Board Thread:Suggestions forum/@comment-86.185.40.111-20181004095159/@comment-37105233-20181007164005

A river basin that does not flow into the global ocean is called an endorheic basin. They essentially form a closed loop where the water flows into a lake or inland sea, evaporates, then precipitates down at the edges of the basin and starts the cycle again.

On Earth the largest such basin is in central asia and flows into the caspian sea (which is salt water). However there are also a few that are entirely fresh water systems e.g. in the Sahara, the Andes and the Rockies. As you may have noticed these are all either mountains or deserts and you're right. The reason for this is that erosion usually ends up connecting these systems to other river systems that do connect to the global ocean, so the only ones that stick around are in places with very little water, so very little erosion or where there is a lot of ground to erode before you can reach another river system.

So how does this apply to the mod? Well, the endorheic basin in Rhun is entirely possible although it probably wouldn't stick around for more than a couple hundred thousand years. But this is not a problem since Eru reshaped Arda only about 6500 years ago at the time the mod is situated.

However, there would still be a line of hills, mountains or deserts at the watershed (edge) of the basin so having that detail would be a nice acknowledgement of real world geography. The location of the watershed is of course entirely up to Mevans and the mod team since Tolkien didn't really provide much detailed information on the rivers of Rhun.