By studying the subtidal archaeology of Chichester Harbour, we can improve our knowledge of the pre-historic landscapes.

Geophysical survey (sub-bottom profiling)

A geophysical survey of the sub-tidal zone was undertaken by Titan Surveys Ltd in 2005, using a specially-adapted survey vessel. The survey showed that Chichester Channel, south of Bosham Channel, had been active for a prolonged period, with Holocene deposition mainly concentrated downstream in the estuary, with much thinner deposition up the creeks. This implied that the creeks were not significantly deeper now than at the beginning of the Holocene. In contrast, the survey showed that the mouth of the estuary had silted up considerably over the past 10,000 years and also that the margin of the main channel as it turned southward had migrated west over time. In Fishbourne Channel there was less evidence of sediment deposition than in Bosham Channel.

One of the most significant findings was that there was no evidence of a deep channel extending up Fishbourne Channel beyond Copperas Point, suggesting that only vessels with a relatively shallow draught would have been able to travel further north. In the Roman period, therefore, it is unlikely that ocean-going vessels could have reached Fishbourne Palace. The implication is that there could have been a Roman harbour at or near Copperas Point where goods for the Palace and beyond could have been offloaded.

The survey also highlighted the problems with interpreting data from such geophysical surveys. Excavation can test geophysical surveys on land, but this option is not as easy if the area of survey is underwater. Identifying Roman features in Fishbourne Channel is important because of the relationship with the Palace, yet no one knows what a Roman dredged channel would look like, for example, or what features would distinguish it from a natural channel.

Available reports
Desk based assessment of borehole and core information by Martin Bates 2005
Chichester Harbour geophysical survey by Titan Environmental Surveys 2005
Chichester Harbour geophysical and auger survey by Wessex Archaeology 2005
Fishbourne meadows watching brief by Wessex Archaeology 2006.