So make the navigable river hexsides between DH and Cal into ‘land’ and move the navigable river to the W hexside of Cal. One must also make sure one makes the E hexside of hex “!” as a navigable river also.
Now you can get into and out of Cal with no problem, BUTT :: As one traverses into hex ! there are many exits, and one could technically bypass DH if one is beating feet from Cal. This is not good either, since DH is down river from Cal, but still on the river, so one must be forced to pass thru DH going in or going out.
So one must also close off the SW edge of hex ! to prevent exit. I used the reef code block, but one can think of it as an area of swamps and mudflats, just like the area SE of DH. This forces exit from hex ! to go thru DH. Thus sea traffic will go, first, to DH and then to Cal, and from Cal to the sea thru DH, just like IRL. All it adds is one extra hex.
Hope the attached pictures are clear enough to follow along with.
