As has already been stated most believe that the cemetery was outside the Fortification near the river which would have been washed away during the 1927 Mississippi/Arkansas River floods.
However, because of the numbers of sick at Arkansas Post some of the long term cases such as Pneumonia cases were sent back to the General Hospital at Pine Bluff/Camp White Sulphur Springs. However, there is no known records which tells who was sent back to PB/WSS and who remained at Arkansas Post.
The general feeling is that very few were actually keep at Arkansas Post due to the unhealthy enviroment of river and swamps. This seems to be supported because of so few men being listed in federal records as being in the hospital at Arkansas Post when the Fort was captured January 11th 1863. We know that about 100 men, including the regimental commander Col Charles Dawson, from the 19th Arkansas Infantry of Arkansas Post garrison, were in the Hospital at Pine Bluff when Arkansas Post fell, because these men became part of Hardy's Arkansas Infantry afterwards.