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Densely populated south-east coast of India is susceptible to disasters such as tsunami, coastal flooding storm-surge and shoreline erosion. Apart from episodic events, the gradual sea-level rise (SLR) has got more attention to coastal researchers recently relating to the potentially impacted coastal zone, its anthropogenic/environment associations, and the possible future scenarios. Global average SLR rate has increased in recent decades from 1.7 mm year−1 1901 to 2010, 3.1 mm year−1 from 1993 to 2003 and 3.12 mm year−1 from 1993 to 2012. The present study is an aim to assess the impact of future sea-level rise along Pondicherry—Chidambaram coast using Bruun Rule and Modified Bruun Rule. Eight satellite-derived data sets were used to study the shoreline change trends during 1990–2015. 25 years of shoreline change trend reveals that ~ 49% of the coastline is under erosion. Shoreline retreat to an increase in local sea level was also mapped by Bruun Rule. Bruun Rule has some limitations, and hence Modified Bruun Rule was used to analyze the inundation factor. The horizontal inundation of the study area was estimated as ~ 1.1 km (Bruun Rule) and ~ 1.6 km (Modified Bruun Rule). The impacts of SLR in the study area were determined by integrating inundation data with geomorphological and land use/land cover data. The study reveals that about 16.08 sq.km area of geomorphological features is likely to be highly affected, while 17.5 sq.km of the area likely to be affected on land use/land cover features. This study provides an interactive means to identify the vulnerable zone. The output maps can be used to visualize the affected areas spatially.

Current models for long-term shoreline response to sea-level rise ( SLR ), such as the Bruun Rule, have significant limitations as they fail to account for site−specific processes and often misrepresent the influence of dunes, rocky platforms, or estuarine sediment sources and sinks. Here we integrate four previously published formulations into the Composite Shoreline−Retreat Workflow (CoShReW), a compound sequence that can be adapted or expanded according to data availability. The workflow needs several topo−bathymetric variables and shoreline data to calculate the expected shoreline retreat. It is distributed as open source code (GitHub) to guarantee reproducibility. As a first study-case, CoShReW is applied to 1281 cross-shore profiles along the highly heterogeneous Andalusian coast (SW Spain). To capture this coastal variability, we conduct a detailed characterization along the study area using Principal Component Analysis (PCA) of significant wave height, peak period, tidal range and sediment grain size, defining four different profile types. Resulting shoreline retreat projections differ by more than an order of magnitude among these classes, with dune elevation and estuary capacity emerging as dominant controls in dissipative sectors, and historical erosion rates prevailing on reflective or cliff−backed shores. Sensitivity analysis quantifies the relative importance of the governing variables for each profile type, indicating where local data collection would most improve forecast confidence. The present study findings reveal that local geomorphology can equal or exceed SLR as a driver of shoreline change in some habitats, emphasizing the need to consider and integrate site-specific adaptation measures in long-term shoreline retreat assessments for complex coastal environments.

In the current practice of sandy shoreline change assessments, the local sedimentary budget is evaluated using the sediment balance equation, that is, by summing the contributions of longshore and cross-shore processes. The contribution of future sea-level-rise induced by climate change is usually obtained using the Bruun rule, which assumes that the shoreline retreat is equal to the change of sea-level divided by the slope of the upper shoreface. However, it remains unsure that this approach is appropriate to account for the impacts of future sea-level rise. This is due to the lack of relevant observations to validate the Bruun rule under the expected sea-level rise rates. To address this issue, this article estimates the coastal settings and period of time under which the use of the Bruun rule could be (in)validated, in the case of wave-exposed gently-sloping sandy beaches. Using the sedimentary budgets of Stive (2004) and probabilistic sea-level rise scenarios based on IPCC, we provide shoreline change projections that account for all uncertain hydrosedimentary processes affecting idealized coasts (impacts of sea-level rise, storms and other cross-shore and longshore processes). We evaluate the relative importance of each source of uncertainties in the sediment balance equation using a global sensitivity analysis. For scenario RCP 6.0 and 8.5 and in the absence of coastal defences, the model predicts a perceivable shift toward generalized beach erosion by the middle of the 21st century. In contrast, the model predictions are unlikely to differ from the current situation in case of scenario RCP 2.6. Finally, the contribution of sea-level rise and climate change scenarios to sandy shoreline change projections uncertainties increases with time during the 21st century. Our results have three primary implications for coastal settings similar to those provided described in Stive (2004) : first, the validation of the Bruun rule will not necessarily be possible under scenario RCP 2.6. Second, even if the Bruun rule is assumed valid, the uncertainties around average values are large. Finally, despite these uncertainties, the Bruun rule predicts rapid shoreline retreat of sandy coasts during the second-half of the 21st century without strong réductions of greenhouse gas emissions.

At the present time, coastal changes are having a major impact in many regions of the world. Relative sea-level rise would significantly contribute to physical changes in coastal cities. Predicting the magnitude of coastal changes such as erosion and land loss is essential for a better understanding of the impacts on environment and coastal communities, as well as for management, planning and protection in coastal areas. An increase in the rate of sea-level rise and range of potential impacts, including flood and coastal erosion, will likely affect the wide East Coast of Peninsular Malaysia and would cause serious disturbance for sandy beaches, particularly in Kuala Terengganu. This study attempts to predict the future erosion in the coastal area of Kuala Terengganu, Malaysia. The shoreline erosion as a result of sea-level rise was predicted using the Bruun Rule. This is the best known model that provides a rate of shoreline erosion under sea-level rise for sandy beaches. The result of Bruun Model is analysed and presented in a Geographic Information System (GIS). Results indicate an upward trend in the future for erosion in this coastal area. The highest erosion rate is 3.20 m/year and the most sensitive zones are expected to be around Universiti Malaysia Terengganu (UMT) and left bank of Kuala Terengganu from 2015 to 2020. It also can provide the basic information that decision makers need when they are planning any new activity within the coastal area.

Long-term (>decades) coastal recession due to sea-level rise (SLR) has been estimated using the Bruun Rule for nearly six decades. Equilibrium-based shoreline models have been shown to skillfully predict short-term wave-driven shoreline change on time scales of hours to decades. Both the Bruun Rule and equilibrium shoreline models rely on the equilibrium beach theory, which states that the beach profile shape equilibrates with its local wave and sea-level conditions. Integrating these two models into a unified framework can improve our understanding and predictive skill of future shoreline behavior. However, given that both models account for wave action, but over different time scales, a critical re-examination of the SLR-driven recession process is needed. We present a novel physical interpretation of the beach response to sea-level rise, identifying two main contributing processes: passive flooding and increased wave-driven erosion efficiency. Using this new concept, we analyze the integration of SLR-driven recession into equilibrium shoreline models and, with an idealized test case, show that the physical mechanisms underpinning the Bruun Rule are explicitly described within our integrated model. Finally, we discuss the possible advantages of integrating SLR-driven recession models within equilibrium-based models with dynamic feedbacks and the broader implications for coupling with hybrid shoreline models.

Ritphring, S.; Somphong, C.; Udo, K., and Kazama, S., 2018. Projections of future beach loss due to sea level rise for sandy beaches along Thailand's coastlines. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 541–545. Coconut Creek (Florida), ISSN 0749-0208. Coastline recession caused by sea level rise due to climate change has become one of the most significant issues worldwide. Thailand's coastlines is also likely to face erosion, especially in the low-lying areas, and its future projection due to sea level rise is necessary. This study compiled a database of beach characteristics, including grain size diameter, beach slope and beach width, to assess the projections of future beach loss along Thailand's coastlines against sea level rise scenarios of the Coupled Model Intercomparison Project Phase 5 (CMIP5) in 2081–2100, relative to a reference period 1986–2005 by using the Bruun rule. Future national beach loss rates were projected to be 45.8% for RCP2.6, 55.0% for RCP4.5, 56.9% for RCP6.0 and 71.8% for RCP8.5. In addition, the rate against the sea level scenarios projected by each CMIP5 model for RCP4.5 ranges from 49.1% for MPI-ESM-LR to 73.4% for MIROC-ESM-CHEM. Based on the current beach situation, sandy beaches in 8 and 23 out of 51 zones will disappear for RCP2.6 and RCP8.5, respectively. These findings will help governors and stakeholders develop adaptation strategies against beach loss due to sea level rise.

Sharaan, M. and Udo, K., 2020. Projections of proper beach nourishment volume as an adaptation to beach recession based SLR along the Nile Delta coastline of Egypt. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 637-642. Coconut Creek (Florida), ISSN 0749-0208. Beach loss and shoreline recession-based sea-level rise (SLR) is considered one of the most critical coastal issues worldwide. The Nile Delta coastline of Egypt is categorized as a low-lying and sandy coastal area that is prone to impacts of SLR. Beach nourishment is considered one of the most common adaptation strategies for erosion mitigation. Sandy beaches have a significant role in tourism, recreational purposes, and disaster prevention. The projection of proper beach nourishment volume (fill density) as an adaptation to beach loss-based SLR and land subsidence using the Bruun rule were investigated along the Nile Delta coastline of Egypt. The ensemble-mean regional SLR data included Representative Concentration Pathway (RCP) scenarios. Three main steps were applied to estimate the required proper beach nourishment volume. First, the future beach width due to SLR was estimated, and vulnerable areas to shoreline retreat were identified. Second, the targeted beach width to be protected in terms of coastal conservation, tourism purposes, and maintenance of the present beach was proposed based on Egyptian polices. Third, proper sand beach nourishment volume was estimated for four RCP scenarios, when local land subsidence is considered. The results show that the proper volume of beach nourishment required to maintain the beach width along the whole Nile Delta coastline varies from 24.8×106 to 145.5×106 m3 in 2100, with respect to RCP2.6 and RCP8.5, respectively.

Densely populated coastal zones of India are highly exposed to natural environment. These are impacted by episodic natural events, continuous coastal process, gradually rising sea levels and coexisting human interventions. The present study is an attempt to assess the implication of the sea level rise and coastal slope in the coastal erosion for entire mainland of India. In this regard, two methods were employed to estimate the shoreline change rate (SCR): (1) satellite-derived SCR using the Landsat TM and ETM+ acquired during 1989–2001 and (2) SCR derived by Bruun Rule using the parameters coastal slope and sea level trend derived from satellite altimetry. Satellite-derived SCR has been compared with the shoreline change estimated based on Bruun Rule, revealing a better agreement with each other in terms of trend. Peaks of shoreline retreat calculated using Bruun model and satellite-observed SCR offset by 25–50 km. Offset in these peaks was observed due to net drift towards north in the east coast and south in the west coast of India, revealing the applicability of the Bruun Rule along the Indian coast. The present study demonstrates that coastal slope is an additional parameter responsible for the movement of shoreline along with sea level change. The results of satellite-derived SCR reveal the highest percentage of erosion along West Bengal coast with 70% followed by Kerala (65%), Gujarat (60%) and Odisha (50%). The coastlines of remaining states recorded less than 50% of coasts under erosion. Results of this study are proving critical inputs for the coastal management.

Takeda, Y. and Udo, K., 2020. Effect of spatial resolution on nationwide projection of future beach loss rate in Japan. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1310–1314. Coconut Creek (Florida), ISSN 0749-0208 The amount of sea-level rise (SLR) changing along with climate change greatly affects beaches. Projecting nationwide future beach loss requires datasets having sufficient spatial resolutions; however, there has been no case study for an appropriate level of spatial resolution. The present study aims to clarify the effect of spatial resolution on the nationwide projection of future beach-loss rates. We divided the 77 coastal zones specified with reference to Japan's Coast Act, into 586 coastal zones set by the fundamental plan of coastal preservation formulated by prefectures, whose beach length was further separated by nearly every 10 km, resulting in 886 coastal zones. Regarding these 77, 586, and 886 zones, we projected future beach-loss rates in Japan in response to SLR based on the RCP2.6, RCP4.5, RCP6.0, and RCP8.5 scenarios using the Bruun rule. Our projection results showed that the beach-loss rates of the 886 zones decreased by about 6% at maximum compared to those of the 77 zones. The projection results derived from the 586 and 886 zones were nearly the same. This study indicates that higher spatial resolutions less than 20 km in beach length are desirable to project future beach loss in Japan on a nationwide scale.

The Bruun rule, widely used to predict transgression due to sea level rise on decade to century timescales based on a fixed nearshore profile, neglects the influence of inland topography and substrate lithology, leading to physically unreasonable predictions on longer timescales. We use a new approach, the shoreline Exner equation, to model shoreline transgression on wave‐dominated coasts over timescales of decades to millennia. Our results show that interactions between nearshore processes and inland topography, neglected by Bruun‐style models, drive morphologic evolution which modulates shoreline retreat. Analytical solutions suggest that while short‐term shoreline retreat will sometimes follow the Bruun rule, long‐term transgression will always follow the slope of the inland topography. Moreover, our results show that the slope of the inland landscape, relative to the nearshore slope, exerts a first‐order control on coastal morphology, such that steep coasts tend to form cliff‐backed beaches while gentle coasts tend to form barrier island‐lagoon systems. However compositional variations between the inland landscape and nearshore system can alter this pattern.