The Tigris commonly begins to rise early in March, and reaches its greatest height in the first or second week of May, after which it rapidly declines, and returns to its natural level by the middle of June.

The Euphrates first swells about the middle of March, and is not in full flood till quite the end of May or the beginning of June; it then continues high for above a month, and does not sink much till the middle of July, after which it gradually falls till September.

The country inundated by the Tigris is chiefly that on its lower course, between the 32d and 31st parallels, the territory of the Beni Lam Arabs.

The territory which the Euphrates floods is far more extensive.

As high up as its junction with the Khabour, that stream is described as, in the month of April, "spreading over the surrounding country like a sea." From Hit downwards, it inundates both its banks, more especially the country above Baghdad (to which it is carried by the Saklawiyeh canal), the tract west of the Birs Nimrud and extending thence by way of Nedjif to Samava and the territory of the Affej Arabs, between the rivers above and below the 32d parallel.