Skip to main content


Title: Wave attenuation over saltmarsh surfaces August 1996
Author: T. Spencer
Author: I. Moeller
Document Type: Monograph
Annotation: EA additional title info: wave attenuation over salt marsh surfaces
Over large areas of lowland Britain, agricultural land and settlements are protected from flooding by walls, embankments and fronting salt marshes. Salt marshes are an important asset for flood defence because they act as a buffer which helps dissipate wave and tidal energy. This has implications for the cost of defence structures. This project provides the first comprehensive datasets on wave energy dissipation over open coast intertidal salt marsh surfaces on the UK coastline. This report describes the measurement of water level variations using a pressure gauge methodology, and the processing of these records for the extraction of wind wave statistics. Field measurements were made at Stiffkey, North Norfolk for a range of tidal and meteorological conditions across a 300m sandflat salt marsh transect. Over the sandflat, wave height decreased on average by ca. 15 per cent and across the salt marsh by 58 per cent. Total spectral energy loss was 26 per cent and 80 per cent respectively. Preliminary mathematical modelling of wave attentuation showed that shoaling, viscous friction and percolation gate negligible controls on attenuation and that friction from surface roughness accounts for at least 70 per cent of wave energy dissipation over the sandflat and at least 90 per cent over the salt marsh. Wave attenuation can be accurately reproduced by a model on the basis of known surface slope, grain size of surface sediments, incident wave and water depth conditions and estimated friction factors. The replacement of 200 m of salt marsh by sandflat would, for example, result on waves heights circa 78 per cent higher at the landward margin. A future wave attenuation research programme should seek to provide a series of guidelines for Field managers to rapidly assess salt marsh characteristics in relation to wave attenuation potential at individual sites and to evaluate the likely flood defence impacts of natural and anthropogenic modification to the salt marsh environment.
Publisher: National Rivers Authority
Publication Date: 1996
Publication Place: Peterborough
Subject Keywords: Flood controlFlood defence structuresCoastal managementSalt marshesModellingField experimentationWater levels
Geographic Keywords: North Norfolk catchmentNorfolk
Extent: 10
Total file downloads: 41

Download PDF    Display PDF in separate tab