This project revealed that the physical cohesion imparted by cohesive clay within mixed sand-mud substrates has a profound influence on the dimensions and dynamics of sandy bedforms such as ripples, dunes and bars. It also identified the significant role that biological extracellular polymeric substances (EPS) has in generating cohesion and influencing bed form dynamics. Results showed that bedform height, length and steepness decrease linearly with clay and biological content; existing equations that predict bedform dimensions significantly over-predicted those dimensions for all but the smallest clay contents examined. The profound effect substrate clay content has on bedform dimensions has a number of important implications for interpretation in a range of modern and ancient environments, and offers a step-change in our understanding of bedform formation and dynamics in these environments. In particular, project outcomes will help: 1. improve engineering predictions of bedform dimensions, which will help guarantee engineering success when extracting sediment or building structures in and on the sea bed (e.g. pipelines, wind turbines, tidal barrages, oil platforms); 2. provide a vehicle for facilitating more reliable palaeo-environmental reconstructions; and 3. improve confidence in reconstructing and predicting the porosity and permeability of sedimentary rocks in cores and outcrops. These latter outcomes bring significant benefits to the hydrocarbon industry.