Mapping tide elevations?

Curious if anyone has used CalTopo to map high and low tides? I'm planning a trip along a coastline and am curious to see which trails will be underwater at high tide for the dates I'll be out there. 

I tried a simple custom DEM layer that highlights everything below a certain elevation, but apparently it's more complicated than that because tide charts are generated for datums other than WGS84. Using "MSL" as the datum seems to line up fairly closely with the edge of beaches in satellite imagery, but it's different enough that I'm not sure it's accurate. My research says that WGS84 is based on MSL though...

Tide Predictions - NOAA Tides & Currents.

Aside from creating a layer based on the DEM, has anyone come across a pre-existing WMS layer that shows high/low tide?

Thanks!