 The Floating Harbour was constructed in 1809 , isolating the Avon and Frome from tides between Cumberland Basin and Totterdown Lock . The increasing use of the Frome as an open sewer combined with the loss of the scouring action of the tides meant that it was now becoming a health hazard and in 1825 it was again diverted , with locks at Stone House , channelling the main flow through Mylne 's Culvert to the tidal Avon at New Cut , to the east of what is now Gaol Ferry Bridge . Up to 1858 the Frome was open along its whole length , and crossed by some 13 bridges . During the latter half of the nineteenth century , a culvert was built from Wade Street in St Judes to Stone Bridge , covering this stretch completely : Rupert Street , Fairfax Street and Broad Weir run over this culverted section . St Augustine 's Trench from Stone Bridge to Draw Bridge ( near the northern end of Baldwin Street ) was covered over in 1893 and the section between that point and the bottom of Park Street was covered over in 1938 . 
