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Spatial planning & Flood risk : development of a spatial planning framework for the mitigation of flood risks

Bakker, O.S. (2022) Spatial planning & Flood risk : development of a spatial planning framework for the mitigation of flood risks.

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Abstract:Due to large housing shortages in the Netherlands, large scale housing projects are planned across the country, with plans to build up to 1 million new houses till 2030. Most of those new houses are planned in areas that are at risk of flooding, which has several negative consequences. The arrival of new inhabitants and new spatial structures increases the severity of flood events, leading to extra flood risk. The last effect is directly related to the introduction of the new Dutch flood safety system for primary flood defences in 2017. This system is based on the computation of the most stringent flood safety standard from three flood risk criteria: the social cost benefit analysis (SCBA), the local individual risk (LIR) and the group risk (GR). The SCBA flood safety standard is based on an economic optimum between expected flood damage and the expected costs to improve flood defences. Thus, the construction of new spatial structures behind the dikes is of direct influence on the strictness of flood safety standards and the total flood risk. Therefore, this study aims to research whether it is possible to develop and test an effective spatial planning framework. The aim of this spatial planning framework is to consider flood risk in a certain area and adjust the current spatial planning, to minimize increases in flood risk associated with new spatial developments. The study used three dike ring areas as case studies. First, the impact of current spatial planning on the flood risk and financial flood damage for case study 1 was quantified. This was done using the SSM2017 (damage and casualty module) model for the computation of financial flood damage and (fatal) flood casualties. All new residences and industrial objects planned in the period 2021-2030 were implemented in the damage model. The results showed that following the official spatial planning for the next decade leads to a significant increase in flood risk for case study 1. Similarly, large increases in financial flood damage were computed in case study 1. Next was the development of the spatial planning framework. The spatial planning framework considers four damage categories: family homes, apartments, industrial objects, and casualties. Two versions of the spatial planning framework were made: a basic and an extended version, where the latter version also included flood probability. Both framework versions were applied to case study 1. The results of the framework application showed that both versions of the framework were very effective in the reduction of financial flood damage related to new spatial developments compared to the financial flood damage and flood risk computed based on the official spatial planning. The third and final step was to apply the extended framework to case studies 2 and 3. The choice for the extended spatial framework was made because the validation results showed that the extended framework has the same financial flood damage reduction capability as the basic framework, while including the element of flood probability, which is relevant for the computation of flood risk. Application of the framework led to significant decreases in financial flood damage for both case studies, although on a different scale. The main conclusion of the study is that it is possible to develop in a well-structured manner an effective spatial planning framework that can decrease flood risk for different types of spatial objects in different dike ring areas. The effectivity of the spatial planning framework highly depends on the spatial scale at which the framework is used: increasing the area within which spatial structures can be relocated leads to larger reductions in flood risk and damage compared to use of the framework within smaller areas. Furthermore, the dominant flood type is also important: the framework leads to higher flood risk reductions in dike ring areas which have a more varied flood type compared to dike ring areas that have a uniform flood type pattern. It is recommended to integrate a cost-benefit component into the framework, with which it can be determined whether the reduction in flood risk is worth the extra costs in utilities and infrastructure for housing relocated further away from existing population centres.
Item Type:Essay (Master)
Royal HaskoningDHV, Amersfoort, The Netherlands
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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