Assessing flood risk associated with waste disposals: methodology, application and uncertainties

Abstract

Waste disposal sites are mostly located in lowland areas close to residential areas inducing a long-term risk of potential environmental contamination due to flooding. During recent flood events, these areas were reportedly exposed to inundations. This paper aims to develop a qualitative approach to assess flood risk associated with flood-prone waste disposals at the basis of Austrian case studies. Risk is investigated as a function of the probability of an event and the consequences of that event. The presented assessment approach is characterized as qualitative as consequences are expressed in risk categories but not in expected (monetary) losses. The probability of inundation, the hydrodynamic impacts on considered waste disposal sites and the expected consequences to the environment (potential emissions of hazardous substances) were linked. Derived risk categories from ''minor risk'' to ''serious risk'' were used to express flood risk to environmental goods like groundwater bodies, nature reserves and recreation areas. A screening of 1,064 waste disposals yielded roughly 30% of sites located within or close to flood risk zones. Three representative case study areas were selected and investigated in detail by applying 2D hydrodynamic models to calculate flow depths and shear stress and by developing emission scenarios. The hydrodynamic modelling covered three hydrologic scenarios with statistical recurrence intervals of 30, 100 and 300 years. Derived leaching scenarios ranged from minor emissions up to total erosion of the waste disposal site. Based on four parameters representing flood characteristics, the susceptibility to erosion (flow velocity and shear stress) and the estimated leaching behaviour, a flood risk evaluation matrix (FREM) was elaborated. The study outlines that in case of flooding the hazardous emissions could lead to partly tremendous impacts on environmental goods. Identified uncertainties associated with considered processes were considerably high. However, the developed qualitative approach provides a decision support aid to identify waste disposals with imminent risk for humans and the environment.

Risk screening assessment for ranking historic coastal landfills by pollution risk

“…If a series of overall risk index value thresholds were set to provide categories of risk (e.g., very high, high, moderate, low, and very low), then this would mitigate the issue of having multiple sites with the same or similar index values. Note a zero risk category is deliberately not included as there is always a residual risk of a site eroding and causing pollution (Neuhold and Nachtnebel 2011). A categorical risk approach would also have the advantage of allowing the end-user greater discretion in determining the order in which sites are considered for further investigation and (or) remedial action, which would better support management of limited budgets.…”

“…The main parameters identified as important for assessing drivers of coastal landfill erosion on low-lying coasts are wave exposure, storm climate, flooding, and tidal range (Laner et al 2008(Laner et al , 2009McLaughlin and Cooper 2010;Neuhold and Nachtnebel 2011;Neuhold 2013;Rosendahl Appelquist 2013). There is little variation in mean wind speeds and wind gust speeds around England (Met Office 2016) and, therefore, storm climate was not considered.…”

“…Existing landfill risk ranking methods (Laner et al 2008(Laner et al , 2009Neuhold and Nachtnebel 2011;Neuhold 2013; Alaska Department of Environmental Conservation 2015) determine the hazard posed by assuming the entire landfill will erode, as saturated waste is known to be mechanically unstable (Blight and Fourie 2005;Liang et al 2015). The area of historic landfill sites can be determined from the Historic Landfill Sites National Dataset (Environment Agency 2017) and GIS mapping software (e.g., ArcMap); however, the dataset does not provide information on waste volumes.…”

“…These typically only consider the risk of pollution when the waste is fully encapsulated, do not consider inundation, and focus on the risk from leachates and gases (e.g., Kumar and Alappat 2005;Sharma et al 2008;Singh et al 2009;Okaneya et al 2013). Where erosion of waste as a pollutant pathway has been considered, methods are too location specific for wide application (Laner et al 2008(Laner et al , 2009Neuhold and Nachtnebel 2011;Neuhold 2013;Alaska Department of Environmental Conservation 2015). Hence, a new region-specific method is required for assessing coastal landfills that can be applied in both England and physically similar temperate coastal environments.…”

Integrating River Bed Dynamics to Flood Risk Assessment

“…Therefore, the influence of sediment transport on the respective water surface elevation is investigated in this study. As this additional process is considered it is obvious that uncertainty increases (Neuhold et al, 2010 a, b;Neuhold & Nachtnebel, 2011). The identification of potential impacts on the water surface elevation and accordingly the possible inundation depth as well as delineation could, however, lead to an increase of awareness and adaptation of flood risk management strategies.…”