I came across this outline of the water basins around the Black Sea. I think it aligns quite well with f82r.
1. Danube delta = top left nymph standing in upright tube. Note backward arm showing the way she came.
2. Dniester delta = mnemonic rock and river combo pouring into the sea. Note that if you consider the rock part to be the Carpathian mountains, the river does flow in the direction shown, which looks upward to many. However it would be a tributary that then flows into the Dnieper which flows the opposite way, semi parallel to the mountain(s), and would need to be tilted approximately 45 degrees. So the river itself is not drawn, but rather, the source, like the one with a name in the drawing below, lowest dot in the upper section. It is like the brown mountain part of the diagram below, with only that tributary drawn. It goes up, but then joins the main river and goes back down, that part is not drawn, only implied.
3. Bug and Dnieper deltas = next nymph to the right. Note two arms up indicating the two river directions. (Bug is the unnumbered river between 2 and 3 similar in size to 2.) Her arms mimic the two sections of green to either side of the red line between the unnumbered section and section 3.
4. & 5. Tanais aka Don, Azov, and Kerch Strait = The next nymph stands in Crimea. Note that it is drawn in the vms the same way as the red line and ignores that which drains into the Black sea. Her arms go back to touch the area near the strait, i think to indicate that there is water at the top of Crimea also, it is apart from the land above it. The next water spray motif is the strait mnemonic. I think it is saying that there is no level difference at this point in the waters, and they come from the point of a triangular shape. The triangular shape i think refers to the Sea of Azov which is otherwise not shown on this page. In many maps it is portrayed as roughly triangular. It is always 'pointy', even if drawn in the more rectangular way that it resembles in reality. I think section 4 is referred to as the ultimate source of these waters, at least indirectly, as the Don river feeds into the Sea of Azov at the pointy part. The Don was sometimes thought to be the left part of the T in TO maps, the border between Europe and Asia.
6. Phasis aka Rioni = far right nymph. This was also a river considered to be a boundary between Europe and Asia. Another mountain river, hence the blue water and the mnemonic for flooding requiring human assistance to clear, an upward tube with hand clearing silt. Evidently it became swampy in antiquity without drainage maintenance.
7. Various rivers in Trebizond area = Three small nymphs. You can see how either side of 7 with the unnumbered area in the middle can be denoted by the three nymphs. See below in the diagram for 8 for the actual river courses.
8. Kizilirmak = Large nymph lower middle. The unnumbered section above to the left would correspond to the small nymph beside her to the left.
Unnumbered Ankara section = Large leftward nymph standing at the bosphorus to the Sea of Marmora, near Constantinople.
Unnumbered section to the east = small nymph pointing out the shared bosphorus of her side and that of the larger nymph.