Also whether there are any dried up canals, disused canals, etc in the country which would be viable to become train lines.
Given Birmingham's over capacity and it's canal network, is there anything usable there?
Viable? Maybe. Usable without a big fight, almost none. Most abandoned canals that are not already under a railway have a preservation movement, most of which are actively undertaking that preservation.
And I've worked on quite a few of those as a volunteer. For a start I spent a large chunk of my life working on the Hereford and Gloucester basin at Over. I also live on a boat on a restored canal, the Basingstoke.
Many, if not most, canals arena't all that suitable, at least for a modern non-freight railway, they are either Contour Canals, which wind along at the same level for long distances, taking huge detours, without changing levels, with curves that callenge even a 70ft boat, or ones with changes of level that would be a problem for a railway. The ones that were suitable tended to have had railways built on, or in some cases beside, them...
In Birmingham most of the out of use canals have been built on or are short. The reason the Birmingham Canal Navigations was in intensive use for so many years after the railways arrived, and thus survived to this day, is that it wasn't practical to replace them with railways so factories kept using them. Where sections of the BCN have closed it is usually because someone built a road or factory on them.
What is/was feasible and common is the use of the same corridor. The stretch of the SW Main Line from West Byfleet to Farnborough follows the canal. The reasons for this are threefold, first the canal often follows the best geographical route (gaps in hills etc.), secondly the population centres or industries are served and thirdly the population centres and industries have often been influenced by the canal. For instance the army camps at Aldershot were built where they were, rather than another bit of heathland, because of the availability of material and ammunition transport by canal.
Often the last burst of profitability a canal saw was due to the traffic that built the railway that took its trade. That was certainly true of the Basingstoke.
The section of railway in Portsmouth is that between Portsmouth & Southsea and Fratton stations. The towpath is extant as a footpath elsewhere and the lock into Langstone Harbour also exists. This was part of the Portsmouth and Arundel Canal that linked the two places and allowed traffic to and from London via the Wey and Arun Junction Canal, the River Wey Navigation and the Thames. The P&A is under active restoration for the section that forms the Chichester Canal, the W&A is under active restoration for its whole length.
IIRC there was a bit of a fight going on between canal restoration and railway preservation groups over the Utoxeter Canal, which was later built over by a railway that is now closed. But now the plan is to for the canal to parallel the railway and use it to bring in materials.
