The funnelling of the water further up the river caused its level to rise even higher. The situation was worsened by capital dredging which had been carried out between 1909 and 1928, deepening the river channel by about 2 metres (6 ft) to allow access for deeper-draughted vessels to the Port of London. This had the side-effect of making it easier for seawater to flow up the Thames on a high tide, increasing the flow on a mean tide by about 4% and raising the tidal range by about 0.7 metres (2 ft).