Long-term morphological change in the Ribble Estuary, northwest England

Abstract

Morphological change in the Ribble Estuary (northwest England) has been studied, using bathymetric charts, topographical surveys and remote sensing data. A sediment budget has been prepared from the analysis of these data. The results reveal a net accretional trend over the last 150 years. The main channels experienced major infilling. Sediment also accumulated in higher parts of the intertidal zone (salt marshes and sand banks), while the sediment volume in the lower intertidal zone remained essentially the same. There were both zones of net erosion and deposition in the outer estuary, with a small net gain in subtidal sediment volume. Infilling, associated with major morphological change, was accelerated in the nineteenth century and early twentieth century, principally as a result of human activities. The triggering factors for increased sedimentation were embankment construction and reclamation after 1810, which progressively reduced the intertidal area, tidal prism and current velocities within the estuary. Additionally, construction of a trained channel between 1847 and 1910 to secure navigation, and maintenance of this channel by dredging, concentrated the ebb flow in this overdeepened channel and reduced periodic scour over the sand banks on both sides, enhancing sedimentation. Thus, the effects of human activities have outstripped those of changes in natural forcing factors on the morphological development in the area.