Sonar-based investigations into the morphology and sedimentology of northern Weymouth Bay by the author in 198611987 revealed the presence of a variety of topographic forms including surficial sediment provinces and bedforms, extensive near shore boulder spreads and structurally controlled exposed bedrock The nearshore boulder spreads are considered to be static, with little present day terrestrial or submarine input Present day coastal configuration and the presence of these localised boulder spreads may indicate the likely effects of fluctuating sea levels during the past 10000 years Such fluctuations have caused periodic exposure of extensive tracts of sea floor, and the marked marine transgression that followed the retreat of the Devensian ice sheets resulted in rapid coastline erosion and cliffline retreat The rock debris flows and boulder fields produced have since been submerged by post-glacial nse in sea level
Additional side-scan sonar investigations (1996) have revealed interesting structural features which deserve further investigation, and are shedding new light on the geomorphological development of embayments along the Dorset coast, in particular, Lulworth Cove and Worbarrow Bay The data from the surveys 1s also being considered for regional marine resource management and conservation purposes The current paucity of physical and benthic data on shallow coastal waters in general means that resource managers have little reliable background data upon which to make decisions as to the best use of coastal seabed resources Remotely sensed acoustic information such as that described in this study lends itself well to broadscale habitat mapping, the assessment of commercially and biologically interesting features, environmental assessment applications and can also be used effectively to raise community awareness and involvement in marine environmental management strategies
Initially developed for military use, side scan sonar is now a standard technique for navigational charting and commercial surveys of the seabed as it gives wide coverage allowing for detalled investigation of areas between sounding lines As a rapid survey technique the wlde variety of sonar applications has been realised in the commercial world, in particular, Inspection of engineering structures, mineral resource exploration and exploitation, location of waste dumping grounds, surveying routes for communication, cables and pipelines and salvage operations However, repeatable side scan sonar surveys with accurate navigational control carried out by commercial hydrographers rarely warrant publication, despite their significance to the collection of environmental data
Repeated surveys can indicate the stability of the seafloor, a feature of great importance to cable and pipeline routering, drilling rig and platform positioning, whilst the presence and arrangement of bedforms can provide an indication of the magnitude and frequency of hydrodynamic forces The permanence of man-made features such as wrecks or scar marks from trawling and dredging gear may indicate the lack of bottom mobility and the amount of damage being done to benthic communities
Inshore features and deposits very close to the shore have largely been ignored by coastal geomorphologists and commercial interests, although they have the potential to be mapped to provide a wealth of data for environmental assessment and resource management purposes, whilst detailed interpretation may help further the understanding of coastline evolution and present day sediment transport pathways
