Improved long-term coastal management as a result of a large-scale spatial perspective

Horstman, E.M. (2008) Improved long-term coastal management as a result of a large-scale spatial perspective.

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Abstract:Problem definition & research objective Present coastal management policy in the Netherlands mainly consists of reacting to observed changes and acting in anticipation of expected short-term changes for the next 50 years. Longer-term developments are only accounted for in outlooks that are applied for considering the no-regret level of proposed projects. Projects forthcoming from this approach often have a confined spatial scope. Meanwhile, no reliable expectations are available on the requirements of the coastal defences within the next 200 years. It is also unknown whether this long-term perspective may introduce new insights with respect to the existing coastal management policy. A quick scan on the issue of scaling up in both coastal management and water management in general, shows that this long-term perspective increases the relevance of a larger spatial scale perspective. Until now however, no systematic studies have been accomplished into the potential advantages of developing long-term strategies for enhancing the coastal defences at larger spatial scales. Therefore, the goal of this research is: To establish whether a long-term perspective raises the need for new coastal management strategies at a larger spatial scale than the present coastal management practice and to explore the consequences of implementing such new coastal management strategies. Outline of this research To find out whether a long-term perspective introduces new insights to coastal management, this research presents the results of a case study based on the area consisting of the mainland coasts of the provinces of Noord-Holland and Zuid-Holland in the Netherlands. The first step consists of a study into long-term climate change effects and their impacts on coastal safety. Next, eight coastal management strategies are derived for preserving the present safety level of the coastal defences up to 200 years from now. Afterwards, an assessment methodology is set-up and applied in order to find out how these proposed strategies compare to each other. This brings us to some new insights on the implications of a long-term perspective for coastal management policy. Future developments Available literature on climate change impacts is applied to derive three scenarios for the increasing hydraulic boundary conditions for the coastal defences up to 2200. Additionally, it is supposed that the bed levels of the coastal zone seaward of the dunetoes will keep up with sea level rise due to ongoing nourishments. Subsequently, the safety of the future coastal defences is assessed according to the increased hydraulic boundary conditions. The existing assessment method for coastal defences is applied, including a longshore component to account for longshore discontinuities in the dune profiles. These assessments show that by the year 2200, more than 70% of the coastal defences will be disapproved if the most extreme climate change scenario will come true. For the intermediate and the lower scenarios, these figures are 60% and 40% respectively. Spatial scales This study identifies two reasons why future developments do raise the need to consider coastal management strategies at larger spatial scales. First, assessing the coastal defences for the impeding boundary conditions indicates a significant expansion of the spatial scale of the weak links that will occur on the long term. This inherently raises the need to look for coastal enhancement strategies at increased spatial scales. Secondly, there are some potential measures for enhancing the coastal defences that are unsuitable to be implemented at confined spatial scales. So both the problems and the solutions ask for a larger spatial scale perspective. However, there are also measures that are incompatible with a large spatial scale implementation, so smaller spatial scales are also included. Coastal management strategies are considered at four different spatial scales within this study: ▪ Uniform coast; one solution for the entire study area. ▪ Large spatial scale; separating the southern, densely populated part and the northern, less densely populated part of the study area. ▪ Intermediate spatial scale; dividing the study area into twelve longshore sections according to major land use characteristics. ▪ Small spatial scale; dividing the study area in many short longshore sections that are related to very specific characteristics of each area (e.g. land use and attributes of the defences). Coastal management strategies Different (existing) measures are connected to these spatial scales. This way, eight different coastal management strategies are created for preserving the present safety level of the coastal defences over the next 200 years. The proposed strategies are: ▪ Two islands in front of the entire coast of the study area. ▪ Artificial but dynamic sandbanks in front of the entire coast. ▪ A new row of foredunes in front of the existing foredunes for the entire coast. ▪ An island in front of the southern part of the study area and new foredunes at the northern part. ▪ New foredunes in front of the southern part of the coast and sandbanks at the northern part. ▪ An intermediate scale seaward strategy combining seaward dune extensions with new sandbanks and artificial reefs, depending on the major land use functions. ▪ An intermediate scale landward strategy consisting of landward dune extensions and some minor seaward dune extensions, depending on the major land use functions. ▪ The small scale basic alternative representing the continuation of present small-scale coastal management policies being very well adjusted to the specific, local land use functions and showing a major longshore variation in the measures for improving the coastal defences. The required dimensions of the measures within these strategies are derived for both the highest and the lowest climate change scenarios. Assessment framework Until now, little is known on how new coastal management strategies compare to the continuation of the present coastal management policy. Moreover, scientific publications still mainly concentrate on the technical feasibility of new strategies. This study compares the proposed coastal management strategies to the basic alternative by applying a mainly qualitative assessment method that is partly based on rough estimates of the (socioeconomic) costs and benefits. All strategies are assessed on a wide range of criteria, representing costs, welfare impacts, non-welfare impacts (intrinsic value of nature) and some other criteria (technical complexity, robustness, phasing and governmental complexity). Different views are set-up that each award different weights to the criteria and leave some criteria out of the assessment. These views are applied to explore the influence of different policy outlooks. Since the assessments on some of the criteria are quite uncertain, this study only considers significant values of the total scores on these views. Minor deviations from the score of the basic alternative are left out of the analysis. A sensitivity analysis shows that this method results into rather stable results. Conclusions Concerning the results of the assessments of the proposed coastal management strategies for all policy views and for both the highest and the lowest climate change scenario, some general conclusions are found. First, the small scale strategy representing the continuation of present coastal management practice appeared to be not the best strategy. Other strategies, applying larger spatial scales, create better chances for enhancing the coastal defences and the related spatial impacts. The basic alternative (small scale strategy) is ranked relatively high for both a ‘leading criteria’ view (based on the criteria most important at present) and for a ‘risk averting’ view. It turns out that there are three alternative strategies that show some major advantages over the basic alternative, both when the highest and the lowest climate scenarios are considered: ▪ The uniform coast strategy with a new row of foredunes in front of the entire coast. This strategy is assessed best from a sustainability point of view since a new, smooth coastline is established. Moreover, new nature will be created which might be useful for recreational purposes. ▪ The large scale strategy with an island in front of the southern part of the study area and new foredunes for the northern part is assessed best from a spatial development point of view since new space would be created to relieve the ever-increasing densities in this region. However, it is assessed negative from a risk averting point of view. ▪ The intermediate scale landward strategy, consisting of landward dune extensions and some minor seaward dune extensions depending on the major land use functions, is assessed best from a risk averting point of view. This is caused by its rather low maintenance costs and the possibility to separate the construction in phases. The uniform strategy with two islands in front of the entire coast of the study area also shows some major advantages in comparison to the basic alternative, especially on spatial development. However, this goes along with significant disadvantages for some other views like sustainability. A main characteristic of those strategies that are assessed best is that they aim at maintaining the longshore smooth, concave shape of the coast. This shape represents some sort of natural equilibrium situation of the coastal morphology, in contrary to the disruptions of this smooth coastline caused by the basic alternative. So accounting for and cooperating with the natural dynamics of the coastal system could significantly contribute to improving coastal management. Possibilities to do so increase when a larger spatial scale perspective is applied for developing coastal management strategies. This research shows that rankings of the proposed coastal management strategies do not change too much for the two climate change scenarios that are studied, despite of the large uncertainties that are inherent to the long-term future. For more detailed designs that are based on the proposed strategies however, these uncertainties are certainly important and therefore flexible solutions should be preferred. This should enable the possibility of the coastal defences to be extended over time in accordance with the latest predictions of the boundary conditions for the next decades. From this point of view, static solutions are less preferable. The results of this study indicate that a solid analysis can be accomplished of the significant advantages and disadvantages of different strategies for long-term coastal management, although future uncertainties are quite large. So there is no need to wait with establishing a new direction for coastal management until all future uncertainties are reduced as much as possible. This study underlines the usefulness of increasing the temporal and spatial scales at the basis of our coastal management policy. A long-term strategy based on a larger spatial scale perspective can result in significant advantages compared to the continuation of the present small-scale and project-wise approach of coastal management.
Item Type:Essay (Master)
Clients:
Witteveen + Bos
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
Link to this item:http://purl.utwente.nl/essays/58136
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