areas between Nunnington and Great Habton, and also affecting other local villages such as West Ness and Butterwick. In the upper reaches on the Derwent there is extensive flooding affecting areas around Yedingham and extending back to East/West Ayton. Whereas downstream of the Derwent-Rye confluence there is limited fluvial flooding indicated through Malton and Norton-on-Derwent and further downstream. There is limited flood risk along the entire length of the River Esk, with the surrounding higher land of the North York Moors restricting the flood extents. Additionally the small coastal streams are known to have certain associated flooding problems at some locations due to the flashy nature of these small watercourses discharging into the sea. Most notably at Filey there is known to be issues related to the Filey Ravines where previous streams are now culverted and cause extensive flooding when heavy rainfall events produce high runoff from the steep surrounding hillsides. At the southerly boundary of the sub-region the lower sections of the Rivers Ouse and Aire through the Selby District exhibit the effects of the significant tidal flooding around the Humber Estuary. Along the coast the natural cliff defences provide significant defence along much of the coastline and the extents of coastal flood risk are limited. Although coastal flooding is known to affect some locations, however, notably around Whitby, Scarborough and Filey. In addition to river and tidal flooding, there is likely to be extensive flood risk related to surface water/drainage across the sub-region, particularly within heavily urbanised areas, although the key risk locations are not defined. There have been numerous previous reports of flooding within the district as follows:
Regarding flooding from sewers, however, there are the following reported incidents:
Further detail on historic flooding within the North Yorkshire sub-region can be found in the local Catchment Flood Management Plan (CFMP) documents that have been produced by the Environment Agency: the Aire CFMP, Yorkshire Ouse CFMP, Esk and Coastal Streams CFMP, and Derwent CFMP. These documents are soon to be finalised and will be publicly available. Flood defences As well as the formal defences most stretches of the main river channels are managed and actively maintained by the Environment Agency against blockages and debris. In total there are over 622 km of raised flood defences in the North Yorkshire sub-region, with a further 811 km of formally maintained river channel. The importance of the formal flood defences was demonstrated through the effectiveness of the defences in York during the flooding in 2000, when operation of the flood defence structures in response to flood warnings given prior to the heavy rains resulted in minimal impacts from flooding at the defended locations. Surface water/Drainage Typically foul systems will comprise a network of drainage sewers, often combining areas of separate and combined drainage, leading to a sewage treatment works. The foul/combined systems will often be connected, possibly via pumping, to a single local treatment works. In rural areas several small villages will often be inter-linked to a single local works. There are 292 identified sewage treatment works sites within the North Yorkshire sub-region. Various ancillary structures will be included through the system to assist network performance, primarily pumping stations, combined sewer overflows (CSOs), and storage tanks. CSOs provide an overflow release from the drainage system into local watercourses or surface water systems during times of high flows. In the rural areas, some of the properties are likely to be unconnected to the foul drainage system altogether, and will have their own septic tanks. Surface water systems will typically collect surface water drainage separately from the foul sewerage. These typically discharge directly into local watercourses, although in more constrained historic urban areas may often be linked to discharge into the foul/combined system.
Impacts Current impacts Notably, within the more extreme fluvial flood risk zone there are the following critical assets and properties at risk:
Click here for further details on properties in flood zone 2 and 3. An additional key risk in popular tourist rural areas is the significant risk to caravan parks and camping sites. There are 68 caravan parks and camping identified to be at risk of flooding within the sub-region. These are highly vulnerable sites due to the significant personal safety risks to people resident at the sites during times of flooding, and cars and caravans are particularly hazardous as they can be easily picked up and carried along by flood flows causing significant damage to other properties and risk to life. Also for the current flood risk (“undefended”) the Residential impacts to the local population have been determined. Residential properties are classed as medium risk vulnerability. The Communities and Local Government department hold information on social deprivation which identifies the particular vulnerability of local populations to flooding. Most of the areas affected are in the medium to low vulnerability class. Scarborough falls into the lower deprivation class, although flooding to populations in this district is limited. The table below indicates the number of Residential properties that are also currently identified at risk of flooding within the sub-region.
Regarding transport networks, the following sections of the road and rail system within North Yorkshire are identified to be at risk (“undefended”) from current flooding(“undefended”):
There are several fords across watercourses within the upland rural areas and these can become significantly dangerous to cross when river levels are high following heavy rainfall. This poses a serious hazard particularly on smaller watercourses in the upland areas that might not be accounted for here. Flooding incident records for the sewer and drainage systems within North Yorkshire indicate the following locations to be currently at risk of flooding from the sewer system:
These figures represent properties that will be affected by typical storms up to 5% AEP, and there are likely to be a significantly greater number of properties and areas affected by sewer and surface water flooding during higher intensity, more extreme storms, as we have seen with the flooding in summer 2007. The data on existing flood problems gives a good indication of the extent of recurrent problems related to the sewer system, however, in addition to the recorded/known incidents there will be numerous other locations which are also liable to flood situated in outlying areas where properties are not affected and therefore only limited information is available. Low gradient urban areas are particularly likely to be affected where surrounding areas are steep and have significant proportions of impermeable area creating large volumes of surface water runoff that will overwhelm the local drainage systems. Additional to those locations on the Yorkshire Water flood register, key highway and localised surface water flooding will readily occur, but in rural areas anecdotal reports are not as readily available.Climate changes In addition there is likely to be an increase in the intensity and magnitude of individual rainfall events, particularly over the upland areas. At the coast and lowland areas there is generally some reduction in the magnitude of events, except for the longer sub-daily frequent events (12-hour 50% AEP events). In the uplands the shorter sub-daily events are likely to reduce, however beyond events longer than 6-hours the magnitude of individual events is projected to increase by up to 6%. Despite a general reduction in summer rainfall, this effect is likely to produce more severe, high intensity thunderstorm events during the summer periods, as experienced with the unprecedented events of summer 2007. Future impacts
Of even greater concern than the additional number of properties affected by future flood level increases, will be the increasing frequency of large rainfall events and the impact that this will have on the properties currently identified to be at risk. These assets will face an increasing risk of flooding as the present day extreme rainfall and flood events become more frequent. Locations and communities in the upland areas will be at a greater flood risk due to faster flood flows and the limited response time available from flood warnings. This is likely to increase with the increasing seasonality of rainfall bringing higher intensity, flashy flood flows, particularly during the summer months. The increasing seasonality of rainfall and autumn and winter wetness, will lead to greater saturation of the ground, particularly in upland areas. Greater saturation will cause a higher volume and rate of runoff flows and increase the likelihood of sheet run off from the saturated ground surface, which will exacerbate the problems discussed above. This is likely to further increase the frequency and extent of problems and their impacts. Additional impacts of climate change on river and tidal flooding and flood defences are also likely to become apparent, as follows.
With regard to sewer and surface water flooding, with increasing winter rainfall due to climate changes the occurrence of incidents at the known foul and surface water sewer flooding locations will become significantly more frequent during the winter months. Other problem locations will arise due to the increasing magnitude of events, but it is difficult to easily ascertain where these may occur. Low gradient areas within the urban centres, particularly where there are significant extents of impermeable area, are likely to be the most susceptible, and low points on the road and rail networks will be vulnerable to increasing flooding, particularly where these are surrounded by steeper areas that will produce fast runoff flows from the projected more frequent and higher intensity storms. In addition, fast flowing surface water runoff in the steep valleys in the upland areas are likely to be most susceptible. These upland areas already experience higher levels of rainfall, and more severe storms, throughout the year. Similarly to river flooding, the impacts of climate change will produce increases in the number and frequency of flooding events, particularly during the winter period and during summer months due to high intensity thunderstorms. Other future impacts that are likely to come about are:
Description The sub-region is bounded by the route of the A1(M) in the east and extends westerly to Todmorden, further west of Huddersfield. In addition, the M62 cuts across the middle of the sub-region, from east to west, and the M1 approaches form the south to meet the A1(M) at Leeds. As well as Leeds, Bradford and Huddersfield, the area also includes the key towns of Keighley in the north-east, Ilkley and Otley on the northern boundary, Dewsbury and Wakefield in the centre, and Pontefract in the west. The sub-region also includes Leeds-Bradford International Airport. This area is dominated by the heavily populated central urban areas. There are occasional small villages and towns around the outskirts of these to the east and west linked to the big cities by the M1, M62 and other major roads. Land elevations rise steeply to the west, towards the Pennines, reaching maximum heights of more than 400 metres. The landscape undulates with scarp ridges and deep valleys, particularly as the land sharply falls towards the River Aire and Calder valleys, at a level of around 15 metres, which reach into the centre of the sub-region. Surrounding land uses around the main urban sprawl are for agriculture and grazing. To the west, in the upper areas of Calderdale, there are a number of reservoirs, relative to the altitude and subsequent rainfall, which serve the communities below. The West Yorkshire topography is defined by the steep hills of the Pennines falling towards the sharp valleys of the River Aire and River Calder. The tributary rivers from the western areas are steep and fast flowing leading into these rivers. The source of the River Aire is towards Malham Cove in the Yorkshire Dales where the limestone landscape produces small becks from the cavern and limestone pavement above. Outside of the sub-region, at Skipton (Craven District), the several small becks combine to form the larger River Aire. This river flows south-east through Airedale and is joined by the River Worth, which flows through the centre of Keighley. The Aire then continues on to the south-east through Shipley, to the north of Bradford, and on through the centre of Leeds. Following its confluence with the River Calder at Castleford, it continues towards its discharge into the Humber Estuary. Additionally, at this point the Aire and Calder Navigation channel is formed which also continues towards the Humber Estuary. The River Calder originates in the Pennines near Todmorden and flows to the north of Huddersfield and on through a selection of large and small towns, including Wakefield, until it joins with the Aire near Castleford. Its two main tributaries are the Hebble and the Colne. Along much of its lower reaches the river is canalised as it passes through the heavily populated urban areas. The River Wharfe forms much of the northern boundary of the sub-region, and passes through the main towns of Ilkley, Otley and Wetherby on its route to join the Ouse near Selby. Sources of flood risk Both the Aire and the Calder have identified flood zones along their entire lengths. There are a number of locations of key flood risk on the Aire, such as around Keighley, Bingley, and Leeds. On the Calder key flood risk is indicated on the outskirts of Dewsbury, which then increases further downstream around Wakefield. In the centre of Leeds there are around 2,000 properties and 1,000 businesses at risk from the 1 in 200 event. There are few formal flood defences provided through the city and in some places the standard of protection to properties is less than 20% AEP. In the lower reaches, there is significant flood risk indicated around the confluence of the two rivers. The low-lying land allows it to cover a wide flood plain enveloping Mickletown and the surrounding rural areas. There are further areas of flood risk indicated along the length of the Wharfe, notably at Ilkey and Otley; on the River Colne through Huddersfield; on the River Worth at Keighley; on the Hebble Brook at Halifax; and on the River Spen at Dewsbury. In addition to river and tidal flooding, there is likely to be extensive flood risk related to surface water/drainage across the sub-region, particularly within heavily urbanised areas, although the key risk locations are not defined. There have been previous reports of flooding within the district as follows:
Regarding flooding from sewers, however, there are the following reported incidents:
Further detail on historic flooding within the West Yorkshire sub-region can be found in the local Catchment Flood Management Plan (CFMP) documents that have been produced by the Environment Agency: the Calder CFMP, Aire CFMP, and the Yorkshire Ouse CFM. These documents are soon to be finalised and will be publicly available. Flood defences Surface water/Drainage Typically foul systems will comprise a network of drainage sewers, often combining areas of separate and combined drainage, leading to a sewage treatment works. The foul/combined systems will often be connected, possibly via pumping, to a single local treatment works. In rural areas several small villages will often be inter-linked to a single local works. There are 57 identified sewage treatment works sites within the West Yorkshire sub-region. Various ancillary structures will be included through the system to assist network performance, primarily pumping stations, combined sewer overflows (CSOs), and storage tanks. CSOs provide an overflow release from the drainage system into local watercourses or surface water systems during times of high flows. In the upland rural areas, some of the properties are likely to be unconnected to the foul drainage system altogether, and will have their own septic tanks. Surface water systems will typically collect surface water drainage separately from the foul sewerage. These typically discharge directly into local watercourses, although in more constrained historic urban areas may often be linked to discharge into the foul/combined system. In the heavily urbanised central areas of the sub-region there are likely to be significant risks of urbanised flooding from surface water sources, where the large areas of impermeable surfaces produce significant volumes of runoff following intense rainfall events that overwhelm the local drainage systems. The events of summer 2007 indicated the scale of the potential problems with over two thirds of the affected properties reported to have suffered from flooding from local sewers. There is no mapping currently available of potential areas at risk, however the data that is available is discussed in the following, Impacts, section.
Impacts Current impacts Notably, within the more extreme fluvial flood risk zone there are the following critical assets and properties at risk:
Click here for further details on properties in flood zone 2 and 3. Also for the current flood risk (“undefended”) the Residential impacts to the local population have been determined. Residential properties are classed as medium risk vulnerability. The Communities and Local Government department hold information on social deprivation which identifies the particular vulnerability of local populations to flooding. Several of the areas at risk within the sub-region are in the highest vulnerability class, with Bradford and Wakefield identified as particularly vulnerable areas, as well as areas of Leeds and Huddersfield. The table below indicates the number of Residential properties that are also currently identified at risk of flooding within the sub-region.
Regarding transport networks, the following sections of the road and rail system within West Yorkshire are identified to be at risk (“undefended”) from current flooding:
Flooding incident records for the sewer and drainage systems within West Yorkshire indicate the following locations to be currently at risk of flooding from the sewer system:
These figures represent properties that will be affected by typical storms up to 5% AEP, and there are likely to be a significantly greater number of properties and areas affected by sewer and surface water flooding during higher intensity, more extreme storms, as we have seen with the flooding in summer 2007. The data on existing flood problems gives a good indication of the extent of recurrent problems related to the sewer system, however, in addition to the recorded/known incidents there will be numerous other locations which are also liable to flood where properties are not affected and therefore only limited information is available. Low gradient urban areas are particularly likely to be affected where surrounding areas are steep and have significant proportions of impermeable area creating large volumes of surface water runoff that will overwhelm the local drainage systems. Additional to those locations on the Yorkshire Water flood register, key highway and localised surface water flooding will readily occur, but can often be numerous and go unreported or unrecorded, especially in outlying unpopulated areas. Climate changes In addition the climate data indicates that there is likely to be a general reduction in the magnitude of individual events, for both the frequent and extreme rainfall events. In the higher upland areas, however, results in the Yorkshire Dales indicate that there is likely to be an increase in the intensity and magnitude of events. In addition, despite a general reduction in summer rainfall, the extended drying period is likely to produce more severe, high intensity thunderstorm events during the summer months, as experienced with the unprecedented events of summer 2007. Future impacts
Of even greater concern than the additional number of properties affected by future flood level increases, will be the likely increasing frequency with which large rainfall events may occur and the impact that these will have on the properties currently identified to be at risk. These assets will face an increasing risk of flooding as the present day extreme rainfall and flood events become more frequent. Locations and communities in the upland areas on the outskirts of the urban areas to the west of the sub-region will be at a greater flood risk due to faster flood flows and the limited response time available from flood warnings. This is likely to increase with the increasing seasonality of rainfall bringing higher intensity, flashy flood flows, particularly during the summer months. The increasing seasonality of rainfall and autumn and winter wetness, will lead to greater saturation of the ground, particularly in upland areas. Greater saturation will cause a higher volume and rate of runoff flows and increase the likelihood of sheet run off from the saturated ground surface, which will exacerbate the problems discussed above. This is likely to further increase the frequency and extent of problems to downstream areas and the scale of their impacts. Additional impacts of climate change on river and tidal flooding and flood defences are also likely to become apparent, as follows.
With regard to sewer and surface water flooding, with increasing winter rainfall due to climate changes the occurrence of incidents at the known foul and surface water sewer flooding locations will become significantly more frequent during the winter months. Other problem locations will arise due to the increasing magnitude of events, but it is difficult to easily ascertain where these may occur. Low gradient areas within the urban centres, particularly where there are significant extents of impermeable area, are likely to be the most susceptible, and low points on the road and rail networks will be vulnerable to increasing flooding, particularly where these are surrounded by steeper areas that will produce fast runoff flows from the projected more frequent and higher intensity storms. In addition, fast flowing surface water runoff from the upland areas in the steep valleys on the outskirts of towns to the west are likely to be most susceptible. The upland areas already experience higher levels of rainfall, and more severe storms, throughout the year. Similarly to river flooding, the impacts of climate change will produce increases in the number and frequency of flooding events, particularly during the winter period and during summer months due to high intensity thunderstorms. Other future impacts that are likely to come about are:
Description Highest elevations in the north and along the central ridge rise to above 100 metres, but these fall steeply to the adjacent low lying areas across East Riding which generally lie below 20 metres. Closer to the estuary elevations reduce further to less than 10 metres, and across Kingston-upon-Hull areas are very low-lying at approximately 2 metres, with many areas below sea level. Urban populations on the north side are focussed in the low-lying city of Kingston-upon-Hull settled on the north bank of the Humber Estuary. Beyond this there are a number of significant towns across East Riding, such as Goole (to the west), Beverley and Market Weighton (central), and Pocklington and Driffield (to the north). Along the coastline the key coastal towns are Bridlington (to the north), Hornsea, and Withernsea (to the south), with a further number of smaller tourist-based settlements. The sparse population lends itself to much of the flat fertile land across the flood plain being cultivated for agriculture. On the south side of the estuary the principle towns are Scunthorpe in the centre of North Lincolnshire, and Grimsby at the mouth of the Humber. Beyond these, there are very few large settlements and the majority are small towns and villages spread across the area. Elevations close to the Humber are low-lying, but rise to the west where the high ridge from the north continues to the south. Outside of the main urban centres the area is generally used for agricultural purposes. To the east the Immingham Docks are situated immediately to the north of Grimsby with associated industrial areas surrounding them. The Humber sub-region is dominated by the River Humber Estuary. The Humber is a major estuary and drains one fifth of the total land area of England and Wales. Several major rivers pass through the area to discharge into the estuary, including the River Trent and River Ancholme from the south, the River Ouse from the west, and River Hull from the north. There are several other minor tributary rivers and land drains which discharge from the surrounding hills into the main rivers. In addition there are several coastal streams which discharge directly to the sea along the East Riding coastline. The River Ouse originates in the Yorkshire Dales and is formed from the combination of several main rivers: Swale, Ure, Nidd, Wharfe, Aire, Calder, Derwent, and Don. It enters the sub-region from the west and passes Goole before its confluence with the River Trent to begin the Humber Estuary. The source of the River Trent is in Staffordshire and flows through The Midlands to join the River Ouse near Alkborough. The River Ancholme is a short navigable channel of approximately 27km which flows through Lincolnshire. The river has been engineered to flow a direct course across the low-lying adjacent agricultural areas. The source of the River Hull is in the northern Yorkshire Wolds. It flows through Driffield and past Beverley before cutting through the industrial centre of Kingston-upon-Hull city to discharge into the Humber Estuary. Sources of flood risk The predominant flood risk across the sub-region is related to tidal flood levels in the Humber Estuary which could result in extensive inundation in adjacent areas, particularly at the head of the estuary. Flooding around the Humber is the largest area at risk from tidal flooding in the country, with the greatest value of assets at risk outside of the Thames Estuary. There is currently 90,000 hectares of land and 400,000 people with the identified flood risk areas, mostly in Kingston-upon-Hull and Grimsby, in addition to major industries, including power stations and the country’s largest port complex (Immingham), and other businesses. At the upstream end of the estuary the flood zones extend across the wide flood plain, enveloping the whole south-east corner of the sub-region, including Goole and the surrounding towns, villages and roads. The extensive flood risk is related to tidal flooding from high spring tides and tidal surges within the Humber Estuary in combination with high fluvial flows from the significant main rivers (Ouse, Aire, Don and Trent) which converge at this location. Rising water levels in the Humber Estuary cause backing up of tributary watercourses, producing flooding along these rivers. The tide-locking of smaller tributaries and drains also leads to increased flood risk in other areas adjacent to the estuary, such as Hedon and Burstwick. There is additional tidal flood risk indicated along the mouth of the estuary, which to the south extends from Barton upon Humber through to Grimsby, and to the north covers the whole district area of Kingston-upon-Hull and extends across a wide area through to the estuary mouth, at Sunk Island Sands. In combination with the high tidal levels in Kingston-upon-Hull, the wide flood risk area extends back along the River Hull up as far as North Frodingham. Mostly only rural areas are affected, although the outskirts of Beverley are shown to be included. Further upstream on the tributaries only minor flooding is indicated. On the Ancholme again the combination of high tide levels and fluvial flooding indicates a wide flood plain area in between the two ridges of higher ground. Flooding here again mostly affects only rural areas and the outskirts of the adjacent towns. Due to the nature of the natural defences provided, there is no coastal flooding indicated along the East Riding coastline. In addition to river and tidal flooding, there is likely to be extensive flood risk related to surface water/drainage across the sub-region, particularly within heavily urbanised areas, although the key risk locations are not defined. There is also the potential for the outfalls from surface water drainage systems to become tide-locked, causing systems to back-up leading to increased flooding if significant rainfall events occur during high tide periods. With extensive low-lying areas along the Humber Estuary, most notably in Kingston-upon-Hull and surrounding towns/villages such as Hessle and Paull, there are several important areas which already lie close to sea level and are likely to suffer significant flooding during these combined events. There have been previous reports of flooding within the district as follows:
Regarding flooding from sewers there are the following reported incidents:
Further detail on historic flooding within the Humber sub-region can be found in the local Catchment Flood Management Plan (CFMP) documents that have been produced by the Environment Agency: the Derwent CFMP, Hull and Coastal Streams CFMP, Trent CFMP, Ancholme CFMP, and Lough Coastal Streams CFMP. These documents are soon to be finalised and will be publicly available. Flood defences On the River Trent, River Ouse, and Dutch River (Don) the river sections through the sub-region have raised defences provided along their full length. On the River Hull there are occasional raised defences in upstream areas, mostly protecting rural areas, and from Beverley downstream to the Humber outfall there are raised defences provided along the full length through the centre of Kingston-upon-Hull. In addition, the Hull Tidal Surge Barrier, at the outfall of the River Hull into the Humber Estuary, provides tidal flood protection to the centre of the city. Along the East Riding coastline most of the ‘defences’ are provided by natural features, although raised defences are provided at occasional locations, notably Bridlington, Hornsea and Withernsea. With much of the defence line provided by natural cliffs the result of erosion increases the potential future risk of flooding to areas behind. As well as the formal defences most stretches of the main river channels are managed and actively maintained by the Environment Agency against blockages and debris. In total there are over 617 km of raised flood defences in the Humber sub-region, with a further 800 km of formally maintained river channel. In addition, there are also 14 km of raised coastal defences Surface water/Drainage Typically foul systems will comprise a network of drainage sewers, often combining areas of separate and combined drainage, leading to a sewage treatment works. The foul/combined systems will often be connected, possibly via pumping, to a single local treatment works. In rural areas several small villages will often be inter-linked to a single local works. There are 119 identified sewage treatment works sites within the sub-region. Various ancillary structures will be included through the system to assist network performance, primarily pumping stations, combined sewer overflows (CSOs), and storage tanks. CSOs provide an overflow release from the drainage system into local watercourses or surface water systems during times of high flows. In the rural areas, some of the properties are likely to be unconnected to the foul drainage system altogether, and will have their own septic tanks. Surface water systems will typically collect surface water drainage separately from the foul sewerage. These typically discharge directly into local watercourses, although in more constrained historic urban areas may often be linked to discharge into the foul/combined system. Due to the significance of tidal levels along the Humber Estuary it is known that several of the sewer, and minor river, outfalls become tide-locked during periods of high tides. This restricts the discharge from the outfalls and causes flows to back-up within the system and can lead to localised flooding. This is known to be a significant problem in Kingston-upon-Hull, where much of the city is low-lying with 90 per cent of the area below the high tide level. Also, in the heavily urbanised area of Kingston-upon-Hull, and the other large towns (Scunthorpe, Grimsby, Immingham, Beverley, Driffield, etc), there are significant risks of urbanised flooding from surface water sources, where the large areas of impermeable surfaces produce significant volumes of runoff following intense rainfall events that overwhelm the local drainage systems. The events of summer 2007 indicated the scale of the potential problems with over two thirds of the affected properties reported to have suffered from flooding from local sewers. There is no mapping currently available of potential areas at risk, however the data that is available is discussed in the following, Impacts, section.
Impacts Current impacts Notably, within the more extreme flood risk zone there are the following critical assets and properties at risk:
Click here for further details on properties in flood zone 2 and 3. An additional key risk in tourist rural areas is the significant risk to caravan parks and camping sites. There are 19 caravan parks and camping identified to be at risk of flooding within the sub-region. These are highly vulnerable sites due to the significant personal safety risks to people resident at the sites during times of flooding, and cars and caravans are particularly hazardous as they can be easily picked up and carried along by flood flows causing significant damage to other properties and risk to life. Also for the current flood risk (“undefended”) the Residential impacts to the local population have been determined. Residential properties are classed as medium risk vulnerability. The Communities and Local Government department hold information on social deprivation which identifies the particular vulnerability of local populations to flooding. Several of the areas at risk within the sub-region are in the highest vulnerability class, with Kingston-upon-Hull identified as one of the most vulnerable in the country and also North East Lincolnshire in the most vulnerable category. Areas affected to the west of the sub-region in East Riding and North Lincolnshire medium to low vulnerability class. The table below indicates the number of Residential properties that are also currently identified at risk of flooding within the sub-region.
Regarding transport networks, the following sections of the road and rail system within the Humber sub-region are identified to be at risk (“undefended”) from current flooding:
Across the rural areas, particularly in East Riding, there are several fords across watercourses and these can become significantly dangerous to cross when river levels are high following heavy rainfall. This poses a serious hazard particularly on smaller watercourses in the outlying areas that might not be accounted for here. Flooding incident records for the sewer and drainage systems within South Yorkshire indicate the following locations to be currently at risk of flooding from the sewer system:
These figures represent properties that will be affected by typical storms up to 5% AEP, and there are likely to be a significantly greater number of properties and areas affected by sewer and surface water flooding during higher intensity, more extreme storms, as we have seen with the flooding in summer 2007. The data on existing flood problems gives a good indication of the extent of recurrent problems related to the sewer system, however, in addition to the recorded/known incidents there will be numerous other locations which are also liable to flood situated in outlying areas where properties are not affected and therefore only limited information is available. Low gradient urban areas are particularly likely to be affected where surrounding areas are steep and have significant proportions of impermeable area creating large volumes of surface water runoff that will overwhelm the local drainage systems. Additional to those locations on the Yorkshire Water flood register, key highway and localised surface water flooding will readily occur, but in rural areas anecdotal reports are not as readily available. Climate changes In addition there is likely to be an increase in the intensity and magnitude of individual rainfall events, particularly over the higher ground areas. There is projected to be increases in the magnitude of both frequent and extreme events. More frequent events are likely to increase by up to 6%, with more extreme events likely to see increases of greater than 10%. There is a general reduction for short, sharp showers, but typically the shorter duration (1 and 2-day duration) rainfall events see the greater increases indicating the increasing likelihood of heavier short-bursts. Despite a general reduction in summer rainfall, this effect is likely to produce more severe, high intensity thunderstorm events during the summer periods, as experienced with the unprecedented events of summer 2007. Along with changes in rainfall patterns, climate change will cause significant sea level rise along the East of England coastline. Mean sea levels in the Humber Estuary and along the Yorkshire coast are estimated to have risen at rates of between 1.5 and 3.6 mm per year over the last 80 years. Mean sea levels are projected to rise by up to 300mm by 2050, based on current guidance from Defra, and extreme sea surge levels are likely to be even more exaggerated. Future impacts
Of even greater concern than the additional number of properties affected by future flood level increases, will be the increasing frequency of large rainfall events and the impact that this will have on the properties currently identified to be at risk. These assets will face an increasing risk of flooding as the present day extreme rainfall and flood events become more frequent. Locations and communities in the higher ground rural areas to the north of the sub-region are likely to be at a greater flood risk due to faster flood flows and the limited response time available from flood warnings. This is likely to increase with the increasing seasonality of rainfall bringing higher intensity, flashy flood flows, particularly during the summer months. The increasing seasonality of rainfall and autumn and winter wetness, will also lead to greater saturation of the ground. The higher groundwater recharge rates, particularly in the chalk aquifers across East Riding, will produce increased baseflows and groundwater levels. With greater saturation causing a higher volume and rate of runoff flows and increasing the likelihood of sheet run off from the saturated ground surface, which will exacerbate the problems discussed above. This was a key function of flooding across East Riding during summer 2007 when heavy rainfall events followed an extended period of significant rainfall (the wettest May-June on record), and is likely to further increase the frequency and extent of problems and their impacts. The overall reduction of storage in permeable catchment soils during the winter months will lead to increased flooding. Most of the significant flooding in the Humber area is related to extreme tidal levels. Future rises in extreme sea levels and increased storminess will lead to increased extents of flooding due to overtopping, bypassing and breaching of the coastal defences, affecting a greater number of properties than currently, and on a more frequent basis. Studies of the identification of the extents of future tidal flooding are ongoing through the current revision to the Humber Shoreline Management Plan along the estuary and the Humber Strategy. These will ascertain the specific areas which are likely to be affected by rising sea levels, and propose recommended management methods to cope with the flooding. Additional impacts of climate change on river and tidal flooding and flood defences are also likely to become apparent, as follows.
With regard to sewer and surface water flooding, with increasing winter rainfall due to climate changes the occurrence of incidents at the known foul and surface water sewer flooding locations will become significantly more frequent during the winter months. Other problem locations will arise due to the increasing magnitude of events, but it is difficult to easily ascertain where these may occur. Low gradient areas within the urban centres, particularly where there are significant extents of impermeable area, are likely to be the most susceptible, and low points on the road and rail networks will be vulnerable to increasing flooding, particularly where these are surrounded by steeper areas that will produce fast runoff flows from the projected more frequent and higher intensity storms. Similarly to river flooding, the impacts of climate change will produce increases in the number and frequency of flooding events, particularly during the winter period and during summer months due to high intensity thunderstorms. Other future impacts that are likely to come about are:
Description To the west the moors of the Pennines are quite rugged and barren, becoming quickly more heavily populated through the central urban areas of Sheffield, Rotherham and Barnsley and the surrounding towns. The high altitude moorland to the west is populated by grazing sheep with occasional hamlets, and a significant number of reservoirs collecting water supply for the populations below. The western areas are just covered by the edge of the Pennines National Park Area. Across the central areas outlying towns are generally swallowed by the sprawl from the main conurbations of Sheffield, Barnsley and Rotherham. Further east Doncaster becomes more rural with the main town bridging the gap between the urban sprawl and the low-lying agricultural areas, at approximately 5 metres, of the Humber flood plain to the east. Also to the east of Rotherham there is a less dense population and a higher agricultural land use value. The sub-region includes a network of motorways and main roads with the M1, A1(M) and M18 all cutting through the area. The topography of the South Yorkshire region is dominated by the descent from the Pennines to the large flat flood plain of the Humber below. The rivers which descend from the steep hills of the Pennines National Park fall rapidly from the west of the region and form steep and fast flowing local tributaries into the main river through the sub-region, the River Don. The Don follows its main route to the east of Sheffield, and then through the centres of Rotherham and Doncaster before discharging into the engineered Dutch River and then on into the Ouse at the head of the Humber Estuary at Goole. The main tributary to the Don is the River Dearne which joins from further north and passes through the centre of Barnsley prior to joining the Don at Mexborough. Sources of flood risk In its upper reaches the flooding indicated on the Don is fairly discrete. The flood plains through the central areas of Sheffield and Rotherham are confined due to the surrounding development and topography, yet the potential impacts of flooding in these heavily built up areas are high. Likewise on the Dearne the indicative flood risk through Barnsley is confined although there has been significant historic flooding here in recent years. This increases further downstream around Bolton upon Dearne and Mexborough, although this mostly affects only open rural areas. The dominant flood risk evident in the South Yorkshire sub-region is the significant predicted flooding across the Humber flood plain. Approaching Doncaster the topography changes as the area spreads out across the flat low-lying flood plain areas. The flood zone here covers an extensively wide area leading towards the newly navigated confluence with the Ouse at Goole. The flooding is related to tidal flooding from high spring tides within the Humber Estuary in combination with high fluvial flows from the significant main rivers, including the Don (and also Aire, Ouse, and Trent) which converge at this location. Within the sub-region the flooding mostly affects rural areas on the northern outskirts of Doncaster, but also envelopes the towns in this area, notably Stainforth, Hatfield, Thorne and Moorend. In addition to river and tidal flooding, there is likely to be extensive flood risk related to surface water/drainage across the sub-region, particularly within heavily urbanised areas, although the key risk locations are not defined. There have been previous reports of flooding within the district as follows:
Regarding flooding from sewers, however, there are the following reported incidents:
Further detail on historic flooding within the South Yorkshire sub-region can be found in the local Catchment Flood Management Plan document that has been produced by the Environment Agency: the Don CFMP. This document is soon to be finalised and will be publicly available. Flood defences Surface water/Drainage Typically foul systems will comprise a network of drainage sewers, often combining areas of separate and combined drainage, leading to a sewage treatment works. The foul/combined systems will often be connected, possibly via pumping, to a single local treatment works. In outlying rural areas several small villages will often be inter-linked to a single local works. There are 72 identified sewage treatment works sites within the South Yorkshire sub-region. Various ancillary structures will be included through the system to assist network performance, primarily pumping stations, combined sewer overflows (CSOs), and storage tanks. CSOs provide an overflow release from the drainage system into local watercourses or surface water systems during times of high flows. In the upland rural areas, some of the properties are likely to be unconnected to the foul drainage system altogether, and will have their own septic tanks. Surface water systems will typically collect surface water drainage separately from the foul sewerage. These typically discharge directly into local watercourses, although in more constrained historic urban areas may often be linked to discharge into the foul/combined system. In the heavily urbanised central areas of the sub-region there are likely to be significant risks of urbanised flooding from surface water sources, where the large areas of impermeable surfaces produce significant volumes of runoff following intense rainfall events that overwhelm the local drainage systems. The events of summer 2007 indicated the scale of the potential problems with over two thirds of the affected properties reported to have suffered from flooding from local sewers. There is no mapping currently available of potential areas at risk, however the data that is available is discussed in the following, Impacts, section.
Impacts Current impacts Notably, within the more extreme fluvial flood risk zone there are the following critical assets and properties at risk:
Click here for further details on properties in flood zone 2 and 3. An additional key risk in tourist rural areas is the significant risk to caravan parks and camping sites. There are several caravan parks and camping identified to be at risk of flooding within the sub-region. These are highly vulnerable sites due to the significant personal safety risks to people resident at the sites during times of flooding, and cars and caravans are particularly hazardous as they can be easily picked up and carried along by flood flows causing significant damage to other properties and risk to life. Also for the current flood risk (“undefended”) the Residential impacts to the local population have been determined. Residential properties are classed as medium risk vulnerability. The Communities and Local Government department hold information on social deprivation which identifies the particular vulnerability of local populations to flooding. Several of the areas at risk within the sub-region are in the highest vulnerability class, with Barnsley and Doncaster identified as particularly vulnerable areas, as well as areas of Sheffield and Rotherham. The table below indicates the number of Residential properties that are also currently identified at risk of flooding within the sub-region.
Regarding transport networks, the following sections of the road and rail system within South Yorkshire are identified to be at risk (“undefended”) from current flooding:
Flooding incident records for the sewer and drainage systems within South Yorkshire indicate the following locations to be currently at risk of flooding from the sewer system:
These figures represent properties that will be affected by typical storms up to 5% AEP, and there are likely to be a significantly greater number of properties and areas affected by sewer and surface water flooding during higher intensity, more extreme storms, as we have seen with the flooding in summer 2007. The data on existing flood problems gives a good indication of the extent of recurrent problems related to the sewer system, however, in addition to the recorded/known incidents there will be numerous other locations which are also liable to flood where properties are not affected and therefore only limited information is available. Low gradient urban areas are particularly likely to be affected where surrounding areas are steep and have significant proportions of impermeable area creating large volumes of surface water runoff that will overwhelm the local drainage systems. Additional to those locations on the Yorkshire Water flood register, key highway and localised surface water flooding will readily occur, but can often be numerous and go unreported or unrecorded, especially in outlying unpopulated areas. Climate changes In addition there is likely to be an increase in the intensity and magnitude of individual rainfall events, particularly over the upland areas with rainfall events similar to those in the Yorkshire Dales. There is projected to be little change in the magnitude of the frequent events; however extreme events are likely to increase, particularly for the 1 and 2-day duration events, indicating the increasing likelihood of heavier short-bursts. Despite a general reduction in summer rainfall, this effect is likely to produce more severe, high intensity thunderstorm events during the summer periods, as experienced with the unprecedented events of summer 2007. Future impacts
Of even greater concern than the additional number of properties affected by future flood level increases, will be the likely increasing frequency with which large rainfall events may occur and the impact that these will have on the properties currently identified to be at risk. These assets will face an increasing risk of flooding as the present day extreme rainfall and flood events become more frequent. Locations and communities in the upland areas on the outskirts of the urban areas to the west of the sub-region will be at a greater flood risk due to faster flood flows and the limited response time available from flood warnings. This is likely to increase with the increasing seasonality of rainfall bringing higher intensity, flashy flood flows, particularly during the summer months. The increasing seasonality of rainfall and autumn and winter wetness, will lead to greater saturation of the ground, particularly in upland areas. Greater saturation will cause a higher volume and rate of runoff flows and increase the likelihood of sheet run off from the saturated ground surface, which will exacerbate the problems discussed above. This is likely to further increase the frequency and extent of problems to downstream areas and the scale of their impacts. Additional impacts of climate change on river and tidal flooding and flood defences are also likely to become apparent, as follows.
With regard to sewer and surface water flooding, with increasing winter rainfall due to climate changes the occurrence of incidents at the known foul and surface water sewer flooding locations will become significantly more frequent during the winter months. Other problem locations will arise due to the increasing magnitude of events, but it is difficult to easily ascertain where these may occur. Low gradient areas within the urban centres, particularly where there are significant extents of impermeable area, are likely to be the most susceptible, and low points on the road and rail networks will be vulnerable to increasing flooding, particularly where these are surrounded by steeper areas that will produce fast runoff flows from the projected more frequent and higher intensity storms. In addition, fast flowing surface water runoff from the upland areas in the steep valleys on the outskirts of towns to the west are likely to be most susceptible. The upland areas already experience higher levels of rainfall, and more severe storms, throughout the year. Similarly to river flooding, the impacts of climate change will produce increases in the number and frequency of flooding events, particularly during the winter period and during summer months due to high intensity thunderstorms. Other future impacts that are likely to come about are:
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