Fa-tawassaṭā is a dual past verb meaning that the two reached the middle. ʿUrḍa al-sariyy locates the action across or within the small stream, with sariyy as the genitive complement. Masjūratan describes an implied pool or water-filled place.
Mutajāwiran qallāmuhā shows the plants clustered near one another. The poet presents the location through three spatial details: its shape, the water filling it, and its enclosing vegetation.