Landfills and flood risks
According to estimations based on limited mapping results, tens of thousands of historic landfills in the EU are situated in coastal and alluvial areas. In general, it was common to install landfills on floodplains due to their lower land value1. Such areas are prone to flooding or inundation and when there are landfills situated in these areas, flooding could pose a significant threat to the environment. On the one hand, flooding will increase the amount of erosion, which can result in increased amounts of eroded waste ending up in rivers and seas. On the other hand, when a landfill site is flooded, the volume of generated leachate will increase due to increasing percolation of water, resulting in a higher rate of leachate leakage ending up in the environment. Both pathways could affect protected areas in the vicinity of the landfill. The main risks come from higher rainfall intensity in short intervals causing erosion and flooding. Change in precipitation patterns is a direct consequence of climate change, but its impact on landfills has been barely studied. However, studies demonstrated that landfills located in lower areas will be vulnerable to the effects of climate change (e.g. sea level rise)2.
The environmental consequences due to higher flooding patterns were seldomly taken into account in the commonly used risk models. Therefore, it is recommended to consult flood hazard maps before launching a landfill mining project. In terms of prevention, flood hazard maps can be a great asset in landfill management as they will show where potential adverse consequences may arise. Based on this kind of maps, a vulnerability index for historic landfill sites could be determined, where resources and attention might best be focused. For the latter, landfill mining could be a solution as the landfilled material and associated pollution would be either reduced or totally removed, resulting in a safer environment in case of flooding. Furthermore, landfills can also be an opportunity for climate adaptation: when well-managed, landfills can contribute to a multi-layer flooding safety management system2. In the Landfill miner guide, two examples are provided: one related to coastal erosion and associated floods (the RAWFILL pilot site of Lingreville, France) and one related to the flood of the Gave de Pau river (Bordes landfill, France). In such projects, it is important that the final artificial landform meets the geotechnical requirements to ensure long-term stability and prevent potential natural hazards affecting the area such as floods, storms and erosion3.
In Flanders, a specific website is available where information on many water related aspects in Flanders is included. With the website, the government aims to inform the public as correctly as possible regarding flooding and droughts in the region. All measurements and forecasts are brought together within one single platform. In that way, the preventive measures can be taken to avoid damage by e.g. flooding.
There are two interesting tools available on the website that enable the user to get the right information very quickly:
Watertoetstool: This tool brings the user to a map, where he/she can click on the location of interest. Then the user will receive a brief report on the situation at that location.
A map catalogue where the user can find all different maps related to water in Flanders (e.g. flooding areas, precipitation, water quality, drainage).
For Wallonia, a lot of interesting information is available on the Walloon GIS geoportal "WalOnMap". A thematic map on flood hazards can be consulted. This map compiles both flood hazard related to overflowing streams and concentrated water runoff. The flood hazard map therefore represents areas and axes where there is a probability of flooding, even where no flooding is historically known. Conversely, the absence of a hazard zone or axis on the map cannot guarantee that this part of the territory is safe from flooding. Other types of flooding may occur than overflowing streams or runoff as part of this mapping.
For Germany, data on flooding is available on the German Geoportal in which different thematic maps and data sources are included. In case of flooding, there is a thematic map for severe weather/heavy rain precipitations conditions. Flooding occurs regularly, which can lead to significant damages after intense rainy seasons (in summer) or after the snowmelt (in spring). For some regions (for instance the Brandenburg region), detailed maps are available based on data sets about the flood retention potentials in these specific areas.
Data is also provided on regional geoportals. For example, on the GIS platform of North Rhine-Westphalia, a flood hazard map is available. This kind of map provides information about the possible spatial extent and depth of flooding. The map shows the local flood situation for recurrent flood events.
In the United Kingdom, detailed flood hazard maps are available as well. These maps visualise estimations of the areas that would be inundated by floods with a 100-year return period level from non-tidal rivers, in the absence of flood defences. These flood risk maps can be used by planners and also landfill owners or project managers, to assess the risk of flooding to proposed developments.