Environment Intertidal mud runnels in the Severn Estuary Description of Research Multiple linear, parallel runnels typically 1 to 2 metres apart, running parallel to tidal currents and cut into mudflats and in the muddy bottom of the continental shelf, have been described widely around the coast of the UK and elsewhere. Although common they are little-studied; how these features are formed and maintained was unknown before this investigation. Are they erosional and depositional, or both? What are their hydrodynamic and sedimentological properties? What practical applications are there for understanding of these features? These questions were addressed using state-of-the-art field and laboratory equipment . Application of Research A model of hydrodynamic control by helical flow and sedimentological response has been developed, for the first time. Quantified conditions of bed roughness, flow speeds and suspended sediment regime can be extracted which aid understanding of mudflat dynamics and substratum stability indicators. Results can inform the management of the sediment fauna as a food source for conservation of wading birds and aid in understanding of the impact of estuarine barrages on sediment dynamics. Additional applications to exploration of the continental shelf and the interpretation of possible water-related landforms on Mars Publications: Carling et al. 2009, Continental Shelf Research, Impact factor: 2.136 Williams et al. 2008, Estuarine, Coastal and Shelf Science, Impact factor: 2.072 for further information please contact: P. A. Carling1, J.J. Williams2, C.L. Amos1, P.S. Bell3 & I. Croudace1 1Southampton University, 2Plymouth University, 3POL, Liverpool