Storm & Flood Damage Recovery in Portsmouth, NH

That is coastal flooding rather than a drainage fault, and it is worth distinguishing because the responses differ. A surge on top of an already high tide raises the river above the level of the low streets, and the drainage that normally discharges there is under water. Nothing is blocked. The astronomical tide combined with the surge forecast predicts it far better than any rainfall figure.

Manageably damp is the honest target. A stone or rubble wall has no continuous surface to seal, and coatings applied inside tend to move water rather than stop it, sometimes into the mortar higher up. What works is managing water before it reaches the wall with grading and roof drainage, then handling what still arrives with an interior drain and a sump. Expecting a finished dry room out of that space is what leads to expensive disappointment.

Yes, and it argues for slower drying rather than faster. Old plaster, lime mortar, and original woodwork can be damaged by aggressive drying as much as by the water, and replacing them is rarely straightforward. A contractor experienced with historic fabric will use gentler drying over a longer schedule and will know what can be saved. It is worth asking about that experience specifically before work starts in the core.