Case study: Applying ASMITA to UK estuaries

Introduction

Over 170 estuaries with a variety of physical characteristics, spatial extents and management issues dissect the coastline of the United Kingdom (Pontee & Cooper, 2005). Many have some form of nature protection designation and intertidal areas are particularly important for numerous species, including migrating birds. Intertidal areas provide important natural coastal defences, protecting the low lying land surround estuaries from flooding. Estuaries may also be used for recreational activities such as sailing, fishing and walking and are economically important as ports, fishing grounds and for aggregate extraction (Townend, 2002). The diverse uses and morphologies of estuaries can lead to complex and sometimes conflicting management demands. In order to manage estuaries effectively it is important to be able to predict how they are likely to change in the future, both to natural and anthropogenic forcing. This poster looks at historical morphological development of four UK estuaries and uses a model (ASMITA) to predict the maximum rate of sea-level rise each estuary can undergo before intertidal areas are lost completely.

Issues

Sea-level rise

Sea-level rise is predicted to accelerate over the 21st Century, with a global-mean rise of 9 to 88 cm, with the largest relative sea-level rise in the UK in the south (Hulme et al, 2002). As sea-level rises, the water volume of the estuarine channels increases, while the intertidal sediment volume decreases (Fig.1). With high rates of sea-level rise major changes in the morphology of the estuary may occur, including loss of intertidal areas, leading to habitat loss, shoreline erosion and flooding of low lying areas around estuaries.

The Model

ASMITA (Aggregated Scale Morphological Interaction between Inlets and Adjacent coast, Stive et al, 1998) represents the estuary as a series of morphological elements (Fig.2). Each element evolves towards an empirically derived equilibrium volume and interacts with adjacent elements by sediment exchange. ASMITA was calibrated to reproduce historic estuary evolution for four UK estuaries. Calibrated models were used to predict the maximum rate of sea-level rise (SLRCRIT) each estuary can undergo before intertidal areas are lost.