Palaeolothic and mesolithic - Before 5,000 BC
Palaeolithic hand axes, Mesolithic footprints and stone tool scatters recovered from the foreshore indicate the presence hunter-gatherer groups present before the introduction of farming. Just outside the estuary, at Westward Ho! in the Bristol Channel evidence of reed burning and tree burning close to settlements make it probable that humans were using fire to influence their environment, perhaps to encourage favourable grazing for their quarry.
Sea level rise has been 60 metres in the last 10,000 years, so the estuary these people knew was very different to our own. Imagine Flat Holm island as a hill, rising up above a vast area of marshy land, our hunter-gather ancestors using it as a lookout to spot animals to hunt, or as high ground to escape to in times of flood.
Campsites from these people are preserved in the alluvium and peat. Peat is especially fruitful, as it preserves wood as well as a record of the changing environment over thousands of years. The distribution of such sites shows a marked bias towards the intertidal zone, since this is where the alluvium that overlies the prehistoric landscape has been eroded away. Many more archaeological sites are likely to lie inland in the peat, but lie undiscovered.
Links-
-'Footprints in the sand' a NERC Planet Earth Article Autumn 2004
-Glamorgan Archaeological Trust
-Severn Estaury Levels Research Commitee