The river Schelde is unpassable for any army, including one supported by the Royal Navy, from the coast to Rupelmonde. The first bridge is at Dendermonde, which was fortified. If the French get between the British field army and Dendermonde, their only option is a Dunkirk style evacuation on a coast with a 9 meters tide.

During the Napoleonic era, most of the fortified towns in Belgium lost the status of forteresses and the fortifications were torn down, the land sold. Ostend and Nieuwpoort had coastal fortification, no major defences toward the landside. So no fancy cordon type manoeuvering, Austrian style, in Flanders 1815.
Hudson lowe made up a detailled report on the defences in Belgium in winter 1814. It is kept in the Brussels army museum. I believe that Peter Hofschröer had plans to publish it.

Best regards,

Bruno