Popyane — the basin of the Pyana River, the area adjoining the Mordva Pyana River.
It drains into the basin of the Sura River, and in the Nizhny Novgorod Region borders Pourzhe.
The Pyana delights the eye with its beauty. Its right bank is rocky in places, resembling fortresses of clay, marl, and gypsum that glitters in the sun. Exposed riverbank sections alternate with the vivid green of oak groves and clusters of birch trees. On the left bank, as far as the eye can see, there are meadows, fields, and sweeping expanses of wildgrass.
Features
Karst processes are widespread throughout Popyane, which is precisely why the river is so winding. It carves its channel through easily soluble rock — limestone, gypsum, and anhydrite. During floods, after rains, or when snow melts, water seeps underground and then flows back into the river through cracks, cavities, and underground channels, dissolving rock along the way, enlarging hollows, and creating new paths for the riverbed. The terraces of the Pyana offer no flat ground anywhere: everywhere there are sinkholes, pits, and oddly shaped ponds. When the waters erode the ridges between them, the river veers off, forming a new meander.
The Pyana is exceptionally winding in its lower reaches as well — between Buturlino and Akuzovo, where karst processes are not as pronounced as in the upper and middle sections of the river.