MNBEERDRINKER:

Those pilings are likely leftover from the construction of the concrete piers, built between 1896 and 1902, or remnants of the original wooden north pier. Postcard is likely from a photo taken in 1902, as the light poles are standing but the actual lights have not been installed on them. Prior to 1896, the canal had wooden piers and was much more narrow and shorter. They made the canal wider going south, and built the concrete north pier "behind" the original wooden north pier.