Excavation methods and techniques

The Natière site is located less than a nautical mile from the walls of Saint-Malo. It lies on the eastern flank of the large fairway leading to the harbour, near the port side channel marker known as the Basse du Buron. Depending on the tide, the site lies between nine and eighteen metres below the surface. The water is generally clear, with visibility often reaching two to three metres. The wrecks rest on a sandy conchiferous bed bounded to the north and south by two rocky outcropping known as the Banc de la Natière. On the tip of the northern rock sometimes emerges from the sea during exceptionally low tides. The major difficulty with the site is the existence of powerful currents that sweep through the area. The bay's extreme tidal range (nearly 13 metres at spring tide), generates such strong ebbs and flows that the water is only calm at high and low tide.
Even these periods of respite are subject – particularly at low tide – to the workings of the tidal power station located at the mouth of the Rance River in line with the main Saint-Malo channel. Thus, slack tides range from 15 minutes at low tide to 75 minutes when the tide is full. These short periods thus determine the diving calendar, and affect everything from getting equipment into the water to bringing archaeological objects to the surface.

Multimedia

Frédéric Osada (Images Explorations) © MCC / DRASSM
Aerial photo of the Hermine-Bretagne, the excavation's support ship, anchored at the Natière site. The mouth of the Rance River and the tidal power station can be seen in the background. (Cliché : NAT01_E0019)
Teddy Seguin (Adramar) © MCC / DRASSM
Aerial view of the Hermine-Bretagne anchored at the Natière rocks, which form a genuine "ship-trap". (Cliché : Nat07_M0145)
Teddy Seguin (Adramar) © MCC / DRASSM
Visibility underwater is different at high and low tide. It is also affected by the actions of the underwater archaeologists. (Cliché : NAT06_SM0031)
Teddy Seguin (Adramar) © MCC / DRASSM
Visibility underwater is different at high and low tide. It is also affected by the actions of the underwater archaeologists. (Cliché : Nat07_SM0585)
© Thomas Sagory (du-ciel.com)
Aerial kite photograph of the Hermine-Bretagne. Off the stern, one can see air bubbles from the divers' air tanks. (Ref. : Nat08_M0335)
Teddy Seguin (Adramar) © MCC / DRASSM
The indispensable (and reassuring) lifeline, which connects the support ship with the archaeological site, and guides the divers. (Réf. : NAT06_SM0120)
Teddy Seguin (Adramar) © MCC / DRASSM
A strong current can often hamper work underwater. (Réf. : Nat06_SM0167)
Frédéric OSADA (Images Explorations) © MCC / DRASSM
The Natière site is located near heavily-travelled channels. This means that vigilance is important at all times, and that safety conditions must be followed to the letter. (Picture: 2001-1-50-03)

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