Understanding the effects of seawall construction using a combination of analytical modelling and remote sensing techniques: Case study of Fansa, Gujarat, India

Abstract

The effect of seawall on the adjacent beaches and coastal dynamics has not been well documented in literature. The purpose and function of coastal structures, especially seawalls, have often been misunderstood, as in some cases, seawalls lead to coastal erosion, contrary to protecting the shoreline for which they are generally constructed. Seawalls have been reportedly causing changes in the near-shore process, specifically the sediment dynamics by affecting the onshore/ offshore and, to some extent, the longshore sand transport. Therefore, it becomes imperative to understand the effect of seawalls on the adjoining beach to make sure more informed decisions are made on their installation. This article discusses the effects of seawall construction along the coast of Fansa, South Gujarat, India. A numerical model has been used to estimate the wave parameters along the selected coast, the results of which are subsequently utilized in an analytical model (parabolic shape model) to predict the end-wall effect. Independently, remote sensing datasets of CARTOSAT 1 with spatial resolution of 2.5 m are used to understand the shoreline change dynamics in this region, post-construction of this seawall. It is found empirically that the net longshore sediment transport rate is approximately 1.9 Mm 3 per year along the coast. The results of the analytical model predict a maximum landward erosion of about 20 m and an alongshore erosion of 200 m on the down-drift side of the seawall. These estimations agree with those obtained by the remote sensing-based analysis, which estimates an erosion of approximately 40 m by the year 2014.

Advances in Numerical Reynolds-Averaged Navier–Stokes Modelling of Wave-Structure-Seabed Interactions and Scour

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“…The long-term stability of the shoreline depends on the balance between the LST and sediment characteristics at wave breaking (Longuet-Higgins, 1970a, b;Komar and Inman, 1970;USACE, 1984;Kamphuis, 1991;Bayram et al, 2007). Because a new shoreline planform induced by down- drift erosion may reach a stable condition, it is imperative to assess its equilibrium status using an appropriate model, empirical and/or numerical (Balaji et al, 2017). Among the empirical models available for embayed beaches, which include a logarithmic spiral (Krumbein, 1944;Yasso, 1965), a parabolic bay shape model (PBSE; Hsu and Evans, 1989) and a hyperbolic tangent model (Moreno and Kraus, 1999), only the parabolic model is derived for the static equilibrium planform (SEP).…”

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