Inhabiting the Shifting Edge: Increasing the Adaptive Capacity of Coastal Sand Spit Communities in a Changing Climate

<p>This masters thesis uses urban design and landscape architecture to investigate the role of open spaces in increasing the adaptive capacity of New Zealand's sand spit communities in the face of climate related change. In order to respond to potential climate related change, the design of open spaces should acknowledge the crucial role that natural processes and ecosystems play in protecting coastal environments. Urban design and landscape architecture have the potential to encourage interaction at the interface of the social and ecological systems within these coastal communities. The design of public open space can encourage more sensitive development patterns and increase the communities' awareness of coastal processes. These spaces can become the focus of social capital building while ensuring the environment has the capacity to absorb potential climate related changes. This research focuses on three sand spit resort communities on the east coast of New Zealand's North Island. Through a series of design studies, a range of strategies are proposed and tested in response to the potential impacts of climate change and sea level rise. The exclusive and expensive coastal development trend is augmented to provide for all potential beach users. Diversification in both the users, and types of use, in these coastal areas will increase the social capital investment and awareness, further building the adaptive capacity of the spit system.</p>

Inhabiting the Shifting Edge: Increasing the Adaptive Capacity of Coastal Sand Spit Communities in a Changing Climate

<p>This masters thesis uses urban design and landscape architecture to investigate the role of open spaces in increasing the adaptive capacity of New Zealand's sand spit communities in the face of climate related change. In order to respond to potential climate related change, the design of open spaces should acknowledge the crucial role that natural processes and ecosystems play in protecting coastal environments. Urban design and landscape architecture have the potential to encourage interaction at the interface of the social and ecological systems within these coastal communities. The design of public open space can encourage more sensitive development patterns and increase the communities' awareness of coastal processes. These spaces can become the focus of social capital building while ensuring the environment has the capacity to absorb potential climate related changes. This research focuses on three sand spit resort communities on the east coast of New Zealand's North Island. Through a series of design studies, a range of strategies are proposed and tested in response to the potential impacts of climate change and sea level rise. The exclusive and expensive coastal development trend is augmented to provide for all potential beach users. Diversification in both the users, and types of use, in these coastal areas will increase the social capital investment and awareness, further building the adaptive capacity of the spit system.</p>

Observing and Predicting Coastal Erosion at the Langue de Barbarie Sand Spit around Saint Louis (Senegal, West Africa) through Satellite-Derived Digital Elevation Model and Shoreline

Coastal erosion at Saint Louis in Senegal is affecting the local population that consists of primarily fishermen communities in their housing and their access to the sea. This paper aims at quantifying urban beach erosion at Saint Louis, Senegal, West Africa which is located on the northern end of the 13 km long Langue de Barbarie sand spit. The coastal evolution is examined quantitatively over a yearly period using Pleiades sub-metric satellite imagery that allows for stereogrammetry to derive Digital Elevation Models (DEMs). The comparison with ground truth data shows sub-metric differences to the satellite DEMs. Despite its interest in remote areas and developing countries that cannot count on regular surveys, the accuracy of the satellite-derived topography is in the same order as the coastal change itself, which emphasizes its current limitations. These 3D data are combined with decades-long regular Landsat and Sentinel-2 imagery derived shorelines. These observations reveal that the sand spit is stretching, narrowing at its Northern part while it is lengthening downdrift Southward, independently from climatological changes in the wave regime. A parametric model based on a stochastic cyclic sand spit behaviour allows for predicting the next northern opening of a breach and the urban erosion at Saint Louis.

Recent Shoreline Changes Due to High-Angle Wave Instability along the East Coast of Lingayen Gulf in the Philippines

A small perturbation on the shoreline may develop under high-angle wave conditions, resulting in the formation of sand spits along the shoreline. Serizawa et al. explained the development of sand spits caused by the instability mechanism using the BG model (a model for predicting 3-D beach changes based on Bagnold’s concept). However, examples of the development of sand spits caused by this mechanism in the field are limited in number. Lingayen Gulf in the Philippines has a large aspect ratio, so shoreline instability occurs along the coastline, significantly affecting the shore protection along the coast. In this study, the shoreline instability along the river delta coasts around the Balili and Aringay Rivers flowing into Lingayen Gulf and a sand spit were investigated using satellite images together with field observation. The shoreline changes observed south of the Aringay River mouth were compared with those observed in a previous study on the development of a sand spit by San-nami et al. The rate of longshore sand transport to form a sand spit at Santo Tomas in Lingayen Gulf was estimated to be approximately 1.3 × 105 m3/yr, which is in good agreement with the value measured on the Shimizu coast in Suruga Bay, with a comparable aspect ratio of 1.2 relative to 1.3 in Lingayen Gulf. It was concluded that shoreline undulations have evolved downcoast of two river deltas owing to high-angle wave instability along the east coast of Lingayen Gulf and the formation of a sand spit has occurred. A soft measure, such as sand bypassing, would be better to be adopted along the coasts in Lingayen Gulf instead of hard measures against erosion, to prevent rapid expansion of an artificial, protected coastline.

Assessment of a Sand Spit Morphodynamics Under Extreme Flood Events

&lt;p&gt;Spits are landforms that present a complex morphology, which depends on currents, waves, sediment transport, tidal range and anthropic-induced changes. Their position and shape is subject to extreme events like flood river discharges and storms. They can also respond to processes that take place at larger time scales, as plate tectonics, sea level rise or even climatological patterns with teleconnections all over the world, as the well know North Atlantic Oscillation (NAO) or El Ni&amp;#241;o-Southern Oscillation (ENSO). This is the case of the Douro river mouth sand spit located on the northern coast of Portugal. This naturally dynamic sand spit, which has moved landwards over the past decades, has caused frequent nuisance to navigation, affecting width and depth of the navigation channel. Therefore, a breakwater was constructed in an attempt to stabilise the sand spit and the estuary inlet.&lt;/p&gt;&lt;p&gt;Validated hydrodynamic numerical models (openTELEMAC-MASCARET and Delft3D) of the Douro river estuary have demonstrated ability to accurately describe the estuarine hydrodynamic patterns and water elevation under extreme flood conditions. Model results showed that for higher river flow discharges the sand spit is partially inundated.&lt;/p&gt;&lt;p&gt;In this work a morphodynamic model (Delft3D) of the estuary was implemented to assess both the morphodynamics of the sand spit under extreme events, including the effect of sea level rise due to climate change, and the variation of extreme water levels along the estuary due to spit erosional processes that can occur during flood events.&lt;/p&gt;&lt;p&gt;Preliminary results show that the sand spit will be locally eroded for the higher river flood discharges, forming a two-secondary-channels system, with one channel located near the breakwater&amp;#8217;s southern extremity and the other, narrower, near the south bank. Associated with these two channels, two depositional bars will be formed in front of the channels at the coastal platform. However, the inner immersed sand spit will be suffering a sedimentation process for all of the simulated scenarios. This way, neither the river mouth discharge conditions nor the water levels inside the estuary will suffer significant changes according to the simulated scenarios.&lt;/p&gt;&lt;p&gt;These results will be complemented with further analyses considering the sediment size influence, tidal level, storm surge, sea level rise and river flood discharges.&lt;/p&gt;&lt;p&gt;Acknowledgements: To the Strategic Funding UIDB/04423/2020 and UIDP/04423/2020 (FCT and ERDF) and to the project EsCo-Ensembles (PTDC/ECI-EGC/30877/2017, NORTE 2020, Portugal 2020, ERDF and FCT). The authors also want to acknowledge the data provided by EDP and IH.&lt;/p&gt;