Watermouth represents a medium sized terminus of an imaginary GWR branch running south from Chard to the coast near Charmouth. Just short of the terminus on the north bank of the estuary, the branch is joined at Watermouth Junction by a GWR/SR joint line running down from Axminster and Kilmington. The line crosses the tidal estuary by a timber viaduct and enters Watermouth Riverside which is also assumed to have a branch running on to Watermouth Docks. The station arrangement draws inspiration from Kingsbridge, Weymouth and Kingswear. Watermouth Docks are assumed to be an embarkation port for steamers to the Continent and the track plan is designed to accommodate busy summer passenger traffic, including a daily Sleeper to London and through trains from the Midlands, London and Taunton as well as local branchline services. In addition to the main terminus, there is also a smaller through station representing the junction for the GWR and SR routes. In the Master Plan, this station lies on the opposite bank of the estuary and a single line section on a long bridge over the estuary (based on the Taw bridge at Barnstaple) links the two stations. Because this bridge has a weight restriction, 'large' engines come off their trains at the Junction and go to a small MPD, whilst the train is taken on to the main terminus by a lighter locomotive. The corresponding empty stock and light engine workings should allow for a variety of interesting traffic movements.