Water and Effluent Treatment Magazine
Issue link: https://read.utilityweek.co.uk/i/283328
Five million-plus properties in the UK are at risk from flooding, and even properties situated far from common sources of river and coastal flooding may be at risk from groundwater. Affecting infrastructure, groundwater causes two to four times the damage to buildings and can take considerable time to recede. Mark Fermor, hydrogeologist and managing director, ESI, reveals all. The challenge: Keeping groundwater at bay INSIGHT FLOOD RISK MANAGEMENT Groundwater flooding can be the catalyst for surface water floods because the saturated ground prevents rainfall infiltration O verview: Groundwater flooding represents one of the natural hazards faced in the UK and mapping of groundwater flood risk areas provides an important support to land use planning and in the assessment of climate change impacts. However, previous ap- proaches have suggested prob- lems are far more widespread than they really are, and ESI's work has helped to show that the issues are actually quite lo- calised" Groundwater flooding occurs when the sub-surface water emerges from the ground at the surface, or into Made Ground and structures. This could be as a result of persistent rainfall that recharges aquifers until they are full, or may be a result of high river lev- els or tides driving water through near-surface deposits. Compared to surface water flooding, groundwater flooding can last considerably longer, with incidents lasting anything from a week to several months, which is why it can prove sub- stantially more costly to land and property owners than other types of flooding. The new groundwater flood risk maps now available help to identify where groundwater may reach the surface or into base- ments and other infrastructure, and can also help to indicate areas where surface water flood- ing may be exacerbated or more persistent, although further research is still needed to better represent the surface water / groundwater interactions. Emergent groundwater tends to be clear and relatively clean compared to muddy fluvial flood waters but becomes con- taminated by sewers and brown- field sites. Rising groundwater infiltrates sewers and adds to the challenges of preventing sewer flooding, and within the water industry it is recognised to cause significant issues. Catalyst At ESI, we have recently devel- oped a methodology for the reduction of sewer infiltration and is working with the water industry to address these issues. This should reduce the inci- dence of river pollution and the pumping and treatment costs involved. Groundwater flooding can itself also be the catalyst for many surface water floods because the saturated ground prevents rainfall infiltration. The Law Society published recently a new practice note directing solicitors overseeing property transactions to make their clients explicitly aware of any potential flood risks before completion. And this new focus on the need to consider all sources of flooding has focused the atten- tion of a wide variety of sectors, from property development and construction, to local authori- ties, planners, architects and allied professionals on improved estimation of risk. Until recently, the British Geological Survey's (BGS) 2007 National Susceptibility to Groundwater Flooding dataset at a scale of 1:50,000 was the only available resource to assist with consideration of ground- water flooding. BGS clearly states this resource was intended for regional or national planning purposes, but was not to be used in isolation to make plan- ning decisions at any scale. However, in the absence of any other resources, it has been repeatedly relied on for just that purpose. n "Compared to surface water flooding, groundwater flooding can last considerably longer, with incidents lasting anything from a week to several months" Mark Fermor THE CONCEPT • The Groundwater Flood Risk Map provides coverage for England and Wales, and it is planned that Scotland will be available soon • The map is designed to take advantage of all the available data and provide a preliminary indication of groundwater flood risk • Version 1 of the national scale map uses a 1 in 200 year return period to give an indication of the area appropriate to the more extreme events • ESI's team includes nine PhDs, 32 MScs and seven Chartered Geologists, and this combination of technical expertise and professional experience gives ESI the ability to advise on groundwater flooding issues and the next steps required in the event that a property or proposed development lies within an area at risk of groundwater flooding • The map is particularly useful to the insurance industry, property development, and decisions under the UK planning regime NEED TO KNOW 1 It is estimated that around one in six homes across the UK are at risk from flooding - about 5.2 million properties 2 Groundwater flooding can last considerably longer than other forms of flooding, with incidents lasting anything from a week to several months, and so it often proves substantially more costly to land and property owners, although the problems are much more localised than hitherto understood before the publication of ESI's national map 3 Prior to the launch of ESI's Groundwater Flood Risk Map the only national resource available was the British Geological Survey's 2007 National Susceptibility to Groundwater Flooding dataset at a scale of 1:50,000 4 ESI's Groundwater Flood Risk Map has identified that the number of homes, businesses, and areas at actual risk from groundwater flooding is considerably less than previously thought 5 Dozens of Lead Local Flood Authorities across England and Wales have already joined ESI's User Group, which provides free access to its Groundwater Flood Risk Map and vital information relevant to the Flood and Water Management Act 2010 in return for ongoing information to help evolve and update the map THE VERDICT • NA move to a risk-based model can only be good news for the hundreds of homes and landowners finally freed from the potential issues which come with being branded a risk in the past, and more in-depth and appropriate information can only help with planning projects and infrastructure in the future. • MARCH 2014 WET NEWS 29