[1] A coupled storm surge and overland flow model is used to simulate extreme coastal flooding of Canvey Island, a dense urban area located at the mouth of the Thames Estuary, U.K. The flood model is based on a shock-capturing numerical scheme and resolves the terrain and buildings of the study area with high-resolution topographic data. Repeat simulation is used to propagate uncertainties in model inputs and parameters through to uncertainties in model outputs, and the main sources of uncertainties are described. The greatest uncertainties originate from the forcing inputs to the flood model, including coastal water levels and sea defense failures, rather than its internal boundaries, such as the model terrain and bottom friction. This is consistent with studies in rural and semideveloped floodplains and reflects a combination of high sensitivity to, and uncertainty in, the forcing inputs. However, other numerical and physical variables introduce significant uncertainties, of which many are specific to, or altered by, the urban floodplain. In particular, model predictions are sensitive to the spatial resolution (Ds) of the numerical grid. This includes the effects of Ds on boundary features (walls, hedges, etc.), which are described in the bed friction coefficient, and on the representation of buildings, which are described in the model terrain. Finally, model predictions are integrated across multiple combinations of breach width and location to explore the ''relative'' hazards (i.e., spatial and temporal variations in hazard) associated with the floodplain geography.
Barrier island' refers to a diverse collection of coastal landforms that often support substantial human populations, critical infrastructures, and ecosystems. Globally, many coastal barriers are experiencing climatically altered environmental forcing coupled with increasing anthropogenic pressures. This paper undertakes high resolution shoreline change analysis to reveal how Blakeney Point, a mixed sandy-gravel barrier located on the UK's East Coast, has evolved over centennial, decadal and event timescales. We seek to establish the implications of barrier evolution, under contrasting management regimes, for present erosion and flooding hazards. Interrogating a series of alternative shoreline proxies reveals a series of interdependent behaviors. Over the 130-year period of study, Blakeney Point is shown to be rolling landward at a mean rate of 0.60 m a-1. Assuming continued landward retreat over the coming decades, future flood-generating storm events will encounter more landward shoreline positions than today. Superimposed on this trend, we observe the presence of alongshore migrating erosional hotspots which give rise to unpredictable morphologies at any given location on the spit. Finally, we find that instances of barrier setback are driven by individual storm events, which makes barrier retreat both highly variable and discontinuous in time and space. This is illustrated by the presence of overwash, particularly along stretches of the barrier that have experienced a recent shift in management regime towards a non-interventionist approach.
Salt marshes are globally distributed, vegetated intertidal wetlands and marsh edge erosion is common on many shores. To understand how and why marsh edge erosion occurs, the response of salt marsh substrates to applied shear and vertical stress must first be quantified. This response is likely influenced by marsh substrate biological, geochemical and sedimentological composition. However, currently there is little systematic research into the between‐marsh variability in these properties and how they affect both marsh edge erosion processes and the ability of a marsh to maintain its position vertically within the tidal frame. This paper compares two marshes of contrasting sedimentology at Tillingham marsh, East England and Warton marsh, Northwest England. Soil shear strength and compressibility are determined by applying geotechnical methods to determine marsh resistance to shear and vertical effective stresses. This research was able to isolate the influence of roots on substrate shear strength in a three‐dimensional sample. In response to vertical effective stress, both the expected displacement magnitude and the vertical recovery potential of a marsh substrate are affected by past stress conditions on the marsh, particularly those resulting from desiccation. The substrate response to vertical effective stress also influences substrate shear strength through the effect of consolidation on the void ratio (or bulk density). We present evidence for the connection between marsh composition and substrate behaviour under applied stress. The results shed light on potential determinants of marsh resistance to edge erosion, which is ultimately essential for the informed implementation of both nature‐based coastal flood defences and coastal restoration schemes.
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