NATURAL DESIGN AND MANAGEMENT OF AN ESTUARY MOUTH SYSTEM

Abstract

Estuaries often are the focus of both man-made infrastructure and valuable flora and fauna. Sand spits are common at the mouth of estuaries, and are one of the key features that influence hydrodynamics and geomorphology in estuaries. The Environment Agency has delivered a long term coastal management scheme, which has recently been designed and built, to manage the Dawlish Warren sand spit at the mouth of the Exe Estuary, in south Devon, UK. This scheme is designed to - Protect 3,000 properties and critical national infrastructure from flooding. - Restore 2km of internationally designated (SAC) dune and associated ecology continue protection to the SPA bird assemblages in the Exe Estuary. - Provide a flexible way forward through this century for the sand spit to be managed in a sustainable and balanced manner. The Exe Estuary is macrotidal with a range of 4m, and main tributary inflows of the order of 20-400m3/s. Dawlish Warren sand spit covers three quarters of the estuary mouth width, sheltering the estuary from the coastal wave and tide climate. Consequently, the inestuary extreme wave heights are limited to less than 1.1m, with storm surges of up to 1-2m. The estuary exhibits high tidal velocities through its mouth, with flood/ebb tidal deltas and offshore banks present. The sand spit has breached around 13 times over the last two centuries, prompting reactive construction of concrete, rock armour and