प्रावृषि in rainy season, नवाम्भसा with fresh water, स्पृष्टम् contacted, महानद्याः mighty river's, कूलम् इव like bank, मम my, इदम् this, हृदयम् heart, यत् for which reason, न दीर्यते does not break, स्थिरम् firm (hard), मन्ये am thinking.
I think my heart must be very firm (hard) like the bark of a great river which, touched by (a flood of) fresh water in the rainy season does not disintegrate.