the witham originally flowed into the wash at bicker haven, where the port of drayton was established in the welland estuary, and it was only as a result of massive flooding in 1014 that it diverted itself to flow into the haven at boston. this gave rise to the growth of boston as a port in the 12th and 13th centuries, exporting wool and salt to the hanseatic league, though boston only received its charter in 1545.