Siddharth Narayan

A Bayesian network model for assessments of coastal inundation pathways and probabilities

Coastal flood assessments often require the analysis of a complex system of flood sources, pathways and receptors. This can be challenging for traditional numerical modelling approaches. In this paper we use a Bayesian networks approach to assess coastal floodplains as networks of inter-linked elements. A Bayesian network (Bn) model is built to describe flood pathways and estimate flood extents for different extreme events. The network of the Bn model is constructed from a quasi-2D Source – Pathway – Receptor (SPR) systems diagram. The Bn model is applied in Teignmouth in the UK, a coastal floodplain of typical complexity. It identifies two key flood pathways and assesses their sensitivity to changes in sea levels, beach widths and coastal defences. The advantages, utility and limitations of the Teignmouth Bn model are discussed. The process of 2D SPR and Bn model construction helps identify gaps in floodplain understanding and description. The Bn model quantifies inundation probabilities and facilitates the rapid identification of critical pathways and elements, before committing resources to further detailed analysis. The approach is transferable and can be readily applied in local-scale coastal floodplains to obtain a systems-level understanding and inform numerical modelling assumptions.

Uniendo ingeniería y ecología: la protección costera basada en ecosistemas

Resumen En un contexto de crecientes impactos y riesgos socio-económicos en las costas del planeta, la protección costera basada en ecosistemas surge como un nuevo paradigma que une los principios de protección, sostenibilidad y resiliencia, a la vez que proporciona múltiples beneficios. Este artículo ofrece una perspectiva sobre qué son y cómo se pueden utilizar las defensas naturales en el diseño, planificación y gestión de costas. La política pública muestra un creciente interés por su implementación general y el cuerpo de conocimiento y experiencia alrededor de la también denominada infraestructura ‘verde’ es creciente, pero aún existen importantes barreras que salvar. Una de ellas es estandarizar su diseño en términos ingenieriles, así como reconocer los aspectos que los diferencian respecto a enfoques tradicionales. La adaptación climática y la reducción de riesgos son áreas en las que su utilización puede ser más significativa, debido a la variedad de servicios que ofrecen. Tanto desde el punto de vista técnico como económico, existen argumentos sólidos para evitar la degradación de los ecosistemas, avanzando su restauración y conservación, como también desde la perspectiva de la defensa de las costas.

Valuing protective services of mangroves in the Philippines : technical report

Mangroves and other coastal ecosystems act as natural defenses that protect people and property from storms, floods, erosion, and other coastal hazards, reducing coastal risk. Mangroves protect coastlines by decreasing the risk of flooding and erosion. The roots of mangroves retain sediments and prevent erosion, while the prop roots, trunks and canopy reduce the force of incoming wind and waves and reduce flooding. The Philippines has lost hundreds of thousands of hectares of mangroves in the last century. When mangroves are degraded or destroyed, the coast line becomes more exposed to the destructive impacts of waves and storm surge, and coastal communities have greater risks from the impacts of storms, floods, and sea level rise. The Philippines is at high risk from coastal hazards and natural defenses can help reduce these risks. This Technical Report, and its accompanying Policy Brief, provide a social and economic valuation of the flood protection benefits from mangroves in the Philippines. This work aims to support decisions across development, aid, risk reduction and conservation sectors as they seek to identify sustainable and cost-effective approaches for risk reduction. This Technical Report applies the Expected Damage Function approach recommended by the World Bank to quantify the risk reduction benefits from mangroves in the Philippines. Using high-resolution flooding models, the Report examines the flooding that would occur with and without mangroves under different storm conditions throughout the Philippines, and estimates the annual expected benefits of mangroves for protecting people and property in social and economic terms.