Houston Guide and Handbook, 1968 (continued)

Here is a map of the Houston Ship Channel from the Houston Guide and Handbook published in 1968.  I've taken the Boliver ferry recently, and I can confirm that the Ship Channel is a very busy shipping lane.
  

The Channel was dredged to 25 ft. when it opened in 1915.  In later years, it was dredged to a depth of 45 ft.  Click here to view a Wikipedia article on the Houston Ship Channel.