A canal was cut in 1915 to facilitate shipping south from Port Townsend. Ferries served the area from 1920 until a bridge was built in 1952.
1841 chart
Georeferenced* chart
1856 NOAA chart
Georeferenced* chart
We see that part of the Chimakum Portage remains south of the mud flats. It seems that dredging spoils (not necessarily from the initial canal building) blocked the drainage of the mud flats to the east. At some point between the date of that part of the DEM and the date of the photo, waters broke through more of the relict Chimakum Portage.
We have used this information to alter the DEM on which our updated post-glacial simulation will be based.
*Harvey georeferenced the charts. Maybe you could do better.