Which DEM to use for storm surge

 A few days ago I mentioned my storm surge flooding model of Annapolis  and wanted to use the new lidar data.

Soccer fields and seawall.  This shows the four DEMs, two each from 2011 and 2017.  The DTM is the "bare earth", and removes water, vegetation, fences, cars, and other man-made features.  In 2011 it has many holes where there were no returns on the ground, which could be smoothly interpreted over.  The DSM is a surface model, and includes evertyhing the lidar beam encountered.  Note the seawall, chain link fences, and a few automotbiles appear in 2017, which has much more detail than the 2011 data.

Cross section from the soccer field to the river.  In red, the chain link fence appears at about 8 m on the horizontal axis.  The fence barely shows on the 2011 DSM; the slight rise at 11 m might be a parked car.  The 2017 DSM shows the seawall at 24 m, about three quarters of a meter high.  The seawall barely appears on the 2011 DSM.  Both DTMs show only a gently sloping surface.

This is the seawall; note the drain in the center of the image.  The drain would allow water to flood the soccer fields if the water level rose above that level (as would the storm drains).  Should the flooing model assume the seawall will provide protection, or use the DEM?  Additionally the chain link fence appears as a wall in the DSM, how should it be handled?  This is an artefact for the DEM structure; similarly, bridges acts as dams in a DEM flooding model.  The water would probably flow on the road around the soccer fields, but the fields themselves might appear to be an unflooded region.