before 2013, mont-saint-michel was linked to the mainland with a tidal causeway. it was a path covered at high tide and shown at low tide. this connection changed over the centuries. the coastal flats (the sand) have been polderised to make pastureland. this means mont-saint-michel became closer to the coast. the couesnon river was canalised. this helped make the flow of water similar every time the tide rises or falls. however, it developed a silting-up of the bay. in 1879, the tidal causeway was changed into a raised, dry causeway. this stopped the tide from cleaning the silt around the mount.