There are both Big Rivers and small creeks. big rivers are big enough for a ship (of certain size) to sail through, not sure about how land units can walk over. (and this would be something like Mississipi, Nile, Menam (Up to Ayutthaya or slightly north, back in the past Portuguese Naus can sail all the way into the very city but the river at that point might also be silted, so by the end of 18th Century after Ava Kaungbaung Empire defeated Ayutthaya Kingdom, Phaya Tak (Leader of the city survivors, or originally he's the man who the King ordered to muster troops in the southeastern city of Chantaburi to lift the siege but he arrived to the destination abit too late and Kaungbaung sacked the Capitol already) eventually evicted Kaungbaung garrison units out of Ayutthaya ruins, he instead opted to found a new city of Thonburi at the small town originally known as Bang Kok ... inside a vauban fort built about a century earlier.... this might also mean that Ayuuthaya ports no longer capable to accept big ships but ones of the new city can.
both kind of rivers now takes up a full space of hex. and not between as it used to. this is good.
but i'm not sure if there will be 'brown water' and 'blue water' unit classes in addition? which means there can be river gunboats, ironclads being riverine warships, and even river monitors just like in 'Nam ?