Matsya Purana — Paurava Genealogy
अधिसोमकृष्णपुत्रस्तु विवक्षुर्भविता नृपः गङ्गया तु हृते तस्मिन् नगरे नागसाह्वये //
adhisomakṛṣṇaputrastu vivakṣurbhavitā nṛpaḥ gaṅgayā tu hṛte tasmin nagare nāgasāhvaye //
O king, Vivakṣu—the son of Adhisoma (also called Kṛṣṇa)—will become a ruler. And when the city known as Nāgasāhvaya is carried away by the River Gaṅgā, the change of seat and the succession of the lineage proceed accordingly.
It does not describe cosmic Pralaya; it refers to a localized calamity—Gaṅgā flooding/eroding Nāgasāhvaya (Hastināpura)—as a historical-geographical marker within dynastic narration.
Indirectly, it frames kingship as a continuous succession (vamśa) where a ruler must preserve stability even amid environmental change; the implied duty is prudent governance and relocation/administration when a capital is damaged by a river.
Architecturally, the verse hints at settlement vulnerability to river-course change; in Vāstu/urban planning terms, it supports choosing and maintaining city-sites mindful of flooding and river erosion—an implicit “Matsya Purana Vastu Shastra tips” takeaway.