No abstract

During the 10 yr, 1970–80 a variety of field measurements using some new techniques have allowed the distribution of muddy sediment in the Severn Estuary and Inner Bristol Channel to be defined. Based on these measurements, a behavioral model has been adopted comprising mobile and stationary suspensions, and settled mud. The regional distribution of mobile suspensions shows a suspended solids front located along the main channel axis with the more turbid water on the southern, English, side. At maximum current velocities on spring tides, vertical suspended sediment profiles are homogeneous. As velocity decreases, a stepped structure develops due to settling, which is then remixed on the next accelerating semidiurnal tidal phase. Over the lunar timescale these steps become more stable, eventually settling to the bed. The steps are unrelated to salinity, temperature, grain-size, or mineralogy. On neap tides, layered, acoustically detectable stationary suspensions, which occasionally consolidate to form settled mud, develop from the mobile suspensions. An idealized "three-zone" model has been devised characterizing the structures developed in the mobile suspensions.Key words: Severn Estuary, vertical profiling, siltmeter, densimeter, suspended solids, fronts, stratification

Modern trends, increases in ship size, improved cargo handling capability, sea level rise and erosion threats to low-lying land, undesirable attributes of certain traditional mud dredging and disposal practices,

No abstract

This paper examines the similarities and contrasts between environmental and water quality changes caused by the 1966 tidal power barrage at La Rance in North Brittany, France and those expected to result from construction of a tidal power barrage in the Severn estuary in the UK. Over the 40-year period since the opening of La Rance, a great deal of knowledge has been accumulated concerning the operation of such schemes and the way water quality and ecosystems have altered. Knowledge gained from experiences at Rance is consequently of great benefit in predicting the effects of the proposed Severn barrage. The nature of the changes anticipated in the Severn estuary is thus unambiguous, but whether this would make the estuary better or worse is a matter of perception. As at Rance, it would be different.