Abstract
One of the measures that has been implemented widely to adapt to the effect of climate change in coastal zones is the implementation of set-back lines. The traditional approach of determining set-back lines is likely to be conservative, and thus pose unnecessary constraints on coastal zone development and fully utilising the potential of these high-return areas. In this study, we apply a newly developed risk-informed approach to determine the coastal set-back line at regional scale in a poor data environment. This approach aims to find the economic optimum by balancing the (potential) economic gain from investing in coastal zones and the risk of coastal retreat due to sea level rise and storm erosion. This application focusses on the east coast of Sri Lanka, which is experiencing rapid economic growth on one hand and severe beach erosion on the other hand. This area of Sri Lanka is a highly data-poor environment, and the data is mostly available from global databases and very limited measurement campaigns. Probabilistic estimates of coastline retreat are obtained from the application of Probabilistic Coastline Recession (PCR) framework. Economic data, such as the discount rate, rate of return of investment, cost of damage, etc., are collated from existing estimates/reports for the area. The main outcome of this study is a series of maps indicating the economically optimal set-back line (EOSL) for the ~200-km-long coastal region. The EOSL is established for the year 2025 to provide a stable basis for land-use planning decisions over the next two decades or so. The EOSLs thus determined range between 12 m and 175 m from the coastline. Sensitivity analyses show that strong variations in key economic parameters such as the discount rate have a disproportionately small impact on the EOSL.
Highlights
The effects of climate change on hydrodynamic forcing, such as sea level rise, changes in wave conditions, changes in the sediment supply from rivers, etc., is already resulting in changes in the rate of coastal erosion/accretion along the sandy coastlines of the world [1,2,3,4,5].In light of climate change and especially coastline retreat due to sea level rise, many countries and coastal zone authorities are developing adaptation plans to protect coastal assets and future investments along their coastlines
A set-back line is a line along the coast, seaward of which certain development activities are prohibited or restricted. This line is determined based on a linear summation of long-term recession due to long-shore sediment transport gradients, the impact of storm erosion for a given return period and long-term recession due to sea level rise
The most important data that was needed for this study were cross-shore beach profiles along the coastline of the study areas. These data were provided by the Coast Conservation Department (CCD) of Sri Lanka
Summary
The effects of climate change on hydrodynamic forcing, such as sea level rise, changes in wave conditions, changes in the sediment supply from rivers, etc., is already resulting in changes in the rate of coastal erosion/accretion along the sandy coastlines of the world [1,2,3,4,5]. A set-back line is a line along the coast, seaward of which certain development activities are prohibited or restricted This line is determined based on a linear summation of long-term recession due to long-shore sediment transport gradients (estimated based on aerial photos or sediment budget modelling), the impact of storm erosion for a given return period (estimated from coastal profile modelling or historical data) and long-term recession due to sea level rise (estimated by the Bruun rule [6]). This method produces a set-back line that is likely to be conservative, resulting in rather severe constraints on coastal zone development. For each of the 83 profiles, the cumulative distribution function of probability of coastal retreat in the future was derived, which fed into the determination of the associated EOSL
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