From the NMR:
The Medway was improved by Navigation Acts of 1664, 1740, 1792, 1802 and 1824. Connecting Tonbridge to the Thames at Sheerness, there are 10 locks between Tonbridge and Allington Lock, below which the river is tidal. Below Allington, river craft up to 180 feet long with a beam of 20 feet could be accomodated. Above Allington Lock, the maximum craft dimensions were 80 feet long by 18 feet 6 inches.

From 1571 to 1626 a series of Commissions of Sewers were appointed by the King. These kept the river clear for drainage purposes but permitted some navigation. Commissions for navigation were appointed in 1627 and 1664, that of 1627 permitting small barges to reach Yalding by 1630. That of 1664 failed to undertake any works. The Act of 1740 permitted real navigation of the upper river and 14 locks were built. These were variously maintained or disused throughout the 19th and 20th centuries. (1)

<1> Michaeol Trueman, 2007, Heritage Audit of the Medway Navigation (Unpublished document). SKE17949.