This part of the river's course, the ancient Assyria, is also a rich agricultural region.
A great change in the river's course occurred in 1851, when a breach was made in the north embankment near Kaifengfu in Honan.
The most serious of all took place in 1887, when it appeared probable that there would be again a permanent change in the river's course.
The city is built on a level site several feet above the river's high-water mark.
Above the river's bed, allowing the water-surface up-stream of the barrage to be raised 7.2 ft., while the pressure on that work itself would not exceed 10 ft.
Course, such as a band of hard rock, may form a flood plain behind it, and indeed anything which checks a river's course and causes it to drop its load will tend to form a flood plain; but it is most commonly found near the mouth of a large river, such as the Rhine, the Nile, or the Mississippi, where there are occasional floods and the river usually carries a large amount of sediment.
This latter portion of the river's course is tortuous, but in spite of this, and although the depth varies from only 7 to 20 ft., and in places at low water does not exceed 4 ft., it is nevertheless navigated by vessels up to 180 tons burden and proposals have been made to embank and dredge it so as to increase this depth to 8 ft.